Cell adhesion and tissue response to hydroxyapatite nanocrystal-coated poly(L-lactic acid) fabric

Yanagida H, Okada M, Masuda M, Ueki M, Narama I, Kitao S, Koyama Y, Furuzono T, Takakuda K.
Department of Bioengineering, Advanced Medical Engineering Center, National Cardiovascular Center Research Institute, 5-7-1 Fujishirodai, Suita, Osaka , Japan.

Cell adhesion and tissue response to poly(l-lactic acid) (PLLA) fabric coated with nanosized hydroxyapatite (HAp) crystals were studied. The HAp nanocrystals were prepared by the wet chemical process followed by calcination at 800 degrees C with an anti-sintering agent to prevent calcination-induced sintering.

After the PLLA fabric was hydrolyzed with an alkaline aqueous solution, the HAp nanocrystals were coated via ionic interaction between the calcium ions on the HAp and the carboxyl groups on the alkali-treated PLLA. The PLLA surface uniformly coated with the HAp nanocrystals was observed by scanning electron microscope. The ionic interaction between the HAp and the PLLA was estimated by FT-IR. Improved cell adhesion to the HAp nanocrystal-coated surface was demonstrated by in vitro testing using a mouse fibroblast cell line L929.

Furthermore, reduced inflammatory response to the HAp nanocrystal-coated PLLA fabric (as compared with a non-treated one) was confirmed by a subcutaneous implantation test with rats. Thus the HAp nanocrystal-coated PLLA developed has possible efficacy as an implant material in the fields of general and orthopedic surgery, and as a cell scaffold in tissue engineering

Stabilization of enzyme activity during the esterification of lactic acid in hydrophobic ethers and ketones as reaction media that are miscible with..

Lipase-catalyzed esterification of lactic acid has thus far achieved only limited success due to high acidity and polarity of lactic acid: acid inactivation of enzymes, and immiscibility of lactic acid with hydrophobic organic solvents that are commonly used for non-aqueous enzyme reactions. Herein, we investigated enzymatic esterification of lactic acid with ethanol by using hydrophobic ethers and ketones as reaction media. Both of the solvents are miscible with lactic acid, and have the basicity to suppress the acid inactivation of enzymes, as well as polar solvents. Nevertheless, these solvents would be less harmful to enzymes rather than polar solvents because of their high hydrophobicity. Using the ethers and ketones, ethyl lactate was successfully synthesized enzymatically even at higher lactic acid concentrations, and the enzyme activity was effectively stabilized even in repeated batch-wise reactions (2.0 M lactic acid, 4 weeks). This effect of some ethers and ketone to stabilize the enzyme was significantly higher than that of polar solvents in the presence of polar alcohols, the other substrate. In addition, more various kinds of lipase could esterify 1.0 M lactic acid, in the hydrophobic ether and ketone rather than those in hydrophobic solvents, polar solvents, and a solvent-free system.

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