The ultrastructure of the bone-hydroxyapatite interface in vitro

Functionalization of biomimetic mineralized collagen for bone tissue engineering

Mineralized collagen (MC) is the basic unit of bone structure and function and is the main component of the extracellular matrix (ECM) in bone tissue. In the biomimetic method, MC with different nanostructures of neo-bone have been constructed. Among these, extra-fibrous MC has been approved by regulatory agencies and applied in clinical practice to play an active role in bone defect repair. However, in the complex microenvironment of bone defects, such as in blood supply disorders and infections, MC is unable to effectively perform its pro-osteogenic activities and needs to be functionalized to include osteogenesis and the enhancement of angiogenesis, anti-infection, and immunomodulation. This article aimed to discuss the preparation and biological performance of MC with different nanostructures in detail, and summarize its functionalization strategy. Then we describe the recent advances in the osteo-inductive properties and multifunctional coordination of MC. Finally, the latest research progress of functionalized biomimetic MC, along with the development challenges and future trends, are discussed. This paper provides a theoretical basis and advanced design philosophy for bone tissue engineering in different bone microenvironments.

Enhanced mechanical performance of mSLA-printed biopolymer nanocomposites due to phase functionalization

Functionalized phases can effectively increase the mechanical properties of nanocomposites through interfacial bonding. This work demonstrates masked stereolithography (mSLA) of biopolymer-based nanocomposites and the improvement of their mechanical properties by the functionalization of both polymer matrix and nanoparticles with methacrylate groups. 3D printable nanocomposite inks were prepared from plant-derived acrylated epoxidized soybean oil (AESO), polyethylene glycol diacrylate (PEGDA), and nano-hydroxyapatite (nHA). Both AESO and nHA were further functionalized with additional methacrylate groups. We hypothesized that the additional functionalization of AESO and surface functionalization of nHA would improve the tensile strength and fracture toughness of these nanocomposites by increasing the degree of crosslinking and the strength of the interface between the matrix and nanoparticles. Curing efficiency, rheology, and print-fidelity of the nanocomposites were evaluated. Mechanical test specimens were prepared by mSLA-based 3D printing. Tensile mechanical properties, Poisson's ratio, and Mode-I fracture toughness were measured by following ASTM standards. Fracture surfaces of the tested specimens were studied using scanning electron microscopy. Thermomechanical behavior, especially glass transition temperature (T_g), was studied using dynamic mechanical analysis (DMA). Functionalized AESO (mAESO) improved rheological, tensile, and fracture mechanical properties. For instance, by replacing AESO with mAESO, tensile strength, Young's modulus, fracture toughness (K_1c), and T_g increased by 33%, 53%, 40%, and 38% respectively. In addition, the combination of both functionalized nHA and mAESO improved the fracture toughness of the 10% volume fraction nHA nanocomposites but made them less extensible presumably due to reduced chain mobility due to greater crosslinking.

mSLA-based 3D printing of acrylated epoxidized soybean oil - nano-hydroxyapatite composites for bone repair

Structural bone allografts are used to treat critically sized segmental bone defects (CSBDs) as such defects are too large to heal naturally. Development of biomaterials with competent mechanical properties that can also facilitate new bone formation is a major challenge for CSBD repair. 3D printed synthetic bone grafts are a possible alternative to structural allografts if engineered to provide appropriate structure with sufficient mechanical properties. In this work, we fabricated a set of novel nanocomposite biomaterials consisting of acrylated epoxidized soybean oil (AESO), polyethylene glycol diacrylate (PEGDA) and nanohydroxyapatite (nHA) by using masked stereolithography (mSLA)-based 3D printing. The nanocomposite inks possess suitable rheological properties and good printability to print complex, anatomically-precise, 'by design' grafts. The addition of nHA to the AESO/PEGDA resin improved the tensile strength and fracture toughness of the mSLA printed nanocomposites, presumably due to small-scale reinforcement. By adding 10 vol% nHA, tensile strength, modulus and fracture toughness (K_Ic) were increased to 30.8 ± 1.2 MPa (58% increase), 1984.4 ± 126.7 MPa (144% increase) and 0.6 ± 0.1 MPa·m^1/2 (42% increase), respectively (relative to the pure resin). The nanocomposites did not demonstrate significant hydrolytic, enzymatic or oxidative degradation when incubated for 28 days, assuring chemical and mechanical stability at early stages of implantation. Apatite nucleated and covered the nanocomposite surfaces within 7 days of incubation in simulated body fluid. Good viability and proliferation of differentiated MC3T3-E1 osteoblasts were also observed on the nanocomposites. Taken all together, our nanocomposites demonstrate excellent bone-bioactivity and potential for bone defect repair.

Bone Regeneration in Load-Bearing Segmental Defects, Guided by Biomorphic, Hierarchically Structured Apatitic Scaffold

The regeneration of load-bearing segmental bone defects remains a significant clinical problem in orthopedics, mainly due to the lack of scaffolds with composition and 3D porous structure effective in guiding and sustaining new bone formation and vascularization in large bone defects. In the present study, biomorphic calcium phosphate bone scaffolds (GreenBone™) featuring osteon-mimicking, hierarchically organized, 3D porous structure and lamellar nano-architecture were implanted in a critical cortical defect in sheep and compared with allograft. Two different types of scaffolds were tested: one made of ion-doped hydroxyapatite/β-tricalcium-phosphate (GB-1) and other made of undoped hydroxyapatite only (GB-2). X-ray diffraction patterns of GB-1 and GB-2 confirmed that both scaffolds were made of hydroxyapatite, with a minor amount of β-TCP in GB-1. The chemical composition analysis, obtained by ICP-OES spectrometer, highlighted the carbonation extent and the presence of small amounts of Mg and Sr as doping ions in GB-1. SEM micrographs showed the channel-like wide open porosity of the biomorphic scaffolds and the typical architecture of internal channel walls, characterized by a cell structure mimicking the natural parenchyma of the rattan wood used as a template for the scaffold fabrication. Both GB-1 and GB-2 scaffolds show very similar porosity extent and 3D organization, as also revealed by mercury intrusion porosimetry. Comparing the two scaffolds, GB-1 showed slightly higher fracture strength, as well as improved stability at the stress plateau. In comparison to allograft, at the follow-up time of 6 months, both GB-1 and GB-2 scaffolds showed higher new bone formation and quality of regenerated bone (trabecular thickness, number, and separation). In addition, higher osteoid surface (OS/BS), osteoid thickness (OS.Th), osteoblast surface (Ob.S/BS), vessels/microvessels numbers, as well as substantial osteoclast-mediated implant resorption were observed. The highest values in OS.Th and Ob. S/BS parameters were found in GB-1 scaffold. Finally, Bone Mineralization Index of new bone within scaffolds, as determined by micro-indentation, showed a significantly higher microhardness for GB-1 scaffold in comparison to GB-2. These findings suggested that the biomorphic calcium phosphate scaffolds were able to promote regeneration of load-bearing segmental bone defects in a clinically relevant scenario, which still represents one of the greatest challenges in orthopedics nowadays.

Beta-phase Stabilization and Increased Osteogenic Differentiation of Stem Cells by Solid-State Synthesized Magnesium Tricalcium Phosphate

In this study, magnesium and strontium-doped β-tricalcium phosphates were synthesized to understand dopant impact on substrate chemistry and morphology, and proliferation and osteogenic differentiation of mesenchymal stem cells. Under solid-state synthesis, magnesium doping stabilized the β-phase in tricalcium phosphate, with 22% less α-phase content than control. Strontium doping increased α-phase formation by 17%, and also resulted in greater surface porosity, leading to greater crystal precipitation in vitro. Magnesium also significantly enhanced the proliferation of stem cells (P < 0.05) and differentiation into osteoblasts with increased alkaline phosphatase production (P < 0.05) at all time points. These results indicated that magnesium stabilizes β-tricalcium phosphate in vitro and enhanced early and late-time-point osteoconduction and osteoinduction of mesenchymal stem cells.

Acrylated epoxidized soybean oil/hydroxyapatite-based nanocomposite scaffolds prepared by additive manufacturing for bone tissue engineering

The mechanical properties and biocompatibility of nanocomposites composed of Acrylated Epoxidized Soybean Oil (AESO), nano-Hydroxyapatite (nHA) rods and either 2-Hydroxyethyl Acrylate (HEA) or Polyethylene Glycol Diacrylate (PEGDA) and 3D printed using extrusion-based additive manufacturing methods were investigated. The effects of addition of HEA or PEGDA on the rheological, mechanical properties and cell-biomaterial interactions were studied. AESO, PEGDA (or HEA), and nHA were composited using an ultrasonic homogenizer and scaffolds were 3D printed using a metal syringe on an extrusion-based 3D printer while simultaneously UV cured during layer-by-layer deposition. Nanocomposite inks were characterized for their viscosity before curing, and dispersion of the nHA particles and tensile mechanical properties after curing. Proliferation and differentiation of human bone marrow-derived mesenchymal stem cells (BM-MSCs) were studied by seeding cells onto the scaffolds and culturing in osteogenic differentiation medium for 7, 14 and 21 days. Overall, each of the scaffolds types demonstrated controlled morphology resulting from the printability of nanocomposite inks, well-dispersed nHA particles within the polymer matrices, and were shown to support cell proliferation and osteogenic differentiation after 14 and 21 days of culture. However, the nature of the functional groups present in each ink detectably affected the mechanical properties and cytocompatibility of the scaffolds. For example, while the incorporation of HEA reduced nHA dispersion and tensile strength of the final nanocomposite, it successfully enhanced shear yield strength, and printability, as well as cell adhesion, proliferation and osteogenic differentiation, establishing a positive effect perhaps due to additional hydrogen bonding.

Nanostructured Biomaterials for Bone Regeneration

This review article addresses the various aspects of nano-biomaterials used in or being pursued for the purpose of promoting bone regeneration. In the last decade, significant growth in the fields of polymer sciences, nanotechnology, and biotechnology has resulted in the development of new nano-biomaterials. These are extensively explored as drug delivery carriers and as implantable devices. At the interface of nanomaterials and biological systems, the organic and synthetic worlds have merged over the past two decades, forming a new scientific field incorporating nano-material design for biological applications. For this field to evolve, there is a need to understand the dynamic forces and molecular components that shape these interactions and influence function, while also considering safety. While there is still much to learn about the bio-physicochemical interactions at the interface, we are at a point where pockets of accumulated knowledge can provide a conceptual framework to guide further exploration and inform future product development. This review is intended as a resource for academics, scientists, and physicians working in the field of orthopedics and bone repair.

Bioinspired Scaffold Action Under the Extreme Physiological Conditions of Simulated Space Flights: Osteogenesis Enhancing Under Microgravity

Prolonged exposure to microgravity (MG) during long-duration space flights is known to induce severe dysregulation of osteoblast functions connected to a significant bone loss, similar to the condition induced by osteoporosis. Hence, we here present MG as a promising model to challenge the effectiveness of new scaffolds designed for bone regeneration in counteracting bone loss. To this end, we carried out an integrative study aimed to evaluate, in the extreme condition of Random Positioning Machine-simulated MG, the osteoinductive potential of nanocrystalline magnesium-doped hydroxyapatite/type I collagen composite scaffold (MHA/Coll), that we previously demonstrated to be an excellent tool for bone tissue engineering. Initially, to test the osteoinductive properties of our bioinspired-scaffold, MHA/Coll structure was fully characterized under MG condition and compared to its static counterpart. Human bone marrow-derived mesenchymal stem cells were used to investigate the scaffold biocompatibility and ability to promote osteogenic differentiation after long-duration exposure to MG (up to 21 days). The results demonstrate that the nanostructure of MHA/Coll scaffold can alleviate MG-induced osteoblast dysfunction, promoting cell differentiation along the osteogenic lineage, with a consequent reduction in the expression of the surface markers CD29, CD44, and CD90. Moreover, these findings were corroborated by the ability of MHA/Coll to induce the expression of genes linked to osteogenesis, including alkaline phosphatase and osteocalcin. This study confirmed MHA/Coll capabilities in promoting osteogenesis even in extreme long-term condition of MG, suggesting MG as an effective challenging model to apply in future studies to validate the ability of advanced scaffolds to counteract bone loss, facilitating their application in translational Regenerative Medicine and Tissue Engineering.

Antimicrobial activity and biologic potential of silver-substituted calcium phosphate constructs produced with self-propagating high-temperature synthesis

There is significant demand for synthetic bone substitute materials that can decrease the incidence of implant-based bacterial infections. The intent of this research was to evaluate the antimicrobial activity and biologic potential of calcium phosphate (CaP) constructs substituted with silver (Ag) that were produced via self-propagating high-temperature synthesis (SHS). SHS is a combustion synthesis technique that has successfully generated porous CaP bioceramics intended for use in bone repair. SHS reactions are highly versatile; dopants can be added to the reactant powders to alter product chemistry and morphology. In this research, Ag powder was added to the reactants generating porous CaP constructs containing 0.5, 1, or 2 wt% Ag. Antibacterial performance of the constructs was assessed against Escherichia coli, a representative model for Gram-negative bacteria. Liquid solutions (1 μg/mL) of CaP-Ag particles to phosphate buffered saline were incubated with 10(5) cells/mL. After 24 h, 10 μL of solution were spread on an LB agar plate and cultured for 24 h at 37 °C. Samples cultured with CaP-Ag showed complete bacterial inhibition while the controls (E. coli only and CaP without Ag) exhibited significant colony formation. The effects of Ag concentration on cytotoxicity and biocompatibility were tested in vitro. At 7 days, osteoblasts uniformly enveloped the CaP-Ag particles and displayed a healthy flattened morphology suggesting the concentrations of Ag incorporated into constructs were not cytotoxic. CaP-Ag constructs produced via SHS represent a source of synthetic bone substitute materials that could potentially inhibit, or reduce the incidence of post-operative bacterial infections.

Mineralization at Titanium Surfaces is a Two-Step Process

Mapping the initial reaction of implants with blood or cell culture medium is important for the understanding of the healing process in bone. In the present study, the formation of low crystalline carbonated hydroxyapatite (CHA) onto commercially pure titanium (Ti) implants from cell culture medium and blood, is described as an early event in bone healing at implants. The Ti-implants were incubated with cell culture medium (DMEM) or whole blood and the surface concentration of Ca, P and HA was analyzed by XPS, EDX and Tof-SIMS. After incubation with DMEM for 16 h and 72 h, EDX and XPS analysis showed stable levels of Ca and P on the Ti-surface. ESEM images showed an even distribution of Ca and P. Further analysis of the XPS results indicated that CHA was formed at the implants. Analysis with ToF-SIMS yielded high m.w. fragments of HA, such as Ca₂PO4 at m/z 174.9 and Ca₃PO₅ at m/z 230.8, as secondary ions at the Ti-surfaces. Analysis of implants incubated in blood for 16 h, with ToF-SIMS, showed initial formation of CHA yielding CaOH as secondary ion. The results indicate that early mineralization at Ti-surfaces is an important step in the healing of implants into bone.

Evaluation of the osteoinductive potential of a bio-inspired scaffold mimicking the osteogenic niche for bone augmentation

Augmentation of regenerative osteogenesis represents a premier clinical need, as hundreds of thousands of patients are left with insufficient healing of bony defects related to a host of insults ranging from congenital abnormalities to traumatic injury to surgically-induced deficits. A synthetic material that closely mimics the composition and structure of the human osteogenic niche represents great potential to successfully address this high demand. In this study, a magnesium-doped hydroxyapatite/type I collagen scaffold was fabricated through a biologically-inspired mineralization process and designed to mimic human trabecular bone. The composition of the scaffold was fully characterized by XRD, FTIR, ICP and TGA, and compared to human bone. Also, the scaffold microstructure was evaluated by SEM, while its nano-structure and nano-mechanical properties were evaluated by AFM. Human bone marrow-derived mesenchymal stem cells were used to test the in vitro capability of the scaffold to promote osteogenic differentiation. The cell/scaffold constructs were cultured up to 7 days and the adhesion, organization and proliferation of the cells were evaluated. The ability of the scaffold to induce osteogenic differentiation of the cells was assessed over 3 weeks and the correlate gene expression for classic genes of osteogenesis was assessed. Finally, when tested in an ectopic model in rabbit, the scaffold produced a large volume of trabecular bone in only two weeks, that subsequently underwent maturation over time as expected, with increased mature cortical bone formation, supporting its ability to promote bone regeneration in clinically-relevant scenarios. Altogether, these results confirm a high level of structural mimicry by the scaffold to the composition and structure of human osteogenic niche that translated to faster and more efficient osteoinduction in vivo--features that suggest such a biomaterial may have great utility in future clinical applications where bone regeneration is required.

Internalized gold nanoparticles do not affect the osteogenesis and apoptosis of MG63 osteoblast-like cells: a quantitative, in vitro study

The long-term toxicity effects of gold nanoparticles (GNPs) on the proliferation and differentiation of a progenitor cell line, MG63 osteoblast-like cells, was investigated. These cells were treated for 20 hours with two media that contained 10 nm GNPs at concentrations of 1 ppm and 10 ppm. The mitosis of the GNP-treated MG63 was observed after at least 21 hours using dark-field and fluorescence microscopy. The TEM, LSCM and dark-field hyperspectral images indicated that the late endosomes in cells that contained aggregated GNPs were caused by vesicle fusion. Subsequently, after 21 days of being cultured in fresh medium, the specific nodule-like phenotypes and bone-associated gene expression of the treated MG63 cells exhibited the same behaviors as those of the control group. Statistically, after 21 days, the viability of the treated cells was identical to that of the untreated ones. During the cell death program analysis, the apoptosis and necrosis percentages of cells treated for 8 or fewer days were also observed to exhibit no significant difference with those of the untreated cells. In summary, our experiments show that the long-term toxicity of GNPs on the osteogenetic differentiation of MG63 is low. In addition, because of their low toxicity and non-biodegradability, GNPs can potentially be used as biomarkers for the long-term optical observation of the differentiation of progenitor or stem cells based on their plasmonic light-scattering properties.

Augmentation of bone tunnel healing in anterior cruciate ligament grafts: application of calcium phosphates and other materials

Bone tunnel healing is an important consideration after anterior cruciate ligament (ACL) replacement surgery. Recently, a variety of materials have been proposed for improving this healing process, including autologous bone tissue, cells, artificial proteins, and calcium salts. Amongst these materials are calcium phosphates (CaPs), which are known for their biocompatibility and are widely commercially available. As with the majority of the materials investigated, CaPs have been shown to advance the healing of bone tunnel tissue in animal studies. Mechanical testing shows fixation strengths to be improved, particularly by the application of CaP-based cement in the bone tunnel. Significantly, CaP-based cements have been shown to produce improvements comparable to those induced by potentially more complex treatments such as biologics (including fibronectin and chitin) and cultured cells. Further investigation of CaP-based treatment in the bone tunnels during ACL replacement is therefore warranted in order to establish what improvements in healing and resulting clinical benefits may be achieved through its application.

Brushite-Forming Mg-, Zn- and Sr-Substituted Bone Cements for Clinical Applications

Calcium phosphate cements have been in clinical use for the last 10 years. Their most salient features include good biocompatibility, excellent bioactivity, self-setting characteristics, low setting temperature, adequate stiffness, and easy shaping to accomodate any complicated geometry. They are commonly used in filling bone defects and trauma surgeries as mouldable paste-like bone substitute materials. Substitution of trace elements, such as Mg, Sr and Zn ions, into the structure of calcium phosphates is the subject of widespread investigation nowadays, because of their impending role in the biological process. Subtle differences in composition and structure of these materials may have a profound effect on their in vivo behaviour. Therefore, the main goal of this paper is to provide a simple, but comprehensive overview of the present achievements relating to brushite-forming cements doped with Mg, Zn and Sr, and to identify new developments and trends. In particular, the influence of ionic substitution on the chemical, physical and biological properties of these materials is discussed.

Electrokinetic properties of hydroxyapatite under flotation conditions

The effect of calcite supernatant, calcium, and carbonate ions on the hydroxyapatite (HA) zeta potential without and in the presence of sodium oleate (1x10(-4) mol L(-1)) was examined within the pH range from 4 to 12. The interpretation of results was based on the HA surface and oleate solution chemistry, and on some floatability tests. HA, with different positive and negative surface sites formed depending on its solubility and pH, had a negative zeta potential over the whole pH range. This mineral is not naturally floatable (flotation recovery, 5%<R<18%). The oleate ions (Ol(-)), present in a very low concentration in an acidic medium (pH from 4.8 to 6), chemisorb individually on HA surface centers [triple bond]Ca(+), [triple bond]HPO(4)Ca(+), and [triple bond]OH(2)(+), increasing the negative zeta potential of the mineral. Within the pH range from 7 to 9, the dominant oleate species Ol(-) ion and ion-molecule complex, H(Ol)(2)(-), adsorbed on HA by head groups toward the solid and associated due to chain-chain interaction in hemimicelles, made the HA surface with zeta potential about -22/-23 mV, and more floatable (R=80-100%) than in 4<pH<7 (R=15-35%) or in pH>9.3. The HA surface is less negatively charged in calcite supernatant than in water from pH 6.6 to 9.2 due to the adsorption on HA negative surface active centers ([triple bond]HPO(4)(-) and [triple bond]PO(4)(2-)) of the Ca(2+), and CaOH(+) ions (present in the calcite supernatant), producing more surface sites [triple bond]HPO(4)Ca(+), [triple bond]PO(4)Ca, [triple bond]HPO(4)CaOH, and [triple bond]PO(4)(-) CaOH, and new centers [triple bond]HPO(4)CaHCO(3) and [triple bond]PO(4)(-) CaHCO(3). In the presence of 1x10(-3) mol L(-1) CaCl(2), the HA sample has positive zeta potential, the same as calcite from the same deposit, up to IEP at pH 11.25. Carbonate ions (1x10(-3) mol L(-1) Na(2)CO(3)) do not affect the HA zeta potential. However, a possible process can be the ion-exchange reaction between bicarbonate (or carbonate) and some anion from the surface sites formed on HA. The obtained values of the HA zeta potential with the collector (1x10(-4) mol L(-1) Na-oleate) added into hydroxyapatite/calcite supernatant suspensions corroborate the weak chemisorption of Ol(-) and H(Ol)(2)(-). The likely processes in this system also are the ion-exchange reactions on [triple bond]HPO(4)CaOH and [triple bond]PO(4)(-) CaOH, [triple bond]HPO(4)CaHCO(3) and [triple bond]PO(4)(-) CaHCO(3) between oleate ion and surface hydroxyl and bicarbonate ions, surface and bulk precipitations of calcium oleate, Ca(Ol)(2), and the surface and bulk precipitations of Ca[H(Ol)(2)(-)](2) over the pH range from 7 to 9. Calcite supernatant does not influence natural floatability of the mineral. However, calcite supernatant depresses the hydroxyapatite flotation in the presence of 1x10(-4) mol L(-1) Na-oleate (pH 9, R approximately 50%), a likely result of the weak chemisorption due to the steric effect of heterogeneous HA surface formed in calcite supernatant, Ca(Ol)(2) and Ca[H(Ol)(2)(-)](2) surface and bulk precipitations.

Effect of a New Titanium Coating Material (CaTiO3-aC) Prepared by Thermal Decomposition Method on Osteoblastic Cell Response

Titanium and hydroxyapatite (HA) are widely used as biomaterials for dental and medical applications. HA-coated titanium implants have excellent biocompatibility and mechanical properties. However, the adherence of HA film formed on titanium substrate is weak because of the lack of chemical interaction between HA and titanium. A solution to this problem is to form an intermediate film on titanium substrate, which provide excellent adherence to both titanium substrate and HA. We developed a novel biomaterial called calcium titanate-amorphous carbon (CaTiO3-aC) coating prepared by modified thermal decomposition method. The purpose of this study was to evaluate the effect of CaTiO 3-aC and HA coating (positive control), and Ti (negative control) on osteoblastic (MT3T3-E1) cell responses. An increased cellular proliferation was observed in CaTiO3-aC coating compared to HA coating. The maximum expressions of ALP activity, Col I and ALP mRNA were higher and achieved in shorter period of time in CaTiO3-aC coating compared to others. These results demonstrated that CaTiO3-aC promoted better cell attachment, cellular proliferation, and osteoblastic differentiation compared with HA. In conclusion, we suggested that CaTiO3-aC could be considered as an important candidate as a coating material.

Interactions of hydroxyapatite surfaces: conditioning films of human whole saliva

Hydroxyapatite is a very interesting material given that it is the main component in tooth enamel and because of its uses in bone implant applications. Therefore, not only the characterization of its surface is of high relevance but also designing reliable methods to study the interfacial properties of films adsorbed onto it. In this paper we apply the colloidal probe atomic force microscopy method to investigate the surface properties of commercially available hydroxyapatite surfaces (both microscopic particles and macroscopic discs) in terms of interfacial and frictional forces. In this way, we find that hydroxyapatite surfaces at physiological relevant conditions are slightly negatively charged. The surfaces were then exposed to human whole saliva, and the surface properties were re-evaluated. A thick film was formed that was very resistant to mechanical stress. The frictional measurements demonstrated that the film was indeed highly lubricating, supporting the argument that this system may prove to be a relevant model for evaluating dental and implant systems.

Modification of Ti implant surface for cell proliferation and cell alignment

Surface properties of implants are the keys for ensuring their long-lasting anchorage to the tissue. This study aims to develop a novel implant surface microstructure with high biocompatibility and ability of guided tissue formation. By a photolithography method, gold (Au) grids (1 x 1 mm(2) square lattices, 10 mum in grid-line width) were deposited on titanium substrates. They were oxidized with H(2)O(2) solution to yield titania (anatase) layer, and the Au grid formed channels due to larger molar volume of anatase than Ti. L-Cysteine and type I collagen were then immobilized on them to yield the target substrates, CHT-Au-cys-col. Apatite deposited within 3 days when they were soaked in Kokubo's simulated body fluid, regardless of the protein coating, but not on the bottom of the Au channel. Osteoblast-like MC3T3-E1 cells were cultured on the CHT-Au-cys-col substrates, showing that (1) the cysteine-collagen coating promoted cell attachment and proliferation, and (2) the Au channels were filled with the cells which were aligned along the channel direction and were connected to the neighboring cells as well as attached to the channel wall with cytoplasmic extensions. The results thus ensured filopodial guidance for the substrates.

Formation of calcium phosphates on titanium implants with four different bioactive surface preparations. An in vitro study

The aim of the present study was to compare the nucleating and growing behaviour on four types of bioactive surfaces by using the simulated body fluid (SBF) model. Titanium discs were blasted and then prepared by alkali and heat treatment, anodic oxidation, fluoridation, or hydroxyapatite coating. The discs were immersed in SBF for 1, 2, 4 and 6 weeks. Calcium phosphates were found on all specimens, as analysed with scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX). After 1 and 2 weeks of SBF immersion more titanium was accessible with SEM/EDX on the blasted surfaces than the four bioactive surface types, indicating a difference in coverage by calcium phosphates. The Ca/P mean ratio of the surfaces was approximately 1.5 after 1 week, in contrast to the fluoridated specimens which displayed a Ca/P mean ratio of approximately 2. Powder X-ray diffraction (P-XRD) analyses showed the presence of hydroxyapatite on all types of surfaces after 4 and 6 weeks of immersion. The samples immersed for 6 weeks showed a higher degree of crystallinity than the samples immersed for 4 weeks. In conclusion, differences appeared at the early SBF immersion times of 1 and 2 weeks between controls and bioactive surface types, as well as between different bioactive surface types.

Hierarchies of Extracellular Matrix and Mineral Organization in Bone of the Craniofacial Complex and Skeleton

Structural hierarchies are common in biologic systems and are particularly evident in biomineralized structures. In the craniofacial complex and skeleton of vertebrates, extracellular matrix and mineral of bone are structurally ordered at many dimensional scales from the macro level to the nano level. Indeed, the nanocomposite texture of bone, with nanocrystals of apatitic mineral embedded within a crosslinked matrix of fibrillar and nonfibrillar proteins, imparts to bone the very mechanical properties and toughness it needs to function in vital organ protection, musculoskeletal movement and mastication. This article focuses on how hierarchies of extracellular matrix protein organization influence bone cell behavior, tissue architecture and mineralization. Additional attention is given to recent work on the molecular determinants of mineral induction in bone, and how the mineralization process is subsequently regulated by inhibitory proteins.

Ultrastructural Characterization of Tissue Response to Sintered Carbonate Apatite in Rabbit Bone

Our previous in vivo and in vitro studies revealed excellent tissue biocompatibility and osteoconductivity of porous sintered carbonate apatite (CA). The present study focused on the ultrastructural details of cells involved in the degradation of CA and new bone formation. Electron microscopy indicated that multinucleated giant cells (MNGCs) were actively involved in CA resorption. MNGCs extended their irregular cytoplasmic protrusions deeply into the interstitial spaces between CA particles. Endophagosomes were formed by encircling partially dissolved or intact CA crystals via the development of pseudopodia-like cytoplasmic protrusions, the configuration of which was somewhat different from that of the typical ruffled border of bone-resorbing osteoclasts. Subsequently, most CA particles in MNGCs were irregular in shape, suggesting that acidic degradation of CA occurred mainly intracellularly. Mononuclear cells, such as macrophage-like and/or fibroblast-like cells, also took up and degraded some CA. Growth of very thin needle-like crystals was observed in close association with CA. Osteoblasts directly faced the CA and secreted osteoid matrix. At the CA-bone interface, an electron-dense and homogeneous thin layer free of collagen fibers was sometimes observed, suggesting an involvement in CA-bone bonding.

Silicon addition to hydroxyapatite increases nanoscale electrostatic, van der Waals, and adhesive interactions

The normal intersurface forces between nanosized probe tips functionalized with COO(-)-terminated alkanethiol self-assembling monolayers and dense, polycrystalline silicon-substituted synthetic hydroxyapatite (SiHA) and phase pure hydroxyapatite (HA) were measured via a nanomechanical technique called chemically specific high-resolution force spectroscopy. A significantly larger van der Waals interaction was observed for the SiHA compared to HA; Hamaker constants (A) were found to be A(SiHA) = 35 +/- 27 zJ and A(HA) = 13 +/- 12 zJ. Using the Derjaguin-Landau-Verwey-Overbeek approximation, which assumes linear additivity of the electrostatic double layer and van der Waals components, and the nonlinear Poisson-Boltzmann surface charge model for electrostatic double-layer forces, the surface charge per unit area, sigma (C/m(2)), was calculated as a function of position for specific nanosized areas within individual grains. SiHA was observed to be more negatively charged than HA with sigma(SiHA) = -0.024 +/- 0.013 C/m(2), two times greater than sigma(HA) = -0.011 +/- 0.006 C/m(2). Additionally, SiHA was found to have increased surface adhesion (0.7 +/- 0.3 nN) compared to HA (0.5 +/- 0.3 nN). The characterization of the nanoscale variations in surface forces of SiHA and HA will enable an improved understanding of the initial stages of bone-biomaterial bonding.

A new in vivo screening model for posterior spinal bone formation: Comparison of ten calcium phosphate ceramic material treatments

This study presents a new screening model for evaluating the influence of multiple conditions on the initial process of bone formation in the posterior lumbar spine of a large animal. This model uses cages designed for placement on the decorticated transverse process of the goat lumbar spine. Five conduction channels per cage, each be defined by a different material treatment, are open to both the underlying bone and overlying soft tissue. The model was validated in ten adult Dutch milk goats, with each animal implanted with two cages containing a total of ten calcium phosphate material treatments according to a randomized complete block design. The ten calcium phosphate ceramic materials were created through a combination of material chemistry (BCP, TCP, HA), sintering temperature (low, medium, high), calcination and surface roughness treatments. To monitor the bone formation over time, fluorochrome markers were administered at 3, 5 and 7 weeks and the animals were sacrificed at 9 weeks after implantation. Bone formation in the conduction channels was investigated by histology and histomorphometry of non-decalcified sections using traditional light and epifluorescent microscopy. According to both observed and measured bone formation parameters, materials were ranked in order of increasing magnitude as follows: low sintering temperature BCP (rough and smooth) approximately medium sintering temperature BCP approximately = TCP > calcined low sintering temperature HA > non-calcined low sintering temperature HA > high sintering temperature BCP (rough and smooth) > high sintering temperature HA (calcined and non-calcined). These results agree closely with those obtained in previous studies of osteoconduction and bioactivity of ceramics thereby validating the screening model presented in this study.

Bone tissue engineering on amorphous carbonated apatite and crystalline octacalcium phosphate-coated titanium discs

Poor fixation of bone replacement implants, e.g. the artificial hip, in implantation sites with inferior bone quality and quantity may be overcome by the use of implants coated with a cultured living bone equivalent. In this study, we tested, respectively, amorphous carbonated apatite (CA)- and crystalline octacalcium phosphate (OCP)-coated discs for their use in bone tissue engineering. Subcultured rat bone marrow cells were seeded on the substrates and after 7 days of culture, the implants were subcutaneously implanted in nude mice for 4 weeks. After 7 days of culture, the cells had formed a continuous multi-layer that covered the entire surface of the substrates. The amount of cells was visually higher on the crystalline OCP-coated discs compared to the amorphous CA-coated discs. Furthermore, the amorphous CA-coated discs exhibited a visually higher amount of mineralized extracellular matrix compared to the crystalline OCP-coated discs. After 4 weeks of implantation, clear de novo bone formation was observed on all discs with cultured cells. The newly formed bone on the crystalline OCP-coated discs was more organized and revealed a significantly higher volume compared to the amorphous CA-coated discs. The percentage of bone contact with the discs was also significantly higher on the OCP-coated discs. Overall, the results suggest that a crystalline OCP coating is more suitable for bone tissue engineering than an amorphous CA coating.

Strengthening mechanisms of bone bonding to crystalline hydroxyapatite in vivo

The formation and strengthening mechanisms of bone bonding of crystalline hydroxyapatite (HA) has been investigated using high-resolution transmission electron microscope (HRTEM) and energy-dispersive X-ray (EDX) analysis. A series of results were obtained: (i) a layer of amorphous HA, which has almost the same chemistry as the implanted HA, was formed on the surface of crystalline HA particles prior to dissolution; (ii) at 3 months a bone-like tissue formed a bonding zone between mature bone and the HA implant, composed of nanocrystalline and amorphous apatite; and (iii) at 6 months, mature bone was in direct contact with HA particles, and collagen fibres were perpendicularly inserted into the surface layer of implanted HA crystals. Findings (i) and (ii) indicated the following dissolution-precipitation process. (i) The crystalline HA transforms into amorphous HA; (ii) the amorphous HA dissolves into the surrounding solution, resulting in over-saturation; and (iii) the nanocrystallites are precipitated from the over-saturated solution in the presence of collagen fibres. A preliminary analysis indicated several conclusions: (i) the transition from crystalline to amorphous HA might be the controlling step in the bone bonding of crystalline HA; (ii) biological interdigitation (or incorporation) of collagen fibres with HA and chemical bonding of a apatite layer were both necessary to strengthen and toughen a bone bond, not only for the bonding between bone and HA at 6 months, but also for the bonding zone at 3 months, which would otherwise be very fragile due to the inherited brittleness of polycrystalline ceramics; and (iii) perpendicular interdigitation is an effective way for collagen fibres to impart their unique combination of flexibility and strength to the interface which they are keying.

Osteoblastic differentiation of cultured rat bone marrow cells on hydroxyapatite with different surface topography

Hydroxyapatite (HA) has been used in orthopedic, dental, and maxillofacial surgery as a bone substitute.

OBJECTIVE

The aim of this investigation was to study the effect of surface topography produced by the presence of microporosity on the response of the rat bone marrow cells, evaluating: cell attachment, proliferation, total protein content, alkaline phosphatase (ALP) activity, and bone-like nodule formation.

METHODS

Cells were cultured on HA discs manufactured by a combination of uniaxial powder pressing and different sintering conditions, with different percentage of microporosity (<5%-HA5, 15%-HA15, and 30%-HA30). For attachment evaluation, cells were cultured for 2 h. Proliferation was evaluated after 7 and 14 days. After 14 days, total protein content and ALP activity were measured. For bone-like nodule formation, cells were cultured for 21 days. Data were compared by ANOVA and Duncan's multiple range test when appropriate.

RESULTS

Cell attachment was not affected by surface topography (p=0.37). Proliferation (p=0.001), total protein content (p=0.039), ALP activity (p=0.050), and bone-like nodule formation (p=0.00001) were all significantly decreased by the most irregular surface (HA30). SIGNIFICANCE. These results suggest that initial cell events were not affected by the surface topography of the HA. However, intermediary and final events such as proliferation, protein synthesis, ALP activity, and bone-like nodule formation favored surfaces with a more regular topography, such as that presents in HA with 15% or less of microporosity.

Proliferation, differentiation, and calcification of preosteoblast-like MC3T3-E1 cells cultured onto noncrystalline calcium phosphate glass

The purpose of this study was to investigate calcium phosphate glass as a potential biomaterial for hard tissue repair. We prepared calcium phosphate glass using the system CaO-CaF(2)-P(2)O(5)-MgO-ZnO and cultured MC3T3-E1 cells onto the glass in alpha-MEM with beta-glycerophosphatase and ascorbic acid. Proliferation of the cells was determined to evaluate the biocompatibility of the prepared calcium phosphate glass. The alkaline phosphatase activity was measured to examine the osteoblast differentiation. Mineralization was evaluated by staining the calcium precipitates with Alizarin red. Culture onto the calcium phosphate glass exhibited no significant influence on cell proliferation compared to the polystyrene chosen as a control in this experiment (p > 0.05). The alkaline phosphatase activity in the experimental group, however, was enhanced by the calcium phosphate glass significantly at 10-18 days after incubation than that of the control group (p < 0.05). The promotion of bone-like tissue formation by the calcium phosphate glass was observed after 7 days and thereafter. The results of the present study indicate that the prepared calcium phosphate glass affects osteogenesis by increasing calcification of the extracellular matrix.

Bone ingrowth in bFGF-coated hydroxyapatite ceramic implants

This experimental study was performed to evaluate angiogenesis, bone formation, and bone ingrowth in response to osteoinductive implants of bovine-derived hydroxyapatite (HA) ceramics either uncoated or coated with basic fibroblast growth factor (bFGF) in miniature pigs. A cylindrical bone defect was created in both femur condyles of 24 miniature pigs using a saline coated trephine. Sixteen of the 48 defects were filled with HA cylinders coated with 50 microg rhbFG, uncoated HA cylinders, and with autogenous transplants, respectively. Fluorochrome labelled histological analysis, histomorphometry, and scanning electron microscopy were performed to study angiogenesis, bone formation and bone ingrowth. Complete bone ingrowth into bFGF-coated HA implants and autografts was seen after 34 days compared to 80 days in the uncoated HA group. Active ring-shaped areas of fluorochrome labelled bone deposition with dynamic bone remodelling were found in all cylinders. New vessels could be found in all cylinders. Histomorphometric analysis showed no difference in bone ingrowth over time between autogenous transplants and bFGF-coated HA implants. The current experimental study revealed comparable results of bFGF-coated HA implants and autogenous grafts regarding angiogenesis, bone synthesis and bone ingrowth.

A stereomorphologic study of bone matrix apposition in HA-implanted cavities observed with SEM, being prepared by a microvascular cast and freeze-fracture method

In order to obtain further understanding of the relationship between hydroxyapatite (HA) with regard to its properties as an implantation bed, dense HA particles were implanted into the tibiae of dogs. Following the healing periods of 2 weeks, 1 month, 2 months, 3 months and 6 months, the specimens were prepared with a combination of a microvascular cast method and a freeze-fracture technique, allowing observations to be made with a scanning electron microscope (SEM). Under SEM, osteogenesis among the HA particles developed in a programmed sequence. The unfolding sequence revealed that the sinusoidal capillaries provided the initial evidence of vascularization preceding new bone formation, with microvessels creeping along the interparticular space among the HA particles. Having established an intimate contact existing between the microvessels, collagen fibres and the HA surface, the HA particles served as a supporting scaffold for the vessels to creep over and to connect with each other to form a vascular network. The way that the collagen fibres attached to the HA particles was either through globular depositions or via directly abutting themselves on to the HA surface. On closer inspection the osteoblasts with extracellular collagen fibrils were observed over the HA surface. By appositional growth, osteoblasts laid down a bone matrix in successive layers, forming a woven bone around the HA particles. As the implantation time increased, bony tissues gradually transformed into mature bone occupying all of the interparticular space. This study successfully revealed the spatial relationship between bone cells, collagen fibres and blood vessels in an osteogenetic sequence among HA particles, as revealed by a microvascular cast and the freeze-fracture method.

Histological evaluation of the bone response to calcium phosphate cement implanted in cortical bone

The aim of this study was to investigate the physicochemical and biological properties of a newly developed calcium phosphate cement (CaP cement) implanted in cortical bone. CaP cement was injected as a paste into tibia cortical bone defects in goats. Polymethylmethacrylate (PMMA) bone cement was used as a control. The animals were killed after 3 days, 2, 8, 16 and 24 weeks. X-ray diffraction and Fourier transform infrared spectroscopy performed at retrieved samples showed that the CaP cement had set as a carbonate apatite and remained stable over time. Light microscopic evaluation showed that after 2 weeks the cement was in tight contact with the bone without any inflammatory reaction or fibrous encapsulation. At later time points, the CaP cement implants were totally covered by a thin layer of bone and osteoclasts, present at the interface, which were clearly resorbing the cement. At locations where CaP cement was resorbed, new bone was deposited. Transmission electron microscopy revealed that indeed a seamless contact existed between CaP cement and bone, as characterized by the occurrence of an electron dense line of 50-60 nm thick that covered the CaP cement. Osteoblasts, in contact with the cement, were depositing new bone. Although the bulk of the material was still in situ after 24 weeks, the progressive osteoclast resorption of the cement followed by new bone formation suggests that all of the material may be replaced eventually. In contrast to the CaP cement, the PMMA reference cement was always surrounded by a thin fibrous capsule. The results indicate that the investigated CaP cement is biocompatible, osteoconductive as well as osteotransductive and is a candidate material for use as a bone substitute.

In vitro investigation of titanium and hydroxyapatite dental implant surfaces using a rat bone marrow stromal cell culture system

In this study, rat bone marrow cells (RBM) were used to evaluate different titanium and hydroxyapatite dental implant surfaces. The implant surfaces investigated were: a titanium surface having a porous titanium plasma-sprayed coating (sample code Ti-TPS), a titanium surface with a deep profile structure (sample code Ti-DPS), an uncoated titanium substrate with a machined surface (sample code Ti-ma) and a machined titanium substrate with a porous hydroxyapatite plasma-sprayed coating (sample code Ti-HA). RBM cells were cultured on the disc-shaped test substrates for 14 days. The culture medium was changed daily and examined for calcium and phosphate concentrations. After 14 days specimens were examined by light microscopy, scanning electron microscopy, energy dispersive X-ray analysis and morphometry of the cell-covered substrate surface. All test substrates facilitated RBM growth of extracellular matrix formation. Ti-DPS and Ti-TPS to the highest degree, followed by Ti-ma and Ti-HA. Ti-DPS and Ti-TPS displayed the highest cell density and thus seem to be well suited for the endosseous portion of dental implants. RBM cells cultured on Ti-HA showed a delayed growth pattern. This may be related to its high phosphate ion release.

The ultrastructure of the plasma-sprayed hydroxyapatite-bone interface predisposing to bone bonding

The deposition of biological apatite and subsequent formation of bone on hydroxyapatite implants depends on the partial dissolution of the implant surface and the reprecipitation of carbonated apatite from the biological milieu. Previous investigations in vitro have shown that the degree of dissolution and reprecipitation decreases as the coating crystallinity increases. These findings prompted the current study of the effects of coating crystallinity on the mechanism of bone bonding. The process of mineralization of bone associated with a hydroxyapatite coating was compared to the normal process of ossification. Plasma-sprayed hydroxyapatite (PSHA) coated titanium alloy (6% Al-4% V) rods as received and annealed for 0.7 h at 600 degrees C in air to increase the coating crystallinity were implanted in the proximal and distal femora and proximal tibiae of adult mongrel dogs for 3 h, 3 and 10 days. Bony sites containing the implant were prepared for ultramicrotomy and transmission electron microscopy using an anhydrous embedding procedure: fixation in ethylene glycol and embedment in Spurr's resin. The results demonstrated the precipitation of biological apatite crystallites on non-annealed PSHA coatings in vivo within 3 h of implantation. After 3 and 10 days there were differences in the ultrastructure of the mineral phase on the surfaces of non-annealed and annealed surfaces. Observations showed that there was little difference in the mechanism of mineralization of bone associated with HA-coated prostheses and the normal process of ossification.

In vitro dissolution behaviour of two morphologically different thermally sprayed hydroxyapatite coatings

Two types of hydroxyapatite coating on titanium substrates were produced by vacuum plasma spraying and detonation gun spraying. The response of the coatings to immersion in Ringer's solution at pH 7.2 and held at 37 degrees C for periods of one, two, four and eight weeks was compared. X-ray diffraction was used to measure changes in crystallinity and residual stresses. Porosity and coating thickness were measured using optical microscopy combined with image analysis. Surface morphology was characterised using scanning electron microscopy and Talysurf measurements. The DGUN coatings were found initially to have a lower crystallinity and porosity but higher surface roughness and residual stress level than the VPS coatings. This resulted in a higher rate of dissolution compared to the more stable VPS coatings.

Missing osteoconductive effect of a resorbable PEO/PBT copolymer in human bone defects: a clinically relevant pilot study with contrary results to previous animal studies

PEO/PBT 70/30 (POLYACTIVE(R) 70/30), a degradable porous copolymer with elastic properties, was found to be osteoconductive in many animal studies. The aim of this study was to determine the osteoconductive effect in a human paired control iliac defect model. In seven patients undergoing anterior spinal interbody fusion surgery, two bicortical iliac defects for autograft harvesting were created. The defect size was identical for both defects measuring about 40 x 15 mm (group I). One defect was filled with the degradable implants, whereas the remaining one was left untreated as a control. The defect site for treatment was chosen randomly. In three further patients, only one defect measuring about 40 x 35 mm was created (group II). All patients were examined clinically and radiologically by spiral-CT after 1, 6, 12, 24, and 52 weeks. Three-dimensional reconstructions as well as CT-volumetric measurements using 1 mm sections were used as evaluation methods. In group I, a two-tailed paired t-test showed that the treated defects had significantly less formation of new bone than the untreated ones (p < 0.05 after 12 weeks, p < 0.01 after 52 weeks). Also, in group II, not much bone ingrowth could be observed. The histological evaluation of one patient in group I revealed no bone within the pores, and a fibrous layer between bone and implant was always present. Therefore, PEO/PBT 70/30 cannot be recommended as a bone substitute for clinical use. Differences in bone regeneration between humans and certain animal species as well as inapplicable defect models in previous animal studies are discussed as possible reasons for the failure.

Effects of new machinable ceramic on behavior of rat bone cells cultured in vitro

The behavior of cultured rat bone cells growing on modified polyethylene terephthalate (mPET), glass, and machinable ceramic substrates containing enstatite (MgO, SiO2) and glass (CaO-P2O5-Al2O3) was studied. Cell attachment was measured directly on the substrates using an image analysis system. Electron microscopy observations and the MTT test revealed that cells are able to spread and proliferate on the material surface, keeping a healthy ultrastructure on all materials tested in the present study. After having colonized the surface of the materials, as shown by immunocytochemistry, the cells synthesize an osteoid-like matrix composed of osteocalcin, type I collagen, and fibronectin fibrils. The titration of alkaline phosphatase activity showed that the cells grown on the ceramic exhibit a greater osteogenic activity than those grown on controls (glass and mPET). This osteogenic activity results in a mineralization of the extracellular matrix in cultures on ceramic or plastic whereas only few calcium phosphate crystallite traces were revealed by Von Kossa staining on glass. Enstatite constitutes, therefore, an environment compatible with in vitro bone cell life.

Effect of a ceramic and a non-ceramic hydroxyapatite on cell growth and procollagen synthesis of cultured human gingival fibroblasts

BACKGROUND

Ceramic hydroxyapatites and non-ceramic hydroxyapatites have been used extensively as alloplastic materials for bone reconstruction. However, different forms of hydroxyapatite induce different types of tissue response.

METHODS

Human gingival fibroblasts (FMM1 cells) were used to analyze ceramic and non-ceramic hydroxyapatite biocompatibility. The cells were grown on surfaces covered either by collagen (control group), collagen plus ceramic hydroxyapatite, or collagen plus non-ceramic hydroxyapatite. Scanning electron microscopy, growth and cell viability curves, and procollagen immunoprecipitation were obtained. For the growth and viability curves, 10(4) cells were seeded on 60 mm dishes. Cells from each group were counted, in triplicate, at 1, 3, 4, 5, and 6 days after seeding using the Trypan blue dye exclusion assay.

RESULTS

The cells grew in close contact with both types of hydroxyapatite particles. No differences were found in the amount of procollagen synthesis among any experimental group. The cultures treated with ceramic hydroxyapatite had a growth delay for the first 5 days. There was no difference in cell viability between the control group and the non-ceramic hydroxyapatite group. However, cultures treated with ceramic hydroxyapatite showed significantly lower viability percentages than the other groups.

CONCLUSIONS

Hydroxyapatite supports cell growth and fibroblast metabolism including collagen production, and hence is biocompatible. Cell viability and structural studies showed that non-ceramic hydroxyapatite has relevant physical and biological properties as an implant material.

Flow cytometry analysis of the effects of pre-immersion on the biocompatibility of glass-reinforced hydroxyapatite plasma-sprayed coatings

Multilayered coatings composed of mixtures of HA and P2O5-based bioactive glasses are of potential clinical benefit in orthopaedic and dental surgery. Pre-immersion of these materials has been reported to further enhance their efficacy in vivo, although the precise biological effects of this treatment are not yet known. In this study we have therefore prepared double-layer plasma-sprayed coatings and evaluated the effects of pre-immersion on the growth and function of human osteosarcoma cells in vitro, using the MTT assay and flow cytometry analysis, respectively. The results showed that the increase in numbers of viable cells was the same or elevated following incubation on the pre-immersed HA and glass-reinforced HA coatings compared with the non-immersed materials. In addition, the expression of bone sialoprotein and fibronectin, two key connective tissue antigens, was up-regulated in cultures grown on the pre-immersed surfaces compared with the non-treated materials. Moreover, cell numbers and antigen expression both improved as the proportion of glass increased, particularly in the pre-immersed samples. Our findings thus suggest that the immersion treatment of these materials appeared to improve the response of these bone-like cells.

Flow cytometry analysis of effects of glass on response of osteosarcoma cells to plasma-sprayed hydroxyapatite/CaO-P(2)O(5) coatings

Multilayered coatings composed of mixtures of hydroxyapatite (HA) and P(2)O(5)-based bioactive glasses offer potential clinical benefits in orthopedic and dental surgery. In this study double-layer plasma-sprayed coatings were prepared and the biological response evaluated in tissue culture using two human osteosarcoma cell lines, MG63 and HOS TE85 (HOS). The cells were cultured on the materials and the effects on cell growth were determined using a spectrophometric assay of a mitochondrial enzyme that is active in viable cells. While none of the materials influenced the growth of the MG63 cells, the HOS cells appeared to undergo less proliferation on all the HA materials. Flow cytometry analysis was carried out using rabbit antibodies against osteonectin, osteopontin, bone sialoprotein, fibronectin, and collagen type I to measure the effects of the materials on key cellular functions. The results showed that the materials downregulated the expression of these extracellular matrix antigens by MG63 cells whereas they had less effect on the HOS cells compared to the same cells incubated on a plastic surface. Notably, with both cell lines the composite with the higher percentage of glass restored the production of connective tissue proteins to levels that were more similar to those present in the control cells.

Bonding behavior of ultrahigh strength unsintered hydroxyapatite particles/poly(L-lactide) composites to surface of tibial cortex in rabbits

Unsintered hydroxyapatite particles/poly(L-lactide) (u-HA/PLLA) composites with an initial bending strength of up to 270 MPa were developed based on the hypothesis that inclusion of u-HA particles in a PLLA matrix might enhance bone bonding. The purpose of this study was to examine the bonding strength and behavior of these u-HA/PLLA composites on the surface of the bone cortex. Composites containing 30 (u-HA30), 40 (u-HA40), or 50 wt % (u-HA50) of fine u-HA particles (3-microm average particle size) were prepared. Semicolumnar plates of these composites and control PLLA plates were fixed with metal screws to the surface of both proximal tibial cortices in 45 rabbits. The loads required to detach the plates from the bone cortex surface, defined as the bonding strengths, were measured at 4, 8, and 25 weeks after implantation. Bonding strengths in the u-HA30 group at 8 weeks and in the u-HA40 and u-HA50 groups at each postimplantation time were significantly greater than in the PLLA group (post hoc test using Fisher's protected least significant difference method). At each postimplantation time histological examinations revealed direct contact between the bone and the u-HA/PLLA composite plates without any intervening fibrous tissue. There was no evidence of any inflammatory or foreign-body response in any group throughout the follow-up periods. The results of this study suggest that the biodegradable PLLA fixation plates amended with u-HA particles could be functionally superior to PLLA plates without particles.

Effect of stainless steel corrosion products on in vitro biomineralization

Osteoblast-like cell cultures have been used as in vitro models to study the interactions of bone tissue with biomaterials and their degradation products. This work reviews the effects of AISI 316L stainless steel (SS) corrosion products on the osteoblastic behavior of rat and human bone cell cultures. Results suggest that such products affect, in a dose-dependent manner, the proliferation and differentiation of osteoblastic cells; these effects depend on the developmental stage of the osteoblastic cells. Above certain nonlethal concentrations, SS corrosion products prevent the mineralization of the extracellular matrix, a process that reflects the complete expression of the osteoblastic phenotype.

Bone induction by implants coated with cultured osteogenic bone marrow cells

The availability of osteoinductive coatings on dental and orthopedic implants will result in an improved fixation of these devices. Those cases where implants are placed in poor-quality bone or where high failure rates are obtained are especially expected to gain from such coatings. This paper presents a novel, biological approach to obtain bioactive and osteoinductive coatings on bone-replacement implant materials. This so-called tissue engineering approach utilizes osteogenic bone marrow cells that are cultured on an implant material to form a bone-like tissue. The implant materials used herein included porous calcium phosphate scaffolds and metallic plates, the latter of which were coated with a biomimetic calcium phosphate coating to facilitate cellular attachment. Bone marrow cells were obtained from a variety of species, including humans, and were grown to facilitate cellular proliferation. The cells were subsequently seeded onto the implants and cultured for an additional week to facilitate osteogenic differentiation and extracellular matrix production. The resulting hybrid implants, encompassing the biomaterial carrier and cultured bone-like tissue, were subsequently implanted subcutaneously in nude mice for 4 weeks, followed by histological examination for de novo bone formation. The results revealed that newly formed bone was seen both in porous implants and on flat metallic surfaces. This bone tissue engineering approach, therefore, offers great potential to enhance bony healing around implants in a compromised bone bed.

Al2O3 doped apatite-wollastonite containing glass ceramic provokes osteogenic differentiation of marrow stromal stem cells

Fresh marrow cells were obtained from femora of Fischer rats and cultured in a medium containing 15% fetal calf serum (FCS) until confluence. After trypsinization, cells were subcultured at a cell density of 100 x 10(3)/35-mm well in the presence of FCS, beta-glycerophosphate, and ascorbic acid phosphate on four different culture substrata. The period of subculture was 2 weeks; the substrata used were the culture dish, apatite-wollastonite containing glass ceramic (AW), hydroxyapatite coated AW (HA/AW), and Al2O3 doped AW (Al/AW). The HA coating was attained by the incubation of AW in simulated physiological solution. The glass matrix of AW and HA/AW contained MgO, CaO, P2O5, and SiO2; Al/AW contained Al2O3 in addition to these components. The subculture on Al/AW substratum showed many alkaline phosphatase (ALP) positive nodules and the highest ALP activity. On a Northern blot analysis the housekeeping gene of beta-actin mRNA was evenly detected from the cells cultured on all substrata; however, bone-specific osteocalcin mRNA was only detected from the cells on Al/AW. These results indicate that Al/AW provokes the osteoblastic differentiation of marrow stromal stem cells.

In vitro osteoblastic differentiation of human bone marrow cells in the presence of metal ions

For periods up to 21 days human bone marrow was cultured in control conditions that favor the proliferation and differentiation of osteoblastic cells. The effect of AISI 316L corrosion products and the corresponding major separate metal ions (Fe, Cr, and Ni) were studied in three different phases of the culture period in order to investigate the effects of metal ions in cell populations representative of osteoblastic cells in different stages of differentiation. Toxicity consequences of the presence of metal ions in bone marrow cultures were evaluated by biochemical parameters (enzymatic reduction of MTT, alkaline phosphatase activity, and total protein content), histochemical assays (identification of ALP-positive cells and Ca and phosphates deposits), and observation of the cultures by light and scanning electron microscopy. Culture media were analyzed for total and ionized Ca and P and also for metal ions (Fe, Cr, and Ni). The presence of AISI 316L corrosion products and Ni salt in bone marrow cultures during the first and second weeks of culture significantly disturbs the normal behavior of these cultures, interfering in the lag phase and exponential phase of cell growth and ALP expression. However, the presence of these species during the third week of culture, when expression of osteoblastic functions occurs (mineralization process), did not result in any detectable effect. Fe salt also disturbs the behavior of bone marrow cell cultures when present during the lag phase and proliferation phase, and a somewhat compromised response between the normal pattern (control cultures) and intense inhibition (AISI 316L corrosion products and Ni salt-added cultures) was observed. Fe did not affect the progression of the mineralization phase. Osteogenic cultures exposed to Cr salt (Cr3+) presented a pattern similar to the controls, indicating that this element does not interfere, in the concentration studied, in the osteoblastic differentiation of bone marrow cells. Quantification of metal ions in the culture media showed that Cr (originated from AISI 316L corrosion products but from not Cr3+ salt) and Ni (originated from AISI 316L corrosion products and Ni salt) appear to be retained by the bone marrow cultures.

Cartilage formation by fetal rat chondrocytes cultured in alginate beads: a proposed model for investigating tissue-biomaterial interactions

Chondrocytes from 21-day-old rat fetal nasal cartilage were cultured in alginate beads for up to 20 days. It was found that chondrocytes retained their spherical shape and typical chondrocytic appearance. During the culture time, chondrocytes underwent differentiation, as demonstrated by the alkaline phosphatase-specific activity and rate of proteoglycan synthesis. Morphological data confirmed chondrocyte differentiation with the appearance of hypertrophic chondrocytes scattered in the alginate gel and a dense extracellular matrix containing filamentous structures and matrix vesicles. In addition, Northern blot analysis performed on day 8 of culture showed that chondrocytes cultured in alginate beads expressed type II collagen mRNA. The alginate bead method also appeared to be suitable for testing biomaterials, and the ready dissolution of the alginate beads by chelating agents provided a simple means for the rapid recovery of encapsulated chondrocytes. Powdered glass-ceramic particles entrapped in the alginate gel were colonized by chondrocytes, which then proliferated and formed a tissue similar to a true calcified cartilaginous structure. These results indicate that the alginate system represents a relevant model for studies of chondrogenesis and endochondral ossification. Furthermore, the encapsulation method could prove useful for studies of tissue-biomaterial interactions in an in vitro environment which more closely mirrors the cartilage matrix than other culture methods.