In vitro assessment of the osteointegrative potential of a novel multiphase anodic spark deposition coating for orthopaedic and dental implants

Hydroxyapatite coatings have been proven to improve the osteointegration of metal implants through a tight binding to the bone mineral phase as well as through favorable osteoblast adhesion and proliferation onto the implant surface. However, hydroxyapatite coatings are not stable and they tend to delaminate from the metal surface when challenged by the mechanical stresses experienced by the implant. Recently, a new multiphase anodic spark deposition (ASD) method has been optimized where the formation of a thick oxide film is followed by the deposition of a calcium phosphate mineral phase and its etching by alkali. The data in this paper demonstrate that this novel type of coating, BioSpark, improves the material osteointegration potential when compared to conventional ASD while offering more mechanical stability. A faster mineralization was obtained by incubation in simulated body fluids and osteoblasts showed better adhesion, proliferation, differentiation, and collagen production. These performances were related to the surface morphology, to the film calcium/phosphate ratio and its surface oxygen content, as well as to a preferential binding of structural proteins such as fibronectin.     

雌激素对大鼠胚胎成骨细胞增殖及胶原合成的影响

目的 研究雌激素对大鼠胚胎成骨细胞增殖及I型胶原代谢的影响。方法 分离大鼠胚胎头盖骨成骨细胞，分别给予不同浓度雌激素培养；观察细胞增殖情况和ALP活性变化；苦味酸天狼星红及I型胶原免疫组织化学染色，从蛋白质水平观察成骨细胞中I型胶原的变化；地高辛标记的I型胶原基因探针进行原位杂交，从mBNA水平观察I型胶原的变化。结果 雌激素可降低大鼠胚胎成骨细胞增殖水平而使ALP活性以及I型胶原蛋白质和mRNA水平均升高。结论 雌激素可促进成骨细胞分化，而抑制增殖。     

The effect of TNFα secreted from macrophages activated by titanium particles on osteogenic activity regulated by WNT/BMP signaling in osteoprogenitor cells

Wear particles are the major cause of osteolysis associated with failure of implant following total joint replacement. During this pathologic process, activated macrophages mediate inflammatory responses to increase osteoclastogenesis, leading to enhanced bone resorption. In osteolysis caused by wear particles, osteoprogenitors present along with macrophages at the implant interface may play significant roles in bone regeneration and implant osteointegration. Although the direct effects of wear particles on osteoblasts have been addressed recently, the role of activated macrophages in regulation of osteogenic activity of osteoblasts has scarcely been studied. In the present study, we examined the molecular communication between macrophages and osteoprogenitor cells that may explain the effect of wear particles on impaired bone forming activity in inflammatory bone diseases. It has been demonstrated that conditioned medium of macrophages challenged with titanium particles (Ti CM) suppresses early and late differentiation markers of osteoprogenitors, including alkaline phosphatase (ALP) activity, collagen synthesis, matrix mineralization and expression of osteocalcin and Runx2. Moreover, bone forming signals such as WNT and BMP signaling pathways were inhibited by Ti CM. Interestingly, TNFα was identified as a predominant factor in Ti CM to suppress osteogenic activity as well as WNT and BMP signaling activity. Furthermore, Ti CM or TNFα induces the expression of sclerostin (SOST) which is able to inhibit WNT and BMP signaling pathways. It was determined that over-expression of SOST suppressed ALP activity, whereas the inhibition of SOST by siRNA partially restored the effect of Ti CM on ALP activity. This study highlights the role of activated macrophages in regulation of impaired osteogenic activity seen in inflammatory conditions and provides a potential mechanism for autocrine regulation of WNT and BMP signaling mediated by TNFα via induction of SOST in osteprogenitor cells.     

In vitro analysis of anionic collagen scaffolds for bone repair

Collagen has been extensively described as a beneficial material in bone tissue engineering due to its biocompatibility, biodegradability, low antigenicity, and high tensile strength. However, collagen scaffolds in their pure form have some drawbacks and improvements in the physical, chemical, and biologic properties of collagen are necessary to overcome those inadequacies. Recently, the selective hydrolysis of carboxyamides of asparagine and glutamine residues of collagen has been employed to increase the number of negative sites and enhance the piezoelectric properties of collagen. Anionic collagen scaffolds were prepared by use of a hydrolysis treatment for either 24 h [bovine pericardium (BP 24)] or 48 h (BP 48). Bovine osteoblasts were cultured on them and on native matrices to understand the cellular interactions responsible for the good osteoconductivity and biocompatibility reported with in vivo tests. Based on the data obtained on cell adhesion, alkaline phosphatase (ALP) and extracellular matrix macromolecule production, and cellular proliferation through histological analysis, we may conclude that the materials tested reveal sufficient biocompatibility level for bone repair. Further, the evidence of some connection between ALP activity and the mineralization process should be emphasized. BP 48 presented the most promising results stimulating in vitro mineralization, ALP production, and possible osteoblast differentiation.     

Bone tissue engineering on patterned collagen films: an in vitro study

This study aimed at guiding osteoblast cells from rat bone marrow on chemically modified and patterned collagen films to study the influence of patterns on cell guidance. The films were stabilized using different treatment methods including crosslinking with carbodiimide (EDC) and glutaraldehyde, dehydrothermal treatment (DHT), and deposition of calcium phosphate on the collagen membrane. Mesenchymal osteoprogenitor cells were differentiated into osteoblasts and cultured for 7 and 14 days on micropatterned (groove width: 27 microm, groove depth: 12 microm, ridge width: 2 microm) and macropatterned (groove width: 250 microm, groove depth: 250 microm, ridge width: 100 microm) collagen films to study the influence of pattern dimensions on osteoblast alignment and orientation. Fibrinogen was added to the patterned surfaces as a chemical cue to induce osteoblast adhesion. Cell proliferation on collagen films was determined using MTS assay. Deposition of calcium phosphate on the surface of the film increased surface hydrophilicity and roughness and allowed a good cell proliferation. Combined DHT and EDC treatment provided an intermediate wettability, and also promoted cell proliferation. Glutaraldehyde crosslinking was found to lead to the lowest cell proliferation but fibrinogen adsorption on glutaraldehyde treated film surfaces increased the cell proliferation significantly. Macropatterns were first tested for alignment and only microscopy images were enough to see that there is no specific alignment. As a result of this, micropatterned samples with the topography that affect cell alignment and guidance were used. Osteoblast phenotype expression (ALP activity) was observed to be highest in calcium phosphate deposited samples, emphasizing the effect of mineralization on osteoblast differentiation. In general ALP activity per cell was found to decrease from day 7 to day 14 of incubation. SEM and fluorescence microscopy revealed good osteoblast alignment and orientation along the axis of the patterns when micropatterned films were used. This study shows that it is possible to prepare cell carriers suitable for tissue engineering through choice of appropriate surface topography and surface chemistry. Presence of chemical cues and micropatterns on the surface enhance cell orientation and bone formation.     

兔BMSCs体外培养及其向成骨细胞分化的实验研究

目的　探讨培养兔骨髓基质干细胞向成骨细胞的分化,为骨组织工程研究提供种子细胞。方法　取 2月龄新西兰大耳白兔,麻醉后取骨髓,直接进行原代培养,传代后观察其生长特性,绘制生长曲线并加诱导液使其 向成骨细胞方向分化,并分别用钙钴法检测碱性磷酸酶,茜素红染色检测钙结节,免疫组化染色检测Ⅰ型胶原,透 射电镜观察胞质中钙质成分。结果　原代培养中出现大量细胞克隆,传代后细胞呈旋涡状密集生长,加入诱导液 后细胞形态发生改变并向成骨细胞分化,胞质内见有呈黑色的碱性磷酸酶颗粒和Ⅰ型胶原反应产物,并见有多个 细胞形成的钙化结节,电镜下观察到胞质中含有许多基质小泡,几天内成骨细胞数可达1×106/L。结论　培养兔 骨髓基质干可向成骨细胞方向分化,作为骨组织工程的种子细胞。     

The promotion of osteointegration under diabetic conditions using chitosan/hydroxyapatite composite coating on porous titanium surfaces

Composited Chitosan/Hydroxyapatite (CS/HA) material coated on titanium surface (cTi) is a promising approach to produce biomaterials with better osseointegration capacity, but its bio-performance under diabetic conditions and the mechanisms involved remain elusive. We propose that the alterations in the Wnt/β-catenin pathway may play a role in mediating the improvement effect of cTi on diabetes-induced impaired implant osteointegration. To confirm the hypothesis, primary rat osteoblasts incubated on Ti and cTi were subjected to normal serum (NS), diabetic serum (DS), DS + Wnt3a (a specific Wnt agonist) and DS + Dkk1 (a specific Wnt antagonist) treatment. In vivo study was performed on diabetic sheep implanted with Ti or cTi into the bone defect on crista iliaca. Results showed that diabetes depressed osteoblast function evidenced by impaired cell adhesion and morphology, decreased cell proliferation and ALP activity, and higher apoptotic rate on Ti. Importantly, both cTi and Wnt3a treatment ameliorated osteoblastic dysfunction and apoptosis under diabetic condition. Implantation with cTi significantly improved osteointegration evidenced by Micro-CT and histological examinations compared with Ti. Moreover, the aforementioned promotive effects afforded by cTi were abolished by blocking Wnt pathway with Dkk1. Our study explicitly demonstrates that CS/HA composite material improves diabetes-induced impaired osteointegration of Ti via the reactivation of Wnt/β-catenin pathway and provides a target point for biomaterial modification to attain better clinical performance in diabetic patients.     

Tissue transglutaminase (TG2) activity regulates osteoblast differentiation and mineralization in the SAOS-2 cell line

Tissue transglutaminase (type II, TG2) has long been postulated to directly promote skeletal matrix calcification and play an important role in ossification. However, limited information is available on the expression, function and modulating mechanism of TG2 during osteoblast differentiation and mineralization. To address these issues, we cultured the well-established human osteosarcoma cell line SAOS-2 with osteo-inductive conditioned medium and set up three time points (culture days 4, 7, and 14) to represent different stages of SAOS-2 differentiation. Osteoblast markers, mineralization, as well as TG2 expression and activity, were then assayed in each stage. Furthermore, we inhibited TG activity with cystamine and then checked SAOS-2 differentiation and mineralization in each stage. The results showed that during the progression of osteoblast differentiation SAOS-2 cells presented significantly high levels of osteocalcin (OC) mRNA, bone morphogenetic protein-2 (BMP-2) and collagen I, significantly high alkaline phosphatase (ALP) activity, and the increased formation of calcified matrix. With the same tendency, TG2 expression and activity were up-regulated. Furthermore, inhibition of TG activity resulted in a significant decrease of OC, collagen I, and BMP-2 mRNA and of ALP activity and mineralization. This study demonstrated that TG2 is involved in osteoblast differentiation and may play a role in the initiation and regulation of the mineralization processes. Moreover, the modulating effects of TG2 on osteoblasts may be related to BMP-2.     

Hybrid bone implants: self-assembly of peptide amphiphile nanofibers within porous titanium

Over the past few decades there has been great interest in the use of orthopedic and dental implants that integrate into tissue by promoting bone ingrowth or bone adhesion, thereby eliminating the need for cement fixation. However, strategies to create bioactive implant surfaces to direct cellular activity and mineralization leading to osteointegration are lacking. We report here on a method to prepare a hybrid bone implant material consisting of a Ti-6Al-4V foam, whose 52% porosity is filled with a peptide amphiphile (PA) nanofiber matrix. These PA nanofibers can be highly bioactive by molecular design, and are used here as a strategy to transform an inert titanium foam into a potentially bioactive implant. Using scanning electron microscopy (SEM) and confocal microscopy, we show that PA molecules self-assemble into a nanofiber matrix within the pores of the metallic foam, fully occupying the foam's interconnected porosity. Furthermore, the method allows the encapsulation of cells within the bioactive matrix, and under appropriate conditions the nanofibers can nucleate mineralization of calcium phosphate phases with a Ca:P ratio that corresponds to that of hydroxyapatite. Cell encapsulation was quantified using a DNA measuring assay and qualitatively verified by SEM and confocal microscopy. An in vivo experiment was performed using a bone plug model in the diaphysis of the hind femurs of a Sprague Dawley rat and examined by histology to evaluate the performance of these hybrid systems after 4 weeks of implantation. Preliminary results demonstrate de novo bone formation around and inside the implant, vascularization around the implant, as well as the absence of a cytotoxic response. The PA-Ti hybrid strategy could be potentially tailored to initiate mineralization and direct a cellular response from the host tissue into porous implants to form new bone and thereby improve fixation, osteointegration, and long term stability of implants.     

Effects of alpha-TCP and TetCP on MC3T3-E1 proliferation,differentiation and mineralization

Calcium phosphates with high solubility in water such as alpha-tricalcium phosphate (alpha-TCP) and tetracalcium phosphate (TetCP) have received considerable attention as components of bone-substitution materials. However, the osteoblast response to these materials has not yet been clearly understood. This study examined the effects of alpha-TCP and TetCP on osteoblast proliferation, differentiation and mineralization in the culture system of MC3T3-E1 cells. Cells were cultured in a differentiation medium with or without alpha-TCP or TetCP at 1 or 10 microM, and the number of cells attached to the culture plates was determined. To examine osteoblast differentiation, the alkaline phosphatase (ALP) activity was measured and the expression of osteoblastic markers analyzed by RT-PCR. In addition, mineralization was evaluated by staining the calcium deposit with Alizalin red. Culture in the presence of alpha-TCP or TetCP showed no significant influence on cell proliferation. ALP activities of the cells were enhanced by both calcium phosphates for 3d and the expression of type I collagen was promoted at 12h and 1d after incubation. Enhancement of bone-like tissue formation by the addition of alpha-TCP or TetCP at 10 microM was observed after 7d incubation and thereafter. The results of the present study indicate that alpha-TCP and TetCP promote osteogenesis by increasing collagen synthesis and calcification of the extra-cellular matrix.     

Interaction of TGF-beta1 and rhBMP-2 on human bone marrow stromal cells cultured in collagen gel matrix.

Transforming growth factor-beta1 (TGF-beta1) and bone morphogenetic protein-2 (BMP-2) are abundant proteins in the bone matrix. However, their interaction in controlling osteoblast differentiation is not clearly understood. In this study, HBMSCs were cultured in collagen gel matrix with different condition of exogenous rhBMP-2 and TGF-beta1 in order to determine the interaction of BMP-2 and TGF-beta1 on human bone marrow stromal cells (HBMSCs) differentiation. The cultured cells were analyzed for cell proliferation, alkaline phophatase (ALP) activity and mineralization staining with Von-Kossa. The cells treated with TGF-beta1 exhibited a higher rate of cell growth than those without. However, the cells cultured in collagen gel matrix showed a lower rate of cell growth than the cells cultured in a monolayer. To investigate the effects of both cytokines on osteoblast differentiation, the cells were treated with 0, 1, 5, 10 ng/ml of TGF-beta1 for 2 days. This was followed by culturing with 0, 1, 5, and 10 ng/ml of TGF-beta1 and 100 ng/ml of rhBMP-2 together for 3 days with the alkaline phosphatase (ALP) activity measured. The cells treated with 1 ng/ml of TGF-beta1 responded efficiently to rhBMP-2 and expressed ALP activity with a level equivalent to that exhibited by cells that were not treated with TGF-beta1. The cells treated with 5 and 10 ng/ml of TGF-beta1 showed a dramatic decrease in ALP activity. The cells treated with 10 ng/ml of TGF-beta1 followed by rhBMP-2 alone exhibited an intermediate ALP activity. The cells treated with 100 ng/ml of rhBMP-2 demonstrated Von-Kossa positive solid deposits after 3 weeks, while there were few Von-Kossa positive solid deposits when the cells treated with 10 ng/ml of TGF-beta1. These results show that TGF-beta1 inhibits the effects of rhBMP-2 on the osteoblast differentiation of HBMSCs in a dose dependant manner. Furthermore, the effects of TGF-beta1 on HBMSCs are reversible. This suggest that TGF-beta1 and rhBMP-2 are coordinately controlled during the osteoblast differentiation of HMBSCs.     

The effect of purmorphamine on osteoblast phenotype expression of human bone marrow mesenchymal cells cultured on titanium

Purmorphamine is a new molecule with osteogenesis-inducing activity in multipotent progenitor cells. The aim of this study was to evaluate whether purmorphamine maintains its osteogenic potential on human bone marrow mesenchymal cells cultured on commercially pure titanium (cpTi). Cells were cultured either in the absence or presence of purmorphamine 3 microm on cpTi in supplemented alpha-MEM. At 7, 14, and 21 days, cell proliferation, viability, total protein content, collagen content, and alkaline phosphatase (ALP) activity were evaluated. Bone-like nodule formation was evaluated at 21 days. All experiments were done in quintuplicate and data were compared by ANOVA or t-test. Purmorphamine did not affect cell proliferation (p = 0.619), viability (p = 0.831), and collagen content (p = 0.088). Total protein content (p = 0.047), ALP activity (p = 0.001), and bone-like nodule formation (p = 0.002) were increased by purmorphamine. The present results indicate that events related to osteoblast differentiation, including increased ALP activity and bone-like nodule formation, are enhanced by purmorphamine in the presence of cpTi. It means that this molecule could be useful as an adjunct therapy to improve the osseointegration of the implants in the fields of dentistry and orthopaedics.     

Poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) supports in vitro osteogenesis

Studies have demonstrated that polymeric biomaterials have the potential to support osteoblast growth and development for bone tissue repair. Poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) (PHBV), a bioabsorbable, biocompatible polyhydroxy acid polymer, is an excellent candidate that, as yet, has not been extensively investigated for this purpose. As such, we examined the attachment characteristics, self-renewal capacity, and osteogenic potential of osteoblast-like cells (MC3T3-E1 S14) when cultured on PHBV films compared with tissue culture polystyrene (TCP). Cells were assayed over 2 weeks and examined for changes in morphology, attachment, number and proliferation status, alkaline phosphatase (ALP) activity, calcium accumulation, nodule formation, and the expression of osteogenic genes. We found that these spindle-shaped MC3T3-E1 S14 cells made cell-cell and cell-substrate contact. Time-dependent cell attachment was shown to be accelerated on PHBV compared with collagen and laminin, but delayed compared with TCP and fibronectin. Cell number and the expression of ALP, osteopontin, and pro-collagen alpha1(I) mRNA were comparable for cells grown on PHBV and TCP, with all these markers increasing over time. This demonstrates the ability of PHBV to support osteoblast cell function. However, a lag was observed for cells on PHBV in comparison with those on TCP for proliferation, ALP activity, and cbfa-1 mRNA expression. In addition, we observed a reduction in total calcium accumulation, nodule formation, and osteocalcin mRNA expression. It is possible that this cellular response is a consequence of the contrasting surface properties of PHBV and TCP. The PHBV substrate used was rougher and more hydrophobic than TCP. Although further substrate analysis is required, we conclude that this polymer is a suitable candidate for the continued development as a biomaterial for bone tissue engineering.     

锌修饰硅酸钙陶瓷涂层与骨整合

BACKGROUND: Zinc-modified calcium silicate (CaSiO3) bioceramics coating on the titanium surface prepared in preliminary experiments has good chemical stability and antibacterial property. OBJECTIVE: To observe the effects of zinc-modified CaSiO3 bioceramics coating on osteointegration. METHODS: MC3T3-E1 cells were respectively cultured on the titanium with zinc-modified CaSiO3 bioceramics coating (experiment group), titanium with CaSiO3 bioceramics coating (control group) and pure titanium (blank control group). Then, cell adhesion, proliferation, calcification rate and the expression of type I collagen and osteocalcin were detected. The implant materials mentioned above were respectively inserted into the femurs of New Zealand white rabbits, and after 1.5 months, the osteoproliferation and osteointegration between the implants and the host were tested. RESULTS AND CONCLUSION: In vitro experiment: The number of adhesive cells at 12 hours after co-culture was significantly increased in the experimental group compared with the control group and blank control group (P < 0.05). At 14 days after co-culture, cell proliferation ability and ability of calcium nodule formation in the experiment group were significantly better than those in the other groups (P < 0.05). At 21 days after co-culture, there was no significant difference in the expression of type I collagen, but the expression of osteocalcin in the experiment group was higher than that in the control group and blank control group (P < 0.05). In vivo experiment: In the experiment group, a large amount of bone substances were detected, the coating materials directly contacted with the bone interface, new bone tissues and little fibrous tissues were observed at the interface. In contrast, there was a small amount of bone hyperplasia in the control group and almost no bone hyperplase in the blank control group. Moreover, a small part of the implant directly contacted with the bone interface and the most part was separated from bone trabeculae by fibrous tissues. These findings indicate that zinc-modified CaSiO3 bioceramics coating can enhance the ability of osteointegration between titanium implants and the host.      

Osteoblast response on Ti- and Zr-based bulk metallic glass surfaces after sand blasting modification

The present study aimed to evaluate the osteoblast response on Ti- and Zr-based BMG surfaces sand blasted with different grit corundums for implant application, with mechanically polished disks before sand blasting as control groups. The surface properties were characterized by scanning electron microscopy (SEM), contact angle, and roughness measurements. Further evaluation of the surface bioactivity was conducted by MG63 cell attachment, proliferation, morphology, and alkaline phosphatase (ALP) activity on the sample surfaces. It was found that corundum sand blasting surfaces significantly increased the surface wettability and MG63 cell attachment, cell proliferation, and ALP activity in comparison with the control group surfaces. Besides, the sample surface treated by large grit corundum is more favorable for cell attachment, proliferation, and differentiation than samples treated by small grit corundum, indicating that it might be effective for improving implant osseointegration in vivo. ? 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2012.     

Tricalcium phosphate and glutaraldehyde crosslinked gelatin incorporating bone morphogenetic protein--a viable scaffold for bone tissue engineering

Bone defects caused by various etiologies must be filled with suitable substances to promote bone repair. Autogenous iliac crest graft is most frequently used, but is often associated with morbidities. Several bone graft substitutes have been developed to provide osteoconductive matrices as well as to enhance osteoinductivity. A tricalcium phosphate and glutaraldehyde crosslinked gelatin (GTG) scaffold, incorporated with bone morphogenetic proteins (BMPs), was developed to provide an alternative mean of bone tissue engineering. This study investigated differences between GTG and BMP-4 immobilized GTG (GTG-BMP) scaffolds on neonatal rat calvaria osteoblast activities. The GTG scaffold possessed an average pore size of 200 microm and a porosity of 75%. HE staining revealed uniform cell distribution throughout the scaffold 24 h post cell seeding. Alkaline phosphatase (ALP) activity of the GTG samples increased initially and then stabilized at 3 weeks postseeding. ALP activity of the GTG-BMP samples was similar to that of the GTG samples in the second and third weeks, but it continued increasing and became significantly greater than that of the GTG samples by the fourth week. Gla-type osteocalcin (Gla-OC) activity of the GTG-BMP samples was initially lower, but also became significantly greater than that of the GTG samples by the fourth week. An HE stain revealed greater numbers of attached cells and a richer matrix deposits in the GTG-BMP samples. A von Kossa stain showed larger mineralizing nodules, in greater numbers, after 4 weeks of in vitro cultivation. These findings suggest that the GTG scaffold provides an excellent porous structure, conductive to greater cell attachment and osteoblast differentiation, and that utility can be significantly enhanced by the inclusion of BMPs. A GTG-BMP scaffold holds promise as a superior bioactive material for bone tissue engineering.     

SV-40 large-T immortalization of embryonic bone cells: establishment of osteoblastic clonal cell lines

Cells derived from embryonic rat calvariae were immortalized by retroviral delivery of cDNA for the SV-40 large T antigen and the bacterial neomycin resistance gene. After selection with G418, cells were cloned by limiting dilution and screened for expression of osteoblast characteristics. One clone (RCT-3), derived from cells collected during the third period of enzymatic digestion, showed high constitutive expression of alkaline phosphatase (ALP), synthesized type I collagen in the virtual absence of type III and exhibited a parathyroid hormone (PTH)-responsive adenylate cyclase (EC50, 10 nM). Messenger RNAs for osteonectin and osteopontin were present in RCT-3 cells and osteopontin mRNA was enhanced by 1,25 (OH)2 vitamin D3 treatment. The other cell line (RCT-1), derived from cells released during the first 10 min of digestion, expressed osteoblast features only after 3 d treatment with 1 microM retinoic acid (RA). ALP activity increased from 0.003 to 0.25 mumole/min/mg protein, there was a substantial increase in the steady-state level of type I collagen mRNA and a dose-dependent and saturable response to PTH was induced (EC50, 10 nM). Osteopontin mRNA was induced by 1,25 (OH)2D3. This study has provided two new cell lines which may be useful models for studies of differentiation-related gene expression in bone cells.     

Relationship between bone ingrowth, mineral apposition rate, and osteoblast activity

To better understand skeletal attachment of porous coated total hip and knee implants over time, this study investigated the dynamics of osteoblast populations at the interface of porous coated implants in a weight-bearing ovine model. The relationship between cancellous bone ingrowth, mineral apposition rate (MAR), and osteoblast activity indicators such as osteoblast area, relative osteoblast number, osteoid width, and osteoid area (O.Ar.) were investigated. The data demonstrated that the percent O.Ar. was a marginally significant predictor of bone ingrowth and MAR over time, suggesting that the amount of osteoid present influenced bone ingrowth and MAR in the porous coated implants. The data also demonstrated that all osteoblast activity indicators were significantly greater in the porous coated region compared to the host bone region, while controlling for in situ time (p < 0.05). This may have been due to the trauma of implantation or the influence of the implant load on the bone tissue promoting a regional acceleratory phenomenon. The localized response suggests that specific therapies may be developed to affect the physiology of osteoblasts at the interface of implants, which may allow for improve skeletal attachment of biomaterials and clinical outcomes of cementless joint replacements.     

Probing the influence of SIBLING proteins on collagen-I fibrillogenesis and denaturation

Bone tissue is comprised of collagen, non-collagenous proteins, and hydroxyapatite and the SIBLING (small integrin binding, N-linked glycoprotein) family of proteins is the primary group of non-collagenous proteins. By replicating the native interactions between collagen and the SIBLING proteins at the interface of an implant, it is believed that a bone scaffold will more easily integrate with the surrounding tissue. In this work, bone sialoprotein, osteopontin (OPN), dentin sialoprotein (DSP), dentin phosphoprotein (DPP), C-terminal fragment of dentin matrix protein 1 (DMP1-C), and proteoglycan versions of DSP (DSP-PG) and DMP1 (DMP1-PG) were tested individually to determine their roles in collagen fibrillogenesis and the prevention of denaturation. It was shown that DSP and DPP slowed down fibrillogenesis, while other SIBLINGs had limited impact. In addition, the denaturation time was faster in the presence of DSP and OPN, indicating a negative impact. The role of calcium ions in these processes was also investigated. The presence of calcium ions sped up fibrillogenesis in all scenarios tested, but it had a negative impact by reducing the extent. Calcium also sped up the denaturation in most cases, with the exception of DMP1-C and DSP where the opposite was seen. Calcium had a similar effect on the proteoglycan variants in the fibrillogenesis process, but had no impact on the denaturation process in the presence of these two. It is believed that incorporating DMP1-C or DSP on the surface of a bone implant may improve the collagen interactions with the implant, thereby facilitating improved osteointegration.