Patent Publication Number: US-2021162682-A1

Title: Manufacture of microstructures

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/943,152, filed Dec. 3, 2019, and U.S. Provisional Application No. 62/943,153, filed Dec. 3, 2019, the entireties of each of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     This disclosure relates generally to the field of drug delivery devices, and in particular, to devices used for transdermal delivery of therapeutic agents and methods and apparatuses for manufacturing the same. 
     Microneedles and microneedle patches have been contemplated as mechanisms for transdermal delivery of various therapeutic agents. For effective and efficient delivery of therapeutic agents, microneedles need to have the right combination of materials, size, and mechanical properties. However, manufacturing and, in particular, mass manufacturing of microneedles with the appropriate combination of these factors remains a challenge. 
     SUMMARY 
     In accordance with some embodiments disclosed herein is the realization that it is difficult to manufacture a microstructure, such as a microneedle array, that is suitable for transdermal delivery of therapeutic agents at a commercially viable throughput and yield. For example, it has been discovered that there are substantial manufacturing challenges due to the size and aspect ratio of individual microstructures, such as microneedles within an array, especially when trying to achieve advantageous physical properties and specific microstructure arrangements, as discussed further herein. In order to address this and other challenges, the apparatuses and methods disclosed herein enable high-throughput mass manufacturing of microstructures, such as microneedle arrays, while avoiding breakage and waste and while facilitating advantageous microstructure arrangements and geometries using a variety of material and/or active agent combinations. 
     For example, some embodiments provide for a method of manufacturing a microneedle array that may include a pulling fibers from a continuous film of a viscous polymer using a pin template while simultaneously drying the pulled fibers. The inventors of the present disclosure have discovered that in some embodiments, simultaneous drying can provide uniformity of size, viscosity and hardness of the fibers. The pulled, partially dried fibers are then cut to at a suitable length to form the microneedle array. Advantageously, some embodiments of the method can significantly minimize breakage and waste by cutting the fibers at a distal end thereof rather than removing and separating the microneedles from a mold, as done in a typical microneedle manufacturing process. 
     Therefore, in accordance with some embodiments, the microstructures disclosed herein can be made in an efficient, precise, assembly-line-like execution of steps. This precision manufacturing and enable production that significantly reduces risk of damage to the microstructures, substantially improves consistency and quality, thereby enabling a manufacturer employing the highest of quality controls to achieve production of a high-quality product with minimal waste product and associated expense. These and other aspects of the methods and apparatuses disclosed herein can be especially valuable considering the relatively high cost of active agents and other pharmaceuticals that may be incorporated into the microstructures. 
     Accordingly, in some embodiments, a microstructure can be provided that includes one or more protrusions (e.g., microneedles) extending from a sheet of solidified viscous polymer. 
     In some embodiments, the polymer composition can include a plasticizer. For example, the plasticizer can make the polymer more flexible in dried form, thereby reducing the interfacial stresses that develop between the rigid substrate during the formation of the microneedles by stretching and similar deformation of the polymer. The reduction in the interfacial stress makes the microneedle protrusions and the supporting layer less prone to spontaneous out-of-plane deformation and premature or spontaneous peeling or adhesion loss that can result from such deformation, thereby increasing the yield during a manufacturing process. 
     In accordance with some embodiments, a method of manufacturing a microstructure includes disposing a viscous polymer onto a substrate to form a continuous, viscous film layer and contacting a template having a plurality of contact points against a surface of the viscous film layer. The template is then separated from the viscous film layer while urging air towards the viscous film layer from the template to form a plurality of fiber-like projections of the viscous polymer. The projections can then be permitted to solidify and cut to form microneedles. 
     The air flow during the separation of the template from the viscous film layer enables a uniform drying and/or solidification of the viscous polymer, thereby increasing the uniformity of the microneedles being formed. Additionally, the air flow also increases the rate of drying, thereby increasing the throughput of the manufacturing process. 
     In accordance with some embodiments, an apparatus for manufacturing a microstructure includes a substrate carrier and a template holder. The substrate carrier can be configured to carry a substrate and the template holder can be configured to carry a template having a plurality of contact points and enable a flow of air through outlet apertures provided in the template. An assembly can be configured to move the substrate holder relative to the template holder so as to enable the plurality of contact points to contact a surface of a viscous polymer layer disposed on the substrate and draw the viscous polymer at points of contact between the surface of the viscous polymer and the plurality of contact points to form protrusions of the viscous polymer. The assembly is further configured to permit the protrusions to solidify in place. 
     The apparatus disclosed herein enables faster manufacturing of microneedles. Additionally, the apparatus improves the uniformity of the manufacturing, thereby increasing the yield and precision of manufacturing. 
     Additional features and advantages of the subject technology will be set forth in the description below, and in part will be apparent from the description, or may be learned by practice of the subject technology. The advantages of the subject technology will be realized and attained by the structure particularly pointed out in the written description and embodiments hereof as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the subject technology. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       In the present disclosure, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Some embodiments may be used, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
         FIG. 1  illustrates a microstructure having one or more microneedles coupled to an underlying substrate, according to some embodiments. 
         FIG. 2  illustrates an apparatus used for manufacturing microstructures, in accordance with some embodiments. 
         FIG. 3  illustrates a portion of the apparatus for manufacturing microstructures, in accordance with some embodiments. 
         FIG. 4  illustrates a template mount and a substrate holder, in accordance with some embodiments. 
         FIG. 5  illustrates a template mount and a substrate holder accommodating an overdrive of the substrate holder, in accordance with some embodiments. 
         FIG. 6  shows a perspective view of an airflow ingress channel, in accordance with some embodiments. 
         FIG. 7  shows a perspective bottom view of an airflow ingress channel in conjunction with a template, in accordance with some embodiments. 
         FIG. 8  shows a perspective view of a template used for manufacturing microstructures, in accordance with some embodiments. 
         FIG. 9  shows a top view of a template used for manufacturing microstructures, in accordance with some embodiments. 
         FIG. 10  shows a side view of a template used for manufacturing microstructures, in accordance with some embodiments. 
         FIG. 11  shows an enlarged perspective view of a template used for manufacturing microstructures, in accordance with some embodiments. 
         FIG. 12  shows an enlarged bottom view of a template used for manufacturing microstructures, in accordance with some embodiments. 
         FIGS. 13A and 13B  illustrate a method of forming a continuous layer of a viscous polymer with uniform thickness, in accordance with some embodiments. 
         FIGS. 14-22  illustrate the apparatus for manufacturing the microstructure during various stages of performing a method of manufacturing the microstructure, in accordance with some embodiments. 
         FIG. 23  illustrates a non-contact method of loading microneedles with an active agent, in accordance with some embodiments. 
         FIG. 24  shows a photomicrograph of the cross-section of a microneedle loaded with a hydroalcoholic solution of sodium fluorescein, in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     It is understood that various configurations of the subject technology will become readily apparent to those skilled in the art from the disclosure, wherein various configurations of the subject technology are shown and described by way of illustration. As will be realized, the subject technology is capable of other and different configurations and its several details are capable of modification in various other respects, all without departing from the scope of the subject technology. Accordingly, the summary, drawings and detailed description are to be regarded as illustrative in nature and not as restrictive. 
     The detailed description set forth below is intended as a description of various configurations of the subject technology and is not intended to represent the only configurations in which the subject technology may be practiced. The appended drawings are incorporated herein and constitute a part of the detailed description. The detailed description includes specific details for the purpose of providing a thorough understanding of the subject technology. However, it will be apparent to those skilled in the art that the subject technology may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring the concepts of the subject technology. Like components are labeled with identical element numbers for ease of understanding. 
     Some embodiments of the present disclosure relate to microstructures for transdermal delivery of therapeutic agents, methods of manufacturing such microstructures, apparatuses for manufacturing such microstructures, and methods of treatment using such microstructures. The microstructures can be useful in a variety of treatments and indications. Such microstructures can be incorporated into or used in combination with other treatment modalities and medical devices. 
     Among the various advantages and benefits disclosed herein, in some embodiments, the manufacturing apparatus can reliably produce microstructures at a commercially viable throughput and yield. The methods and apparatuses disclosed herein can produce microstructures, such as microneedle arrays, in a manner that is more cost efficient and effective than prior methods and apparatuses. As a result, various advantages and benefits, including certain features of the microstructure, as disclosed herein, can be achieved and realized whereas such advantages and benefits were formerly not possible. 
     In accordance with some embodiments, the manufacturing apparatus can comprise an airflow mechanism that directs air during the manufacturing process toward the microstructures to enable a uniform drying and/or solidification of the viscous polymer forming the microstructures. Further, various methods, systems, and microstructures are disclosed herein that facilitate precise manufacturing, drug loading, microstructure removal, separation, and packaging, which can each make possible various advantageous, cost-saving, and quality-improving benefits, as noted here. 
     Microstructures 
     Referring now to the figures,  FIG. 1  illustrates a microstructure having one or more microneedles coupled to an underlying substrate.  FIG. 1  shows a microneedle patch  100  having a base layer  102  and a plurality of microneedles  104  extending from the base layer  102 . In some embodiments, the material for the base layer  102  can be the same as the material for the microneedles  104 . Optionally, the base layer  102  and the microneedles  104  can be compositionally homogenous, i.e., formed as a monolithic, continuous piece. Some features of the microstructures disclosed herein can be implemented using aspects of the disclosures of U.S. Pat. Nos. 8,366,677 and 10,377,062, the entireties of each of which are incorporated herein by reference. 
     In some embodiments, the patch  100  can optionally include a substrate layer  106  disposed over the base layer  102  and the microneedles  104  are formed on the substrate layer  106 . In some embodiments, the material for the substrate layer  106  and the microneedles  104  may be same. In some embodiments, the material for the microneedles  104  and the materials for the base layer  102  and/or the substrate layer  106  are different. In some embodiments, the microneedles  104  include a polymer. In some embodiments, the microneedles  104  are predominantly formed of a polymer, e.g., a water soluble polymer. The polymer can be a biocompatible or a biodegradable polymer or a polymer that undergoes physiological clearance, for example, in vertebrate animals. 
     In some embodiments, the microneedles  104  can comprise a therapeutic agent such as, for example, a toxin having therapeutic properties. Treatment methods using the patch  100  can be performed by applying the patch  100  to the skin of a subject such that the microneedles  104  penetrate the skin surface. In embodiments where the microneedles  104  are formed of a biodegradable polymer or a physiologically cleared polymer, the microneedles  104  may dissolve upon penetration into the skin surface. Further, in embodiments in which the microneedles  104  include or are loaded with a therapeutic agent, the therapeutic agent may be delivered to the subject upon penetration into the skin surface. In other words, the patch  100  in some embodiments can be used for transdermal delivery of a therapeutic agent to the subject. 
     Manufacturing Apparatuses for Microstructures 
       FIG. 2  and  FIG. 3  illustrate a portion of an apparatus  200  used for manufacturing microstructures, in accordance with some embodiments of the present disclosure. The apparatus  200  can be used for mass manufacturing microstructures such as, for example, an array of patches  100 . Moreover, the process of manufacturing the microstructures can be automated and scaled for commercial manufacturing using the apparatus  200 , which can provide reliable, high-throughput manufacturing of the microstructures that are compliant with regulator standards, e.g., for therapeutic use. 
     Referring to  FIG. 2 , the apparatus  200  can include a table  230  having a plurality of slots  236  that can each be configured to hold at least one stamping assembly  250 . In some embodiments, each of the slots  236  can additionally be provided with an airflow ingress channel  232 . The airflow ingress channels  232  can be connected to an air hose  234  for providing forced air flow through the airflow ingress channels  232 . The air flowing through the airflow ingress channels  232  may be directed to flow toward the stamping assemblies  250  during the process of manufacturing the microstructures, as will be explained in detail elsewhere herein. 
     An embodiment of the stamping assembly  250  is illustrated in  FIG. 3 , along with an embodiment of the template  201 . As illustrated, the stamping assembly  250  can comprise a template mount  202  and a substrate holder  210 . The template mount  202  can comprise one or more alignment arms  252  and one or more alignment pins. The alignment arms  252  and the alignment pins can support or direct movement of the substrate holder  210 , tending to ensure that the substrate holder  210  remains aligned within a horizontal plane when being vertically translated during manufacture of the microstructure. 
     For example, the alignment arms  252  can engage with and support four separate alignment pins. The substrate holder  210  can comprise four alignment apertures, each being disposed at a respective corner of the substrate holder  210 , which can receive and slide along a respective alignment pin of the stamping assembly  250 . During movement of the substrate holder  210  relative to the template mount  202 , the engagement between the alignment apertures of the substrate holder  210  and the alignment pins can maintain the substrate holder  210  in a horizontal plane. As will be appreciated by a person of skill in the art, the maintenance of the substrate holder  210  (and thereby the substrate  212 ) in a horizontal plane during the manufacturing process ensures that the microstructure can be repeatably and reliably produced. The structure and function of the stamping assembly and apparatus disclosed herein provide unique and superior benefits that achieve these objectives. 
     Additionally, and advantageously, the arrangement of template mount  202  and the stamping assembly  250  enables stabilization of the microneedle structures in a final position after the formation of the microneedles. Moreover, because the microneedle structures are formed relatively quickly in comparison to the complete drying to form the sufficiently rigid structures to be free-standing without collapsing, the template mount  202  may be moved away from the stamping assembly  250  to allow complete drying while additional microneedle formation steps are performed under the airflow conditions provided by the airflow ingress channels  232 . 
     Referring again to  FIG. 2 , the apparatus  200  can comprise a drive assembly  240  that is configured to drive relative motion of the various components of the stamping assembly  250  during the manufacture of the microstructure. The drive assembly  240  can include one or more stamper arms  242  and a drive mechanism or actuator  244 . The stamper arm  242  can be configured to engage with at least a portion of the stamping assembly  250  to facilitate the manufacturing process discussed herein. 
     For example, the stamper arm  242  can include a magnetic chuck or a vacuum chuck (not explicitly shown) for coupling to and moving the substrate holder  210  relative to the template mount  202 , which can in turn, cause movement of the substrate  212 . The coupling between the stamper arm  242  and the substrate holder  210  can allow the stamper arm  242  to maintain the substrate holder  210  in a horizontal plane while the drive assembly  240  moves stamper arm  242  (and the substrate holder  210  coupled thereto) vertically relative to the table  230  and the template mount  202 . In this manner, the stamper arm  242  can move the substrate  212  toward or away from the template  201 , allowing the operator to perform the manufacturing steps to form the microstructures, such as the patch  100  described above. 
     In some embodiments, during the process of manufacturing the microstructures, the drive assembly  240  as a whole or the stamper arm  242  alone may be moved laterally from one slot  236  to another slot  236  to allow engagement different stamping assemblies. This can advantageously permit the apparatus  200  to perform mass manufacturing of the microstructures. The configuration and components of the apparatus  200  can also be built to a scale suitable to support a desired manufacturing output using the principles disclosed herein. 
     In some embodiments, the actuator  244  can comprise one or more actuators or motors that are configured to provide both course and fine movement or adjustments to the stamper arm  242 , whether in vertical and/or horizontal direction(s). For example, the actuator  244  can move the stamper arm  242  with a precision of between about 0.1 μm to about 2.5 μm over a distance in a range from about 50 μm to about 500 mm, such as from about 50 μm to about 100 μm, from about 50 μm to about 250 μm, from about 50 μm to about 500 μm, from about 50 μm to about 1000 μm, from about 50 μm to about 2 mm, from about 50 μto about 5 mm, from about 50 μm to about 10 mm, from about 50 μm to about 50 mm, from about 50 μm to about 100 mm, from about 50 μm, to about 250 mm, from about 100 μm to about 250 μm, from about 100 μm to about 500 μm, from about 100 μm to about 1 mm, from about 100 μm to about 5 mm, from about 100 μm to about 10 mm, from about 100 μm to about 50 mm, from about 100 μm to about 100 mm, from about 500 μm to about 1 mm, from about 500 μm to about 5 mm, from about 500 μm to about 50 mm, or any other range between any two of these ranges or any distance within any of these ranges, and at rates ranging from about 0.1 mm/minute to about 200 mm/minute, e.g., from about 0.1 mm/minute to about 1 mm/minute, about 0.1 mm/minute to about 2.5 mm/minute, from about 0.1 mm/minute to about 5 mm/minute, from about 0.1 mm/minute to about 10 mm/minute, from about 0.1 mm/minute to about 50 mm/minute, from about 0.1 mm/minute to about 100 mm/minute, from about 1 mm/minute to about 10 mm/minute, from about 1 mm/minute to about 20 mm/minute, from about 1 mm/minute to about 50 mm/minute, from about 1 mm/minute to about 100 mm/minute, or any other range between any two of these ranges or any rate within any of these ranges. It will be appreciated that the optimal rate at which the substrate  212  is separated from the template  201  will depend on several factors such as, for example, the composition of the viscous polymer disposed on the substrate  212 , the molecular weight of the viscous polymer, the amount of solvent present in the viscous polymer, etc. that determine the rheological characteristics of the polymer. 
     In some embodiments, the actuator  244  may include, for example, a pneumatic, hydraulic, magnetic, electrical, piezoelectric or other type of mechanical and/or electromechanical actuators that can move the stamper arm  242  relative to the table  230 . 
     Referring again to  FIG. 3 , the stamping assembly  250  can be configured such that the template mount  202  is configured to hold a template  201 , and the substrate holder  210  is configured to hold a substrate  212  on which a composition can be placed and from which the microstructures are formed. As noted above, the substrate  212  can be moved relative to the template  201  in order to form the microstructure from the composition disposed on the substrate  212 . 
     In accordance with some embodiments, the template  201  can comprise a template holder  203 , a template base  204 , and an array of pins  206  mounted to and extending from the template base  204 . The template  201  can be replaceably coupled to the template mount  202  of the stamping assembly  250 . 
     In some embodiments, the template mount  202  can include a coupling device, such as magnetic or vacuum chucks, for coupling to or engaging with the template  201  to immobilize the template  201  relative to the template mount  202  during the manufacturing process. Similarly, in some embodiments, the substrate holder  210  may include a coupling device, such as magnetic or vacuum chucks, for coupling the substrate  212  to the substrate holder  210 . In some embodiments, such a coupling can advantageously permit the template  201  to be fixed relative to the template mount  202  and the substrate  212  to be fixed relative to the substrate holder  210  in order to ensure that the template  201  and the substrate  212  are properly aligned. 
     Accordingly, some embodiments thereby permit the substrate holder  210  to be moved vertically relative to the template mount  202  in a precise and controlled manner that permits the manufacturing of a microstructure having specific structural properties. As noted above, the stamper arm  242  can engage with the substrate holder  210  for moving the substrate holder  210  vertically relative to the template  201 . For example, once the template  201  and the substrate  212  are aligned with respect to each other, the stamper arm  242  may be engaged with the substrate holder  210 . Thereafter, the actuator  244  can move the stamper arm  242 , and thereby the substrate holder  210 , toward template  201 . The apparatus  200  can thereby cause contact points  207  of the pins  206  of the template  201  to come in contact with a surface of a composition, such as a viscous polymer disposed on the substrate  212 . 
       FIGS. 4 and 5  illustrate a template mount  202  in accordance with some embodiments of the present disclosure. In some embodiments, the template mount  202  may include a spring-loaded template mounting structure to hold the template  201  in place while allowing the template  201  as a whole can comply with an overdrive of the substrate  212 . Compliance of the template  201  may prevent deformation of the pins  206 . The template mount  202  of the stamp assembly  250  can, in some embodiments, include one or more alignment arms or spring-loaded template detent contacts  252  that capture the template  201  and allow the template  201  to move downward by a small distance if, e.g., by accident the substrate  212  is moved beyond a point at which the pins  206  of the template  201  contact the substrate  212  by an overdrive of the stamper arm  242 . In some embodiments, the template detent contacts  252  can comply against an uneven force independently of each other as can be seen in  FIG. 4 . Such independent compliance allows the template  201  to tilt at an angle if the substrate  212  contacts the template  201  at an angle, e.g., as seen in  FIG. 5 . The downward and tilting movement enabled by the template detent contacts  252  prevents the pins from buckling under the force exerted by the substrate  212  (which, in some embodiments, may be rigid and non-compliant), and prevents damage to the substrate  212 . 
     In some embodiments, the substrate holder  210  may optionally include a spring-loaded substrate mounting structure to hold the substrate  212  in place. The substrate mounting structure may include spring-loaded substrate detent contacts  260  to enable the substrate  212  to comply against the template  201  to guard against substrate overdrive. Similarly to the template detent contacts  252  discussed herein with respect to the template mount  202 , the substrate detent contacts  260  allow the substrate  212  to comply and/or tilt in case of an overdrive of the substrate holder  210  by the stamper arm  242 . 
     Advantageously, such a compliance feature of the template mount  202  and/or the substrate holder  210  affords the possibility of slightly overdriving the stamper arm  242  so as to ensure full contact of the maximum number of pin structures  206  with the substrate  212 , and thereby, maximal embedding of the pin structures  206  in the polymer layer so as to produce a maximally uniform set of the resulting microstructures formed upon withdrawal of the pin template  201 . 
     Once the composition is brought into contact with the pins  206  of the template  201 , the substrate  212  can thereafter be moved away from the pins  206  of the template  201  to draw the composition into a plurality of corresponding projections or needles. 
     For example, in some embodiments, the pins  206  can be placed into contact with the composition disposed on the substrate  212  for a predetermined amount time. Once the predetermined amount time has elapsed, the actuator  244  can move the substrate holder  210  away from template  201  such that the viscous polymer layer disposed on the substrate  212  is “pulled” (interchangeably referred to herein as drawn or elongated) to create fiber-like, elongate protrusions. The fiber-like protrusions (and the viscous polymer layer) are then dried under a drying air flow (either at room temperature or at a slight elevated temperature such as, for example, in a range from about 40° C. to about 80° C.) for a predetermined amount of time so as to solidify the fiber-like protrusions. 
     Referring back to  FIG. 3 , in some embodiments, the template mount  202  includes guide posts  238  and spring members  222  positioned concentrically around the guide posts  238 . The spring members  222  support the motion of the substrate holder  210  relative to the template mount  202 . The spring members  222  provide a restoring force such that in normal condition, the substrate holder  210  is distant from the template mount  202 , and more specifically, distant from the contact points  207  of template  201 . In some embodiments, during operation, the stamper arm  242  may provide a downward force, compressing the spring members  222 , thereby causing the substrate holder  210  to move toward the template  201 . The movement of the substrate holder  210  towards the template  201  causes the polymer disposed on the substrate  212  to come in contact with contact points of the template  201 . In some embodiments, after a predetermined time of contact between the contact points of the template  201  and the polymer disposed on the substrate  212 , the stamper arm  242  may release the downward force in a controlled manner to allow the spring members  222  to move the substrate holder  210  away from the template  201  at a predetermined rate. The movement of the substrate holder  210  away from the template  201  causes the template  201  to “pull” or “draw” microneedles from the polymer disposed on the substrate  212 . 
     Advantageously, the spring members  222  obviate the need for providing upward or pulling force to the substrate holder  210 , thereby simplifying the drive assembly  240  used for moving the stamper arm  242 . Moreover, because the maximum separation between the template  201  and the substrate holder  210  can be controlled by the spring members  222 , the template mount  202  can be moved away from the stamper arm  242  (either by translating the stamper arm  242  or by translating the template mount  202 ) and replaced with a new template mount  202  while the microstructure formed on the preceding template mount  202  dries. In other words, the spring loaded substrate holder  210  with a stamper arm  242  applying force in one direction enables formation of an assembly line for a high-throughput production of the microstructures such as the patch  100  described above. 
     In some embodiments, the assembly line structure may be further facilitated by structuring the table  230  to hold a plurality of template mounts  202  which can be translated over different airflow ingress channels  232 . In some embodiments, the different airflow ingress channels  232  may have different airflow characteristics depending on, e.g., whether the corresponding template mount  202  is undergoing the “pulling” step or whether a microstructure has already been formed (i.e., the template mount  202  already has a microstructure that is in process of drying). In some embodiments, the table  230  may be mounted to an assembly (not shown) to allow multiple tables  230  to be translated across the airflow ingress channels  232 . The tables  230  may further include alignment structures such as, e.g., overhang handles on opposite corners (not shown), to enable the tables  230  to nest together into a continuous line without mechanical interference. In some embodiments, the tables  230  may additionally or optionally include indexing notches to facilitate automated positions relative to the airflow ingress channels  232 . The airflow ingress channels  232  may also be fitted with locking structures (not shown) such as, for example, spring detents that reversibly lock the tables  230  over corresponding airflow ingress channels  232 . 
     Advantageously, the present disclosure enables the creation of specific microstructure configurations and as discussed herein, and some embodiments can perform such manufacturing faster and more accurately than previously possible. 
     Forced Airflow Mechanism for the Manufacturing Apparatus 
     As noted above, in some embodiments, the apparatus  200  can optionally comprise an airflow mechanism that directs air during the manufacturing process toward the microstructures to enable a uniform drying and/or solidification of the viscous polymer forming the microstructures. Without wishing to be bound by theory, air flow during solidification of the viscous polymer can provide a faster solidification and a more uniform solidification of the viscous polymer, thereby increasing the manufacturing speed (i.e., throughput), yield, and reliability of the manufacturing process. Further, when testing the microstructure products formed by the methods disclosed herein, metrology confirms the efficacy and consistency of the process. Therefore, given the speed improvements, as well as improvements in the results, substantial cost and time savings can be achieved using the methods disclosed herein. 
       FIG. 2  illustrates an aspect of the forced airflow system. The apparatus  200  illustrated in  FIG. 2  includes both the airflow ingress channels  232  and the inflow hose  234 . In some embodiments, the airflow ingress channel  232  facilitates an airflow during the manufacturing of the microstructures. 
       FIGS. 6 and 7  illustrate perspective views of the airflow ingress channel  232 , in accordance with some embodiments of the present disclosure. As shown, the airflow ingress channel  232  may include a mount or an attachment plate  402  that can connect the airflow ingress channel  232  to one of the slots  236  of the table  230 . The airflow ingress channel  232  can be formed as a hollow channel and have an inflow structure  404  that connects the attachment plate  402  to the air hose  234 . In this manner, the inflow end of the airflow ingress channel  232  can be in fluid communication with the outflow and at the attachment plate  402 . Therefore, the airflow ingress channel  232  can permit airflow  410  to the template base  204  of the template  201 . 
     In some embodiments, air may be provided to the airflow ingress channel  232  by the air hose  234  (see  FIG. 2 ), to create airflow  410  towards slot  236  and a corresponding stamping assembly  250 . Optionally, the stamping assembly  250  can comprise one or more outlet apertures that permit the airflow  410  to be directed toward the substrate  212 . In some embodiments, the template itself can comprise outlet apertures for permitting airflow therethrough to be directed toward the substrate. 
       FIG. 8  illustrates a perspective view of the template  201  that can be used for manufacturing the microstructures, in accordance with some embodiments of the present disclosure. An embodiment of the template  201  that can be used for manufacturing the microstructures is shown in a plan view in  FIG. 9  and in a side view in  FIG. 10 , to best illustrate aspects of the template, in accordance with some embodiments of the present disclosure. 
     Template Design: Raised Structures 
     The template may include a textured, raised, or other surface or structure that enables the template to be contacted against a planar surface at a plurality of contact points. These contact points can be formed from raised structures, such as a plurality of pins, bumps, pillars, and/or other structures protruding from the template. 
     For example, as shown in  FIG. 8 , the template  201  includes raised structures or points such as, for example, the pins  206  that form a plurality of contact points. These raised structures (e.g., pins  206  or bumps that have been formed by stamping or pressing the template base  204 ) can be regularly spaced on the template base  204 . 
     In some embodiments of the template  201  that include bumps formed on the template base  204 , the bumps may be formed integrally on the surface of the template base  204  (i.e., have the same material as the template base  204 ) or by externally depositing a different material on the surface of the template base  204  of the template  201 . In some embodiments, the externally provided bumps may include a second viscous polymer and a therapeutic agent. 
     The raised structures can be arranged in any of a variety of arrays or patterns. For example, the raised structures or pins  206  can be arranged in a series of rows, concentric circles, or other such patterns. The arrays can be arranged as square or rectangular arrays, comprising from 10 to 100, from 15 to 50, from 20 to 40, or about 30 contact points per row and from 10 to 100, from 15 to 50, from 20 to 40, or about 30 contact points per column. In some embodiments, the raised structures and/or the arrays can be arranged in a hexagonal configuration. Further, in some embodiments, the arrangement of the raised structures can be modified or prepared by excising certain shapes from a larger array. Other patterns can also be used, with irregular or random spacing of the protrusions, or with specific asymmetric patterns that may be tailored to be appropriate for specific body structures and surfaces desired for treatment. Additionally, multiple patches, including excised patches, can be combined into a larger composite patch, embodying specific needle densities or patterns, as desired. 
     For example, as shown in  FIGS. 8-10 , in some embodiments, the template  201  can include an array of pins (e.g., with sharp tips) or pillars (e.g., with flat heads) that extend from the template base  204  of the template  201 . In some embodiments, the length (or height) of the pins or pillars  206  can range from about 0.2 mm to about 20 mm, e.g., about 0.5 mm, about 1 mm, about 2 mm, about 5 mm, about 7.5 mm, about 10 mm, about 12.5 mm, about 15 mm, about 17.5 mm, about 20 mm, or any height between any two of these values. 
     The area, density, spacing, height, base dimensions, contact point dimensions, composition, contact point flatness, etc. attributes of the raised regions of the template  201  are not particularly limited, and can be determined by those skilled in the art based on the particular application for which the microstructure is being manufactured. 
     Accordingly, the number of raised structures on the template base  204  can be varied in accordance with a desired design or specification of the microstructure to be formed using the template  201 . In this manner, the raised structures can serve as the textured or other surface or structure that can contact a surface of the substrate  212  or a polymer disposed thereon. 
     Template Design: Airflow Apertures 
     As noted herein, providing an airflow during the manufacturing process may advantageously increase the uniformity of the airflow, increase the uniformity of drying and solidification of the composition, and decrease the processing time by accelerating the drying and solidification process. These substantial benefits can be achieved using one of the various embodiments disclosed herein. 
     These benefits and others can be achieved, for example, using airflow from the template directed toward the substrate holder through the outlet apertures in the template. 
     For example, referring now to  FIGS. 8-12 , the template  201  can optionally be configured to include one or more airflow apertures that enable airflow to be directed through the template  201  toward the substrate. As illustrated in  FIGS. 10-12 , the template  201  can include outlet apertures  208  for redirecting the airflow from the airflow ingress channel  232  out through the template  201  and toward the substrate holder  210  and substrate  212  during the manufacturing process. 
     In some embodiments, as illustrated in  FIG. 10 , the template  201  can include outlet apertures  208  spaced alternately with the pins (or pillars or bumps)  206 , to permit air outflow at the base of each pin  206 , facilitating rapid and even drying of the polymer in contact with the plurality of contacts points  207  when the template  201  is brought in contact with a polymer disposed on the substrate  212  and drawn into projections (as discussed in detail elsewhere herein). 
     The outlet apertures  208  may be formed in the template base  204  that receive air through an air ingress provided at the template holder  202 . For example, in some embodiments, air may be provided through the air hose  234 , and directed to the template  201  by the airflow ingress channel  232 . The air is the pushed through the outlet apertures  208  of the template  201  towards the substrate  212 , thereby drying and solidifying the polymer in contact with the plurality of contact points  207  of the template  201 . Without wishing to be bound by theory, an outlet aperture  208  between every adjacent pair of pins  206  of the template  201  may facilitate a uniform air flow to the viscous polymer in contact with the pins  206 . 
       FIGS. 11 and 12  illustrate an enlarged, detail view of the template  201  showing the outlet apertures  208  provided in the template base  204 . In some embodiments, as shown in  FIGS. 9 and 10 , the outlet apertures  208  are positioned between every adjacent pair of pins  206  of the template  201  and extend from a first surface  262  of the template base  204  to a second opposing surface  264  of the template base  204 . The first surface  262  in some embodiments is disposed on the template holder  202  such that the pins  206  extend from the second surface  264 . Thus, the outlet apertures  208  in some embodiments provide a path for flow of air provided through the airflow ingress channel provided at the template holder  202  to the base of each of the pins  206 . 
     The size, density, spacing, height, base dimensions, contact point dimensions, composition, contact point flatness, etc. attributes of the outlet apertures  208  of the template  201  are not particularly limited, and can be determined by those skilled in the art based on the particular application for which the microstructure is being manufactured. 
     Manufacture of the Microstructures 
     In another aspect of the present disclosure, methods of manufacturing a microstructure are described herein. The methods described herein result in microstructures that are continuous with the layer over which the microstructures are formed, thereby increasing the strength of the individual microstructures. Additionally, the method allows high-throughput and reliable manufacturing of the microstructure using, e.g., the apparatus  200  described herein. Moreover, as further described in detail herein, because a continuous film of a viscous polymer is contacted with a template, a need for aligning the template with the viscous polymer is eliminated, further increasing the throughput of the process. 
       FIGS. 14-22  illustrate the apparatus  200  for manufacturing the microstructure during various stages of performing a method of manufacturing the microstructure, in accordance with some embodiments of the present disclosure. 
     In some embodiments, a method of manufacturing a microstructure can include depositing a layer  216  of composition, such as a viscous polymer, onto a substrate  212  and contacting a template  201  having a plurality of contact points  207  against a surface of the viscous polymer layer  216 . The template  201  can be separated from the surface of the viscous polymer layer  216  to draw the viscous polymer into a plurality of projections  218 . The projections  218  are then permitted to solidify. 
       FIG. 14  shows an initial configuration where the template  201  and the substrate  212  are spaced apart such that there is a gap between the contact points  207  of the template  201  and the surface of the polymer layer  216 . In some embodiments, contacting the contact points  207  of the template against the surface of the viscous polymer layer  216  (also referred to herein as “needle-forming layer” or a “microneedle-forming layer”) may include moving the substrate  212  relative to the template  201  vertically, as illustrated in  FIG. 15 , to bring the contact points  207  in contact with the surface of the viscous polymer layer  216 , as illustrated in  FIG. 15 . 
     In some embodiments, a certain amount of time may be allowed to pass before separating the template  201  from the substrate  212  so as to form the microneedles. Such time may allow localized diffusion of the therapeutic agent into the viscous polymer so that the microstructure formed using such a template are formed loaded with the therapeutic agent. The amount of time for which the template  201  remains in contact with the substrate  212  before being separated may range from 1 second to a few minutes. For example, the time may be 1 seconds, 5 seconds, 10 seconds, 15 seconds, 20 seconds, 25 seconds, 30 seconds, 40 seconds, 50 seconds, 1 minute, 1.25 minutes, 1.5 minutes, 1.75 minutes, 2 minutes, 2.5 minutes, 3 minutes, 3.5 minutes, 4 minutes, 4.5 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, or any amount of time between any two of these values. It will be appreciated that the amount of time provided herein may be approximate within the tolerance limits of the manufacturing process. For example, the time may deviate from an intended time because of a number of factors related to the manufacturing process such as, for example, a delay in activation of the various actuators, or a delay in sensing that the template  201  and the substrate  212  are in contact. Thus, a deviation about 10% from the intended value is contemplated within the scope of the disclosure. 
     In some embodiments, the pins or pillars  206  of the template  201  may be provided with a second viscous polymer and/or a therapeutic agent. For example, the template  201  can be contacted with a layer or reservoir of the second viscous polymer in which the therapeutic agent has been dispersed prior to contacting the template  201  with the viscous polymer layer disposed on the surface of the substrate  212  on which the microstructure is to be formed. In such embodiments, the therapeutic agent may diffuse into the viscous polymer during the formation of the microneedles such that the tips of the microneedles formed using such “coated” pin/pillar array are formed loaded with the therapeutic agent. 
     Any suitable substrate  212  may be used for manufacturing the microstructures. Suitable substrates may have certain properties that enable appropriate handling and manufacturing tolerances. For example, suitable substrates may have an appropriate combination of mechanical rigidity, thickness, flatness and surface finish. 
     In some embodiments, the manufacturer of the microstructures can provide for a computer-executed program that accounts for substrate thicknesses, compositional layer thicknesses, and desired microstructure dimensions, such as length and thickness. An accurate measurement of thickness enables handling of the substrate and subsequently manufactured devices as well as knowledge of the position of an upper surface of the substrate during the manufacturing process. 
     For example, an accurate measure of layer thicknesses can enable the system to precisely control the movement of the components of the apparatus and precisely position the composition disposed on the substrate relative to the raised structures of the template. Such precise computer or manual control can facilitate movement of the upper surface of the substrate relative to a mounting surface during the manufacturing process, with known layer thicknesses enabling the system to understand and move the substrate to a position in which the mounting surface is in contact with the upper or lower surface of the substrate. Further, the system can employ any of a variety of optical sensors to control movement of its components during the manufacturing procedure. 
     For example, in accordance with some embodiments disclosed herein is the realization that if the substrate  212  is placed so that the bottom surface is in contact with a piece of equipment, the position of the top surface of the substrate  212  can be precisely defined, permitting, for example, the thickness of a polymer layer spread across the top surface to be controlled to the same precision. Further, the thickness of the substrate may impact the relative rigidity, weight, heat-capacity, and other physical characteristics of the substrate, and variations in these properties within a population of substrates can impact quality by increasing variability in the processing environment experienced by each polymer film produced. In order to account for such variations, the system can “learn” the properties of the substrates and compositions applied thereto using any of a variety of sensors and develop a suitable program or process that accounts for variation in such parameters. Additional suitable methods of casting polymers are described in U.S. Publication No. 2016/0279401, which is herein incorporated by reference in its entirety. 
     Further Aspects of Microstructure Manufacturing Processes and Systems, and Their Products 
     In addition to other details and aspects of the methods disclosed herein, the inventors of the present technology have also made certain novel and inventive realizations regarding the processes, equipment, and products disclosed herein. 
     For example, one of the aspects in accordance with some embodiments is that suitable substrates should have an appropriate amount or level of flatness. Appropriate amount/level of flatness may enable uniform spreading of the viscous polymer layer when disposed on the substrate. Moreover, variation in flatness may adversely affect the uniformity of the size of the microstructures being manufactured by causing variation in points of contact between the surface of the viscous polymer and the points of contact of the template. Similarly, variation in flatness may also result in misregistration and instability of the substrate relative to the mounting substrate. 
     In accordance with some embodiments, an appropriate surface finish of the substrate may reflect a combination of surface properties such as, for example, roughness, waviness, reflectivity and other aspects related to the microscopic topology of the substrate surface. One aspect that can be strongly dependent upon the surface finish is the tendency of the polymer solution film to adhere to the substrate, or conversely to peel away from the substrate during and after the process of drying the layer of the viscous polymer. For instance, a mirror-like surface (i.e., a very smooth, reflective surface finish) may not provide sufficient roughness to adequately anchor the drying polymer film, resulting in spontaneous peeling, while an overly grainy, rough surface tends to promote over-adhesion such that removal of the film requires such force that the microneedle arrays may be damaged. 
     Additionally, in accordance with some embodiments, surface finish can impact cleanliness, and excessive pitting can be undesirable in that such pockets could harbor bacteria and hinder removal of contaminants. Further, the reflectivity of the substrate may have a strong effect upon optical imaging of the microneedle structures formed upon the surface, and a mirror-like, highly reflective surface may make the imaging for quality analysis and inspection difficult. Some surface roughness can be desirable in order to provide a visually grainy background for imaging of the overlying transparent layer of the viscous polymer. 
     In accordance with some embodiments, suitable substrates can be of any appropriate solid or porous material onto which a polymer solution can be applied such as, for example, glass, quartz, steel, copper, backing layer materials including woven and non-woven material, polymethylmethacrylate (PMMA), etc. The thickness of the substrate may be, for example, in a range from about 0.1 inches to about 1.5 inches, with a flatness in a range from about 0.001 inches to about 0.05 inches. In some embodiments, the substrate can have a thickness of 0.7±0.002 inches. Similarly, the substrate may have a surface roughness of about N16 or smoother. For example, in some embodiments, the substrate may have a surface roughness of about N8 (i.e., average profile roughness of about 125 μm (or 3.2 μm). 
     Compositions for Microneedle Products 
     As disclosed herein, some embodiments can provide a composition that is useful to be drawn into a microneedle product. The composition can comprise a viscous polymer suitable for such applications, and optionally, one or more drugs or active agents. 
     The term “viscous polymer” used herein can refer to a composition that contains a viscous material. The viscosity of the viscous polymer may be appropriately adjusted by changing the kinds, concentrations, and temperature of a viscous material and other materials contained in the viscous polymer or by adding a viscosity modifier. Although the viscosity of the viscous polymer may not be limited to a particular value, in some embodiments, the viscosity can be 200,000 cSt or less. 
     An example of the viscous material that can be contained in the viscous polymer is a cellulose polymer such as, e.g., hydroxypropyl methylcellulose, hydroxyalkyl cellulose (preferably, hydroxyethyl cellulose or hydroxypropyl cellulose), ethyl hydroxyethyl cellulose, alkyl cellulose, and carboxymethylcellulose. Non-limiting examples of the viscosity modifier may include hyaluronic acid and salts thereof, polyvinylpyrrolidone (PVP), cellulose polymer, dextran, gelatin, glycerin, polyethylene glycol, polysorbate, propylene glycol, povidone, carbomer, gum ghatti, guar gum, glucomannan, glucosamine, dammer resin, rennet casein, locust bean gum, microfibrillated cellulose, psyllium seedgum, xanthan gum, arabino galactan, gum arabic, alginic acid, gelatin, gellan gum, carrageenan, karaya gum, curdlan, chitosan, chitin, tara gum, tamarind gum, tragacanthgum, furcelleran, pectin, or pullulan. 
     In some embodiments, the viscous polymer may contain only a viscous material. In some embodiments, the viscous polymer can further include at least one active ingredient such as, for example, a therapeutic agent. In some embodiments, the active ingredient includes drug molecules or biomolecules (i.e., biological entities). In some embodiments, the active ingredient comprises an antigen, antibody, or toxin. In still some embodiments, the active ingredient is a neurotoxin such as a botulinum toxin, for example. Botulinum toxin of types A, B, C, D and/or E can be present in the microneedle arrays. In some embodiments, the botulinum toxin is selected from the group consisting of Botulinum toxin serotype A (BoNT/A), Botulinum toxin serotype B (BoNT/B), Botulinum toxin serotype C1 (BoNT/C1), Botulinum toxin serotype D (BoNT/D), Botulinum toxin serotype E (BoNT/E), Botulinum toxin serotype F (BoNT/F), Botulinum toxin serotype G (BoNT/G), Botulinum toxin serotype H (BoNT/H), Botulinum toxin serotype X (BoNT/X), Botulinum toxin serotype J (BoNT/J), and mosaic Botulinum toxins and/or variants thereof. Examples of mosaic toxins include BoNT/DC, BoNT/CD, and BoNT/FA. In some embodiments, the botulinum toxin can be a sub-type of any of the foregoing botulinum toxins. Other suitable therapeutic agents that can be used in conjunction with the microstructures disclosed herein are discussed in U.S. Publication No. 2018/0236215 which is incorporated herein by reference in its entirety. 
     The viscous polymer, in some embodiments, may further contain at least one biocompatible material and/or a biodegradable material. The term “biocompatible material” can refer to a material that is substantially non-toxic in a human body, chemically inactive, and deficient in immunogenicity. The term “biodegradable material” can refer to a material that is degradable by body fluids or microorganisms in living bodies. The biocompatible or biodegradable material serves as a skeletal material of microstructures according to the present invention. 
     Non-limiting examples of the biocompatible material and/or biodegradable material may include polyester, polyhydroxyalkanoates (PHAs), poly(α-hydroxy acid), poly(β-hydroxy acid), poly(3-hydroxybutyrate-co-valerate) (PHBV), poly(3-hydroxy proprionate) (PHP), poly(3-hydroxyhexanoate) (PHH), poly(4-hydroxy acid), poly(4-hydroxybutyrate), poly(4-hydroxyvalerate), poly(4-hydroxyhexanoate), poly(ester amide), polycaprolactone, polylactide, polyglycolide, poly(lactide-co-glycolide) (PLGA), polydioxanone, poly(ortho ester), polyetherester, polyanhydride, poly(glycolic acid-co-trimethylene carbonate), polyphosphoester (PPE), PPE urethane, poly(amino acid), polycyanoacrylate, poly(trimethylene carbonate), poly(iminocarbonate), poly(tyrosine carbonate), polycarbonate (PC), poly(tyrosine arylate), polyalkylene oxalate, polyphosphazene, PHA-PEG, ethylenevinyl alcohol copolymer (EVOH), polyurethane, silicon, polyester, polyolefin, polyisobutylene-ethylene-α-olefin copolymer, stylene-isobutylene-stylene triblockcopolymer, acryl polymers and copolymers, vinyl halide polymers and copolymers, polyvinyl chloride, polyvinyl ether, polyvinyl methylether, polyvinylidene halide, polyvinylidene fluoride, polyvinylidene chloride, polyfluoroalkene, polyperfluoroalkene, polyacrylonitrile, polyvinyl ketone, polyvinyl aromatics, polystyrene, polyvinyl ester, polyvinyl acetate, ethylene-methyl methacrylate copolymers, acrylonitrile-stylene copolymer, polyvinyl alcohol (PVA), polyacrylates, polymers of ethylene-vinyl acetates, and other acyl substituted cellulose acetates, polyurethanes, polystyrenes, polyvinyl fluoride, polyethylene oxide, chlorosulphonate polyolefins, poly(vinyl imidazole), poly(valeric acid), poly butyric acid, poly lactides, polyglycolides, polyanhydrides, polyorthoesters, polysaccharides, gelatin, ABS resin-ethylene-vinyl acetate copolymer, polyamide, alkyde resin, polyoxymethylene, polyimide, polyether, polyacrylate, polymethacrylate, polyacrylic acid-co-maleic acid, chitosan, dextran, cellulose, heparin, hyaluronic acid, alginate, inulin, starch, glycogen and the like, mixtures, and copolymers thereof. 
     The biocompatible material or biodegradable material can have a certain level of viscosity when it is dissolved in a solvent. Examples of the solvent may include, but not limited to, water, absolute or hydrous lower alcohol having 1 to 4 carbon atoms, acetone, ethyl acetate, chloroform, 1,3-butylene glycol, hexane, diethyl ether, and butylacetate. 
     For example, in some embodiments, PVA solutions are used. A composition using a specific PVA polymer raw material (Emprove™ 40-88, USP, MilliporeSigma, Darmstadt, Germany) comprises high-purity, pharmaceutical grade, low-endotoxin polymer of a nominal average molecular weight in a range from about 50 kDa to about 5000 kDa, e.g., about 75 kDa, about 100 kDa, about 150 kDa, about 200 kDa, about 500 kDa, about 750 kDa, about 1000 kDa, about 2500 kDa, about 4000 kDa, or any molecular weight between any two of these values. Advantageously, this material produces solutions with appropriate rheological properties to efficiently produce optimally-shaped microneedles using the methods described herein. Use of a lower molecular weight grade of PVA may result in needles of incorrect/inferior morphology and reduces the yield of viable microneedle devices thus produced. 
     In some embodiments, a layer of PVA solution can be spread directly onto a steel substrate, and needle structures are formed directly from that layer, with no intervening layers or drying steps. The polymer solution used for this single-layer embodiment may be between 25-35% PVA, and for some embodiments, preferably 30%. If the polymer solution concentration is too low, thin needles will result, and fiber-like intermediate structures will tend to rupture prematurely, not forming useful needles. If the polymer solution is too high, bridging between adjacent needles may frequently occur, causing deformation and conjoined needle structures that are not useful, reducing the production yield. 
     It must be noted that production of uniform aqueous solutions containing 20% or more PVA polymer may be non-trivial. For example, it was found that in some instances, the material required substantial energy input in the form of temperature and shear, and further was highly prone to entrainment of air, forming bubbles that may be difficult to remove from the resulting high-viscosity solution. 
     Further, dissolution and full hydration of the long polymer chains may take substantial time, and incomplete or uneven processing may result in inhomogeneous solution product, with lumps or inclusions of incompletely dissolved or dispersed material. The presence of bubbles and/or lumps both create localized inhomogeneity in the polymer films utilized in the methods described herein, and produce either point-defects in which one or more needles in that region are compromised, or in the case of a lump dragged across the film during spreading, leaving a trench of non-uniform thickness, the entire film area can be compromised. Thus, the method of processing PVA to obtain a solution of requisite molecular weight and wt. % is also disclosed herein. 
     For example, in some embodiments, PVA having the requisite molecular weight is mixed with water in requisite ratio using a centrifugal mixer, which uses centrifugal force generated by a rotor arm to exert shear in an independently rotating off-axis process cup, positioned at the end of the rotor arm, which can itself be swinging the rotating cup in a continuous arc. The process cup may be heated, e.g., in a common microwave oven, and may contain both the granular PVA polymer material and the water used to form the solution. In some embodiments, the solution can be briefly boiled, promptly mixed at, a predetermined rpm for a predetermined amount of time (based on parameters such as the molecular weight of the polymer, the amount of solvent, other additives, etc.), and then left for several hours, during which time the exterior channel ions of the polymer granules hydrate further. After this hydration “rest” period, the process can be repeated, to disperse and incorporate the hydrated polymer into the solution bulk. Gradually, e.g., through 5-10 such cycles, the granules may be hydrated and eroded to the point of complete incorporation into a homogeneous polymer solution. 
     In some embodiments, the method for obtaining a PVA solution described herein, however, may generate many fine bubbles, due both to entrainment in the granular polymer raw material and to the heating cycles, which may produce localized boiling in portions of the polymer mixture, especially around incompletely dissolved granules. It is noted that generally bubbles in the highly viscous resulting solutions do not spontaneously clear by buoyancy in useful time periods, especially fine bubbles, which will remain suspended for days or weeks without further processing. Therefore, the solutions produced by this method, in some embodiments, are heated to above 50° C., and centrifuged for at least several hours, or until clear. Centrifugation at 1000×g for 3 hr at 40° C. (produces a solution with high clarity, showing few if any entrained bubbles over about 100 μm in diameter. In some embodiments, the solutions are kept under vacuum for a certain period of time to allow degassing. 
     In some embodiments, a programmable mixer with a paddle agitator can be used to slowly stir the mixture of PVA and water at a process temperature of about 90° C. for several hours until uniform. Without wishing to be bound by theory, by use of a sufficiently slow stirring speed (low enough that bubbles are not entrained into the solution) the solution can be produced with sufficiently low bubble content that a centrifugation or degassing step may not be necessary. 
     In some embodiments, the viscous polymer further can include plasticizers. Plasticizers can improve adhesion between the substrate and the polymer layer and can further improve compatibility between two polymer layers if multiple layers of polymer(s) are used. Examples of plasticizers include, but are not limited to, polyethylene glycol, glycerin, and citrate esters. 
     In some embodiments, the plasticizer can include polyethylene glycol 400 and triethyl citrate. Plasticizers make the polymer more flexible in dried form, such that the interfacial stresses that develop between the rigid substrate and the drying polymer solution, which contracts as it dries, can be relieved by stretching and similar deformation of the polymer, making it less prone to out-of-plane deformation that can result in premature or spontaneous peeling or adhesion loss. However, the flexibility can also make the microneedle structures themselves more prone to flexion, compromising skin penetration during application. Therefore, useful ranges of plasticizers are typically low, under 1% content. 
     In some embodiments, the viscous polymer can include polyvinyl alcohol (PVA). In some embodiments, the viscous polymer can include or sodium hyaluronate or hyaluronic acid (both referred to herein as HA). 
     Preparation of the Substrate for Manufacturing 
     Aspects of the manufacturing methods are recited generally herein and include contacting a plurality of raised structures against a composition disposed on a substrate. Aspects of preparation and placement of the composition on the substrate will now be described. 
     Any suitable method of disposing the viscous polymer on the substrate may be used so long as it provides a generally continuous layer with a uniform thickness. For example, in some embodiments, the viscous polymer can be disposed on the substrate using spin coating, wherein a certain amount of viscous polymer can be poured on the substrate and the substrate can be spun at a certain RPM. The RPM typically determines the thickness of the layer. In some embodiments, the substrate may be placed on a magnetic or a vacuum chuck or substrate carrier so as to immobilize the substrate during the spinning. 
     In some embodiments, the viscous polymer can be poured on a leveled substrate and allowed to spread under gravity. In some embodiments, a certain amount of viscous polymer can be poured on the substrate and a layer of desired thickness can be obtained by sliding a single-edged razor blade across the substrate at a certain separation. 
       FIGS. 13A and 13B  illustrate a method of forming a continuous layer of a viscous polymer with uniform thickness in accordance with some embodiments. In at least one embodiment, the viscous polymer is poured on a leveled substrate  1302 , and a bar (also referred to herein as a “draw bar”)  1306  is drawn across the leveled substrate  1302 . The bar  1306  may be a precision ground cylinder in an embodiment. In some embodiments, the bar may have other cross-sections such as, a rectangle, an I-beam or other suitable shapes. 
     A precise gap may be maintained between the draw bar  1306  and the substrate  1302  while the draw bar  1306  is drawn across the substrate  1302  so as to spread the viscous polymer on the substrate  1302  at a uniform thickness. The gap between the draw bar  1306  and the substrate  1302  may be set by leveling the substrate  1302  relative to two parallel rails  1308  flanking the substrate  1302 . It will be appreciated that the gap between the draw bar  1306  and the substrate  1302  determines the thickness of the continuous layer  1310  of the viscous polymer, and as such, the gap may be set based on the desired thickness of the continuous layer  1310 . 
     A stripe  1304  of the viscous polymer may then be disposed on the substrate  1302  at an amount sufficient to form the continuous layer  1310 . The draw bar  1306  may be dragged or drawn across the substrate  1302  along the rails  1308  as indicated by the arrow in  FIGS. 13A and 13B . The rate at which the draw bar  1306  is drawn across the substrate  1302  may be dependent on factors such as the viscosity of the polymer, the shape of the draw bar  1306  the desired thickness of the continuous layer  1310  and the properties of the underlying substrate  1302  (e.g., wettability of the material of the substrate  1302  by the polymer). 
     In at least one embodiment, the draw bar  1306  is biased to maintain a contact with the rails  1308  using, for example, a spring-loaded mechanism (not explicitly shown). Such a bias may be advantageous in ensuring that the gap between the draw bar  1306  and the substrate  1302  remains constant, thereby tightly controlling the thickness of the continuous layer  1310 . 
     In some embodiments, a degassing step may be needed after the layer of the viscous polymer is formed on the substrate to ensure that no air bubbles remain in the layer. 
     In some embodiments, as shown generally in  FIGS. 14, 16, 18, 20, and 21 , a second polymer layer  214 , interchangeably referred to herein as an intermediate layer or a release layer, can be provided between the substrate  212  and the needle-forming layer  216  of the viscous polymer. In accordance with some embodiments, the release layer  214  can improve adhesion or conversely permit clean separation of the overlying viscous polymer layer used for microstructure formation. 
     For example, in some embodiments, the release layer  214  can be formed of the same polymer as the microneedle layer  216 , while in some embodiments, it can be a different polymer. If a different polymer is used as a release layer, that polymer may be water-soluble, as the microneedle-forming layer, or it can be non-water soluble. Examples of water-soluble layers that can be useful as release layers include carboxymethylcellulose and polyvinyl alcohol, or any other water-soluble polymer that dries to form an adherent layer on the underlying substrate (and may further comprise a plasticizer to promote such adhesion). In some embodiments, the release layer  214  comprises polyvinyl alcohol. In some embodiments, the PVA can be applied as a solution between 20% and 30% by weight. 
     The release layer  214  may or may not remain adherent to the upper microneedle-forming polymer layer  216 , and such adherence may not necessarily be a requirement for the release layer  214  to be useful, although one may be selected so as to specifically remain adherent or not, depending upon the desired final product composition. Examples of non-water soluble layers include ethylcellulose, and most particularly a solution of 11% Aqualon EC-N100 ethyl cellulose 11% Aqualon EC-N50 ethyl cellulose (both obtained from Ashland Specialty Ingredients, Covington, Ky.), 10% water, 3% triethyl citrate (Jungbunzlauer, Ladenburg, Germany), and 0.1% glycerin (J.T. Baker, Phillipsburg, N.J.) in ethanol (quantity sufficient to 100%). 
     In embodiments including the release layer  214 , the release layer  214  can be spread over the substrate, dried, and then the needle-forming layer  216  can be spread over the top of the dried release layer  214 . The release layer  214  can typically be a different composition compared to the needle-forming layer  216 . 
     Advantageously, for example, in some embodiments, an array of microneedles can be formed by drawing needles from an HA solution that is spread as a needle-forming layer  216  over a dried PVA film  214  (as the release layer) adherent to a stainless steel substrate  212 . Without the PVA layer, the HA may spontaneously peels off during drying. The PVA layer may make the HA stay attached during drying to produce a highly planar microneedle product. On the other hand, if the HA/PVA composition described above is removed without separating the films, the underlying PVA film may make the microneedle patches much more rigid. However, the dried HA sheet may be separated from the PVA, as a relatively much more flexible product, which has obvious significant benefits and advantages that have not hitherto been achieved for this technology. 
     In some embodiments, the microneedle-forming layer  216  can comprise sodium hyaluronate or hyaluronic acid or other soluble salts of HA. In some embodiments, an aqueous solution comprising from about 10% to about 50% wt HA, from about 10% to about 45% wt, from about 15% to about 45%, from about 20% to about 45%, from about 10% to about 40%, from about 15% to about 40%, or any value within any of these ranges, can be spread into a film on a substrate  212  and further processed in accordance with the method of the present disclosure to form the microneedle structures. 
     Microstructure Films Using Release Layers 
     The present disclosure also contemplates the optional use of a release layer during the manufacturing process. Any of a variety of materials can be used as a release layer, which can be interposed between the microstructure composition and the substrate during the substrate preparation steps of the manufacturing process. 
     In accordance with some embodiments disclosed herein is the realization that HA solutions can contract as they dry and normally do not adhere strongly to a steel substrate surface used in certain embodiments. Such poorly adherent films may, therefore, be prone to spontaneous and/or premature delamination from steel substrates leading to non-planar and out-of-specification microneedle array devices. However, in some embodiments of the present disclosure, unexpectedly and advantageously, the HA solutions described herein readily spread and dry over a previously spread and dried PVA film (i.e., release layer or intermediate layer  214 ), wetting evenly and not rapidly dissolving the PVA layer. 
     Advantageously, in accordance with some embodiments disclosed herein, it was discovered that while PVA can be soluble in water, the hydration time is sufficiently long that an HA layer may be applied without fully solubilizing the PVA. Also surprisingly, in some embodiments, although the PVA layer shows signs of hydration, the loss of water from the overlying HA layer does not make it too viscous to spread evenly. Thus, while one of ordinary skill in the art may expect that either the PVA or the HA layer might be disrupted by the presence of the other material, especially with one in dry form and one in wet form, it was found that the HA layer can be evenly and regularly spread over the dried PVA layer, and will in fact dry to form a second, smooth, even, and planar layer that does not spontaneously peel off as it does from a steel substrate in the absence of the PVA layer. 
     Accordingly, use of a PVA release layer underneath the HA layer was found to be useful, in certain embodiments, to provide an enhancement of adhesion between the HA layer and the underlying steel substrate. This unique and surprising, unexpected result produces advantages and benefits superior to those available in prior microstructure manufacturing techniques and products. 
     Additionally, and advantageously, it was also observed that in some embodiments, the HA and PVA layers remain attached to the steel substrate without spontaneous peeling even when dried to an extreme dry state in a heated vacuum oven (for example 24 h drying at −18 in Hg vacuum at 40° C.). The layers do not peel prematurely, but can be removed as a single (dual layer) film from the steel with minimal force if separated using, for example, an edge of a razor blade to lift one corner from the steel surface. The layers can then be gently lifted using only light finger pressure to separate them from the steel, and remain planar after removal, so long as they are not given prolonged exposure to a humidity source. For example, in some embodiments, room temperature handling for an hour under typical 30%-60% relative humidity at 22° C.-26° C. does not produce curling, although several days&#39; exposure to these conditions will typically generate substantial curling. Storage using a desiccant packet in a closed container may prevent noticeable curling indefinitely. 
     Further, it was unexpectedly observed that, in some embodiments, an HA layer can be readily separated from a PVA layer with similar light finger pressure after lifting one edge of the film. Thus, if the razor separation described herein is performed to lift one edge of only the HA layer, leaving the PVA layer adherent to the underlying steel surface, the HA layer alone will readily peel off of the PVA film without removing the PVA from the steel surface. Without wishing to be bound by theory, it is noted that while the PVA can be hydrated by contact with the HA layer, and in fact shows changes in surface reflectivity consistent with hydration or partial solubilization, the polymer layers from the separate layers do not strongly interdigitate to form a strong interface, but rather remain as largely discrete layers even through the wetting and drying cycle of applying and drying the HA film. 
     Additionally, if the HA film is applied on top of the PVA film as described herein, but overlaps the edge of the PVA film to make contact with the underlying steel substrate, absent any underlying intermediate PVA layer, the HA in contact with the steel will spontaneously peel during drying, and further will delaminate the edge of the underlying PVA film, such that the entire dual film structure will spontaneously delaminate from the underlying steel substrate. In some embodiments, once the out-of-plane deformation of the drying HA layer is commenced, the out-of-plane forces associated with the film curling during drying are substantial enough to overcome the adherence of the PVA to the underlying steel. 
     Interestingly, as described elsewhere herein in discussing laser processing of these dual films, if the overlying HA layer is cut, as by a laser, it may be done to form a shallow cut that does not fully penetrate and sever the underlying PVA layer. Further, in some embodiments, if the PVA layer is mechanically flexed out of plane after removal from the steel substrate, the HA layer spontaneously delaminates from the PVA, providing an unexpectedly convenient method by which to separate the thin layers that does not require direct contact as by lifting the edge with a razor blade. In some embodiments, the HA layer can be removed or delaminated from the PVA layer by applying lateral shear forces by any of a number of means, including for example airflow, pressure differential, or contact methods. 
     Once the contact points  207  of the pins  206  of the template  201  are contacted with the surface of the viscous polymer  216 , the template  201  can be separated by moving the substrate holder  210  vertically away from the template  201 , as illustrated in  FIG. 16 . Such movement results in a separation of the template  201  from the surface of the viscous polymer layer  216  so as to draw the viscous polymer into plurality of projections  218 , e.g., fiber like structures extending between the surface of the viscous polymer layer  216  and the contact points  207  of the template  201 , as illustrated in  FIG. 17 . 
     It is noted that in some embodiments, the separation can be achieved either by moving the substrate  212  on which the viscous polymer is disposed relative to the template  201  or by moving the template  201  relative to the substrate  212 . The rate at which the template  201  and the substrate  212  are moved relative to each other determines the geometry and morphology of the microstructure formed. In some embodiments, the rate of separation ranges from about 2 mm/minute to about 50 mm/minute. The rate selected for making a particular morphology of microstructure, e.g., microneedles, can be dependent on the desired morphology as well as the composition of the viscous polymer and the air flow conditions. 
     For example, for embodiments using PVA as the viscous polymer, separating the substrate and the template at a rate of about 20 mm/minute results in fibers having a length in a range from about 1.5 mm to about 5 mm (depending on the exact composition and viscosity of PVA). Similarly, for embodiments using HA as the viscous polymer, separating the substrate and the template at a rate in a range from about 2 mm/min to about 5 mm/min results in fibers having a length in a range from about 2.5 mm to about 5.5 mm. 
     As illustrated in  FIG. 18 , the projections  218 , i.e., fibers, thus formed are then permitted to solidify. As disclosed herein, the solidification process may, in some embodiments, be accelerated by providing an air flow across the projections  218 . In embodiments where the air flow is facilitated via outlet apertures (e.g., outlet apertures  208 ) provided in the template base  204  of the template  201 , a more uniform pressure distribution may be obtained across the template  201 , thereby improving the uniformity of the morphology of formed projections (i.e., fibers). In some embodiments, the air flow passing through the outlet apertures to reach the viscous polymer layer can be about 0.5 cfm. In some embodiments, heat may also be applied in addition to or in lieu of the air flow to aid or accelerate solidification of the projections. 
     Processing of Microstructure Products 
     After the microstructure has been formed using the drawing techniques disclosed herein, thereby creating a plurality of fiber-like, elongate protrusions, these elongate protrusions can be separated from the raised structures of the template. In some embodiments, as disclosed herein, the substrate and the template can be maintained at a specific separation distance while the fiber-like, elongate protrusions solidify. Thereafter, the fiber-like, elongate protrusions can be cut or broken at a desired point along their length in order to form the microstructure. 
     For example, once the projections  218  extending from the contact points  207  of the template  201  to the surface of the viscous polymer layer  216  are formed and solidified, the projections  218  may be cut, as illustrated in  FIGS. 19 and 20 , at a desired height (from the surface of the viscous polymer) to form the desired microstructure illustrated in  FIG. 19 . Typically, the microstructure formed upon cutting the projections  218  can be an array of microneedles  220 . Depending on the exact process used to form such array of microneedles  220 , the individual microneedles  220  may or may not include a therapeutic agent. The microneedles  220  may have a length in a range from about 10 μm to about 2070 μm. 
     Any suitable method may be used for cutting the projections  218  to form the microneedles  220 . 
     For example, in some embodiments, the cutting of the projections  218  can be performed in a manner in which the template  201  and the substrate  212  on which the viscous polymer is disposed are moved laterally relative to each other to break the projections. 
     In some embodiments, the cutting of the projections  218  can be performed in a manner in which an ultrasound pulse can be applied to either the template  201  or the substrate  212  (or both) so as to break the projections  218 . 
     In some embodiments, the cutting of the projections  218  can be performed in a manner in which the distance (i.e., a vertical or axial distance in the direction of initial separation) between the substrate  212  and the template  201  can be further increased so as to break the protrusions. 
     In some embodiments, the cutting of the projections  218  can be performed in a manner in which a single edged razor blade or a thin, taut string (not shown in the figures) can be passed between the substrate  212  and the template  201  to break the projections  218 . 
     However, care should be taken to ensure that the cutting method provides the desired degree of accuracy. Alternatively stated, the performance of some methods may not be able to provide a sufficient uniformity of the microneedles  220  after breaking the projections because the cutting of individual projections may not be sufficiently controlled. 
     Therefore, in accordance with at least some embodiments disclosed herein is the realization that a highly precise cutting method may be desirable for certain applications or indications. In some embodiments, as illustrated in  FIGS. 19 and 20 , the projections  218  can be cut using a focused laser  302 . Thus, the length (i.e., height) of the microneedles  220  formed can be controlled accurately across the entire array of microneedles. Any suitable laser that can cut the solidified viscous polymer used for forming the projections  218  can be used for this purpose. For example, a continuous wave CO 2  laser  302  with a wavelength of 9.4 μm and 10.6 μm (i.e., in the infrared spectrum) may be used for polymer materials such as PVA. 
     In accordance with some embodiments, the method can be performed by adjusting a power of the laser  302  to a suitable or desired level based on the materials of the microstructure(s). For example, because cutting using such a focused infrared laser  302  is primarily a thermal process, the factors that may be considered when adjusting the power of the laser  302  include, but are not limited to, composition of the viscous polymer, the speed/rate at which the projections  218  are cut (i.e., the amount of time an individual projection  218  is exposed to the laser), tolerance to charring or oxidation at the tip of the microneedle (e.g., depending on whether the microneedle is pre-loaded with a therapeutic agent), possible blunting of the tip of the microneedle, possible localized “flow” at the tip of the microneedle due to heat, etc. For example, in some embodiments, PVA needles are cut to length while still containing high water content (approximately 10%-40% wt), which may reduce the tendency to oxidize or char. However, PVA may also be cut after fully drying (approximately ≤5% wt water) without charring at reduced power. 
     Some materials used for forming the microneedles  220 , e.g., HA, may not be suitable for thermal cutting such as using an infrared laser, as they may readily oxidize and char if treated with such a laser. For such materials, an ultrafast pulsed laser may be used for cutting the projections. 
     For example, without wishing to be bound by theory, a laser pulse of 1 ns duration or shorter can produce a light intensity sufficient to produce a gaseous plasma as it interacts with the HA polymer surface, instantaneously evaporating the material in a so-called “ablative energy regime” as distinct from a “thermal energy regime.” In the ablative energy regime, material can be removed more quickly than thermal transfer processes can occur, leaving the surface relatively cool. The pulsed nature of the laser processing enables a long cooling so-called “dark” cycle, during which any thermal energy generated can dissipate in the bulk material. The combination of ultra-short ablative pulses and proportionally long dark periods makes laser processing of materials like HA very favorable in terms of preventing oxidation or charring during processing. 
     In accordance with some embodiments disclosed herein, the pulsed laser cut of HA as described herein produces needles that have a smooth surface and a sharp transition from non-cut to cut surface, i.e., squared-off, minimal radius at the cut origin. This may be advantageous in relation to skin penetration, presenting a microscopically sharp edge. 
     While materials like PVA are more tolerant of heat, with less susceptibility to oxidation than materials like HA, protrusions formed of materials like PVA can also be cut effectively with a pulsed laser system. In some embodiments, the ultrafast pulsed laser system includes a nanosecond pulsed ultraviolet laser (355 nm). Other examples include, but are not limited to, lasers having femtosecond pulse length range. 
     Referring now to  FIG. 22 , following the formation of microneedles  220 , the now solidified viscous polymer layer  216  can be cut into individual dies which then form patches  224  to be applied to the subject. This can be accomplished by applying dicing cuts to divide the now solidified viscous polymer layer  216  disposed on the substrate  212  from which the microneedles  220  are pulled. 
     For example, in some embodiments, these cuts can be provided mechanically with a blade or blade-like cutter or using a dicing laser  304 . The discussion relating to the applicability of various types of lasers for cutting polymer projections  218  to form the microneedles  220  can be applicable for the dicing cuts as well and will not be repeated herein for brevity, but is incorporated by a specific reference thereto. 
     Thus, in some embodiments, dicing cuts can be performed by a continuous infrared laser while in some embodiments the dicing cuts can be performed by an ultrafast laser, examples of both of which are discussed herein. Among the various considerations when selecting an appropriate laser for the dicing cuts is the material of the substrate  212 , as will be appreciated by a person of skill in the art. 
     For example, in embodiments where a steel substrate is used, the steel substrate is normally unaffected by incident infrared laser light at this power, experiencing at most brief local heating and cooling. Thus, the substrate can be simply cleaned and reused for another cycle of microneedle manufacture after patches are removed. However, the nanosecond pulsed laser cuts produce such high peak energy that an underlying steel substrate  212  can be damaged during cutting. Thus, in instances where a nanosecond pulsed laser is more desirable, e.g., because of the material of the microneedles  220 , a substrate  212  that is transparent to the wavelength of the pulsed laser such as, for example, quartz, may be used as the substrate  212 . 
     In some embodiments, the microneedles  220  fabricated using the methods of the present disclosure are fabricated while still adherent to the underlying substrate  212 . Individual patches  224 , in various embodiments, can be cut (diced) from the continuous polymer layer  216  either while the layer is adherent to the substrate  212  or after it is removed. At some point, however, the layer must be removed from the substrate  212  for packaging. In some embodiments, this can be accomplished by use of a thin or sharpened edge, such as the sharp edge of a razor blade that is inserted under one edge of the polymer layer  216  at the contact point with the substrate  212 . 
     Alternatively, an adhesive contact to an upper surface of the polymer layer  216  can be used to lift one edge of the layer  216 . Without wishing to be bound by theory, it is contemplated that the polymer layer  216  can be strongly adherent to the substrate  212  if removed strictly normal to the surface of the substrate  212 . However, if the polymer layer  216  is peeled away in a non-coplanar orientation relative to the substrate  212 , it may separate relatively cleanly at the point of flexion between the lifted edge and the adherent, as yet planar area still attached to the substrate  212 . 
     When fully dried, the polymer layer  216  can separate from a correctly finished substrate  212  without leaving behind any visible residue on the substrate  212 . In some embodiments, the polymer layer  216  retains the micro-topology of the substrate surface  212 , producing a slight opacity due to light scatter associated with the surface finish. However, in some embodiments, if a sacrificial separation layer (e.g., a release layer  214 ) is used, when the top-most needle-forming layer  216  is separated from the release layer  214 , the needle-forming layer  216  can be observed to be relatively optically clear, not having been in direct contact with the textured substrate surface  212 . 
     Incorporation of Drugs or Therapeutic Agents Into the Microstructures 
     As disclosed herein, the composition used for the microstructure can comprise and/or be coated with one or more drugs or therapeutic agents. Some embodiments of methods for loading a drug or therapeutic agent onto the microstructure will be discussed herein below. 
     In accordance with some embodiments disclosed herein is the realization that because of the geometry and material properties of the microneedles  220 , spontaneous wetting of the microneedles  220 , e.g., by dipping the tips of the microneedles  220  into a solution in which a requisite therapeutic agent is dispersed, may be risky due to forces caused by surface tension at the interface of the tips and the solution. However, in some embodiments, contact loading can be accomplished by contacting the tips of the microneedle  220  structures to the fibrous tip of a marker pen charged with an aqueous solution in which a requisite therapeutic agent is dispersed, or by inserting the tip of each microneedle into the small aperture of a micropipet tip loaded with the aqueous solution. 
     In some embodiments, as discussed in detail with reference to  FIG. 23 , a non-contact method of loading is to dispense nanoliter-scale droplets  604  of the solution of the therapeutic agent into free space above the tip  226  of each microneedle  220 . In some embodiments, a commercially available dispensing tool (e.g., a dispensing robot) is adapted to generate droplets  604  of a fixed volume (depending on the rheological properties of the solution of the therapeutic agent) as the dispensing head  602  moves across the uniformly spaced microneedles  220 , such that the droplets fall regularly onto the tips  226  of the microneedle  220  structures. 
     In some embodiments, a microporous sponge (not explicitly shown) loaded with a solution including the therapeutic agent can be contacted with the tips  226  of the microneedles  220 . Without wishing to be bound by theory, when an aqueous loading solution is charged into the interstitial spaces of a sponge material or a marker pen consisting of a set of parallel microfibers, the surface tension of the solution can be greatly reduced, as if it were wetted in the internal space of a capillary. In this reduced free energy state, the risk of spontaneous catastrophic wetting of the array can be virtually eliminated, and the sponge or marker can be applied to the microneedle arrays as an effective loading method. 
     In some embodiments, patches  224  of microneedles  220  loaded with a therapeutic agent are further dried to reduce the water content therein to prevent compromising the stability of the therapeutic agent and improving the rigidity of the microneedle structures. In some embodiments, the patches  224  are dried to reduce the water content to be less than about 5%, e.g., less than about 1%. The drying, in various embodiments, can be performed by placing the patches  224  under vacuum for a certain amount of time. For example, in some embodiments, the patches  224  are dried by placing the patches  224  under vacuum of about 20 mm Hg for about 12 hours. 
     The dried patches can then be packaged for storage. In some embodiments, microneedle patches  224  loaded with a therapeutic agent can be packaged in a thermoformed blister package. In some embodiments, additional headspace, insulating layers, or other precautions may be included in the design of the blister packages to remove the loaded tips from the hot surface normally used to fuse the foil backing of the blister package to the overlying thermoform plastic pockets so as to prevent thermal degradation of a heat-sensitive therapeutic agent loaded onto the microneedles. In some embodiments, to increase the robustness and storage stability of the microneedle patch loaded with a therapeutic agent, a desiccant and/or oxygen scavenger can be included in the blister package containing the microneedle patch. 
     In various embodiments, microneedle patches  224  manufactured using the methods described herein have, for example, less than about 5% microneedles deviating from normal (i.e., a line perpendicular to the surface of the solidified viscous polymer). Further the microneedle arrays formed using PVA as the viscous polymer are tolerant of levels of gamma irradiation consistent with sterilization (e.g., 18-50 kGy) with no visually discernible changes. In some embodiments, the microneedle patches manufactured using the methods described herein included a toxin complex (obotuluminum A) having an average molecular weight in a range from about 207 kDa to about 900 kDa. 
     The formed microneedles, in some embodiments, are provided with a therapeutic agent such as, for example, a formulation including onabotulinumtoxin A. Referring again to  FIG. 22 , a therapeutic agent can be applied directly to the microneedles using a dispensing device. 
     For example, in some embodiments, a non-contact method of loading can comprise dispensing nanoliter-scale droplets of the solution of the therapeutic agent into free space above the tip of each needle. Such a technique can be considered to be “drip loading” or “bolus dripping.” In some embodiments, a commercially available dispensing tool (e.g., a dispensing robot) is adapted to generate, e.g., approximately 6 nL droplets as the dispensing head moves across the uniformly spaced microneedles, such that the droplets fall regularly onto the tips of the needle structures. 
     Referring still to  FIG. 23 , in some embodiments, a piezoelectric actuator may deliver a pressure pulse perpendicular to the axis of a polyamide dispense tube  602  (“pipe” or dispensing head). The resulting compression shock ejects a droplet or bolus  604  from the tip of the pipe  602 , which almost instantaneously refills by capillary action from a reservoir vertically above the pipe. In some embodiments, the same disposable pipet tip initially utilized to aliquot the loading solution may be reused for each run as the pipe reservoir, so as to minimize the surface area that might adsorb toxin from the loading solution. The robotic dispenser, in some embodiments, can use microstepper motors to provide high positional repeatability such that the bolus  604  is repeatably dispensed on different arrays of microneedles  220 . Without wishing to be bound by theory, if a bolus  604  is released in a near-vertical trajectory in free-air, a well-formed microneedle structure readily captures the bolus  604  delivered from above. 
     In some embodiments, droplets deposit onto the strongly hydrophilic surface of the microneedle tips  226  and may typically remain localized to the top 30% of the needle structure (e.g., approximately 250 μm); droplets do not flow or splash down the sides of the needles, nor splash into smaller droplets. Splash and nonlocalized deposition may be readily apparent when droplet formation and ejection dynamics are not correctly set up, or in the case of irregularly spaced or malformed needles. The dosing of the microneedles using such method may be performed while the patches  224  are still attached to the underlying substrate or have been separated from the substrate, although being attached to the substrate may provide ease of handling and control. Factors that determine reproducible formation of the bolus  604  include, but are not limited to solution viscosity and surface tension. 
     In some embodiments, the microneedle structures may be formed from water-soluble polymers. In such microneedles, it might be expected that superficial application of droplets of aqueous solutions used to load the tips of the microneedles would cause dissolution, swelling, or collapse of the structures, rendering them deformed, dulled, or otherwise unsuitable for use as injection devices. Surprisingly, however, it was found that the tips of the microneedles formed as described are capable of absorbing the moisture from the droplets (as evidenced by the lack of splashing or drip patterns) without apparent ill effect. 
     Following the application of the bolus  604 , when the structures are re-dried, no loss of integrity or skin penetration capability was observed. For example, when a model solution of sodium fluorescein was loaded onto the microneedles  220  and dried, and the microneedles  220  were cut so as to observe the tip cross-section, a fluorescence image showed that the fluorescent compound was distributed upon the exterior of the needle surface. Surprisingly, it was observed that the fluorescent compound had diffused also into the bulk material of the needle tip. Without wishing to be bound by theory, the diffusion may have occurred due to partial hydration of that material carrying the drug to the interior. 
       FIG. 24  shows a photomicrograph of a cross-sectional top view, taken along a longitudinal axis, of a microneedle loaded with a hydroalcoholic solution of sodium fluorescein. The diffusion of the payload (sodium fluorescein) into the interior of the microneedle structure can be clearly seen. The characteristic orange-red color of the concentrated fluorescein material is evident at the exterior surface (demarcated by the region  450 , which extends around the perimeter of the microneedle cross section), while the interior of the needle structure is the bright green of a lower concentration of the material. The microneedle in the image was loaded with the hydroalcoholic solution of sodium fluorescein by the dip-loading method described herein. Thereafter, the microneedle was partially dried and mechanically cut with a razor blade to generate a cross-section. The image was obtained under white light, rather than by a fluorescent microscope, by imaging top-down, looking at the cut surface. It must be noted that while the microneedle seen in  FIG. 24  has a peanut-shaped cross-section, microneedles with other cross-sectional shapes are expected to behave similarly in terms of payload diffusion. 
     One persistent issue in available coated microneedle products has been that the coating layer carrying the drug payload is prone to prematurely separate from the underlying microneedle structure due to the forces applied to these surfaces during skin penetration, leaving the drug payload at the skin surface without delivery to deeper layers. The diffusion of the drug payload into the interior of the soluble microneedles disclosed herein appears to render the loading solution continuously distributed into the microneedle tip, so that the risk of payload loss during skin penetration is vastly reduced. Thus, surprisingly, the hydration of the polymer materials from which the microneedles during the drug loading process does not pose a weakness. Instead, it confers an advantage in regard to effective delivery of the drug payload, rendered integral to the polymer structures by that same property of polymer hydration. From observation of fluorescein payloads, in some embodiments, the distribution of drug may be inferred to be maximal at the needle surface and minimal at the center of the coated tip of the needle, distributed consistent with diffusion laws. Such diffusion pattern is an identifiable characteristic of the presently disclosed microneedles. As the microneedle tips embed in the skin and hydrate to form intracutaneous depots, this drug distribution may further confer advantages in regard to drug release profiles, e.g., during subsequent depot clearance. 
     Illustration of Subject Technology as Clauses 
     Various examples of aspects of the disclosure are described as numbered clauses (1, 2, 3, etc.) for convenience. These are provided as examples, and do not limit the subject technology. Identifications of the figures and reference numbers are provided below merely as examples and for illustrative purposes, and the clauses are not limited by those identifications. 
     Clause 1. A method of manufacturing a microstructure, comprising: disposing a viscous polymer onto a substrate to form a continuous, viscous film layer; contacting a template against a surface of the viscous film layer, the template having a plurality of contact points contacting the viscous film layer surface; while urging air toward the viscous film layer from the template, separating the template from the viscous film layer surface to draw the viscous polymer into a plurality of projections; and permitting the plurality of projections to solidify. 
     Clause 2. The method of Clause 1, wherein the substrate comprises one of steel, copper, glass, quartz, and polymethylmethacrylate (PMMA). 
     Clause 3. The method of any one of the preceding Clauses, wherein the substrate has a surface roughness of about N16 or smoother. 
     Clause 4. The method of any one of the preceding Clauses, wherein dispensing the viscous polymer comprises pouring a predetermined amount of the viscous polymer on the substrate and drawing a bar across the substrate while maintaining a predetermined gap between the bar and the substrate. 
     Clause 5. The method of any one of the preceding Clauses, wherein the template comprises a plurality of pins extending from a base layer, and wherein the tips of the plurality of pins forming the plurality of contact points. 
     Clause 6. The method of any one of the preceding Clauses, wherein the template comprises a plurality of bumps raised from a base layer, the plurality of bumps being formed integrally with the base layer, the plurality of bumps forming the plurality of contact points. 
     Clause 7. The method of any one of the preceding Clauses, wherein the template comprises a plurality of bumps comprising a second viscous polymer disposed thereon, the plurality of bumps forming the plurality of contact points, and wherein the contacting the template comprises contacting the second viscous polymer against the viscous film layer. 
     Clause 8. The method of Clause 7, wherein the plurality of bumps further comprise a therapeutic agent disposed thereon, and wherein contacting the template comprises contacting the therapeutic agent against the viscous film layer. 
     Clause 9. The method of any one of the preceding Clauses, wherein the separating comprises separating the template from the surface of the viscous polymer at a predetermined rate. 
     Clause 10. The method of any one of the preceding Clauses, further comprising an intermediate viscous polymer layer disposed on the substrate intermediate the viscous polymer and the substrate, the intermediate viscous polymer layer comprising a second viscous polymer different from the viscous polymer. 
     Clause 11. The method of Clause 10, wherein the intermediate layer comprises ethyl cellulose (EtC) and the viscous polymer comprises one of hyaluronic acid or a salt thereof (HA) and polyvinyl alcohol (PVA). 
     Clause 12. The method of Clause 10, wherein the intermediate layer comprises PVA and the viscous polymer comprises HA. 
     Clause 13. The method of any one of the preceding Clauses, wherein the template further comprises outlet apertures spaced alternately with the plurality of contact points, and wherein the urging air toward the viscous film layer is performed using the outlet apertures. 
     Clause 14. The method of Clause 13, wherein each of the outlet apertures is fluidly coupled with a respective ingress channel at a base of each of the plurality of contact points. 
     Clause 15. The method of Clauses 14, wherein the permitting the plurality of projections to solidify comprises providing an airflow to projections through the outlet apertures during and/or after the drawing of the viscous polymer into the plurality of projections. 
     Clause 16. The method of Clause 15, wherein the urging air toward the viscous film layer comprises urging heated air toward the viscous film layer. 
     Clause 17. The method of any one of the preceding Clauses, wherein the viscous polymer comprises one or more of a viscous material, a biodegradable or biocompatible material, a solvent, and a plasticizer. 
     Clause 18. The method of any one of the preceding Clauses, wherein the viscous polymer comprises one of polyvinyl alcohol, and hyaluronic acid or a salt thereof. 
     Clause 19. The method of any one of the preceding Clauses, further comprising separating the solidified projections from the template to form the microstructure. 
     Clause 20. The method of Clause 17, wherein the separating the solidified projections comprises cutting the solidified projections using a blade. 
     Clause 21. The method of Clause 17, wherein the separating the solidified projections comprises cutting the solidified projections using an infrared laser 
     Clause 22. The method of Clause 17, wherein the separating the solidified projections comprises cutting the solidified projections using an ultrafast pulsed laser. 
     Clause 23. The method of any one of Clauses 17-20, further comprising contacting the microstructure with a therapeutic agent. 
     Clause 24. The method of Clause 21, wherein the therapeutic agent comprises a toxin complex having an average molecular weight in a range from about 207 kDa to about 900 kDa. 
     Clause 25. The method of any one of Clauses 17-22, further comprising irradiating the microstructure with gamma radiation. 
     Clause 26. A microstructure comprising protrusions from a surface of a continuous layer of a solidified viscous polymer formed by a method comprising: disposing the viscous polymer on a substrate; contacting a surface of the viscous polymer with a template having a plurality of contact points; drawing the viscous polymer at points of contact between the surface of the viscous polymer and the plurality of contact points while urging air toward the viscous film layer from the template to form the protrusions; permitting the protrusions to solidify; and separating the solidified protrusions from the template to form the microstructure. 
     Clause 27. The microstructure of Clause 26, further comprising a therapeutic agent disposed at distal ends of the microstructure away from the surface of the solidified viscous polymer. 
     Clause 28. The microstructure of Clause 27, wherein the therapeutic agent comprises a toxin complex having an average molecular weight in a range from about 207 kDa to about 900 kDa. 
     Clause 29. The microstructure of any one of Clauses 26-28, wherein the microstructure comprises microneedles, wherein less than 5% microneedles deviating from a line normal to the surface of the viscous polymer. 
     Clause 30. The microstructure of Clause 26, wherein the separating the solidified projections comprises cutting the solidified projections using a blade. 
     Clause 31. The microstructure of Clause 26, wherein the separating the solidified projections comprises cutting the solidified projections using an infrared laser. 
     Clause 32. The microstructure of Clause 26, wherein the separating the solidified projections comprises cutting the solidified projections using an ultrafast pulsed laser. 
     Clause 33. The microstructure of any one of Clauses 26-32, wherein the substrate comprises an intermediate layer disposed thereon, the intermediate layer comprising a second viscous polymer different from the viscous polymer. 
     Clause 34. The microstructure of Clause 33, wherein the intermediate layer comprises ethyl cellulose (EtC) and the viscous polymer comprises one of hyaluronic acid or a salt thereof (HA) and polyvinyl alcohol (PVA). 
     Clause 35. The microstructure of Clause 33, wherein the intermediate layer comprises PVA and the viscous polymer comprises HA. 
     Clause 36. The microstructure of any one of Clauses 26-33, wherein the template further comprises outlet apertures spaced alternately with the plurality of contact points, and wherein the method of forming the microstructure comprises urging air through the outlet apertures toward the viscous polymer. 
     Clause 37. The microstructure of Clause 36, wherein each of the outlet apertures is fluidly coupled with a respective ingress channel at a base of each of the plurality of contact points. 
     Clause 38. The microstructure of Clause 36, wherein the permitting the plurality of projections to solidify comprises providing an airflow to projections through the outlet apertures after the viscous polymer is drawn into the plurality of projections. 
     Clause 39. The microstructure of Clause 37, wherein the urging air toward the viscous film layer comprises urging heated air toward the viscous film layer. 
     Clause 40. The microstructure of any one of Clauses 26-39, wherein the viscous polymer comprises one of polyvinyl alcohol, and hyaluronic acid or a salt thereof. 
     Clause 41. The microstructure of any one of Clauses 26-40, wherein the substrate has a surface roughness of about N16 or smoother. 
     Clause 42. The microstructure of any one of Clauses 26-41, wherein the method further comprises cutting the solidified viscous polymer layer on which the microstructure is formed to form microstructure patches. 
     Clause 43. The microstructure of Clause 42, wherein the cutting the solidified viscous polymer layer comprises cutting the solidified viscous polymer layer using a blade. 
     Clause 44. The microstructure of Clause 42, wherein the cutting the solidified viscous polymer layer comprises cutting the solidified viscous polymer layer using a continuous infrared laser. 
     Clause 45. An apparatus for manufacturing a microstructure, comprising: a substrate carrier configured to carry a substrate; a template holder configured to carry a template having a plurality of contact points and enable a flow of air through outlet apertures disposed in the template; and an assembly configured to: enable the plurality of contact points to contact a surface of a viscous polymer layer disposed on the substrate provided on the substrate carrier; draw the viscous polymer at points of contact between the surface of the viscous polymer and the plurality of contact points to form protrusions of the viscous polymer; and permit the protrusions to solidify. 
     Clause 46. The apparatus of Clause 45, wherein the substrate carrier comprises a magnetic chuck configured to immobilize the substrate. 
     Clause 47. The apparatus of Clause 45, wherein the substrate carrier comprises a vacuum chuck configured to immobilize the substrate. 
     Clause 48. The apparatus of any one of Clauses 45-47, wherein the template holder comprises a vacuum chuck configured to immobilize the template. 
     Clause 49. The apparatus of any one of Clauses 45-47, wherein the template holder comprises a magnetic chuck configured to immobilize the template. 
     Clause 50. The apparatus of any one of Clauses 45-49, wherein the template comprises outlet apertures spaced alternately with the plurality of contact points. 
     Clause 51. The apparatus of Clause 50, wherein the template holder comprises an airflow ingress channel configured to provide air through the outlet apertures of the template. 
     Clause 52. The apparatus of any one of Clauses 45-51, wherein the assembly comprises a mechanism to move the template holder relative to the substrate carrier along a line perpendicular to a surface of the viscous polymer layer disposed on the substrate. 
     Clause 53. The apparatus of any one of Clauses 45-51, wherein the assembly comprises a mechanism to move the substrate carrier relative to the template holder along a line perpendicular to a surface of the viscous polymer layer disposed on the substrate. 
     Clause 54. The apparatus of any one of Clauses 52-53, wherein the mechanism comprises one or more of a motorized actuator, a pneumatic actuator and a piezoelectric actuator. 
     Clause 55. The apparatus of any one of Clauses 45-54, further comprising a laser configured to cut the solidified protrusions. 
     Clause 56. The apparatus of Clause 55, wherein the laser is a continuous infrared laser. 
     Clause 57. The apparatus of Clause 55, wherein the laser is an ultrafast pulsed laser. 
     Clause 58. The apparatus of any one of Clauses 45-57, further comprising a laser configured to cut the solidified viscous polymer layer on the substrate. 
     Clause 59. A method of manufacturing a microstructure, comprising: disposing a first water-soluble viscous polymer onto a substrate to form a first layer; disposing a second water-soluble viscous polymer onto the first layer to form a second layer; contacting a template against a surface of the second layer, the template having a plurality of contact points contacting the second layer surface; separating the template from the second layer surface to draw the second viscous polymer into a plurality of projections; and permitting the plurality of projections to solidify. 
     Clause 60. The method of Clause 59, wherein the first viscous polymer is different from the second viscous polymer. 
     Clause 61. The method of any one of Clauses 59-60, wherein the first viscous polymer comprises polyvinyl alcohol and the second viscous polymer comprises hyaluronic acid or a salt thereof. 
     Clause 62. The method of any one of Clauses 59-61, wherein the disposing comprises evenly spreading the second water-soluble viscous polymer over the first water-soluble viscous polymer. 
     Clause 63. The method of any one of Clauses 59-62, wherein when dried, the second layer does not spontaneously peel off of the first layer. 
     Clause 64. The method of any one of Clauses 59-63, wherein the first layer and the second layer are smooth, planar layers. 
     Clause 65. The method of any one of Clauses 59-64, further comprising peeling the microstructure from the substrate as a dual layer microstructure. 
     Clause 66. The method of any one of Clauses 59-65, wherein the first and second layers remain attached to the substrate without spontaneous peeling even when dried in a heated vacuum oven for 24 hours at −18 Hg vacuum at 40° C. 
     Clause 67. The method of any one of Clauses 59-66, wherein the first and second layers remain as manually separable separate layers. 
     Clause 68. The method of any one of Clauses 68-67, wherein the disposing the second water-soluble viscous polymer comprises overlapping the second layer onto the first layer with at least a portion of the second layer extending beyond a perimeter edge of the first layer to contact the substrate. 
     Clause 69. The method of Clause 68, wherein during drying, the second layer in contact with the substrate spontaneously peels away from the substrate. 
     Clause 70. The method of Clause 69, wherein the second layer delaminates from the substrate and causes the first layer to delaminate from the substrate. 
     Clause 71. A method of manufacturing a microstructure, comprising: disposing a viscous polymer onto the intermediate layer to form a continuous layer; contacting a template against a surface of the continuous layer, the template having a plurality of contact points contacting the continuous layer surface; separating the template from the continuous layer surface to draw the viscous polymer into a plurality of projections; permitting the plurality of projections to solidify; separating the plurality of contact points from the solidified projections to form a plurality of microneedles; and disposing a bolus of a therapeutic agent on a tip of each of the plurality of microneedles. 
     Clause 72. The method of Clause 71, wherein the disposing comprises contacting the bolus of the therapeutic agent directly with the tip. 
     Clause 73. The method of any one of Clauses 71-72, wherein the therapeutic agent comprises a toxin complex having an average molecular weight in a range from about 207 kDa to about 900 kDa. 
     Clause 74. The method of any one of Clauses 71-73, wherein separating the template from the continuous layer surface is performed while urging air toward the continuous film layer from the template. 
     Further Considerations 
     The foregoing description is provided to enable a person skilled in the art to practice the various configurations described herein. While the subject technology has been particularly described with reference to the various figures and configurations, it should be understood that these are for illustration purposes only and should not be taken as limiting the scope of the subject technology. 
     There may be many other ways to implement the subject technology. Various functions and elements described herein may be partitioned differently from those shown without departing from the scope of the subject technology. Various modifications to these configurations will be readily apparent to those skilled in the art, and generic principles defined herein may be applied to other configurations. Thus, many changes and modifications may be made to the subject technology, by one having ordinary skill in the art, without departing from the scope of the subject technology. 
     It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. Some of the steps may be performed simultaneously. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented. 
     In some embodiments, any of the clauses herein may depend from any one of the independent clauses or any one of the dependent clauses. In one aspect, any of the clauses (e.g., dependent or independent clauses) may be combined with any other one or more clauses (e.g., dependent or independent clauses). In one aspect, a claim may include some or all of the words (e.g., steps, operations, means or components) recited in a clause, a sentence, a phrase or a paragraph. In one aspect, a claim may include some or all of the words recited in one or more clauses, sentences, phrases or paragraphs. In one aspect, some of the words in each of the clauses, sentences, phrases or paragraphs may be removed. In one aspect, additional words or elements may be added to a clause, a sentence, a phrase or a paragraph. In one aspect, the subject technology may be implemented without utilizing some of the components, elements, functions or operations described herein. In one aspect, the subject technology may be implemented utilizing additional components, elements, functions or operations. 
     The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a microneedle” includes reference to one or more microneedles, and reference to “the polymer” includes reference to one or more polymers. 
     In one or more aspects, the terms “about,” “substantially,” and “approximately” may provide an industry-accepted tolerance for their corresponding terms and/or relativity between items, such as from less than one percent to five percent. 
     The term “subject” refers to a mammal that may benefit from the administration using a transdermal device or method of this disclosure. Examples of subjects include humans, and other animals such as horses, pigs, cattle, dogs, cats, rabbits, and aquatic mammals. 
     As used herein, the term “active agent” or “drug” are used interchangeably and refer to a pharmacologically active substance or composition. Active agents in various embodiments may include small molecule drugs (e.g., nicotine), proteins (e.g., antigens, biologics, etc.), toxins (e.g., neurotoxins such as onabotulinumtoxin A), nucleic acids (e.g., siRNA, genetic vectors, etc.), diagnostic molecules (e.g., radioisotopes, superparamagnetic nanoparticles, etc.), allergens (e.g., extracts of pollen, nuts, egg, wheat, etc.), or combinations thereof. 
     The term “transdermal” refers to the route of administration that facilitates transfer of a drug into and/or through a skin surface wherein a transdermal composition is administered to the skin surface. 
     As used herein, the term “substantially” refers to the complete or nearly complete extent or degree of an action, characteristic, property, state, structure, item, or result. 
     As used herein, sequences, compounds, formulations, delivery mechanisms, or other items may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. 
     As used herein, the term “therapeutic agent” means an agent utilized to treat, combat, ameliorate, prevent or improve an unwanted condition or disease of a patient. Additives such as permeation enhancers, controlled-release membranes, humectants, emollients, and the like may also be included in the therapeutic agent. 
     Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. As an illustration, a numerical range of “about 0.5 to 10 g” should be interpreted to include not only the explicitly recited values of about 0.5 g to about 10.0 g, but also include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 5, and 7, and sub-ranges such as from 2 to 8, 4 to 6, etc. This same principle applies to ranges reciting only one numerical value. Furthermore, such an interpretation should apply regardless of the breadth of the range or the characteristics being described. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although any methods, devices and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, representative methods, devices, and materials are described below. 
     The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over some embodiments. 
     A reference to an element in the singular is not intended to mean “one and only one” unless specifically stated, but rather “one or more.” Pronouns in the masculine (e.g., his) include the feminine and neuter gender (e.g., her and its) and vice versa. The term “some” refers to one or more. Underlined and/or italicized headings and subheadings are used for convenience only, do not limit the subject technology, and are not referred to in connection with the interpretation of the description of the subject technology. All structural and functional equivalents to the elements of the various configurations described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and intended to be encompassed by the subject technology. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the above description. 
     Although the detailed description contains many specifics, these should not be construed as limiting the scope of the subject technology but merely as illustrating different examples and aspects of the subject technology. It should be appreciated that the scope of the subject technology includes some embodiments not discussed in detail above. Various other modifications, changes and variations may be made in the arrangement, operation and details of the method and apparatus of the subject technology disclosed herein without departing from the scope of the present disclosure. Unless otherwise expressed, reference to an element in the singular is not intended to mean “one and only one” unless explicitly stated, but rather is meant to mean “one or more.” In addition, it is not necessary for a device or method to address every problem that is solvable (or possess every advantage that is achievable) by different embodiments of the disclosure in order to be encompassed within the scope of the disclosure. The use herein of “can” and derivatives thereof shall be understood in the sense of “possibly” or “optionally” as opposed to an affirmative capability.