Synthesis and fabrication of gelatin-based elastomeric hydrogels through cosolvent-induced polymer restructuring.

Hydrogels have a wide range of applications in tissue engineering, drug delivery, device fabrication for biological studies and stretchable electronics. For biomedical applications, natural polymeric hydrogels have general advantages such as biodegradability and non-toxic by products as well as biocompatibility. However, applications of nature derived hydrogels have been severely limited by their poor mechanical properties. For example, most of the protein derived hydrogels do not exhibit high stretchability like methacrylated gelatin hydrogel has ∼11% failure strain when stretched. Moreover, protein derived elastomeric hydrogels that are fabricated from low molecular weight synthetic peptides require a laborious process of synthesis and purification. Biopolymers like gelatin, produced in bulk for pharma and the food industry can provide an alternative for the development of elastomeric hydrogels. Here, we report the synthesis of ureidopyrimidinone (Upy) functionalized gelatin and its fabrication into soft elastomeric hydrogels through supramolecular interactions that could exhibit high failure strain (318.73 ± 44.35%). The hydrogels were fabricated through a novel method involving co-solvent optimization and structural transformation with 70% water content. It is anticipated that the hydrogel fabrication method involves the formation of hydrophobic cores of ureidopyrimidinone groups inside the hydrogel which introduced elastomeric properties to the resulting hydrogel.

Synthesis and characterization of site selective photo-crosslinkable glycidyl methacrylate functionalized gelatin-based 3D hydrogel scaffold for liver tissue engineering.

The presented work outlined the development of a new biocompatible hydrogel material that has potential applications in soft tissue engineering. As a proof of concept, human hepatocytes were used to demonstrate the suitability of this material in providing conducive environment for cellular growth and functional development. Herein, a detailed synthesis of novel gelatin derivatives - photo-crosslinkable glycidyl methacrylate (GMA) functionalized gelatins (Gelatin-GMA), and preparation of three-dimensional (3D) hydrogel scaffolds for the encapsulated Huh-7.5 cells is reported. The Gelatin-GMA biopolymers were synthesized at two different pH values of 3.5 (acidic) and 10.5 (basic) where two different photo-crosslinkable polymers were formed utilizing -COOH & -OH groups in acidic pH, and -NH2 & -OH groups in basic pH. The hydrogels were prepared using an initiator (Irgacure I2959) in the presence of UV light. The Gelatin-GMA biopolymers were characterized using spectroscopic studies which confirmed the successful preparation of the polymer derivatives. Rheological measurement was carried out to characterize the mechanical properties and derive the mesh sizes of the 3D hydrogels. Subsequently, detailed in vitro hepatocyte compatibility and functionality studies were performed in the 3D cell seeded hydrogel platform. The 3D hydrogel design with larger mesh sizes utilizes the advantage of the excellent diffusion properties of porous platform, and enhanced cell-growth was observed, which in turn elicited favorable Huh-7.5 response. The hydrogels led to improved cellular functions such as differentiation, viability and proliferation. Overall, it showed that the Gelatin-GMA based hydrogels presented better results compared to control sample (GelMA) because of the higher mesh sizes in Gelatin-GMA based hydrogels. Additionally, the functional group studies of the two Gelatin-GMA samples revealed that the cell functionalities are almost unaffected even after the tripeptide - Arg-Gly-Asp (RGD) in Gelatin-GMA synthesized at pH 3.5 is no longer completely available.

Development of 3D Urchin-Shaped Coaxial Manganese Dioxide@Polyaniline (MnO2@PANI) Composite and Self-Assembled 3D Pillared Graphene Foam for Asymmetric All-Solid-State Flexible Supercapacitor Application.

We have fabricated high-energy-density all-solid-state flexible asymmetric supercapacitor by using a facile novel 3D hollow urchin-shaped coaxial manganese dioxide@polyaniline (MnO2@PANI) composite as positive electrode and 3D graphene foam (GF) as negative electrode materials with polyvinyl alcohol (PVA)/KOH gel electrolyte. The coaxial MnO2@PANI composite was fabricated by hydrothermal route followed by oxidation without use of an external oxidant. The formation mechanism of the 3D hollow MnO2@PANI composite occurs first by nucleation and growth of the MnO2 crystal species via dissolution-recrystallization and oriented attachment mechanisms followed by the oxidation of aniline monomers on the MnO2 crystalline template. The self-assembled 3D graphene block was synthesized by hydrothermal route using vitamin C as a reducing agent. The microstructures of the composites are analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The morphology is characterized by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), which clearly showed the formation of urchin-shaped coaxial MnO2@PANI composite. The electrochemical studies are explored by cyclic voltammetry, electrochemical impedance spectrometry, and cyclic charge-discharge tests. The symmetric all-solid-state flexible MnO2@PANI//MnO2@PANI and GF//GF supercapacitors exhibit the specific capacitance of 129.2 and 82.1 F g-1 at 0.5 A/g current density, respectively. The solid-state asymmetric supercapacitor shows higher energy density (37 Wh kg-1) with respect to the solid-state symmetric supercapacitors MnO2@PANI//MnO2@PANI and GF//GF, where the obtained energy density are found to be 17.9 and 11.4 Wh kg-1, respectively, at 0.5 A/g current density. Surprisingly, the asymmetric supercapacitor shows a high energy density of 22.3 Wh kg-1 at a high current density of 5 A g-1. The solid-state asymmetric supercapacitor shows a good cyclic stability in which ∼11% capacitance loss was observed after 5000 cycles.

Totally embedded hybrid thin films of carbon nanotubes and silver nanowires as flat homogenous flexible transparent conductors.

There is a great need for viable alternatives to today's transparent conductive film using largely indium tin oxide. We report the fabrication of a new type of flexible transparent conductive film using silver nanowires (AgNW) and single-walled carbon nanotube (SWCNT) networks which are fully embedded in a UV curable resin substrate. The hybrid SWCNTs-AgNWs film is relatively flat so that the RMS roughness of the top surface of the film is 3 nm. Addition of SWCNTs networks make the film resistance uniform; without SWCNTs, sheet resistance of the surface composed of just AgNWs in resin varies from 20 Ω/sq to 107 Ω/sq. With addition of SWCNTs embedded in the resin, sheet resistance of the hybrid film is 29 ± 5 Ω/sq and uniform across the 47 mm diameter film discs; further, the optimized film has 85% transparency. Our lamination-transfer UV process doesn't need solvent for sacrificial substrate removal and leads to good mechanical interlocking of the nano-material networks. Additionally, electrochemical study of the film for supercapacitors application showed an impressive 10 times higher current in cyclic voltammograms compared to the control without SWCNTs. Our fabrication method is simple, cost effective and enables the large-scale fabrication of flat and flexible transparent conductive films.