Significance: Disordered materials with heterogeneities at scales ranging from nano- to micrometers usually scatter visible light and become opaque beyond a certain thickness. However, transparent materials are found in nature. The physical origin of transparency in natural and artificial biopolymer materials is still not fully understood. Here, a gap of transparency is found in synthetic fibrillar collagen matrices within a very narrow range of concentration. The transparency results from structural partial order inhibiting light scattering, while preserving mechanical stability, stiffness, and nonlinearity. The potential to produce biomimetic hydrogels with such striking optical properties by self-assembly opens an interesting route in the study of photonic materials and provides new elements in the understanding of the appearance of transparency in natural materials.

While carboxymethyl cellulose (CMC)—a biocompatible and water-soluble cellulose derivative—holds promise for biomedical applications, challenges remain in synthesizing CMC-based hydrogels with covalent crosslinking through free radical polymerization without requiring complex, multi-step processes. In this study, we introduce a facile one-pot strategy that combines CMC with acrylamide (AAm) under cryogelation and low-intensity UV irradiation to achieve covalent bonding and a high polymerization yield. The resulting polyacrylamide/carboxymethyl cellulose (PAAm/CMC) porous gels were systematically evaluated for their chemical, physical, thermal, and drug-release properties, with a focus on the effects of AAm concentration and polymerization temperature (frozen vs. room temperature). Notably, the cryogel synthesized with 2.5 M AAm (PC2.5) exhibited significantly enhanced mechanical properties—that is, an 8.4-fold increase in tensile modulus and a 26-fold increase in toughness—compared with the non-cryo gel. Moreover, PC2.5 demonstrated excellent cyclic compression stability in water and phosphate-buffered saline (PBS), with less than 10% reduction in modulus after 100 cycles. These increases in the mechanical properties of PC2.5 are attributed to the formation of macropores with high polymer density and high crosslinking density at the pore walls. PC2.5 also showed slower drug release in PBS and good cytocompatibility. This study presents a simplified and efficient route for fabricating mechanically robust, covalently crosslinked PAAm/CMC cryogels, highlighting their strong potential for biomedical applications in drug delivery systems.

Anisotropic photonic hydrogels with alternatively stackedpoly(dodecylglyceryl itaconate) (PDGI) bilayers and polyacrylamide (PAAm) gellayers are unique soft materials with various functions. It is knownthat to form the lamellar phase of bilayers, a small amount of co-surfactantsodium dodecyl sulfate (SDS) should be present in the precursor monomersolutions of the gels. However, little is known about the influenceof the co-surfactant on the structure of bilayers and on the mechanicalproperties of such photonic hydrogels. Herein, we chose several co-surfactantsand studied the effect of the co-surfactants on the self-assemblybehavior of the bilayers and on the mechanical properties of the resultingphotonic hydrogels. A macroscopically aligned lamellar phase couldbe induced for all the co-surfactants. Interestingly, the mechanicalresponse of the photonic hydrogels sensitively depends on the chemicalstructure of the co-surfactant, especially at large deformation. Wehypothesize that doping by small amounts of co-surfactants dramaticallychanges the anchoring strength and density of PAAm strands onto thebilayer surface, thereby influencing the load transfer efficiencyfrom the bilayer to the PAAm gel layer at large deformation and therupture of the bilayer. This work provides new understanding in themolecular mechanisms of deformation and strengthening in this softand anisotropic nanocomposite, helping to design more robust photonichydrogels.