there is no such thing as real crosslinking of calcium phosphate and orgamic molecules because HAP is mostly ionic and organics are not! so crosslinking means something like cross-polymerization of organics....however HAP can and does adsorb molecules. One "exception" is HAP substituted with silicon, because in this case the Si group car react forming substituted molecules (grafted) . for example trimethoxysilane-epoxy substituted functions can react with aminogroups of peptides or polymers, and result in peptides or polymers grafted on HAP thanks to the presence of the Silicones incorporated into the HAP structures. However I have no idea about grafing anything on TCP