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  1. Abstract

    Thin polymeric films are being explored for biomedical uses such as drug delivery, biofiltration, biosensors, and tissue regeneration. Of specific interest is the formation of mechanically flexible sheets, which can be formed with controllable thickness for sealing wounds, or as biomimetic cellular constructs. Flexible substrates with precise micro‐ and nanopatterns can function as supports for cell growth with conformal contact at the biointerface. To date, approaches to form free‐standing, thin sheets are limited in the ability to present patterned architectures and micro/nanotextured surfaces. Other materials have a lack of degradability, precluding their application as cellular scaffolds. An approach is suggested using biocompatible and biodegradable films fabricated from silk fibroin. This work presents the fabrication and characterization of flexible, micropatterned, and biodegradable 2D fibroin sheets for cell adhesion and proliferation. A facile and scalable technique using photolithography is shown to fabricate optically transparent, strong, and flexible fibroin substrates with tunable and precise micropatterns over large areas. By controlling the surface architectures, the control of cell adhesion and spreading can be observed. Additionally, the base material is fully degradable via proteolysis. Through mechanical control and directing the adherent cells, it is possible to explore interactions of cells and the microscale geometric topography.

     
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  5. Chitin, one of the most abundant natural amino polysaccharides, is obtained primarily from the exoskeletons of crustaceans, crabs and shrimp. Chitin and its derivative chitosan have gained much attention in the field of biomedical research due to attractive properties such as biocompatibility, non-toxicity, biodegradability, low immunogenicity, and ease of availability. While work has been done on the use of chitin and chitosan as functional biomaterials by imparting specific properties, the potential of chitin as a biomaterial is somewhat limited owing to its intractable processing. In this work, we propose a facile reaction to modify the chitin chain with photoactive moieties for the realization of photocrosslinkable chitin. This chitin derivative is easily usable with a benign solvent formic acid to be able to form mechanically robust, optically transparent sheets. These films exhibit comparable tensile properties to that of native chitin and chitosan and better surface wettability. Most importantly, this material can be used to form precise, high resolution microarchitectures on both rigid and flexible substrates using a facile bench top photolithography technique. These flexible micropatterned 2D sheets of chitin were demonstrated as a dynamic cell culture substrate for the adhesion and proliferation of fibroblasts, wherein the chitin micropatterns act as a template for spatial guidance of cells. This chitin-based biopolymer can find diverse uses in tissue engineering as well as to form components for degradable bioelectronics. 
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  6. Conductive polymers, owing to their tunable mechanical and electrochemical properties, are viable candidates to replace metallic components for the development of biosensors and bioelectronics. However, conducting fibers/wires fabricated from these intrinsically conductive and mechanically flexible polymers are typically produced without protective coatings for physiological environments. Providing sheathed conductive fibers/wires can open numerous opportunities for fully organic biodevices. In this work, we report on a facile method to fabricate core-sheath poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) PEDOT:PSS-silk fibroin conductive wires. The conductive wires are formed through a wet-spinning process, and then coated with an optically transparent, photocrosslinkable silk fibroin sheath for insulation and protection in a facile and scalable process. The sheathed fibers were evaluated for their mechanical and electrical characteristics and overall stability. These wires can serve as flexible connectors to an organic electrode biosensor. The entire, fully organic, biodegradable, and free-standing flexible biosensor demonstrated a high sensitivity and rapid response for the detection of ascorbic acid as a model analyte. The entire system can be proteolytically biodegraded in a few weeks. Such organic systems can therefore provide promising solutions to address challenges in transient devices and environmental sustainability. 
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