Evaluation of surgical cavities filled with three types of calcium sulfate

Titanium mesh-reinforced calcium sulfate for structural bone grafts

Calcium sulfate (CS) possesses many of the requirements for an ideal bone graft material: it is biodegradable, biocompatible, and osteoconductive. However, its relatively low strength and brittleness are major obstacles to its use as a structural bone implant. Although the strength of CS can be improved by reducing porosity, its brittleness remains a major obstacle towards its use as bone graft. Here we combine two powerful toughening strategies which are found in advanced ceramics and in natural bone: Multi-layered architectures and ductile reinforcements. We first used stress analysis and micromechanics to generate design guidelines that ensure the proper failure sequence and maximize properties. We then fabricated and tested fully dense CS by hydrostatic compression layered with layers of titanium woven mesh. Flexural experiments in hydrated conditions confirmed that the ductility and strength of titanium and the adhesion at the titanium-CS interfaces (controlled by the size of the Ti mesh) are critical factors in the mechanical performance of the composite. Our best design exhibited a toughness 180 times larger than that of plain CS, together with a 46% increase in strength.

Maximizing the strength of calcium sulfate for structural bone grafts

Calcium sulfate (CS) combines remarkable properties of biodegradability, biocompatibility, and osteoconductivity but its low strength limits the range of its applications in orthopaedic surgery. In this study we have addressed this limitation by optimizing the fabrication process for pure CS, and by using mechanical testing procedures which are relevant for load carrying, or structural bone grafts (flexural tests in hydrated condition). By optimizing the processing parameters (pressure during setting, CS powder to water ratio, saturated solution) we produced CS samples with the highest flexural strength ever reported in hydrated conditions. Once these optimal conditions are used, the addition of "reinforcing" inclusions in the material decreased its strength because these inclusions actually act as defects instead of reinforcements. In addition, the CS can be formed in precise shapes while maintaining optimal processing conditions and provided a strength similar to that of bone with the same dimensions. Dense and porous materials can be combined to duplicate the trabecular and cortical architecture of long bones, with only a small loss of overall strength.

Cytotoxicity and migration of fibroblasts on two types of calcium sulfate dihydrate

AIM

The aim of the present study was to compare cytotoxicity and migration ability of L929 on medical-grade calcium sulfate dihydrate (MCS) with commercial calcium sulfate dihydrate (CCS).

METHODS

Samples of both freshly-mixed and set states of MCS and CCS were extracted in culture medium and tested for cytotoxicity according to International Organization of Standardization 10993-5:2009. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was used, and the percentage of cell viability was calculated. Thirty petri dishes were divided into three equal groups: polystyrene (control), CCS, and MCS. In each petri dish, triplicate wells were made on the agarose overlay on the material. The central well was occupied with L929 cell suspension, one well was filled with platelet-derived growth factor-BB, and the remaining well with Hanks' Balanced Salt Solution. After incubation, the migration distances were measured and the corrected migration distances were calculated. The final step involved scanning electron microscopy (SEM).

RESULTS

The CCS had significantly less cell viability than MCS at a high extracted concentration (P < 0.001) in both samples. The mean corrected migration of MCS was significantly greater than that of CCS (P < 0.05). SEM showed that L929 cells on MCS exhibited an elongated spindle shape.

CONCLUSION

MCS was less cytotoxic and provided greater migration of L929 fibroblasts compared with CCS.

Cytotoxic Effects and Osteogenic Activity of Calcium Sulfate with and without Recombinant Human Bone Morphogenetic Protein 2 and Nano-Hydroxyapatite Adjacent to MG-63 Cell Line

OBJECTIVES

The aim of this study was to assess the cytotoxic effects and osteogenic activity of recombinant human bone morphogenetic protein (rhBMP2) and nano-hydroxyapatite (n-HA) adjacent to MG-63 cell line.

MATERIALS AND METHODS

To assess cytotoxicity, the 4,5-dimethyl thiazolyl-2,5-diphenyl tetrazolium bromide (MTT) assay was used. Alkaline phosphatase (ALP) activity and osteogenic activity were evaluated using Alizarin red and the von Kossa staining and analyzed by one-way ANOVA followed by Tukey's post hoc test.

RESULTS

The n-HA/calcium sulfate (CS) mixture significantly promoted cell growth in comparison to pure CS. Moreover, addition of rhBMP2 to CS (P=0.02) and also mixing CS with n-HA led to further increase in extracellular calcium production and ALP activity (P=0.03).

CONCLUSION

This in vitro study indicates that a scaffold material in combination with an osteoinductive material is effective for bone matrix formation.

Integration of a novel injectable nano calcium sulfate/alginate scaffold and BMP2 gene-modified mesenchymal stem cells for bone regeneration

The repair of craniofacial bone defects is surgically challenging due to the complex anatomical structure of the craniofacial skeleton. Current strategies for bone tissue engineering using a preformed scaffold have not resulted in the expected clinical regeneration due to difficulty in seeding cells into the deep internal space of scaffold, and the inability to inject them in minimally invasive surgeries. In this study, we used the osteoconductive and mechanical properties of nano-scale calcium sulfate (nCS) and the biocompatibility of alginate to develop the injectable nCS/alginate (nCS/A) paste, and characterized the effect of this nCS/A paste loaded with bone morphogenetic protein 2 (BMP2) gene-modified rat mesenchymal stem cells (MSCs) on bone and blood vessel growth. Our results showed that the nCS/A paste was injectable under small injection forces. The mechanical properties of the nCS/A paste were increased with an increased proportion of alginate. MSCs maintained their viability after the injection, and MSCs and BMP2 gene-modified MSCs in the injectable pastes remained viable, osteodifferentiated, and yielded high alkaline phosphatase activity. By testing the ability of this injectable paste and BMP2-gene-modified MSCs for the repair of critical-sized calvarial bone defects in a rat model, we found that BMP2-gene-modified MSCs in nCS/A (nCS/A+M/B2) showed robust osteogenic activity, which resulted in consistent bone bridging of the bone defects. The vessel density in nCS/A+M/B2 was significantly higher than that in the groups of blank control, nCS/A alone, and nCS/A mixed with MSCs (nCS/A+M). These results indicate that BMP2 promotes MSCs-mediated bone formation and vascularization in nCS/A paste. Overall, the results demonstrated that the combination of injectable nCS/A paste and BMP2-gene-modified MSCs is a new and effective strategy for the repair of bone defects.

Bone graft substitutes: What are the options?

Currently, a number of bone grafting materials are available in the clinical setting to enhance bone regeneration, varying from autologous bone to several bone graft substitutes. Although autologous bone remains the "gold standard" for stimulating bone repair and regeneration, the morbidity from its harvesting and its restricted availability generated the need for the development of other materials or strategies either to substitute autologous bone graft or expand its limited supply. Bone graft substitutes can possess one or more components: an osteoconductive matrix, acting as a scaffold; osteoinductive proteins and other growth factors to induce differentiation and proliferation of bone-forming cells; and osteogenic cells for bone formation. Based on their distinct properties, all these bone grafting alternatives have specific indications, and can be used either alone or in combination. In this review, we summarise the available bone grafting materials, focussing mainly on the various bone substitutes and their characteristics, in an effort to specify the indications for their use.