Osteoconduction of bioceramics in normal and osteopenic rats: comparison between bioactive and bioinert ceramics

The effect of infliximab on bone healing in osteoporotic rats

Purpose:

The aim of this study was to evaluate the effect of the infliximab on autogenous-mediated bone regeneration and resorption of autogenous graft in the ovariectomised rat model.

Materials and methods:

Forty rats underwent ovariectomy and 6 weeks later the animals were randomly assigned to four groups. Critical size defects were created in each rat calvarium. In the control group (C), the flap was closed without any further action. In the only infliximab group (In), the flap was closed without any further action. After the operation, intravenous infliximab was injected. In the autogenous graft group (Ag), autogenous bone was applied in to the defect. In autogenous graft + infliximab group (Ag+In), autogenous graft was placed on the defect. After the operation, intravenous infliximab was injected. The animals were sacrificed at 4 weeks. Bone formation was assessed by micro-computed tomography (micro-CT) scans and stereological analysis.

Results:

The mean new bone volume was the greatest in Ag+In group (1.76 ± 0.20), followed by the Ag group (1.51 ± 0.05) (statistically significant difference at P <0.05). The lowest new bone was found in the control group (1.05 ± 0.09), however no difference was observed from the In group (1.14 ± 0.08) ( P >0.05). Besides there was a statistically significant difference between the Ag+In group (1.00 ± 0.05) and Ag group (0.74 ± 0.04) in terms of the graft volume ( P <0.05).

Conclusion:

This study, despite its limitations, showed that infliximab has a beneficial effect for prevent graft resorption and bone regeneration in osteoporotic rats.

The biomaterial-mediated healing of critical size bone defects in the ovariectomized rat

This study demonstrated an impaired biomaterial-mediated bone regeneration in a critical sized calvarial defect established within an ovariectomized rat model. Histological and microtomographic evidences were supported by an impaired osteoblastic gene expression and altered expression of estrogen receptors and adipogenic markers.

INTRODUCTION

This work aims to address the bone regeneration process in the ovariectomized rat model, by assessing a calvarial critical size defect implanted with a biocompatible bovine bone mineral graft.

METHODS

Animals were randomly divided into two groups: Ovx (bilateral ovariectomy) and Sham (control surgery). Following 8 weeks, all animals were submitted to a surgical bicortical craniotomy (5-mm circular critical size defect), which was filled with a biocompatible mineral graft. Animals were euthanized at 1, 3, and 6 months following graft implantation (n = 10), and results on the orthotopic bone regeneration process were blindly evaluated by radiographic, microtomographic, histological, histomorphometric, and gene expression techniques.

RESULTS

In the attained model, in both Sham and Ovx groups, the bone regenerative process was found to occur in a slow-paced manner. Likewise, a qualitative evaluation of the microtomographic and histological analysis, as well as quantitative data from histomorphometric indexes, revealed reduced bone regeneration in Ovx animals, at the assayed time points. Significant differences were attained at the 3 and 6 months. Gene expression analysis revealed a reduced expression of osteoblastic-related genes and an altered expression of estrogen receptors and adipogenic markers, within the regenerating bone of Ovx animals.

CONCLUSIONS

Due to the similarities between the osteoporotic animal model and the human condition of postmenopausal osteoporosis, it might be relevant to consider the potential clinical implication of the osteoporotic condition in the biomaterial-mediated bone tissue healing/regeneration process.

Bone ingrowth in zirconia and hydroxyapatite scaffolds with identical macroporosity

The role of the material composition, porosity and surface topography of scaffolds for promotion of osteogenesis and osseointegration is not fully understood. The aim of the present study was to evaluate the effects of material composition and surface topography on bone ingrowth and bone contact. Designed macroporous ceramic scaffolds of zirconia and hydroxyapatite were used. Using free form fabrication (FFF) techniques an identical macroporosity in both materials was achieved. The scaffolds were implanted in rabbit tibia (cortical bone) and femur (trabecular bone). After 6 weeks of implantation the tissue response was assessed with histology and histomorphometry. The results showed significantly more bone ingrowth and bone contact in the hydroxyapatite scaffolds compared to the zirconia scaffold. Surface topography had no significant effect on bone contact inside the macropores regardless of material. This was observed in both cortical and trabecular bone sites. The study suggests that the difference between hydroxyapatite and zirconia was due to a difference in material chemistry.

Practice of a testing bench to study the effects of cyclic stretching on osteoblast-orthopaedic ceramic interactions

A new experimental method has been used to study the behaviour of human osteoblasts cultured on bioceramics subjected to mechanical strains. The ceramics were alumina, hydroxyapatite (HA) and a duplex system composed of hydroxyapatite-covered alumina. The system applied 400 microdeformations for a 6-h period with a cycle frequency of 0.5 Hz to osteoblasts growing on ceramic-covered disks. The effects of strains on short-term cell viability, cell growth, alkaline phosphatase (ALP) activity, and collagen biosynthesis were assessed. When possible, the parameters (lactate dehydrogenase) were studied along the experiment in samples of the culture medium, in the other cases by comparison of stretched and unstretched cultures on the same ceramics with the same cell line. In relationship with the coating, mechanical strains resulted in a decrease in DNA corresponding to cell number, an LDH release during straining, an unchanged (alumina) or decreased (HA and duplex) ALP activity, a decrease (HA and duplex) of collagen and total protein synthesis or an increase of it (alumina). The stress-producing device and its associated protocol are shown to be suitable for investigating the behaviour of cells, cultured on biomaterials subjected to mechanical strain.

The use of dual-energy x-ray absorptiometry in animals

The use of dual-energy absorptiometry (DXA) to measure bone mineral content (BMC) and bone mineral density (BMD) is widespread in humans and has been adapted to animals because of the need to examine bone and body composition in longitudinal studies. In this review, the indications and techniques for DXA in small-sized animals (rodents, cats, and rabbits) and large-sized animals (dogs, swine, nonhuman primates, sheep, and horses) are discussed. Now that software has been developed for measuring BMD in small laboratory animals, the most frequent use of DXA in animals is in rats. An ultrahigh-resolution mode of acquisition is used for their small bones but also is necessary for other small-sized animals such as rabbits and cats. In larger-sized animals such as dogs, pigs, and sheep, software used in humans has been adapted successfully to measure BMC/BMD and body composition. The human spine and left and right hip protocols are adapted easily to animals of this size, and the software for body composition has been adapted to dogs. Measurement of bone mass around metallic implants is possible in animals and most studies have involved dogs. To ensure precision of DXA in the noninvasive measurement of BMD in animals, attention to positioning and ability of the operator to define the same region of interest using clearly defined anatomical landmarks on the scan image cannot be overemphasized. This is one of the essential requirements for successful densitometry in animals.

Effects of gamma-alumina and hydroxyapatite coatings on the growth and metabolism of human osteoblasts

The behavior of human osteoblasts cultivated on hydroxyapatite or alumina-coated disks of Ti6AL4V was studied in vitro. Cell anchorage and spreading were observed by scanning electron microscopy. Cell growth was monitored by counting cells and measuring DNA at 5 h and 2,5, and 10 days after cell seeding. Cells grown for 10 days were labeled with 14C-proline and total protein and collagen synthesis were measured; the type of collagen was also determined. Both ceramics showed excellent biocompatibility. At 10 days of culture the cells showed a higher rate of proliferation on alumina than on hydroxyapatite. Neither ceramic altered the collagen biosynthesis or the osteoblast-like properties of the cells, as indicated by the high percentage of type I collagen.