Effect of calcium phosphate coating composition and crystallinity on the response of osteogenic cells in vitro

The importance of being amorphous: calcium and magnesium phosphates in the human body

This article focuses on the relevance of amorphous calcium (and magnesium) phosphates in living organisms. Although crystalline calcium phosphate (CaP)-based materials are known to constitute the major inorganic constituents of human hard tissues, amorphous CaP-based structures, often in combination with magnesium, are frequently employed by Nature to build up components of our body and guarantee their proper functioning. After a brief description of amorphous calcium phosphate (ACP) formation mechanism and structure, this paper is focused on the stabilization strategies that can be used to enhance the lifetime of the poorly stable amorphous phase. The various locations of our body in which ACP (pure or in combination with Mg²⁺) can be found (i.e. bone, enamel, small intestine, calciprotein particles and casein micelles) are highlighted, showing how the amorphous nature of ACP is often of paramount importance for the achievement of a specific physiological function. The last section is devoted to ACP-based biomaterials, focusing on how these materials differ from their crystalline counterparts in terms of biological response.

Bioactive calcium phosphate materials and applications in bone regeneration

BACKGROUND

Bone regeneration involves various complex biological processes. Many experiments have been performed using biomaterials in vivo and in vitro to promote and understand bone regeneration. Among the many biomaterials, calcium phosphates which exist in the natural bone have been conducted a number of studies because of its bone regenerative property. It can be directly contributed to bone regeneration process or assist in the use of other biomaterials. Therefore, it is widely used in many applications and has been continuously studied.

MAINBODY

Calcium phosphate has been widely used in bone regeneration applications because it shows osteoconductive and in some cases osteoinductive features. The release of calcium and phosphorus ions regulates the activation of osteoblasts and osteoclasts to facilitate bone regeneration. The control of surface properties and porosity of calcium phosphate affects cell/protein adhesion and growth and regulates bone mineral formation. Properties affecting bioactivity vary depending on the types of calcium phosphates such as HAP, TCP and can be utilized in various applications because of differences in ion release, solubility, stability, and mechanical strength. In order to make use of these properties, different calcium phosphates have been used together or mixed with other materials to complement their disadvantages and to highlight their advantages. Calcium phosphate has been utilized to improve bone regeneration in ways such as increasing osteoconductivity for bone ingrowth, enhancing osteoinductivity for bone mineralization with ion release control, and encapsulating drugs or growth factors.

CONCLUSION

Calcium phosphate has been used for bone regeneration in various forms such as coating, cement and scaffold based on its unique bioactive properties and bone regeneration effectiveness. Additionally, several studies have been actively carried out to improve the efficacy of calcium phosphate in combination with various healing agents. By summarizing the properties of calcium phosphate and its research direction, we hope that calcium phosphate can contribute to the clinical treatment approach for bone defect and disease.

Deconvoluting the Bioactivity of Calcium Phosphate-Based Bone Graft Substitutes: Strategies to Understand the Role of Individual Material Properties

Calcium phosphate (CaP)-based ceramics are the most widely applied synthetic biomaterials for repair and regeneration of damaged and diseased bone. CaP bioactivity is regulated by a set of largely intertwined physico-chemical and structural properties, such as the surface microstructure, surface energy, porosity, chemical composition, crystallinity and stiffness. Unravelling the role of each individual property in the interaction between the biomaterial and the biological system is a prerequisite for evolving from a trial-and-error approach to a design-driven approach in the development of new functional biomaterials. This progress report critically reviews various strategies developed to decouple the roles of the individual material properties in the biological performance of CaP ceramics. It furthermore emphasizes on the importance of a comprehensive and adequate material characterization that is needed to enhance our knowledge of the property-function relationship of biomaterials used in bone regeneration, and in regenerative medicine in general.

Incorporation of silver nanoparticles into magnetron-sputtered calcium phosphate layers on titanium as an antibacterial coating

A three-layer system of nanocrystalline hydroxyapatite (first layer; 1000nm thick), silver nanoparticles (second layer; 1.5μg Ag cm^-2) and calcium phosphate (third layer, either 150 or 1000nm thick) on titanium was prepared by a combination of electrophoretic deposition of silver nanoparticles and the deposition of calcium phosphate by radio frequency magnetron sputtering. Scanning electron microscopy showed that the silver nanoparticles were evenly distributed over the surface. The adhesion of multilayered coating on the substrate was evaluated using the scratch test method. The resistance to cracking and delamination indicated that the multilayered coating has good resistance to contact damage. The release of silver ions from the hydroxyapatite/silver nanoparticle/calcium phosphate system into the phosphate-buffered saline (PBS) solution was measured by atomic absorption spectroscopy (AAS). Approximately one-third of the incorporated silver was released after 3days immersion into PBS, indicating a total release time of the order of weeks. There were no signs of cracks on the surface of the coating after immersion after various periods, indicating the excellent mechanical stability of the multilayered coating in the physiological environment. An antimicrobial effect against Escherichia coli was found for a 150nm thick outer layer of the calcium phosphate using a semi-quantitative turbidity test.

Promoting spinal fusions by biomineralized silk fibroin films seeded with bone marrow stromal cells: An in vivo animal study

OBJECTIVES

To prepare a biomineralized nano silk fibroin film seeded with bone marrow stromal cells (BMSCs), and to evaluate its performance in spinal fusion.

METHODS

The silk fibroin film was mineralized in a modified, simulated body fluid, seeded with BMSCs, and evaluated in a rat model of posterolateral lumbar fusion, compared with pure silk fibroin, silk fibroin/bone marrow stromal cells, mineralized silk fibroin, mineralized silk fibroin/bone marrow stromal cells, iliac crest bone, and no graft. After 12 weeks, all rats were sacrificed and underwent manual palpation, micro-CT scanning, biomechanical testing, and histology.

RESULTS

The infrared spectrum, X-ray diffraction, and scanning electron microscopy demonstrated deposition of mineral layers on the silk fibroin film surface. The fusion rate, bone volume, relative strength and stiffness, and histological score of the mineralized silk fibroin/bone marrow stromal cells were slightly lower than the autograft, but without any significant difference (p > 0.05). In addition, the mineralized silk fibroin was significantly greater in most parameters than the silk fibroin/bone marrow stromal cells (p < 0.05).

CONCLUSION

The mineralized silk fibroin resembles natural bone structurally, and the cellular and mineral layers of silk fibroin are both critical to bone regeneration. The ability to promote spinal fusion is enhanced when the mineralized silk fibroin is seeded with bone marrow stromal cells.

A new application of cell-free bone regeneration: immobilizing stem cells from human exfoliated deciduous teeth-conditioned medium onto titanium implants using atmospheric pressure plasma treatment

Introduction

Surface modification of titanium (Ti) implants promotes bone formation and shortens the osseointegration period. The aim of this study was to promote bone regeneration and stability around implants using atmospheric pressure plasma (APP) pretreatment. This was followed by immobilization of stem cells from human exfoliated deciduous teeth-conditioned medium (SHED-CM) on the Ti implant surface.

Methods

Ti samples (implants, discs, powder) were treated with APP for 30 seconds. Subsequently, these were immobilized on the treated Ti surface, soaked and agitated in phosphate-buffered saline or SHED-CM for 24 hours at 37 °C. The surface topography of the Ti implants was observed using scanning electron microscopy with energy dispersive X-ray spectroscopy. In vivo experiments using Ti implants placed on canine femur bone were then conducted to permit histological analysis at the bone-implant boundary. For the in vitro experiments, protein assays (SDS-PAGE, Bradford assay, liquid chromatography-ion trap mass spectrometry) and canine bone marrow stromal cell (cBMSC) attachment assays were performed using Ti discs or powder.

Results

In the in vitro study, treatment of Ti implant surfaces with SHED-CM led to calcium phosphate and extracellular matrix protein immobilization. APP pretreatment increased the amount of SHED-CM immobilized on Ti powder, and contributed to increased cBMSC attachment on Ti discs. In the in vivo study, histological analysis revealed that the Ti implants treated with APP and SHED-CM stimulated new bone formation around implants.

Conclusions

Implant device APP pretreatment followed by SHED-CM immobilization may be an effective application to facilitate bone regeneration around dental implants.

MC3T3-E1 proliferation and differentiation on biphasic mixtures of Mg substituted β-tricalcium phosphate and amorphous calcium phosphate

A low temperature aqueous approach was used to synthesize nanocrystalline, high surface area Mg(2+) substituted β-tricalcium phosphate (β-TCMP) to assess its potential use as a synthetic bone graft substitute. X-ray diffraction indicated that β-TCMP was the predominant crystalline phase formed. However, thermal analysis revealed the presence of a secondary amorphous phase which increased with increasing Mg(2+) concentration. Further analysis by Rietveld refinement indicated that the level of ionic substitution of Ca(2+) by Mg(2+) was significantly lower than the amount of Mg(2+) measured using elemental analysis, confirming the formation of a Mg(2+) rich secondary amorphous phase. MC3T3-E1 proliferation on substrates prepared using β-TCMP was assessed using the MTT assay. In comparison to commercially available β-TCP, increased proliferation was observed on samples prepared with 50% Mg, despite elevated Mg(2+) and PO4(3-) concentrations in culture media. Alkaline phosphatase (ALP) activity and qRT-PCR were used to study the effect of varying Mg(2+) substitution on osteogenic differentiation. Cells cultured on β-TCMP substrates prepared with increased Mg(2+) concentrations expressed significantly increased levels of ALP activity and osteogenic genes such as, osteocalcin, collagen-1, and Runx2, in comparison to those cultured on commercially available β-TCP.

Calcium phosphate ceramics in bone tissue engineering: a review of properties and their influence on cell behavior

Calcium phosphate ceramics (CPCs) have been widely used as biomaterials for the regeneration of bone tissue because of their ability to induce osteoblastic differentiation in progenitor cells. Despite the progress made towards fabricating CPCs possessing a range of surface features and chemistries, the influence of material properties in orchestrating cellular events such as adhesion and differentiation is still poorly understood. Specifically, questions such as why certain CPCs may be more osteoinductive than others, and how material properties contribute to osteoinductivity/osteoconductivity remain unanswered. Therefore, this review article systematically discusses the effects of the physical (e.g. surface roughness) and chemical properties (e.g. solubility) of CPCs on protein adsorption, cell adhesion and osteoblastic differentiation in vitro. The review also provides a summary of possible signaling pathways involved in osteoblastic differentiation in the presence of CPCs. In summary, these insights on the contribution of material properties towards osteoinductivity and the role of signaling molecules involved in osteoblastic differentiation can potentially aid the design of CPC-based biomaterials that support bone regeneration without the need for additional biochemical supplements.

Bone repair by periodontal ligament stem cellseeded nanohydroxyapatite-chitosan scaffold

Background

A nanohydroxyapatite-coated chitosan scaffold has been developed in recent years, but the effect of this composite scaffold on the viability and differentiation of periodontal ligament stem cells (PDLSCs) and bone repair is still unknown. This study explored the behavior of PDLSCs on a new nanohydroxyapatite-coated genipin-chitosan conjunction scaffold (HGCCS) in vitro as compared with an uncoated genipin-chitosan framework, and evaluated the effect of PDLSC-seeded HGCCS on bone repair in vivo.

Methods

Human PDLSCs were cultured and identified, seeded on a HGCCS and on a genipin-chitosan framework, and assessed by scanning electron microscopy, confocal laser scanning microscopy, MTT, alkaline phosphatase activity, and quantitative real-time polymerase chain reaction at different time intervals. Moreover, PDLSC-seeded scaffolds were used in a rat calvarial defect model, and new bone formation was assessed by hematoxylin and eosin staining at 12 weeks postoperatively.

Results

PDLSCs were clonogenic and positive for STRO-1. They had the capacity to undergo osteogenic and adipogenic differentiation in vitro. When seeded on HGCCS, PDLSCs exhibited significantly greater viability, alkaline phosphatase activity, and upregulated the bone-related markers, bone sialoprotein, osteopontin, and osteocalcin to a greater extent compared with PDLSCs seeded on the genipin-chitosan framework. The use of PDLSC-seeded HGCCS promoted calvarial bone repair.

Conclusion

This study demonstrates the potential of HGCCS combined with PDLSCs as a promising tool for bone regeneration.

Hydroxyapatite-coated carboxymethyl chitosan scaffolds for promoting osteoblast and stem cell differentiation

The behavior of MC3T3 osteoblasts and human bone marrow stem cells on non-coated and hydroxyapatite (HAP)-coated carboxymethyl chitosan (CMCS) scaffolds was investigated in this study. Four HAP-coated scaffolds with different coating morphology and coverage were prepared by mineralization for 1week in four different mineralizing solutions. Viability, attachment, proliferation, and differentiation of the osteoblasts on these scaffolds were evaluated, and an osteogenic gene expression analysis was carried out to investigate the osteoblastic differentiation of the stem cells. No cytotoxic effects were observed with both the non-coated and coated scaffolds. The non-coated CMCS scaffold supports attachment, proliferation, and differentiation of the osteoblasts and directs stem cell differentiation to osteoblast. Coating the scaffold with HAP substantially enhances these effects on the osteoblasts and stem cells. The main improvement was in the late stage of osteoblast differentiation since osteoblastic differentiation of the osteoblasts and stem cells in this stage was significantly enhanced by the coatings regardless of the variation in morphology and coverage. On the other hand, high HAP coverage was beneficial in stimulating osteoblast attachment and proliferation. This study demonstrates the good potential of HAP-coated CMCS scaffolds as osteogenic scaffolds to stimulate bone healing.

Perfusion electrodeposition of calcium phosphate on additive manufactured titanium scaffolds for bone engineering

A perfusion electrodeposition (P-ELD) system was reported to functionalize additive manufactured Ti6Al4V scaffolds with a calcium phosphate (CaP) coating in a controlled and reproducible manner. The effects and interactions of four main process parameters - current density (I), deposition time (t), flow rate (f) and process temperature (T) - on the properties of the CaP coating were investigated. The results showed a direct relation between the parameters and the deposited CaP mass, with a significant effect for t (P=0.001) and t-f interaction (P=0.019). Computational fluid dynamic analysis showed a relatively low electrolyte velocity within the struts and a high velocity in the open areas within the P-ELD chamber, which were not influenced by a change in f. This is beneficial for promoting a controlled CaP deposition and hydrogen gas removal. Optimization studies showed that a minimum t of 6 h was needed to obtain complete coating of the scaffold regardless of I, and the thickness was increased by increasing I and t. Energy-dispersive X-ray and X-ray diffraction analysis confirmed the deposition of highly crystalline synthetic carbonated hydroxyapatite under all conditions (Ca/P ratio=1.41). High cell viability and cell-material interactions were demonstrated by in vitro culture of human periosteum derived cells on coated scaffolds. This study showed that P-ELD provides a technological tool to functionalize complex scaffold structures with a biocompatible CaP layer that has controlled and reproducible physicochemical properties suitable for bone engineering.

Fabrication and characterization of poly(lactic-co-glycolic acid) microsphere/amorphous calcium phosphate scaffolds

Although hydroxyapatite (HAP) and β-tricalcium phosphate have been used extensively as osteoconductive minerals in biomaterial scaffolds for bone regeneration, they lack the capacity to stimulate osteoblastic differentiation of progenitor cells. In contrast, amorphous calcium phosphates (ACPs), which convert to HAP under aqueous conditions, have the potential to facilitate osteoblastic differentiation through the transient local release of calcium and phosphate ions. Therefore, in this study ACPs were synthesized using zinc and zirconia divalent cations as stabilizers (denoted ZnACP and ZrACP, respectively) and compared to HAP. Analysis of ion release into serum-containing cell culture medium revealed transiently elevated levels of calcium and phosphorous, consistent with the enhanced solubility of ZrACP and ZnACP relative to HAP. In addition, X-ray diffraction analysis revealed partial conversion of ZrACP to HAP but no conversion of ZnACP after 96 h. Next, scaffolds were fabricated by sintering mixtures of 300-500 µm poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres and 0.5 wt% calcium phosphate mineral (HAP, ZrACP or ZnACP) at 70 °C for 24 h. Scanning electron microscopy revealed a porous microsphere matrix with calcium phosphate particulates clinging to the microsphere surfaces both prior to and after 14 days in culture medium. Finally, the incorporation of calcium phosphate resulted in a lower compressive modulus in the range 127 to 74-89 MPa. Taken together, these results indicate that ZrACP, ZnACP and HAP minerals exhibit very different properties, and therefore may elicit different osteoblastic responses in vitro.

Bone growth is enhanced by novel bioceramic coatings on Ti alloy implants

Calcium phosphate ceramics are widely used as coating materials to orthopedic implants and are found to enhance initial bony ingrowth by stimulating osseous apposition to the implant surface. In this study, two novel calcium orthophosphate materials were selected for coating onto the commonly used orthopedic implant material Ti-6Al- 4V. One was calcium alkali orthophosphate with the crystalline phase Ca10[K/Na](PO4)7 with a small addition of SiO2 (AW-Si) and the other was calcium orthophosphate composed of 70 mol % fluorapatite, Ca10(PO4)6F2 and 30 mol % CaZr4(PO4)6 (FA7Z). The coated implants were placed in cortical and cortico-cancellous bone of sheep femur for six weeks. Retrieved samples were tested for osseointegration and mechanical strength. It was found that both coatings produced enhanced bone/implant contact rate compared to the control when implanted in cortico-cancellous bone. This study demonstrates that the two coatings have the capability of encouraging bone growth, and hence the potential for being used as coating materials on Ti implants.

In vitro evaluation of different heat-treated radio frequency magnetron sputtered calcium phosphate coatings

OBJECTIVES

Surface chemical compositions, such as calcium/phosphorus ratio and phase content, have a strong influence on the bioactivity and biocompatibility of calcium phosphate (CaP) coatings as applied on orthopedic and dental implants.

MATERIAL AND METHODS

Hydroxylapatite (HA) and dicalcium pyrophosphate (DCPP) coatings were prepared on titanium substrates by RF magnetron sputter deposition. The surfaces were left as-prepared (amorphous HA coating; A-HA, amorphous DCPP coating; A-DCPP) or heat treated with: infrared (IR) at 550 degrees C (I-HA) or at 650 degrees C (I-DCPP), and a water steam at 140 degrees C (S-HA and S-DCPP). The surface changes of these coatings were determined after incubation in simulated body fluid (SBF). Also, the growth of rat bone marrow cells (RBM) was studied with scanning electron microscopy (SEM).

RESULTS

Both IR and water steam heat treatment changed the sputter-deposited coatings from the amorphous into the crystalline phase. As-prepared amorphous coatings dissolved partially in SBF within 4 weeks of incubation, while heat-treated coatings supported the deposition of a precipitate, i.e., carbonated apatite on both I-HA and S-HA specimens, and tricalciumphosphate on the I-DCPP and S-DCPP specimens. The Ca/P ratio of the A-HA, I-HA, S-HA, A-DCPP, I-DCPP and S-DCPP coatings changed, respectively, from 1.98 to 1.12, 2.01 to 1.76, 1.91 to 1.68, 0.76 to 1.23, 0.76 to 1.26 and 1.62 to 1.55 after 4 weeks of incubation in SBF. Finally, the RBM cells grew well on all heat-treated coatings, but showed different mineralization morphology during cell culturing.

CONCLUSION

The different heat-treatment procedures for the sputtered HA and DCPP coatings influenced the surface characteristics of these coatings, whereby a combination of crystallinity and specific phase composition (Ca/P ratio) strongly affected their in vitro bioactivity.

Wnt signaling stimulates osteoblastogenesis of mesenchymal precursors by suppressing CCAAT/enhancer-binding protein alpha and peroxisome proliferator-activated receptor gamma

Mesenchymal precursor cells have the potential to differentiate into several cell types, including adipocytes and osteoblasts. Activation of Wnt/beta-catenin signaling shifts mesenchymal cell fate toward osteoblastogenesis at the expense of adipogenesis; however, molecular mechanisms by which Wnt signaling alters mesenchymal cell fate have not been fully investigated. Our prior work indicates that multipotent precursors express adipogenic and osteoblastogenic transcription factors at physiological levels and that ectopic expression of Wnt10b in bipotential ST2 cells suppresses expression of CCAAT/enhancer-binding protein alpha (C/EBPalpha) and peroxisome proliferator-activated receptor gamma (PPARgamma) and increases expression of Runx2, Dlx5, and osterix. Here, we demonstrate that transient activation of Wnt/beta-catenin signaling rapidly suppresses C/EBPalpha and PPARgamma, followed by activation of osteoblastogenic transcription factors. Enforced expression of C/EBPalpha or PPARgamma partially rescues lipid accumulation and decreases mineralization in ST2 cells expressing Wnt10b, suggesting that suppression of C/EBPalpha and PPARgamma is required for Wnt/beta-catenin to alter cell fate. Furthermore, knocking down expression of C/EBPalpha, PPARgamma, or both greatly reduces adipogenic potential and causes spontaneous osteoblastogenesis in ST2 cells and mouse embryonic fibroblasts, suggesting that Wnt signaling alters the fate of mesenchymal precursor cells primarily by suppressing C/EBPalpha and PPARgamma.

Improved Neovascularization of PEGT/PBT Copolymer Matrices in Response to Surface Modification by Biomimetic Coating

PEGT/PBT (polyethylene glycol terephthalate/polybutylene terephthalate) copolymer matrices with three different surface coatings [calcium-phosphate (Ca-P), collagen, and gas plasma] were placed into dorsal skinfold chambers of 24 balb/c mice. Untreated PEGT/PBT matrices served as the controls. The basal surfaces of the implants directly contacted the striated skin muscle. Neovascularization of the implants was analyzed by intravital fluorescence microscopy. Microcirculatory observations were performed in the surrounding skin muscle, at the border zone of the implant, and in the center of the implant. The functional vessel density (FVD; mm/mm2), as the length of perfused microvessels per observation area, was measured by computer-assisted analysis. The FVD served as the parameter of neovascularization. At the end of the protocol, histological observation of hematoxylin/eosin-standard-stained sections was performed by light microscopy. The FVD in the center of the implant on day 8 was only observed in gas-plasma-coated (8.8 +/- 10.2 mm/mm2) and Ca-P-coated implants (0.8 +/- 2.0 mm/mm2). None of the other groups showed perfused microvessels in the center of the implant on day 8 (p < 0.05). The FVD values in the center of the gas-plasma-coated and the Ca-P-coated implants were 20.7 +/- 8.2 and 19.2 +/- 15.5 mm/mm2 as compared with 7.1 +/- 17.4 and 7.7 +/- 5.9 mm/mm2 for collagen-coated and untreated implants on day 16. The histological examination confirmed the profound microvascular ingrowth into the matrix pores of the gas-plasma-treated and the Ca-P-coated copolymer matrices in the center of the implants. The study showed that the ingrowth of microvessels into PEGT/PBT matrices can be accelerated by Ca-P coating and gas plasma treatment in the dorsal skinfold chamber in mice.

The influence of the crystallinity of electrostatic spray deposition-derived coatings on osteoblast-like cell behavior, in vitro

This article describes the influence of the crystallinity of carbonate apatite (CA) coatings on osteoblast-like cell behavior. Porous CA coatings were produced with electrostatic spray deposition (ESD), and subsequently, received heat treatments of 400, 500, or 700 degrees C to induce various coating crystallinities. As a result, an amorphous calcium phosphate (ACP), a crystalline CA (CCA), and a crystalline carbonated hydroxyapatite (CHA) structure were formed, respectively. Uncoated titanium substrates served as the control group. After seeding rat osteoblast-like cells, the initial cell attachment was similar between the groups, and approached 100% after 6 h. Between the various coatings, no differences were observed for proliferation, differentiation, or mineralization. However, proliferation of the osteoblast-like cells was lower on all coated substrates after longer culture periods, compared to the uncoated substrates, while at the same time differentiation was stimulated. Furthermore, after 8 and 16 days of incubation, scanning electron microscopy showed more signs of mineralization on coated substrates, compared to the uncoated substrates. In conclusion, porous ESD-derived CA coatings have a positive effect on the in vitro differentiation of osteoblast-like cells, compared to uncoated, as-machined titanium. However, this effect is not further enhanced by the degree of crystallinity of the ESD-derived CA coatings.

Osteoblast response to zirconia-hybridized pyrophosphate-stabilized amorphous calcium phosphate

Calcium phosphate bioceramics, such as hydroxyapatite, have long been used as bone substitutes because of their proven biocompatibility and bone binding properties in vivo. Recently, a zirconia-hybridized pyrophosphate-stabilized amorphous calcium phosphate (Zr-ACP) has been synthesized, which is more soluble than hydroxyapatite and allows for controlled release of calcium and phosphate ions. These ions have been postulated to increase osteoblast differentiation and mineralization in vitro. The focus of this work is to elucidate the physicochemical properties of Zr-ACP and to measure cell response to Zr-ACP in vitro using a MC3T3-E1 mouse calvarial-derived osteoprogenitor cell line. Cells were cultured in osteogenic medium and mineral was added to culture at different stages in cell maturation. Culture in the presence of Zr-ACP showed significant increases in cell proliferation, alkaline phosphatase activity (ALP), and osteopontin (OPN) synthesis, whereas collagen synthesis was unaffected. In addition, calcium and phosphate ion concentrations and medium pH were found to transiently increase with the addition of Zr-ACP, and are hypothesized to be responsible for the osteogenic effect of Zr-ACP.

Fabrication and characterization of poly(DL-lactic-co-glycolic acid)/zirconia-hybridized amorphous calcium phosphate composites

Several minerals, such as hydroxyapatite and beta-tricalcium phosphate, have been incorporated into bioresorbable polyester bone scaffolds to increase the osteoconductivity both in vitro and in vivo. More soluble forms of calcium phosphate that release calcium and phosphate ions have been postulated as factors that increase osteoblast differentiation and mineralization. Recently, a zirconia-hybridized pyrophosphate-stabilized amorphous calcium phosphate (Zr-ACP) has been synthesized allowing controlled release of calcium and phosphate ions. When incorporated into bioresorbable scaffolds, Zr-ACP has the potential to induce osteoconductivity. In this study, 80-90% (w/v) porous poly(DL-lactic-co-glycolic acid) (PLGA) scaffolds were formed by thermal phase separation from dioxane while incorporating Zr-ACP. Scanning electron microscopy revealed a highly porous structure with a pore size ranging from a few microm to about 100 microm, smaller than we had hoped for. Zr-ACP particles were evenly dispersed in the composite structure and incorporated into the pore walls. The amorphous structure of the Zr-ACP was maintained during composite fabrication, as found by X-ray diffraction. Composite scaffolds had larger compressive yield strengths and moduli compared to pure polymer scaffolds. These initial efforts demonstrate that PLGA/Zr-ACP composites can be formed in ways that ultimately serve as promising bone scaffolds in tissue engineering.

In-situ preparation of poly(propylene fumarate)—hydroxyapatite composite

In-situ precipitation of hydroxyapatite (HAp) in the presence of poly(propylene fumarate) (PPF) is investigated. Amorphous calcium phosphate (ACP) precipitates in the presence of the polymer and remains in the amorphous form for a relatively long time, e.g. even after 24 h of coexistence with the mother solution. Our observations suggest that PPF interacts with the surface of the ACP particles and prevents them from transformation to crystalline hydroxyapatite. The PPF polymer seems to be more efficient in hindering the ACP to HAp transformation at higher pH conditions. From spectroscopic observations we hypothesize that the C=O bond of the PPF molecules interact with the calcium ion of the ACP particles. In case of low molecular weight PPF this interaction may lead to the incorporation of the polymer within the growing ACP particles.

The Effect of Sputtered Calcium Phosphate Coatings of Different Crystallinity on Osteoblast Differentiation

BACKGROUND

Coating titanium implants with hydroxyapatite (HA) has been suggested to increase osseointegration by stimulating early osteoblast function. The goal of this study was to determine the extent to which the crystalline content of the HA surface affected osteoblast function in vitro.

METHODS

Osteoblasts were isolated from fetal rat calvaria. Titanium coupons were sputter coated and analyzed. Mineralized nodule formation on plastic using von Kossa staining was compared to tetracycline and procion dye labeling. Cell proliferation, adhesion, alkaline phosphatase activity, morphology and spreading, and cytoskeletal arrangement were analyzed. Reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the expression of mRNA for specific proteins.

RESULTS

The percent crystallinity of coatings was 0% (HA1), 1.9% +/- 0.4% (HA2), and 66.4% +/- 2.8% (HA3). The nodule formation and cell number were greatest on titanium and HA3 compared to HA1 and HA2 (P < 0.01). At weeks 2 to 4, all samples showed strong alkaline phosphatase, osteocalcin, monocyte-colony stimulating factor (M-CSF), and receptor activator of nuclear factor kappa B ligand (RANKL) expression, but the specific activity of alkaline phosphatase decreased. Cell adherence was greater than 60% of applied cells for all surfaces except HA3. The cells were significantly more elongated on titanium, with no difference on the HA-coated surfaces. Actin filaments were arranged peripherally at 5 hours but arranged parallel to the long axis of the cell at 20 hours.

CONCLUSIONS

Procion labeling is a valid method for evaluating mineralized nodule formation on opaque surfaces. There were no major differences in osteoblast function using titanium or high-crystalline coatings, and most functions were decreased on amorphous or low-crystalline coatings.

Histological findings in titanium implants coated with calcium phosphate ceramics installed in rabbit's tibias

Oral reconstruction using osteointegrated implants are widely indicated nowadays. The implant bone anchorage is very important for its functional stability. Thus, ceramic biomaterials are widely used as coatings of the implant surfaces to accelerate local osteogenesis. The purpose of this study is to assess the biocompatibility and the osteoconduction of two types of calcium phosphate ceramics used as titanium dental implant coatings. These implants were installed in rabbit tibia during an 8-week healing period. The light and fluorescent microscopy observations showed that the materials are biocompatible and that they have osteoconductive activities.

The use of temperature-composition combinatorial libraries to study the effects of biodegradable polymer blend surfaces on vascular cells

Controlling cellular and physiological responses such as adhesion, proliferation and migration is a highly desirable feature of engineered scaffolds. One important application would be the design of tissue engineered vascular grafts that regulate cell adhesion and growth. We utilized temperature-composition combinatorial polymer libraries to investigate the effects of surfaces of blended poly(D,L-lactic-co-glycolic acid) (PLGA) and poly(epsilon-caprolactone) (PCL) on murine vascular smooth muscle cells (SMC). In this manner, SMCs were exposed to approximately 1000 distinguishable surfaces in a single experiment, allowing the discovery of optimal polymer compositions and processing conditions. SMC adhesion, aggregation, proliferation, and protein production were highest in regions with mid- to high-PCL concentrations and high annealing temperatures. These regions exhibited increased surface roughness, increased microscale PLGA-rich matrix stiffness, and significant change of bulk PCL-rich crystallinity relative to other library regions. This study revealed a previously unknown processing temperature and blending composition for two well-known polymers that optimized SMC interactions.

A simple and non-radioactive technique to study the effect of monophosphoesters on matrix vesicle-mediated calcification

A simple and non-radioactive technique based on O-cresolpthalein complexone assay was developed to study in vitro non-radioactive calcium (⁴⁰Ca) deposition by isolated matrix vesicles. Using this technique, the effect of various phosphoester substrates including ATP, AMP and β-GP on in vitro MV-calcification was studied. O-cresolpthalein complexone assay with non-radioactive calcium demonstrated that AMP or β-GP were more effective in promoting calcium deposition by isolated MVs than ATP. The application of this non-radioactive technique, which is highly sensitive and simple, would offer a useful alternative approach to the routinely used radiometric biomineralization assay which employs radioactive ⁴⁵Ca.

The modulation of osteogenesis in vitro by calcium titanium phosphate coatings

Calcium phosphate coated titanium and titanium alloy are widely used as dental and orthopaedic implants. This study examines the effect of novel calcium titanium and calcium titanium zirconium phosphates suitable for plasma-spraying onto titanium substrata on the expression of bone-related genes and proteins by human bone-derived cells (HBDC) and compares this behavior to that on native titanium and hydroxyapatite-coated titanium. Test materials were an acid etched and sand-blasted titanium surface (Ti-DPS), a plasma-sprayed hydroxyapatite coating (HA), and five materials which were created from CaTi(4)(PO(4))(6) (CTP) and CaZr(4)(PO(4))(6) (CZP): sintered CaTi(4)(PO(4))(6) (CTP-S1), sintered 46CaO.23TiO(2).31P(2)O(5) (CTP-S2), sintered CaTiZr(3)(PO(4))(6), (CTZP-S1), sintered 46CaO.23ZrO(2).31P(2)O(5) (CTZP-S2) and sintered 55CaO.20TiO(2).31P(2)O(5) (CTP-S3). HBDC were grown on the substrata for 3, 7, 14 and 21 d, counted and probed for various mRNAs and proteins (type I collagen, osteocalcin, osteopontin, osteonectin, alkaline phosphatase and bone sialoprotein). All substrates significantly affected cellular growth and the temporal expression of an array of bone-related genes and proteins. At 14 and 21 d, cells on CTP-S3 displayed significantly enhanced expression of all osteogenic mRNAs. Surfaces of CTP-S1 and CTP-S3 had the most effect on osteoblastic differentiation inducing a greater expression of an array of osteogenic markers than recorded for cells grown on Ti-DPS and HA, suggesting that these novel materials may possess a higher potency to enhance osteogenesis.

The effect of different titanium and hydroxyapatite-coated dental implant surfaces on phenotypic expression of human bone-derived cells

Roughened titanium (Ti) surfaces have been widely used for dental implants. In recent years, there has been the tendency to replace Ti plasma-sprayed surfaces by sandblasted and acid-etched surfaces in order to enhance osseous apposition. Another approach has been the utilization of hydroxyapatite (HA)-coated implants. This study examines the effect of two roughened Ti dental implant surfaces on the osteoblastic phenotype of human bone-derived cells (HBDC) and compares this behavior to that for cells on an HA-coated surface. Test materials were an acid-etched and sandblasted Ti surface (Ti-DPS), a porous Ti plasma-sprayed coating (Ti-TPS), and a plasma-sprayed porous HA coating (HA). Smooth Ti machined surfaces served as control (Ti-ma). HBDC were grown on the substrata for 3, 7, 14, and 21 days, counted and probed for various bone-related mRNAs and proteins (type I collagen, osteocalcin, osteopontin, osteonectin, alkaline phosphatase, and bone sialoprotein). All dental implant surfaces significantly affected cellular growth and the temporal expression of an array of bone-related genes and proteins. HA-coated Ti had the most effect on osteoblastic differentiation inducing a greater expression of an array of osteogenic markers than recorded for cells grown on Ti-DPS and Ti-TPS, thus suggesting that the HA-coated surface may possess a higher potency to enhance osteogenesis. Furthermore, Ti-DPS surfaces induced greater osteoblast proliferation and differentiation than Ti-TPS.