HAp/Col Self-Setting Bone Paste
The HAp/Col self-setting bone paste has better formability than the HAp/Col porous bodies, and we are continuing our researches on developing the HAp/Col to be used in minimally invasive surgery and 3D printing.
Currently, approximately 0.0043 to 0.080% silane coupling agent by mass was contained in the HAp/Col paste, and hardened it by forming a hydrogel consisting of HAp/Col and the silane coupling agent.
Although the strength is not very high, even when the HAp/Col pastes immersed in phosphate buffered saline immediately after mixing the HAp/Col powder and silane coupling agent aqueous solution (before hardening), the wash-out ratios were less than 1% under almost all conditions. Even at the highest powder-to-liquid (P/L) ratio of 1.5 and a silane coupling agent aqueous solution concentration of 10 vol% (approximately 0.0043% by mass of silane coupling agent relative to the entire paste), wash-out ratio was at around 1.3%. Furthermore, all of these pastes hardened in around 30 minutes.
In addition, the pastes filled in syringes were easily pushed out through an 18G needle (inner diameter 0.94 mm) at a P/L ratio of 0.33, and from the tip of the syringe (inner diameter 1.8 mm) at other P/L ratios. In other words, such kind of devices allows the HAp/Col paste to be used in minimally invasive surgery and 3D printing.
Resaerches on the HAp/Col self-setting paste is performed under collaboration with Lecturer Taira Sato and Professor Kanji Tsuru of Fukuoka Dental College, and Associate Professor Yuki Shirosaki of Kyushu Institute of Technology.
Our biggest concern was whether the silane coupling agent would be harmful to the body and/or interfere with the substitution of HAp/Col with bone.
Therefore, with the cooperation of Professors Aizawa and Nagashima of Meiji University, where Lecturer Sato was a Ph.D. candidate at the time, an animal test using pig was pefromed. Two types of the HAp/Col paste of a P/L ratio of 1.0, prepared with silane coupling agent aqueous solution at 1.0% and 10%, were directly injected into bone holes prepared in porcine tibia and were observed for three months.
The pigs were in good health during the observation period. Direct observation of the area where the paste had been injected at three months after injection revealed that the paste was no longer visible and had been replaced by bone. Furthermore, no signs of inflammation or other adverse effects were found in the surrounding area.
X-ray computer tomographic observation indicated that the areas where the paste was injected were indistinguishable from the original pig bones, as shown in the left images.
These results suggested that the HAp/Col paste is a material that is substituted with new bone within about three months without any adverse effects from the silane coupling agent used.