Consistent with the present invention, tissue 
adhesive compositions and an associated 
laser exposure system are provided for bonding or sealing biological tissues. The compositions are comprised of chemically derivatized soluble collagen which is formulated to concentrations 
ranging from 300 mg / ml (30%) to 800 mg / ml (80%) collagen 
protein. In particular, 
Type I collagen, for example, is first prepared by extraction from bovine or porcine hide and purified. The collagen preparations are then chemically derivatized with sulfhydryl reagents to improve 
cohesive strength and with secondary derivatizing agents, such as carboxyl groups, to improve the 
adhesive strength of the solder to the tissue. The compositions are then formed into viscous solutions, gels or 
solid films, which when exposed to energy generated from an 
infrared laser, for example, undergo thermally induced phase transitions. 
Solid or semi-
solid protein compositions become less viscous enabling the 
high concentration protein to penetrate the interstices of treated 
biological tissue or to fill voids in tissue. As 
thermal energy is released into the surrounding environment, the protein compositions again become 
solid or semi-solid, adhering to the treated tissue or 
tissue space.