Calcium sulfate- and calcium phosphate-based bone substitutes. Mimicry of the mineral phase of bone

Single-donor allogeneic platelet fibrin glue and osteoconductive scaffold in orbital floor fracture reconstruction

BACKGROUND

Commonly used materials for orbital floor fracture reconstruction include autologous cranial bone graft and titanium mesh. We have evaluated here a biomaterial combining biphasic calcium phosphate (hydroxyapatite [HA]/β-tricalcium phosphate [TCP]) osteoconductive scaffold with single-donor allogeneic platelet fibrin glue.

METHODS

The study was conducted on 10 consecutive patients with a follow-up of up to 4 years. Platelet fibrin glue was prepared by mixing equal volumes of single-donor platelet-rich plasma and cryoprecipitate with HA/β-TCP followed by activation with human thrombin prepared by plasma activation. Postoperative evaluations included serial photographs, repeated physical examination, and 3-dimensional computed tomography scan performed 2 years after surgery.

RESULTS

The fibrin-rich platelet biomaterial was easy to mold and to apply on the surgical site allowing the surgeon to sculpt accurately the bone defect, providing mechanical stability while avoiding spillage of the scaffold. No infection of the orbit or extrusion of HA/β-TCP was observed. Ocular motility was normal, and no diplopia or enophthalmos of the injured orbit was noted. Coronal computed tomography scans of the reconstructed orbits revealed good restoration of the orbital floor defect in all 10 patients.

CONCLUSIONS

The use of single-donor platelet fibrin glue combined with an osteoconductive scaffold offers a valuable alternative to autologous cranial bone graft or titanium mesh in the reconstruction of orbital floor bone defect.

Metaphyseal bone formation induced by a new injectable β-TCP-based bone substitute: a controlled study in rabbits

PURPOSE

Adequate filling of bone defects still poses a challenge in every day clinical work. As many bone defects are irregularly shaped the need for appropriate scaffolds reaching the complete defect surface are great. The purpose of this pre-clinical pilot study was to investigate the handling, biocompatibility, biodegradation and osteoconductivity of a new pasty bone substitute (pure phase β-TCP, hyaluronic acid, methylcellulose) in bone tissue.

METHODS

In an unilateral tibial defect model the peri-implant and bone tissue response to the new pasty bone substitute was tested in New Zealand white rabbits for up to 24 weeks compared to empty controls. Analysis included HR-pQCT scans, histomorphometric evaluation and quantification of vascularization of un-decalcified histological slices.

RESULTS

After 1 week the experimental group presented significantly higher new bone volume fraction (p = 0.021) primarily consisting of immature bone matrix and higher vessel density compared to controls (p = 0.013). After 4 weeks bone formation was not significantly different to controls but was distributed more evenly throughout the defect. Bone matrix was now mineralized and trabeculae were thicker than in controls (p = 0.002) indicating faster intramedullary bone maturation. Controls presented extensive periosteal bone formation, major fibrous tissue influx and high vascularization. After 12 and 24 weeks there was no new bone detectable. There were no severe signs of inflammation at all time points.

CONCLUSION

The substitute showed an early induction of bone formation. It promoted accelerated intramedullary bone repair and maturation and prevented periosteal bone formation indicating its potential use for reconstructive surgery of bone defects.

Calcium sulfate stimulates pulp stem cells towards osteoblasts differentiation

Calcium sulfate (CaS) is a highly biocompatible material and enhances bone formation in vivo. However, how CaS alters osteoblast activity to promote bone formation is poorly understood. To study how CaS can induce osteoblast differentiation in mesenchymal stem cells, the expression levels of bone related genes and mesenchymal stem cells marker were compared in normal osteoblasts and dental pulp stem cells, using real time Reverse Transcription-Polymerase Chain Reaction. Gene differentially expressed between the two cells type were the trascriptional factor RUNX2, osteopontin (SPP1), COL1A1 (collagen type 1α1) and alkaline phosphatase (ALPL). The obtained results demonstrated that CaS strongly influences the behavior of DPSCs in vitro enhancing proliferation, differentiation and deposition of matrix.

Studies of bone morphogenetic protein-based surgical repair

Over the past several decades, recombinant human bone morphogenetic proteins (rhBMPs) have been the most extensively studied and widely used osteoinductive agents for clinical bone repair. Since rhBMP-2 and rhBMP-7 were cleared by the U.S. Food and Drug Administration for certain clinical uses, millions of patients worldwide have been treated with rhBMPs for various musculoskeletal disorders. Current clinical applications include treatment of long bone fracture non-unions, spinal surgeries, and oral maxillofacial surgeries. Considering the growing number of recent publications related to clincal research of rhBMPs, there exists enormous promise for these proteins to be used in bone regenerative medicine. The authors take this opportunity to review the rhBMP literature paying specific attention to the current applications of rhBMPs in bone repair and spine surgery. The prospective future of rhBMPs delivered in combination with tissue engineered scaffolds is also reviewed.

Osteogenic capacity of nanocrystalline bone cement in a weight-bearing defect at the ovine tibial metaphysis

The synthetic material Nanobone^® (hydroxyapatite nanocrystallines embedded in a porous silica gel matrix) was examined in vivo using a standardized bone defect model in the ovine tibial metaphysis. A standardized 6 × 12 × 24-mm bone defect was created below the articular surface of the medial tibia condyles on both hind legs of 18 adult sheep. The defect on the right side was filled with Nanobone^®, while the defect on the contralateral side was left empty. The tibial heads of six sheep were analyzed after 6, 12, and 26 weeks each. The histological and radiological analysis of the defect on the control side did not reveal any bone formation after the total of 26 weeks. In contrast, the microcomputed tomography analysis of the defect filled with Nanobone^® showed a 55%, 72%, and 74% volume fraction of structures with bone density after 6, 12, and 26 weeks, respectively. Quantitative histomorphological analysis after 6, and 12 weeks revealed an osteoneogenesis of 22%, and 36%, respectively. Hematoxylin and eosin sections demonstrated multinucleated giant cells on the surface of the biomaterial and resorption lacunae, indicating osteoclastic resorptive activity. Nanobone^® appears to be a highly potent bone substitute material with osteoconductive properties in a loaded large animal defect model, supporting the potential use of Nanobone^® also in humans.

Ectopic study of calcium phosphate cement seeded with pBMP-2 modified canine bMSCs mediated by a non-viral PEI derivative

We have evaluated the ectopic new bone formation effects of CPC (calcium phosphate cement) seeded with pBMP-2 (plasmids containing bone morphogenetic protein-2 gene) transfected canine bMSCs (bone marrow stromal cells) mediated by a non-viral PEI (polyethylenimine) derivative (GenEscort™ II) in nude mice. Canine bMSCs were transfected with pBMP-2 or pEGFP (plasmids containing enhanced green fluorescent protein gene) mediated by GenEscort™ II in vitro, and the osteoblastic differentiation was explored by ALP (alkaline phosphatase) staining, ARS (alizarin red S) staining and RT-qPCR (real-time quantitative PCR) analysis. Ectopic bone formation effects of CPC/pBMP-2 transfected bMSCs were evaluated and compared with CPC/pEGFP transfected bMSCs or CPC/untransfected bMSCs through histological, histomorphological and immunohistochemical analysis 8 and 12 weeks post-operation in nude mice. Transfection efficiency was up ∼35% as demonstrated by EGFP (enhanced green fluorescent protein) expression. ALP and ARS staining were stronger with pBMP-2 gene transfection, and mRNA expression of BMP-2 (bone morphogenetic protein-2), Col 1 (collagen 1) and OCN (osteocalcin) in pBMP-2 group was significantly up-regulated at 6 and 9 days. Significantly higher NBV (new bone volume) was achieved in pBMP-2 group than in the control groups at 8 and 12 weeks (P<0.05). In addition, immunohistochemical analysis indicated higher OCN expression in pBMP-2 group (P<0.01). We conclude that CPC seeded with pBMP-2 transfected bMSCs mediated by GenEscort™ II could enhance ectopic new bone formation in nude mice, suggesting that GenEscort™ II mediated pBMP-2 gene transfer is an effective non-viral method and CPC is a suitable scaffold for gene enhanced bone tissue engineering.

Bone tissue engineering: current strategies and techniques--part I: Scaffolds

Bone repair and regeneration is a dynamic process that involves a complex interplay between the (1) ground substance, (2) cells, and (3) milieu. While each constituent is integral to the final product, it is often helpful to consider each component individually. Therefore, we created a two-part review to examine scaffolds and cells' roles in bone tissue engineering. In Part I, we review the myriad of materials use for in vivo bone engineering. In Part II, we discuss the variety cell types (e.g., osteocytes, osteoblasts, osteoclasts, chondrocytes, mesenchymal stem cells, and vasculogenic cells) that are seeded upon or recruited to these scaffolds. In Part III, we discuss the optimization of the microenvironment. The biochemical processes and sequence of events that guide matrix production, cellular activation, and ossification are vital to developing successful bone tissue engineering strategies and are thus succinctly reviewed herein.

Optimising implant anchorage (augmentation) during fixation of osteoporotic fractures: is there a role for bone-graft substitutes?

When stabilising a fracture the contact between the screw and the surrounding bone is crucial for mechanical strength. Through development of screws with new thread designs, as well as optimisation of other properties, improved screw purchase has been gained. Other alternatives to improve screw fixation in osteoporotic bone, as well as normal bone if needed, includes the use of various coatings on the screw that will induce a bonding between the implant surface and the bone implant, as well as application of drugs such as bisphosphonates locally in the screw hole to induce improved screw anchorage through their anticatabolic effect on the bone tissue. As failure of internal fixation of fractures in osteoporotic bone typically occurs through breakage of the bone that surrounds the implant, rather than the implant itself, an alternative strategy in osteoporotic bone can include augmentation of the bone around the screw. This is useful when screws alone are being used for fixation, as it will increase pull-out resistance, but also when conventional plates and screws are used. In angularly stable plate-screw systems, screw back-out is not a problem if the locking mechanism between the screws and the plate works. However, augmentation that will strengthen the bone around the screws can also be useful in conjunction with angle-stable plate-screw systems, as the augmentation will provide valuable support when subjected to loading that might cause cut-out. For many years conventional bone cement, polymethylmethacrylate (PMMA), has been used for augmentation, but due to side effects--including great difficulties if removal becomes necessary--the use of PMMA has never gained wide acceptance. With the introduction of bone substitutes, such as calcium phosphate cement, it has been shown that augmentation around screws can be achieved without the drawbacks seen with PMMA. When dealing with fixation of fractures in osteoporotic bone where screw stability might be inadequate, it therefore seems an attractive option to include bone substitutes for augmentation around screws as part of the armamentarium. Clinical studies now are needed to determine the indications in which bone augmentation with bone-graft substitutes (BGSs) would merit clinical usage.

Injectable bone-graft substitutes: current products, their characteristics and indications, and new developments

More than a decade has passed since the first injectable bone substitutes were introduced for use in orthopaedic trauma, and over recent years the number of commercial products has increased dramatically. Despite the fact that these bone substitutes have been on the market for many years, knowledge amongst potential users on how and when they might be useful is still fairly limited. Most injectable bone substitutes belong to one of two major groups: by far the largest group contains products based on various calcium phosphate (CP) mixtures, whilst the smaller group consists of calcium sulphate (CS) compounds. Following mixing, the CP or CS paste can be injected into--for instance--a fracture space for augmentation as an alternative to bone graft, or around a screw for augmentation if the bone is weak. Within minutes an in situ process makes the substitute hard; the mechanical strength in compression resembles that of cancellous bone, whereas the strength in bending and shear is lower. Over time, CP products undergo remodelling through a cell-mediated process that seems to mimic the normal bone remodelling, whilst CS products are dissolved through a faster process that is not cell-mediated. For CP, a number of clinical studies have shown that it can be useful for augmentation of metaphyseal fractures when a space is present. Randomised studies have verified that CP works especially well in tibial plateau fractures when compared with conventional bone grafting. So far the number of clinical studies on CS products is very low. Development at present seems to be heading towards premixed or directly mixed products as well as new compounds that contain fibres or other components to enhance bending and shear strength. Products that are based on combinations of CP and CS are also being developed to combine the fast-dissolving CS with the stronger and more slowly remodelling CP. Injectable bone substitutes, and especially CS, have also been targeted as potentially good carriers for antibiotics and growth factors.

The in vitro elution characteristics of antifungal-loaded PMMA bone cement and calcium sulfate bone substitute

The use of antimicrobial-loaded delivery vehicles, most often as antibiotic beads, is common practice for the treatment of deep musculoskeletal infections. The elution of antibacterial drugs from various bone cements has been extensively studied. However, much less is known about the elution of other antimicrobials from these materials. In particular, the use of this approach for fungal infections has not been well studied despite growing concern about these difficult-to-treat organisms. Voriconazole is a broad-spectrum and highly effective antifungal that has been used in the treatment of resistant fungal pathogens. We examined the in vitro elution characteristics of voriconazole from nonabsorbable polymethylmethacrylate (PMMA) beads and from absorbable calcium sulfate beads. Voricanazole-containing beads were immersed in a 5-mL bath of phosphate-buffered saline at room temperature and placed on an orbital shaker. Eluent samples were collected over the course of 2 weeks. Concentrations of the antifungal drug in solution were measured using high-performance liquid chromatography. To verify biologic activity of the eluted antifungal, collected samples were also tested against control yeasts. We found that samples collected out to 2 weeks contained relatively high voriconazole concentrations and enough active antifungal activity to inhibit growth of the control yeasts. These data demonstrate that voriconazole retains its antifungal activity when mixed into either PMMA or calcium sulfate beads, and elutes out of beads at biologically effective concentrations over a time period of at least 2 weeks. Therefore, incorporation of voriconazole into either absorbable or nonabsorbable beads appears to be a reasonable strategy for the local delivery of a potent, broad-spectrum antifungal agent to an infected wound bed.

Comparative in vivo study of injectable biomaterials combined with BMP for enhancing tendon graft osteointegration for anterior cruciate ligament reconstruction

This study was to compare effect of osteointegration of grafted tendon in bone tunnels between injected calcium phosphate cement (ICPC) and injected fibrin sealant (IFS) combined with bone morphogenetic protein (BMP) after anterior cruciate ligament (ACL) reconstruction. ACL reconstruction was performed bilaterally in 51 rabbits. ICPC-BMP composite was injected into one knee, with the contralateral knee IFS-BMP composite. The rabbits were killed at postoperative weeks 2, 6, and 12 for testing. Histological observations showed the ICPC composite gradually increased the new bone formation during the whole healing process, while the IFS composite had a burst effect on enhancing the healing of tendon-to-bone at 2 and 6 weeks. By 12 weeks, there was more new cartilage and new bone in the interface in the ICPC-bBMP group. Micro-CT showed that the values of BMD in the ICPC-bBMP group were lower than those in the IFS-bBMP group at 6 weeks, while the values in the ICPC-bBMP group were higher than those in the IFS-bBMP group at 12 weeks (p > 0.05). Fluorescent labels showed that the rate of new bone formation of IFS-BMP composite was significantly higher than that of ICPC composite at 6 weeks (3.45 ± 0.62 µm/day vs. 2.93 ± 0.51 µm/day), but the rate was decreased compared with ICPC composite at 12 weeks (2.58 ± 0.72 µm/day vs. 3.05 ± 0.68 µm/day; p < 0.05). Biomechanically, the ultimate failure load in the ICPC-BMP group was always higher than that in the IFS-BMP group. It is evident that the ICPC composite achieved a more prolonged osteogenic effect than that by IFS composite.

Calcium phosphate combination biomaterials as human mesenchymal stem cell delivery vehicles for bone repair

A new class of biomimetic, bioresorbable apatitic calcium phosphate cement (CPC) was recently developed. The handling characteristics, and the ability to harden at body temperature in the presence of physiological saline, make this material an attractive clinical bone substitute and delivery vehicle for therapeutic agents in orthopedic applications. The major challenge with the material is formulating an injectable paste with options for cell delivery, in order to regenerate new bone faster and with high quality. In this study, three different additives and/or viscosity modifiers (carboxymethylcellulose, silk, and alginate) were incorporated into a CPC matrix. Injectability, cell viability, cell proliferation, surface morphology, and gene expression for osteogenesis of hMSCs were all evaluated. Injectable CPC-gel composites with cell protection were achieved. The CPC modified with alginate provided the best results based on cell proliferation, ALP and collagen production, and osteogenic transcript increases (for ALP, type I collagen, BSP, and OP). Furthermore, osteogenic analysis indicated lineage-specific differentiation of hMSCs into osteogenic outcomes. The results suggest that CPC mixed with alginate can be used as a cell delivery vehicle for bone regeneration.

A review of the mechanical behavior of CaP and CaP/polymer composites for applications in bone replacement and repair

Repair of load-bearing defects resulting from disease or trauma remains a critical barrier for bone tissue engineering. Calcium phosphate (CaP) scaffolds are among the most extensively studied for this application. However, CaPs are reportedly too weak for use in such defects and, therefore, have been limited to non-load-bearing applications. This paper reviews the compression, flexural and tensile properties of CaPs and CaP/polymer composites for applications in bone replacement and repair. This review reveals interesting trends that have not, to our knowledge, previously been reported. Data are classified as bulk, scaffolds, and composites, then organized in order of decreasing strength. This allows for general comparisons of magnitudes of strength both within and across classifications. Bulk and scaffold strength and porosity overlap significantly and scaffold data are comparable to bone both in strength and porosity. Further, for compression, all composite data fall below those of the bulk and most of the scaffold. Another interesting trend revealed is that strength decreases with increasing β-tricalcium phosphate (β-TCP) content for CaP scaffolds and with increasing CaP content for CaP/polymer composites. The real limitation for CaPs appears not to be strength necessarily, but toughness and reliability, which are rarely characterized. We propose that research should focus on novel ways of toughening CaPs and discuss several potential strategies.

Ingrowth of human mesenchymal stem cells into porous silk particle reinforced silk composite scaffolds: An in vitro study

Silk fibroin protein is biodegradable and biocompatible, exhibiting excellent mechanical properties for various biomedical applications. However, porous three-dimensional (3-D) silk fibroin scaffolds, or silk sponges, usually fall short in matching the initial mechanical requirements for bone tissue engineering. In the present study, silk sponge matrices were reinforced with silk microparticles to generate protein-protein composite scaffolds with desirable mechanical properties for in vitro osteogenic tissue formation. It was found that increasing the silk microparticle loading led to a substantial increase in the scaffold compressive modulus from 0.3 MPa (non-reinforced) to 1.9 MPa for 1:2 (matrix:particle) reinforcement loading by dry mass. Biochemical, gene expression, and histological assays were employed to study the possible effects of increasing composite scaffold stiffness, due to microparticle reinforcement, on in vitro osteogenic differentiation of human mesenchymal stem cells (hMSCs). Increasing silk microparticle loading increased the osteogenic capability of hMSCs in the presence of bone morphogenic protein-2 (BMP-2) and other osteogenic factors in static culture for up to 6 weeks. The calcium adsorption increased dramatically with increasing loading, as observed from biochemical assays, histological staining, and microcomputer tomography (μCT) analysis. Specifically, calcium content in the scaffolds increased by 0.57, 0.71, and 1.27 mg (per μg of DNA) from 3 to 6 weeks for matrix to particle dry mass loading ratios of 1:0, 1:1, and 1:2, respectively. In addition, μCT imaging revealed that at 6 weeks, bone volume fraction increased from 0.78% for non-reinforced to 7.1% and 6.7% for 1:1 and 1:2 loading, respectively. Our results support the hypothesis that scaffold stiffness may strongly influence the 3-D in vitro differentiation capabilities of hMSCs, providing a means to improve osteogenic outcomes.

Evaluation of colloidal silica suspension as efficient additive for improving physicochemical and in vitro biological properties of calcium sulfate-based nanocomposite bone cement

In the present study new calcium sulfate-based nanocomposite bone cement with improved physicochemical and biological properties was developed. The powder component of the cement consists of 60 wt% α-calcium sulfate hemihydrate and 40 wt% biomimetically synthesized apatite, while the liquid component consists of an aqueous colloidal silica suspension (20 wt%). In this study, the above mentioned powder phase was mixed with distilled water to prepare a calcium sulfate/nanoapatite composite without any additive. Structural properties, setting time, compressive strength, in vitro bioactivity and cellular properties of the cements were investigated by appropriate techniques. From X-ray diffractometer analysis, except gypsum and apatite, no further phases were found in both silica-containing and silica-free cements. The results showed that both setting time and compressive strength of the calcium sulfate/nanoapatite cement improved by using colloidal silica suspension as cement liquid. Meanwhile, the condensed phase produced from the polymerization process of colloidal silica filled the micropores of the microstructure and covered rodlike gypsum crystals and thus controlled cement disintegration in simulated body fluid. Additionally, formation of apatite layer was favored on the surfaces of the new cement while no apatite precipitation was observed for the cement prepared by distilled water. In this study, it was also revealed that the number of viable osteosarcoma cells cultured with extracts of both cements were comparable, while silica-containing cement increased alkaline phosphatase activity of the cells. These results suggest that the developed cement may be a suitable bone filling material after well passing of the corresponding in vivo tests.

Material properties and composition of soft-tissue fixation

Surgical interference screws and suture anchors for attaching soft tissue, such as ligaments and tendons, to bone are routinely used in arthroscopic surgery and sports medicine. Interference screw fixation provides a press fit between bone, graft/tendon, and screw and is frequently used to attach replacement ligaments in tunnels drilled for anterior and posterior cruciate ligament reconstruction. Suture anchors are used in surgical procedures wherein it is necessary for a surgeon to attach (tie) tissue to the surface of the bone, for example, during joint reconstruction and ligament repair or replacement. The composition of these implants ranges from metals to polymers and composites. Typically, because of the relatively large amount of torque that must be applied during insertion, these screws are constructed from metal. However, interference screws and suture anchors have also been constructed from bioabsorbable polymers and composites. The ideal material would (1) provide adequate mechanical fixation, (2) completely degrade once no longer needed, and (3) be completely replaced by bone. Because no material has been shown to be superior for all applications, the surgeon must weigh the advantages and disadvantages of each to evaluate the optimum material for a given application and patient. The purpose of this article is to present a comprehensive review of the commercially available interference screws and suture anchors, with an emphasis on implant composition, interaction, and design. This article provides the orthopaedic surgeon with a background on biomaterials, specifically those used in interference screws and suture anchors. Because there is no material that is perfect for all surgical situations, this review can be used to make educated decisions on a case-by-case basis.

Bone cements and their potential use in a mandibular endoprosthesis

Bone cement was first used in the 1950s. Since then many modifications have been made and alternatives developed to the original polymethylmethacrylate (PMMA) cement. In view of the use of bone cement in a novel mandibular endoprosthetic system, we performed a review of the current literature on this material. Different cements are described and their potential use in a mandibular endoprosthetic system discussed. The PMMA-based cements are currently the most suitable choice. Plain PMMA has the longest track record and is the default choice for the initial development phase of this system. If there is a significant risk of infection, then an antibiotic-loaded PMMA cement can be selected. However, modified PMMA cements, composite resin cements, osteoinductive calcium phosphate compounds, and cementless fixation are options that offer advantages over PMMA cements, and further research should be conducted to study their suitability.

Bone Substitute Fabrication Based on Dissolution-Precipitation Reactions

Although block- or granular-type sintered hydroxyapatite are known to show excellent tissue responses and good osteoconductivity, apatite powder elicits inflammatory response. For the fabrication of hydroxyapatite block or granules, sintering is commonly employed. However, the inorganic component of bone and tooth is not high crystalline hydroxyapatite but low crystalline B-type carbonate apatite. Unfortunately, carbonate apatite powder cannot be sintered due to its instability at high temperature. Another method to fabricate apatite block and/or granule is through phase transformation based on dissolution-precipitation reactions using a precursor phase. This reaction basically is the same as a setting and hardening reaction of calcium sulfate or plaster. In this paper, apatite block fabrication methods by phase transformation based on dissolution-precipitation reactions will be discussed, with a focus on the similarity of the setting and hardening reaction of calcium sulfate.

Bioceramic vertebral augmentation with a calcium sulphate/hydroxyapatite composite (Cerament SpineSupport): in vertebral compression fractures due to osteoporosis

A prospective, non-randomized multicenter study was initiated to study efficacy and safety of a partly resorbable composite of calcium sulphate and hydroxyapatite (Cerament SpineSupport), a novel, injectable bioceramic, in osteoporotic patients with vertebral compression fractures during 18-month follow-up. Fifteen patients with low-energy trauma and 1-2 vertebral compression fractures verified by magnetic resonance imaging were recruited to undergo percutaneous bioceramic vertebral augmentation under fluoroscopy. The patients were treated with a highly flowable bioceramic containing calcium sulphate, hydroxyapatite and the non-ionic radiocontrast agent iohexol, with final setting time within 1 h. After the procedure, the patients were allowed to mobilize after 2 h. Pain (VAS), occurrence of remote and adjacent fractures, and Quality of Life (QoL; SF-36 and EQ-5D) was recorded during 18 months. The injected volume of the composite material ranged from 2.8 to 9 mL (mean 4.2 mL). Pre-operative VAS score was mean 70.3 (CI95% +/-8.7) with an immediate post-operative pain relief, which was maintained at the 4-week visit (mean 26.4 with CI95% +/-16.1) and 8-week visit (mean 18.0 with CI95% +/-13.5 pain relief). Eighty percent of the patients demonstrated a clinical improvement. The pain relief was maintained over 18 months and no adjacent fractures were observed. There was a statistically significant improvement of physical components in the QoL assessment. No extra-vertebral leakage or neurological deficits were reported in this series. This first prospective multicenter study on a partly resorbable bioceramic material indicate that fracture healing can be achieved with sustained pain relief over a follow-up period of 18 months in an osteoporotic patient population with vertebral compression fractures.

Comparative evaluation of different crystal-structured calcium sulfates as bone-filling materials

The mechanical and handling properties and biological performances of two types of calcium sulfate (betaCS and alphaCS) as bone-filling materials were compared. The influence of two modifiers such as hydroxypropylmethylcellose (HPMC) and fibrin was also examined. alphaCS showed higher strength than, and similar setting time and injectability to those of betaCS. The degradation of CS in a simulated body fluid (SBF) was checked by measuring the amount of calcium released to SBF. alphaCS showed reduced calcium release than betaCS. The modifiers tended to increase the calcium release. The MC3T3-E1 preosteoblasts cultured on alphaCS showed higher levels of alkaline phosphatase (ALP) activity than those cultured on betaCS. alphaCS strongly promoted gene expression of osteoblast phenotypes including Runx2, alpha1(I) collagen, osteocalcin, and bone sialoprotein. There was no significant difference in cell adhesion and proliferation between two types of CS. The addition of modifiers to CS increased cell proliferation, ALP activity, and the gene expression. The osteoclastic differentiation of RAW264.7 monocytes was checked. The cells on both types of CS produced tartrate-resistant acid phosphatase (TRAP) activity with no significant difference. These cell response results indicated that alphaCS promoted osteoblast differentiation over betaCS but not osteoclast differentiation. Conclusively, a particular form of commercially available alphaCS possesses superior properties to betaCS in terms of mechanical properties and supports for osteoblast differentiation, suggesting that alphaCS could be an alternative to the conventionally used betaCS. The addition of HPMC and fibrin could further improve the feasibility of alphaCS as a bone-filling material.

Modulation of the resorption and osteoconductivity of alpha-calcium sulfate by histone deacetylase inhibitors

Calcium sulfate (CS) is an osteoconductive material with a long history of clinical use. However, its resorptive properties are not optimal for bone regeneration. Recently, histone deacetylase inhibitors (HDIs) have been suggested as bone regeneration tools. In this study, we investigated the effects of the HDIs sodium butyrate and trichostatin A on alpha-form CS (alphaCS) performance. MC3T3-E1 pre-osteoblasts cultured on alphaCS containing either HDI (alphaCS/HDI) showed higher levels of alkaline phosphatase activity than those cultured on alphaCS alone. The expression of genes characteristic of the osteoblast phenotype, including Runx2, osteocalcin, and bone sialoprotein, was strongly promoted by alphaCS/HDI. When cultured on alphaCS/HDIs, the osteoclastic differentiation of RAW264.7 monocytes was substantially suppressed, as measured by tartrate-resistant acid phosphatase (TRAP) activity and the expression levels of calcitonin receptor and TRAP. Neither HDI affected the CS setting time, compressive strength, or dissolution in a simulated body fluid. In a rat calvarial model of critical size bone defects, alphaCS/HDIs enhanced osteoblast differentiation, led to new bone formation, and delayed resorption, as confirmed by micro-computed tomography and histological analyses.

Comparison of computed tomography and microradiography for graft evaluation after reconstruction of critical size bone defects using beta-tricalcium phosphate

INTRODUCTION

The aim of the study was to evaluate the accuracy of computed tomography (CT) for in vivo follow up after mandibular reconstruction.

MATERIAL AND METHODS

Unilateral mandibular defects were surgically created in ten sheep and either reconstructed using blood soaked beta-tricalcium phosphate (beta-TCP) cylinders (group A, n=5) or blood soaked beta-TCP cylinders that were additionally loaded with autologous bone marrow (group B, n=5). The two graft designs resulted in different stages of graft ossification representative of different stages of healing. CT datasets were fused with microradiographs and measurements of ceramic area based on both methods were compared.

RESULTS

Two animals (groups A (n=1) and B (n=1)) presented infection and graft dislocation that was visible on CT and were excluded from statistical evaluation. Group A grafts underwent moderate degradation (53.55%+/-9.7) and incomplete bony incorporation representing an intermediate state of healing while ceramic grafts within group B developed a high grade of osseointegration and degradation (94.2%+/-3.3) consistent with progressive healing. Statistical comparison of measurements based on both methods revealed a significant bias (p<0.05) and a non-significant variance for group A and a significant variance (p<0.05) and non-significant bias for group B.

CONCLUSION

Our results indicate that conventional CT is not suitable to objectively evaluate ossification and degradation of a beta-TCP graft in vivo and further attempts to improve clinical visualization of beta-TCP need to be undertaken.

A new biphasic osteoinductive calcium composite material with a negative Zeta potential for bone augmentation

The aim of the present study was to analyze the osteogenic potential of a biphasic calcium composite material (BCC) with a negative surface charge for maxillary sinus floor augmentation. In a 61 year old patient, the BCC material was used in a bilateral sinus floor augmentation procedure. Six months postoperative, a bone sample was taken from the augmented regions before two titanium implants were inserted at each side. We analyzed bone neoformation by histology, bone density by computed tomography, and measured the activity of voltage-activated calcium currents of osteoblasts and surface charge effects. Control orthopantomograms were carried out five months after implant insertion. The BCC was biocompatible and replaced by new mineralized bone after being resorbed completely. The material demonstrated a negative surface charge (negative Zeta potential) which was found to be favorable for bone regeneration and osseointegration of dental implants.

Augmentation of screw fixation with injectable calcium sulfate bone cement in ovariectomized rats

The objective of this study was to determine the effect of augmenting screw fixation with an injectable calcium sulfate cement (CSC) in the osteoporotic bone of ovariectomized rats. The influence of the calcium sulfate (CS) on bone remodeling and screw anchorage in osteoporotic cancellous bone was systematically investigated using histomorphometric and biomechanical analyses. The femoral condyles of 55 Sprague-Dawley ovariectomized rats were implanted with screw augmented with CS, while the contralateral limb received a nonaugmented screw. At time intervals of 2, 4, 8, 12, and 16 weeks, 11 rats were euthanized. Six pair-matched samples were used for histological analysis, while five pair-matched samples were preserved for biomechanical testing. Histomorphometric data showed that CS augmented screws activated cancellous bone formation, evidenced by a statistically higher (p < 0.05) percentage of osteoid surface at 2, 4, and 8 weeks and a higher rate of bone mineral apposition at 12 weeks compared with nonaugmented screws. The amount of the bone-screw contact at 2, 8, and 12 weeks and of bone ingrowth on the threads at 4 and 8 weeks was greater in the CS group than in the nonaugmented group (p < 0.05), although these parameters increased concomitantly with time for both groups. The CS was resorbed completely at 8 weeks without stimulating fibrous encapsulation on the screw surface. Also, the cement significantly increased the screw pull-out force and the energy to failure at 2, 4, 8, and 12 weeks after implantation, when compared with the control group (p < 0.05). These results imply that augmentation of screw fixation with CS may have the potential to decrease the risk of implant failure in osteoporotic bone.

Back-scattered electron imaging and elemental microanalysis of retrieved bone tissue following maxillary sinus floor augmentation with calcium sulphate

OBJECTIVES

To investigate the presence and composition of residual bone graft substitute material in bone biopsies from the maxillary sinus of human subjects, following augmentation with calcium sulphate (CaS).

MATERIAL AND METHODS

Bone cores were harvested from the maxillary sinus of patients who had undergone a sinus lift procedure using CaS G170 granules 4 months after the initial surgery. Samples from seven patients, which contained residual biomaterial particles, were examined by field emission scanning electron microscopy and energy dispersive X-ray spectroscopy was used to determine the composition of the remaining bone graft substitute material.

RESULTS

Residual graft material occurred in isolated areas surrounded by bone and consisted of individual particles up to 1 mm in length and smaller spherical granules. On the basis of 187 separate point analyses, the residual material was divided into three categories (A, B and C) consisting of: A, mainly CaS (S/P atomic% ratio > or =2.41); B, a heterogeneous mixture of CaS and calcium phosphate (S/P=0.11-2.4) and C, mainly calcium phosphate (S/P< or =0.11; C), which had a mean Ca : P ratio of 1.63+/-0.2, consistent with Ca-deficient hydroxyapatite. Linescans and elemental maps showed that type C material was present in areas which appeared dense and surrounded, or were adjacent to, more granular CaS-containing material, and also occurred as spherical particles. The latter could be disintegrating calcium phosphate in the final stages of the resorption process.

CONCLUSIONS

CaS resorption in the human maxillary sinus is accompanied by CaP precipitation which may contribute to its biocompatibility and rapid replacement by bone.

Augmentation of pedicle screw fixation strength using an injectable calcium sulfate cement: an in vivo study

STUDY DESIGN

An in vivo landrace model of cement augmentation of pedicle screw was established, and axial pull-out tests and histological analysis were performed.

OBJECTIVE

To investigate the long-term in vivo biomechanical performance of pedicle screws augmented with calcium sulfate cement.

SUMMARY OF BACKGROUND DATA

Little information is available on the long-term biomechanical performance of pedicle screws augmented with calcium sulfate cement in vivo.

METHODS

Ten pedicle screws were implanted into the lumbar vertebrae of 15 adult females landraces weighing 105 to 115 kg. The pedicle screws were augmented with Polymethyl methacrylate (PMMA), augmented with the calcium sulfate cement, or not augmented. The landraces were randomized into 3 study periods of day 1, 6 weeks, and 12 weeks. At the end of the assigned study periods, the animals were killed and axial pull-out tests and histological analyses were conducted on the isolated specimen vertebrae.

RESULTS

No significant difference was found among the 1-day, 6-week,and 12-week control group (P > 0.18), no significant difference was found among the 1-day, 6-week and 12-week PMMA group (P > 0.59), and no significant difference was found among the 1-day, 6-week and 12-week calcium sulfate group (P > 0.27). The maximum POS of the PMMA groups was significantly greater than that of the calcium sulfate groups (P < 0.002), the maximum POS of the calcium sulfate groups was significantly greater than that of the control groups (P < 0.004). Histologically progressive absorption of the calcium sulfate was evident. The bone walls around the screws in the 12-week calcium sulfate group were statistically significantly thicker than that of the 12-week control group and that of the 12-week PMMA group.

CONCLUSION

Results of this study demonstrate that the injectable calcium sulfate cement can significantly improve the immediate POS of pedicle screw fixation, and this effect can be maintained even if the calcium sulfate cement has been absorbed completely, which may result from that the calcium sulfate cement resorption paralleled bone ingrowth.

A novel surface treatment for porous metallic implants that improves the rate of bony ongrowth

Rapid implant fixation could prove beneficial in a host of clinical applications from total joint arthroplasty to trauma. We hypothesized that a novel self-assembled monolayer of phosphonate molecules (SAMP) covalently bonded to the oxide surface of titanium alloy would enhance bony integration. Beaded metallic rods were treated with one of three coatings: SAMP, SAMP + RGD peptide, or hydroxyapatite. Rods were inserted retrogradely into both distal femurs of 60 rabbits. Fifteen rabbits were sacrificed at 2, 4, 8, and 16 weeks. At each time, seven specimens for mechanical pull-out testing and three for histomorphometric analysis were available for each coating. At four weeks, both SAMP groups had significantly higher failure loads when compared to hydroxyapatite (p < 0.01). No significant differences were found among groups at other times, though the SAMP-alone group remained stronger at 16 weeks. Histology showed abundant new bone formation around all the three groups, though more enhanced formation was apparent in the two SAMP groups. With this novel treatment, with or without RGD, the failure load of implants doubled in half the time as compared with hydroxyapatite. Where early implant fixation is important, the SAMP treatment provides a simple, cost-effective enhancement to bony integration of orthopaedic implants.

Innovations in osteosynthesis and fracture care

Over the years giant steps have been made in the evolution of fracture fixation and the overall clinical care of patients. Better understanding of the physiological response to injury, bone biology, biomechanics and implants has led to early mobilisation of patients. A significant reduction in complications during the pre-operative and post-operative phases has also been observed, producing better functional results. A number of innovations have contributed to these improved outcomes and this article reports on the advances made in osteosynthesis and fracture care.

Effects of chitosan-coated pressed calcium sulfate pellet combined with recombinant human bone morphogenetic protein 2 on restoration of segmental bone defect

A chitosan-coated pressed calcium sulfate pellet combined with recombinant human bone morphogenetic protein 2 (rhBMP-2) has been developed with increased compressive strength and osteoinduction, but with a resorption profile only slightly slower than uncoated pellet. A radial segmental defect model of rabbit was used to study the restoration effect on defect treated with chitosan-coated pressed calcium sulfate pellet combined with rhBMP-2, coated pressed calcium sulfate pellet, and uncoated pressed calcium sulfate pellet. Nothing was implanted in the control group. After 4, 8, and 12 weeks, the results indicated that coated pressed calcium sulfate pellet combined with rhBMP-2 and coated pressed calcium sulfate pellet facilitated new bone formation on defected bone and that particularly the former was more effective than the latter.

Silicates and bone fusion

Autologous bone grafting remains the gold standard for bone grafting in clinical practice. Although it has withstood the test of time, it remains associated with multiple comorbidities. The search for an alternative bone graft substitute harnessing bone's osteoconductive, osteoinductive, and osteogenic properties remains a challenge. This article examines the various bone grafting materials currently in use and highlights the current properties and uses of silicon-substituted calcium phosphates as a competitive substitute for high cost materials used today.

Calcium sulfate acts on the miRNA of MG63E osteoblast-like cells

Calcium sulfate (CaS) is a highly biocompatible material and enhances bone formation in vivo. However, how CaS alters osteoblast activity to promote bone formation is incompletely understood. We therefore investigated the translation regulation in osteoblasts exposed to CaS by using microRNA microarray techniques. Transduction, transcription, and translation are the three levels of regulation of cell activity. Recently, a new type of translation regulation has been identified: RNA interference (RNAi). RNAi is a process in which microRNA, (miRNA), that is, noncoding RNAs of 19-23 nucleotides can induce sequence-specific mRNA degradation and/or translational repression. The human genome encodes a few hundred miRNAs that can post-transcriptionally repress thousands of genes. The miRNA oligonucleotide microarray provides a novel method of carrying out genome-wide miRNA profiling in human samples. By using miRNA microarrays containing 329 probes designed from Human miRNA sequences, we identified in osteoblast-like cells line (MG-63) cultured with CaS (Surgiplaster, Classimplant, Roma, Italy) several miRNA whose expression is significantly modified. The data reported are, to our knowledge, the first study on translation regulation in osteoblasts exposed to CaS. They could be relevant to a better understanding of the molecular mechanism of bone regeneration and as a model for comparing other materials with similar clinical effects.

Anterior corpectomy with iliac bone fusion or discectomy with interbody titanium cage fusion for multilevel cervical degenerated disc disease

STUDY DESIGN

Clinical and radiologic study evaluating the outcome after anterior corpectomy with iliac bone fusion compared with discectomy with interbody titanium cage fusion for multilevel cervical degenerated disc disease.

OBJECTIVES

To investigate the safety and effectiveness of interbody titanium cage with plate fixation in multilevel postdiscectomy fusion.

SUMMARY OF BACKGROUND DATA

The operation for segmental multilevel cervical degenerated disc disease remains controversial. Data on safety and efficacy of titanium cages in multilevel postdiscectomy fusion are rarely available. We investigated the safety and effectiveness of interbody fusion cages with plate fixation and compared the clinical and radiographical results between anterior corpectomy and iliac bone fusion with plate fixation and multilevel discectomy and cage fusion with plate fixation.

METHODS

Sixty-two patients were treated with either a multilevel discectomy and cage fusion with plate fixation (27 patients, group A) or an anterior corpectomy and iliac graft fusion with plate fixation (35 patients, group B). We evaluated the patients for cervical lordosis, fusion status, and stability 24 months postoperatively on the basis of spine radiographs. The patients' neurologic outcomes were assessed by the Japanese Orthopedic Association (JOA) scores. Neck pain was graded using a 10-point visual analog scale.

RESULTS

Both groups A and B demonstrated a significant increase in the JOA scores (preoperatively 11.1+/-2.1 and 10.4+/-3.5, postoperatively 14.3+/-2.4 and 13.9+/-2.1, respectively) and a significant decrease in the visual analog pain scores (preoperatively 8.5+/-1.1 and 8.7+/-1.5, postoperatively 2.9+/-1.8 and 3.0+/-2.0, respectively). However, there was no significant difference between groups A and B. Both groups A and B showed a significant increase in the cervical lordosis after operation and reached satisfactory fusion rates (96.3% and 91.4%, respectively). Three patients (two 2-level corpectomies and one 3-level corpectomy) had construct failures that required a second operation. Eight of 35 patients who underwent iliac bone fusion had donor site pain. The hospital stay in group A was significantly shorter than that in group B (P=0.022).

CONCLUSIONS

Either a multilevel discectomy and cage fusion with plating or a corpectomy and iliac bone fusion with plating provides good clinical results and similar fusion rates for cervical degenerative disc disease. However, absence of donor site complications and construct failures and shorter hospital stay make the multilevel discectomy and cage fusion with plate fixation better than corpectomy and strut graft fusion with plate fixation.

Tissue engineering of bone: material and matrix considerations

When the normal physiologic reaction to fracture does not occur, such as in fracture nonunions or large-scale traumatic bone injury, surgical intervention is warranted. Autografts and allografts represent current strategies for surgical intervention and subsequent bone repair, but each possesses limitations, such as donor-site morbidity with the use of autograft and the risk of disease transmission with the use of allograft. Synthetic bone-graft substitutes, developed in an effort to overcome the inherent limitations of autograft and allograft, represent an alternative strategy. These synthetic graft substitutes, or matrices, are formed from a variety of materials, including natural and synthetic polymers, ceramics, and composites, that are designed to mimic the three-dimensional characteristics of autograft tissue while maintaining viable cell populations. Matrices also act as delivery vehicles for factors, antibiotics, and chemotherapeutic agents, depending on the nature of the injury to be repaired. This intersection of matrices, cells, and therapeutic molecules has collectively been termed tissue engineering. Depending on the specific application of the matrix, certain materials may be more or less well suited to the final structure; these include polymers, ceramics, and composites of the two. Each category is represented by matrices that can form either solid preformed structures or injectable forms that harden in situ. This article discusses the myriad design considerations that are relevant to successful bone repair with tissue-engineered matrices and provides an overview of several manufacturing techniques that allow for the actualization of critical design parameters.

Use of 3D beta-tricalcium phosphate (Vitoss) scaffolds in repairing bone defects

Vitoss is the most porous (90%) of a number of beta-tricalcium phosphate osteoconductive bone fillers. Its inherent limitations are those of the calcium phosphate class, being a purely osteoconductive product without inherent structural stability and with a moderate resorption rate. Currently, a number of additives, composites and related compounds are under study at various stages. In animal experiments, Vitoss performs well in comparison with other synthetic grafts, and with marrow added in various ways, it rivals autograft. Clinical efficacy is established for Vitoss as a spinal graft extender, as well as for periodontal, dental and orthopedic tumor defects. Apart from recombinant human platelet-derived growth factor, clinical data is lacking on the addition of bone marrow, stem cells and growth factors.

Reconstruction of critical size calvarial bone defects in rabbits with glass–fiber-reinforced composite with bioactive glass granule coating

The aim of this study was to evaluate glass-fiber-reinforced composite as a bone reconstruction material in the critical size defects in rabbit calvarial bones. The bone defect healing process and inflammatory reactions were evaluated histologically at 4 and 12 weeks postoperatively. Possible neuropathological effects on brain tissue were evaluated. The release of residual monomers from the fiber-reinforced composite (FRC) was analyzed by high performance liquid chromatograph (HPLC).

RESULTS

At 4 weeks postoperatively, fibrous connective tissue ingrowth to implant structures was seen. Healing had started as new bone formation from defect margins, as well as woven bone islets in the middle of the defect. Woven bone was also seen inside the implant. Inflammation reaction was slight. At 12 weeks, part of the new bone had matured to lamellar-type, and inflammation reaction was slight to moderate. Control defects had healed by fibrous connective tissue. Histological examinations of the brain revealed no obvious damage to brain morphology. In HPLC analysis, the release of residual 1,4-butanedioldimethacrylate and methylmethacrylate from polymerized FRC was low.

CONCLUSIONS

This FRC-implant was shown to promote the healing process of critical size calvarial bone defect in rabbits. After some modifications to the material properties, this type of implant has the potential to become an alternative for the reconstruction of bone defects in the head and neck area in the future.

A review of the association between osteoporosis and alveolar ridge augmentation

OBJECTIVE

Because of increasing life expectancy and popularity of dental implants, surgeons face a larger number of osteoporotic patients who require bone augmentation. Relationship between low bone density/osteoporosis and bone graft success is still not clear. The purpose of this article is to review and summarize the literature regarding the success of alveolar bone augmentation in osteoporosis.

STUDY DESIGN

The study design includes a literature review of relevant preclinical and clinical articles that address the association between osteoporosis and alveolar bone augmentation.

RESULTS

Increased rate of complications such as resorption of bone graft, non-integration of bone graft, delayed healing time, and implant failure in augmented bone especially in the maxilla may be associated with compromised bone health.

CONCLUSIONS

Despite the decreased success rate, osteoporosis is not an absolute contraindication for bone augmentation and dental implant placement. The modifiable risk factors for osteoporosis should be eliminated before surgery.

Synthetic bone grafts, the role of the gypsum in bone substitution; molecular biological approach

A csontpótlást igénylő műtéti beavatkozások során a beültetésre kerülő csontpótló graft tulajdonságai meghatározzák az eljárás kimenetelét, rövid és hosszú távú sikerét. Munkánk első részében áttekintést adunk a modern csontpótló eljárások előnyeiről-hátrányairól, illetve részletesen foglalkozunk a gipsz szintetikus csontpótló graftként történő alkalmazásának lehetőségével. A kísérletes klinikai leírások biztonsággal és jó hosszú távú eredménnyel alkalmazható csonthiánykitöltő anyagként írják le a kalcium-szulfát-dihidrátot, azonban a gipsz csontsejtekre kifejtett hatása, a csontpótlás mechanizmusa nem ismert. Molekuláris biológiai módszerekkel vizsgáltuk a gipsz csontsejtekre gyakorolt hatását. Az egér-praeosteoblastok szaporodására ideális tenyésztőfelületnek bizonyult a gipsz, míg a klinikumban gyakran csonthiánykitöltő anyagként alkalmazott polimetil-metakrilát-csontcement gátolta a sejtek osztódását. A gipsz megváltoztatta a sejtek génkifejeződési profilját, a csontképződés irányába mutató gének expresszálódtak nagyobb mértékben a gipszes tenyészetekben, és ezekben a sejtkultúrákban emelkedett alkalikusfoszfatáz-aktivitást mértünk. Eredményeink molekuláris biológiai szempontból támasztották alá a gipsz szintetikus csontpótló graftként történő alkalmazásának létjogosultságát, a kalcium-szulfát-dihidrát új – a csontgyógyulást támogató – tulajdonságát is kimutatva.

Characteristics of calcium sulfate/gelatin composite biomaterials for bone repair

A novel hybrid biomaterial composed of calcium sulfate (CS) and gelatin (GEL) was prepared with the potential of being used as bone filler or scaffold owing to its osteoconduction. Such composite biomaterial, cross-linked or un-cross-linked, could provide a suitable absorbing rate and prevent the CS crystals migrating from the implant for tissue engineering. The structure of the composite was analyzed with infrared (IR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that the crystal pattern of CS was affected by the addition of GEL. The GEL part affected the development of the CS dihydrate (CSD) crystal by slowing the conversion from CS hemihydrate (CSH) to CSD; thus, the composite actually contained CSD, CSH and GEL. The compressive strength of the CS/CLGEL composite was also investigated. The compressive strength was correlated to the weight proportions of CS in the CS/cross-linked GEL (CS/CLGEL) composite, and the highest compressive strength of 82 MPa was obtained for the composite containing 40 wt% CS. The in vitro absorption test and the SEM results showed that a porous scaffold was formed in situ with the absorption of CS in the CS/CLGEL composite in a certain time. Therefore, the CS/CLGEL composite material can be used as an in situ porous scaffold with a high initial mechanical strength, and the remaining porous GEL scaffold will enable further in-growth of cells. Human osteoblasts were cultured in contact with the CS/CLGEL composite and the primary results suggested that human osteoblasts could attach and spread on the surface of CS/CLGEL films. The preliminary animal model experiment was operated for assessing the potential of the CS/CLGEL composite as a biodegradable bone substitute. The primary results showed that the CS/CLGEL composite filler could promote new bone in-growth, which will stimulate further study.

Histologic evaluation of a provisional implant retrieved from man 7 months after placement in a sinus augmented with calcium sulphate: a case report

Little is known about the in vivo healing processes at the interface of implants placed in different grafting materials. For optimal sinus augmentation, a bone graft substitute that can regenerate high-quality bone and enable the osseointegration of load-bearing titanium implants is needed in clinical practice. Calcium sulphate (CaS) is one of the oldest biomaterials used in medicine, but few studies have addressed its use as a sinus augmentation material in conjunction with simultaneous implant placement. The aim of the present study was to histologically evaluate an immediately loaded provisional implant retrieved 7 months after simultaneous placement in a human sinus grafted with CaS. During retrieval bone detached partially from one of the implants which precluded its use for histologic analysis. The second implant was completely surrounded by native and newly formed bone, and it underwent histologic evaluation. Lamellar bone, with small osteocyte lacunae, was present and in contact with the implant surface. No gaps, epithelial cells, or connective tissues were present at the bone-implant interface. No residual CaS was present. Bone-implant contact percentage was 55% +/- 8%. Of this percentage, 40% was represented by native bone and 15% by newly formed bone. CaS showed complete resorption and new bone formation in the maxillary sinus; this bone was found to be in close contact with the implant surface after immediate loading.

Elution characteristics and mechanical properties of calcium sulfate-loaded bone cement containing teicoplanin

BACKGROUND

Acrylic bone cement is the most widely used drug delivery system clinically. It has already been shown that antibiotic release is significantly increased when calcium sulfate-loaded acrylic bone cement is used. However, there is no information yet about the mechanical responses of these composite materials. Thus, the purpose of this study was to investigate the effect of calcium sulfate on the elution characteristics and mechanical behavior of teicoplanin-loaded acrylic bone cement.

METHODS

Four groups of acrylic bone cements (GI, GII, GIII, GIV) were prepared using the same liquid/powder ratios. After mixing, the bone cement and additive mixtures were packed into different-type molds to prepare the specimens for the elution and mechanical tests. All of the specimens were tested for two conditions (dry and human plasma solution). The mechanical tests included the setting time (hardness) and tensile, bending, and compression strengths. The fracture surfaces of the failed samples were also examined by scanning electron microscopy.

RESULTS

Teicoplanin release in the calcium sulfate powder added groups (GIII and GIV) was higher than that of GII. When the calcium sulfate and teicoplanin were added on acrylic bone cement, the compressive, bending and tensile strength, hardness values, and elastic modulus decreased. Also, further reductions were evident in human plasma solution.

CONCLUSIONS

Although mechanical properties of tested specimens decreased, all of the results obtained were higher than those required by the American Society for Testing and Materials Standards, but further investigations are necessary before making definitive statements for clinical applications.