Injectable cell-laden silk acid hydrogel.

This study presents an injectable cell-laden hydrogel system based on silk acid, a carboxylated derivative of natural silk fibroin, which exhibits promising applications in biomedicine. The hydrogel is produced under physiological conditions (37 °C and pH 7.4) via physical crosslinking. Notably, the hydrogel demonstrates remarkable cytocompatibility, enabling efficient cell encapsulation, and exhibits good injectability. These promising results strongly indicate the potential of silk acid hydrogel for transformative applications, including 3D cell culture, targeted cell delivery, and tissue engineering.

Silk Acid as an Implantable Biomaterial for Tissue Regeneration.

Silk fibroin derived from the domesticated silkworm Bombyx mori is a protein-based biopolymer with low immunogenicity, intrinsic biodegradability, and tunable mechanical properties, showing great potential in biomedical applications. Using chemical modification to alter the primary structure of silk fibroin enables the expanded generation of new silk-based biomaterials. Inspired by the molecular structure of hyaluronic acid, which is enriched in carboxyl groups, an efficient method with scaling-up potential to achieve controlled carboxylation of silk fibroin to prepare silk acid (SA) is reported, and the biological properties of SA are further studied. The SA materials show tunable hydrophilicity and enzymatic degradation properties at different carboxylation degrees (CDs). Subcutaneous implantation in mice for up to 1 month reveals that the SA materials with a high CD present enhanced degradation while causing a mild foreign-body response, including a low inflammatory response and reduced fibrotic encapsulation. Immunofluorescence analysis further indicates that the SA materials show pro-angiogenesis properties and promote M2-type macrophage polarization to facilitate tissue regeneration. This implies great promise for SA materials as a new implantable biomaterial for tissue regeneration.

Degradable silk-based soft actuators with magnetic responsiveness.

Soft actuators with stimuli-responsiveness have great potential in biomedical applications such as drug delivery and minimally invasive surgery. In this study, protein-based soft actuators with magnetic actuation are fabricated using naturally occurring silk proteins and synthesized Fe3O4 magnetic nanoparticles (NPs). Briefly, magnetic silk films are first prepared by solution casting of a mixture containing silk proteins, synthesized Fe3O4 NPs, and glycerol. The molecular structures of the magnetic silk films are characterized by FTIR spectroscopy, which show that the ß-sheet content in the films is about 20%. The mechanical tests show that the magnetic silk films can be stretched to over 200% under wet conditions and Young's modulus is estimated to be 4.89 ± 0.69 MPa, matching the stiffness of soft tissues. Furthermore, the enzymatic degradability, good biocompatibility, and in vivo X-ray visibility of the films are demonstrated by the in vitro enzymatic degradation test, in vivo biocompatibility test, and micro-CT imaging, respectively. Degradable silk-based soft actuators with magnetic responsiveness are successfully prepared by thermal forming or plastic molding of the magnetic silk films. The fabricated soft actuators can be actuated and move with precise locomotive gaits in solutions using a magnet. In addition, the retention of the soft actuators and localized drug delivery in gastrointestinal tracts by attaching a magnet to the abdominal skin are demonstrated using model systems. The degradable silk-based soft actuators provide many opportunities for improving current therapeutic strategies in biomedicine.

Cellular Concentrations of Nucleotide Diphosphate-Chelated Magnesium Ions Accelerate Catalysis by RNA and DNA Enzymes.

RNAs are involved in myriad cellular events. In general, RNA function is affected by cellular conditions. For instance, molecular crowding promotes RNA folding through compaction of the RNA. Metabolites generally destabilize RNA secondary structure, which improves RNA folding cooperativity and increases the fraction of functional RNA. Our recent studies demonstrate that cellular concentrations of amino acid-chelated magnesium (aaCM) stimulate RNA folding and catalysis while protecting RNAs from magnesium ion-induced degradation. However, effects of other cellular magnesium ion chelators on RNA function have not been tested. Herein, we report that nucleotide diphosphate-chelated magnesium, which is of intermediate strength, promotes RNA catalysis much like aaCM. Nucleotides are some of the major metabolites in cells and have one to three phosphates, which have increasingly tight binding of magnesium. On the basis of binding calculations, ∼85% ATP, ∼40% ADP, and only 5% AMP are estimated to possess a magnesium ion under cellular conditions of 0.50 mM Mg2+free. We tested the self-cleaving activity of the hammerhead ribozyme in the presence of these chelated magnesium species. Our results indicate that NTP-chelated magnesium and NMP-chelated magnesium do not appreciably stimulate RNA catalysis, whereas NDP-chelated magnesium promotes RNA catalysis up to 6.5-fold. Inspired by NDP, we observed similar stimulatory effects for several other Mg2+ diphosphate-containing metabolites, including UDP-GlcNAC and UDP-Glc; in addition, we found similar effects for a DNAzyme. Thus, rate stimulatory effects are general with respect to the diphosphate and nucleic acid enzyme. These results implicate magnesium-chelated diphosphate metabolites as general facilitators of RNA function inside cells.