Surface instability of calcium phosphate ceramics in tissue culture medium and the effect on adhesion and growth of anchorage-dependent animal cells

Short-time pre-washing of brushite-forming calcium phosphate cement improves its in vitro cytocompatibility

A pre-washing protocol was developed for resorbable, brushite-forming calcium phosphate cements (CPCs) to avoid harmful in vitro effects on cells. CPC discs (JectOS+, Kasios; self-developed CPC) were pre-washed with repeated changes of phosphate-buffered saline (PBS; 24h total). Unwashed or PBS-pre-washed discs were incubated in culture medium (5% fetal calf serum; up to 10days) and then tested for their influence on pH/calcium/phosphate levels in H₂O extracts. Effects on pH/calcium/phosphate levels in culture supernatants, and morphology, adherence, number, and viability of ATDC5 cells and adipose-tissue derived stem cells were analyzed in co-culture. Pre-washing did not alter CPC surface morphology or Ca/P ratio (scanning electron microscopy; energy-dispersive X-ray spectroscopy). However, acidic pH of unwashed JectOS+ and self-developed CPC (5.82; 5.11), and high concentrations of Ca (2.17; 2.40mM) and PO₄ (38.15; 49.28mM) in H₂O extracts were significantly counteracted by PBS-pre-washing (pH: 7.92; 7.92; Ca: 0.64; 1.11mM; PO₄: 5.39-5.97mM). Also, PBS-pre-washing led to physiological pH (approx. 7.5) and PO₄ levels (max. 5mM), and sub-medium Ca levels (0.5-1mM) in supernatants and normalized cell morphology, adherence, number, and viability. This CPC pre-washing protocol improves in vitro co-culture conditions without influencing its structure or chemical composition.

Biomaterials for polynucleotide delivery to anchorage-independent cells

Comparison of various chemical vectors used for polynucleotide delivery to mammalian anchorage-independent cells.

Inducing bioactivity of dental ceramic/bioactive glass composites by Nd:YAG laser

OBJECTIVES

Aims of this study were to investigate the optimal conditions of laser irradiation of a novel Bioactive Glass/Dental Ceramic-BP67 composite for acceleration of hydroxyapatite-HA formation and to assess cellular responses on the precipitated HA region.

METHODS

BP67 (Bioactive Glass: 33.3%, Dental Ceramic: 66.7%) was fabricated by the sol-gel method. A laser assisted biomimetic-LAB process was applied to BP67 sintered specimens immersed in 1.5-times concentrated simulated body fluid-1.5×-SBF. The effect of various energy densities of pulsed nanosecond Nd-YAG (1064nm) laser and irradiation exposure times (30min, 1 and 3h) were evaluated for HA precipitation. The HA film was characterized by FTIR, XRD, SEM and micro Raman techniques. ICP-AES was used for revealing changes in chemical composition of the 1.5×-SBF during irradiation. Cell viability and morphological characteristics of periodontal ligament fibroblasts-PDLFs, human gingival fibroblasts-HGFs and SAOS-2 osteoblasts on the HA surface were evaluated by MTT assays and SEM.

RESULTS

At optimal energy fluence of 1.52J/cm² and irradiation time for 3h followed by immersion in 1.5×-SBF at 60°C, a dense HA layer was formed on laser-irradiated BP67 within 7 days. The resulting HA film was tightly bonded to the underlying substrate and had mineral composition similar to cementum. MTT assay showed a consistent reduction of cell proliferation on the HA layer in comparison to conventional control ceramic and BP67 for all 3 cell lines studied.

SIGNIFICANCE

These findings suggest LAB is an effective method for acceleration of HA formation on materials with low bioactivity, while cellular responses need further investigation.

Calcium phosphate nanoparticles-based systems for siRNA delivery

Despite the enormous therapeutic potential of siRNA as a treatment strategy, the delivery is still a problem due to unfavorable biodistribution profiles and poor intracellular bioavailability. Calcium phosphate (CaP) co-precipitate has been used for nearly 40 years for in vitro transfection due to its non-toxic nature and simplicity of preparation. The surface charge of CaP will be tuned into positive by surface modification, which is important for siRNA loading and crossing cell membrane without enzymatic degradation. The new siRNA carrier system will also promote the siRNA escape from lysosome to achieve siRNA sustained delivery and high-efficiency silence. In this review, we focus on the current research activity in the development of CaP nanoparticles for siRNA delivery. These nanoparticles are mainly classified into lipid coated, polymer coated and various other types for discussion.

Preparation, characterization and in vitro dissolution behavior of porous biphasic α/β-tricalcium phosphate bioceramics

The ideal bone tissue engineering scaffolds are long-cherished with the properties of interconnected macroporous structures, adjustable degradation and excellent biocompatibility. Here, a series of porous α/β-tricalcium phosphate (α/β-TCP) biphasic bioceramics with different phase ratios of α-TCP and β-TCP were successfully synthesized by heating an amorphous calcium phosphate precursor. The chemical and morphological characterization showed that α- and β-TCP phases co-existed in the α/β-TCP bioceramics and they had interconnected pore structures with size between 200 and 500μm. The in vitro dissolution behavior and bioactivity of the dual α/β-TCP were also probed in static and dynamic SBF for the first time. The results revealed that α/β-TCP scaffolds had good in vitro bioactivity, as the formation of bone-like apatite layers was induced on the scaffolds after mineralization in SBF. Moreover, dissolution rate of α/β-TCP bioceramics in dynamic environment was higher than that under static condition. Compared with monophasic TCP ceramics, these porous α/β-TCP bioceramics displayed a tailored dissolution rate proportionate to the TCP content (α and β) in the materials. Further, the degradation profile of porous α/β-TCP was well-described by Avrami equation. The porous dual α/β-TCP bioceramics with controllable degradation behavior hold great potential to be applied in bone tissue engineering as bone substitutes.

The influence of target stoichiometry on early cell adhesion of co-sputtered calcium-phosphate surfaces

The nature of the initial interaction between calcium phosphate (Ca-P) thin films and osteoblasts can be influenced by a number of different properties including the phase, crystallinity, stoichiometry and composition of the surface. There is still a strong interest in developing and studying Ca-P surfaces that have the ability to accurately control the osteoblast response. Radio frequency (RF) magnetron sputtering is a technique that allows for accurate control of the properties of deposited Ca-P coatings and has been studied extensively because of this fact. In this work, Ca-P coatings were co-deposited using RF magnetron sputtering in order to study the effect of changing the target stoichiometry on the initial in vitro behavior of MG63 osteoblast-like cells. The samples produced were analysed both as-deposited and after thermal annealing to 500 °C. After annealing XPS analyses of the samples co-deposited using tricalcium phosphate (TCP) materials gave a Ca/P ratio of 1.71 ± 0.01, as compared to those co-deposited from hydroxyapatite (HA) materials, with a Ca/P of 1.82 ± 0.06. In addition to this, the curve fitted XPS data indicated the presence of low levels of carbonate in the coatings. Despite this the XRD results for all of the annealed coatings were shown to be characteristic of pure HA with a preferred 002 orientation. The atomic force microscopy results also highlighted that both types of coatings had surface features of a similar size (200-220 nm). Both surfaces exhibited a degree of surface degradation, even after 1 h of cell culture. However, the TCP derived surfaces showed an enhanced osteoblastic cell response in terms of cell adhesion and cell proliferation in the earlier stages of cell culture than the surfaces deposited from HA. An improvement in the initial cell attachment and a potential for increased cell proliferation rates is viewed as a highly advantageous result in relation to controlling the osteoblast response on these surfaces.

Substitutions of strontium in mesoporous calcium silicate and their physicochemical and biological properties

Calcium silicate (Ca-Si) based bioceramics have been regarded as a potential bioactive materials for bone tissue regeneration. In this study, we have successfully prepared ordered mesoporous strontium (Sr)-substituted CaSiO3 (Sr-CaSiO3) materials by using a triblock copolymer (P123) as a structure-directing agent. The microstructure and porosity of mesoporous Sr-CaSiO3 materials were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and the N2 adsorption-desorption technique. The substitution of Sr for Ca in mesoporous CaSiO3 did not change the mesoporous structure, but the surface area and pore volume decreased with increasing Sr substitution. The effects of the Sr substitution on the physiochemical and biological properties of mesoporous CaSiO3 materials were evaluated by the ion dissolution, apatite-forming ability, proliferation and alkaline phosphatase (ALP) activity of osteoblast-like MC3T3-E1 cells. The results showed that the increasing Sr substitution decreased the dissolution rate of Ca and Si ions from mesoporous CaSiO3 materials and enhanced the ability to stabilize the pH environment. Mesoporous Sr-CaSiO3 materials have a similar apatite-forming ability to mesoporous CaSiO3 material, and stimulated the proliferation and ALP activity of MC3T3-E1 cells. Furthermore, using gentamicin as a model drug, mesoporous Sr-CaSiO3 materials exhibited a sustained drug release property which could be used in local drug delivery therapy. Furthermore, the drug release rate decreased to some extent with increasing Sr substitution in mesoporous CaSiO3 materials. Therefore, mesoporous Sr-CaSiO3 materials have more potential for application in bone tissue regeneration.

Fabrication and characterization of novel nano hydroxyapatite/β-tricalcium phosphate scaffolds in three different composition ratios

The biphasic calcium phosphate (BCP) concept was introduced to overcome disadvantages of single phase biomaterials. Different composition ratios of BCP bioceramics have been studied, yet controversies regarding the effects of ratio on biomaterial behavior still exist. In this study, BCP scaffolds were prepared from nano hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) that were synthesized via a solid state reaction. Three different composition ratios of pure BCP and collagen-based BCP scaffolds (%HA/%β-TCP; 30/70, 40/60, and 50/50) were produced using a polymeric sponge method. Physical and mechanical properties of all materials and scaffolds were investigated. SEM showed overall distribution of both macropores (80-200 μm) and micropores (0.5-2 μm) with high interconnected porosities. Total porosity of pure BCP (90% ± 3%) was found to be higher than collagen-based BCP (85% ± 2%). It was observed that following sintering process, dimensional shrinkage of large scaffolds (39% ± 4%) was lower than small ones (42% ± 5%) and scaffolds with high HA ratios (50%) experienced higher dimensional changes than those with higher β-TCP (70%) ratios (45% ± 3% and 36% ± 1%, respectively). Compressive strength of both groups was less than 0.1 MPa and collagen coating had almost no influence on mechanical behavior. Further studies may improve the physical properties of these scaffolds and investigate their exact biological behaviors.

Ion reactivity of calcium-deficient hydroxyapatite in standard cell culture media

Solution-mediated surface reactions occur for most calcium phosphate-based biomaterials and may influence cellular response. A reasonable extrapolation of such processes observed in vitro to in vivo performance requires a deep understanding of the underlying mechanisms. We therefore systematically investigated the nature of ion reactivity of calcium-deficient hydroxyapatite (CDHA) by exposing it for different periods of time to standard cell culture media of different chemical composition (DMEM and McCoy medium, with and without osteogenic supplements and serum proteins). Kinetic ion interaction studies of principal extracellular ions revealed non-linear sorption of Ca²⁺ (∼50% sorption) and K⁺ (∼8%) as well as acidification of all media during initial contact with CDHA (48h). Interestingly, inorganic phosphorus (P(i)) was sorbed from McCoy medium (∼50%) or when using osteogenic media containing β-glycerophosphate, but not from DMEM medium. Non-linear sorption data could be perfectly described by pseudo-first-order and pseudo-second-order sorption models. At longer contact time (21 days), and with frequent renewal of culture medium, sorption of Ca²⁺ remained constant throughout the experiment, while sorption of P(i) gradually decreased in McCoy medium. In great contrast, CDHA began to release P(i) slowly with time when using DMEM medium. Infrared spectra showed that CDHA exposed to culture media had a carbonated surface chemistry, suggesting that carbonate plays a key role in the ion reactivity of CDHA. Our data show that different compositions of the aqueous environment may provoke opposite ion reactivity of CDHA, and this must be carefully considered when evaluating the osteoinductive potential of the material.

Differentiation of human mesenchymal stem cells on niobium-doped fluorapatite glass-ceramics

OBJECTIVE

Our goal was to characterize the response of human mesenchymal stem cells (hMSCs) to a niobium-doped fluorapatite-based glass-ceramic (FAp).

METHODS

The glass was prepared by twice melting at 1525 °C for 3 h, and cast into cylindrical ingots later sectioned into discs and heat-treated to promote crystallization of fluorapatite submicrometer crystals. Tissue culture polystyrene (TCP) was used as control. The surface of the FAp discs was either left as-heat treated, ground or etched. Initial cell attachment was assessed at 3 h. Proliferation and alkaline phosphatase (ALP) expression data were collected at days 1, 4, and 8. Cell morphology was examined using SEM, at days 2 and 4. Mineralization was evaluated by Alizarin Red staining and SEM.

RESULTS

Initial cell attachment on as heat-treated, etched, or ground surfaces was similar to that of the positive control group (p>0.05). The percentage of area covered by living cells increased significantly on as heat-treated, etched, or ground surfaces between days 1 and 8 (p<0.05). There was no significant difference among groups in cell coverage at day 8, compared to TCP control. SEM revealed well spread polygonal cells with numerous filopodia, either attached to the ceramic surface or connected to neighboring cells. ALP expression at day 8 was significantly higher in osteogenic media compared to growth media on both FAp and control. FAp discs stained positively with Alizarin Red and calcium-rich mineralized granules associated with fibrils were observed by SEM at day 35.

SIGNIFICANCE

hMSCs displayed excellent attachment, proliferation, and differentiation on niobium-doped FAp glass-ceramic.

Effects of serum protein on ionic exchange between culture medium and microporous hydroxyapatite and silicate-substituted hydroxyapatite

It has been proposed that one of the underlying mechanisms contributing to the bioactivity of osteoinductive or osteoconductive calcium phosphates involves the rapid dissolution and net release of calcium and phosphate ions from the matrix as alternatively a precursor to subsequent re-precipitation of a bone-like apatite at the surface and/or to facilitate ion exchange in biochemical processes. In order to confirm and evaluate ion release from sintered hydroxyapatite (HA) and to examine the effect of silicate substitution into the HA lattice on ion exchange under physiological conditions we monitored Ca(2+), PO(4)(3-) and SiO(4)(4-) levels in Earl's minimum essential medium (E-MEM) in the absence (serum-free medium, SFM) or presence (complete medium, C-MEM) of foetal calf serum (FCM), with both microporous HA or 2.6 wt% silicate-substituted HA (SA) sintered discs under both static and semi-dynamic (SD) conditions for up to 28 days. In SFM, variation in Ca(2+) ion concentration was not observed with either disc chemistry or culture conditions. In C-MEM, Ca(2+) ions were released from SA under static and SD conditions whereas with HA Ca(2+) was depleted under SD conditions. PO(4)(3-) depletion occurred in all cases, although it was greater in C-MEM, particularly under SD conditions. SiO(4)(4-) release occurred from SA irrespective of medium or culture conditions but a sustained release only occurred in C-MEM under SD conditions. In conclusion we showed that under physiological conditions the reservoir of exchangeable ions in both HA and SA in the absence of serum proteins is limited, but that the presence of serum proteins facilitated greater ionic exchange, particularly with SA. These observations support the hypothesis that silicate substitution into the HA lattice facilitates a number of ionic interactions between the material and the surrounding physiological environment, including but not limited to silicate ion release, which may play a key role in determining the overall bioactivity and osteoconductivity of the material. However, significant net release of Ca(2+) and PO(4)(3-) was not observed, thus rapid or significant net dissolution of the material is not necessarily a prerequisite for bioactivity in these materials.

Osteoblast interactions within a biomimetic apatite microenvironment

Numerous reports have shown that accelerated apatites can mediate osteoblastic differentiation in vitro and bone formation in vivo. However, how cells interact within the apatite microenvironment remains largely unclear, despite the vast literature available today. In response, this study evaluates the in vitro interactions of a well-characterized osteoblast cell line (MC3T3-E1) with the apatite microenvironment. Specifically, cell attachment, spreading, and viability were evaluated in the presence and absence of serum proteins. Proteins were found to be critical in the mediation of cell–apatite interactions, as adherence of MC3T3-E1 cells to apatite surfaces without protein coatings resulted in significant levels of cell death within 24 h in serum-free media. In the absence of protein–apatite interaction, cell viability could be “rescued” upon treatment of MC3T3-E1 cells with inhibitors to phosphate (PO₄³⁻) transport, suggesting that PO₄³⁻ uptake may play a role in viability. In contrast, rescue was not observed upon treatment with calcium (Ca²⁺) channel inhibitors. Interestingly, a rapid “pull-down” of extracellular Ca²⁺ and PO₄³⁻ ions onto the apatite surface could be measured upon the incubation of apatites with α-MEM, suggesting that cells may be subject to changing levels of Ca²⁺ and PO₄³⁻ within their microenvironment. Therefore, the biomimetic apatite surface may significantly alter the microenvironment of adherent osteoblasts and, as such, be capable of affecting both cell survival and differentiation.

Influence of crystallite size of nanophased hydroxyapatite on fibronectin and osteonectin adsorption and on MC3T3-E1 osteoblast adhesion and morphology

The characteristic topographical features (crystallite dimensions, surface morphology and roughness) of bioceramics may influence the adsorption of proteins relevant to bone regeneration. This work aims at analyzing the influence of two distinct nanophased hydroxyapatite (HA) ceramics, HA725 and HA1000 on fibronectin (FN) and osteonectin (ON) adsorption and MC3T3-E1 osteoblast adhesion and morphology. Both substrates were obtained using the same hydroxyapatite nanocrystals aggregates and applying the sintering temperatures of 725°C and 1000°C, respectively. The two proteins used in this work, FN as an adhesive glycoprotein and ON as a counter-adhesive protein, are known to be involved in the early stages of osteogenesis (cell adhesion, mobility and proliferation). The properties of the nanoHA substrates had an important role in the adsorption behavior of the two studied proteins and clearly affected the MC3T3-E1 morphology, distribution and metabolic activity. HA1000 surfaces presenting slightly larger grain size, higher root-mean-square roughness (Rq), lower surface area and porosity, allowed for higher amounts of both proteins adsorbed. These substrates also revealed increased number of exposed FN cell-binding domains as well as higher affinity for osteonectin. Regarding the osteoblast adhesion results, improved viability and cell number were found for HA1000 surfaces as compared to HA725 ones, independently of the presence or type of adsorbed protein. Therefore the osteoblast adhesion and metabolic activity seemed to be more sensitive to surfaces morphology and roughness than to the type of adsorbed proteins.

A new biphasic osteoinductive calcium composite material with a negative Zeta potential for bone augmentation

The aim of the present study was to analyze the osteogenic potential of a biphasic calcium composite material (BCC) with a negative surface charge for maxillary sinus floor augmentation. In a 61 year old patient, the BCC material was used in a bilateral sinus floor augmentation procedure. Six months postoperative, a bone sample was taken from the augmented regions before two titanium implants were inserted at each side. We analyzed bone neoformation by histology, bone density by computed tomography, and measured the activity of voltage-activated calcium currents of osteoblasts and surface charge effects. Control orthopantomograms were carried out five months after implant insertion. The BCC was biocompatible and replaced by new mineralized bone after being resorbed completely. The material demonstrated a negative surface charge (negative Zeta potential) which was found to be favorable for bone regeneration and osseointegration of dental implants.

Biological response of human bone cells to zinc-modified Ca-Si-based ceramics

Calcium silicate (CaSiO(3)) ceramics have received considerable attention in recent years due to their excellent bioactivity and degradability. However, their poor chemical stability limits their biological applications. Hardystonite (Ca(2)ZnSi(2)O(7)) ceramics are Ca-Si-based materials developed by incorporating zinc into the Ca-Si system to improve their chemical stability. However, the biological responses of Ca(2)ZnSi(2)O(7) to bone cells are unknown. The objective of this study is to investigate and compare the in vitro responses of human osteoblast-like cells (HOBs) and osteoclasts when cultured on Ca(2)ZnSi(2)O(7) and CaSiO(3) ceramic disks. The ability of Ca(2)ZnSi(2)O(7) ceramics to support HOB attachment, cytoskeleton organization, proliferation and differentiation was assessed by scanning electron microscopy, confocal microscopy, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, alkaline phosphatase activity and quantitative real-time polymerase chain reaction. Our results show that Ca(2)ZnSi(2)O(7) supported HOB attachment with a well-organized cytoskeleton structure, and significantly increased cellular proliferation and differentiation compared to CaSiO(3). In addition, Ca(2)ZnSi(2)O(7) showed increased expression levels of osteoblast-related mRNAs (alkaline phosphatase, collagen type I, osteocalcin, receptor activator of NF(kappa)B ligand and osteoprotegerin) compared to CaSiO(3). Ca(2)ZnSi(2)O(7) ceramic supported the formation of mature and functional osteoclasts and formed resorption imprints. On CaSiO(3) ceramics, the cells failed to differentiate from the monocytes into osteoclasts. Taken together, these results indicate that Hardystonite ceramics are conducive to both types of bone cells, osteoblast-like cells and osteoclasts, suggesting their potential use for skeletal tissue regeneration and as coatings onto currently available orthopedic and dental implants.

Osteoblast-like cell proliferation on tape-cast and sintered tricalcium phosphate sheets

The influence of sintering temperature on the in vitro proliferation of osteoblast-like cells to sintered tricalcium phosphate (TCP) sheets prepared by tape-casting was investigated. Green sheets of tape-cast beta-TCP were sintered for 2h in a furnace at atmospheric pressure at five different sintering temperatures: 900, 1000, 1100, 1150 and 1200 degrees C. The number of osteoblast-like (MC3T3-E1) cells deposited onto TCP sheets was counted after cell cultivation for 1week and was found to have increased with increasing sintering temperature. The TCP sheets sintered at 900 degrees C exhibited a significantly lower cell number than TCP sheets sintered at 1000, 1100, 1150 and 1200 degrees C. In the attenuated total reflection infrared spectra, the peaks around 900-1150cm(-1), corresponding to the P-O vibration mode of the phosphate group, gradually decreased and shifted to lower wavenumbers with increasing sintering temperature. Meanwhile, the zeta potential of TCP sintered at 900 degrees C showed a highly negative charge when compared with the other groups. This would suggest that the higher solubility of the TCP sheets sintered at 900 degrees C exerted the higher negative charge obtained from zeta potential measurement. Within the limitations of this study, it was indicated that osteoblast-like cell proliferation increased with increasing sintering temperature. The biological stability of the sintered TCP sheet surface was considered to have affected cell proliferation.

In vitro osteogenesis on fluorcanasite glass-ceramic with three different chemical compositions

This study aimed at investigating in vitro osteogenesis on three fluorcanasite glass-ceramic compositions with different solubilities (K3, K5, and K8). Osteoblastic cells were obtained from human alveolar bone fragments and cultured under standard osteogenic condition until subconfluence. First passage cells were cultured on K3, K5, and K8 and on Bioglass((R)) 45S5 (45S5-control). Cell adhesion was evaluated at 24 h. For proliferation and viability, cells were cultured for 1, 4, and 10 days. Total protein content and alkaline phosphatase (ALP) activity were measured at 7, 14, and 21 days. Cultures were stained with Alizarin red at 21 days, for detection of mineralized matrix. Data were compared by ANOVA followed by Duncan's test. Cell adhesion, cell proliferation, viability, total protein content, and ALP activity were not affected by fluorcanasite glass-ceramic composition and solubility. Bone-like formation was similar on all fluorcanasite glass-ceramics and was reduced compared to 45S5. The changes in the chemical composition and consequently solubility of the fluorcanasite glass-ceramics tested here did not significantly alter the in vitro osteogenesis. Further modifications of the chemical composition of the fluorcanasite glass-ceramic would be required to improve bone response, making this biomaterial a good candidate to be employed as a bone substitute.

In vitro biological evaluation of β–TCP/HDPE—A novel orthopedic composite: A survey using human osteoblast and fibroblast bone cells

Beta-tricalcium phosphate reinforced high density polyethylene (beta-TCP/HDPE) was prepared to simulate bone composition and to study its capacity to act as bone tissue. This material was produced by replacing the mineral component and collagen soft tissue of the bone with beta-TCP and HDPE, respectively. The biocompatibility of the composite samples with different volume fractions of TCP (20, 30 and 40 vol %) was examined in vitro using two osteoblast cell lines G-292 and Saos-2, and also a type of fibroblast cell isolated from bone tissue, namely human bone fibroblast (HBF) by proliferation, and cell adhesion assays. Cell-material interaction with the surface of the composite samples was examined by scanning electron microscopy (SEM). The effect of beta-TCP/HDPE on the behavior of osteoblast and fibroblast cells was compared with those of composite and negative control samples; polyethylene (PE) and tissue culture polystyrene (TPS), respectively. In general, the results showed that the composite samples containing beta-TCP as reinforcement supported a higher rate of proliferation by various bone cells after 3, 7, and 14 days of incubation compared to the composite control sample. Furthermore, more osteoblast cells were attached to the surface of the composite samples when compared to the composite control samples after the above incubation periods (p < 0.05), while in the case of HBF an equal or even higher number of cells adhered to PE was observed. The number of adhered osteoblast cells was almost equal and in some days even higher than the number of adhered cells on negative control sample, while in the case of fibroblast this difference was significantly higher than TPS (p < 0.05). Adhered cells presented a normal morphology by SEM and many of the cells were observed to be undergoing cell division. These findings indicate that beta-TCP/HDPE composites are biocompatible, nontoxic, and act to stimulate proliferation and adhesion of the cells, whether osteoblast or fibroblast.

Comparative performance of three ceramic bone graft substitutes

BACKGROUND CONTEXT

A number of different synthetic calcium-based bone graft substitutes (BGS) are currently available for clinical use. There is, however, a lack of comparative performance data regarding the relative efficacy of these materials when placed in an osseous defect site.

PURPOSE

To compare the rate, quality, and extent of osseous healing in a standard rabbit defect model for three commercially available BGS materials by measuring early bone formation and completion of defect healing and to identify whether rapid scaffold resorption stimulated or impaired bone healing.

STUDY DESIGN

Osteochondral defects, 4.8 mm in diameter and 6 to 7 mm deep, were made through the articular surface into the subchondral bone of the femoral condyle of New Zealand White rabbits and filled with cylindrical pellets of one of three commercially available BGS materials: dense calcium sulfate (DCaS), ultraporous tricalcium phosphate (beta-TCP), and porous silicated calcium phosphate (Si-CaP). The repair response was examined at 1, 3, 6, and 12 weeks after surgery (n=4 per BGS per time point).

METHOD

Qualitative histological and quantitative histomorphometric (% new bone, % bone graft substitute, capillary index, and mineral apposition rates) analysis.

RESULTS

Rapid resorption of D-CaS, primarily through dissolution, elicited a mild inflammatory response that left the defect site empty before significant quantities of new bone were formed. Both beta-TCP and Si-CaP scaffolds supported early bone apposition (<1 week). However, beta-TCP degradation products subsequently provoked an inflammatory response that impaired and reversed bone apposition within the defect site. The Si-CaP scaffolds appeared to be more stable and supported further bone apposition, with the development of an adaptive bone-scaffold composite; cell-mediated resorption of scaffold and new bone were observed in response to local load and contributed to the production of a functional repair within the defect site.

CONCLUSIONS

Rapid BGS resorption impaired the regenerative ability of local bone via three pathways: 1) insufficient persistence of an osteoconductive scaffold to encourage bone apposition, 2) destabilization of early bony apposition through scaffold disintegration, and 3) stimulation of an inflammatory response by elevated levels of particulate degradation products. This had a significant impact on the ultimate rate of healing. D-CaS did not stimulate early bone apposition, but bone repair was more advanced in D-CaS-treated defects at 12 weeks as compared with those treated with beta-TCP, despite the beta-TCP supporting direct bone apposition at 1 week. Si-CaP appeared to provide a more stable osteoconductive scaffold, which supported faster angiogenesis and bone apposition throughout the defect site, with the development of a functionally adaptive trabecular structure through resorption/remodelling of both scaffold and new bone. There was rapid formation of mineralized tissue at week 1 within the center of the defect and complete infiltration with dense, predominantly mature bone by weeks 3 to 6. The progressive remodeling of bone ingrowth and scaffold to reflect the distribution of local host tissue, combined with histological evidence of targeted osteoclastic resorption of both scaffold and bone, suggest that bone adaptation within the scaffold could be in response to Wolff's law. Although this model may not directly translate to a spinal fusion model and the products may vary according to the environment, these results suggest that, in patients in whom bone regeneration may be compromised, the degradation observed with some resorbable bone grafts may contribute to the decoupling of bone regeneration and resorbtion within the graft site, which may ultimately lead to incomplete bone repair.

Effect of reinforcement particle size onin vitro behavior of β-tricalcium phosphate-reinforced high-density polyethylene: A novel orthopedic composite

Beta-tricalcium phosphate-reinforced high-density polyethylene (beta-TCP/HDPE) is a new biomaterial, which was made to simulate bone composition and study its capacity to act like bony tissues. This material was produced by replacing mineral component and collagen soft tissue of bone with beta-TCP and HDPE, respectively. The biocompatibility of composite samples with different volume fractions of TCP (20, 30, and 40 vol %) and two different particle sizes (80-100 and 120-140 mesh size) was examined in vitro using the osteoblast cell line G-292 by proliferation, alkaline phosphatase (ALP) production, and cell adhesion assays. Cell-material interaction on the surface of the composites was observed by scanning electron microscopy (SEM). The effect of beta-TCP particle size on behavior of the osteoblast cell line was compared between two groups of the composite samples containing smaller and larger reinforcement particle sizes as well as with those of a negative control. In general, results showed that the composite samples containing larger particles supported a higher rate of proliferation and ALP production by osteoblast cells after 3, 7, and 14 days of incubation compared to the composite samples with smaller particle size and control. Furthermore, more cells were attached to the surface of composite samples containing larger particle size when compared to the smaller particle size composites (p<0.05). This number was nearly equal with numbers adhered on negative control [tissue culture polystyrene (TPS)] and significantly higher in comparison with composite control [polyethylene (PE)] (p<0.05). Adhered cells presented a normal morphology by SEM and many of the cells were seen to be undergoing cell division. These findings indicate that beta-TCP/HDPE composites are biocompatible, nontoxic, and in some cases, act to stimulate proliferation of the cells, ALP production, and cell adhesion when compared to the control counterparts. Furthermore, beta-TCP/HDPE samples with larger reinforcement particle size were shown to possess better biological properties.

The mechanical properties of calcium phospate ceramics modified by collagen coating and populated by osteoblasts

Bioceramics containing hydroxyapatite (HA), tricalcium phosphate (TCP) or composites which combine the best properties of both materials are among the principal candidates for bone replacement grafts. In this study we have investigated the mechanical strength of HA, TCP and composites of the two in the ratios 75;25 (H75), 50:50 (H50) and 25:75 (H25). The strength of each material was investigated in the presence and absence of collagen coating, and the influence of osteoblast culture for up to 28 days on strength was determined. TCP, H25 and H75 were significantly weakened by collagen coating, the strengths of the other materials were either not affected (HA) or increased (H50). Culture with osteoblasts significantly increased the strength of uncoated HA and H50, but this effect was not observed when the materials were coated with collagen. Our results indicate that ceramic composition affects the interactions between collagen coating, culture with osteoblasts and mechanical strength of the material. Although collagen coating has been found to increase the proliferation of osteoblasts into these ceramic materials, it may be necessary to stabilise and optimise the coating process to minimise effects on mechanical strength.

Influence of hydroxyapatite microstructure on human bone cell response

Microstructure of calcium phosphate ceramics has been shown to influence long-term in vitro cellular events like proliferation and differentiation, and to favor bone integration in vivo. As long-term cellular events are known to be dependent of early cell adhesion events, we decided to study the in vitro influence of the microstructure of a microporous hydroxyapatite (mHA) and a nonmicroporous hydroxyapatite (pHA) ceramic on serum protein adsorption and SaOs-2 human bone cells attachment after 30 min, 1, 4, and 24 h and cell growth after 96 h. Plastic coverslips were used as controls. Hydroxyapatite composition of mHA and pHA was confirmed by X-ray diffraction and Fourier transform infra-red spectroscopy. The surface energies of ceramics were calculated from contact-angle measurements in di-iodomethane, water or complete culture medium. The total surface energy was 44.8 mJ/m(2) for pHA and 48.7 mJ/m(2) for plastic. The contact-angle measurement was impossible on mHA likely because they displayed 12% of open microporosity, pHA ceramic exhibiting only closed pores (2.5%). Moreover, the roughness amplitude was largely higher on mHA (Sa = 4.35 microm) than on pHA (Sa = 0.065 microm) and plastic (Sa = 0.042 microm). Three different techniques were used to evaluate protein adsorption on the ceramics. SDS-PAGE of desorbed proteins demonstrated that more proteins desorbed from mHA (66.02 microg/m(2)) than from pHA (17.2 microg/m(2)) or plastic (0.08 microg/m(2)). A new method was used to evaluate in situ the quantity of adsorbed total proteins: the temperature-programmed desorption (TPD) analysis coupled with mass spectrometry. The TPD analysis confirmed that 10-fold more proteins adsorbed on mHA compared with those on pHA. A direct immunolabeling on ceramics revealed than more fibronectin and serum albumin adsorbed on microporous ceramic than on dense ceramic. The morphology of SaOs-2 cells was the same on all the substrates after 30 min. At later time points, cell morphology on mHA was radically different than on other surfaces, with the particularity of the cytoplasmic edge that appeared undistinguishable from the surface. Only the extremity of the cells and lamellipodia were visible. Cells seemed like "adsorbed" by the mHA surface, whereas on plastic and pHA surfaces the cells displayed classical aspects of polygonal spreading. The cells displayed on mHA the highest initial attachment potential after 30 min, 1, 4, 24 h but the lower proliferation potential after four days. This study confirms that a microporous ceramic surface can modulate the adsorption of proteins and further the adhesion and proliferation of human bone cells.

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.

Osteoblast interactions with calcium phosphate ceramics modified by coating with type I collagen

Complications associated with the use of autogenous bone in the repair or replacement of tissue lost through injury or disease have driven the search for alternative sources of graft material. Bioceramics containing hydroxyapatite (HA), tricalcium phosphate (TCP), or composites that combine the best properties of both of these materials are among the principal candidates. In this study, we have investigated the in vitro proliferation, morphology, and viability of an immortalized rat osteoblast cell line cultured on HA, TCP, and composites of the two in the ratios 75:25 (H75), 50:50 (H50), and 25:75 (H25) for 28 days. The biocompatibility of each material was examined in the presence and absence of a collagen coating. With the exception of H50, cell proliferation, quantified by carboxyfluorescein fluorescence, was enhanced by collagen coating of all materials for the first 14 days, although at later time points cell numbers were unaffected. It is notable that the collagen coating was least stable on H50, the only material not to show enhancement of cell growth on coating. Confocal laser scanning microscopy confirmed that cell growth was more extensive on coated materials over the first 7-14 days in culture, and the development of cell extensions and bridges across the pores in the materials was observed. Results indicate that collagen coating of calcium phosphate ceramics may also increase their compatibility and osseointegration in vivo.

Mediation of biomaterial-cell interactions by adsorbed proteins: a review

An appropriate cellular response to implanted surfaces is essential for tissue regeneration and integration. It is well described that implanted materials are immediately coated with proteins from blood and interstitial fluids, and it is through this adsorbed layer that cells sense foreign surfaces. Hence, it is the adsorbed proteins, rather than the surface itself, to which cells initially respond. Diverse studies using a range of materials have demonstrated the pivotal role of extracellular adhesion proteins--fibronectin and vitronectin in particular--in cell adhesion, morphology, and migration. These events underlie the subsequent responses required for tissue repair, with the nature of cell surface interactions contributing to survival, growth, and differentiation. The pattern in which adhesion proteins and other bioactive molecules adsorb thus elicits cellular reactions specific to the underlying physicochemical properties of the material. Accordingly, in vitro studies generally demonstrate favorable cell responses to charged, hydrophilic surfaces, corresponding to superior adsorption and bioactivity of adhesion proteins. This review illustrates the mediation of cell responses to biomaterials by adsorbed proteins, in the context of osteoblasts and selected materials used in orthopedic implants and bone tissue engineering. It is recognized, however, that the periimplant environment in vivo will differ substantially from the cell-biomaterial interface in vitro. Hence, one of the key issues yet to be resolved is that of the interface composition actually encountered by osteoblasts within the sequence of inflammation and bone regeneration.

In vitro studies of calcium phosphate glass ceramics with different solubility with the use of human bone marrow cells

Two glass ceramics in the CaO--P2O5--MgO system with the incorporation of K2O or TiO2 oxides were prepared with the goal of using them as potential bone graft substitutes. The incorporation of TiO2 and K2O led to the preparation of specific crystalline phases in the structure of the glass ceramics, which show different degrees of biodegradation. In fact, the 45CaO--45P2O5--5MgO--5K2O has been previously demonstrated to be much more soluble in aqueous solutions than the 45CaO--37P2O5--5MgO--13TiO2 glass ceramic. The in vitro biological activity of the two calcium phosphate glass ceramics was studied with the use of human bone marrow osteoblast cell cultures maintained for 28 days, and seeded materials were assessed for cell proliferation and function. The Ti-containing glass ceramic showed a stable surface throughout the culture time, on macroscopic and SEM observation. Osteoblast cells proliferated gradually, especially during the third week, with a high alkaline phosphatase activity and formation of a mineralized matrix. On SEM observation, attached cells appeared with a spread-polygonal morphology typical of the osteoblast cells, with extensive cell-to-cell contact. Cell behavior on the seeded material was similar to that found on cultures performed on tissue-culture-grade polystyrene; except for the presence of lower cell numbers during the first 2 weeks. By contrast, the K-containing glass ceramic showed a highly instable surface with dissolution/precipitation processes occurring throughout the culture time. Few cells adhered to the material surface, and subsequent proliferation was also hindered, especially from the first week onwards. Cell numbers were significantly lower than those observed in the Ti-containing glass ceramic during most of the incubation time. Results suggest that the different in vitro biological behavior of these two glass ceramics is mainly due to the significant differences in the surface degradation rate, which is directly correlated to the chemical composition of the mother glass.

Removal of surface by-products from sintered hydroxyapatite: Effect of a chelation treatment on fibronectin adsorption and cell adhesion

It was observed that fibronectin precipitates when deposited on hydroxyapatite (HA) ceramics. Fibronectin's known affinity for calcium and the composition of the ceramic itself suggested that calcium release could be the main cause of this aggregation effect. It was then decided to investigate the effect of a surface chelation treatment on fibronectin adsorption, and MG63 cell adhesion, onto porous ceramics of hydroxyapatite (HA), beta-tricalcium phosphate (beta-TCP), and HA/TCP biphasic material (BCP). Those ceramics were immersed in an EDTA solution and the effect of this treatment on the material composition was assayed. X-ray diffraction data showed the presence of alpha- and beta-TCP phases in HA and BCP materials, which were both completely removed by the chelation treatment in the case of HA. On BCP, alpha-TCP was removed and beta-TCP partially dissolved. The TCP material, which was pure beta-TCP, underwent a mass loss, but no change in composition was observed. Adhesion of MG63 cells was overall higher on the fibronectin-coated EDTA-treated HA material, but was especially enhanced on EDTA-treated HA. Changes in surface morphologies, as compared with the use of scanning electron microscopy, did not seem to be related to the effects observed. The EDTA treatment proved to be a very efficient way of removing by-products of HA sintered materials, and thus enhancing the biocompatibility of the material.

Ionic modification of calcium phosphate cement viscosity. Part I: hypodermic injection and strength improvement of apatite cement

A broadening of the indications for which calcium phosphate cements (CPC) can be used, for example, in the field of vertebroplasty, would require injectable and higher strength materials. Unmodified CPC are not injectable due to a filter-pressing effect during injection. In this work we demonstrated that an effective method for improving the injection properties of CPC was by the use of sodium citrate solution as a liquid component. Cement consisting of tetracalcium phosphate (TTCP) and monetite (DCPA) mixed with water up to a powder:liquid ratio (P:L) of 3.3 g/ml had an injectability of approximately 60%. The use of 500 mM trisodium citrate solution instead of water decreased the viscosity of the cement paste to a point, where complete injectability (>95%) through an 800 microm diameter hypodermic needle could be achieved at low loads. The reduction in water demand of the cement effected by the use of sodium citrate enabled high P:L mixes to be formed which were 400% stronger than cements made with water. The effect was less pronounced with compacted cements such that at 9 MPa applied pressure, 58% improvement was obtained and at 50 MPa 36% improvement was measured yielding a cement with a compressive strength of 154 MPa. The liquefying effect of sodium citrate was thought to derive from a strong increase in the surface charge of both the reactants and the product as determined by zeta-potential measurement.

Surface reactivity of calcium phosphate based ceramics in a cell culture system

Surface reactivity of Calcium Phosphate materials--Hydroxyapatite (HA), Tricalcium Phosphate (beta-TCP), Hydroxyapatite-Tricalcium Phosphate (HA-TCP) were elucidated in a cell culture system. MG-63 osteoblast-like cells were seeded onto the ceramic discs to evaluate changes in the cell morphology and functionality with respect to the different substrates. The dissolution and re-precipitation of calcium phosphate phases on the surface of the discs in the culture medium was found to be prominent on beta-TCP when compared with HA. Low calcium (Ca), magnesium (Mg) and alkaline phosphatase (ALP) levels and high phosphorous (P) levels in the medium of beta-TCP were observed. This indicated that P must have leached out into the medium from beta-TCP and Ca in turn deposited from the medium onto beta-TCP resulting in the apatite phase transformation. The low ALP activity in beta-TCP medium is however an indication of low osteoblastic activity. Under the phase contrast microscope, the osteoblast cells around HA material were found to be confluent and viable, while in the vicinity of beta-TCP only cellular debris was observed. In the case of HA-TCP, only a few viable cells surrounded the material amidst the debris. Scanning electron microscopy revealed numerous cells on the surface of HA showing different cell behaviour like anchorage, attachment, adhesion and spreading in the early time period as the surface was only slightly disturbed with re-crystallisation. But with time the entire surface of HA had changed due to precipitation and re-crystallization which did not support cell behaviour while the cells surrounding the material showed normal growth. On the contrary, cells were scarcely observed on the entirely changed surface of beta-TCP and HA-TCP even from the earlier days of the culture and the morphology of cells surrounding the material too started changing. These results establish that HA promoted the activity of osteoblast cells. HA surface remained unaltered for some time, while the surface of beta-TCP underwent dissolution of surface ions and resulted in the re-crystallization of apatite over the surface. The resulting changes in the surrounding milieu of beta-TCP with high phosphate and low Ca levels probably was responsible for the death of the cells.

Increasing hydroxyapatite incorporation into poly(methylmethacrylate) cement increases osteoblast adhesion and response

Poly(methylmethacrylate) (PMMA) is the current standard for cement held prostheses. It forms a strong bond with the implant, but the bond between the cement and the bone is considered to be weak, with fibroblastic cells observed at the implant site, rather than direct bone contact, a contributing factor leading to implant failure. Incorporation of hydroxyapatite (HA) increases the biological response to the cement from tissue around the implant site, thus giving increased bone apposition. In this study, PMMA discs with 0, 4.6 and 8.8 vol%. HA were examined. Primary human osteoblast-like cells (HOBs) were used for the biological evaluation of the response to the cements in vitro. Morphology was observed using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Measurement of tritiated thymidine (3H-TdR) incorporation and alkaline phosphatase (ALP) activity were used to assess proliferation and differentiation. A synergy between increasing focal contact formation, cytoskeletal organisation, cell proliferation and expression of phenotype was observed with increasing HA volume. Preferential anchorage of HOBs to HA rather than PMMA was a prominent observation.

Initial interaction of osteoblasts with the surface of a hydroxyapatite-poly(methylmethacrylate) cement

Failure of the bone/cement interface in cemented joint prostheses is a contributor to implant loosening. The introduction of a bioactive phase, such as hydroxyapatite (HA), to cement may enhance fixation by encouraging direct bone apposition rather than encapsulation of the implant by fibrous tissue. The effect of poly(methylmethacrylate) (PMMA) bone cement (incorporating 17.5% HA wt.) on bioactivity has been investigated using primary human osteoblast-like cells (HOB). A significantly higher cell proliferation and differentiation was seen on the PMMA/HA cement compared to the PMMA cement alone, with retention of phenotype up to 21 days of culture on both materials.

Fluorine ion-implanted polystyrene improves growth and viability of vascular smooth muscle cells in culture

Vascular smooth muscle cells derived from the rat aorta were cultured on unmodified or F(+) ion-implanted polystyrene (5 x 10(12) or 5 x 10(14) ions/cm(2), energy 150 keV). In 1-day-old cultures, the cells adhered to the modified polystyrene in higher numbers and over larger contact areas. Increased resistance of the cells to trypsin-mediated detachment from the growth support indicated an improved adhesion of cells to the modified polymer at later culture intervals. The cells cultured on ion-modified polymers also were larger and had a higher total protein content. By use of immunocytochemistry, several specific protein species were increased, including the cytoskeletal alpha-actin and vimentin and the plasma membrane-associated vinculin, talin, alpha-v integrins, ICAM-1, and VCAM-1, which account for stronger cell-cell and cell-extracellular matrix adhesion. The lower number of cells found floating in the medium suggests that the spontaneous detachment of cells from the modified polystyrene was lower and that the viability of the adhered cell population was higher. As was shown by the two-parameter flow-cytometric measurements of BrdU incorporation and DNA content, as well as by (3)H-thymidine autoradiography, the cell proliferation on samples modified by the dose of 5 x 10(12) ions/cm(2) was similar to that in controls; and at the dose of 5 x 10(14) ions/cm(2), it tended to be even lower. The cells grown on the polymer implanted with the dose of 5 x 10(12) ions/cm(2) responded to a new artificially created cell-free area in a confluent cell layer by more intense migration whereas at the dose of 5 x 10(14) ions/cm(2), the migration ability of cells was similar to that on the unmodified polymer. The data revealed a higher biocompatibility of ion-implanted polystyrene with vascular smooth muscle cells in culture. There was better adhesion, differentiation, and survival, and there was neither excessive migration nor proliferation.

Growth and adhesion of osteoblast-like cells derived from neonatal rat calvaria on calcium phosphate ceramics

The effects of biocompatible ceramics on the growth and adhesion of osteoblast-rich rat calvarial cell cultures were investigated. Osteoblast-like cells and mouse fibroblast-like L-929 cells were cultured on composite sinters of hydroxyapatite (HAP) and beta-tricalcium phosphate (TCP) culture carriers, whose Ca/P molar ratios were adjusted to values of 1.50, 1.55, 1.60, 1.64 and 1.67. The growth rates of both cell types were accelerated on the TCP-HAP ceramics as compared to those on polystyrene plastic (LUX) or bioinert zirconia ceramics. The population of osteoblast-like cells reached a density of 2.28 x 10(5) cells/cm2 on 100% HAP (Ca/P ratio 1.67) at 9 d of culture, while the corresponding cell density was 1.66 x 10(5) cells/cm2 on LUX and 1.26 x 10(5) cells/cm2 on zirconia. Adhesion of the osteoblast-like cells on TCP-HAP ceramics was similarly increased as compared with that on LUX or zirconia ceramics. The adhesion of L-929 cells on TCP-HAP ceramics was found to be weaker than that on cultures on LUX or zirconia ceramics. The time-dependent variations in the alkaline phosphatase activity of the osteoblast-like cells showed that the osteoblastic phenotype was potentiated by culturing the cells in calcium-rich media. The surface analyses of the Ca/P ratio and the microstructure by XRD and FTIR suggest that the Ca-rich surface was newly formed by recombination on the surface layer in the culture medium containing fetal bovine serum. These results suggest that the surface of TCP-HAP ceramics, especially that of 100% HAP ceramics, are effective for accelerating growth and differentiation of osteoblast-like cells. This is most probably due to the chemical and physical instability and composition of 100% HAP, which promote the formation of a Ca-rich layer at the cell-material interface and provision of Ca ions to the osteoblast-like cells.

Hydrophobicity, surface tension, and zeta potential measurements of glass-reinforced hydroxyapatite composites

Wettability and zeta potential studies were performed to characterize the hydrophobicity, surface tension, and surface charge of P2O5-glass-reinforced hydroxyapatite composites. Quantitative phase analysis was performed by the Rietveld method using GSAS software applied to X-ray diffractograms. Surface charge was assessed by zeta potential measurements. Protein adsorption studies were performed using vitronectin. Contact angles and surface tensions variation with time were determined by the sessile and pendent drop techniques, respectively, using ADSA-P software. The highest (-18.1 mV) and lowest (-28.7 mV) values of zeta potential were found for hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP), respectively, with composite materials presenting values in between. All studied bioceramic materials showed similar solid surface tension. For HA and beta-TCP, solid surface tensions of 46.7 and 45.3 mJ/m2, respectively, were obtained, while composites presented intermediate surface tension values. The dispersive component of surface tension was the predominant one for all materials studied. Adhesion work values between the vitronectin solution and HA and beta-TCP were found to be 79.8 and 88.0 mJ/m2, respectively, while the 4.0 wt % glass composites showed slightly lower values than the 2.5 wt % ones. The presence of beta-TCP influenced surface charge, hydrophobicity, and protein adsorption of the glass-reinforced HA composites, and therefore indirectly affected cell-biomaterial interactions.