Patent Publication Number: US-2023146045-A1

Title: Catheter-deployable soft robotic sensor arrays and processing of flexible circuits

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63/015,344, entitled “CATHETER-DEPLOYABLE SOFT ROBOTIC SENSOR ARRAYS AND PROCESSING OF FLEXIBLE CIRCUITS,” filed Apr. 24, 2020, the contents of each of which are hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Atrial fibrillation (AFib) is the most common form of cardiac arrhythmia, with a worldwide prevalence of more than 33 million people worldwide. AFib causes an irregular and often rapid heart rate that may cause symptoms like palpitations, fatigue, and shortness of breath. It originates from the interplay between genetic predisposition, ectopic electrical activity, and abnormal atrial tissue substrate. AFib can affect the efficiency of cardiac output and promote the formation of blood clots inside the left atrium (particularly the left atrial appendage). If these clots embolize and travel from the heart to the brain, they could result in a stroke. AFib is associated with a 1.5- to 2-fold increase in death and heart failure and about 3- to 5-fold higher risk of stroke. Furthermore, AFib is also associated with a greater risk of hospitalization, with 10 to 40% of patients with this disease hospitalized annually. 
     Radiofrequency catheter ablation has emerged as an established and widespread technique for the treatment of AFib via a minimally invasive catheter procedure. Cardiac electrograms can be mapped using a sensing catheter, and then radiofrequency energy is applied to the heart muscle at particular locations to cauterize the circuits that trigger AFib, using an ablation catheter. This procedure can provide rhythm control in patients with paroxysmal and persistent AFib. There is strong evidence that AFib ablation therapy improves quality of life, reduces health resource utilization, and improves heart function in patients with heart failure. For the ablation procedure, electro-anatomical mapping techniques have been developed to guide the procedure. By recording the electrical activity inside the heart, the circuits that are generating AFib can be identified. 
     Cardiac mapping and ablation helps provide an effective means of treatment for Atrial fibrillation (AFib). Accurate and efficient cardiac mapping and ablation calls for medical devices capable of conforming to the internal structure of the heart chamber of interest. Manufacturing such devices that can also be deployed to the heart chamber of interest poses various technical challenges. 
     SUMMARY 
     In various potential embodiments, the systems, devices and methods described in this disclosure relate to fabrication of durable soft robotic devices and fabrication of flexible circuits as well as implementations of such robotic devices and flexible circuits. The soft robotic devices described herein are suitable for efficient left atrial mapping as well as other applications, and are catheter deployable. Once deployed, the soft robotic device can be actuated to expand and conform to the internal structure of an organ of interest. Conforming to the internal structure of the organ of interest or other anatomical structures allows for more precise mapping or sensing of signals generated by the organ. Different geometric configurations can be provided for different anatomical configurations. The fabrication of flexible circuits can involve using scalable circuits, e.g., printed circuit boards (PCBs), and applying selective removal of insulation layers while retaining the integrity of the circuit. The flexible circuit can be fixated or laminated on an outer surface of a soft actuator to form the soft robotic device. 
     At least one aspect of the present disclosure is directed to a method. The method can include identifying one or more regions of a printed circuit board (PCB) for selectively removing insulation material. The PCB can include one or more electrically conductive structures arranged on an insulation layer. The method can include applying, within each region of the one or more regions, thermal energy via a heat source to a surface of the PCB within the region such that insulation material of the insulation layer is removed from the region while a portion of the insulation layer beneath the one or more electrically conductive structures is maintained. 
     In some implementations, applying the thermal energy can include applying the thermal energy along a raster path within the region. In some implementations, the method can further include determining an output thermal energy range of the heat source to cause the insulation material of the insulation layer to be removed from the region while maintaining the portion of the insulation layer beneath the one or more electrically conductive structures, and setting the heat source to generate the thermal energy according to the output thermal energy range prior to applying the thermal energy to the surface of the PCB. In some implementations, the output thermal energy range is determined based on a first temperature specific to the insulation layer and a second temperature specific to the one or more electrically conductive structures. In some implementations, the output thermal energy range can be based on a thickness of the insulation layer. In some implementations, the output thermal energy range can be based on a thickness of the one or more electrically conductive structures. 
     In some implementations, the heat source can be a laser cutter and applying the thermal energy to the surface of the PCB can include applying a laser beam of the laser cutter to the surface of the PCB according to a raster path within the region. In some implementations, the method can further include determining an output power range of the laser cutter to cause the insulation material of the insulation layer to be removed while maintaining the portion of the insulation layer beneath the one or more electrically conductive structures, and setting the laser cutter according to the output power range prior to applying the laser beam to the surface of the PCB. 
     In some implementations, the PCB can include one or more sensors and identifying one or more regions can include identifying one or more first regions of the PCB that do not include any of the one or more sensors. The one or more sensors can be located within one or more second regions of the PCB where the insulation layer is not removed. In some implementations, the one or more sensors can include a plurality of sensors, and the one or more second regions include a plurality of second regions. The plurality of sensors can be distributed among the plurality of second regions. 
     In some implementations, the one or more electrically conductive structures can include copper traces. In some implementations, the insulation layer can include a polymer layer. In some implementations, the one or more electrically conductive structures can be exposed within the one or more regions to sense electrical voltage of a surrounding environment. In some implementations, the one or more electrically conductive structures can have a serpentine shape to allow the one or more electrically conductive structures to stretch within the one or more regions when the insulation layer is removed. In some implementations, the maintained portion of the insulation layer beneath the one or more electrically conductive structures can allow the one or more electrically conductive structures to maintain mechanical integrity within the region. In some implementations, the PCB can include a flexible PCB. 
     In some implementations, the PCB can include a plurality of insulation layers. The thermal energy can be applied, within each region of the one or more regions, to the surface of the PCB, such that insulation material of the plurality of insulation layers is removed from the region while a portion of one or more insulation layers beneath the one or more electrically conductive structures is maintained. 
     At least one other aspect of the present disclosure is directed to an apparatus. The apparatus can include a plurality of blocks of an insulation layer including a one or more circuit components. Each block connected to an adjacent block via one or more connectors made from the insulation layer. The apparatus can include one or more electrically conductive structures deposited on and defining a first surface of the one or more connectors. The one or more electrically conductive structures extending between and across the plurality of blocks. 
     In some implementations, the one or more circuit components can include one or more sensors distributed among the plurality of blocks of the insulation layer. In some implementations, the one or more electrically conductive structures can include copper traces. In some implementations, the insulation layer includes a polymer layer. In some implementations, a portion of the one or more electrically conductive structures extending between the plurality of blocks can be exposed to sense electrical voltage of a surrounding environment. 
     In some implementations, a thickness of the plurality of blocks is about about 30 μm, about 35 μm, about 40 μm, about 45 μm, about 50 μm, about 55 μm, about 60 μm, about 65 μm, about 70 μm, about 75 μm, about 80 μm, about 85 μm, about 90 μm, about 95 μm, about 100 μm, about 105 μm, about 110 μm, about 115 μm, about 120 μm, about 125 μm, about 130 μm, about 135 μm or about 140 μm. In some implementations, a thickness of the one or more connectors can be about 15 μm, about 20 μm, about 25 μm, about 30 μm, about 35 μm, about 40 μm, about 45 μm, about 50 μm, about 55 μm, about 60 μm, about 65 μm, about 70 μm or about 75 μm. In some implementations, a thickness of the one or more electrically conductive structures is about 15 μm, about 20 μm, about 25 μm, about 30 μm, about 35 μm, about 40 μm, about 45 μm, about 50 μm, about 55 μm, about 60 μm, about 65 μm, about 70 μm or about 75 μm. 
     At least one other aspect of the present disclosure is directed to a method. The method can include aligning at least one flexible circuit with a soft actuator. Each flexible circuit of the at least one flexible circuits can include a plurality of blocks of an insulation layer including a one or more circuit components, and one or more electrically conductive structures deposited on and defining a first surface of the one or more connectors. Each block can be connected to an adjacent block via one or more connectors made from the insulation layer. The one or more electrically conductive structures can extend between and across the plurality of blocks. The method can include laminating the at least one flexible circuit with a polymer sheet on a surface of the soft actuator to form a soft robotic device. The polymer sheet can be configured to provide, for the at least one flexible circuit, insulation and mechanical fixation to the soft actuator. 
     In some implementations, the soft actuator can include a plurality of beams and the method can include aligning each flexible circuit of a plurality of flexible circuits to a corresponding beam of the plurality of beams, and laminating each flexible circuit with a separate polymer sheet on a surface of the corresponding beam of the soft actuator. In some implementations, the soft robotic device can be a cardiac mapping device deployable into a heart chamber using a catheter. In some implementations, the polymer sheet can be a polyurethane sheet. In some implementations, the soft actuator can include nitinol. 
     In some implementations, the soft actuator can include polymer and the method can further include manufacturing the soft actuator. Manufacturing the soft actuator can include arranging a sheet of water soluble polymer between two layers of polymer, and thermally bonding the two layers of polymer around respective borders. The sheet of water soluble polymer can act as a sacrificial layer to form an inflatable closed channel between the two bonded layers of polymer. In some implementations, the method can further include making a plurality of cutouts in the sheet of water soluble polymer, and thermally bonding the two layers of polymer at the plurality of cutouts to achieve bending regions in the soft actuator when the soft actuator is actuated. The plurality of cutouts can be distributed along a length of the sheet of water soluble polymer. In some implementations, the water soluble polymer can include polyvinyl alcohol. 
     In some implementations, the method can further include making one or more cutouts in the polymer sheet. The one or more cutouts partially exposing portions of the one or more electrically conductive structures extending between the plurality of blocks of the insulation layer. In some implementations, the one or more electrically conductive structures and the one or more connectors can have serpentine shapes. In some implementations, one or more electrically conductive structures can include copper traces. In some implementations, each connector of the one or more connectors can be substantially aligned with the conductive structure deposited on the connector 
     At least one other aspect of the present disclosure is directed to apparatus. The apparatus can include an inflatable actuator and one or more flexible circuits laminated with one or more polymer sheets on a surface of the inflatable actuator. Each flexible circuit can include a plurality of blocks of an insulation layer including a one or more circuit components, where each block is connected to an adjacent block via one or more connectors made from the insulation layer, and one or more electrically conductive structures deposited on and defining a first surface of the one or more connectors, the one or more electrically conductive structures extending between and across the plurality of blocks. 
     In some implementations, each connector of the one or more connectors can be substantially aligned with a corresponding conductive structure deposited on the connector. In some implementations, the apparatus can be a cardiac mapping device deployable into a heart chamber using a catheter. In some implementations, the inflatable actuator can include nitinol. In some implementations, the inflatable actuator can include polymer. 
     In some implementations, the inflatable actuator can include a sheet of water soluble polymer arranged between two layers of polymer. The two layers of polymer can be thermally bonded around respective borders and the sheet of water soluble polymer can act as a sacrificial layer to form an inflatable closed channel between the two bonded layers of polymer. In some implementations, the water soluble polymer can include polyvinyl alcohol. In some implementations, the sheet of water soluble polymer can include a plurality of cutouts distributed along a length of the sheet of water soluble polymer. The two layers of polymer can be thermally bonded at the plurality of cutouts to achieve bending regions in the inflatable actuator. 
     In some implementations, the one or more polymer sheets can include one or more cutouts exposing portions of the one or more electrically conductive structures extending between the plurality of blocks of the insulation layer. In some implementations, the one or more electrically conductive structures can include copper traces deposited on the one or more connectors. 
     At least one other aspect of the present disclosure is directed to a method for manufacturing flexible sensor arrays. The method can include identifying one or more regions of a flexible printed circuit board (PCB) for selectively removing polymer. The flexible PCB can include one or more sensors and one or more electrically conductive serpentine structures between a first polymer layer and a second polymer layer. Each electrically conductive serpentine structure can be connected to a corresponding sensor of the one or more sensors. The method can include applying, within each region of the one or more regions, thermal energy via a heat source to a first surface of the flexible PCB along a raster path within the region such that polymer in the first polymer layer and the second polymer layer is removed from the region while a portion of the second polymer layer beneath the one or more electrically conductive serpentine structures is maintained. 
     These and other aspects and implementations are discussed in detail below. The foregoing information and the following detailed description include illustrative examples of various aspects and implementations, and provide an overview or framework for understanding the nature and character of the claimed aspects and implementations. The drawings provide illustration and a further understanding of the various aspects and implementations, and are incorporated in and constitute a part of this specification. Aspects can be combined and it will be readily appreciated that features described in the context of one aspect of the invention can be combined with other aspects. Aspects can be implemented in any convenient form. For example, by appropriate computer programs, which can be carried on appropriate carrier media (computer readable media), which can be tangible carrier media (e.g. disks) or intangible carrier media (e.g. communications signals). Aspects can also be implemented using suitable apparatus, which can take the form of programmable computers running computer programs arranged to implement the aspect. As used in the specification and in the claims, the singular form of ‘a’, ‘an’, and ‘the’ include plural referents unless the context clearly dictates otherwise. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are not intended to be drawn to scale, unless specifically indicated in a particular drawing. Like reference numbers and designations in the various drawings indicate like elements. For purposes of clarity, not every component can be labeled in every drawing. In the drawings: 
         FIG.  1    depicts an example PCB, according to example embodiments of the current disclosure; 
         FIG.  2    depicts a flowchart illustrating a method of manufacturing flexible circuits, according to example embodiments of the current disclosure; 
         FIGS.  3 A- 3 G  depict a selective material removal process and related experimental results, according to example embodiments of the current disclosure; 
         FIG.  4 A- 4 B  depict a sample flexible PCB and corresponding simulation and experimental results illustrating material removal temperatures for a single pulse of various powers, according to example embodiments of the current disclosure; 
         FIGS.  5 A- 5 D  depict experimental and simulation results illustrating heat masking and processing windows to achieve successful self-aligned removal, according to example embodiments of the current disclosure; 
         FIGS.  6 A- 6 E  depict experimental and simulation results illustrating processing windows, with respect to thickness and resolution of metallic structures to achieve successful self-aligned removal, according to example embodiments of the current disclosure; 
         FIG.  7    depicts an example flexible/stretchable circuit, according to example embodiments of the current disclosure; 
         FIG.  8    shows a flowchart illustrating a method  500  of fabricating/manufacturing soft robotic devices, according to example embodiments of the current disclosure; 
         FIGS.  9 A- 9 H  show diagrams illustrating various steps a process of manufacturing a stretchable/flexible soft robotic device, according to example embodiments of the current disclosure; 
         FIG.  10 A- 10 D  depict durability experimental results illustrating the durability of the soft robotic device; and 
         FIG.  11    depicts experimental results of Micro CT conformability experiments to assess conformability of the soft robotic device. 
     
    
    
     DETAILED DESCRIPTION 
     Devices or systems that perform cardiac mapping and ablation to treat AFib can provide an effective means of treatment. Existing cardiac mapping devices, however, have limitations that either require tedious point-by-point mapping of a cardiac chamber or have limited ability to conform to the complex anatomy of a patient&#39;s cardiac chamber. For instance, some electro-anatomical mapping systems have limited spatiotemporal resolution for detecting localized AFib drivers because of their sequential spatiotemporal characteristics, intermittent firing, and complex atrial anatomy. These are some of the reasons for suboptimal outcomes after ablation in some forms of AFib. Subsequently developed advanced mapping catheters, such as basket catheters, with multi-electrode arrays mitigate this drawback. The advantages of multi-electrode mapping include quicker voltage mapping and more accurate assessment of activation sequence. However, conventional multi-electrode catheter designs are fabricated from sensor arrays that are deployed on a cage of inelastic materials (either metal wire or narrow strips of inelastic polymer film) designed to passively engage with tissue. These designs have limited conformability and other non-ideal mechanical response, such as spline bunching (e.g., a non-uniform distribution of the sensor arrays due to improper deployment/expansion of the device in the left atrium). The effective result of these unintended mechanical responses is that less than 50% of the sensors provide meaningful data. 
     In this disclosure, implementations of soft robotic devices, e.g., multi-electrode soft robotic sensor array (SRSA) devices, and methods for developing such soft robotic devices are described. The soft robotic device can be equipped with a flexible, and/or stretchable, circuit such as an array of flexible/stretchable electronic sensors for voltage mapping. The form factor of the soft robotic device can be intended to match that of an entire cardiac chamber (e.g., left atrium) or other anatomical chamber, and can have a hydraulically actuated soft structure whose profile can facilitate deployment from a 13.5-Fr catheter. For instance, the SRSA device can uniformly conform at least 128 flexible sensors to the cardiac chamber (e.g., left atrium) tissue by hydraulically actuating a thin-walled polymer cage. In experimental testing, manufactured SRSA devices were deployed in four soft three-dimensional printed atrial models, and experimental testing results show that an average of about 85 to 90% of the sensors made tissue contact or were close enough (e.g., less than 2 mm distance, as assessed by micro-computed tomography (μ-CT)) to a left atrium inner wall to establish robust near-field sensing. Furthermore, the robustness of various designs were experimentally illustrated by deploying the devices from a 13.5-Fr catheter tube, and showing that sensors could undergo 100 cycles of actuation without reduction of performance. 
     The development of the soft robotic devices poses several challenges, such as scalable fabrication, integration and associated mechanical durability. To achieve conformable soft robotic devices, approaches for fabricating soft actuator designs with high degrees of complexity are used. The focus was on designs with the ability to conform to patient atria, or more generally to a complex chamber. Also, an approach for post-processing PCBs (e.g., flexible PCBs (flex-PCBs)) with electrically conductive structures (e.g., serpentine sensor array designs) can be used to fabricate stretchable and/or flexible circuits (e.g., flexible/stretchable sensor arrays). Specifically, a self-aligned post-processing method can be used to remove inelastic substrates (or insulation layers) of the flexible PCB (flex-PCB), and therefore increase the flexibility of the circuit or sensor array. The resulting flexible circuit (e.g., sensor array) can then be integrated or fixated on a soft actuator. Approaches for soft actuator fabrication are employed to develop complex geometry SRSAs capable of mounting at least 128 sensors, or other complex geometry circuits. 
     The processes and techniques described herein allow for fabrication of soft robotic devices without costly and time-consuming clean-room fabrication, using scalable PCB or flex-PCB manufacturing. The principles, procedures, and techniques described herein are valuable tools not only for cardiac mapping, but also for a wide variety of applications where sensor arrays or electric circuits are integrated on soft actuators, especially when thin or low-profile designs are needed. Embodiments of the systems and methods described in this disclosure are suitable for conformable medical devices that leverage the characteristics of stretchable electronics and soft robotics. 
     The remainder of the description is organized into multiple sections. For the purposes of reading the remainder description of the various implementations and techniques described herein, the following brief descriptions of the sections of the Specification may be helpful. 
     Section A describes flexible circuits and respective manufacturing processes. 
     Section B describes soft robotic devices and respective manufacturing processes. 
     A. Flexible Circuits and Respective Manufacturing Processes 
     Referring to  FIG.  1   , a PCB  100  is shown, according to example embodiments of the current disclosure. The PCB  100  can include one or more circuit components  102  and one or more electrically conductive structures  104 . The one or more circuit components  102  and the one or more electrically conductive structures  104  can be arranged on an insulation layer  106  (also referred to as an insulation substrate). 
     In some implementations, the PCB  100  can be a flexible PCB where the insulation layer  106  can be, or can include, a polymer (or polyimide) layer. In some implementations, the PCB  100  can include a plurality of insulation layers  106 . The plurality of insulation layers  106  can include, or can be, polymer layers. In such implementations, the circuit components  102  and/or the electrically conductive structures  104  can be arranged or sandwiched between two insulation layers (or polymer layers) of the plurality of insulation layers  106 . 
     While  FIG.  1    shows a plurality of circuit components  102  and a plurality of electrically conductive structures  104 , the PCB can include any number of (e.g., one or more) circuit components  102  and any number of (e.g., one or more) electrically conductive structures  104 . In some implementations, the circuit components  102  can include one or more sensors. The one or more sensors can include an electric voltage sensor, an electric impedance/resistance sensors, a force sensor, a shear sensor, an ultrasound senor, a thermal sensor, a position sensor, an electrocardiogram sensor, an electrochemical sensor or a combination thereof, among others. 
     In some implementations, each electrically conductive structure  104  can have a serpentine or flexuous shape that is bending or winding alternately from side to side. The electrically conductive structures  104  can also be referred to as metallic structures  104 . The serpentine or flexuous shape can allow the electrically conductive structures  104  to stretch longitudinally, e.g., if not sealed to, or integrated on, the insulation layer  106 . The electrically conductive structure(s)  104  can be electrically connected to the circuit component(s)  12  or sensor(s) a corresponding sensor  102 . In some implementations, each electrically conductive structure  104  can be connected to a corresponding sensor. When in contact with, or in proximity to, organ tissue, the electrically conductive structure  104  can carry electric signals between the tissue to the corresponding sensor. The electrically conductive structures  104  can include (or can be) metallic traces, such as copper traces or traces of other conductive metals. The electrically conductive structures  104  can be relatively narrow (in width), e.g., acting as electric wires or electric connections. 
     Referring now to  FIG.  2   , a flowchart illustrating a method  200  of manufacturing flexible circuits is shown, according to example embodiments of the current disclosure. The method  200  can include identifying one or more regions of a PCB for selective removal or of insulation material (STEP  202 ). The PCB can include one or more circuit components and one or more electrically conductive structures arranged on an insulation layer. The method  200  can include applying thermal energy to a surface of the flexible PCB to remove the insulation layer within the one or more regions while maintaining a portion of the insulation layer beneath the one or more electrically conductive structures (STEP  204 ). 
     Referring to  FIGS.  1  and  2   , the method  200  can include identifying one or more regions of PCB  100  for selectively removing insulation material (STEP  202 ). The PCB  100  can be as described above with regard to  FIG.  1   . For instance, PCB  100  can include or can be a flexible PCB and/or may include a plurality of insulation layers. In some implementations, identifying the one or more regions can include identifying one or more first regions of the PCB that do not include any of the circuit components  102 , or do not include any of the sensors. For instance, the one or more regions can include the electrically conductive structure(s)  104 , but not any of the circuit component(s) or not any of the sensors. The one or more regions can be window regions. For instance, each of the one or more regions can be a rectangular (or other shaped) region extending entirely along one dimension of the PCB  100 . If a plurality of regions are defined, the regions can be non-overlapping. The regions may be parallel to one another. 
     The method  200  can include applying, within each region of the one or more regions, thermal energy via a heat source to a surface of the PCB within the region, such that insulation material of the insulation layer is removed from the region while a portion of the insulation layer beneath the one or more electrically conductive structures is maintained (STEP  204 ). The applied thermal energy can cause the insulation material of the insulation layer (or of the plurality of insulation layers) within the one or more regions to be removed, except the portion of the insulation material that is beneath the one or more electrically conductive structures within the one or more regions. The portion of the insulation material that is maintained can be viewed as an extension, within the one or more regions, to the one or more electrically conductive structures along a depth direction (e.g., a direction perpendicular to the surface of the PCB  100  which the heat is applied) of the PCB  100  or a depth direction of the one or more one or more electrically conductive structures. The portion of the insulation material that is maintained can be directly beneath the one or more electrically conductive structures, e.g., sealed to (or in contact with) a side of the one or more electrically conductive structures that is opposite to the surface of the PCB  100  to which the thermal energy is applied. 
     In some implementations, applying the thermal energy can include applying the thermal energy along a raster path within each region of the one or more regions. For instance, the heat source can be a laser cutter and applying the thermal energy to the surface of the PCB can include applying a laser beam of the laser cutter to the surface of the PCB according to a raster path within each region of the one or more regions. 
     Referring now to  FIGS.  3 A- 3 G , diagrams and images illustrating post-processing of electronics or PCBs to remove insulation layers within predefined regions and the effect of such post-processing, according to example embodiments of the current disclosure.  FIG.  3 A  shows a flexible PCB  300  including circuit components  302  and electrically conductive structures  304  integrated on a polymer layer  306 , and a laser cutter  314  for applying thermal energy to a surface of the PCB  300 , e.g., top surface of PCB  300  in  FIG.  3 A . The electrically conductive structures  304  have serpentine or flexuous shapes, e.g., that are bending or winding alternately from side to side. The electrically conductive structures  304  are copper traces. In some implementations, the electrically conductive structures  304  can include other metallic traces. The electrically conductive structures  304  can as act electric wires or connections. 
     Referring now to  FIG.  3 B , the laser cutter  314  is moved according to the raster path illustrated by the dashed lines within region  308  while applying a laser beam to the top surface of the PCB  300 . Applying the laser beam according to the raster path causes the insulation material of the insulation layer  306  to be removed within region  308 . Referring to  FIG.  3 C , the insulation material (e.g., polymer) is now removed from regions  308   a  and  308   b  by further applying the laser beam, according to another raster path within region  308   b , to the top surface of the PCB  300 . The insulation layer  306  is maintained within regions  310   a ,  310   b  and  310   c . The serpentine or flexuous shapes allow the electrically conductive structures  304  to stretch, especially within regions  308   a  and  308   b  where the insulation layer  306  is removed. 
     As illustrated in  FIG.  3 C , the circuit components  302  or sensors can be located within regions  310   a ,  310   b  and  310   c  of the PCB  300  where the insulation layer  306  is not removed. In other words, regions where the insulation material is removed, e.g., regions  308   a  and  308   b , can be selected, determined or identified as regions that do not include any of the circuit components  302  (or sensors). The circuit components  302  or sensors are distributed among the plurality of regions  310   a ,  310   b  and  310   c . The portions  312  of the insulation region  306  that are beneath the electrically conductive structures  304  are maintained within region  308   a  after applying the laser beam to the surface of the PCB within region  308   a . The same applies to region  308   b  where the laser beam also applied. The portions  312  can be viewed, and referred to, as connectors  312  that are made from the insulation layer  306 . 
     The flexible circuit  316 , obtained after removing the insulation material at least within regions  308   a  and  308   b , includes a plurality of portions or blocks  310   a - 310   c  of the insulation layer  306 . The portions or blocks  310   a - 310   c  include circuit components  302 . Each portion or block is connected to an adjacent portion or block via one or more connectors made from the insulation layer  306 . For instance, portion or block  310   a  of the insulation layer  306  is connected to portion or block  310   b  of the insulation layer  306  via the connectors  312 . The flexible circuit  316  includes electrically conductive structures  304  that are deposited on and defining a top surface of the connectors  312 . The electrically conductive structures  304  extend between and across the plurality of blocks  310   a - 310   c . The portions or blocks  310   a - 310   c  can include a plurality of insulation layers. For instance, the circuit components  302  and/or the electrically conductive structures  304  can be integrated between two or more insulation layers within portions or blocks  310   a - 310   c . In such case, the connectors  112  are made of insulation layer(s) that is/are beneath the circuit components  302  and the electrically conductive structures  304 . The circuit components  302  can include sensors, in which case the flexible circuit can be viewed as a flexible sensor array. 
     Experimental tests were performed on the flexible circuit  316  and the PCB  300  to assess the efficiency and reliability of the selective removal of the insulation layer(s)  306 . The results are shown in  FIGS.  3 D- 3 G .  FIG.  3 D  shows a cross sectional (end on) confocal image of the electronics, or PCB  300 , before laser cutting. The scale bar, shown in white, in the confocal image of  FIG.  3 D  is 0.1 mm long.  FIG.  3 E  shows a cross sectional (end on) confocal image of the electronics, or PCB  300 , after laser cutting. The scale bar, shown in white, in the confocal image of  FIG.  3 E  is 0.1 mm long.  FIG.  3 F  shows a scanning electron microscope (SEM) image of the final laser cut stretchable circuit. The central region of the SEM image depicts a region of the PCB where the insulation material was removed. The scale bar, shown as a white rectangle, in the SEM image is 0.3 mm long.  FIG.  3 G  shows results for a tensile test before and after selective removal of the insulation layer(s)  306 . The enhanced stretchability of the post-processed circuit (or sensor array)  316  can be clearly observed. 
     According to various embodiments, the flexible electronics (or flexible PCB)  300  may be manufactured initially in a flex house (PCB universe), for example, to ensure scalable production. The design may comprise two or more layers. These layers can include a layer of electrically conductive (or metallic) structures, e.g., copper or other metallic traces, that is deposited on an insulation layer (or polyimide (PI) layer) or may be sandwiched between two or more insulation layers (e.g., PI layers). In various embodiments, the electrically conductive structures may comprise serpentine traces connected to, for example, electrodes on each flexible circuit board. The selective removal of the insulation layer(s) provides windows, sections or regions where the electrically conductive structures are exposed for contact. In various embodiments, the thickness of the insulation layer (e.g., PI layer) may be, for example, between about 15 μm and about 75 μm. Also, the thickness of the electrically conductive structures (e.g., copper traces) may be, for example, between about 15 μm and about 75 μm. As such, the flexible PCB (or PCB) may initially have a uniform thickness of, for example, between about 30 and 150 μm. The stretchability of the flex PCB may be a direct function of its thickness. 
     A laser (e.g., CO2 laser (Universal Laser, power 23%, speed 50%)) may be used to selectively remove the insulation material (e.g., PI or polymer) from sections or regions (e.g., regions  308   a  and  308   b ) of the flex PCB as shown in  FIGS.  3 B and  3 C . The laser, or heat source, may raster as indicated by dashed lines in  FIG.  3 B  thereby removing the insulation material (e.g., PI or polymer) from the regions to which thermal energy or the laser beam was applied. 
     In various embodiments, working conditions (or settings) of the heat source or laser  314  may be optimized to preserve or maintain the insulation material (e.g., PI or polymer) underneath the electrically conductive structures  304  (e.g., metallic/copper traces). The selective removal process makes use (or takes advantage) of thermal masking, whereby the electrically conductive structures (e.g., metallic/copper traces) allow for heat applied to them to be rapidly spread, therefore reducing peak temperatures, and preventing the underlying insulation layer(s) (e.g., PI or polymer layers) from reaching temperatures sufficient for removal. Meanwhile, regions of insulation layers (e.g., PI or polymer), which are usually thermally insulating, that are directly exposed to the heat source and are not beneath (or in contact with) the thermally conductive metallic structures (e.g., copper traces) may reach higher peak temperatures and may be subsequently removed. 
     The selective removal process can be referred to as a self-aligned thermal energy based (or laser based) conversion approach. Simulations were made and various simulation parameters were look examined to explore the effect of thermal masking in the self-aligned thermal energy based (or laser based) conversion approach. A single pulse ablation model was applied, and the energy density and fluence distribution of a Gaussian laser beam were simulated on sections of the flex-PCB. The simulation results for studying the working conditions (or settings) of the heat source or laser, thickness of layers, and the resolution of this approach comprehensively using this model to elaborate on factors to be considered to employ this technique for large scale processing. 
     Referring to  FIG.  4 A , two representative, adjacent serpentine traces are modeled in the simulation which contain two electrodes at their ends (e.g., for connecting to circuit components such as sensors). Serpentine traces are chosen in the simulation since they offer maximum stretchability. A layer of polyimide is modeled in contact with copper traces. The thermal conductivity is defined based on a harmonic mean. All other material properties including specific heat and density are defined as well. Insulation on the bottom service of the flex-PCB was applied, and a convective boundary was also applied across all the faces of the model. Initially two regions of interest identified, and point Gaussian heat flux was applied in these regions to observe the temperature distribution. Note that a point Gaussian laser heat source is applied in this study in order to better calibrate the simulations with experiments and also reduce the inconsistencies associated with speed and pulse per inch (PPI) setting of the laser which are specific to the laser cutter used in our laboratory. The Gaussian beam profile of a laser beam can be defined as: 
     
       
         
           
             
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     Using these parameters, a custom code was used to define a Gaussian beam pulse on a desired location on the model. A single pulse was chosen to order to minimize the inconsistencies associated with speed, and PPI parameters which are unique to a certain laser cutting system and the way certain systems are designed to maintain these parameters. In order to verify if these models are accurate, calibration experiments were conducted using the Universal laser. The laser beam used in these experiments have a maximum power 30 W and all the power values mentioned in this study are a percentage of this total power. Referring to  FIG.  4 B , simulation and experimental results illustrating material removal temperatures for a single pulse of various powers, are shown. The experimental material removal temperatures correspond to material removal temperatures observed the simulations, which validates the simulation model. 
     In the calibration experiments, a standard CO2 laser (universal laser) is used, and single pulses were applied on regions of the flexible PCB consisting of only Kapton and Kapton &amp; copper. Similar single pulses were simulated using the model described earlier. Knowing the decomposition temperature of Kapton to be 520 OC, the average temperature from the simulation heat map can be compared with Kapton removal from the experiment to calibrate the simulations. 
     Upon validating the model, simulations were run for varying thicknesses of copper and Kapton exposed to various laser pulse powers in order to elucidate under what conditions self-aligned removal can be achieved and when it does not.  FIGS.  5 A and  5 B  show the heat maps for a region where thermal masking phenomenon occurs, and a region where only bare Kapton exists. 
     It should be appreciated that the output and application of the thermal energy source can be calibrated, fine-tuned or configured based on various factors. In particular, a distance between the thermal energy source from which the thermal energy is emitted and the PCB surface to which the thermal energy is applied can be selected to successfully remove the insulation material. In addition, the amount of thermal energy emitted from the heat source can also be selected. The distance and the amount of thermal energy to select can be based on the thickness of the electrically conductive structures and the thickness of the insulation material to be removed as well as the decomposition, melting and/or state change temperatures of the insulation material and the electrically conductive structures. The goal of the selection or determination of the conditions or parameters for applying the thermal is to achieve the desired selective removal of the insulation material, such that the insulation material is removed within given regions of the PCB except beneath the electrically conductive structures  304 . 
     Referring to  FIG.  5 C , heat maps for under-heating, optimal and overheating conditions for the self-aligned material removal process are shown. During the under-heating condition, the temperature of bare Kapton remains below Kapton decomposition temperature. In the optimal condition, the temperature of bare Kapton is above the decomposition temperature. However, the temperature of Kapton below the copper is under the decomposition temperature. The overheating condition can be subdivided into two regimes. When the temperature of Kapton underneath copper is above the decomposition temperature but the temperature of copper is below its melting point, and when the temperatures of both Kapton and copper are above their respective decomposition and melting points. 
     A processing window is defined as the set of conditions (sample geometry, laser power, etc.) where self-aligned removal is achieved successfully. This can be evaluated by conducting thermal simulations for a wide variety of conditions.  FIG.  5 D  shows the processing window for varying copper thicknesses. The boundaries of this plot are determined by obtaining conditions where the process fails in one of three conditions, which are (i) when the temperature is lower than decomposition temperature for Kapton in bare Kapton region, (ii) when the temperature of Kapton below the copper traces is above the decomposition temperature, and (iii) when the temperature of copper is above its melting point. While describing the processing window for a specific thickness of copper and Kapton, these conditions determine the limits up to which this process can be employed. 
       FIG.  6 A  shows the processing power window as a function of copper thickness, which is an indication of how sensitive the success of the process is to input power provided by the laser. As illustrated by the plot in  FIG.  6 A , it is easier to achieve self-aligned laser based conversion successfully for samples with thicker copper (or electrically conductive) traces. This is mainly because with increasing copper thickness, the critical power required for overheating increases, thereby giving a larger processing power window. The processing power window is also critical because a variety of factors influence the power that is actually delivered to the sample, such as the z-axis alignment between the laser and the sample. The larger the power processing window, the easier it is to achieve uniform self-aligned selective laser removal, over the entire sample without the need for high precision tools. To illustrate this effect, the same laser cutter used in the calibration experiments (Universal laser) was used to make multiple cuts by varying the z-values as shown in  FIG.  6 B . The z-values represent the distance between the laser cutter and the surface of the PCB to which the laser beam is to be applied. This demonstrates the process moving from under-heating to optimal to overheating with varying z values. Therefore, there exist optimal z values where the process is most effective. This highlights the need for larger processing windows so as to accommodate for z axis variations that might present during the process. 
     In the z-axis experiments, an inclined ramp with height varying between 1 mm and 5 mm was 3D printed in the lab and the flexibled PCB was mounted on the ramp. Based on the desired height, a series of linear cuts were programmed on the laser cutter at the specified location along the ramp. 
     Another key parameter that is worth highlighting while designing the flex-PCBs and employing this process is the resolution or distance between the traces. This is important because it determines the sample geometries for which this process can be reliably applied. An analysis was performed with linear trace geometries. Referring to  FIG.  6 C , the samples in column  1  illustrate the effect of trace spacing schematically. In order to demonstrate the effect of resolution on process parameters, a point is chosen on  FIG.  4 A  (20 μm thickness of Kapton and 40 μm thickness of copper). Column  2  in  FIG.  6 C  shows the heat maps when the laser beam (6% power) is irradiated at a central point between the two traces (d/2). 
     Here, when trace spacing is large, the heating in the region between traces is not impacted by the electrodes, and the behavior observed is similar to the examples discussed above. As the traces move closer together they begin to partially mask the laser spot, reducing the energy delivered to the Kapton between the traces for removal. The resulting effect is to increase the power required to achieve complete removal, thus narrowing the power processing window. 
     The effect of resolution on working conditions is shown in  FIGS.  6 D and  6 E .  FIG.  6 D  is an adaptation of  FIG.  5 D  (processing window) to indicate the effect of trace spacing. For very large trace spacing, the left sided boundary of the processing window is the same as observed in  FIG.  5 D  and is defined by the Kapton thickness. The small box or square shows the data point that corresponds to a large spacing, e.g., 140 μm. As the spacing is reduced, masking from the electrodes reduced the laser energy that reaches the substrate, requiring higher power and moving the left sided boundary of the processing window to higher power. For spacing between 30 and 9 μm, the left boundary moves past the right hand boundary, indicating that for this Kapton and Cu thickness, self-aligned removal cannot be achieved. The decomposition temperature of Kapton is also indicated in the plots of  FIG.  6 E . At powers above the intersection points between the Kapton decomposition and the temperature curves, the Kapton underneath is removed. Therefore, this region is not in the workable range for this process. This phenomenon is also highlighted in  FIG.  6 E  where, according to these intersection points, the original point for 20 μm thickness of Kapton and 40 μm thickness of copper moves to the right until it moves out of the processing window. Therefore, this is defined as the limiting factor for resolution of traces that can be used for this laser post-processing technique. 
     Referring back  FIG.  2   , the method  200  can include determining an output thermal energy range of the heat source to cause the insulation material of the insulation layer to be removed from the region while maintaining the portion of the insulation layer beneath the one or more electrically conductive structures, and setting the heat source to generate the thermal energy according to the output thermal energy range prior to applying the thermal energy to the surface of the PCB. While the simulation and experimental results in  FIGS.  5 A- 5 B and  6 A- 6 E  relate to the use of a laser cutter and applying a laser beam, the same concept of thermal masking also applies for other types of heat sources. The output thermal energy range can be determined based on simulation results and/or experimental results. 
     The output thermal energy range can be determined based on a first temperature specific to the insulation layer and a second temperature specific to the one or more electrically conductive structures. The first temperature specific to the insulation layer can represent a removal temperature of the insulation layer when the thermal energy is directly applied to the insulation layer. Such temperature can include, for example, a decomposition temperature, a sublimation temperature, an ablation temperature, a spallation temperature or a melting temperature of the insulation layer. The output thermal energy range can be determined based a third temperature that represents a removal temperature of the insulation material beneath the electrically conductive structures. The second temperature specific to the one or more electrically conductive structures can represent a melting temperature, an oxidation temperature or a phase change temperature of the electrically conductive structures. As discussed above with regard to  FIGS.  6 A- 6 E , the output thermal energy range can be based on a thickness of the insulation layer and/or a thickness of the one or more electrically conductive structures. 
     In the case where the heat source is a laser cutter, the method  200  can include determining an output power range of the laser cutter to cause the insulation material of the insulation layer to be removed while maintaining the portion of the insulation layer beneath the one or more electrically conductive structures, and setting the laser cutter according to the output power range prior to applying the laser beam to the surface of the PCB, as discussed above with regard to  FIGS.  6 A- 6 E . 
     The selective removal process can be viewed as a self-aligned removal process because it allow for accurate alignment between the electrically conductive structures and the insulation material maintained beneath the electrically conductive structures within the regions where thermal energy was applied. The boundaries of the electrically conductive structures and those of the insulation material maintained beneath the electrically conductive structures can be aligned along a depth direction of the original insulation layer (before material removal). The self-aligned removal process allows provides accurate alignment even with a relatively low cost laser or heat source. 
     The material removal process allows for exposing the one or more electrically conductive structures within the one or more regions where thermal energy is applied, to sense electrical voltage of a surrounding environment. The maintained portions of the insulation layer beneath the one or more electrically conductive structures allows the one or more electrically conductive structures, and the flexible circuit  316  as a whole, to maintain mechanical integrity within the region. 
     The initial PCB can include a plurality of insulation layers. In such a case, the thermal energy can be applied, within each region of the one or more regions, to the surface of the PCB, such that insulation material of the plurality of insulation layers is removed from the region while a portion of one or more insulation layers beneath the one or more electrically conductive structures is maintained. 
     Referring to  FIG.  7   , an example flexible/stretchable circuit  400  is shown, according to example embodiments of the current disclosure. The flexible circuit  400  can include a plurality of portions or blocks of an insulation layer  402 . The blocks or portions  402  can include a one or more circuit components  404 . Each block can be connected to an adjacent block via one or more connectors (not shown in  FIG.  7   ) made from the insulation layer. The flexible/stretchable circuit  400  can include one or more electrically conductive structures  406  deposited on and defining a first surface of the one or more connectors. The one or more electrically conductive structures  406  can extend between and across the plurality of blocks  402 . A connectors can be arranged beneath each electrically conductive structure  406 . 
     The one or more circuit components  404  can include one or more sensors. For instance, the flexible/stretchable circuit  400  can be a flexible/stretchable sensor array. The sensors can be distributed among the plurality of blocks  402  of the insulation layer. The one or more electrically conductive structures  406  can include copper (or other metallic) traces. The insulation layer can includes a polymer or PI layer. The one or more electrically conductive structures  406  (or a portion thereof) extending between the plurality of blocks  402  can be exposed to sense electrical voltage of a surrounding environment. For instance, when such portions are in contact with, or in proximity to, to an organ tissue, the electrically conductive structures  406  can sense the electric voltage of the tissue. 
     In some implementations, a thickness of the insulation layer can between about 15 μm and about 75 μm, such as about 15 μm, about 20 μm, about 25 μm, about 30 μm, about 35 μm, about 40 μm, about 45 μm, about 50 μm, about 55 μm, about 60 μm, about 65 μm, about 70 μm or about 75 μm. In some implementations, a thickness of the one or more connectors can be between about 15 μm and about 75 μm, such as about 15 μm, about 20 μm, about 25 μm, about 30 μm, about 35 μm, about 40 μm, about 45 μm, about 50 μm, about 55 μm, about 60 μm, about 65 μm, about 70 μm or about 75 μm. In some implementations, a thickness of the blocks  402  can be between about 30 μm and about 140 μm, such as about 30 μm, about 35 μm, about 40 μm, about 45 μm, about 50 μm, about 55 μm, about 60 μm, about 65 μm, about 70 μm, about 75 μm, about 80 μm, about 85 μm, about 90 μm, about 95 μm, about 100 μm, about 105 μm, about 110 μm, about 115 μm, about 120 μm, about 125 μm, about 130 μm, about 135 μm or about 140 μm. 
     It is to be noted that properties of the flexible/stretchable circuit  316  discussed above with regard to  FIGS.  3 A- 3 G  can also apply to the flexible/stretchable circuit  402 . Also, the polymer layer or polymer substrate can include at least one of a urethane polymer, a polyurethane polymer, a copolymer, a silicone polymer, or an elastomer. Each exposed portion of the electrically conductive structure can detect a signal from one or more surfaces of a tissue structure (or other structure in proximity). Transmission lines can transmit the signals detected from each of the plurality of electrically conductive structures to an external measurement device through wired or wireless means. The flexible/stretchable circuit  400  may be manufactured or fabricated as discussed above with regard to method  200 . 
     B. Soft Robotic Devices and Respective Manufacturing Processes 
     The flexible/stretchable circuits  316  and  402  discussed above in section A can be used to manufacture soft robotic devices, such as soft robotic sensor arrays (SRSAs) or other medical devices. The soft robotic devices described herein may have other applications other than medical applications. 
     Referring to  FIG.  8   , a method  500  of fabricating/manufacturing soft robotic devices can include aligning at least one flexible circuit with a soft actuator (STEP  502 ). The method  500  can include laminating the at least one flexible circuit with a polymer sheet on a surface of the soft actuator to form a soft robotic device (STEP  504 ). The polymer sheet can be configured to provide, for the at least one flexible circuit, insulation and mechanical fixation to the soft actuator. As used herein, a soft actuator can be viewed, or can be referred to, as an inflatable actuator that is made of a deformable material. 
     Referring now to  FIG.  8    and  FIGS.  9 A- 9 H , the method  500  can include aligning the at least one flexible circuit with a soft actuator (STEP  502 ).  FIGS.  9 A and  9 B  show photographs of a manufactured flexible/stretchable circuit  602  and a manufactured linear bending soft actuator  604 . The flexible/stretchable circuit  602  can be manufactured or fabricated as discussed above with regard to method  200 . Each flexible circuit  602  of the at least one flexible circuits can include a plurality of blocks of an insulation layer including a one or more circuit components, and one or more electrically conductive structures deposited on and defining a first surface of the one or more connectors. Each block can be connected to an adjacent block via one or more connectors made from the insulation layer. The one or more electrically conductive structures can extend between and across the plurality of blocks. Aligning the at least one flexible circuit  602  with the soft actuator  604  can include arranging the at least one flexible circuit  602  on the soft actuator  604 . The soft actuator can include, or can be made of nitinol or polymer such as polyurethane polymer or any other suitable material. The soft actuator  604  can include one or more indentations  606  to facilitate bending of the soft actuator  604 , when the actuator is inflated. The indentations  606  can represent bending regions of the soft actuator  604 . The flexible circuit(s)  602  can be similar to the flexible circuit  316  or  402  discussed in section A. The flexible circuit(s)  602  can be manufactured according to method  200 . 
     Referring now to  FIGS.  9 C- 9 E , diagrams illustrating an example process of manufacturing the soft actuator  604  using polymers are shown, according to example embodiments of the current disclosure. Manufacturing the soft actuator  604  can include laser cutting layers of polymer  610  and a sheet of water soluble polymer  608  according to desired shapes, arranging the sheet of water soluble polymer  608  between two or more layers of polymer  610 , and thermally bonding (e.g., via heat press) the two layers of polymer  610  around respective borders. The sheet of water soluble polymer  608  can act as a sacrificial layer to form an inflatable closed channel between the two bonded layers of polymer. The inflatable closed channel can be inflated via the inlet or pressure line  612 .  FIG.  9 D  shows the soft actuator  602  in non-inflated state.  FIG.  9 E  shows the soft actuator  602  when inflated, and illustrates how the indentations  606  facilitate bending of the soft actuator when inflated. The indentations  606  form bending regions along which the soft actuator  602  can bend easier than other regions. The indentations  606  can be distributed along a length of the soft actuator  604 . The indentations  606  can be arranged transverse to a longitudinal axis or dimension of the soft actuator  604 . 
     To achieve the indentations  602 , the method  500  can further include making a plurality of cutouts  614  in the sheet of water soluble polymer  608 , and thermally bonding the two layers of polymer  610  at the plurality of cutouts  614 . The plurality of cutouts  614  can be distributed along a length (or a longitudinal dimension) of the sheet of water soluble polymer  608 . The cutouts  614  can be arranged transverse to a longitudinal axis or longitudinal dimension of the water soluble polymer  608 . In some implementations, the water soluble polymer can include polyvinyl alcohol. 
     The method  500  can include laminating the at least one flexible circuit  602  with a polymer sheet on a surface of the soft actuator  604  to form a soft robotic device (STEP  504 ). The polymer sheet can be wrapped around one side (an outer side or surface) of the at least one flexible circuit  602  to attach, seal mechanical fixate the at least one flexible circuit  602  to the soft actuator  604 . The polymer sheet can also provide an insulation to the soft actuator.  FIG.  9 F  shows photographs of two sides of manufactured soft robotic device (or SRSA)  616 . In some implementations, the polymer sheet can be, or include, a polyurethane sheet. 
     The method  500  can further include making one or more cutouts in the polymer sheet. The one or more cutouts can partially expose portions of the electrically conductive structures extending between the plurality of insulation layer blocks of the flexible circuit  602 . Since the polymer sheet acts as an insulation, the cutouts allow for exposure of the electrically conductive structures to nearby environment, such as organ tissue. The one or more electrically conductive structures and the one or more connectors can have serpentine shapes. The one or more electrically conductive structures can include copper traces. Each connector of the one or more connectors can be substantially aligned with the conductive structure deposited on the connector as discussed above in section A. 
     Referring now to  FIG.  9 G , a complex soft robotic device (or SRSA)  618  having a plurality of beams or elements  620  is shown according to example embodiments of the current disclosure. The soft robotic device (or SRSA)  618  can be fabricated by combining a plurality of the soft robotic devices  616  into a cage soft robotic (or SRSA) device. In some implementations, the soft robotic device (or SRSA)  618  can be fabricated by using a complex soft actuator having a plurality of beams or inflatable channels. The method  500  can include aligning each flexible circuit of a plurality of flexible circuits with a corresponding beam (or inflatable channel) of the plurality of beams (e.g., before inflating), and laminating each flexible circuit with a separate polymer sheet on a surface of the corresponding beam of the soft actuator. The soft robotic device  618  can be a cardiac mapping device deployable into a heart chamber using a catheter. 
     The method  500  allows for actuator geometries with significant complexity. It also has the benefit that because it consists of assembly of 2D planar actuator designs, these designs are intrinsically compatible with most scalable manufacturing methods for electronics. This is in contrast to many alternative methods to fabricate soft robotic actuators which require complex embedded 3D channels to allow for integration of sensors or electronics. In addition, most other actuators are intrinsically high strain to yield actuation, thus they rely on materials with greater intrinsic stretchability than conventional flex-PBCs, which limits the scalability of such designs. 
     According to at least one other aspect of the present disclosure, an apparatus (such as soft robotic device  616  or  618 ) can include an inflatable actuator and one or more flexible circuits laminated with one or more polymer sheets on a surface of the inflatable actuator. Each flexible circuit can include a plurality of insulation layer blocks  402  including a one or more circuit components  404 , where each block can be connected to an adjacent block via one or more connectors  312  made from the insulation layer, and one or more electrically conductive structures  406  deposited on and defining a first surface of the one or more connectors  312 , the one or more electrically conductive structures  406  can extend between and across the plurality of insulation layer blocks  402 . 
     In some implementations, each connector  312  of the one or more connectors  312  can be substantially aligned with a corresponding conductive structure  314  deposited on the connector. In some implementations, the apparatus can be a cardiac mapping device deployable into a heart chamber using a catheter, as depicted in  FIG.  9 H . In some implementations, the inflatable actuator can include nitinol or a polymer such polyurethane. 
     The inflatable actuator can include a sheet of water soluble polymer  608  arranged between two layers of polymer  610 . The two layers of polymer  610  can be thermally bonded around respective borders and the sheet of water soluble polymer  608  can act as a sacrificial layer to form an inflatable closed channel between the two bonded layers of polymer. In some implementations, the water soluble polymer can include polyvinyl alcohol. In some implementations, the sheet of water soluble polymer  608  can include a plurality of cutouts  614  distributed along a length of the sheet of water soluble polymer  608 . The two layers of polymer  610  can be thermally bonded at the plurality of cutouts  614  to achieve bending regions  606  in the inflatable actuator  602 . 
     In some implementations, the one or more polymer sheets can include one or more cutouts exposing portions of the one or more electrically conductive structures extending between the plurality of blocks of the insulation layer. The one or more electrically conductive structures may include copper traces deposited on the one or more connectors. 
     According to at least one other aspect of the present disclosure, a method for manufacturing flexible sensor arrays can include identifying one or more regions of a flexible printed circuit board (PCB) for selectively removing polymer. The flexible PCB can include one or more sensors and one or more electrically conductive serpentine structures between a first polymer layer and a second polymer layer. Each electrically conductive serpentine structure can be connected to a corresponding sensor of the one or more sensors. The method can include applying, within each region of the one or more regions, thermal energy via a heat source to a first surface of the flexible PCB along a raster path within the region such that polymer in the first polymer layer and the second polymer layer is removed from the region while a portion of the second polymer layer beneath the one or more electrically conductive serpentine structures is maintained. 
     Durability Analysis of Stretchable Electronics Integrated Balloons 
     Referring to  FIGS.  10 A- 10 D , two separate experiments were conducted to evaluate durability of the SRSAs or soft robotic devices, such as device  618 . These results are shown in  FIGS.  10 A- 10 D . In one experiment, a single linear SRSA actuator, such as actuator  616 , with a design matching that of one leg of the SRSA cage was actuated multiple times and the resulting conductivity of the individual sensor traces were subsequently assessed (using Signatone probe station, Tektronics 4200 parameter analyzer), as shown in  FIG.  10 A . The actuation was carried out by applying a pressure of 10 PSI which yielded a level of overall actuation consistent with those observed in the device  616  and repeated for 100 iterations in order to evaluate long term durability of the electronics under repeated loading and deformation. For each electrode, the I-V sweep was recorded, and the resistance values were plotted as shown in  FIG.  10 A . The values remain within the standard deviation even after 100 iterations showing excellent durability of the stretchable electronics. Resistance values for each trial is tabulated in Ohms. 
       FIG.  10 B  shows μ-CT images and volume rendered segmentations of individual linear SRSA. The inset shows the stretchable sensor arrays on the soft robotic actuator. One reason these designs are able to demonstrate this type of durability is the low strain actuator design employed. To understand the local strain observed in the sensor arrays themselves strain in the copper traces along the length of stretchable electronics was evaluated experimentally using confocal imaging and FEA simulations (ANSYS workbench) were performed to validate these results. Note that maximum deformation occurs in pockets which are along the length of the actuator legs. The pockets (e.g., indentations  606 ) are part of the linear actuator design applied here, that allow for low strain actuation. They are formed by patterning the sacrificial PVA layer in a manner to allow the polymer layers to fuse in regions of the actuators such that it subsequently inflates in discrete pockets. This can be clearly observed in  FIG.  10 B . This pocket section is considered to measure maximum strain both in experiments and simulations. 
     In order to evaluate the strain experimentally, confocal images of the balloon with electronics both in the non-actuated state and in actuated stated were recorded. Average strain in each section of the traces is calculated using the deformation values between the two states. FEA analysis was conducted using the static structural module of ANSYS workbench. A hyperplastic model was defined and the balloon (e.g., device  618 ) was actuated by applying a uniform pressure loading of 10 psi. Details of the simulation is explained further in the SI. Comparison between experimental and simulated results are shown in  FIGS.  10 C and  10 D . The figures illustrate negligible strain along the length of the traces in the actuated state. The strain is maximum at the ends of the pocket region. We believe this is due to the constrain that is provided based on the design of these actuators. However, this maximum strain is well within the design limits for copper, thereby allowing these stretchable electronics to go through many actuation cycles. The alignment between experimental observation and simulation provides insight into the robustness and durability of these designs. 
     Micro CT Conformability Experiments 
     One goal of creating soft robotic devices or SRSAs with active soft actuators is to provide designs for sensor arrays that have the ability to conform to complex patient anatomies. In order to assess the conformability of these designs, an SRSA was deployed in four patient specific 3D printed left atria and actuated at 10 psi to obtain its final configuration within the left atrium. Volume rendered segmentations and μ-CT images (Siemens Inveon Multimodality Scanner) of deployed SRSA were used to analyze its conformability. The results are shown in  FIG.  11   . The first row shows the SRSA deployed into the 3D printed atria via a mock catheter through the puncture made in the Foramen ovale in the patient&#39;s septal wall. The balloons conform to the atrial surface effectively and show no spline bunching (i.e. the individual linear actuators that form the SRSA were evenly distributed within the atria). Using mesh Boolean operations, the regions of intersections were obtained for each of these atria. Prior studies have shown that the signals can be detected by the sensors at distances greater than 2 mm from the atrial surface. Considering these values, different distances from 0 to 2 mm were color coded analogous to a thermal heat map. The heat maps are superimposed on the SRSA to show regions that are in direct contact with the atrial tissue. Graphs of proportion of sensors within a given distance from the atrial surface are plotted for each atrium. For these calculations, sensors not near tissue because they were adjacent to anatomic features such as the pulmonary veins or the left atrial appendage were ignored. SRSA shows an average conformability of ˜85-90% for these randomly chosen patient specific 3D printed patient atria. Atrium  4  shows the least conformability of 75%. We believe this is associated with the buckling of SRSA that can be clearly observed from the figure. Designs that mitigate this type of buckling may represent a strategy to further increase the conformability of these devices. 
     In this disclosure, the development of soft robotic sensor arrays, that exhibit excellent mechanical durability and conformability when deployed within patient specific 3D printed left atria, is reported. This method employed to create these SRSAs illustrates a promising strategy for integration of soft robotics and flexible electronics for medical applications, especially those deployed via minimally invasive catheter. The mechanical durability of these devices is demonstrated by showing that sensors could undergo 100 cycles of actuation without reduction of performance. Furthermore, simulations were performed to assess the strain in electronics which showed good match with the experimental values. The SRSA was deployed using a 13.5 Fr mock catheter into patient specific soft 3D printed left atria (soft materials mimicking the atrial tissue) to analyze its conformability. SRSA shows an average conformability of ˜85-90% within these atria. The current disclosure provides a novel method for scalable fabrication and integration of flexible electronics that provides a versatile approach for creating a wide variety of complex geometry actuator/sensor arrays that is broadly applicable. This enables future development of efficient devices for better treatment of AFib and cardiac arrhythmias. 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any implementations or of what may be claimed, but rather as descriptions of features specific to particular implementations of the systems and methods described herein. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. 
     Having now described some illustrative implementations and implementations, it is apparent that the foregoing is illustrative and not limiting, having been presented by way of example. In particular, although many of the examples presented herein involve specific combinations of method acts or system elements, those acts and those elements may be combined in other ways to accomplish the same objectives. Acts, elements and features discussed only in connection with one implementation are not intended to be excluded from a similar role in other implementations. 
     The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including” “comprising” “having” “containing” “involving” “characterized by” “characterized in that” and variations thereof herein, is meant to encompass the items listed thereafter, equivalents thereof, and additional items, as well as alternate implementations consisting of the items listed thereafter exclusively. In one implementation, the systems and methods described herein consist of one, each combination of more than one, or all of the described elements, acts, or components. 
     Any references to implementations or elements or acts of the systems and methods herein referred to in the singular may also embrace implementations including a plurality of these elements, and any references in plural to any implementation or element or act herein may also embrace implementations including only a single element. References in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements to single or plural configurations. References to any act or element being based on any information, act or element may include implementations where the act or element is based at least in part on any information, act, or element. 
     Any implementation disclosed herein may be combined with any other implementation, and references to “an implementation,” “some implementations,” “an alternate implementation,” “various implementation,” “one implementation” or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described in connection with the implementation may be included in at least one implementation. Such terms as used herein are not necessarily all referring to the same implementation. Any implementation may be combined with any other implementation, inclusively or exclusively, in any manner consistent with the aspects and implementations disclosed herein. 
     References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms. 
     Where technical features in the drawings, detailed description or any claim are followed by reference signs, the reference signs have been included for the sole purpose of increasing the intelligibility of the drawings, detailed description, and claims. Accordingly, neither the reference signs nor their absence have any limiting effect on the scope of any claim elements. 
     The systems and methods described herein may be embodied in other specific forms without departing from the characteristics thereof. Although the examples provided herein relate to controlling the display of content of information resources, the systems and methods described herein can include applied to other environments. The foregoing implementations are illustrative rather than limiting of the described systems and methods. Scope of the systems and methods described herein is thus indicated by the appended claims, rather than the foregoing description, and changes that come within the meaning and range of equivalency of the claims are embraced therein. 
     Having described certain embodiments of methods and systems, it will now become apparent to one of skill in the art that other embodiments incorporating the concepts of the disclosure may be used. Therefore, the disclosure should not be limited to certain embodiments, but rather should be limited only by the spirit and scope of the following claims.