PURPOSE: To improve a biological compatibility and make hardly capsulate by forming a water containing layer made of water-soluble polymer materials on the outer surface of an artificial biological organ through the intermediary of a reactive functional group material.

CONSTITUTION: A material which is implanted in a living body by a long term may by merely coated over at least its outer surface of an artificial biological organism material adapted to made contact with a biological structure, with a water-soluble polymer material or the derivative thereof. The water-soluble polymer used for forming the cover layer is fixed onto the artificial biological organism material by ionic bond or covalent bond. Such a water-soluble polymer material is generally linear and has no cross-link, but has a hydrophilic group such as-OH,-CONH2,-COOH,-NH2,-COO-, SO3-,-NR3+ or the like. Accordingly, by ionic bond or covalent bond of the material with a reactive functional group surface of the artificial biological organism material, a water containing layer can be formed being carried on the artificial biological organism material.