Characterization of α/β-TCP Based Injectable Calcium Phosphate Cement as a Potential Bone Substitute

The aim of this study was to evaluate the clinical applicability and biological behavior of a newly developed injectable calcium phosphate (Ca-P) cement as bone filler for gaps around oral implants. Twenty-four step-like implants, creating gaps of 1 and 2 mm, were inserted into the trabecular bone of the medial femoral condyles of six goats. Four different situations were tested: (1) implant + gaps; (2) implant + gaps, but covered with a polylactic acid membrane; (3) implant + gaps that were filled with Ca-P cement; and (4) implant + gaps that were filled with Ca-P cement and covered with a membrane. All implants were left in place for 12 weeks. Histological and quantitative histomorphometrical measurements demonstrated that implants + gaps had generally poor bone contact at the implant base. Furthermore, fibrous encapsulation was observed in the gap part. In contrast, the presence of a membrane promoted bone ingrowth into the gap and also the bone contact at the implant base. Injection of Ca-P cement resulted in an almost complete filling of the gaps around the implant. The cement surface was completely covered by bone. Active resorption and remodeling of cement particles was observed, suggesting a pattern of slow resorption associated with full replacement with newly formed bone. Additional use of a membrane did not result in adjunctive benefits. Bone-to-implant contact at the implant base was comparable with the implants provided only with a membrane. In conclusion, the Ca-P cement used here showed excellent clinical handling properties combined with a superior bone behavior. On the other hand, the degradation rate of the material was still very slow. This current characteristic can hamper the final clinical applicability of the material as gap filler for periimplant or periodontal defects.

In the present study, ZrO2 was added into the injectable calcium phosphate cements (CPCs) to improve their mechanical strength. Different mass fractions of ZrO2 (5 %, 10 %, 15 %, 20%) were mixed with the powder components consisted of tricalcium phosphate (α-TCP) and hydroxyapatite (HA). Then formed the paste via adding the liquid component consisted of citric acid. The compressive strength, the injectability, the initial setting time and finial time of CPC were measured, respectively. X-ray diffraction (XRD) was employed to analyse the phase of as-prepared CPC. Scanning Electron Microscope (SEM) and Energy dispersive spertrum (EDS) were used to observe the morphology and indicate the element components of CPC. The compressive strength of ZrO2-CPC was higher than that of CPC without added ZrO2. The compressive strength got the maximal when the mass fraction of ZrO2 was 15%. It had no effect on the injectability with adding ZrO2, which were 89 % to 92 %. It had a slight down-regulation of the initial and final setting time with adding ZrO2. SEM showed that there was amounts needle-like substance in CPC, which might be related to the improvement of compressive strength of CPC. XRD showed that there were HA, a few of α-TCP and ZrO2 diffraction peaks in CPCs. The present results indicate that it is feasible to improve the compressive strength of injectable CPC via adding ZrO2.

A simple and effective approach to prepare injectable macroporous calcium phosphate cement for bone repair: Syringe-foaming using a viscous hydrophilic polymeric solution

Enhancement of initial stability of press-fit femoral stems using injectable calcium phosphate cement: an in vitro study in dog bones

The in vivo study was performed to evaluate the biocompatibility and osteogenous ability of injectable fast-setting calcium phosphate cement (CPC). Eighteen four-week-old New Zealand white rabbits were divided into six groups randomly, three in each group. According to the principle of selfcontrast at the same time, cavities of 5mm in diameter and 6mm in depth were drilled in femoral condyle of rabbits. The materials were implanted into cavities of the left leg, the right leg as the blank control group. Rabbits were sacrificed at 2, 4, 8, 12, 16 and 24 weeks after surgery. The microstructure of specimens was observed using ESEM. The results showed that injectable fast-setting CPC had good fluidity and plasticity; it could be injected into bone defects and fast-set in situ. The start setting time was 5-8 min and the compressive strength was 25-30 MPa. The CPC had good biocompatibility and osteoconductivity, and benefited to the repair of bone defects.

4:25 Repair of osteoporotic vertebral compression fracture by transpedicular injection of bioactive calcium phosphate cement into the vertebral body

Mechanical and rheological properties and injectability of calcium phosphate cement containing poly (lactic-co-glycolic acid) microspheres

Injectable and macroporous calcium phosphate cement scaffold

Calcium phosphate cement (CPC) sets in situ with intimate adaptation to the contours of defect surfaces, and forms an implant having a structure and composition similar to hydroxyapatite, the putative mineral in teeth and bones. The objective of the present study was to develop an injectable CPC using dicalcium phosphate dihydrate (DCPD) with a high solubility for rapid setting. Two agents were incorporated to impart injectability and fast-hardening to the cement: a hardening accelerator (sodium phosphate) and a gelling agent (hydroxypropyl methylcellulose, HPMC). The cement with DCPD was designated as CPC(D), and the conventional cement was referred to as CPC(A). Using water without sodium phosphate, CPC(A) had a setting time of 82 +/- 6 min. In contrast, CPC(D) exhibited rapid setting with a time of 17 +/- 1 min. At 0.2 mol/L sodium phosphate, setting time for CPC(D) was 15 +/- 1 min, significantly faster than 40 +/- 2 min for CPC(A) (Tukey's at 0.95). Sodium phosphate decreased the paste injectability (measured as the paste mass extruded from the syringe divided by the original paste mass inside the syringe). However, the addition of HPMC dramatically increased the paste injectability. For CPC(D), the injectability was increased from 65% +/- 12% without HPMC to 98% +/- 1% with 1% HPMC. Injectability of CPC(A) was also doubled to 99% +/- 1%. The injectable and rapid-setting CPC(D) possessed flexural strength and elastic modulus values overlapping the reported values for sintered porous hydroxyapatite implants and cancellous bone. In summary, the rapid setting and relatively high strength and elastic modulus of CPC(D) should help the graft to quickly attain strength and geometrical integrity within a short period of time postoperatively. Furthermore, the injectability of CPC(D) may have potential for procedures involving defects with limited accessibility or narrow cavities, when there is a need for precise placement of the paste, and when using minimally invasive surgical techniques.

Alpha-bsm® is a first generation self-setting, injectable and moldable apatitic calcium phosphate cement (CPC) based on amorphous calcium phosphate (ACP). ACP was prepared using low temperature double decomposition technique, from a calcium solution (0.16 M), and phosphate solution (0.26 M) in a basic (pH~13) media. ACP was than stabilized using three crystal growth inhibitors (CO32-, Mg2+, P2O74-), freeze-dried, and heated (450 °C, 1h) to remove additional moisture and some inhibitors. Dicalcium phosphate dehydrate (DCPD) was also prepared using wet chemistry at room temperature from calcium and phosphate solution, respectively, 0.3 M and 0.15 M. ACP and DCPD powder were combined at a 1:1 ratio and ground to produce Alpha-bsm® bone cement. The cement is supplied as a powder and when mixed with an appropriate amount (0.8 ml/g) of physiological saline at room temperature, forms an injectable putty-like paste. The paste has a working time of about 45 minutes at room temperature, when stored in a moist environment. The setting reaction proceeds isothermically at body temperature (37°C) in less than 20 minutes, forming a hardened, porous (total porosity 50 to 60%), low crystalline (40% comparing with HA), apatitic calcium phosphate cement with a compressive strength range of 10 to 12 MPa. Extensive pre-clinical studies (rabbit radius critical sized defect, canine tibia osteotomy, sheep tibia, primate fibula fracture healing, and primate fibula critical size defect) demonstrate that Alpha-bsm® undergoes remodeling in conjunction with new bone formation. The next generation of Bone Substitute Materials (Beta-bsmTM and Gamma-bsm TM) are formulated based on the Alpha-bsm® chemistry but differ in powder processing (e.g. milling) technique. These materials are also self-setting, injectable and/or moldable apatitic calcium phosphate cements with improved handling and mechanical properties. The setting & hardening reaction of these new CPCs proceeds isothermically in less than 5 minutes at 37°C and once hardened demonstrate a compressive strength of 30 to 50 MPa. The final product (after full conversion) is a low crystalline (40% compared with Hydroxyapatite), calcium deficient (Ca/P atomic ratio = 1.45) carbonated apatite similar to the composition and structure of natural bone mineral (crystal size: length = 26 nm, width thickness = 8 nm). A desirable feature of these cements is their high surface chemistry (with specific surface area of about 180-200 m2/g) which is ideal for remodeling and controlled release of growth factors. A pilot rabbit critically sized femoral defect study comparing the three synthetic family products demonstrate that they share similar remodeling and resorption characteristics up to 52 weeks. Physico-chemical and mechanical performance of these next generation CPCs are favorable when compared with existing CPCs in the market, specifically material working time (at room temperature), cohesivity in a wet environment and fast setting & hardening rate (at body temperature).

In this study, the cytocompatibility and early osteogenic characteristics of rat bone marrow cells (RBMCs) on injectable calcium phosphate (CaP) cement (Calcibon) were investigated. In addition to unmodified CaP cement discs, 2 other treatments were given to the discs: preincubation in MilliQ and sintering at different temperatures. After primary culture, RBMCs were dropwise seeded on the discs and cultured for 12 days. The samples were evaluated in terms of cell viability, morphology (live and dead assays and scanning electron microscopy (SEM)), cell proliferation (deoxyribonucleic acid (DNA) analyses), early cell differentiation (alkaline phosphatase (ALP) activity), and physicochemical analyses (x-ray diffraction (XRD)). The live and dead, DNA, and SEM results showed that Calcibon discs without any additional treatment were not supporting osteoblast-like cells in vitro. There were fewer cells, and cell layers were detached from the disc surface. Therefore, different preincubation periods and sintering temperatures were evaluated to improve the cytocompatibility of the CaP cement. Preincubating discs in MilliQ for periods of 1, 4, 8, and 12 weeks resulted in the hydrolysis of alpha-tri calcium phosphate (TCP) into an apatite-like structure with some beta-TCP, as shown with XRD, but the material was not cytocompatible. Sintering the discs between 800 degrees C and 1100 degrees C resulted in conversion of alpha-TCP to beta-TCP with some hydroxyapatite and an increase in crystallinity. Eventually, the discs sintered at 1100 degrees C achieved better cell attachment, more-abundant cell proliferation, and earlier differentiation than other sintered (600 degrees C, 800 degrees C, and 1000 degrees C), preincubated, and unmodified specimens. On basis of our results, we conclude that in vivo results with CaP-based cements do not guarantee in vitro applicability. Furthermore, unmodified Calcibon is not cytocompatible in vitro, although preincubation of the material results in a more-favorable cell response, sintering of the material at 1100 degrees C results in the best osteogenic properties. In contrast to in vivo studies, the Calcibon CaP cement is not suitable as a scaffold for cell-based tissue-engineering strategies.

Mechanical augmentation of the vertebral body by calcium phosphate cement injection

Enhancing degradation of poorly degrading injectable calcium phosphate (CaP) cements (CPCs) can be achieved by adding poly(lactic-co-glycolic acid) (PLGA) microparticles, generating porosity after polymer degradation. CPC-PLGA has proven to be biodegradable, although its long-term biological performance is still unknown. Optimization of injectability could be achieved via addition of carboxymethyl cellulose (CMC). Here, we evaluated the long-term in vivo performance of CPC-PLGA with or without the lubricant CMC in comparison to the devitalized bovine bone mineral (DBBM) predicate device Bio-Oss®. Rabbit femoral bone defects were injected with a CPC-formulation or filled with Bio-Oss® granules. Samples were retrieved at 6 and 26 weeks. Material degradation for Bio-Oss® was marginal, starting with 57% material remnants at implantation, 49% at 6 weeks, and 35% at 26 weeks, respectively. In contrast, CPC-PLGA and CPC-PLGA-CMC showed significant material degradation, starting with 100% material remnants at implantation, 56 and 78% at 6 weeks, and 8 and 21% at 26 weeks. Bone formation showed to be rapid for Bio-Oss®, with 24% at 6 weeks, and a similar value (27%) at 26 weeks. Both CPC-PLGA and CPC-PLGA-CMC showed a continuous temporal increase in bone formation, with 13 and 6% at 6 weeks, and 44 and 32% at 26 weeks. This study showed that CPC-PLGA induces favorable bone responses with >90% degradation and >40% new bone formation after an implantation period of 26 weeks.

Apatitic calcium phosphate cements (CPCs) have been widely used as bone grafts due to their excellent osteoconductive properties, but the degradation properties are insufficient to stimulate bone healing in large bone defects. A novel approach to overcome the lack of degradability of apatitic CPC involves the development of biphasic CPCs (BCPC) based on tricalcium phosphate (TCP) in both α- and β-polymorphs. The aim of the current study was to prepare and analyze the physicochemical properties of BCPCs based on dual phase α/β-TCP as obtained by heat treatment of pure α-TCP. The handling and mechanical characteristics of the samples as well as the degradation behavior under in vitro condition were investigated and compared with a standard monophasic α-TCP-based CPC. The results showed that different heat treatments of commercially available α-TCP allowed the formation of biphasic calcium phosphate powder with a variety of α/β-TCP ratios. The use of biphasic powder particles as a reactant for CPCs resulted into increased setting and injectability times of the final BCPCs. During hardening of the cements, the amount of apatite formation decreased with increasing β-TCP content in the biphasic precursor powders. The morphology of the monophasic CPC consisted of plate-like crystals, whereas needle-like crystals were observed for BCPCs. In vitro degradation tests demonstrated that dissolution rate and corresponding calcium release from the set cements increased considerably with increasing β-TCP content, suggesting that apatitic CPCs can be rendered degradable by using biphasic α/β-TCP as powder precursor phase.

Calcium phosphate cements (CPCs) have been widely used as bone graft substitutes for many years. The aim of this study was to evaluate the biocompatibility of two novel injectable, bioactive cements: β-tricalcium phosphate (β-TCP)/CPC and chitosan microsphere/CPC in vitro and in vivo. This was accomplished by culturing mouse pre-osteoblastic cells (MC3T3-E1) on discs and pastes of CPCs. Cell growth, adhesion, proliferation and differentiation were assessed by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide and alkaline phosphatase assays as well as by scanning electron microscopy and fluorescence. The effect of CPC paste curing was also evaluated. Implantation of two materials into the muscle tissue of rabbits was also studied and evaluated by histological analysis. Cell analysis indicated good biocompatibility in vitro. The fluorescence assay suggested that the cured material discs had no obvious effect on cell growth, while the curing process did. Histological examination showed no inflammatory cell infiltration into soft tissue. These data suggest that β-TCP/CPC and chitosan microsphere/CPC composites may be promising injectable material for bone tissue engineering.