Banded structures in collagen vitrigels for corneal injury repair

Coacervation-Based Method for Constructing a Multifunctional Strain-Stiffening Crystalline Polyvinylamine Hydrogel

Strain-stiffening hydrogels are essential in the development of ionic skin, as human skin possesses a strain-stiffening property for self-protection. Semicrystalline polymers such as poly(vinyl alcohol) (PVA) have been widely investigated to fabricate strain-stiffening hydrogels via freeze-thaw cycling or chemical cross-linking but with limited adjustable properties. Compared with PVA, polyvinylamine (PVAm) has a higher reactive activity, making it easier to achieve multifunctionalities including strain-stiffening in a PVAm hydrogel. However, the amine moieties in the backbone tend to be ionized and form strong ionic hydrogen bonds with water, resulting in difficulties in forming crystalline hydrogels by conventional methods. Herein, a one-pot method to induce crystallinity and achieve multifunctional hydrogel is devised via coacervation of PVAm. Different from a published coacervation method to fabricate hydrogels with various properties via noncovalent interactions between different chemicals, coacervation occurs between PVAm to form aggregated and loose PVAm in our devised system. Such a strategy lowers the amine-water binding energy in the polymer-dense phase to achieve crystallinity and subsequently the strain-stiffening property; meanwhile, self-healability, self-adhesion, and ionic conductivity can be realized in the polymer-loose phase. The obtained hydrogel integrates stretchability (∼1300% elongation), toughness (227 kPa), the strain-stiffening property (∼10 times increase), self-adhesion (90 J m^-2), self-healability (∼80% healing efficiency in toughness), and ionic conductivity (0.22 mS m^-1). This convenient strategy will open a new horizon to design multifunctional skin-mimic materials.

Naturally derived proteins and glycosaminoglycan scaffolds for tissue engineering applications

Tissue engineering (TE) aims to mimic the complex environment where organogenesis takes place using advanced materials to recapitulate the tissue niche. Cells, three-dimensional scaffolds and signaling factors are the three main and essential components of TE. Over the years, materials and processes have become more and more sophisticated, allowing researchers to precisely tailor the final chemical, mechanical, structural and biological features of the designed scaffolds. In this review, we will pose the attention on two specific classes of naturally derived polymers: fibrous proteins and glycosaminoglycans (GAGs). These materials hold great promise for advances in the field of regenerative medicine as i) they generally undergo a fast remodeling in vivo favoring neovascularization and functional cells organization and ii) they elicit a negligible immune reaction preventing severe inflammatory response, both representing critical requirements for a successful integration of engineered scaffolds with the host tissue. We will discuss the recent achievements attained in the field of regenerative medicine by using proteins and GAGs, their merits and disadvantages and the ongoing challenges to move the current concepts to practical clinical application.