Abstract:The innate ability of poly(N-isopropylacrylamide) (PNIPAAm) thermo-responsive hydrogel to copolymerize and to graft synthetic polymers and biomolecules, in conjunction with the highly controlled methods of radical polymerization which are now available, have expedited the widespread number of papers published in the last decade-especially in the biomedical field. Therefore, PNIPAAm-based hydrogels are extensively investigated for applications on the controlled delivery of active molecules, in self-healing materials, tissue engineering, regenerative medicine, or in the smart encapsulation of cells. The most promising polymers for biodegradability enhancement of PNIPAAm hydrogels are probably poly(ethylene glycol) (PEG) and/or poly(ε-caprolactone) (PCL), whereas the biocompatibility is mostly achieved with biopolymers. Ultimately, advances in three-dimensional bioprinting technology would contribute to the design of new devices and medical tools with thermal stimuli response needs, fabricated with PNIPAAm hydrogels.

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Ultrathin films of poly[N-(2-cyanoethyl)pyrrole] and poly(N-methylpyrrole) and their composites with Au nanoparticles were used for the electrochemical detection of small concentrations (10 mM-100 μM) of dopamine, a neurotransmitter related with neurological disorders. Results indicated that Au nanoparticles improve the sensing abilities of the two polymers, even though they are not essential to obtain effective and fast responses toward the presence of dopamine. Furthermore, although both polymers have been found to be highly sensitive to low concentrations of dopamine, the response of poly[N-(2-cyanoethyl)pyrrole] is better and more effective than the response of poly(N-methylpyrrole). Experimental results were corroborated with quantum mechanical calculations on model systems, which also indicated that the interaction of oxidized dopamine with poly[N-(2-cyanoethyl)pyrrole] is stronger than that with poly(N-methylpyrrole). This behavior has been attributed to two different factors: (i) the flexibility of the cyanoethyl groups, which allows maximize the number of attractive van der Waals interactions, and (ii) the dipole of the cyano group, which interacts favorably with the dipole of the CO bonds of oxidized dopamine. Finally, theoretical results were used to propose an atomistic model that explains the interaction behavior between the oxidized dopamine and the conducting polymers.

This work reports a comprehensive study about cell adhesion and proliferation on the surface of different electroactive substrates formed by pi-conjugated polymers. Biological assays were performed considering four different cellular lines: two epithelial and two fibroblasts. On the other hand, the electroactivity of the three conducting systems was determined in physiological conditions. Results indicate that the three substrates behave as a cellular matrix, even though compatibility with cells is larger for PPy and the 3-layered system. Furthermore, the three polymeric systems are electro-compatible with the cellular monolayers.

Solid-state organic electrochemical supercapacitors (OESCs) have been fabricated using poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes, a biohydrogel as electrolyte system, and polyaniline fibers as redox additive. The effectivity of sodium alginate, kappa-carrageenan, chitosan and gelatin hydrogels as electrolytic media has been evaluated considering different criteria. Results indicate that kappa-carrageenan-based hydrogel is the most suitable to perform as electrolyte due to the appropriate combination of properties: mechanical stability, ease of preparation, lack of water leaking, and good medium for the electrochemical response of PEDOT electrodes. Cyclic voltammetry and galvanostatic charge-discharge assays indicate that OESCs based on PEDOT electrodes and kappa-carrageenan hydrogel as electrolyte exhibits a good supercapacitor response in terms of specific capacitance, cycling stability, small leakage current and low self-discharging tendency. On the basis of these good properties, four OESC devices were assembled in series and used to power a red LED, confirming that, in addition to advantageous characteristics (e.g. elimination of liquid leaking and enhancement of the device compactness), the designed biohydrogel-containing OESC exhibits potential for practical applications. On the other hand, preliminary assays have been performed loading the kappa-carrageenan hydrogel with polyaniline nanofibers, which act as a redox additive. OESC devices prepared using such loaded biohydrogel have been found to be very promising and, therefore, future work is oriented towards the improvement of their design.Peer ReviewedPostprint (author's final draft

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