Silk has attracted widespread attention due to its superlative material properties and promising applications. However, the determinants behind the variations in material properties among different types of silk are not well understood. We analysed the physical properties of silk samples from a variety of silkmoth cocoons, including domesticated Bombyx mori varieties and several species from Saturniidae. Tensile deformation tests, thermal analyses, and investigations on crystalline structure and orientation of the fibres were performed. The results showed that saturniid silks produce more highly-defined structural transitions compared to B. mori, as seen in the yielding and strain hardening events during tensile deformation and in the changes observed during thermal analyses. These observations were analysed in terms of the constituent fibroin sequences, which in B. mori are predicted to produce heterogeneous structures, whereas the strictly modular repeats of the saturniid sequences are hypothesized to produce structures that respond in a concerted manner. Within saturniid fibroins, thermal stability was found to correlate with the abundance of poly-alanine residues, whereas differences in fibre extensibility can be related to varying ratios of GGX motifs versus bulky hydrophobic residues in the amorphous phase.

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The toughness of polybenzoxazine can effectively be improved by alloying with isophorone diisocyanate (IPDI)‐based urethane prepolymers (PU) or with flexible epoxy (EPO732). The experimental results, i.e., flexural testing and dynamic mechanical analysis, reveal that the toughness of the alloys of the rigid polybenzoxazine and the PU or the EPO732 systematically increases with the amount of either toughener, due to the addition of more flexible molecular segments in the polymer hybrids. The curing temperature of the benzoxazine resin (bisphenol A‐aniline type [BA‐a]) at about 225°C shifts to a higher value when the fraction of BA‐a in either alloy decreases. Interestingly, the enhancement in the glass transition temperature (Tg) of BA‐a/PU alloys is clearly observed, i.e., Tg of the BA‐a/PU alloys are significantly higher (Tg beyond 200°C) than those of the parent resins, i.e., 165°C for BA‐a and −70°C for PU. However, this characteristic is not observed in the BA‐a/EPO732 alloy systems. The enhanced Tg of the BA‐a/PU alloy at a 70/30 mass ratio is found to be 220°C, while that of BA‐a/EPO732 at the same mass ratio is observed to be only 95°C, which further decreases as the content of epoxy fraction increases. Furthermore, the degradation temperature based on 5% weight loss in the thermogravimetric analyzer (TGA) thermograms of the BA‐a/PU alloys is found to improve with the presence of the PU, though the opposite trend is observed in the BA‐a/EPO732 systems. The char yield of both alloy systems is steadily enhanced with the increased benzoxazine content because the char yield of the polybenzoxazine is inherently higher than that of the two tougheners. Therefore, the polybenzoxazine alloys with the IPDI‐based urethane prepolymer, e.g., the 70/30 BA‐a/PU, are a promising system for a tough, high thermal stability polymeric network, suitable for both bulk and composite matrix applications. POLYM. ENG. SCI. 45:288–296, 2005. © 2005 Society of Plastics Engineers.

The present study investigated the chemical properties and antityrosinase activities of SS (silk sericin) extracted from different Thai silk strains via various extraction methods. Different silk strains contain distinct SS with various amino acid compositions, which are significantly influenced by the extraction method used. Urea extraction of SS was the only method that provided clearly distinguishable bands and had the most significant impact on SS conformation as illustrated by FTIR (Fourier-transform infrared) spectra. The use of urea or either acidic or alkaline chemicals in the extraction process also influenced SS thermal behaviour. With regard to biological activity, SS extracted using urea exhibited the highest antityrosinase activity, whereas alkali-degraded SS showed no inhibition of mushroom tyrosinase. Pigments, primarily flavonoids and carotenoids from silk cocoons, were also found to enhance tyrosinase inhibition of SS.

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Biopolymer blends between collagen and chitosan have the potential to produce cell scaffolds with biocompatible properties. However, the relationship between the molecular weight of chitosan and its effect on physical and biological properties of collagen/chitosan scaffolds has not been elucidated yet. Porous scaffolds were fabricated by freeze-drying the solution of collagen and chitosan, followed by cross-linking by dehydrothermal treatment. Various types of scaffolds were prepared using chitosan with various molecular weights and blending ratios. Fourier transform infrared spectroscopy proved that collagen and chitosan scaffolds at all blending ratios contained mainly electrostatic interactions at the molecular level. The compressive modulus decreased with increasing the concentration of chitosan. Equilibrium swelling ratios of approximately 6-8, determined in phosphate-buffered saline at physiological pH (7.4), were found in case of collagen-dominated scaffolds. The lysozyme biodegradation test demonstrated that the presence of chitosan, especially the high-molecular-weight species, could significantly prolong the biodegradation of collagen/chitosan scaffolds. In vitro culture of L929 mouse connective tissue fibroblast evidenced that low-molecular-weight chitosan was more effective to promote and accelerate cell proliferation, particularly for scaffolds containing 30 wt% chitosan. The results elucidated that the blends of collagen with low-molecular-weight chitosan have a high potential to be applied as new materials for skin-tissue engineering.

In this work, a new method for producing acellular dermis (ADM), a natural scaffold used for dermal replacement, from porcine skin was developed. Fresh porcine skin from local slaughterhouse was dehaired by sodium sulphide following by epidermis removal using glycerol. After fat removal by chloroform/methanol (2/1 v/v) solvent, cellular components were removed using enzymatic treatment incorporated with a periodic pressurized technique. The effects of enzyme type (trypsin and dispase II) and periodic pressurized conditions on the efficiency of cell removal were investigated. When periodic pressure was applied, enzymatic treatment time could be shorten since the enzyme solution was able to penetrate into tight dermis. As a result, cells could be easily removed from porcine skin as noticed quantitatively by DNA assay and qualitatively by H&E staining. When enzyme refreshment was introduced into the decellularized process, the percentage of cell removal was further enhanced. This ensured that no inhibitions effect from the removed cells on enzyme-substrate interaction. Moreover, short-time enzymatic treatment with periodic pressurized technique could prevent the disruption of dermal structure, as observed by SEM. Dispase II can be used to remove cell better than trypsin in the periodic pressurized technique. However, in vivo study indicated that numerous fibroblast from the host tissue infiltrated into ADM prepared using both enzymes. Neo-collagen and neo-capillaries were produced in both implanted ADMs. The result elucidated that the use of periodic pressurized technique with enzymatic treatment has a high potential to be a new method to produce ADM for skin tissue engineering.