Wei Lin

Modification of collagen with a natural cross-linker, procyanidin

We have investigated the modification of collagen with a natural plant polyphenol, procyanidin under acidic conditions. Fourier transform infrared spectroscopy (FTIR) and Atomic force microscopy (AFM) studies demonstrate that the hydrogen bond interactions between collagen and procyanidin does not destroy the triple helix conformation of collagen, and the fibril aggregation occurs because of the cross-linking with procyanidin. The water contact angle (WCA) tests indicate that the hydrophobicity of the procyanidin modified collagen films can be improved. Whereas, the water vapor permeability (WVP) of the films decrease with the increasing procyanidin content due to the formation of denser structure. Moreover, differential scanning calorimetry (DSC) and thermogravimetric (TG) measurements reveal that the collagen/procyanidin films have improved thermal stability in comparison with pure collagen. The present study reveals that procyanidin stabilizes collagen as a cross-linker and preserves its triple helical structure.

Gelatin Particle-Stabilized High Internal Phase Emulsions as Nutraceutical Containers

In this paper, we report for the first time the use of a well-dispersed gelatin particle as a representative of natural and biocompatible materials to be an effective particle stabilizer for high internal phase emulsion (HIPE) formulation. Fairly monodispersed gelatin particles (∼200 nm) were synthesized through a two-step desolvation method and characterized by dynamic light scattering, ζ-potential measurements, scanning electron microscopy, and atomic force microscopy. Those protein latexes were then used as sole emulsifiers to fabricate stable oil-in-water Pickering HIPEs at different concentrations, pH conditions, and homogenization times. Most of the gelatin particles were irreversibly adsorbed at the oil-water interface to hinder droplet coalescence, such that Pickering HIPEs can be formed by a small amount of gelatin particles (as low as 0.5 wt % in the water phase) at pH far away from the isoelectric point of the gelatin particles. In addition, increasing homogenization time led to narrow size distribution of droplets, and high particle concentration resulted in more solidlike Pickering HIPEs. In vitro controlled-release experiments revealed that the release of the encapsulated β-carotene can be tuned by manipulating the concentration of gelatin particles in the formulation, suggesting that the stable and narrow-size-distributed gelatin-stabilized HIPEs had potential in functional food and pharmaceutical applications.

Effects of Cr3+ on the Structure of Collagen Fiber

We have investigated the effects of Cr3+ on the hierarchical structure of pigskin collagen fibers by use of scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), wide-angle X-ray diffraction (WAXD), confocal laser micro-Raman spectroscopy (CLRS), and circular dichroism (CD). Our results demonstrate that the introduction of Cr3+ leads to the formation of a cluster of 20-40 nm between collagen fibrils, while the unique axial periodic structure (D periodicity) of the fibrils does not change. As the Cr3+ concentration increases, the order of intermolecular lateral packing, crystallite structure within helical chains, and N and C telopeptide regions decrease. The present study reveals that Cr3+ only cross-links with collagen but does not disrupt its triple helical structure.

A Novel Approach for Synthesis of Zwitterionic Polyurethane Coating with Protein Resistance

We have developed a novel approach to introduce zwitterions into polyurethane for the preparation of antibiofouling coating. First, the thiol-ene click reaction between 2-(dimethylamino)ethyl methacrylate (DMAEMA) and 3-mercapto-1,2-propanediol (TPG) is used to synthesize dihydroxy-terminated DMAEMA (DMA(OH)2) under UV catalysis. The product has been proved by gel permeation chromatography (GPC), Fourier transform infrared spectrum (FT-IR), proton nuclear magnetic resonance ((1)H NMR), and high resolution mass spectrometry (HRMS). DMA(OH)2 is then incorporated into polyurethane as side groups by polyaddition with diisocyanate and further reacts with 1,3-propane sultone to obtain the zwitterionic polyurethanes. The presence of sulfobetaine zwitterions side groups has been demonstrated by FT-IR and X-ray photoelectron spectroscopy (XPS). Thermal analysis indicates that the thermal stability is decreased with the increasing content of zwitterionions. The antibiofouling property of polyurethanes has been investigated by the measurement of adsorption of fibrinogen, bovine serum albumin (BSA), and lysozyme on the polyurethanes surface using quartz crystal microbalance with dissipation (QCM-D). The results show that the polyurethane coatings exhibit effective nonspecific protein resistance at higher content of zwitterionic side groups.

Collagen cryogel cross-linked by naturally derived dialdehyde carboxymethyl cellulose.

We present the use of a natural derivative, dialdehyde carboxymethyl cellulose (DCMC) as the cross-linker for the preparation of spongy collagen cryogels by freezing-thawing method. The DCMC has been characterized by laser light scattering (LLS), showing the molecular weight of 2.38 × 10(5)g/mol. FT-IR studies demonstrate that the cross-linking reaction and the cryogenic treatment do not destroy the triple helix of collagen. SEM images indicate that the cryogel has a heterophase structure with interconnecting macropores. DSC measurements reveal that the incorporation of a very small amount of DCMC can significantly improve the thermal stability of collagen. Moreover, the cryogels exhibit fast swelling rate, and their equilibrium swelling ratio is related to DCMC content and pH-dependent. The in vitro blood-compatibility tests prove that the introduction of DCMC does not cause the reducing performance in hemolysis and blood clotting compared with pure collagen. Hence, the low-cost and non-toxic nature of DCMC confers the cryogel great potential in tissue engineering and other biomedical applications.

Gelatin Effects on the Physicochemical and Hemocompatible Properties of Gelatin/PAAm/Laponite Nanocomposite Hydrogels

In recent years, inorganic nanoparticles such as Laponite have frequently been incorporated into polymer matrixes to obtain nanocomposite hydrogels with hierarchical structures, ultrastrong tensibilities, and high transparencies. Despite their unique physical and chemical properties, only a few reports have evaluated Laponite-based nanocomposite hydrogels for biomedical applications. This article presents the synthesis and characterization of a novel, hemocompatible nanocomposite hydrogels by in situ polymerization of acrylamide (AAm) in a mixed suspension containing Laponite and gelatin. The compatibility, structure, thermal stability, and mechanical properties of the resulting NC gels with varied gel compositions were investigated. Our results show that the prepared nanocomposite hydrogels exhibit good thermal stability and mechanical properties. The introduction of a biocompatible polymer, gelatin, into the polymer matrix did not change the transparency and homogeneity of the resulting nanocomposite hydrogels, but it significantly decreased the hydrogels pH-responsive properties. More importantly, gelatins that were incorporated into the PAAm network resisted nonspecific protein adsorption, improved the degree of hemolysis, and eventually prolonged the clotting time, indicating that the in vitro hemocompatibility of the resulting nanocomposite hydrogels had been substantially enhanced. Therefore, these nanocomposite hydrogels provide opportunities for potential use in various biomedical applications.

Ring‐opening polymerization of genipin and its long‐range crosslinking effect on collagen hydrogel

Polymeric genipin macromers, prepared by ring-opening polymerization at various pH values, are used as crosslinking agents to fix collagen hydrogels. The results indicate that as the dark color of polymeric genipin itself and the networks formed by long-range intermolecular crosslinking, the genipin-fixed collagen hydrogels displace darker color. The polymeric genipin prepared at higher pH value needs longer time to fully crosslink with collagen molecules. Moreover, polymerization of genipin reduces the yield of genipin-fixed collagen hydrogels due to low extent of crosslinking. Specially, the microscope photographs present the porous networks structures of genipin-fixed collagen hydrogels. The pore size increases with the increase in polymerization degree of genipin. The data of FTIR indicate the likely transition of -NH(2) groups in collagen chains into C=N. Owning to much more number of hydrophilic groups and more porous networks, collagen hydrogels fixed by genipin with higher polymerization degree have higher water absorption capacity. The equilibrium swelling of genipin-fixed collagen hydrogels is pH-responsive, which show M type changes with the pH values. The results obtained in the study suggest that the polymeric genipin prepared at various pH values lead to significant influence to the crosslinking characteristics and properties of collagen hydrogels.

Novel hemocompatible nanocomposite hydrogels crosslinked with methacrylated gelatin

Methacrylated gelatin (MA-gelatin) is a gelatin derivative synthesized by the reaction with methacrylic anhydride; the degree of substitution (DS) of primary amines by methacrylamide groups in the gelatin is closely related to the dosage of methacrylic anhydride. In this work, MA-gelatin has been developed as a macromolecular crosslinker to prepare novel nanocomposite hydrogels (NC gels) based on polyacrylamide (PAAm) and LAPONITE® nanoclay. Compared with unmodified gelatin, MA-gelatin improves the stability of the LAPONITE® suspension in the pre-gel system. FTIR results confirm the success of gelatin modification, in agreement with the 1H NMR result, and the copolymerization of MA-gelatin and acrylamide monomers in the NC gel network. The increasing DS of MA-gelatin thus reduces the equilibrium swelling ratio (ESR) and pore sizes, and enhances the mechanical properties of the NC gels, due to the macromolecular crosslinking effect. Unlike the small molecular crosslinker N,N′-methylenebisacrylamide (BIS), MA-gelatin shows a stronger influence on the swelling behaviours and mechanical properties of NC gels. Moreover, the MA-gelatin crosslinked NC gels exhibit decreased bovine serum albumin (BSA) adsorption, prolonged blood-clotting time and nonhemolytic nature, indicating the improved antithrombogenicity. The results show that MA-gelatin can be a hemocompatible macromolecular crosslinker for the fabrication of biomedical materials.

Tailor-made zwitterionic polyurethane coatings: microstructure, mechanical property and their antimicrobial performance

Antimicrobial coating is of great important in leather finishing. Herein, we report a newly synthesized polyurethane with zwitterionic sulfobetaine side groups and evaluate their performance in the antifouling leather coatings. The microstructure of the synthesized zwitterionic polyurethane (iNPU) films has been examined by Fourier transform infrared (FTIR), X-ray diffraction (XRD) and atomic force microscopy (AFM) in order to understand how it influences the mechanical and surface properties. Our results show that introduction of zwitterionic groups into polyurethane can markedly increase the degree of micro-phase separation between the hard and soft segments of the PU chains since the incorporated zwitterionic group leads to more hydrogen bonding and polar interactions, making the hard components to be more thermodynamically incompatible with the soft segments. As the content of the incorporated zwitterionic content increases, the ordered structure in PU chains is reduced, and the micro-phase separation degree is increased. Therefore, the tensile strength and elongation at break of the iNPU films are significantly improved. Dynamic mechanical thermal analysis (DMTA) results further indicate that the Tg of the iNPU coatings decreases, and the deformability greatly increases at a higher content of zwitterionic group. Water contact angle (WCA) measurements reveal the improved surface wetting property due to the presence of zwitterionic group. The antibacterial testing shows that the iNPU coated leather surfaces exhibit reasonably good anti-mold adhesion performance, although the iNPU films do not show apparent contact-killing antibacterial property against E. coli and S. aureus. The present zwitterionic polyurethane is thus can be potentially used as antimicrobial adhesive leather coating materials.

Diffusion and Binding of Laponite Clay Nanoparticles into Collagen Fibers for the Formation of Leather Matrix

Understanding accessibilityxa0and interactions of clay nanoparticles with collagen fibers is an important fundamental issue for the conversion of collagen to leather matrix. In this study, we have investigated the diffusion and binding of Laponite into the collagen fiber network. Our results indicate that the diffusion behaviors of Laponite into the collagen exhibit the Langmuir adsorption, verifying its affinity for collagen. The introduction of Laponite leads to a shift in the isoelectric point of collagen from ∼6.8 to ∼4.5, indicating the ionic bonding between the positively charged amino groups of the collagen and negatively charged Laponite under the tanning conditions. Fluorescence microscopy, atomic force microscopy, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and wide-angle X-ray diffraction analyses reveal that Laponite nanoparticles can penetrate into collagen microstructure and evenly distributed onto collagen fibrils, not altering native D-periodic banding patterns of collagen fibrils. Attenuated total reflectance-Fourier transform infrared and Raman spectroscopy detections further demonstrate the presence of noncovalent interactions, namely, ionic and hydrogen bonding, between Laponite and collagen. These findings provide a theoretical basis for the use of Laponite as an emerging tanning agent in leather manufacture.