Augmentation of bone tunnel healing in anterior cruciate ligament grafts: application of calcium phosphates and other materials.

Bone tunnel healing is an important consideration after anterior cruciate ligament (ACL) replacement surgery. Recently, a variety of materials have been proposed for improving this healing process, including autologous bone tissue, cells, artificial proteins, and calcium salts. Amongst these materials are calcium phosphates (CaPs), which are known for their biocompatibility and are widely commercially available. As with the majority of the materials investigated, CaPs have been shown to advance the healing of bone tunnel tissue in animal studies. Mechanical testing shows fixation strengths to be improved, particularly by the application of CaP-based cement in the bone tunnel. Significantly, CaP-based cements have been shown to produce improvements comparable to those induced by potentially more complex treatments such as biologics (including fibronectin and chitin) and cultured cells. Further investigation of CaP-based treatment in the bone tunnels during ACL replacement is therefore warranted in order to establish what improvements in healing and resulting clinical benefits may be achieved through its application.

Electrically active bioceramics: a review of interfacial responses.

Electrical potentials in mechanically loaded bone have been implicated as signals in the bone remodeling cycle. Recently, interest has grown in exploiting this phenomenon to develop electrically active ceramics for implantation in hard tissue which may induce improved biological responses. Both polarized hydroxyapatite (HA), whose surface charge is not dependent on loading, and piezoelectric ceramics, which produce electrical potentials under stress, have been studied in order to determine the possible benefits of using electrically active bioceramics as implant materials. The polarization of HA has a positive influence on interfacial responses to the ceramic. In vivo studies of polarized HA have shown polarized samples to induce improvements in bone ingrowth. The majority of piezoelectric ceramics proposed for implant use contain barium titanate (BaTiO(3)). In vivo and in vitro investigations have indicated that such ceramics are biocompatible and, under appropriate mechanical loading, induce improved bone formation around implants. The mechanism by which electrical activity influences biological responses is yet to be clearly defined, but is likely to result from preferential adsorption of proteins and ions onto the polarized surface. Further investigation is warranted into the use of electrically active ceramics as the indications are that they have benefits over existing implant materials.

Electrical characterization of hydroxyapatite-based bioceramics.

This paper studies the AC conductivity and permittivity of hydroxyapatite (HA)-based ceramics from 0.1 Hz-1 MHz at temperatures from room temperature to 1000 degrees C. HA-based ceramics were prepared either as dense ceramics or in porous form with interconnected porosity and were sintered in either air or water vapour. Samples were thermally cycled to examine the influence of water desorption on AC conductivity and permittivity. Surface-bound water was thought to contribute to conductivity for both dense and porous materials at temperatures below 200 degrees C. At temperatures below 700 degrees C the permittivity and AC conductivity of HA was also influenced by the degree of dehydration and thermal history. At higher temperatures (700-1000 degrees C), bulk ionic conduction was dominant and activation energies were of the order of approximately 2 eV, indicating that hydroxyl ions are responsible for conductivity.