Patent Publication Number: US-11641699-B2

Title: Temperature controlled electrospinning substrate

Description:
This application is a divisional application of U.S. application Ser. No. 15/952,174, filed on Apr. 12, 2018, which claims the benefit of U.S. Provisional Application No. 62/484,513, filed on Apr. 12, 2017. These applications and all other publications and patent documents referred to throughout this nonprovisional application are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure is generally related to devices used in electrospinning and/or heat sealing. 
     DESCRIPTION OF RELATED ART 
     Electrospun mats or biopapers, such as those described in US Pat. Appl. Pub. No. 2017/0183622 and U.S. Pat. No. 8,669,086, are useful for many cell culture processes (Bischel et al., “Electrospun gelatin biopapers as substrate for in vitro bilayer models of blood-brain barrier tissue”  J. Biomed. Mat. Res. A,  104(4), 901-909). However, fundamental aspects such as their thin profile and degradable nature make them very delicate. They are not easily sealed to devices using standard ultrasonic horns, as the vibrations damage the biopapers. The biopapers can be sealed with precise application of heat, but the application has to be only applied to small areas where bonding is desired. Furthermore, too much heat in either intensity or duration will degrade the paper and ruin its function. This process when done by hand is time consuming, increasing cost and limiting scalability. 
     BRIEF SUMMARY 
     Disclosed herein is a device comprising: an article having a flat surface and a lower surface opposed to the flat surface; a cavity formed in the lower surface forming a complete loop surrounding a central portion of the article; a heating element having the same shape as the complete loop disposed in the cavity and positioned to warm a portion of the flat surface adjacent to the heating element when the heating element is activated; a cooling device positioned to cool a portion of the flat surface in the central portion; and a release layer on the flat surface. 
     Also disclosed herein is a device comprising: an article having an upper surface; a heating element disposed on the upper surface forming a complete loop surrounding a central portion of the article; and an electrically insulating material disposed on the upper surface within the central portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation will be readily obtained by reference to the following Description of the Example Embodiments and the accompanying drawings. 
         FIG.  1 A  illustrates a single heat sealing unit and  FIG.  1 B  illustrates an arranged array of sealing units for high-throughput. 
         FIG.  2    shows a cross section view (as viewed from the side) of the heat sealing unit. 
         FIG.  3    shows a heat sealing process of deposited biomaterial to substrate. 
         FIG.  4    shows the flat surface of an array. 
         FIG.  5    shows an alternative arrangement of the device. 
         FIG.  6    shows an array of the devices with electrospinning substrates and a mask. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     In the following description, for purposes of explanation and not limitation, specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to one skilled in the art that the present subject matter may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods and devices are omitted so as to not obscure the present disclosure with unnecessary detail. 
     Disclosed is a biomaterial heat sealing array to heat seal a biomaterial to an appropriate substrate (e.g. plastic frame) in defined geometries by combining resistive heating and fluid cooling. Also disclosed is a device for electrospinning deposition and further such heat sealing. 
     A first embodiment is illustrated in  FIGS.  1 A-B . Individual heat sealing units ( FIG.  1 A ) may be arranged into an array ( FIG.  1 B ), allowing for high-throughput fabrication of heat-sealed biomaterials. Each individual unit, as well as the array as a whole, may fabricated from a metal or metal alloy. The array may be fabricated from a single piece of material or by individual units placed next to each other (e.g. interlocking). After fabrication, a thin release layer or non-stick coating layer (e.g. PTFE) is added to the bottom of the array. For illustration purposes, a circular geometry for the heat sealing has been shown in all figures however some frames or substrates may have a different geometry, such as for example square, rectangular, or triangular. 
       FIG.  1 A  shows device  10  with the article  15  having a lower surface  20 . The flat surface is unseen on the other side of the article  15  and has a nonstick release layer, such as polytetrafluoroethylene. The device  10  includes a cavity  25 , which defines the geometry of the heat seal, surrounding a circular middle section or central portion  30 . A heating element  35  is placed within the cavity  25  to warm the flat surface. A cooling element  40  is within the central portion  30  to cool the flat surface. In this example, the cooling element includes metal cooling fins. 
       FIG.  1 B  shows an apparatus  100  having multiple devices  110  formed from a single article. The devices have a common flat surface (not shown). 
       FIG.  2    shows a vertical cross-section of the device  10  and article  15 , with the lower surface shown  20  at the top and the flat surface  22  shown at the bottom. The cavity  25  extends nearly to the flat surface  22  surrounding the central portion  30 , with the heating element  35  at the bottom. The cooling element includes the flow of a coolant  45  through a coolant inlet  70 , a hollow chamber  75  over the central portion  30 , and a coolant outlet  80 . The black area  50  is heated by the heating element  35 . 
     In this example, the outer cavity is a circle. The outer cavity has an electrically insulated resistive heating wire laid within the continuous loop. To heat seal the biomaterial, a current is passed through the wire, transferring heat from the wire to the metal alloy of the heat sealing unit. Heat transfer is primarily through conduction, passing through the thin metal between the outer cavity and the bottom of the heat sealing unit. Heat transferred from the resistive wire to the interior area of the outer cavity is dispersed by fluid cooling in the middle section. The middle section consists of two holes in which a fitting can be placed, and through which a fluid coolant (water or another coolant) may flow. The fitting holes connect tubing located outside of the unit to a hollow chamber, which directs the path of the fluid coolant. Coolant is circulated by means of a fluid pump; the coolant flows through the tubing, into the hollow chamber, and then back out of the chamber in a closed circuit. The bottom surface of the hollow chamber has several solid metal cooling fins designed to transfer heat from the metal to the fluid coolant. An alternative arrangement could use a thermoelectric cold plate (e.g. Peltier cooling with heat conducting fingers cooling the center area rather than fluid cooling) with electrical connections and an insulating material between cooling fingers and heat coils. 
     The process consists of depositing the biomaterial to be sealed to the flat surface of the heat sealing array, on top of the non-stick coating, as shown in  FIG.  3   . The deposition method may be by electrospinning. Alternatively, an already-formed membrane, such as those disclosed in US Pat. Appl. Pub. No. 2017/0183622 and U.S. Pat. No. 8,669,086, may be placed onto the flat surface. Such membranes may have a porous polymeric film permeated by a first extracellular matrix material and a topcoat layer comprising a second extracellular matrix gel disposed on the film. The substrate  65  to which the biomaterial  60  will be sealed is positioned above the heat sealing array, lowered, and placed in direct contact with the biomaterial. The depicted substrate  65  has a number of transwell inserts whose edges align with the heating regions of the array. Electrical current is supplied to the (insulated) resistive heating wire in the outer cavity of each heat sealing unit in the array, while the cooling element is activated. The shape, timing, and amperage of the current pulse can all be tuned to affect the desired surface temperature required for optimal heat sealing. Simultaneously, fluid coolant will be pumped through the middle section, causing the outer rim to be heated, while the inner circle is cooled. This causes sealing to the substrate in the heated section, while the cooled section remains unsealed. The release layer  55  allows for removing the sealed biomaterial from the flat surface. 
       FIG.  4    shows the flat surface of an array. The heated sections (black) are defined by electrical current flowing through the insulated wire. Cooled regions (lined), caused by fluid coolant, confine the transfer of heat to only the defined circular geometry. This image illustrates only the temperature profile; the actual surface is flat and unmarked, providing a uniform receiving substrate for electrospinning or for a prefabricated membrane. 
       FIG.  5    illustrates a second embodiment of a device  110  where the relevant features are on an upper surface  121  of an article  115 . A heating element  135  as described above (shown before placement) is disposed on the upper surface  121  around the central portion  130 . An electrically insulating material  185  is on the central portion  130  to prevent the heating element  135  from short-circuiting across the central portion  130 . The article  115  and/or the electrically insulating material  185  may comprise a polymer, as electrical isolation between multiple devices in an array may be needed. A cooling element (not shown) such as a thermoelectric material, may be positioned under the central portion  130 . 
       FIG.  6    shows an array  200  of the devices  110 , which may be formed from a single article or may be separate devices attached to each other. Such an array, or a single device, may be used by placing an electrically conducting substrate  190  on each heating element and the electrically insulting material. The electrically conducting substrates  190  may be grounded through the heating elements so that they may receive electrospun material. An electrically insulting mask  195  having one or more holes  197  are placed on the electrically conducting substrate  190 . The holes  197  are positioned over the electrically conducting substrates  190 . A membrane of biocompatible material is then electrospun over the entire array  200 , after which the mask  195  may optionally be removed. As described above, a substrate is then applied to the membrane(s) and the heating and any cooling elements are activated to heat seal the membrane(s) to the substrate(s). 
     A potential advantage is the ability to more uniformly create heat sealed biopaper constructs, and do so more quickly, at higher volume and with less effort. Through the use of materials with high thermal conductivity (e.g. metal) and small surface area/volume ratios, heat can be transferred quickly to the defined heat sealing pattern, drastically decreasing the amount of time needed for complete sealing. The ability to heat seal multiple substrates at once greatly increases the volume that can be produced in a given time compared to manual methods. As currently described, the heat sealing process requires little human intervention; the biomaterial deposition, heat sealing, and fluid cooling can all be controlled through automated processes. 
     The overall design may be highly adaptable, and may be easily altered to fit a number of different heat sealing geometries, biomaterials, and deposition methods. Different biomaterials may require different temperatures for heat sealing, which can be simply controlled by varying the electrical current supplied to the resistive heating wire. The heat sealing array could also be revised for other deposition methods, such as extrusion bioprinting (Ozbolat et al., “Current advances and future perspectives in extrusion-based bioprinting”  Biomaterials,  76, 321-343 (2016)) or microcontact printing (Qin et al., “Soft lithography for micro- and nanoscale patterning”  Nature Protocols,  5(3), 491-502 (2010)), amongst others. The only constraint of the deposition process is that it produces a uniform layer of the biomaterial over a defined area. The implementation of individual heat sealing units clustered into an array provides the potential for high scalability, as the deposition area can be as large or small as desired. 
     The scalability heat sealing array design and process may be particularly attractive for commercial applications. The primary costs and constraints are associated with the design of the heat sealing geometry and the size of the array. Once the geometry design has been finalized and the array fabricated, the device can be repeatedly used indefinitely. Much like commercial plastic injection molding, the price per heat sealed unit will drastically decrease as higher volumes are needed. 
     Obviously, many modifications and variations are possible in light of the above teachings. It is therefore to be understood that the claimed subject matter may be practiced otherwise than as specifically described. Any reference to claim elements in the singular, e.g., using the articles “a”, “an”, “the”, or “said” is not construed as limiting the element to the singular.