Journal of Materials Science: Materials in Medicine

Koh, Mi-Young; Kamitakahara, Masanobu; Kim, Ill; Kikuta, Koichi; Ohtsuki, Chikara

doi: 10.1007/s10856-009-3868-0pmid: 19756965

The osteoconduction potential of artificial materials is usually evaluated in vitro by apatite formation in a simulated body fluid (SBF) proposed by Kokubo and his colleagues. This paper reports the compositional dependence of apatite formation on organic–inorganic hybrids in the CaO–SiO2–PO5/2–poly(tetramethylene oxide) system, initiated from tetraethoxysilane (TEOS), triethyl phosphate (OP(OEt)3), calcium chloride (CaCl2) and poly(tetramethylene oxide)(PTMO) modified with alkoxysilane. Formation of an apatite layer was observed on the surface of the organic–inorganic hybrids with molar ratios of TEOS/OP(OEt)3 ranging from 100/0 to 20/80. The rate of apatite formation remarkably decreased when the hybrids were synthesized with TEOS/OP(OEt)3 ratios of 40/60 or less. Hybrids without TEOS showed no apatite formation in SBF for up to 14 days. Addition of small amounts of OP(OEt)3 to TEOS in the hybrids led to the high dissolution of calcium and silicate, while addition of large amounts of OP(OEt)3 decreased the dissolution of calcium and silicate ions and resulted in reduced apatite formation regardless of the dissolution of phosphate ions from the hybrids.

Jayasuriya, A.; Kibbe, Shane

doi: 10.1007/s10856-009-3874-2pmid: 19756963

The aim of this study was to prepare bone like mineral (BLM) layers rapidly on the exterior surfaces of chitosan (CS) microparticles (MPs). The CS MPs were fabricated using a scale-up double emulsification method. The CS MPs were in the spherical shape and the size of 30–60 μm. The MPs were then placed in 5× concentrated simulated body fluid (5 × SBF) and allowed to undergo biomineralization to form a BLM layers on the surface of CS MPs at 37°C over a 24 h period. The BML layers on the exterior surface of CS MPs were characterized using wide angle X-ray diffraction (XRD), Fourier transform infrared microscopy (FTIR), and scanning electron microscopy (SEM). Insulin like growth factor-1 (IGF-1) was dissolved at a concentration of 1 μg/ml in 5 × SBF to incorporate into the BLM layer. The CS MPs (100 mg) were incubated in a sample of 4 ml of 5 × SBF containing IGF-1 at a concentration of 1 μg/ml for 24 h. The IGF-1 release from BML layers on CS MPs were studied by placing MPs in 4 ml of phosphate buffered saline (PBS) and incubating MPs at 37°C for 30 days. Samples (100 μl) were taken over the course of the 30 days and analyzed using Enzyme-linked Immunosorbent assay (ELISA). The release IGF-1 from BML layers was in a burst manner followed by a sustained release during the 30-day period. This study suggests that the CS MPs have the potential to be used to help deliver therapeutic drugs to localized areas and hence increase and accelerate bone growth.

Quilitz, Mario; Steingröver, Klaus; Veith, Michael

doi: 10.1007/s10856-009-3875-1pmid: 19768396

Nanoscaled hydroxyapatite (n-HAp) was prepared by a wet chemical precipitation method, pressed to pellets and sintered at various temperatures between 900 and 1200°C. With input stoichiometries of Ca/P ratios between 1.4 and 2.0, compositions in the substoichiometric range of Ca/P between 1.45(1) and 1.62(3) were determined after preparation. After sintering, final values of the Ca/P ratio between 1.45(8) and 1.66(4) were found. Capacitances and dielectric losses were determined in the frequency range between 20 Hz and 1 MHz and dielectric constants calculated from the capacitances. Dependencies of the dielectric properties on the composition, as well as on sintering temperature and frequencies were investigated. The dielectric constants generally tend to increase with increasing Ca-content. Different behaviour was observed for low frequencies (below 103 Hz) and for compositions far from the stoichiometric point of hydroxyapatite (Ca/P: 1.67). Comparable results were found for dielectric losses.

Tejero, Ricardo; Bierbaum, Susanne; Douglas, Timothy; Reinstorf, Antje; Worch, Hartmut; Scharnweber, Dieter

doi: 10.1007/s10856-009-3879-xpmid: 19941043

Glucuronic acid (GlcA) and phosphoserine (pS) carrying acidic functional groups were used as model molecules for glycosaminoglycans and phosphoproteins, respectively to mimic effects of native biomolecules and influence the mineralization behaviour of collagen I. Collagen substrates modified with GlcA showed a stable interaction between GlcA and collagen fibrils. Substrates were mineralized using the electrochemically assisted deposition (ECAD) in a Ca2+/H x PO 4 (3−x) electrolyte at physiological pH and temperature. During mineralization of collagen–GlcA matrices, crystalline hydroxyapatite (HA) formed earlier with increasing GlcA content of the collagen matrix, while the addition of pS to the electrolyte succeeded in inhibiting the transformation of preformed amorphous calcium phosphate (ACP) to HA. The lower density of the resulting mineralization and the coalesced aggregates formed at a certain pS concentration suggest an interaction between calcium and the phosphate groups of pS involving the formation of complexes. Combining GlcA-modified collagen and pS-modified electrolyte showed dose-dependent cooperative effects.

Suwanprateeb, J.; Suvannapruk, W.; Wasoontararat, K.

doi: 10.1007/s10856-009-3883-1pmid: 19784760

The conversion of newly developed three dimensionally printed calcium sulfate hemihydrate (70–90% wt/wt CaSO4·0.5·H2O) based materials to calcium phosphate bioceramics by phosphorization in di-sodium hydrogen phosphate solution at 80°C for 4, 8, 16 and 24 h was studied. It was found that transformation rate, phase composition and mechanical properties were influenced by porosity in the fabricated samples and by the duration of the phosphorization treatment. Formulation with 85% CaSO4·0.5 H2O showed the fastest transformation rate and resulted in the highest flexural modulus and strength. Depending on the materials formulation, XRD, FT-IR and EDS revealed that calcium deficient hydroxyapatite (CDHA) or a mixture of CDHA and dicalcium phosphate anhydrous (DCPA) were the resulting phases in the transformed samples. After cell culturing for 14 and 21 days, human osteoblast cells were observed to attach to and attain normal morphology on the surface of the transformed sample containing 85% CaSO4·0.5 H2O. Various sizes and shapes of mineralized nodules were also found after 21 days.

Pina, S.; Torres, P.; Ferreira, J.

doi: 10.1007/s10856-009-3890-2pmid: 19851845

The influence of magnesium- and strontium-substitutions on injectability and mechanical performance of brushite-forming α-TCP cements has been evaluated in the present work. The effects of Mg- and Sr-substitutions on crystalline phase composition and lattice parameters were determined through quantitative X-ray phase analysis and structural Rietveld refinement of the starting calcium phosphate powders and of the hardened cements. A noticeable dependence of injectability on the liquid-to-powder ratio (LPR), smooth plots of extrusion force versus syringe plunger displacement and the absence of filter pressing effects were observed. For LPR values up to 0.36 ml g−1, the percentage of injectability was always higher and lower for Mg-containing cements and for Sr-containing cements, respectively, while all the pastes could be fully injected for LPR > 0.36 ml g−1. The hardened cements exhibited relatively high wet compressive strength values (~17–25 MPa) being the Sr- and Mg-containing cements the strongest and the weakest, respectively, holding an interesting promise for uses in trauma surgery such as for filling bone defects and in minimally invasive techniques such as percutaneous vertebroplasty to fill lesions and strengthen the osteoporotic bone.

Yamaguchi, Seiji; Takadama, Hiroaki; Matsushita, Tomiharu; Nakamura, Takashi; Kokubo, Tadashi

doi: 10.1007/s10856-009-3904-0pmid: 19842018

Ti–15Zr–4Nb–4Ta alloy free from cytotoxic elements shows high mechanical strength and high corrosion resistance. However, simple NaOH and heat treatments cannot induce its ability to form apatite in the body environment. In the present study, this alloy was found to exhibit high apatite-forming ability when it was treated with NaOH and CaCl2 solutions, and then subjected to heat and hot water treatments to form calcium titanate, rutile, and anatase on its surface. Its high apatite-forming ability was maintained even in 95% relative humidity at 80°C after 1 week. The surface layer of the treated alloy had scratch resistance high enough for handling hard surgical devices. Thus, the treated alloy is believed to be useful for orthopedic and dental implants.

Generosi, A.; Rau, J.; Rossi Albertini, V.; Paci, B.

doi: 10.1007/s10856-009-3905-zpmid: 19834786

The crystallization process in recently developed toothpastes, containing nanoparticles of carbonate substituted hydroxyapatite (nano-CHA), was investigated. For this purpose, the non-conventional Energy Dispersive X-Ray Diffraction technique, that demonstrated to be a powerful tool to follow in situ phase transformations, was applied, for the first time, to products of pharmaceutical-cosmetic interest. Two types of toothpastes, containing 15 and 20 wt% of nano-CHA, respectively, have been studied. It was observed that, after mixing the toothpastes with water and saliva in order to reproduce in vivo conditions, a crystallization of nano-CHA takes place. Such process occurs in a characteristic time of (22 ± 1) min for the toothpaste containing 15 wt% of nano-CHA and of (3.9 ± 0.5) min for the one containing 20% of nano-CHA. For both toothpastes, a 10% increase in grain dimensions was observed over an average characteristic time of (55 ± 5) min.

Walton, Robin; Brand, David; Czernuszka, Jan

doi: 10.1007/s10856-009-3910-2pmid: 19851839

Type I collagen is widely used in various different forms for research and commercial applications. Different forms of collagen may be classified according to their source, extraction method, crosslinking and resultant ultrastructure. In this study, afibrillar and reconstituted fibrillar films, derived from acid soluble and pepsin digested Type I collagen, were analysed using Lateral Force Microscopy (LFM), Fourier Transform Infra-Red Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and enzymatic stability assays to asses the influence of telopeptides, fibrils and crosslinking. LFM proved to be a useful technique to confirm an afibrillar/fibrillar ultrastructure and to elucidate fibril diameters. FTIR has proved insensitive to ultrastructural differences involving telopeptides and fibrils. DSC results showed a significant increase in Td for crosslinked samples (+22–28°C), and demonstrated that the thermal behaviour of hydrated, afibrillar films is more akin to reconstituted fibrillar films than monomeric solutions. The enzymatic stability assay has provided new evidence to show that afibrillar films of Type I collagen can be significantly more resistant to collagenase (by up to 3.5 times), than reconstituted fibrillar films, as a direct consequence of the different spatial arrangement of collagen molecules. A novel mechanism for this phenomenon is proposed and discussed. Additionally, the presence of telopeptide regions in afibrillar tropocollagen samples has been shown to increase resistance to collagenase by greater than 3.5 times compared to counterpart afibrillar atelocollagen samples. One-factor ANOVA analysis, with Fisher’s LSD post-hoc test, confirms these key findings to be of statistical significance (P < 0.05). The profound physicochemical effects of collagen ultrastructure demonstrated in this study reiterates the need for comprehensive materials disclosure and classification when using these biomaterials.

Wang, Jianfeng

doi: 10.1007/s10856-009-3919-6pmid: 19882305

A structural model with three compositional phases and two levels of hierarchical organization is proposed for predicting Young’s modulus of porous bones with microstructural variations and anisotropy based on their geometric similarity to metal foams. It has been shown that the proposed single model provides predictions of Young’s modulus with high accuracy up to ±30% for cortical and cancellous bones compared with measured data from the literature. In addition, the conversion of the solid bone shape from “Plate-like” to “Rod-like” at a porosity of 70% or higher (BV/TV 30% or lower)—verified by observations—can be predicted using the proposed model.