Experimental Study of Bone Formation Ability with the Periosteum on Rat Calvaria

Carbonate apatite versus β-tricalcium phosphate for rat vertical bone augmentation: A comparison of bioresorbable bone substitutes using polytetrafluoroethylene tubes

This study radiologically and histologically compared two bioresorbable bone substitutes with different compositions carbonate apatite (Cytrans® Granules; CGs) and β-tricalcium phosphate (β-TCP) for vertical bone augmentation on a rat skull using a polytetrafluoroethylene (PTFE) tubes. This PTFE tube was placed at the center of the skull, fixed with Super Bond, and augmented with CGs or β-TCP granules. Specimens with surrounding tissue were harvested at 4, 8, and 12 weeks postoperatively, and radiological and histological evaluations were performed. The bone volume to total volume ratio (BV/TV) of the β-TCP-implanted group was markedly higher than that of the CG-implanted group at 4 and 12 weeks postoperatively. Compared to CGs, β-TCP exhibited the ability to form blood vessels into the graft material for a short period after transplantation, as well as an elevated production of collagen into β-TCP granules during the bone formation process.

Biodegradable polymerized simvastatin stimulates bone formation

Previous research from our labs demonstrated the synthesis of polymerized simvastatin by ring-opening polymerization and slow degradation with controlled release of simvastatin in vitro. The objective of the present study was to evaluate the degradation and intramembranous bone-forming potential of simvastatin-containing polyprodrugs in vivo using a rat calvarial onlay model. Poly(ethylene glycol)-block-poly(simvastatin) and poly(ethylene glycol)-block-poly(simvastatin)-ran-poly(glycolide) were compared with simvastatin conventionally encapsulated in poly(lactic-co-glycolic acid) (PLGA) and pure PLGA. The rate of degradation was higher for PLGA with and without simvastatin relative to the simvastatin polyprodrugs. Significant new bone growth at the circumference of poly(ethylene glycol)-block-poly(simvastatin) disks was observed beginning at 4 weeks, whereas severe bone resorption (4 weeks) and bone loss (8 weeks) were observed for PLGA loaded with simvastatin. No significant systemic effects were observed for serum total cholesterol and body weight. Increased expression of osteogenic (BMP-2, Runx2, and ALP), angiogenic (VEGF), and inflammatory cytokines (IL-6 and NF-ĸB) genes was seen with all polymers at the end of 8 weeks. Poly(ethylene glycol)-block-poly(simvastatin), with slow degradation and drug release, controlled inflammation, and significant osteogenic effect, is a candidate for use in bone regeneration applications. STATEMENT OF SIGNIFICANCE: Traditional drug delivery systems, e.g., drug encapsulated in poly(lactic-co-glycolic acid) (PLGA), are typically passive and have limited drug payload. As an alternative, we polymerized the drug simvastatin, which has multiple physiological effects, into macromolecules ("polysimvastatin") via ring-opening polymerization. We previously demonstrated that the rate of degradation and drug (simvastatin) release can be adjusted by copolymerizing it with other monomers. The present results demonstrate significant new bone growth around polysimvastatin, whereas severe bone loss occurred for PLGA loaded with simvastatin. This degradable biomaterial with biofunctionality integrated into the polymeric backbone is a useful candidate for bone regeneration applications.

Periosteal distraction osteogenesis versus immediate periosteal elevation in a rat model: Histological and micro-CT analysis

PURPOSE

The aim of the present study was to compare periosteal distraction osteogenesis (PDO) to immediate periosteal elevation (IPE) in terms of de novo bone formation.

MATERIAL AND METHODS

Animals of PDO Group were subjected to a 7-day latency period and a 10-day distraction period. Distraction device in IPE Group were activated for 1 mm at placement. Both groups of animals were euthanized at 17, 31 and 45-day following surgery and the samples analyzed histologically and by micro-CT. Total gap region (TG) was divided in two subregions, less than 0.5 mm (LG) and over 0.5 mm of the gap height (HG).

RESULTS

Bone formation in PDO Group was observed in the distal region of the distraction gap, whereas in IPE Group proximally and distally from the distraction gap. Bone volume increased in both groups in LG, HG and TG (p < 0.001), while bone mineral density only in HG (p = 0.001). More new bone was observed in PDO than in IPE Group in HG (p = 0.017) and in TG (p < 0.001), without differences found in bone mineral density.

CONCLUSIONS

The function of immediately elevated periosteum is limited to the distance to the underlying bone. PDO may be successfully applied to maintain the osteogenic capacity of elevated periosteum.

Relative contributions of osteogenic tissues to new bone formation in periosteal distraction osteogenesis: histological and histomorphometrical evaluation in a rat calvaria

BACKGROUND

The relative contributions of different, potential factors to new bone formation in periosteal distraction osteogenesis are unknown.

PURPOSE

The aim of the present study was to assess the influence of original bone and periosteum on bone formation during periosteal distraction osteogenesis in a rat calvarial model by means of histology and histomorphometry.

METHODS

A total of 48 rats were used for the experiment. The contribution of the periosteum was assessed by either intact or incised periosteum or an occlusive versus a perforated distraction plate. The cortical bone was either left intact or perforated. Animals were divided in eight experimental groups considering the three possible treatment modalities. All animals were subjected to a 7-day latency period, a 10-day distraction period and a 7-day consolidation period. The newly formed bone was analyzed histologically and histomorphometrically.

RESULTS

New, mainly woven bone was found in all groups. Differences in the maximum height of new bone were observed and depended on location. Under the distraction plate, statistically significant differences in maximum bone height were found between the group with perforations in both cortical bone and distraction plate and the group without such perforations.

CONCLUSIONS

If the marrow cavities were not opened, the contribution to new bone formation was dominant from the periosteum. If the bone perforations opened the marrow cavities, a significant contribution to new bone formation originated from the native bone.