Synthesis of Silk Fibroin–Glycopolypeptide Conjugates and Their Recognition with Lectin

Silk fibroin (SF), the natural fibrous protein created by the Bombyx mori silk worm, is being increasingly explored as a biomaterial for tissue engineering due to its excellent mechanical strength, high oxygen/water permeability, and biocompatibility. It is also well known that surface modification of SF with organic ligands such as the extracellular protein binding Arg-Gly-Asp (RGD) peptides help adhesion and proliferation of cells bettera key requirement for it to function as extracellular matrices. In this work, we have conjugated synthetic glycopolypeptides (GPs) that were synthesized by controlled ring-opening polymerization of α<i>-manno</i>-lys <i>N</i>-carboxyanhydrides (NCAs) onto SF by using Cu catalyzed click reaction to synthesize a new hybrid material (SF–GP), which we believe will have both the mechanical properties of native SF and the molecular recognition property of the carbohydrates in the GP. By controlling the amount of GP grafted onto SF, we have made three SF–GP conjugates that differ in their ability to assemble into films. SF–GP conjugates having a very high content of GP formed completely water-soluble brush-like polymer that displayed very high affinity toward the lectin concanavalin-A (Con-A). Films cast from SF–GP conjugates using lower amounts of grafted GP were more stable in water, and the stability can be modulated by varying the amount of GP grafted. The water-insoluble film SF–GP₂₅ was also found to bind to fluorescently labeled Con-A, as was seen by confocal microscopy. Such SF–GP hybrid films may be useful as mimics of extracellular matrices for tissue engineering

Sol–Gel Assisted Fabrication of Collagen Hydrolysate Composite Scaffold: A Novel Therapeutic Alternative to the Traditional Collagen Scaffold

Collagen is one of the most widely used biomaterial for various biomedical applications. In this Research Article, we present a novel approach of using collagen hydrolysate, smaller fragments of collagen, as an alternative to traditionally used collagen scaffold. Collagen hydrolysate composite scaffold (CHCS) was fabricated with sol–gel transition procedure using tetraethoxysilane as the silica precursor. CHCS exhibits porous morphology with pore sizes varying between 380 and 780 μm. Incorporation of silica conferred CHCS with controlled biodegradation and better water uptake capacity. Notably, 3T3 fibroblast proliferation was seen to be significantly better under CHCS treatment when compared to treatment with collagen scaffold. Additionally, CHCS showed excellent antimicrobial activity against the wound pathogens <i>Staphylococcus aureus, Bacillus subtilis</i>, and <i>Escherichia coli</i> due to the inherited antimicrobial activity of collagen hydrolysate. In vivo wound healing experiments with full thickness excision wounds in rat model demonstrated that wounds treated with CHCS showed accelerated healing when compared to wounds treated with collagen scaffold. These findings indicate that the CHCS scaffold from collagen fragments would be an effective and affordable alternative to the traditionally used collagen structural biomaterials

Silk Fibroin-Sophorolipid Gelation: Deciphering the Underlying Mechanism

Silk fibroin (SF) protein, produced by silkworm Bombyx mori, is a promising biomaterial, while sophorolipid (SL) is an amphiphilic functional biosurfactant synthesized by nonpathogenic yeast Candida bombicola. SL is a mixture of two forms, acidic (ASL) and lactonic (LSL), which when added to SF results in accelerated gelation of silk fibroin. LSL is known to have multiple biological functionalities and hence hydrogels of these green molecules have promising applications in the biomedical sector. In this work, SANS, NMR, and rheology are employed to examine the assembling properties of individual and mixed SLs and their interactions with SF to understand the mechanism that leads to rapid gelation. SANS and NMR studies show that ASL assembles to form charged micelles, while LSL forms micellar assemblies and aggregates of a mass fractal nature. ASL and LSL together form larger mixed micelles, all of which interact differently with SF. It is shown that preferential binding of LSL to SF causes rapid unfolding of the SF chain leading to the formation of intermolecular beta sheets, which trigger fast gelation. Based on the observations, a mechanism for gelation of SF in the presence of different sophorolipids is proposed

Lamellar Melting, Not Crystal Motion, Results in Softening of Polyoxymethylene on Heating

We probe temperature-dependent changes in the semicrystalline microstructure of polyoxymethylene using a combination of modulated DSC, SAXS, and solid-state NMR to characterize macroscopic behavior, lamellar-level structure, and molecular environments, respectively, and correlate these with the change in mechanical properties probed using DMA and AFM. Two model samples are investigated: a melt crystallized sample prepared by injection molding and a sample obtained by crystallization from dilute solution. Our investigations reveal that, for both samples, there is an increase in crystalline motions and in the amorphous content on heating. DMA and AFM measurements reveal that the modulus of the molded sample decreases on heating to about 100 °C; however, there is a significant difference in behavior of the solution crystals, where we observe no significant decrease in stiffness (from AFM measurements). Thus, in contrast to previous reports, we demonstrate that the decrease in modulus on heating polyoxymethylene does not correlate with chain motions in the crystalline regions. We use SAXS to probe the semicrystalline morphology for the samples on heating and show that, for the molded sample, there is a distribution of lamellar thickness at room temperature and that the thin lamellae in this distribution melt on heating. In contrast to the behavior of the melt crystallized samples, the solution crystals exhibit no change in the lamellar stacking on heating to 150 °C. We also demonstrate that, on heating, the amorphous regions in the solution crystals always appear to have restricted mobility while there are mobile and low mobility amorphous regions in the molded samples. Our results suggest that, contrary to conventional belief, the decrease in modulus on heating polyoxymethylene arises not from motions in the crystalline lamellae but primarily from melting of thin lamellae