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We fabricated a transparent nonfibrillar collagen gel using gamma irradiation (5 kGy) and cultured rat mesenchymal stem cells (MSCs) on both the gamma-irradiated collagen gel and on unirradiated fibrillar collagen gel. Cells attached well and proliferated with high viability on the surface of both gels. The cells cultured on the gamma-irradiated nonfibrillar gel had a unique elongated shape and adhered to each other in culture. After 21 days of culture in dexamethasone-containing culture medium, the contents of bone-specific osteocalcin and calcium on the gamma-irradiated nonfibrillar gel were 1.4 and 1.9 times higher than those on fibrillar collagen gel, respectively. These data show that osteogenic differentiation of MSCs was promoted more efficiently on the gamma-cross-linked nonfibrillar gel than on the fibrillar gel and demonstrate the potential of the gamma-irradiated collagen gel for use in bone tissue engineering., (Copyright © 2014 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.)

Gelatin hydrogels cross-linked by y-ray irradiation using 60Co as gamma-ray source were prepared. As a model of controlled release of low-molecular-weight compounds, absorption and release of methylene blue, a water-soluble cationic dye, was investigated. Irradiated gelatin hydrogels did not redissolve at temperatures over 40 degrees C, while unirradiated gels were thermoplastic and reversibly changed the stage between gel and sol. Measurement of both the wet weight after swelling in distilled water and dry weight after freeze-drying showed that the higher-dose irradiation gave stiffer and more compact gels with the lower specific water content, irrespective of the absorbed dose rate. The time-course of absorption and release of methylene blue in aqueous solution was measured. Since absorption of dye into gelatin gels was much affected by liquid phase pH, amount of absorption was higher in pH above an IEP of gelatins. Moreover, the absorption and release of methylene blue with Type-B gelatin were higher than with Type-A gelatin, respectively. Therefore, absorption and release of the dye depend on the electrostatic interaction between the dye molecule and gelatin.

We made a new type of collagen gel by γ-ray irradiation of an acidic solution of type-I collagen, and performed comparative studies on a conventional gel and the new type of gel. The neutral gel, a conventional 0.3% (w/v) collagen gel, was formed at neutral pH and then irradiated by γ-rays. The acidic gel, a 0.3% (w/v) collagen gel, was formed directly from the acidic solution of collagen by γ-ray irradiation. Both types of gel were prepared, swollen in water and then dried for the measurement of specific water content. The neutral gel showed a relatively high specific water content and shrunk moderately, depending on the dose, while the acidic gel showed lower specific water content and shrunk clearly by γ-ray irradiation. A three-dimensional tangled network of microfibrils was clearly observed in the neutral gels by scanning electron microscopy, but not in the acidic gels. From these results, we concluded that the acidic gel was quite different from a conventional collagen gel. Sodium dodecylsulfate-polyacrylamide gel electrophoresis showed that the α 1 subunit and α 2 subunit of the collagen molecule were cross-linked. The triple-helical structure of collagen was only partially perturbed, but not denatured completely, because the circular dichroism spectrum of the collagen solution irradiated at 1.3 kGy was similar to that of native collagen solution. Amino-acid analysis revealed that tyrosine, phenylalanine and histidine decreased by irradiation in the neutral gel. In the case of the acidic gel, these three amino acids and methionine decreased. We considered that these amino acids were cross-linking points between the collagen subunits during the γ-ray irradiation. [ABSTRACT FROM AUTHOR]