Evaluation of Bone Regeneration with a Collagen Model Polypeptides/Alpha-Tricalcium Phosphate Sponge
1, Statement of the Problem
In oral and maxillofacial surgery, bone defects commonly occur due to infections, trauma, tumors, and cysts, as well as clefts of the alveolar bone and palate. Autologous bone is widely regarded as the gold standard graft material. However, a limited amount of autologous bone can be harvested from an individual, and the procedure is relatively invasive. Therefore, scaffold materials are required, which should be bioabsorbable and able to be ultimately replaced by autologous tissue.
Tanihara et al. previously reported the chemical synthesis of collagen model polypeptidesconsisting of a proline-hydroxyproline-glycine (poly(PHG)) sequence thatforms a triple-helical structure. In this study, we used a dehydrothermal cross-linking method to construct a poly(PHG) and porous alpha-tricalcium phosphate(alpha-TCP) sponge as a scaffold for the regeneration of alveolar bone defects. The effects of the poly(PHG)/alpha-TCP scaffold on bone regeneration were evaluated in surgically induced canine tibia defects.
2, Material and method
Alpha-TCP particles were mixed with the aqueous poly(PHG) solution. The mixture was then poured into plastic molds, and all samples were immediately frozen to -80°C and freeze-dried for 24 hours. The freeze-dried poly(PHG)/alpha-TCP constructs resembled sponge-like structures, and were subsequently cross-linked in vacuo at 140°C for 10 hours. Identical defects were made under general anesthesia and infiltration anesthesia. The defects were randomly filled with one of the two treatments as follows: the experimental group (animals with a transplanted mixture of poly(PHG) and alpha-TCP) and the control group (animals transplanted with poly(PHG) alone). Assessments were made at three different time periods (2, 4, and 8 weeks) after surgery.
3, Method of date analysis
Poly(PHG)/alpha-TCP Sponges were characterized by X-ray diffraction and scanning electron microscopy (SEM). The tibias were harvested for microradiographic examination using a micro-computed tomography (CT) apparatus. In the 3D analysis, the total volume and bone volume were measured using the software based on the obtained CT values. The tibias were sectioned in the coronal plane and stained with hematoxylin and eosin.
4, Results
SEM image shows that the poly(PHG)/alpha-TCP sponges were composed of alpha-TCP particles and a 3D porous structure with an anatomizing network. The diffraction peaks of poly(PHG)/alpha-TCP were reduced compared to those of the original alpha-TCP particles in XRD, however, corresponded with alpha-TCP data registered. At 2 and 4 weeks, the volume density of new bone was higher in the poly(PHG)/alpha-TCP group than poly(PHG) alone group (p < 0.05); however, there was no difference at 8 weeks (p > 0.05). Histological evaluation at 4 weeks after implantation revealed that the poly(PHG) had degraded and newly formed bone was present on the surface of the alpha-TCP particles. At 8 weeks, continuous cortical bone formation with a Haversian structure covered the top of the bone defects and no histological marker indicative of an inflammatory response was observed in either group.
5, Conclusions
This study demonstrated that a sponge created using porous alpha-TCP particles and poly(PHG), which is a chemically synthesized collagen model polypeptide, is sufficiently adaptable for treating bone defects. Furthermore, the biodegradable poly(PHG)/alpha-TCP sponge was replaced by newly formed bone without any adverse responses. Therefore, this newly developed sponge composite may be useful for bone tissue engineering.
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