Analysis of Bone Mineral Profile After Prolonged Every-Other-Day Feeding in C57BL/6J Male and Female Mice

Intermitted fasting or every-other-day feeding (EOD) has many positive effects in rodents and humans. Our goal was to describe how EOD influences bone mineral composition in female and male mice under prolonged EOD feeding. Male and female adult mice were fed EOD for 9 months. After this time, we used a direct method of measurement of mineral components in ashes of long bones (humerus and radius) to estimate the content of calcium (Ca), phosphorus (P), potassium (K), magnesium (Mg), and sodium (Na). We also performed histological analysis of sections of long bones. We found no significant changes in mineral composition between ad libitum and EOD fed males and females. We noted higher Ca and P contents in control males vs. females and lower content of Mg in control males vs. females. We observed the presence of marrow adipose tissue (MAT) in sections of EOD-fed females. EOD without supplementation during feeding days did not increase loss of mineral content of bones in C57BL/6J mice, but the presence of MAT only in EOD females indicates a gender-dependent response to EOD treatment in C57BL/6J mice.

Giant cells and osteoclasts present in bone grafted with nacre differ by nuclear cytometry evaluated by texture analysis

Nacre (mother of pearl) is a natural biomaterial used to prepare orthopedic devices. We have implanted screws and plates made with nacre in five sheeps. Bone were harvested after two months and embedded in poly(methyl methacrylate). Blocks were saws and the thick slabs were grinded, polished and surface stained. Sections were photographed at an ×1000 magnification. Giant cells were found in contact with nacre in eroded areas and true osteoclasts were found at distance in the neighboring bone in Howship lacunae. A texture analysis of the nuclei of giant cells and osteoclasts was done using the run-length method of the MaZda freeware. The size of the nuclei was reduced in osteoclast and their mean gray level appeared reduced. Texture analysis revealed that chromatin had a completely different pattern in giant cells when compared to osteoclasts. Giant cells had a fine repartition of the chromatin with large clear areas around prominent nucleoli. On the contrary, osteoclast nuclei had chromatin blocks evenly dispersed in the nuclei. This reflects the different origin of these cells expressing different functions.

Chemical-Physical Characterization and in vitro Preliminary Biological Assessment of Hyaluronic Acid Benzyl Ester-Hydroxyapatite Composite

HYAFF®11 is a biocompatible, biodegradable benzyl ester of hyaluronic acid. However, in order to use it for orthopedic application, its mechanical performance needs to be improved. In this study, a novel composite based on HYAFF®11 polymer matrix reinforced with hydroxylapatite (HA) has been developed. Its advantage is having a similar component of the mineral phase of bone resulting in favorable osteoconductive properties. The present study has examined the compressive mechanical and surface chemical-physical properties of the novel HYAFF®11-HA composite. Preliminary biological investigations, including pH and cytotoxicity studies of the material extracts, have also been performed using an in vitro primary human osteoblast-like cell model. Moreover, protein, especially fibronectin adsorption has been investigated following incubation in culture medium and human plasma. The results show a grainy surface topography composed mainly of C, P, and Ca, with a Ca/P atomic ratio indicating HA on the composite surface. Mechanical analysis shows an improvement of the compressive properties of HYAFF11 matrix, both in the dry and swollen states, with values in the range of that of spongy bone. No cytotoxic effects and no inhibition of cell proliferation have been observed in the presence of the material extracts with pH values within acceptable ranges for cell vitality. Protein studies reveal a similar pattern, but a higher amount of fibronectin following incubation in human plasma when compared with culture medium. The results show that the novel HYAFF®11-HA composite shows a great potential for application in orthopedic fields, especially as vertebral trabecular bone substitute.

In vivo Performance of Biodegradable Calcium Phosphate Glass Ceramics using the Rabbit Model: Histological and SEM Observation

Two MK5 (45CaO-45P2O5-5MgO-5K2O, in mol%) and MT13 (45CaO-37P2O5-5MgO-13TiO2, in mol%) glasses are prepared in the meta- and pyrophosphate regions and crystallized to obtain MK5B and MT13B, respectively. MK5B was obtained by controlled crystallization, and MT13B by powder sintering. As a result of these heat treatment processes, the crystalline phases precipitated in the glassy matrix are KCa(PO3)3, β-Ca(PO3)2, β-Ca2P2O7and Ca4P6O19phases for MK5B and CaTi4(PO4)6, TiP2O7, α- and β-Ca2P2O7phases for MT13B. To assess the in vivo biological behavior of these glass ceramics, a mixed granulometry in the range 250-355 μm and 355-425 μm with a ratio of 1/1 was implanted for 2, 4, and 12 weeks in the tibiae of Japanese white rabbits. The results showed that the in vivo behavior was strongly affected by their solubility. All implanted materials, MK5B and MT13B, and β-tricalcium phosphate (β-TCP) as control material, showed signs of degradation in vivo. However, the levels of degradation were quite different throughout the implantation periods. The highest degradation was observed for MK5B glass ceramic and the lowest for MT13B with β-TCP in-between. All implanted materials allow for new bone formation in the bone defect area. At the longest implantation period (12 weeks), the MT13B and β-TCP materials were almost completely surrounded by new bone tissue, whereas MK5B showed some unfilled spaces. This behavior is discussed in terms of the high degradation observed in previous studies.

Influence of Starting Powders on Hydroxyapatite Coatings Fabricated by Room Temperature Spraying Method

Three types of raw materials were used for the fabrication of hydroxyapatite coatings by using the room temperature spraying method and their influence on the microstructure and in vitro characteristics were investigated. Starting hydroxyapatite powders for coatings on titanium substrate were prepared by a heat treatment at 1100 °C for 2 h of bovine bone, bone ash, and commercial hydroxyapatite powders. The phase compositions and Ca/P ratios of the three hydroxyapatite coatings were similar to those of the raw materials without decomposition or formation of a new phase. All hydroxyapatite coatings showed a honeycomb structure, but their surface microstructures revealed different features in regards to surface morphology and roughness, based on the staring materials. All coatings consisted of nano-sized grains and had dense microstructure. Inferred from in vitro experiments in pure water, all coatings have a good dissolution-resistance and biostability in water.

The in vivo performance of CaP/PLGA composites with varied PLGA microsphere sizes and inorganic compositions

Enrichment of calcium phosphate (CaP) bone substitutes with poly(lactic-co-glycolic acid) (PLGA) microspheres to create porosity overcomes the problem of poor CaP degradation. The degradation of CaP-PLGA composites can be customized by changing the physical and chemical properties of PLGA and/or CaP. However, the effect of the size of dense (solid rather than hollow) PLGA microspheres in CaP has not previously been described. The present study aimed at determining the effect of different dense (i.e. solid) PLGA microsphere sizes (small (S) ~20μm vs. large (L) ~130μm) and of CaP composition (CaP with either anhydrous dicalcium phosphate (DCP) or calcium sulphate dihydrate (CSD)) on CaP scaffold biodegradability and subsequent bone in-growth. To this end mandibular defects in minipigs were filled with pre-set CaP-PLGA implants, with autologous bone being used as a control. After 4weeks the autologous bone group outperformed all CaP-PLGA groups in terms of the amount of bone present at the defect site. On the other hand, at 12weeks substantial bone formation was observed for all CaP-PLGA groups (ranging from 47±25% to 62±15%), showing equal amounts of bone compared with the autologous bone group (82±9%), except for CaP with DCP and large PLGA microspheres (47±25%). It was concluded that in the current study design the difference in PLGA microsphere size and CaP composition led to similar results with respect to scaffold degradation and subsequent bone in-growth. Further, after 12weeks all CaP-PLGA composites proved to be effective for bone substitution.

Evaluation of collagen/heparin coated TCP/HA granules for long-term delivery of BMP-2

Bone morphogenetic proteins (BMPs) are the most potent osteoinductive growth factors. However, a delivery system is essential to take advantage of the osteoinductive effect of BMPs. The purpose of this study was to develop a sustained delivery system for recombinant human bone morphogenetic protein-2 (BMP-2). We covalently attached heparin to a cross-linked collagen type I coated tricalciumphosphate/hydroxyapatite (TCP/HA) bone substitute and subsequently loaded it with BMP-2. To systematically evaluate the contribution of each component with respect to the binding and release of BMP-2, six constructs were prepared and characterized: TCP/HA, TCP/HA with collagen (TCP/HACol), and TCP/HA with collagen and heparin (TCP/HAColHep) with and without BMP-2 (B). More BMP-2 bound to the TCP/HAColHep + B (92.9 ± 4.8 ng BMP-2/mg granule) granules as compared to the TCP/HACol + B (69.0 ± 9.6 ng BMP-2/mg granule) and TCP/HA + B granules (62.9 ± 5.4 ng BMP-2/mg granule). No difference in release pattern was found between the TCP/HA + B and TCP/HACol + B granules. Up to day 14, BMP-2 was still bound to the TCP/HAColHep + B granules, whereas most BMP had been released from TCP/HACol + B and TCP/HA + B granules at that time. After 21 days most BMP-2 also had been released from the TCP/HAColHep + B granules. The local and sustained delivery system for BMP-2 developed in this study may be useful as a carrier for BMP-2 and could possibly enhance bone regeneration efficacy for the treatment of large bone defects.

A hybrid PHB–hydroxyapatite composite for biomedical application: production, in vitro and in vivo investigation

Samples of a hybrid composite of polyhydroxybutyrate (PHB), a biodegradable polyester, and hydroxyapatite (HA), with different PHB/HA ratios, have been prepared using mechanical-physical method. Electron microscopy, X-ray structure analysis and differential thermal analysis have been used to investigate the structure and physicochemical properties of the composite, depending on the PHB/HA ratio. The properties of the surface of the HA-loaded composite are significantly different from those of the pure polymer. As the HA percentage in the composite increases, free interface energy, the cohesive force, i.e., the strength of the adhesive bond between the composite surface and the water phase, and surface wettability increase. The HA percentage of the composite does not influence its melting temperature, but affects the temperature for the onset of decomposition: as the HA content increases from 0 to 10% (w/w), Td decreases from 260 degrees C to 225 degrees C. The degree of crystallinity of PHB/HA increases from 77% to 89% with an increase in the HA fraction from 10% to 50%. Functional properties of the composites have been investigated in vitro and in vivo. The best parameters of growth and differentiation of murine marrow osteoblasts are registered on PHB/HA samples containing 10% and 20% HA. In ectopic bone formation assay it has been proven that the hybrid PHB/HA composites can function as scaffolds and that bone tissue develops on their surface and in pores.

Charge specific protein placement at submicrometer and nanometer scale by direct modification of surface potential by electron beam

The understanding and the precise control of protein adsorption is extremely important for the development and optimization of biomaterials. The challenge resides in controlling the different surface properties, such as surface chemistry, roughness, wettability, or surface charge, independently, as modification of one property generally affects the other. We demonstrate the creation of electrically modified patterns on hydroxyapatite by using scanning electron beam to tailor the spatial regulation of protein adsorption via electrostatic interactions without affecting other surface properties of the material. We show that domains, presenting modulated surface potential, can be created to precisely promote or reduce protein adsorption.

Biofilm formation on bone grafts and bone graft substitutes: comparison of different materials by a standard in vitro test and microcalorimetry

We analyzed the initial adhesion and biofilm formation of Staphylococcus aureus (ATCC 29213) and S. epidermidis RP62A (ATCC 35984) on various bone grafts and bone graft substitutes under standardized in vitro conditions. In parallel, microcalorimetry was evaluated as a real-time microbiological assay in the investigation of biofilm formation and material science research. The materials beta-tricalcium phosphate (beta-TCP), processed human spongiosa (Tutoplast) and poly(methyl methacrylate) (PMMA) were investigated and compared with polyethylene (PE). Bacterial counts (log(10) cfu per sample) were highest on beta-TCP (S. aureus 7.67 +/- 0.17; S. epidermidis 8.14 +/- 0.05) while bacterial density (log(10) cfu per surface) was highest on PMMA (S. aureus 6.12 +/- 0.2, S. epidermidis 7.65 +/- 0.13). Detection time for S. aureus biofilms was shorter for the porous materials (beta-TCP and processed human spongiosa, p < 0.001) compared to the smooth materials (PMMA and PE), with no differences between beta-TCP and processed human spongiosa (p > 0.05) or PMMA and PE (p > 0.05). In contrast, for S. epidermidis biofilms the detection time was different (p < 0.001) between all materials except between processed human spongiosa and PE (p > 0.05). The quantitative analysis by quantitative culture after washing and sonication of the material demonstrated the importance of monitoring factors like specific surface or porosity of the test materials. Isothermal microcalorimetry proved to be a suitable tool for an accurate, non-invasive and real-time microbiological assay, allowing the detection of bacterial biomass without removing the biofilm from the surface.

Ultrastructural evaluation of in vitro mineralized calcium phosphate phase on surface phosphorylated poly(hydroxy ethyl methacrylate-co-methyl methacrylate)

The in vitro functionality of surface phosphorylated poly(hydroxy ethyl methacrylate-co-methyl methacrylate), poly(HEMA-co-MMA) to induce bioinspired mineralization of calcium phosphate phase is evaluated. The primary nucleation of calcium phosphate on the surface phosphorylated copolymer occurs within 3 days of immersion when immersed in 1.5x simulated body fluid and the degree of mineralization is proportional to the hydroxy ethyl methacrylate content in the copolymer. The calcium phosphate phase is identified as hydroxyapatite by X-Ray diffraction analysis. The transmission electron microscopic evaluation combined with selected area diffraction pattern and energy dispersive analysis exemplified that the primary nuclei of amorphous calcium phosphate transforms to crystalline needle like calcium rich apatite, within a period of 3 days immersion in simulated body fluid. The atomic force microscopic results corroborate the c-axis growth of the crystals within 3 days immersion in SBF.

Development of a novel bone grafting material using autogenous teeth

We developed a novel bone grafting material that incorporates autogenous teeth (AutoBT), and provided the basis for its clinical application. AutoBT contains organic and inorganic mineral components and is prepared from autogenous grafting material, thus eliminating the risk of an immune reaction that may lead to rejection. AutoBT was used at the time of implant placement, simultaneously with osteoinduction surgery, and excellent bony healing by osteoinduction and osteoconduction was confirmed.

In vitro cellular adhesion and antimicrobial property of SiO2-MgO-Al2O3-K2O-B2O3-F glass ceramic

The aim of the present study was to examine the cellular functionality and antimicrobial properties of SiO(2)-MgO-Al(2)O(3)-K(2)O-B(2)O(3)-F glass ceramics (GC) containing fluorophlogopite as major crystalline phase. The cellular morphology and cell adhesion study using human osteoblast-like Saos-2 cells and mouse fibroblast L929 cells reveals good in vitro cytocompatibility of GC. The potential use of the GC for biomedical application was also assessed by in vitro synthesis of the alkaline phosphatase (ALP) activity of Saos-2 cells. It is proposed that B(2)O(3) actively enhances the cell adhesion and supports osteoconduction process, whereas, fluorine component significantly influences cell viability. The Saos-2 and L929 cells on GC shows extensive multidirectional network of actin cytoskeleton. The in vitro results of this study illustrate how small variation in fluorine and boron in base glass composition influences significantly the biocompatibility and antimicrobial bactericidal property, as evaluated using a range of biochemical assays. Importantly, it shows that the cell viability and osteoconduction can be promoted in glass ceramics with lower fluorine content. The underlying reasons for difference in biological properties are analyzed and reported. It is suggested that oriented crystalline morphology in the lowest fluorine containing glass ceramic enhanced cellular spreading. Overall, the in vitro cell adhesion, cell flattening, cytocompatibility and antimicrobial study of the three different compositions of glass ceramic clearly reveals that microstructure and base glass composition play an important role in enhancing the cellular functionality and antimicrobial property.

Biomorphous porous hydroxyapatite-ceramics from rattan (Calamus Rotang)

The three-dimensional, highly oriented pore channel anatomy of native rattan (Calamus rotang) was used as a template to fabricate biomorphous hydroxyapatite (Ca(5)(PO(4))(3)OH) ceramics designed for bone regeneration scaffolds. A low viscous hydroxyapatite-sol was prepared from triethyl phosphite and calcium nitrate tetrahydrate and repeatedly vacuum infiltrated into the native template. The template was subsequently pyrolysed at 800 degrees C to form a biocarbon replica of the native tissue. Heat treatment at 1,300 degrees C in air atmosphere caused oxidation of the carbon skeleton and sintering of the hydroxyapatite. SEM analysis confirmed detailed replication of rattan anatomy. Porosity of the samples measured by mercury porosimetry showed a multimodal pore size distribution in the range of 300 nm to 300 microm. Phase composition was determined by XRD and FT-IR revealing hydroxyapatite as the dominant phase with minimum fractions of CaO and Ca(3)(PO(4))(2). The biomorphous scaffolds with a total porosity of 70-80% obtained a compressive strength of 3-5 MPa in axial direction and 1-2 MPa in radial direction of the pore channel orientation. Bending strength was determined in a coaxial double ring test resulting in a maximum bending strength of approximately 2 MPa.

[Preparation and biocompatibility evaluation of novel cartilage acellular matrix sponge]

OBJECTIVE

To explore the method of preparing spongy and porous scaffold materials with swine articular cartilage acellular matrix and to investigate its applicability for tissue engineered articular cartilage scaffold.

METHODS

Fresh swine articular cartilage was freeze-dried and freeze-ground into microparticles. The microparticles with diameter of less than 90 microm were sieved and treated sequentially with TNE, pepsin and hypotonic solution for decellularization at cryogenic temperatures. Colloidal suspension with a mass/volume ratio of 2% was prepared by dissolving the microparticles into 1.5% HAc, and then was lyophilized for molding and cross-linked by UV radiation to prepare the decellularized cartilage matrix sponge. Physicochemical property detection was performed to identify aperture, porosity and water absorption rate. Histology and scanning electron microscope observations were conducted. The prepared acellular cartilage matrix sponge was implanted into the bilateral area of spine in 24 SD rats subcutaneously (experimental group), and the implantation of Col I sponge served as control group. The rats were killed 1, 2, 4, and 8 weeks after operation to receive histology observation, and the absorption and degeneration conditions of the sponge in vivo were analyzed. BMSCs obtained from femoral marrow of 1-week-old New Zealand white rabbits were cultured. The cells at passage 3 were cultured with acellular cartilage matrix sponge lixivium at 50% (group A), acellular cartilage matrix sponge lixivium at 100% (group B), and DMEM culture medium (group C), respectively. Cell proliferation was detected by MTT method 2, 4, and 6 days after culture.

RESULTS

The prepared acellular cartilage matrix sponge was white and porous. Histology observation suggested that the sponge scaffold consisted primarily of collagen without chondrocyte fragments. Scanning electron microscope demonstrated that the scaffold had porous and honeycomb-shaped structure, the pores were interconnected and even in size. The water absorption rate was 20.29% +/- 25.30%, the aperture was (90.66 +/- 21.26) microm, and the porosity of the scaffold was 90.10% +/- 2.42%. The tissue grew into the scaffold after the subcutaneous implantation of scaffold into the SD rats, angiogenesis was observed, inflammatory reaction was mild compared with the control group, and the scaffold was degraded and absorbed at a certain rate. MTT detection suggested that there were no significant differences among three groups in terms of absorbance (A) value 2 and 4 days after culturing with the lixivium (P > 0.05), but significant differences were evident among three groups 6 days after culturing with the lixivium (P < 0.05).

CONCLUSION

With modified treatment and processing, the cartilage acellular matrix sponge scaffold reserves the main components of cartilage extracellular matrix after thorough decellularization, has appropriate aperture and porosity, and provides even distribution of pores and good biocompatibility without cytotoxicity. It can be used as an ideal scaffold for cartilage tissue engineering.

Microspheres of Collagen/β-TCP with an Open Network Fibrillar Structure Strengthened by Chitosan

A novel method of preparing collagen/beta-tricalcium phosphate microspheres with chitosan as the mechanical strength enhancer has been developed in this study. The process involved firstly droplet formation by discharging a mixture of collagen, beta-tricalcium phosphates and alginate into an aqueous solution of CaCl(2) by extruding through an air jet-syringe at 4 degrees C. The gel beads thus formed were collected and subsequently coated with chitosan to stabilize the surface of gel bead. Collagen within the gel beads was then reconstituted while the entrapped alginate was liquefied and drained by incubating in phosphate buffer at 37 degrees C. Microspheres comprised of fibrillar collagen and well-dispersed beta-tricalcium phosphate particulates were obtained by this process. And the mechanical strength of these microspheres was significantly enhanced by chitosan coating. These chitosan-coated collagen/beta-tricalcium phosphate microspheres have an open fibrillar network structure with a great potential for future application as biodegradable bone grafting materials.

Quantitative assessment of growth factors in reaming aspirate, iliac crest, and platelet preparation

Large bony defects and non-unions are still a complication in trauma and orthopedic surgery. Treatment strategies include the use of autogenous materials (iliac crest), allogenic bone, bone substitutes, and currently stimulation with growth factors such as BMP-2, BMP-7 or the growth factors containing platelet-rich plasma (PRP). Another source of bone graft material might be the cuttings produced during intramedullary reaming. The aim of this study was to compare the quantity of various growth factors found within iliac crest, bony reaming debris, reaming irrigation fluid, and platelet-rich plasma. Iliac crest and reaming debris and irrigation samples were harvested during surgery. PRP was prepared from blood. The growth factors in the bony materials (iliac crest or reaming debris) and of the liquid materials (platelet-poor plasma (PPP), platelet-rich plasma (PRP) or reaming irrigation) were compared. Elevated levels of FGFa, PDGF, IGF-I, TGF-beta1 and BMP-2 were measured in the reaming debris as compared to iliac crest curettings. However, VEGF and FGFb were significantly lower in the reaming debris than from iliac crest samples. In comparing PRP and PPP all detectable growth factors, except IGF-I, were enhanced in the platelet-rich plasma. In the reaming irrigation FGFa (no measurable value in the PRP) and FGFb were higher, but VEGF, PDGF, IGF-I, TGF-beta1 and BMP-2 were lower compared to PRP. BMP-4 was not measurable in any sample. The bony reaming debris is a rich source of growth factors with a content comparable to that from iliac crest. The irrigation fluid from the reaming also contains growth factors.

Framework for optimal design of porous scaffold microstructure by computational simulation of bone regeneration

In bone tissue engineering using a biodegradable scaffold, geometry of the porous scaffold microstructure is a key factor for controlling mechanical function of the bone-scaffold system in the regeneration process as well as after the regeneration. In this study, we propose a framework for the optimal design of the porous scaffold microstructure by three-dimensional computational simulation of bone tissue regeneration that consists of scaffold degradation and new bone formation. The rate of scaffold degradation due to hydrolysis, that leads to decrease in mechanical properties, was simply assumed to relate to the water content diffused from the surface to the bulk material. For the new bone formation on both bone and scaffold surfaces, the rate equation of trabecular surface remodeling driven by mechanical stimulation was applied. Solving these two phenomena in the same time frame, the bone regeneration process in the bone-scaffold system was predicted by computational simulation using a voxel finite element method. The change in the mechanical function of the bone-scaffold system during the regeneration process was quantitatively evaluated by measuring the change in total strain energy, and this was used for the evaluation function to optimize the scaffold microstructure that provides the desired mechanical function during and after the bone regeneration process. A case study conducted for the scaffold with a simple microstructure demonstrated that the proposed simulation method could be applied to the design of a porous scaffold microstructure. In addition, the regeneration process was found to be very complex even though the simple rate equations for scaffold regeneration and new bone formation were used because of the coupling effects of these phenomena.

Cemented Cup Stability during Lever-Out Testing after Acetabular Bone Impaction Grafting with Bone Graft Substitutes Mixes Containing Morselized Cancellous Bone and Tricalcium Phosphate-Hydroxyapatite Granules

Bone defects after failed total hip arthroplasty can be reconstructed with impacted morselized bone grafts and a cemented cup. In the near future the amount of bone grafts available for surgical purposes will be insufficient. Ceramic calcium phosphates [tricalcium phosphate (TCP) and hydroxyapatite (HA)] have been widely considered as potential bone graft substitutes or bone graft extenders. In the past, mechanical experiments have been performed to determine implant stability of bone grafts and ceramic TCP-HA granules mixes under a compressive load. However, in-vivo migration studies suggest that shear loading may be equally important. This in-vitro study investigated the initial stability of cups reconstructed with various mixes of bone grafts and ceramic TCP-HA granules in a lever-out situation, where shearing is the predominant loading mode. It was found that the cups reconstructed with mixes of bone graft and TCP-HA granules exhibited greater mechanical stability than the cups reconstructed with bone grafts only. It is concluded that from a mechanical standpoint, when considering shear force resistance, 50–50 per cent volume mix and 25–75 per cent volume mix of morselized cancellous bone graft and TCP-HA granules both provide adequate initial cup stability and can be used for acetabular reconstructions with the bone impaction grafting technique.

Efficiency of 1H --> 31P NMR cross-polarization in bone apatite and its mineral standards

Human bone mineral was studied using solid-state 31P NMR with cross-polarization (CP) from protons. The CP efficiency was determined for trabecular and cortical bone tissue from human adults and compared with synthetic mineral standards. The study shows the similarity between carbonatoapatite of type B and bone mineral as shown by their CP behaviour. The method can be used for the characterization of synthetic apatite-based implant materials.

Structure and properties of clinical coralline implants measured via 3D imaging and analysis

The development and design of advanced porous materials for biomedical applications requires a thorough understanding of how material structure impacts on mechanical and transport properties. This paper illustrates a 3D imaging and analysis study of two clinically proven coral bone graft samples (Porites and Goniopora). Images are obtained from X-ray micro-computed tomography (micro-CT) at a resolution of 16.8 microm. A visual comparison of the two images shows very different structure; Porites has a homogeneous structure and consistent pore size while Goniopora has a bimodal pore size and a strongly disordered structure. A number of 3D structural characteristics are measured directly on the images including pore volume-to-surface-area, pore and solid size distributions, chord length measurements and tortuosity. Computational results made directly on the digitized tomographic images are presented for the permeability, diffusivity and elastic modulus of the coral samples. The results allow one to quantify differences between the two samples. 3D digital analysis can provide a more thorough assessment of biomaterial structure including the pore wall thickness, local flow, mechanical properties and diffusion pathways. We discuss the implications of these results to the development of optimal scaffold design for tissue ingrowth.

Synthesis and characterization of single-phase silicon-substituted α-tricalcium phosphate

Silicon-substituted calcium phosphate (CaP) powders with a Ca/(P+Si) ratio of 1.50 have been prepared by a wet chemical method, with silicon contents up to 2.16 weight percent (wt%). Sintering for 2 h at 1250 degrees C yields single-phase silicon-substituted alpha tricalcium phosphate (Si-alpha-TCP) for compositions between 0.59 and 1.14 wt% silicon. The sintered powders have been characterized with X-ray fluorescence (XRF) spectrometry, X-ray diffraction (XRD), attenuated total reflection infrared spectroscopy (ATR-IR) and transmission electron microscopy (TEM). Compositions with less than 0.59 wt% silicon result in mixtures of Si-alpha-TCP, beta-TCP, and calcium hydroxyapatite (HA), while compositions with more than 1.14 wt% silicon result in mixtures of Si-alpha-TCP and HA. The lattice parameters of single-phase Si-alpha-TCP prepared with 0.87 wt% silicon are a=12.874(1)A, b = 27.372(2) A, c = 15.225(1) A, and beta = 126.38(1) degrees .

Mechanical and histological evaluation of a PMMA-based bone cement modified with gamma-methacryloxypropyltrimethoxysilane and calcium acetate

Polymethylmethacrylate (PMMA) bone cement is widely used for prosthetic fixation in orthopaedic surgery; however, the interface between bone and cement is a weak zone. We developed a bioactive PMMA cement through modification with gamma-methacryloxypropyltrimethoxysilane (MPS) and calcium acetate. The purpose of this study was to compare the handling, mechanical and histological properties of the modified bone cement with those of the conventional cement. The modified specimens exhibited higher bonding strength between bone and implant. Histological observation and micro-focus X-ray computed tomogram (micro-CT) images showed that the modified cement exhibited osteoconduction, which the conventional PMMA bone cement lacked. The modification was found to be effective in enabling osteoconduction with PMMA bone cement, thus providing stable fixation for a long period after implantation.

Indirect selective laser sintering of an apatite-mullite glass-ceramic for potential use in bone replacement applications

The feasibility of using indirect selective laser sintering (SLS) to produce parts from glass-ceramic materials for bone replacement applications has been investigated. A castable glass based on the system SiO2 Al2O3 P2O5 CaO CaF2 that crystallizes to a glass-ceramic with apatite and mullite phases was produced, blended with an acrylic binder, and processed by SLS. Green parts with good structural integrity were produced using a wide range of processing conditions, allowing both monolayer and multilayer components to be constructed. Following SLS the parts were post-processed to remove the binder and to crystallize fully the material, evolving the apatite and mullite phases. The parts were heated to 1200O C using a number of different time-temperature profiles, following which the processed material was analysed by differential thermal analysis, X-ray diffraction, and scanning electron microscopy, and tested for flexural strength. An increase in strength was achieved by infiltrating the brown parts with a resorbable phosphate glass, although this altered the crystal phases present in the material.

Design variables for mechanical properties of bone tissue scaffolds

The reconstruction of segmental defect in long bone is a clinical challenge. Multiple surgeries are typically required to restore the structure and function of the affected defect site. In order to overcome this defect a biodegradable bone tissue engineering scaffold is used. This scaffold acts as a carrier of proteins and growth factors, while also supporting the load that the bone would normally sustain, until the natural bone can regenerate in its place. Work was done to optimize an existing solid free-form scaffold design. The goal of the optimization was to increase the porosity of the scaffold while maintaining the strength of a previously-tested prototype design. With this in mind, eight new designs were created. These designs were drawn using CAD software and then through the use of finite element analysis the theoretical ultimate compressive strength of each design was obtained. Each scaffold design was constructed by casting a thermal-curable poly(propylene fumarate)/tricalcium phosphate (PPF/TCP) suspension into wax molds fabricated on inkjet printing rapid prototyping machine. The constructs were then experimentally tested by applying a uniaxial compressive load. The theoretical and experimental values of ultimate compressive strength and specific strength of each design were compared. Theoretically, the best scaffold design produced from this work improved upon the current design by increasing the porosity by 46% and also increasing the ultimate compressive strength by 27%. The experimental data was found to match the theoretical strength in four designs, but deviate from the theoretical strength in five designs. The reasons for the deviations and their relation to the rapid prototyping manufacturing technique were discussed. The results of this work show that it is possible to increase the porosity and strength of a bone tissue engineering scaffold through simple iterations in architectural design.

Micro-architecture of calcium phosphate granules and fibrin glue composites for bone tissue engineering

Calcium phosphate ceramics are currently used as bone graft substitutes in various types of clinical applications. Fibrin glue is also used in surgery due to its haemostatic, chemotactic and mitogenic properties. By combining these two biomaterials, new composite scaffolds were prepared. In this study, we attempt to analyse whether thrombin concentration in the fibrin glue could influence the properties of the composite. The association between fibrin glue and calcium phosphate ceramic granules was characterized at the ultra structural level. Micro and macroporous biphasic calcium phosphate ceramic granules with a diameter of 1-2mm composed of hydroxyapatite and beta-tricalcium phosphate (60/40) were associated to fibrin glue. The composites were observed by scanning and transmission electron microscopy and microcomputed tomography. Fibre thickness, porosity and homogeneity of the fibrin clot were modified by increased the thrombin concentration. Mixing fibrin glue with calcium phosphate granules (1:2) did not modify the microstructure of the fibrin clot in the composite. Nevertheless, thrombin interacted with the bioceramic by inducing the nucleation of crystalline precipitate at the ceramic/fibrin glue interface. Combining fibrin sealant and calcium phosphate ceramics could lead to new scaffolds for bone tissue engineering with the synergy of the properties of the two biomaterials.

Calcium phosphate cement composites in revision hip arthroplasty

Loosening of the femoral component in a total hip arthroplasty with concomitant bone loss can pose a problem for revision surgery due to inadequate structure in the remaining femur. While impaction allografting has shown promise, it has also shown serious complications, especially with moderate to severe bone loss. It may be possible to stabilize the graft layer with a bioresorbable cement to improve clinical results. This study examines the mechanical properties of a potential morsellized bone-bioresorbable composite. Morsellized bone was mixed with a commercially available bioresorbable cement (alpha-BSM, Etex Corp.) in compositions of 0%, 25%, 50% and 75% bone. Unconfined compression and diametral tensile and confined compression tests were performed to determine the composite mechanical properties. The composition containing 50% bone tended to exhibit the highest uniaxial strengths, as well as the highest confined compression modulus. The uniaxial compressive strength and stiffness of this composition was in the range of cancellous bone. Uniaxial compressive modulus decreased with increasing bone fraction whereas elongation exhibited the opposite trend. Bone fraction had a significant effect on compressive strength (p < 0.0001), compressive modulus (p < 0.0001), elongation (p < 0.01), tensile strength (p < 0.0001) and confined compressive modulus (p = 0.04). The addition of a bioresorbable cement to the allograft layer may improve the properties of the layer, preventing early subsidence seen in some clinical studies of impaction allografting, and therefore improving the clinical results. Further testing is required to evaluate the in vitro mechanical performance, as well as in vivo remodelling characteristics.

Surface charge and the effect of excess calcium ions on the hydroxyapatite surface

This paper describes the use of surface titration as a more direct probe of the surface chemistry of hydroxyapatite (HA) than zeta-potential measurements. The variation in HA surface charge with pH for two different KCl electrolyte concentrations was determined titrimetrically and the point of zero charge (PZC) found to be at a pH of 7.3 +/- 0.1. The curves also demonstrated that HA accumulates positive charge more readily below the PZC than it accumulates negative charge above it. Extended titration data indicated that dissolution occurred more rapidly in increasingly acidic conditions, but was inhibited by increasing electrolyte strength. Similar experiments with 2.5 mM Ca(2+) in the electrolyte show that Ca(2+) adsorption balances loss of H(+) to give a near-neutral surface at any pH above 7 (subject to availability of calcium ions and adsorption sites). The mechanism for adsorption has been shown to be deprotonation of adjacent surface HPO(4)(2-) sites and subsequent adsorption of a calcium ion to the lattice surface site. Furthermore, inhibition of dissolution under alkaline conditions in the presence of Ca(2+) suggested that dissolution was driven by desorption of Ca(2+). Modelling of the adsorption/desorption processes demonstrated that in both pure water and under physiological conditions phosphate groups will predominate at the HA surface. Furthermore, the (200) plane was identified as the likely form of the HA surface. These methodologies and findings are particularly relevant to investigation of biological response with respect to modification of surface hydrophobicity and surface energy or charge.

Sol–gel synthesis of a multifunctional, hierarchically porous silica/apatite composite

In this study, a degradable, hierarchically porous silica/apatite composite material is developed from a simple low-temperature synthesis. Mesoporosity is induced in the silica portion by the use of supramolecular templating. The template is further removed by calcination. Firstly, hydroxyapatite is synthesized through a sol-gel method at near room temperature conditions. After the mineralization process, the crystal surface is coated with a mesoporous silica matrix using the templates already present in the bulk solution. The material is characterized by XRD, N(2)-sorption, FT-IR, SEM/EDS, and TEM. The coating layer is distributed fairly homogeneously over the apatite surface and the coating thickness is easily adjustable and dependent on the amount of added silica precursor. The hybrid material is shown to efficiently induce calcium phosphate formation under in vitro conditions and simultaneously work as a carrier system for drugs.

Effectiveness of three extraction techniques in the development of a decellularized bone–anterior cruciate ligament–bone graft

In this study, porcine bone-anterior cruciate ligament-bone (B-ACL-B) grafts were decellularized using one of three protocols incorporating surfactants lauryl sulfate (SDS), Triton X-100, and/or an organic solvent (tributyl phosphate (TnBP)). The effectiveness of Triton-SDS, Triton-Triton or Triton-TnBP treatments in removing cellular materials was determined and possible changes in biochemical composition and mechanical properties due to each treatment were investigated. Treatment with Triton-SDS was most effective at removing cell nuclei and intracellular protein (vimentin) from the ACL but affected both the collagen and glycosaminoglycan (GAG) components of the extracellular matrix while increasing the tensile stiffness of the ligament. Triton-Triton was the least effective of the three treatments in terms of cellular extraction, but did not significantly change the mechanical and biochemical properties of the ACL. Triton-TnBP matched the level of decellularization achieved by Triton-SDS in terms of visible cell nuclei; however, the extraction of intracellular vimentin was less consistent. TnBP treatment also slightly decreased the collagen content of the ACL but did not alter its mechanical properties. Overall, all three decellularization treatments maintained adequate mechanical and biochemical properties of B-ACL-B grafts to justify the further investigation of all three decellularization protocols. The selection of a superior treatment will depend on future studies of the propensity of treated tissues for repopulation by host ACL fibroblasts and, ultimately, on any immunogenic and/or remodeling host response induced in vivo.

High strength, low stiffness, porous NiTi with superelastic properties

Near-stoichiometric NiTi with up to 18% closed porosity was produced by expansion at 1200 degrees C of argon-filled pores trapped by powder metallurgy within a NiTi billet. When optimally heat-treated, NiTi with 6-16% porosity exhibits superelasticity, with recoverable compressive strains up to 6% at a maximum compressive stress up to 1700 MPa. The apparent Young's modulus of NiTi with 16% porosity, measured during uniaxial compression, is in the range of 15-25 GPa (similar to human bone), but is much lower than measured ultrasonically (approximately 40 GPa), or predicted from continuum elastic mechanics. This effect is attributed to the reversible stress-induced transformation contributing to the linear elastic deformation of porous NiTi. The unique combination of low stiffness, high strength, high recoverable strains and large energy absorption of porous superelastic NiTi, together with the known biocompatibility of NiTi, makes this material attractive for bone-implant applications.

Nano-composite of poly(-lactide) and surface grafted hydroxyapatite: Mechanical properties and biocompatibility

In order to improve the bonding between hydroxyapatite (HAP) particles and poly(L-lactide) (PLLA), and hence to increase mechanical properties of the PLLA/HAP composite as potential bone substitute material, the HAP nano-particles were surface-grafted with PLLA and further blended with PLLA. The structure and properties of the composites were subsequently investigated by the mechanical property testing, the differential scanning calorimeter measurements (DSC), the scanning electron microscopy (SEM), the polarized optical microscopy (POM), and the cell culture. The PLLA molecules grafted on the HAP surfaces, as inter-tying molecules, played an important role in improving the adhesive strength between the particles and the polymer matrix. At a low content (approximately 4 wt%) of surface grafted-HAP (g-HAP), the PLLA/g-HAP nano-composites exhibited higher bending strength and impact energy than the pristine PLLA, and at a higher g-HAP content (e.g., 20 wt%), the modulus was remarkably increased. It implied that PLLA could be strengthened as well as toughened by g-HAP nano-particles. The results of biocompatibility test showed that the g-HAP existing in the PLLA composite facilitated both adhesion and proliferation of chondrocytes on the PLLA/g-HAP composite film.

A poly(lactic acid)/calcium metaphosphate composite for bone tissue engineering

A new method to prepare PLA/CMP (poly-L-lactide/calcium metaphosphate) composite scaffolds was developed for effective bone tissue engineering. This novel sintering method is composed of pressing the mixture of PLA, CMP, and salt particles at 150 MPa for 3 min followed by heat treatment at 210 degrees C for 30 min. The scaffolds had a homogeneously interconnected porous structure without a skin layer, and they exhibited a narrower pore size distribution and higher mechanical strength in comparison with scaffolds made by a solvent casting method. The scaffolds were seeded by osteoblasts and cultured in vitro or implanted into nude mice subcutaneously for up to 5 weeks. The number of cells attached to and proliferated on the scaffolds at both in vitro and in vivo was in the order of; PLA by novel sintering < PLA/CMP by solvent casting < PLA/CMP by novel sintering. In addition, the alkaline phosphatase activity of and calcium deposition in the scaffolds explanted from mice were enhanced significantly for the scaffolds by novel sintering compared to them by solvent casting. The in vitro results agreed well with the in vivo data. Such a superior characteristic of the novel sintering method should have resulted from the fact that the CMP particles could contact directly with cells/tissues to stimulate the cell proliferation and osteogenic differentiation, while the CMP particles would be coated by polymers and hindered to interact with cells/tissues in the case of a solvent casting method. As the novel sintering method does not use any solvents it offers another advantage to avoid problems associated with solvent residue.

Synthesis and characterization of porous β-tricalcium phosphate blocks

Porous beta-tricalcium phosphate (beta-TCP) blocks with four different macropore sizes (pore larger than 50 microm were synthesized using "calcium phosphate emulsions", and characterized by optical, geometrical, gravimetric, and radiological methods. The reproducibility of the synthesis method was excellent. Moreover, the macropore size could be easily controlled without modifying the microporosity (pore smaller than 50 microm) or the total porosity (microporosity+macroporosity). Based on the initial composition of the blocks and their final apparent density, the microporosity, macroporosity, and the total block porosity were calculated to be close to 21%, 54%, and 75%, respectively. These values were confirmed by microcomputed tomography (microCT). The mean macropore diameters were close to 150, 260, 510 and 1220 microm, as measured optically. Consistently lower values (25% lower) were obtained by microCT, but the linear correlation between microCT and optical method was high (r(2)>0.97). The macropore size distribution calculated from microCT scans appears to be narrow and normally distributed. The very good correlation between the results of the various methods and the possibility to determine the pore size distribution suggest that microCT is an ideal tool to non-destructively characterize macroporous calcium phosphate bone substitutes.

Compositional effects on the formation of a calcium phosphate layer and the response of osteoblast-like cells on polymer-bioactive glass composites

Biodegradable polymer-ceramic composites are attractive systems for bone tissue engineering applications. These composites have the combined advantages of the component phases, as well as the inherent ease in optimization where desired material properties can be tailored in a well-controlled manner. This study focuses on the optimization of a polylactide-co-glycolide (PLAGA) and 45S5 bioactive glass (BG) composite for bone tissue engineering. The first objective is to examine the effects of composition or overall BG content on the formation of a Ca-P layer on the PLAGA-BG composite. It is expected that with increasing BG content (0%, 10%, 25%, 50% by weight), the required incubation time in a simulated body fluid (SBF) for the composite to form a detectable surface Ca-P layer will decrease. Both the kinetics and the chemistry will be determined using SEM+EDAX, FTIR, and mu-CT methods. Solution phosphorous and calcium concentrations will also be measured. The second objective of the study is to determine the effects of BG content on the maturation of osteoblast-like cells on the PLAGA-BG composite. It is hypothesized that mineralization will increase with increasing BG content, and the composite will support the proliferation and differentiation of osteoblasts. Specifically, cell proliferation, alkaline phosphatase activity and mineralization will be monitored as a function of BG content (0%, 10%, 50% by weight) and culturing time. It was found that the kinetics of Ca-P layer formation and the resulting Ca-P chemistry were dependent on BG content. The response of human osteoblast-like cells to the PLAGA-BG composite was also a function of BG content. The 10% and 25% BG composite supported greater osteoblast growth and differentiation compared to the 50% BG group. The results of this study suggest that there is a threshold BG content which is optimal for osteoblast growth, and the interactions between PLAGA and BG may modulate the kinetics of Ca-P formation and the overall cellular response.

Helical rosette nanotubes: a biomimetic coating for orthopedics?

Helical rosette nanotubes (HRN) are obtained through an entropically driven self-assembly process of low-molecular-weight synthetic modules under physiological conditions. Counter-intuitively, these materials undergo extensive self-assembly under the effect of temperature, resulting in networks of very long nanotubes. We have previously shown, using an in vitro model, that titanium (Ti) coated with HRN containing a lysine side chain (HRN-K1) displayed enhanced osteoblast (OB) adhesion when compared to uncoated Ti (p < 0.01). Because it has been widely known that proteins play a critical role in OB adhesion on nanophase materials, here we examine OB adhesion on heated (+T) and unheated (-T) HRN-K1-coated Ti under serum (+S, presence of proteins) and serum-free (-S, absence of proteins) conditions. The results demonstrated that (a) while proteins enhanced OB adhesion on +T HRN-K1-coated Ti, they had no effect on -T HRN-K1-coated Ti, suggesting an active role played by the rosette nanotubes in promoting OB adhesion, and (b) under -S conditions, +T HRN-K1 induced the same level of OB adhesion as uncoated Ti under +S conditions, suggesting that +T HRN-K1 acts as a protein substitute. Finally, transmission electron microscopy and atomic force microscopy studies of +T and -T HRN-K1-coated Ti revealed a significant change in surface coverage, density and hierarchical organization of the nanotubes upon heating, which was correlated with their ability to promote cell adhesion.

Computer-Aided Tissue Engineering of a Human Vertebral Body

Tissue engineering is developing into a less speculative science involving the careful interplay of numerous design parameters and multidisciplinary professionals. Problem solving abilities and state of the art research tools are required to develop solutions for a wide variety of clinical issues. One area of particular interest is orthopedic biomechanics, a field that is responsible for the treatment of over 700,000 vertebral fractures in the United States alone last year. Engineers are currently lacking the technology and knowledge required to govern the subsistence of cells in vivo, let alone the knowledge to create a functional tissue replacement for a whole organ. Despite this, advances in computer-aided tissue engineering are continually growing. Using a combinatory approach to scaffold design, patient-specific implants may be constructed. Computer-aided design, optimization of geometry using voxel finite element models or other optimization routines, creation of a library of architectures with specific material properties, rapid prototyping, and determination of a defect site using imaging modalities highlight the current availability of design resources. This study proposes a novel methodology from start to finish which could, in the future, be used to design a tissue-engineered construct for the replacement of an entire vertebral body.

Preparation and characterization of porous beta-tricalcium phosphate/collagen composites with an integrated structure

Porous beta-tricalcium phosphate (TCP)/collagen composites with different beta-TCP/collagen weight ratio were prepared. The influences of the preparation conditions on the microstructure of porous composite and the joint status of beta-TCP particles with collagen fibrils were characterized by X-ray diffractometer, scanning electron microscopy and transmission electron microscopy. The results showed: (1) an acid treatment could effectively disassemble collagen fibrils; (2) in the resulting porous composites, beta-TCP particles homogenously existed on the skeleton of the collagen fibril network and bonded tightly to both the fibrils and themselves. The tight bonding formation could be due to the reaction between Ca ions in the particles and carboxyl groups in collagen polypeptide chains and due to the reprecipitation of partially dissolved beta-TCP during synthesis. The tight bonding between beta-TCP particles and collagen fibrils in the composites demonstrated an integrated structure, which was reproducible when beta-TCP/collagen ratio ranged from 2 to 4. Such integrated structure would make significant contributions in reliably tailoring properties of the porous composites by varying beta-TCP content. In addition, the porous composites had large porosity (approximately 95%) and appropriate pore size (approximately 100 microm), showed no negative impact in cytotoxicity assay and complete bone tissue regeneration after 12 weeks in animal test.

Nucleation and growth of calcium phosphate on amine-, carboxyl- and hydroxyl-silane self-assembled monolayers

Upon implantation, calcium phosphate (Ca-P) surfaces form on materials that are bone bioactive. In this study, the evolving surface characteristics associated with calcium phosphate precipitation are modeled using self-assembled monolayers (SAMs), in a one-step nucleation process. SAMs were used to create amine (-NH2), carboxyl (-COOH) and hydroxyl (-OH) functionalized surfaces by grafting 3-aminopropyltriethoxysilane, 3-triethoxysilylpropyl succinic anhydride and glycidoxypropyl tri-methoxysilane, respectively, onto oxidized silicon wafers. The SAM surfaces were characterized using ellipsometry to establish the presence of grafted molecules. On the surfaces incubated in simulated physiological fluids for 7 days, the thickness of Ca-P layer grew slowly over the first few hours, increasing strongly between 1 and 5 days and then slowed down again. FTIR showed the dependence of calcium phosphate morphology on the type of surface groups, with stronger P-O bands seen on the OH-terminated surface. SEM analysis showed dispersed Ca-P precipitates on the -COOH and -OH terminated surfaces after 1 day immersion. After 7 days, all SAM surfaces were covered with uniformly dispersed and denser Ca-P precipitates. The underlying Ca-P layer showed cracks on the -NH2-terminated surface. Rutherford backscattering spectrometry (RBS) data analysis confirmed that Ca/P ratio is in excellent agreement with the theoretical value of 1.67 for hydroxyapatite. X-ray diffraction (XRD) analysis also showed evidence of apatite formation on all the surfaces, with stronger evidence on the -OH-terminated surface. Highly porous Ca-P precipitates were observed on the SAM surfaces portrayed by the AFM scans with nanoscale RMS roughness. Thus, using highly controlled surface chemistry, under physiological conditions, in vitro, this study demonstrates that a hydroxylated surface enhances Ca-P nucleation and growth relative to other surfaces, thereby supporting the concept of its beneficial effect on bone tissue formation and growth.

The complete process of bioresorption and bone replacement using devices made of forged composites of raw hydroxyapatite particles/poly l-lactide (F-u-HA/PLLA)

Here we document the complete process of bioresorption and bone replacement of rods made of forged composites of unsintered hydroxyapatite particles/poly l-lactide (F-u-HA/PLLA) implanted in the femoral medullary cavities of rabbits. Bioresorption, osteoconductive bioactivity and bone replacement were compared in three implantation sites. In the first site, the end of the rod was located near the endosteum in the proximal medullary cavity. In the second, the rod was located at the centre of the bone marrow space without contacting the endosteum. In the third, the rod was in direct contact with cancellous bone within the distal femoral condyle. Micro-computerised tomography, scanning electron microscopy and photomicrographs of stained sections were used to document the complete process of bioresorption and bone replacement. At the first implantation site, the rod was completely resorbed and unbound u-HA particles were detected in and around the endosteum 5-6 years after implantation. At the second site, the rod showed significant shrinkage 4-5 years after implantation due to the release of almost all the PLLA, although a contracted cylindrical structure containing a few u-HA persisted even after approximately 6 years. At the third site, u-HA particles were almost completely replaced with bone after 5-6 years. Conversely, PLLA-only rods showed little bone conduction, and small amounts of degraded PLLA debris and intervening some tissue persisted even after long periods. Namely, the u-HA/PLLA composites were replaced with bone in the distal femoral condyle, where they were in direct contact with the bone and new bone formation was anatomically necessary. By contrast, composite rods were resorbed without replacement in the proximal medullary cavity, in which new bone growth was not required. We therefore conclude that the F-u-HA30/40 composites containing 30 wt%/40 wt% u-HA particles are clinically effective for use in high-strength bioactive, bioresorbable bone-fixation devices with the capacity for total bone replacement.

Carbonate-containing hydroxyapatite derived from calcium tripolyphosphate gel with urea

Carbonate containing hydroxyapatite (CO3HAp) is one of the candidate materials as a bioresorbable bone substitute. In the present work, CO3HAp was efficiently prepared by a hydrothermal treatment of calcium tripolyphosphate gel with urea at 140 degrees C for 24 h. Chemical potential plots of the CO3HAp for estimation of its dissolution behavior suggested that the CO3HAp is more soluble than hydroxyapatite (HAp) and is as soluble as octacalcium phosphate (OCP) and/or beta -tricalcium phosphate (TCP). This material is expected to be applied to bioresorbable materials such as bone fillers.

Macroporous calcium phosphate glass-ceramic prepared by two-step pressing technique and using sucrose as a pore former

Macroporous calcium phosphate glass-ceramic with an initial glass composition of 60CaO.30P2O5.3TiO2.7Na2O in mol% was successfully prepared by sintering the mixture compact consisting of calcium phosphate glass and sucrose powders, which was formed using a two-step pressing technique. After burning off the sucrose phase, a 3D interconnected macroporous structure was formed in the sintered body, in which the skeleton consisting of the calcium phosphate glass-ceramic (including beta-calcium pyrophosphate and beta-tricalcium phosphate as the crystalline phases) was transformed from the initial glass during the sintering. The macropores with several hundred microns in diameter and the large interconnection size (approximately 100 microm), which result from the controllably large-sized sucrose particles and the hot-pressing at a little higher temperature than the sucrose's melting point, are believed to meet the requirements for cell adhesion and bone tissue regeneration well. Moreover, in vitro dissolution behavior study indicates that the calcium phosphate glass-ceramic is soluble to an acetic acid solution of pH 5-7. These, together with the simplicity and feasibility of the innovative fabrication method itself, show that the formed porous glass-ceramic has a promising potential for application to a scaffold for bone tissue engineering.

Processing of an apatite-mullite glass-ceramic and an hydroxyapatite/phosphate glass composite by selective laser sintering

The work presented details the results of an investigation into the feasibility of using Selective Laser Sintering (SLS) to directly produce customised bioceramic implants. The materials used were bioactive in nature and included a glass-ceramic and a combination of hydroxyapatite and phosphate glass. The glass-ceramic was selected from the range of apatite-mullite materials in the SiO2.Al2O3.CaO.CaF2.P2O5 series, due to their potentially suitable biological and mechanical properties. The hydroxyapatite and phosphate glass combination was chosen to allow an alternative production approach to be investigated. The viability of using both these materials with the SLS process was assessed and the process route and resulting material properties characterised using a variety of techniques including Differential Thermal Analysis (DTA), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The results obtained indicate that it was possible to produce multiple layer components from both materials using the SLS process. The glass-ceramic materials could only be processed at very low scan speeds and powers, yielding relatively brittle components. It was though possible to produce parts from the hydroxyapatite and phosphate glass combination across a much wider range of parameters, producing parts which had a greater potential for possible implant production.

Synthesis of bioactive PMMA bone cement via modification with methacryloxypropyltri-methoxysilane and calcium acetate

Bone cement consisting of polymethylmethacrylate (PMMA) powder and methylmethacrylate (MMA) liquid is clinically used for fixation of implants such as artificial hip joints. However, it does not show bone-bonding ability, i.e., bioactivity. The lack of bioactivity would be one of factors which cause loosening between the cement and the implant. The present authors recently showed the potential of bioactive PMMA-based bone cement through modification with gamma-methacryloxypropyltrimethoxysilane (MPS) and calcium acetate. In this study, the effects of the kinds of PMMA powder on setting time, apatite formation and compressive strength were investigated in a simulated body fluid (Kokubo solution). The cement modified with calcium acetate calcined at 220 degrees C could set within 15 min when the PMMA powder had an average molecular weight of 100,000 or less. The addition of calcium acetate calcined at 120 degrees C in the PMMA powder required a much longer period for setting. The modified cements formed an apatite layer after soaking in the Kokubo solution within 1 day for cement starting from PMMA powder with a molecular weight of 100,000 or less. Compressive strengths of the modified cements were more than 70 MPa for cements starting from 100,000 and 56,000 in molecular weight. After soaking in Kokubo solution for 7 days, the modified cement consisting of PMMA powder of 100,000 in molecular weight showed a smaller decrease in compressive strength than that consisting of 56,000 in molecular weight. These results indicate that bioactive PMMA cement can be produced with appropriate setting time and mechanical strength when PMMA powders with a suitable molecular weight are used. Such a type of design of bioactive PMMA bone cement leads to a novel development of bioactive material for bone substitutes.

The crystallization of Hydroxyapatite in the presence of sodium alginate

The effect of sodium alginate on the crystal growth of hydroxyapatite (HAP) was investigated at sustained supersaturation by the constant composition technique. Sodium alginate was found to inhibit HAP crystal growth at low concentrations and reduced the crystal growth rates by 42-86% for inhibitor concentrations of 2.1x10(-7)-12.6x10(-7) mol/l. The inhibition effect on the crystal growth rate may be explained possibly through adsorption onto the active growth sites. A detailed kinetics analysis suggested a Langmuir-type adsorption of the alginate on HAP surface and a value of 1.63x10(7) l/mol was obtained for the affinity constant of sodium alginate for the surface of HAP. The apparent order for the crystallization reaction was determined to be approximately 2, thus suggesting a surface diffusion controlled spiral growth mechanism.

Effect of fiber diameter on spreading, proliferation, and differentiation of osteoblastic cells on electrospun poly(lactic acid) substrates

Electrospinning is a promising method to construct fused-fiber biomaterial scaffolds for tissue engineering applications, but the efficacy of this approach depends on how substrate topography affects cell function. Previously, it has been shown that linear, parallel raised features with length scales of 0.5-2 microm direct cell orientation through the phenomenon of contact guidance, and enhance phenotypic markers of osteoblastic differentiation. To determine how the linear, random raised features produced by electrospinning affect proliferation and differentiation of osteoprogenitor cells, poly(lactic acid) and poly(ethylene glycol)-poly(lactic acid) diblock copolymers were electrospun with mean fiber diameters of 0.14-2.1 microm onto rigid supports. MC3T3-E1 osteoprogenitor cells cultured on fiber surfaces in the absence of osteogenic factors exhibited a lower cell density after 7 and 14 days of culture than cells cultured on spin-coated surfaces, but cell density increased with fiber diameter. However, in the presence of osteogenic factors (2 mM beta-glycerophosphate, 0.13 mM L-ascorbate-2-phosphate), cell density after 7 and 14 days of culture on fiber surfaces was comparable to or exceeded spin-coated controls, and alkaline phosphatase activity after 14 days was comparable. Examination of cell morphology revealed that cells grown on fibers had smaller projected areas than those on planar surfaces. However, cells attached to electrospun substrates of 2.1 microm diameter fibers exhibited a higher cell aspect ratio than cells on smooth surfaces. These studies show that topographical factors designed into biomaterial scaffolds can regulate spreading, orientation, and proliferation of osteoblastic cells.

Process and kinetics of bonelike apatite formation on sintered hydroxyapatite in a simulated body fluid

The surfaces of two hydroxyapatites (HA), which have been sintered at different temperatures of 800 and 1200 degrees C, was investigated as a function of soaking time in simulated body fluid (SBF) using transmission electron microscopy (TEM) attached with energy-dispersive spectrometry (EDX) and laser electrophoresis spectroscopy. The TEM-EDX indicated that after soaking in SBF, both the HAs form bonelike apatite by undergoing the same surface structural change, i.e., formations of a Ca-rich amorphous or nano-crystalline calcium phosphate (ACP) and a Ca-poor ACP, which eventually crystallized into bonelike apatite. Zeta potential characterized by the electrophoresis indicated that during exposure to SBF, the HA surfaces reveal negative surface charge, thereby interacting with the positive calcium ions in the fluid to form the Ca-rich ACP, which gains positive surface charge. The Ca-rich ACP on the HAs then interacts with the negative phosphate ions in the fluid to form the Ca-poor ACP, which stabilizes by being crystallized into bonelike apatite with a low solubility in the SBF. The exposure times for formations of these phases of the Ca-rich ACP, the Ca-poor ACP as well as the apatite were, however, all late on HA sintered at 1200 degrees C, compared with the HA sintered at 800 degrees C. This phenomenon was attributed to a lower initial negative surface charge of the HA sintered at 800 degrees C than of that one sintered at 1200 degrees C, owing to poverty in surface hydroxyl and phosphate groups which are responsible for the surface negativity of the HA. These indicate that sintered temperature of HA might influence not in terms of the process but in terms of the rate of formation of biologically active bonelike apatite on its surface, through which the HA integrates with living bone.

Microstructures and bond strengths of plasma-sprayed hydroxyapatite coatings on porous titanium substrates

Hydroxyapatite (HA) coating was carried out by plasma spraying on bulk Ti substrates and porous Ti substrates having a Young's modulus similar to that of human bone. The microstructures and bond strengths of HA coatings were investigated in this study. The HA coatings with thickness of 200-250 microm were free from cracks at interfaces between the coating and Ti substrates. XRD analysis revealed that the HA powder used for plasma spraying had a highly crystallized apatite structure, while the HA coating contained several phases other than HA. The bond strength between the HA coating and the Ti substrates evaluated by standard bonding test (ASTM C633-01) were strongly affected by the failure behavior of the HA coating. A mechanism to explain the failure is discussed in terms of surface roughness of the plasma-sprayed HA coatings on the bulk and porous Ti substrates.

The effect of processing on the structural characteristics of vancomycin-loaded amorphous calcium phosphate matrices

Calcium polyphosphate antibiotic delivery matrices were prepared using a unique processing technique involving the exposure of calcium polyphosphate pastes to high humidity for 0, 5, 24 or 48 h to induce gelling. Subsequently, samples were dried for a minimum of 24 h. The mild conditions associated with matrix fabrication readily allowed for vancomycin incorporation within an environment that did not disrupt antibiotic activity. While reproducible from a processing standpoint, the gelling and drying process did contribute to a decrease in matrix tensile strength and the formation of significant pores near the surface of the matrices. Generally, the core of the gelled matrices appeared to be denser than their non-gelled counterparts. The degree of phosphate chain lysis during the gelling and drying stages was quantified using solution 31P nuclear magnetic resonance (NMR) spectroscopy. Both NMR and Raman spectroscopy indicated that the presence of vancomycin did not appreciably alter the matrix formation process. The ability to incorporate clinically relevant levels of antibiotic within this degradable bone substitute matrix suggests the potential of this approach for creating a localized antibiotic delivery system to treat osteomyelitis infections.

Composite formation from hydroxyapatite with sodium and potassium salts of polyphosphazene

The low temperature synthesis of composites potentially suitable as bone substitutes which form in vivo, was investigated. The composites were comprised of stoichiometric hydroxyapatite (SHAp) and water-soluble poly phosphazenes. These constituents were selected because of their biocompatibility, and were mixed as powders with a phosphate buffer solution (PBS) to form the composites. The effects of poly[bis(sodium carboxylatophenoxy)phosphazene] (Na-PCPP) or poly[bis(potassium carboxylatophenoxy) phosphazene] (K-PCPP) on stoichiometric hydroxyapatite (SHAp) formation from tetracalcium phosphate and anhydrous dicalcium phosphate were assessed. The kinetics and reaction chemistries of composite formation were followed by isothermal calorimetry, X-ray diffraction, infrared spectroscopy and scanning electron microscopy. In the presence of 1% by weight of polyphosphazenes, composites comprised of SHAp and calcium cross-linked polymer salts were formed. Thus a mechanism for binding between polymer chains was established. Elevated proportions (5 and 10% by weight) of polyphosphazene, however, resulted in the inhibition of SHAp formation. This is attributed to the formation of viscous polymer solution coatings on the calcium phosphate precursors, retarding their reaction, and consequently inhibiting SHAp formation.