Immobilization of Chinese herbal medicine onto the surface-modified calcium hydrogenphosphate

To accelerate the healing of bone defects or for healing to take place, it is often necessary to fill them with suitable substance. Various artificial materials defects have been developed. Among these, calcium phosphates and bioactive glass have been proven to be biocompatibile and bioactive materials that can chemically bond with bone, and have been successfully used clinically for repair of bone defects and augmentation of osseous tissue. However, those bioceramics have only the property of osteoconduction without any osteoinduction. Many ligands have been physicochemically absorbed onto substrates to enhance cell-substrate interactions. Although widely developed, they are still limited to use in long-term implantation because of their half-life period. Thus, some interfacial modification will be required for enhancing the efficacy of the delivery system. These models involve the immobilization of biologically active ligands of natural and synthetic origin onto various substrates to produce an interface with stronger chemical bond between ligand and substrate. The advantage of covalently immobilizing a ligand is that a chemical bond is present to prevent ligand or medicine from desorption. In our study, a two-step chemical immobilization was performed to surface-modified calcium hydrogenphosphate powders. The first was to modify the surface of calcium hydrogen-phosphate (CHP) with a coupling agent of hexanmethylene diisocyanate (HMDI). CHP surface modified by HMDI is abbreviated as MCHP. The linkage between CHP and HMDI will be characterized by FTIR. The second step was to immobilize chemically Gusuibu onto MCHP. Moreover, the sorption and desorption of Gusuibu was evaluated and quantitatively analyzed by spectrophotometer and HPLC. Bioceramic CHP was surface-modified by a two-step chemical immobilization. First, the surface of calcium hydrogen-phosphate (CHP) was successfully modified with coupling agent of hexanmethylene diisocyanate (HMDI). The first step was also activated the surface of CHP to induce primary amine terminator. The reaction of this functional group with Gusuibu was the second step. We confirmed simultaneously that Gusuibu could be immobilized chemically onto the surface of MCHP. Although some immobilized Gusuibu was also released rapidly at the first 12h, the degree of the released Gusuibu was lower than both by Gusuibu-adsorbing MCHP and Gusuibu-adsorbing CHP.