Structure and dynamics of biodegradable polyurethane-silk fibroin composite materials in the dry and hydrated states studied using 13C solid-state NMR spectroscopy

Self-reinforced silk nanofibrils networks enable ultrafine fibroin monofilament sutures applied in minimally invasive surgery

Superfine recycled regenerated silk fibroin (RRSF) monofilament sutures are designed to minimize surgical incisions, prevent scar formation, and facilitate precise suturing in cosmetic and plastic surgeries. However, balancing fineness and strength remains a challenge because the RRSF extraction process disrupts the hierarchical structure of natural silk fibers, leading to suboptimal mechanical properties. This study employed mechanical peeling and grinding to exfoliate β-sheets-rich silk fibroin nanofibrils (SFNF), which served as homologous reinforcing materials uniformly dispersed in the RRSF spinning system. Water-soluble, biocompatible polyvinyl alcohol (PVA) was introduced to enhance ductility. The fiber underwent extensive water immersion stretching to produce ultrafine fibers and foster a highly oriented internal self-reinforcing SFNF network structure. Monofilament surgical sutures were successfully fabricated following surface coating with chitosan. Our results showed that with 0.1 wt% SFNF and a stretching multiplier of 2.5, the tensile strength of the fibers increased by 33 % compared to those without SFNF. Fluorescence staining confirmed the presence of highly oriented SFNF networks within the fibers. Mechanical simulations validated the pronounced reinforcement effect of this network structure. The sutures, measuring 39.38 μm in diameter and exhibiting a tensile strength of 0.31 N, met USP standards for 9-0 surgical sutures, making them suitable for microsurgery. Additionally, they demonstrated antibacterial properties, biocompatibility, and degraded at a rate of 43.09 % within 30 days. In animal trials, the sutures facilitated wound closure, reduced inflammatory responses, and minimized scar formation.

Subcritical Hydrothermal Liquefaction as a Pretreatment for Enzymatic Degradation of Polyurethane

Enzymatic digestion is a promising alternative in the upconversion of plastic waste compared to traditional chemical recycling methods, because it warrants the use of milder conditions. However, enzymes are hardly able to penetrate the bulk of the plastic material; thus, a pretreatment is necessary to promote the reaction. In this study we investigate hydrothermal liquefaction as a thermal pretreatment of a commercial polyurethane before performing an enzymatic digestion. The feedstock is a rigid polyurethane foam. The structure and chemical composition of the feedstock were analyzed through FTIR analysis and solid-state ¹³C NMR. The polyurethane was then subjected to hydrothermal liquefaction using either ultrapure water or KOH as a basic catalyst. Enzymatic digestion was then performed on the organic fraction obtained from both experiments using a lipase extracted from Candida rugosa. The LC-MS analysis of the digests shows an increase in some signal intensities due to the degradation of oligomeric fragments. This new way of recycling allows the recovery of important chemicals such as quinolines and 4,4'-methylenedianiline. With this study we demonstrate that hydrothermal liquefaction coupled with enzymatic digestion is a suitable alternative for handling polyurethane waste.

Ancient fibrous biomaterials from silkworm protein fibroin and spider silk blends: Biomechanical patterns

Silkworm silk protein fibroin and spider silk spidroin are known biocompatible and natural biodegradable polymers in biomedical applications. The presence of β-sheets in silk fibroin and spider spidroin conformation improves their mechanical properties. The strength and toughness of pure recombinant silkworm fibroin and spidroin are relatively low due to reduced molecular weight. Hence, blending is the foremost approach of recent studies to optimize silk fibroin and spidroin's mechanical properties. As summarised in the present review, numerous research investigations evaluate the blending of natural and synthetic polymers. The effects of blending silk fibroin and spidroin with natural and synthetic polymers on the mechanical properties are discussed in this review article. Indeed, combining natural and synthetic polymers with silk fibroin and spidroin changes their conformation and structure, fine-tuning the blends' mechanical properties. STATEMENT OF SIGNIFICANCE: Silkworm and spider silk proteins (silk fibroin and spidroin) are biocompatible and biodegradable natural polymers having different types of biomedical applications. Their mechanical and biological properties may be tuned through various strategies such as blending, conjugating and cross-linking. Blending is the most common method to modify fibroin and spidroin properties on demand, this review article aims to categorize and evaluate the effects of blending fibroin and spidroin with different natural and synthetic polymers. Increased polarity and hydrophilicity end to hydrogen bonding triggered conformational change in fibroin and spidroin blends. The effect of polarity and hydrophilicity of the blending compound is discussed and categorized to a combinatorial, synergistic and indirect impacts. This outlook guides us to choose the blending compounds mindfully as this mixing affects the biochemical and biophysical characteristics of the biomaterials.

Characterization of a Water-Dispersed Biodegradable Polyurethane-Silk Composite Sponge Using 13C Solid-State Nuclear Magnetic Resonance as Coating Material for Silk Vascular Grafts with Small Diameters

Recently, Bombyx mori silk fibroin (SF) has been shown to be a suitable material for vascular prostheses for small arteries. In this study, we developed a softer SF graft by coating water-dispersed biodegradable polyurethane (PU) based on polycaprolactone and an SF composite sponge on the knitted SF vascular graft. Three kinds of 13C solid-state nuclear magnetic resonance (NMR), namely carbon-13 (13C) cross-polarization/magic angle spinning (MAS), 13C dipolar decoupled MAS, and 13C refocused insensitive nuclei enhanced by polarization transfer (r-INEPT) NMR, were used to characterize the PU-SF coating sponge. Especially the 13C r-INEPT NMR spectrum of water-dispersed biodegradable PU showed that both main components of the non-crystalline domain of PU and amorphous domain of SF were highly mobile in the hydrated state. Then, the small-diameter SF artificial vascular grafts coated with this sponge were evaluated through implantation experiments with rats. The implanted PU-SF-coated SF grafts showed a high patency rate. It was confirmed that the inside of the SF grafts was covered with vascular endothelial cells 4 weeks after implantation. These results showed that the water-dispersed biodegradable PU-SF-coated SF graft created in this study could be a strong candidate for small-diameter artificial vascular graft.