Aim. Implant-associated infection usually require prolonged treatment or even removal of the implant. Local application of antibiotics is used commonly in orthopaedic and trauma surgery, as it allows reaching higher concentration in the affected compartment, while at the same time reducing systematic side effects. Ceftriaxone release from calcium sulphate has a particularly interesting, near-constant release profile in vitro, making it an interesting drug for clinical application. Purpose of the present study was to investigate the potential cytotoxicity of different ceftriaxone concentrations and their influence on osteogenic differentiation of human pre-osteoblasts. Method. Human pre-osteoblasts were cultured up to 28 days in different ceftriaxone concentrations, ranging between 0 mg/L and 50’000 mg/L. Cytotoxicity was determined quantitatively by measuring lactate dehydrogenase release, metabolic activity, and cell proliferation. Gene expression analysis of bone-specific markers as well as mineralization and protein expression of collagen-I (Col-I) were investigated to assess osteogenic differentiation. Results. Cytotoxic effects on human pre-osteoblasts could be shown above 15’000 mg/L after 1 and 2 days, whereas subtoxic effects could be observed at concentrations at 500 mg/L after 10 days. Cell proliferation showed no clear alteration up to 1000 mg/L, though a notable decline at 1500 mg/L could be seen after 10 days. Gene and protein expression of Col-I showed a concentration-dependent decrease at day 10 and 14, but also mineralization levels of human pre-osteoblasts presented a similar trend at day 28. Interestingly, the degree of mineralization was already impaired at concentrations above 250 mg/L. Conclusions. These findings provided extensive insights into the influence of different ceftriaxone concentrations on viability, proliferation, gene, and protein expression but also mineralization of human bone pre-osteoblasts. While short-term cytotoxicity is observed only at very high concentrations, metabolism may be impaired at much lower concentrations when exposure is prolonged. Release of ceftriaxone expected from calcium sulphate however remains below thresholds of impaired bone mineralization, even after 4 weeks of exposure. This study demonstrates the importance of properly selecting and monitoring antibiotic concentrations during clinical application

Numerous investigators have described osteogenic differentiation of bone marrow stromal cells obtained from both murine and human sources over the past decade. The ease of access and large available quantity of adipose tissue, however, makes Adipose-Derived Stem Cells (ADSC) a far more practical alternative for clinical applications, such as operative treatment of non-unions and regeneration of critical bone defects. Therefore, the primary goal of this research endeavor is to achieve osteogenic differentiation of ADSC. Previous work has already demonstrated that bone morphogenetic protein receptor 1A (BMP receptor 1A) signaling is required for healing critical bone defects. Based on this evidence, we used a lentiviral vector to increase expression of BMP receptor 1A by our stem cell population in order to direct their differentiation into the osteoblastic lineage. We harvested subcutaneous adipose tissue intraoperatively from consenting patients undergoing elective lipoplasty and panniculectomy procedures. The stromal vascular fraction was isolated from this tissue and further refined by passaging in selective media to yield a stable population of ADSC in primary culture. Both the identity and homogeneity of this stem cell population was confirmed using adipogenic induction media and differentiation cocktails. In addition, we subcloned an expression plasmid containing the BMP receptor 1A locus in tandem with green fluorescent protein (GFP) under the transcriptional control of a single promoter. This plasmid was packaged into a lentiviral vector to provide a reliable method of achieving both genomic integration and long-term expression of the BMP receptor 1A gene. Hence, transduction of ADSC using this vector resulted in overexpression of BMP receptor 1A by these multipotent cells. The GFP was then utilized as a reporter gene to screen and enrich the ADSC population for only those stem cells with a robust expression of BMP receptor 1A. The ADSC that overexpressed BMP receptor 1A were found to achieve osteogenic differentiation after 18 to 20 days of in vitro culture, as revealed by immunohistochemistry assays for osteocalcin. Osteogenic differentiation was further confirmed by alizarin red staining and quantitative PCR for alkaline phosphatase gene expression as a biomarker for the osteoblastic lineage. Our results demonstrate that stem cells derived from the adipose tissue of a patient represent a viable means of culturing autologous osteoblasts in vitro for future implantation at the site of critical bone defects. This method of attaining osseous regeneration is intuitively appealing, given the minimal donor site morbidity associated with removing subcutaneous fat. By transducing the ADSC with a lentiviral vector, we have also collected further evidence implicating the critical importance of signaling mediated by the BMP receptor 1A during osteogenesis. Further tissue engineering studies are now in progress to evaluate the osteogenic differentiation potential of these stem cells under hydrostatic and fluid flow shearing mechanical loads

A novel injectable hydrogel based on DNA and silicate nanodisks was fabricated and optimized to obtain a suitable drug delivery platform for biomedical applications. Precisely, the hydrogel was designed by combining two different type of networks: a first network (type A) made of interconnections between neighboring DNA strands and a second one (type B) consisting of electrostatic interactions between the silicate nanodisks and the DNA backbone. The silicate nanodisks were introduced to increase the viscosity of the DNA physical hydrogel and improve their shear-thinning properties. Additionally, the silicate nanodisks were selected to modulate the release capability of the designed network. DNA 4% solutions were heated at 90°C for 45 seconds and cooled down at 37°C degree for two hours. In the second step, the silicate nanodisks suspension in water at different concentrations (0.1 up to 0.5%) were then mixed with the pre-gel DNA hydrogels to obtain the nanocomposite hydrogels. Rheological studies were carried out to investigate the shear thinning properties of the hydrogels. Additionally, the hydrogels were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron microscopy. The hydrogels were loaded with the osteoinductive drug dexamethasone and its release was tested in vitro in phosphate buffer pH 7.4. The drug activity upon release was tested evaluating the osteogenic differentiation of human adipose derived stem cells (hASCs) in vitro through analysis of main osteogenic markers and quantification of alkaline phosphatase activity and calcium deposition. Finally, the hydrogels were tested in vivo and injected into cranial defects in rats to assess their biocompatibility and bone regeneration potential. The inclusion of the silicate nanodisks increased the viscosity of the hydrogels and the best results were obtained with the highest concentration of the nanoclay (0.5%). The hydrogels possessed shear-thinning properties as demonstrated by cyclic strain sweep tests and were able to recover their original storage modulus G' upon removal of strain. Such improvement in the injectable properties of the formulated hydrogels was mainly attributed to the formation of electrostatic interactions between the silicate nanodisks and the phosphate groups of the DNA backbone as confirmed by XPS analysis of the O, N, and P spectra. Additionally, laponite was able to sustain the release of the osteoinductive drug dexamethasone which was instead completely released from the DNA-based hydrogels after a week. The drug after being released was still active and promoted the osteogenic differentiation of hASCs as confirmed by ALP expression and expression of main osteogenic markers including ALP and COLA1. Finally, the gels proved to be biocompatible in vivo when injected into cranial defects and promoted bone formation at the periphery of the defect after a month post-treatment. A novel injectable shear-thinning DNA-based hydrogel was characterized and tested for its drug delivery properties. The hydrogel can promote the sustain release of a small molecule like dexamethasone and be biocompatible in vitro and in vivo. Due to these promising findings, the designed system could find also applicability for the delivery of growth factors or other therapeutic molecules

Previous studies have described an age-dependent distortion of bone microarchitecture for α-CGRP-deficient mice (3). In addition, we observed changes in cell survival and activity of osteoblasts and osteoclasts isolated from young wildtype (WT) mice when stimulated with α-CGRP whereas loss of α-CGRP showed only little effects on bone cell metabolism of cells isolated from young α-CGRP-deficient mice. We assume that aging processes differently affect bone cell metabolism in the absence and presence of α-CGRP. To further explore this hypothesis, we investigated and compared cell metabolism of osteoblasts and bone marrow derived macrophages (BMM)/osteoclast cultures isolated from young (8–12 weeks) and old (9 month) α-CGRP-deficient mice and age matched WT controls. Isolation/differentiation of bone marrow macrophages (BMM, for 5 days) to osteoclasts and osteoblast-like cells (for 7/14/21 days) from young (8–12 weeks) and old (9 month) female α-CGRP−/− and WT control (both C57Bl/6J) mice according to established protocols. We analyzed cell migration of osteoblast-like cells out of femoral bone chips (crystal violet staining), proliferation (BrdU incorporation) and caspase 3/7-activity (apoptosis rate). Alkaline phosphatase (ALP) activity reflects osteoblast bone formation activity and counting of multinucleated (≥ 3 nuclei), TRAP (tartrate resistant acid phosphatase) stained osteoclasts reflects osteoclast differentiation capacity. We counted reduced numbers of BMM from young α-CGRP−/− mice after initial seeding compared to young WT controls but we found no differences between old α-CGRP−/− mice and age-matched controls. Total BMM number was higher in old compared to young animals. Migration of osteoblast-like cells out of bone chips was comparable in both, young and old α-CGRP−/− and WT mice, but number of osteoblast-like cells was lower in old compared to young animals. Proliferation of old α-CGRP−/− BMM was higher when compared to age-matched WT whereas proliferation of old α-CGRP−/− osteoblasts after 21 days of osteogenic differentiation was lower. No differences in bone cell proliferation was detected between young α-CGRP−/− and age-machted WT mice. Caspase 3/7 activity of bone cells from young as well as old α-CGRP−/− mice was comparable to age-matched controls. Number of TRAP-positive multinucleated osteoclasts from young α-CGRP−/− mice was by trend higher compared to age-matched WT whereas no difference was observed in osteoclast cultures from old α-CGRP−/− mice and old WT. ALP activity, as a marker for bone formation activity, was comparable in young WT and α-CGRP−/− osteoblasts throughout all time points whereas ALP activity was strongly reduced in old α-CGRP−/− osteoblasts after 21 days of osteogenic differentiation compared to age-matched WT. Our data indicate that loss of α-CGRP results in a reduction of bone formation rate in older individuals caused by lower proliferation and reduced activity of osteogenic cells but has no profound effects on bone resorption rate. We suggest that the osteopenic bone phenotype described in aged α-CGRP-deficient mice could be due to an increase of dysfunctional matured osteoblasts during aging resulting in impaired bone formation

INTRODUCTION. The uncertainty of the biological effects of wear and corrosion from Metal-on-metal (MoM) implants has initiated a debate on their safety and use. Generally, the release of wear particles from MoM hip implants can clinically manifest in aseptic osteolysis. In our study, the effect of MoM-wear particles and particle originated Co and Cr ions on mesenchymal stromal cells (MSCs) was investigated [1]. The lead hypotheses were that (1) dissociated Co and Cr, originated from MoM-wear particles, accumulate in the bone marrow and (2) apparently impair the osteogenic function of local MSCs. This impairment could be one element contributing to the manifestation of periprosthetic osteolyses. METHODS. The study was approved by the local ethical committee (EA1/194/13); all donors gave written informed consent. Blood (B), Synovial fluid (SF) periprosthetic tissue (PT) and bone marrow (BM) were collected from patients with at least one osteolytic lesion, undergoing a revision of a MoM hip implant. Patients undergoing primary THA served as controls. Metal wear particles were isolated from PT by enzymatic digestion and their size and shape characterized by transmission electron microscopy (TEM). Local and systemic levels of Co and Cr were analyzed by graphite furnace atomic absorption spectroscopy. MoM-MSCs and control-MSCs were isolated from BM for in vitro assessment of their viability, proliferation, migration and multilineage differentiation. In addition, control-MSCs were in vitro exposed to Co and Cr ions and assessed for their viability, proliferation and osteogenic differentiation. RESULTS. We confirmed the presence of nanoscaled particles that appeared heterogeneous in size and shape (mean diameter: 34.7 ± 16.2 nm; n = 64). Second, we confirmed the exposure to Co and Cr and quantified its particulate and dissociated amounts. Local metal levels exceed systemic ones by several magnitudes and dissociated Co and Cr was found in periprosthetic compartments including BM (peak BM Co concentration: 977 µg/L, peak BM Cr concentration: 2,875 µg/L; n = 10). While in vivo exposure to MoM-wear did not influence MSCs' viability, proliferation, migration capacity, adipogenic- and chondogenic differentiation, it decreased osteogenic matrix mineralization and cellular ALP activity (FIGURE 1). In vitro exposure of control-MSCs to Co(II) and Cr(III) ions, at concentrations detected in BM, confirmed the decrease in osteogenic matrix mineralization and ALP activity (FIGURE 2). DISCUSSION. We found that extensive amounts of Co and Cr occurred in their dissociated state within the periprosthetic region (SF, PT, BM), indicating that vast amounts of particulate wear in degraded. Our work represents an important piece in the puzzle of the clinical manifestation of periprosthetic osteolysis: dissociated Co and Cr at clinically relevant concentrations impair the bone forming function of MSCs. The study's data indicate an influence of MoM-wear on BM residing MSCs' osteogenic differentiation that is relevant for maintaining vital bone structure, thus confirming the lead hypothesis. The use of CoCrMo alloys for articulating surfaces in hip implants needs critical reconsideration. For figures/tables, please contact authors directly.

Aims. Disease transmission, availability and economic costs of allograft have resulted in significant efforts into finding an allograft alternative for use in impaction bone grafting (IBG). Biotechnology offers the combination of skeletal stem cells (SSC) with biodegradable polymers as a potential solution. Recently polymers have been identified with both structural strength and SSC compatibility that offer the potential for clinical translation. The aim of this study was to assess whether increasing the porosity of one such polymer via super critical CO. 2. fluid foaming (SCF) enhanced the mechanical and cellular compatibility characteristics for use as an osteogenic alternative to allograft in IBG. Methods. High molecular weight PLA scaffolds were produced via traditional (solid block) and SCF (porous) techniques, and the differences characterised using scanning electron microscopy (SEM). The polymers were milled, impacted, and mechanical comparison between traditional vs SCD created scaffolds and allograft controls was made using a custom shear testing rig, as well as a novel agitation test to assess cohesion. Cellular compatibility tests for cell number, viability and osteogenic differentiation using WST-1 assays, fluorostaining and ALP assays were determined following 14 day culture with SSC's. Results. SEM showed increased porosity of the SCF produced PLA scaffolds, with pores between 50–100µm. Shear testing showed the SCF polymer exceeded the shear strength of allograft controls (P< 0.001). Agitation testing showed greater cohesion between the particles of the SCF polymer (P< 0.05). Cellular studies showed increased cell number, viability and osteogenic differentiation on the SCF polymer compared to traditional polymer (P< 0.05) and allograft (P< 0.001). Conclusions. The use of supercritical C0. 2. to generate PLA scaffolds significantly improves the cellular compatibility and cohesion compared to traditional non-porous PLA, without substantial loss of mechanical shear strength. The improved characteristics are critical for clinical translation as a potential osteogenic composite for use in IBG

Osteoporosis accounts for a leading cause of degenerative skeletal disease in the elderly. Osteoblast dysfunction is a prominent feature of age-induced bone loss. While microRNAs regulate osteogenic cell behavior and bone mineral acquisition, however, their function to osteoblast senescence during age-mediated osteoporosis remains elusive. This study aims to utilize osteoblast-specific microRNA-29a (miR-29a) transgenic mice to characterize its role in bone cell aging and bone mass. Young (3 months old) and aged (9 months old) transgenic mice overexpressing miR-29a (miR-29aTg) driven by osteocalcin promoter and wild-type (WT) mice were bred for study. Bone mineral density, trabecular morphometry, and biomechanical properties were quantified using μCT imaging, material testing system and histomorphometry. Aged osteoblasts and senescence markers were probed using immunofluorescence, flow cytometry for apoptotic maker annexin V, and RT-PCR. Significantly decreased bone mineral density, sparse trabecular morphometry (trabecular volume, thickness, and number), and poor biomechanical properties (maximum force and breaking force) along with low miR-29a expression occurred in aged WT mice. Aging significantly upregulated the expression of senescence markers p16INK4a, p21Waf/Cip1, and p53 in osteoporotic bone in WT mice. Of note, the severity of bone mass and biomechanical strength loss, as well as bone cell senescence, was remarkably compromised in aged miR-29aTg mice. In vitro, knocking down miR-29a accelerated senescent (β-galactosidase activity and senescence markers) and apoptotic reactions (capsas3 activation and TUNEL staining), but reduced mineralized matrix accumulation in osteoblasts. Forced miR-29a expression attenuated inflammatory cytokine-induced aging process and retained osteogenic differentiation capacity. Mechanistically, miR-29a dragged osteoblast senescence through targeting 3′-untranslated region of anti-aging regulator FoxO3 to upregulate that of expression as evident from luciferase activity assessment. Low miR-29a signaling speeds up aging-induced osteoblast dysfunction and osteoporosis development. Gain of miR-29a function interrupts osteoblast senescence and shields bone tissue from age-induced osteoporosis. The robust analysis sheds light to the protective actions of miR-29a to skeletal metabolism and conveys a perspective of miR-29a signaling enhancement beneficial for aged skeletons

Surgical failure, mainly caused by loosening implants, causes great mental and physical trauma to patients. Improving the physicochemical properties of implants to achieve favourable osseointegration will continue to be the focus of future research. Strontium (Sr), a trace element, is often incorporated into hydroxyapatite (HA) to improve its osteogenic activity. Our previous studies have shown that miR-21 can promote the osteogenic differentiation of mesenchymal stem cells by the PI3K/β-catenin pathway. The aim of this study is to fabricate a SrHA and miR-21 composite coating and it is expected to have a favorable bone healing capability. Ti discs (20 mm diameter and one mm thickness for the in vitro section) and rods (four mm diameter and seven mm length for the in vivo section) were prepared by machining pure Ti. The Ti cylinders were placed in a Teflon-lined stainless-steel autoclave for treating at 150°C for 24 h to form SrHA layer. The miR-21 was encapsulated in nanocapsules. The miR-21 nanocapsules were mixed with CMCS powder to form a gel-like sample and uniformly coated on the SrHA modifed Ti. Osteoblast-like MG63 cells were cultured on SrHA and miR-21 modified Ti, Cell proliferation activity and osteogenesis-related gene expression were evaluated. A bone defect model was established with mature New Zealand to evaluate the osseointegration. Cylindrical holes (four mm in diameter) were created at the distal femur and tibial plateau. Each rabbit was implanted with four of the aforementioned rods (distal femur and tibial plateau of the hind legs). After implantation for one, two and three months, the rabbits were observed by X-ray and scanned using u-CT. Histological and Immunohistochemical analysis were performed to examine the osteogenic markers. A biomechanical push-in test was used to assess the bone-implant bonding strength. Both SrHA nanoparticles with good superhydrophilicity and miR-21 nanocapsules with uniform sizes were distributed evenly on the surface of the Ti. In vitro experiments revealed that the composite coating was beneficial to osteoblast proliferation, differentiation and mineralization. In vivo evaluations demonstrated that this coating could not only promote the expression of angiogenic factor CD31 but also enhance the expression of osteoblastic genes to facilitate angio-osteogenesis. In addition, the composite coating also showed a decreased RANKL expression compared with the miR-21 coating. As a result, the SrHA/miR-21 composite coating promoted new bone formation and mineralization and thus enhanced osseointegration and bone-implant bonding strength. A homogeneous SrHA and miR-21 composite coating was fabricated by generating pure Ti through a hydrothermal process, followed by adhering miR-21 nanocapsules. This coating combined the favorable physicochemical properties of SrHA and miR-21 that synergistically promoted angiogenesis, osteogenesis, osseointegration, bone mineralization and thus bone-implant bonding strength. This study provided a new strategy for surface modification of biomedical implants

Osteoarthritis (OA) is the fastest growing global health problem, with a total joint replacement being the only effective treatment for patients with end stage OA. Many groups are examining the use of bone marrow or adipose derived mesenchymal stem cells (MSCs) to repair cartilage, or modulate inflammation to promote healing, however, little efficacy in promoting cartilage repair, or reducing patient symptoms over temporary treatments such as micro-fracture has been observed. There is a growing body of literature demonstrating that MSCs derived from the synovial lining of the joint are superior in terms of chondrogenic differentiation and while improvements in clinical outcome measures have been observed with synovial MSCs, results from clinical studies are still highly variable. Based on our results, we believe this variability in clinical studies with MSCs results in part from the isolation, expansion and re-injection of distinct MSCs subtypes in normal vs. OA tissues, each with differing regenerating potential. However, it remains unknown if this heterogeneity is natural (e.g. multiple MSC subtypes present) or if MSCs are influenced by factors in vivo (disease state/stage). Therefore, in this study, we undertook an ‘omics’ screening approach on MSCs from normal and OA knee synovial tissue. Specifically, we characterized their global proteome and genomic expression patterns to determine if multiple MSC from normal and OA joints are distinct at the protein/gene expression level and/if so, what proteins/genes are differentially expressed between MSCs derived from normal and OA synovial tissue. Synovium tissue was collected from OA patients undergoing joint replacement and normal cadaveric knees. The in vitro adipogenic, chondrogenic and osteogenic differentiation potential of the MSCs was analyzed via qPCR and histology. Fully characterized MSC populations where then analyzed through an unbiased shotgun proteomics, and microarray analysis. Synovial MSCs isolated from both OA and normal knees demonstrated similar multipotent differentiation capacity. Likewise, both OA and normal MSCs display the typical MSCs cell surface marker profile in vitro (CD90+, CD44+, CD73+, CD105+). Using shotgun proteomics, 7720 unique peptides corresponding to 2183 proteins were identified and quantified between normal and OA MSCs. Of these 2183 proteins, 994 were equally expressed in normal and OA, MSCs, 324 were upregulated in OA MSCs (with 50 proteins exclusively expressed in OA MSCs), 630 proteins were upregulated in normal MSCs (with 16 proteins exclusively expressed in normal MSCs). Microarray analysis of normal and OA MSCs demonstrated a similar result in where, 967 genes were differentially expressed between normal and OA MSCs, with 423 genes upregulated in OA, and 544 genes upregulated in normal MSCs. In this project, we have demonstrated that although normal and OA synovial derived MSCs demonstrate similar multipotent differentiation potential and cell surface markers expression, these cells demonstrated significant differences at the molecular level (protein and gene expression). Further research is required to determine if these differences influence functional differences in vitro and/or in vivo and what drives this dramatic change in the regulatory pathways within normal vs. OA synovial MSCs

There is currently no cure for osteoarthritis (OA), although there are ways to manage it, but most require quite invasive surgeries. There is a resident mesenchymal progenitor cell (MPC) population within the synovial membrane of the joint that have the ability to differentiate into bone, fat, and cartilage. We hypothesise that in vivo and in vitro cell surface marker expression comparisons of the MPCs can determine which population has the highest chondrogenic capacity and is best suited for future clinical trials. Method optimisation protocol: Synovial biopsies (2 or 5mm) were obtained from patients undergoing surgery. The biopsies were digested in either collagenase type I, IA, IV or II at a concentration of 0.5 or 1.0 mg/mL. Digestion was conducted at 37°C for 30, 60, 90 or 120min. To assay for the number of MPCs obtained, the cell suspension was stained with CD90 (a synovial MPC marker) and magnetically purified. The purified cells were then assayed by flow cytometry (Co-stained with a live/dead cell marker, BV510) or bright-field microscopy. Study protocol: Synovial tissues were digested in type IV collagenase for two hours to obtain a single cell suspension. The cells were subsequently stained with mesenchymal stem cell markers, including CD 90, CD 271, CD 44, CD73, and CD105, a macrophage marker, CD68. The macrophages were excluded and the remaining cells were index sorted into 96-well plates. The cells were expanded, and underwent 21-day chondrogenic, adipogenic, and osteogenic differentiation. Differentiation was assayed using RT-qPCR and histological methods. Additionally, the cells were re-analysed for marker expression after culturing. Optimisation: Synovial biopsies of 5mm produced a greater number of live CD90+ cells than 2mm biopsies. It was observed that type IV collagenase at 1mg/ML treatment for 120 min (hip) and 90 min (knee) obtained the greatest number of CD90+ MPCs from the synovium. Results: A single cell was isolated from an OA hip biopsy and was positive for the markers CD90, CD44, CD73, and negative for the markers CD68, CD271, CD105. Following differentiation, PCR analysis suggested that the cell line was able to differentiate into chondrocytes and adipocytes, but not osteoblasts. Histology data agreed with the PCR data with the adipocytes and chondrocytes having positive staining, whereas the osteoblasts were negative. FACS analysis following proliferation showed that the expression in vivo versus in vitro was the same except CD105 that became positive after proliferation in vitro. MPCs express cell surface markers that provide information as to populations have the best cartilage regeneration abilities. By determining the properties of the MPCs in OA hips that allow for better chondrogenic differentiation abilities in vitro, selecting the optimal cells for regenerating cartilage can be done more efficiently for novel cell therapies for OA

INTRODUCTION. Trabecular Titanium. ™. (TT) is a novel material with a structure similar to trabecular bone, already used for prosthetic clinical applications. Being the bone-implant interface the weakest point during the initial healing period, the association of TT with a hydrogel enriched with progenitor cells and osteoinductive factors may represent a promising strategy to improve prosthesis osteointegration. In a previous in vitro study we evaluated the ability of an ammidated carboxymethylcellulose hydrogel (CMCA) and of TT enriched with CMCA to support bone marrow mesenchymal stem cells (BMSCs) viability and osteogenic differentiation [1]. The aim of this study was to evaluate in vivo if the association of TT with CMCA enriched with strontium chloride (SrCl. 2. ) and BMSCs could ameliorate TT osteointegration. METHODS. This study combines TT with CMCA, SrCl. 2. and BMSCs. To mimic prosthesis-bone implants, TT discs were seeded with human BMSCs predifferentiated in osteogenic medium, then press-fit into engineered bone. A total of 36 athymic mice were implanted subcutaneously, each animal received 2 constructs as un-seeded TT and TT+CMCA or cell seeded TT+BMSCs and TT+CMCA+BMSCs. After 4, 8 and 12 weeks, osteodeposition, bone mineral density (BMD) and osteointegration were evaluated by fluorescence imaging, micro-CT, SEM, histology and pull-out tests. RESULTS. Micro-CT analysis demonstrated the homogeneity of the engineered bone in all experimental groups, supporting the reproducibility of our novel engineered model. Macroscopic evaluation of explanted constructs after 4 weeks revealed their integration with mice subcutaneous structures. In pull-out biomechanical tests, increases in extraction energy and peak force from 4 to 12 weeks were observed in all the experimental groups, except TT+CMCA. TT+CMCA+BMSCs showed the highest value of peak force and the greatest increase in comparison to samples explanted at 4 weeks. In vivo fluorescence imaging showed osteodeposition activity inside the constructs, observation confirmed by the ex-vivo analyses revealing a higher activity in TT+BMSCs and in TT+CMCA+BMSCs in comparison to acellularized TT samples. SEM evaluation of ECM deposition at the interface between bone scaffolds and TT disks revealed a significant difference between TT+CMCA+BMSCs and the other experimental groups with the former showing an almost complete filling of the space between the integration surfaces already after 4 weeks. In histomorphometric analyses of tissue ingrowth at 8 weeks, TT+BMSCs and TT+CMCA+BMSCs showed a greater tissue ingrowth compared to TT and TT+CMCA samples. DISCUSSION. Several efforts have been made to improve osteointegration with particular attention to critical cases such as implant revision surgeries. The association of porous structures with osteoinductive factors enriched hydrogels and stem cells represents a novel and promising strategy for more effective osteointegration to reduce prosthesis mobilization risks. Our results demonstrate that the association of Trabecular Titanium. ™. with a SrCl. 2. enriched hydrogel and BMSCs increases the production of ECM and may thus represent a valid approach to accelerate prosthesis osteointegration. Further validation of these data will include construct implantation in large animal orthotopic models to better mimic surgical procedures

Recently, the osteoregenerative properties of allograft have been enhanced by addition of autogenous skeletal stem cells to treat orthopaedic conditions characterised by lost bone stock. There are multiple disadvantages to allograft, and trabecular tantalum represents a potential alternative. This metal is widely used, although in applications where there is poor initial stability, or when it is used in conjunction with bone grafting, loading may need to be limited until sound integration has occurred. Strategies to speed up implant incorporation to surrounding bone are therefore required. This may improve patient outcomes, extending the clinical applications of tantalum as a substitute for allograft. Aim. To use tissue engineering strategies to enhance the reconstructive properties of tantalum, as an alternative to allograft. Methods. Human bone marrow stromal cells (5×10. 5. cells/ml) were cultured on blocks of trabecular tantalum or allograft for 28 days in basal and osteogenic media. Molecular profiling, confocal and scanning electron microscopy, as well as live/dead staining and biochemical assays were used to detail cell adherence, proliferation and phenotype. Results. Cells displayed extensive adherence and proliferation throughout trabecular tantalum. Samples cultured in osteogenic conditions showed abundant matrix production. Electron microscopy confirmed significant cellular growth through tantalum to a depth of 5mm. In contrast to cells cultured with allograft in both basal and osteogenic conditions, cell proliferation and biochemical assays showed significantly higher activity with tantalum than allograft. Furthermore, alkaline phosphatase (ALP) assay and molecular profiling confirmed no significant difference in expression of ALP, Runx-2, Col-1 and Sox-9 between cells cultured on tantalum and allograft. Conclusions. These studies demonstrate trabecular tantalum supports cell growth and osteogenic differentiation at least as well as allograft. Trabecular tantalum represents a good alternative to allograft for tissue engineering osteoregenerative strategies in the context of lost bone stock. Further mechanical testing and in vivo studies are on-going

Biomaterials used in regenerative medicine should be able to support and promote the growth and repair of natural tissues. Bioactive glasses (BGs) have a great potential for applications in bone tissue engineering [1, 2]. As it is well known BGs can bond to host bone and stimulate bone cells toward osteogenesis. Silicate BGs, e.g. 45S5 Bioglass® (composition in wt.%: 45 SiO. 2. , 6 P. 2. O. 5. , 24, 5 Na. 2. O and 24.5 CaO), exhibit positive characteristics for bone engineering applications considering that reactions on the material surface induce the release of critical concentrations of soluble Si, Ca, P and Na ions, which can lead to the up regulation of different genes in osteoblastic cells, which in turn promote rapid bone formation. BGs are also increasingly investigated for their angiogenic properties. This presentation is focused on cell behavior of osteoblast-like cells and osteoclast-like cells on BGs with varying sample geometry (including dense discs for material evaluation and coatings of highly porous Al. 2. O. 3. -scaffolds as an example of load-bearing implants). To obtain mechanically competent porous samples with trabecular architecture analogous to those of cancellous bone, in this study Al. 2. O. 3. scaffolds were fabricated by the well-known foam replication method and coated with Bioglass® by dip coating. The resulted geometry and porosity were proven by SEM and μCT. Originating from peripheral blood mononuclear cells formed multinucleated giant cells, i.e. osteoclast-like cells, after 3 weeks of stimulation with RANKL and M-CSF. Thus, the bioactive glass surface can be considered a promising material for bone healing, providing a surface for bone remodeling. Osteoblast-like cells and bone marrow stromal cells were seeded on dense bioactive glass substrates and coatings showing an initial inhibited cell attachment but later a strong osteogenic differentiation. Additionally, cell attachment and differentiation studies were carried out by staining cytoskeleton and measuring specific alkaline phosphatase activity. In this context, 45S5 bioactive glass surfaces can be considered a highly promising material for bone tissue regeneration, providing very fast kinetics for bone-like hydroxyapatite formation (mineralization). Our examinations revealed good results in vitro for cell seeding efficacy, cell attachment, viability, proliferation and cell penetration onto dense and porous Bioglass®-coated scaffolds. Recent in vivo investigations [3] have revealed also the angiogenic potential of bioactive glass both in particulate form and as 3D scaffolds confirming the high potential of BGs for bone regeneration strategies at different scales. Implant surfaces based on bioactive glasses offer new opportunities to develop these advanced biomaterials for the next generation of implantable devices and tissue scaffolds with desired tissue-implant interaction

Bone morphogenetic proteins (BMPs) are able to induce osteogenic differentiation in many cells, including muscle cells. However, the actual contribution of muscle cells to bone formation and repair is unclear. Our objective was to examine the capacity of myogenic cells to contribute to BMP-induced ectopic bone formation and fracture repair. Osteogenic gene expression was measured by quantitative PCR in osteoprogenitors, myoblasts, and fibroblasts following BMP-2 treatment. The MyoD-Cre x ROSA26R and MyoD-Cre x Z/AP mouse strains were used to track the fate of MyoD+ cells in vivo. In these double-transgenic mice, MyoD+ progenitors undergo a permanent recombination event to induce reporter gene expression. Ectopic bone was produced by the intramuscular implantation of BMP-7. Closed tibial fractures and open tibial fractures with periosteal stripping were also performed. Cellular contribution was tracked at one, two and three week time points by histological staining. Osteoprogenitors and myoblasts exhibited comparable expression of early and late bone markers; in contrast bone marker expression was considerably less in fibroblasts. The sensitivity of cells to BMP-2 correlated with the expression of BMP receptor-1a (Bmpr1a). Pilot experiments using the MyoD-Cre x Rosa26R mice identified a contribution by MyoD expressing cells in BMP-induced ectopic bone formation. However, false positive LacZ staining in osteoclasts led us to seek alternative systems such as the MyoD-cre x Z/AP mice that have negligible background staining. Initially, a minor contribution from MyoD expressing cells was noted in the ectopic bones in the MyoD-cre x Z/AP mice, but without false positive osteoclast staining. Soft tissue trauma usually precedes the formation of ectopic bone. Hence, to mimic the clinical condition more precisely, physical injury to the muscle was performed. Traumatising the muscle two days prior to BMP-7 implantation: (1) induced MyoD expression in quiescent satellite cells; (2) increased ectopic bone formation; and (3) greatly enhanced the number of MyoD positive cells in the ectopic bone. In open tibial fractures the majority of the initial callus was MyoD+ indicating a significant contribution by myogenic cells. In contrast, closed fractures with the periosteum intact had a negligible myogenic contribution. Myoblasts but not fibroblasts were highly responsive to BMP stimulation and this was associated with BMP receptor expression. Our transgenic mouse models demonstrate for the first time that muscle progenitors can significantly contribute to ectopic bone formation and fracture repair. This may have translational applications for clinical orthopaedic therapies

CPT is a uniquely difficult condition, often associated with Neurofibromatosis (NF1), where bone healing is compromised. Although rare, the severity of this condition and the multiple procedures often entailed in treating it, warrant research attention. As study material is limited, animal models of the disorder are desirable for testing new treatments. We sought to create a model of CPT where both copies of the NF1 gene were ablated at the fracture site, as has been found in some clinical specimens. NF1 floxed mice had fracture surgery; both closed fracture and open osteotomy were performed. Either a Cre- or control GFP-adenovirus was injected into the fracture site at day zero. Recombination was confirmed in ZAP reporter mice. Additionally, cell culture studies were used to examine the possible responses of NF1+/+ (wild type) NF1+/− or NF1−/− to drugs which may rescue the dysregulated Ras/MAPK pathway in NF1. In closed fractures, radiographic bridging was 100% in NF1+/+ calluses and <40% in NF1−/− calluses (P<0.05). In open fractures, radiographic bridging was 75% in NF1+/+ calluses and <30% in NF1−/− calluses (P<0.05). In both fracture repair models the NF1−/− state was associated with a significant up to 15-fold increase in fibrotic tissue invading the callus by week 3. In NF1−/− fractures, large numbers of TRAP+ cells were observed histologically in the fibrotic tissue. Closed fractures also showed a significant increase in BRDU labelled proliferating cells in the callus. In cell culture models of NF1 deficient osteogenesis, NF1−/− progenitors were found to be significantly impaired in their capacity to form a calcified matrix as measured by Alizarin Red S staining and osteogenic markers (Runx2, Osteocalcin, Alp expression). However, when differentiated calvarial NF1 floxed osteoblasts were treated with Cre adenovirus, mineralization was not affected, suggesting that NF1 impacts on osteogenic differentiation rather than mature cell function. Treatment with MEK inhibitor PD0325901 was found to rescue the NF1−/− progenitor differentiation phenotype and permit robust mineralization. Treatment with the JNK inhibitor SP600125 was also able to improve ALP activity and mineralization in NF1+/− osteoprogenitors compared to control cells. This model of NF1 −/− induction at a fracture or osteotomy site closely replicates the clinical condition of CPT, with lack of bone healing and fibrous tissue invasion. Underlying defects in bone cell differentiation in NF1 deficiencies can be at least partially rescued by JNK and MEK inhibitors

Purpose. The data regarding the effects of noggin on bone morphogenetic protein (BMP)-induced osteogenesis of mesenchymal stem cells (MSCs) are controversial. Most studies performed in rodent cells/models indicated that noggin was a negative regulator of BMP-2-induced osteogenesis; however, one study conducted with human MSCs in culture showed that the addition of noggin induced osteogenesis in vitro. To clear the controversy, we designed this study to evaluate the effects of knocking down noggin gene expression on BMP-2-induced osteogenesis of human bone marrow-derived primary MSCs in vitro. Method. MSCs were isolated from human tibial bone marrow by density gradient centrifugation. Two noggin small interfering RNAs (siRNAs) were used in this study to knockdown noggin gene expression. There were four study groups: MSCs with no transfection of siRNA (named as NT group), MSCs transfected with non-targeting negative control siRNA (named as control group), MSCs transfected with noggin siRNA1 (named as NOGsi1 group), and MSCs transfected with noggin siRNA2 (named as NOGsi2 group). After transfection, MSCs were induced to undergo osteogenic differentiation by incubating in basal medium containing 0.1 μg/ml BMP-2 for 35 days. The expression levels of osteoblastic marker genes were measured by real-time quantitative PCR on day 14. Also assessed was alkaline phosphatase (ALP) activity by a colorimetric kinetic assay and Fast Blue B staining on day 14. Calcium deposition was determined by the calcium assay on day 35. Results. The expression levels of integrin binding sialoprotein (IBSP) and osteocalcin (OC) were significantly decreased in both NOGsi1 and NOGsi2 groups compared with NT and control groups (all p<0.038). Although the expression level of runt-related transcription factor 2 (RUNX2) was also reduced in NOGsi1 and NOGsi2 groups compared with NT and control groups, it did not reach statistical significance. ALP activity was significantly lower in NOGsi1 and NOGsi2 groups than that of NT group (both p<0.024). The same pattern was also observed in ALP Fast Blue B staining. Calcium deposition was also significantly decreased in both NOGsi1 and NOGsi2 groups compared with NT group (both p<=0.048). Conclusion. Noggin suppression by siRNA inhibits BMP-2-induced osteogenesis of human bone marrow-derived MSCs. Our results, contrary to the extensive studies conducted in rodent cells/models, corroborated with the previous study that the addition of noggin in the cell culture increased osteogenesis of human MSCs. This suggests that the effects of noggin on BMP-2-induced osteogenesis of MSCs might be species-specific

Peri-prosthetic osteolysis and subsequent aseptic loosening is the most common reason for revising total hip replacements. Wear particles originating from the prosthetic components interact with multiple cell types in the peri-prosthetic region resulting in an inflammatory process that ultimately leads to peri-prosthetic bone loss. These cells include macrophages, osteoclasts, osteoblasts and fibroblasts. The majority of research in peri-prosthetic osteolysis has concentrated on the role played by osteoclasts and macrophages. The purpose of this review is to assess the role of the osteoblast in peri-prosthetic osteolysis.

In peri-prosthetic osteolysis, wear particles may affect osteoblasts and contribute to the osteolytic process by two mechanisms. First, particles and metallic ions have been shown to inhibit the osteoblast in terms of its ability to secrete mineralised bone matrix, by reducing calcium deposition, alkaline phosphatase activity and its ability to proliferate. Secondly, particles and metallic ions have been shown to stimulate osteoblasts to produce pro inflammatory mediators in vitro. In vivo, these mediators have the potential to attract pro-inflammatory cells to the peri-prosthetic area and stimulate osteoclasts to absorb bone. Further research is needed to fully define the role of the osteoblast in peri-prosthetic osteolysis and to explore its potential role as a therapeutic target in this condition.

Cite this article: Bone Joint J 2013;95-B:1021–5.