Silk fibroin sponges have been widely studied and reported in literature for tissue engineering applications. Several fabrication methods have been proposed during the years to cover most of the demands in terms of properties, which should be adapted to the considered tissue. Most of these procedures are based on the secondary structure transition of the protein to the stable β crystalline form. This transition, known as physical cross-linking, makes the sponge resistant to dissolution in water, and, in general, increases the sponge stiffness. In our work, we propose an alternative method to ensure the stability of the sponge based on chemical crosslinking of a methacrylated version of silk fibroin (Sil-MA) obtained via chemical modification. The Sil-MA water solution with the addition of a photoinitiator (LAP) allows the opening, under UV radiation, of a double carbon−carbon bond and radical polymerization. The incorporation of air bubbles (that serves as a template for the pores) was accomplished by a mixer; then, the foam was stabilized under UV light and the excess water was removed by freeze-drying. Because of the cytotoxicity of the photoinitiator (found when used at a high concentration), an additional washing step in water has been introduced to eliminate the residues and improve the cells' viability. Fourier transform infrared (FTIR) analysis confirmed the functionalization of the protein. To evaluate the effect of the composition on the sponge properties, a 2 3 full factorial design of the experiment has been adopted. FTIR analysis revealed that the sponge composition did not affect the protein's secondary structure. The analysis of images obtained by SEM allowed some statistical measures of the porosity curves to be studied and modeled. The same modeling procedure was applied to the dissolution test in a simulated body fluid, to the water absorption, and to the cell viability (tested by the MTT and LDH assays). An empirical model for each property was built, showing how by changing the composition it is possible to tune the sponge properties.

Over the past few decades, gellan gum (GG) has attracted substantial research interest in several fields including biomedical and clinical applications. The GG has highly versatile properties like easy bio-fabrication, tunable mechanical, cell adhesion, biocompatibility, biodegradability, drug delivery, and is easy to functionalize. These properties have put forth GG as a promising material in tissue engineering and regenerative medicine fields. Nevertheless, GG alone has poor mechanical strength, stability, and a high gelling temperature in physiological conditions. However, GG physiochemical properties can be enhanced by blending them with other polymers like chitosan, agar, sodium alginate, starch, cellulose, pullulan, polyvinyl chloride, xanthan gum, and other nanomaterials, like gold, silver, or composites. In this review article, we discuss the comprehensive overview and different strategies for the preparation of GG based biomaterial, hydrogels, and scaffolds for drug delivery, wound healing, antimicrobial activity, and cell adhesion. In addition, we have given special attention to tissue engineering applications of GG, which can be combined with another natural, synthetic polymers and nanoparticles, and other composites materials. Overall, this review article clearly presents a summary of the recent advances in research studies on GG for different biomedical applications.

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Biomaterials designed to replace the diseased cornea could be used to treat corneal blindness where human donor tissue is in short supply, but challenges are the integration of biomaterials with host tissue and cells, avoiding a rapid material degradation and maintaining corneal transparency. Additionally, implantation surgery often triggers an aggressive wound healing response that can lead to corneal thinning and opacity. Here, we report a collagen-based hydrogel with transparency and mechanical properties suitable for replacing a substantial portion of a damaged or diseased corneal stroma. The porous hydrogel permitted migration and population by host cells while maintaining transparency and thickness six months after surgical implantation in an in vivo model of human corneal surgery. With a novel hybrid surgical implantation technique inspired by LASIK refractive surgery, rapid wound healing occurred around implants to maintain biomaterial integrity, transparency and function. Host stromal cell repopulation and regeneration of host epithelium and nerves were observed, as necessary steps towards corneal regeneration. Finally, as a proof-of-principle, the hydrogel loaded with a neuroregenerative drug achieved sustained slow-release drug delivery in vitro. The proposed hydrogel and novel implantation technique together represent a therapeutic approach with translational potential for replacing and regenerating diseased corneal stromal tissue.

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