An aqueous solution containing a water miscible organic solvent, polyethylene glycol and heparine, is used to modify the tissue reactivity of an autologous tissue freshly obtained from a host mammal and to render the tissue temporarily more rigid than in its native state, and better suited for shaping, molding, handling and cutting prior to implantation into the host patient. The implant is highly resistant or immune to thickening, contraction and reduced fibrin deposition after it is implanted and exposed to the bloodstream of the host.