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Blood compatibility of a novel elastic gelatin gel (e-gel) from salmon collagen was evaluated. After a 10-min incubation of the e-gel with rat whole blood, there was a macroscopically small thrombus formation on the e-gel. Microscopic observation revealed that few platelets had adhered to the e-gel. Furthermore, the platelet adhesion rate was markedly lower on the e-gel compared to collagen-coated and fibrinogen-coated surfaces. Comparable results were obtained with re-crosslinked e-gel. In conclusion, the e-gel demonstrated good blood compatibility.

With a view to reducing the thrombogenic potential of artificial blood-contact devices and natural tissues, we developed a novel aqueous antithrombogenic coating material, comprising a heparin bioconjugate that incorporated a thermoresponsive cationic polymer as a surfactant. The polymer was prepared by the sequential steps of initiator-transfer agent-terminator (iniferter)-based living radical photopolymerization of N-[3-(dimethylamino)propyl]acrylamide, followed by the polymerization of N-isopropylacrylamide from tetra(N,N-diethyldithiocarbamylmethyl)benzene as a multifunctional iniferter. The polymer obtained possessed four branched chains, each consisting of a cationic PDMAPAAm block (Mn: ca. 3000 g.mol(-1)) forming an inner domain for heparin binding and a thermoresponsive PNIPAM block (Mn: ca. 6000 g.mol(-1)) forming an outer domain for surface fixation; bioconjugation of the polymer with heparin occurred immediately upon simple mixing in an aqueous medium. Because the lower critical solution temperature of the heparin bioconjugate was approximately 35 degrees C, it could be coated from an aqueous solution at room temperature. The excellent adsorptivity and high durability of the coating below 37 degrees C was demonstrated on several generally used polymers by wettability measurement and surface chemical compositional analysis, and on collagen sheets and rat skin tissue by heparin staining. Blood coagulation was significantly prevented on the heparin bioconjugate-coated surfaces. The thermoresponsive bioconjugate developed therefore appeared to satisfy the initial requirements for a biocompatible aqueous coating material.

A novel non-viral gene transfection method in which DNA complexes were kept in contact with a deposition surface (deposition transfection) was developed. We designed a novel aqueous thermoresponsive adsorbent material for DNA deposition, which was a star-shaped copolymer with 4-branched chains. Each chain is comprised of a cationic poly(N,N-dimethylaminopropyl acrylamide) (PDMAPAAm) block (Mn: ca. 3000 g center dot mol(-1)), which formed an inner domain for DNA binding and a thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) block (Mn: ca. 6000 g center dot mol(-1)), which formed an outer domain for surface adsorption. Complex formation between the copolymer and the luciferase-encoding plasmid DNA occurred immediately upon simple mixing in an aqueous medium; polyplexes approximately 100 nm in size were formed. Because the lower critical solution temperature of the polyplexes was approximately 35 degrees C, they could deposit on the substrate by precipitation from an aqueous solution upon warming, which was confirmed by quartz crystal microbalance (QCM) method and water contact angle measurement. When COS-I cells were cultured on the polyplex-deposited substrate in a culture medium, the luciferase activity observed was higher than that observed on a DNA-coated substrate with or without the cationic polymer before and after complete adhesion and by conventional solution transfection using the polyplexes. The activity was enhanced with an increase in the charge ratio (surfactant/pDNA) with permissible cellular cytotoxicity. (c) 2007 Elsevier B.V. All rights reserved.

Collagen-based biomaterials have been widely used in medical applications, because of its many advantages, including low antigenicity, abundant availability, biodegradability, and biocompatibility [1]. Collagen represents the major structural protein, accounting for nearly 30% of all vertebrate body protein. The collagen molecule comprises three polypeptide chains (α-chains) which form a unique triple-helical structure (Fig. 1) [2]. Each of the three chains has the repeating structure glycine–X–Y, where X and Y are frequently the imino acids proline and hydroxyproline (Fig. 1b). The collagen molecules self-aggregate through fibrillogenesis into microfibrils forming extracellular matrix (ECM) in the body [3-5]. The fibrils provide the major biomechanical matrix for cell growth (Fig. 1a), allowing the shape of tissues to be defined and maintained. The main application of collagen for biomaterials is as a scaffold for tissue engineering and a carrier for drug delivery [2, 6-9]. Many different forms of collagen biomaterials, such as film [10, 11], gel [12-17], sponge [18-20], micro/nano-particle [21, 22], and fiber [23], have been fabricated and used in practice. However, most collagen biomaterials become brittle and fail under quite low strains, which limit their application to biomedical engineering fields that need larger mechanical properties, especially elasticity [16]. Recently, we reported a novel crosslinking method of improving the mechanical properties and thermal stability of collagen [24]. The method mimics actual biological events to form collagen matrix in the body; monomeric collagens extruded from cells into extracellular environment initially form microfibrillar aggregates, then lysyl oxidase crosslinking during their assembly to form fibrils (Fig. 1). The in vitro crosslinking during collagen fibrillogenesis, namely “bio-inspired crosslinking”, creates a crosslinked collagen fibrillar gel with high mechanical properties at certain crosslinking agent concentrations [25, 26]. Fibril formation involves the aggregation and alignment of collagen molecules, and helps increase the collagen’s thermal stability. The introduction of crosslinking during fibril formation further increases the thermal stability of collagen. The synergistic effects of crosslinking and fibril formation are found to enable an increase in the thermal stability of