Preparation and characterization of silk fibroin nanocrystals

Structural evolution of in situ polymerized poly(L-lactic acid) nanocomposite for smart textile application

This present study demonstrated the preparation of a highly crystalline anatase (ana) form of titanium oxide (TiO₂) doped silk nanocrystal (SNC) nanohybrid (ana-TCS) of diameter (7.5 ± 1.4 nm) by the sol–gel method using titanium (IV) butoxide as the hydrolysis material. This prepared nanohybrid with surface hydroxyl groups acted as a co-initiator for the synthesis of poly(L-lactic acid) (PLLA)-g-ana-TSC nanocomposite with grafted PLLA chains via the in situ polymerization technique, using tin-octoate as a catalyst. The fabricated nanocomposite had a high number average molecular weight of 83 kDa with good processibility. This prepared nanocomposite was hydrophobic in nature, with a contact angle of 105°, which was further enhanced to 122 ± 1° when processed via electrospinning technique into a non-woven fabric. The prepared nanocomposite could degrade up to 43% methylene blue dye in 15 days. This nanocomposite showed no significant molecular weight reduction after 1 h of aqeous treatment, which could be attributed to its hydrophobic nature, inhibiting its degradation. However, 50% degradation was observed for the nanocomoposite whereas, PLLA demonstrated 25% degradation in 15 days, after its end-of-life. Thus, this study revealed that the in situ synthesized PLA-ana-TCS nanocomposite could be targeted for use as a hydrophobic, self-cleaning, dye-degradable fabric.

Influence of addition of organic fillers on the properties of mechanically recycled PLA

Poly(lactic acid) (PLA) is one of the most used biobased and biodegradable polymers. Due to their high stability, some of the newest grades of PLA are only degradable under severe industrial conditions. For these grades, mechanical recycling is a viable end-of-life option, with great environmental advantages. However, the polymer undergoes degradation during its service life and in the melt reprocessing, which leads to a decrease in properties that can compromise the recyclability of PLA. The goal of this work was to evaluate the usefulness of adding small amounts of two organic fillers, chitosan, and silk fibroin nanoparticles, during the recycling process for improving the properties of the recycled plastic. The degradation level of the aged polymer and the nature and amount of filler affect the performance of the recycled plastics. The fillers reduce the degradation during the melt reprocessing of PLA previously subjected to severe hydrolysis, thus increasing the intrinsic viscosity of the recycled plastic. A careful selection of the added organic filler lead to recycled plastics with improvements in some key mechanical, thermal, and barrier properties. Thus, the use of organic fillers represents a cost-effective and environmentally sound way for improving the mechanical recycling of bioplastics.

Liquid-Exfoliated Mesostructured Collagen from the Bovine Achilles Tendon as Building Blocks of Collagen Membranes

Mesoscaled assemblies are organized in native collagen tissues to achieve remarkable and diverse performance and functions. In this work, a facile, low-cost, and controllable liquid exfoliation method was applied to directly extract these collagen mesostructures from bovine Achilles tendons using a sodium hydroxide (NaOH)/urea aqueous system with freeze-thaw cycles and sonication. A series of collagen fibrils with diameters of 26-230 nm were harvested using this process, and in situ observations under polarizing microscopy (POM) and using molecular dynamics simulations revealed the influence of the NaOH/urea system on the tendon collagen. FTIR and XRD results confirmed that these collagen fibrils preserved typical structural characteristics of type I collagen. These isolated collagen fibrils were then utilized as building blocks to fabricate free-standing collagen membranes, which exhibited good stability in solvents and outstanding mechanical properties and transparency, with potential for utility in optical and electronic sensors. Moreover, in vitro and vivo evaluations demonstrated that these new resulting collagen membranes had good cytocompatibility, biocompatibility, and degradability for potential applications in biomedicine. This work provides a new approach for collagen processing by liquid exfoliation with utility for the formation of robust collagen materials that consist of native collagen mesostructures as building blocks.

Nanosilk-Grafted Poly(lactic acid) Films: Influence of Cross-Linking on Rheology and Thermal Stability

This article reports a novel fabrication of branched cum cross-linked poly(lactic acid) (PLA) with nanosilk fibroin with graft chain topology by reactive extrusion process. It could be possible by the addition of a small amount of radical initiator (dicumyl peroxide (DCP)). Grafting of silk nanocrystals (SNCs) on PLA macromolecules that provides remarkable improvement in the rheological and thermal properties of the latter are confirmed by ¹H NMR and Fourier transform infrared investigation. Significant improvement is observed in zero shear viscosities, and the crossover point shifts to lower frequencies as compared to the branched and cross-linked PLA system. Along with SNC grafting, the crystallization process is also enhanced and stable crystals appeared during cooling, which results in a single melting peak. The rate of crystallization of PLA has been improved although the percentage crystallinity reduces with DCP content, as higher grafting and cross-linking restricts the chain segmental motion, which is critical for crystallization process. Furthermore, SNC grafting increases the reprocessability performance of PLA and provides higher rheological properties as compared to the branched and cross-linked PLA at all reprocessing cycles.

Microstructural change of degummed Bombyx mori silk: an in situ stretching wide-angle X-ray-scattering study

The microstructural change of degummed Bombyx mori silk was examined by in situ wide-angle X-ray-scattering (WAXS) with applied stretching force. WAXS patterns confirmed that the crystalline and amorphous regions coexist in the silk fibers. The crystallites with β-sheet structure have an orthorhombic unit cell with lattice parameters: a=9.10 Å, b=9.71 Å and c=6.80 Å. The crystallite size, crystallite orientation and crystallinity were also estimated based on the WAXS patterns. The results demonstrate that the crystallite size is almost unchanged with the stretching strain. The crystallinity is approximately linearly increasing with the applied stretching force. However, the change of the unit-cell orientation degree with c-axis along the fiber axis behaves as a fast stage and an approximately unchanged stage during the in situ stretching process. All these experimental phenomena confirm that the microstructure of the degummed silk fibers can be well explained by the model of oriented β-sheet structure with a banded feature.