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Like most major ampullate silks of spider, the length of Antheraea pernyi silkworm silk can shrink to a certain degree when the fiber is in contact with water. However, what happens in terms of molecule chain level and how it correlates to the mechanical properties of the silk during its contraction is not yet fully understood. Here, we investigate the water-induced mechanical property changes as well as the structure transition of two kinds of A. pernyi silk fiber, which are forcibly reeled from two different individuals (silkworm a and silkworm b; the silk fiber from either one represents the lower and upper limit of the distribution of mechanical properties, respectively). The tensile test results present that most of the mechanical parameters except the post-yield modulus and breaking strain for both silk fibers have the same variation trend before and after their water contraction. Synchrotron FTIR and Raman spectra show that the native filament from silkworm a contains more α-helix structures than that in silkworm b filament, and these α-helices are partially converted to β-sheet structures after the contraction of the fibers, while the order of both β-sheet and α-helix slightly increase. On the other side, the content and orientation of both secondary structural components in silkworm b fiber keep unchanged, no matter if it is native or contracted. C CP/MAS NMR results further indicate that the α-helix/random coil to β-sheet conformational transition that occurred in the silk of silkworm a corresponds the Ala residues. Based upon these results, the detailed structure transition models of both as-reeled A. pernyi silk fibers during water contraction are proposed finally to interpret their properties transformation.

Candida -associated denture stomatitis (CADS), caused by colonization and biofilm-formation of Candida species on denture surfaces, is a significant clinical concern. We show here that modification of conventional denture materials with functional groups can significantly increase drug binding capacity and control drug release rate of the resulting denture materials for potentially managing CADS. In our approach, poly(methyl methacrylate) (PMMA)-based denture resins were surface grafted with three kinds of polymers, poly(1-vinyl-2-pyrrolidinone) (PNVP), poly(methacrylic acid) (PMAA), and poly(2-hydroxyethyl methacrylate) (PHEMA), through plasma-initiated grafting polymerization. With a grafting yield as low as 2 wt%, the three classes of new functionalized denture materials showed significantly higher drug binding capacities toward miconazole, a widely used antifungal drug, than the original PMMA denture resin control, leading to sustained drug release and potent biofilm-controlling effects against Candida. Among the three classes of functionalized denture materials, PNVP-grafted resin provided the highest miconazole binding capability and the most powerful antifungal and biofilm-controlling activities. Drug binding mechanisms were studied. These results demonstrated the importance of specific interactions between drug molecules and functional groups on biomaterials, shedding lights on future design of CADS-managing denture materials and other related devices for controlled drug delivery.

The objective of this study was to evaluate the effects of fluorination on the antimicrobial and biofilm-controlling activities of N-halamine-based additives for polymers. A fluorinated N-halamine, 1-chloro-3-1H,1H,2H,2H-perflurooctyl-5,5-dimetylhydantoin (Cl-FODMH), and its un-fluorinated counterpart, 1-chloro-3-octyl-5,5-dimethylhydantoin (Cl-ODMH), were synthesized and characterized with FT-IR, 1H-NMR, and DSC studies. Polyurethane (PU) films containing Cl-ODMH and Cl-FODMH as antimicrobial additives were fabricated through solvent casting. With the same additive contents (1wt%-5 wt%), PU films with Cl-FODMH showed higher contact angle values. AFM, SEM and DSC results revealed that while Cl-ODMH distributed evenly within PU, Cl-FODMH aggregated and formed macro-domains in PU. Antimicrobial studies showed that PU films with Cl-ODMH had higher antimicrobial and biofilm-controlling potency against Gram-positive and Gram-negative bacteria than PU samples with Cl-FODMH. These results demonstrated the importance of distribution of additives in polymers on antimicrobial performances, shedding lights on future antimicrobial material design strategies.