Osteoinduction by calcium phosphate biomaterials

Different materials were implanted in muscles of dogs to study the osteoinduction of calcium phosphate biomaterials. Bone formation was only seen in calcium phosphate biomaterials with micropores, and could be found in hydroxyapatite (HA) ceramic, tricalcium phosphate/hydroxyapatite ceramic (BCP), -TCP ceramic and calcium phosphate cement. The osteoinductive potential was different in different materials. The results indicate that osteoinduction can be a property of calcium phosphate biomaterials when they exhibit specific chemical and structural characteristics. © 1998 Kluwer Academic Publishers     

Dynamic compaction of calcium phosphate biomaterials

The purpose of this study was to apply the dynamic compaction process to calcium phosphate biomaterials. this new technique is currently used to compact metallic powders at room temperature but has not been previously applied to biomaterials. A detailed study of hydroxyapatite compacts was carried out to determine shock compaction parameters. Low static precompaction (3.1 MPa) resulted in slight peripheral cracks. A compaction degree of about 70% and macrohardness of 51 Hv were achieved for a striker velocity of about 50 m/s. FTIR spectroscopy and X-ray diffraction showed no differences in structure and composition after dynamic compaction. Two other infrequently used biomaterials were also tested: an unstable octacalcium phosphate and -calcium metaphosphate fibres. Scanning electron microscopy showed that dynamic compaction preserved the initial fibre structure of the material. No major structural or chemical changes were noted after shock consolidation. Our results show that dynamic compaction could extend the range of bioceramics.     

Si complexes in calcium phosphate biomaterials

Silicon complexes in silicon doped calcium phosphate bioceramics have been studied using ²⁹Si magic angle spinning nuclear magnetic resonance spectroscopy with the objective of identifying the charge compensation mechanisms of silicon dopants. Three different materials have been studied: a multiphase material composed predominantly of a silicon stabilized α-tricalcium phosphate (α-TCP) phase plus a hydroxyapatite (HA) phase, a single phase Si-HA material and a single phase silicon stabilized α-TCP material. NMR results showed that in all three materials the silicon dopants formed Q¹ structures in which two silicate tetrahedra share an oxygen, creating an oxygen vacancy which compensated the substitution of two silicon for phosphorus. This finding may explain the phase evolution previously found where silicon stabilized α-TCP is found at low temperature after sintering.     

Osteoinduction of calcium phosphate biomaterials in small animals

Although osteoinduction mechanism of calcium phosphate (CP) ceramics is still unclear, several essential properties have been reported, such as chemical composition, pore size and porosity, etc. In this study, calcium phosphate powder (Ca₃(PO₄)₂, CaP, group 1), biphasic calcium phosphate ceramic powder (BCP, group 2), and intact BCP rods (group 3) were implanted into leg muscles of mice and dorsal muscles of rabbits. One month and three months after implantation, samples were harvested for biological and histological analysis. New bone tissues were observed in 10/10 samples in group 1, 3/10 samples in group 2, and 9/10 samples in group 3 at 3rd month in mice, but not in rabbits. In vitro, human mesenchymal stem cells (hMSCs) were cultured with trace CaP and BCP powder, and osteogenic differentiation was observed at day 7. Our results suggested that chemical composition is the prerequisite in osteoinduction, and pore structure would contribute to more bone formation.     

Preparation and characterization of biphasic calcium phosphate ceramics of desired composition

A modified processing route for fabricating dense and porous biphasic calcium phosphate (BCP) ceramics of desired and reproducible phase composition (hydroxyapatite (HA)/beta-tricalcium phosphate (beta-TCP) ratio) has been developed. The principal idea of the route was combining a precipitation and a solid phase methods. First, a nonstoichiometric (slightly carbonated calcium-deficient) HA (CdHA) precipitate was synthesized by mixing a calcium carbonate (CaCO(3)) water suspension with an orthophosphoric acid (H(3)PO(4)) solution in abundance (related to the amount resulting in a stoichiometric HA) under definite conditions, and a powder of the precipitate was prepared and calcinated in air (860 degrees C, 1.5 h). In the second stage, a BCP ceramics of the composition determined by the calcium-deficiency in a calcinated powder (the acid abundance in a mixture) was processed by sintering powder compacts with or without a porosizer under appropriate conditions (1,200 degrees C, 2h). A calibrating dependence of the HA/beta-TCP ratio in the ceramics on the acid abundance has been plotted which enabled a controlled preparation of BCP ceramics. A correlation based on unresolved bands in nu(4)-PO (4) (3-) domain in IR-spectra of nanostructured BCP materials was found. Using the correlation, the process of CdHA --> beta-TCP transformation could be easily monitored. The density and microhardness of the BCP ceramics neglectly depended on the composition, however, the compressive strength did: the lower the HA/beta-TCP ratio, the higher the strength in the dense materials.     

Surface structural biomimetics and the osteoinduction of calcium phosphate biomaterials

From the point of view of materials, many natural tissues could be regarded as materials with certain nanostructure thus have special biological function. These natural nanostructures are generally formed under soft biological condition and show excellent biocompatibility and biological functions. To get materials with certain biological function, it is expectable to construct some nanostructure by mimicking the natural soft process. In this study, the porous biphasic calcium phosphate (BCP) ceramic was used to study the relationship of surface micro/nano structure and the biological function of osteoinductivity. Surface structural biomimetic was achieved by a soft technology of surface treating with simulated body fluid (SBF) or SBF containing protein molecules (BSA-SBF). The biological function of osteoinduction was tested by studying the bone formation in the samples implanted in dog nonosseous sites. The results showed that by the soft biomimetic process, the surface was re-constructed and the surface characteristics varied with the biomimetic process. The biological function of osteoinductivity depended on the surface characteristics. The present of protein molecules was likely to construct a surface structure which was different from that without the protein molecules and showed higher osteoinductivity. The study gave the evidence of material surface structural biomimetic to promote biological function as well as the possibility of the application of soft-nano technology to construct a micro/nano structural surface/interface of biomaterials with certain biological function.     

Preparation and characterization of an electrodeposited calcium phosphate coating associated with a calcium alginate matrix

A new way of optimizing osteoconduction of biomaterials is to bring to them biological properties. In this work, we associated a novel release system with an electrodeposited calcium phosphate (CaP) coated titanium alloy Ti6Al4V. The characterization of this material was performed by means of light microscopy, scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and X-ray energy dispersive spectroscopy (EDXS). The electrodeposited CaP coating was a tricalcium phosphate, and the release system was composed of microcapsules entrapped in an alginate film. We observed that the alginate matrix had a close contact with the coating. An intermediate layer containing calcium and phosphorus appeared at the interface between the alginate matrix and the CaP coating. These results allowed us to conclude that the association of two techniques, i.e. electrodeposition followed by deposition of a calcium alginate matrix, led to the elaboration of a new biomaterial.     

Microstructural investigation into calcium phosphate biomaterials by spatially resolved cathodoluminescence

From cathodoluminescence (CL) investigations of synthetic and natural calcium phosphates it can be concluded that the CL of pure synthetic apatite is mainly characterized by intrinsic luminescence, whereas the luminescence of naturally occurring apatites is frequently activated by trace elements. CL revealed internal structures within plasma‐sprayed hydroxyapatite coatings which were not discernible by SEM‐BSE imaging. However, cathodoluminescence microscopy alone can presently not be used in every case to characterize synthetic calcium phosphate biomaterials because of the dominant intrinsic blue CL emission. In the future, optimum results will likely be achieved by using a combination of CL microscopy and spectroscopy with other spatially resolved analytical methods such as SEM‐BSE, SEM‐CL or micro‐Raman spectroscopy. In the present study, different types of tetracalcium phosphate dental cements could be distinguished due to varying CL colours and CL spectra that are caused by a different content of impurity Mn. These results emphasize the advantages of spectral CL measurements for spatially resolved detection of trace elements in solids.     

QF/PEN复合生物材料的制备与表征

通过挤出法制备了石英纤维(quartz fiber,QF)/聚萘二甲酸乙二醇酯(poly ethylene naph-thalate,PEN)复合材料,通过燃烧实验对复合材料中石英纤维含量和材料的均一性进行了检测;用材料力学实验机测试了材料的力学性能;通过IR、XRD、SEM对复合材料进行了表征;用L929成纤维细胞与材料复合培养进行了细胞毒性评价。结果表明,石英纤维在PEN基体中的分布均匀;QF与PEN基体之间有氢键的结合,形成了稳定的界面;复合材料的力学强度比单纯聚合物基体有明显增强,当纤维含量为30%和45%时,QF/PEN复合材料的拉伸强度分别为80.21和87.96MPa,弯曲强度分别为125.71和137.79MPa,与骨组织生物力学匹配;细胞实验表明两类复合材料细胞毒性为1级,无细胞毒性。可见,QF/PEN复合材料是一种潜在的承重骨修复材料。     

Preparation and characterization of novel silica-butyrylchitosan hybrid biomaterials*

Novel silica-butyrylchitosan hybrid biomaterials were produced by a sol–gel technique, using butyrylchitosan as the organic species incorporated into the silicon alkoxide (TEOS) based network. 3-acryloxypropyl trimethoxysilane (MPTMS) was used effectively to combine the organic and inorganic species to form uniform hybrid biomaterials. All the samples made were in the form of thin, flexible films with transparent clarity. The blood-clotting and platelet adhesion assay confirmed that these hybrid biomaterials displayed potential good blood compatibility.     

Preparation and characterization of injectable calcium phosphate cement paste modified by polyethylene glycol-6000

An ICPC with high structure recoverability and paste stability was successfully developed directly incorporating PEG-6000 into the liquid phase of CPC. The rheological behavior of ICPC was investigated with rheometric scientific ARES902-30004 controlled strain rheometer. Novel approaches of flow rate, shear thinning index (SI), shear stress slowdown (Δτ) and thixotropy loop area have been applied to assess the injectability and structure recoverability of the ICPC paste. The addition of PEG-6000 to ICPC resulted in a thixotrophic structure with shortened setting time, slightly increased viscosity, larger thixotropic hysteresis loop area and lower Δτ, with the improvement largely dependent on the PEG-6000 content. With acceptable injectability and shortened setting time, ICPC (1%) showed the lowest Δτ and the highest SI, endowing the paste good structure recoverability and paste stability. The ICPC (1%) was bioactive and facilitated cell attachment and proliferation. The optimized ICPC (1%) paste with a relatively good structure stability and paste stability may serve as a good candidate for tooth root-canal fillings and percutaneous vertebroplasty in microinvasive surgery.     

磷酸钙骨水泥/明胶复合组织工程支架材料的制备及其结构与性能

磷酸钙骨水泥组织工程支架材料具有良好的生物相容性和骨传导性,是一种良好的骨组织工程支架材料,但是这种材料存在力学性能差的缺点,限制了它的应用.本文采用生物相容性良好的可降解明胶材料与磷酸钙骨水泥支架进行复合,制备出的明胶/磷酸钙骨水泥复合支架材料,其压缩强度可达3.7MPa,比复合前磷酸钙支架材料的强度提高了37倍,而且材料具有良好的柔韧性,适合用作为非承重部位骨组织缺损修复用组织工程支架材料.     

In vitro characterisation of calcium phosphate biomaterials loaded with lidocaine hydrochloride and morphine hydrochloride

Calcium phosphate substitutes drug delivery systems are well known substances used in minor bone void-filling to release their therapeutic agent in situ. Few studies associating anaesthetics and analgesics have been performed to date. The aim of this work was to study the association of the analgesic, morphine, and the local anaesthetic, lidocaine, with a calcium deficient apatite matrix. Three types of biomaterials i.e. powders, granules and blocks, were prepared by isostatic compression, wet granulation and a combination of the two, evaluated and compared. The chemical structure of the associated therapeutic agent was studied and the characteristics of the drug delivery systems were appraised in terms of drug release. The integrity of the lidocaine hydrochloride structure, as determined by RMN ¹H, was confirmed regardless of the formulation technique used (isostatic compression or wet granulation). However, analyses of morphine hydrochloride by RMN ¹H revealed slight structural modifications. The association and formulation techniques that were used made it possible to obtain an in vitro release time varying from 1 to 4 days for lidocaine hydrochloride and from 1 to 3 days for morphine hydrochloride.     

Preparation and properties of some magnesium-containing calcium phosphate cements

Attempts were made to prepare magnesium-containing calcium phosphate cements. These were successful at the composition CaMg₂(PO₄)₂xH₂O. X-ray diffraction showed that such a compound is not formed but that the cement consists of magnesium phosphate precipitated on the calcium phosphate admixture. The pH of this formulation is around 10 during setting and after. The cement is injectable. Its setting time is about 10 min. In this study compressive strength values were as high as 11 MPa and the diametral tensile strength was over 2 MPa. Animal experiments must show whether it is suitable for replacement or augmentation of bone in non-load bearing situations.     

Preparation of octacalcium phosphate from calcium carbonate powder

We have studied a process for the preparation of apatite precursors through calcium carbonate conversion into dicalcium phosphate dihydrate, which is then hydrolyzed to octacalcium phosphate. The process enables the preparation of both phase-pure octacalcium phosphate and calcium phosphate mixtures with variable dicalcium phosphate dihydrate : octacalcium phosphate and hydroxyapatite : octacalcium phosphate ratios.     

Developments in injectable multiphasic biomaterials. The performance of microporous biphasic calcium phosphate granules and hydrogels

Calcium phosphate bioceramic granules associated with hydrosoluble polymers were developed as bone substitutes for various maxillofacial and orthopaedic applications. These injectable bone substitutes, support and regenerate bone tissue and resorb after implantation. The efficiency of these multiphasic materials is due to the osteogenic and osteoconductive properties of the microporous biphasic calcium phosphate. The associated hydrosoluble polymers are considered as carriers in order to achieve the rheological properties of injectable bone substitutes (IBS). In this study, we used 2 semi synthetic hydrosoluble polymers of polysaccharidic origin. The hydroxy propyl methyl cellulose (HPMC), with and without silane, was combined with microporous BCP granules. The presence of silane induced considerable gelation of the suspension. The 2 IBS used (without gelation, IBS1, with gelation, IBS2) were implanted in critical size femoral epiphysis defects in rabbits. No foreign body reactions were observed in either sample. However, because of the higher density from gelation, cell colonisation followed by bone tissue ingrowth was delayed over time with IBS2 compared to the IBS1 without gelation. The results showed resorption of the BCP granule and bone ingrowth at the expense of both IBS with different kinetics. This study demonstrates that the hydrogel cannot be considered merely as a carrier. The gelation process delayed cell and tissue colonisation by slow degradation of the HPMC Si, compared to the faster release of HPMC with IBS1, in turn inducing faster permeability and spaces for tissue ingrowth between the BCP granules.     

PVA复合磷酸钙骨水泥的制备和性能研究

将含有不同质量分数聚乙烯醇(PVA)的PVA-KH2PO4-Na2HPO4体系缓冲溶液作为骨水泥的调和液,将其与磷酸钙骨水泥粉末混合后成型。将试样在接近生理条件(相对湿度100%,温度(37±1)℃)下养护24h,发现PVA掺入量为1%时的抗压强度达到31.71MPa,比未掺入的提高了将近70%。     

Preparation and mechanical properties of calcium phosphate/copoly-L-lactide composites

New artificial bone materials were prepared using calcium phosphates, hydroxyapatite and -tricalicum phosphate, and copoly-L-lactide, CPLA. Calcium phosphate powder and CPLA were mixed at 453 K for 10 min with various mixing ratios. Scanning electron microscope observations indicated that the composites of -tricalicum phosphate and CPLA were homogeneously dispersed and highly adhesive. Youngs modulus of the composites was the same as bone, and bending strength was over half that of bone. The improvement of Youngs modulus compared to the original two materials was due to a composite effect. The composites are expected to be usable as artificial bone materials.     

Preparation of porous apatite granules from calcium phosphate cement

A versatile method for preparing spherical, micro- and macroporous (micro: 2–10 and macro: 150–550 μm pores), carbonated apatitic calcium phosphate (Ap-CaP) granules (2–4 mm in size) was developed by using NaCl crystals as the porogen. The entire granule production was performed between 21 and 37 °C. A CaP cement powder, comprising α-Ca₃(PO₄)₂ (61 wt.%), CaHPO₄ (26%), CaCO₃ (10%) and precipitated hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂ (3%), was dry mixed with NaCl crystals varying in size from 420 μm to 1 mm. Cement powder (35 wt.%) and NaCl (65 wt.%) mixture was kneaded with an ethanol–Na₂HPO₄ initiator solution, and the formed dough was immediately agitated on an automatic sieve shaker for a few minutes to produce the spherical granules. Embedded NaCl crystals were then leached out of the granules by soaking them in deionized water. CaP granules were micro- and macroporous with a total porosity of 50% or more. Granules were composed of carbonated, poorly crystallized, apatitic CaP phase. These were the first spherical and porous CaP granules ever produced from a self-setting calcium phosphate cement. The granules reached their final handling strength at the ambient temperature through the cement setting reaction, without having a need for sintering. Certain commercial equipment, instruments or materials are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the author, nor does it imply that the equipment or materials identified are necessarily the best available for the purpose.