Mesenchymal Stem Cell Therapy for Bone Repair of Human Hip Osteonecrosis with Bilateral Match-Control Evaluation: Impact of Tissue Source, Cell Count, Disease Stage, and Volume Size on 908 Hips.

We investigated the impact of mesenchymal stem cell (MSC) therapy on treating bilateral human hip osteonecrosis, analyzing 908 cases. This study assesses factors such as tissue source and cell count, comparing core decompression with various cell therapies. This research emphasizes bone repair according to pre-treatment conditions and the specificities of cell therapy in osteonecrosis repair, indicating a potential for improved bone repair strategies in hips without femoral head collapse. This study utilized a single-center retrospective analysis to investigate the efficacy of cellular approaches in the bone repair of osteonecrosis. It examined the impact on bone repair of tissue source (autologous bone marrow concentrate, allogeneic expanded, autologous expanded), cell quantity (from none in core decompression alone to millions in cell therapy), and osteonecrosis stage and volume. Excluding hips with femoral head collapse, it focused on patients who had bilateral hip osteonecrosis, both pre-operative and post-operative MRIs, and a follow-up of over five years. The analysis divided these patients into seven groups based on match control treatment variations in bilateral hip osteonecrosis, primarily investigating the outcomes between core decompression, washing effect, and different tissue sources of MSCs. Younger patients (<30 years) demonstrated significantly better repair volumes, particularly in stage II lesions, than older counterparts. Additionally, bone repair volume increased with the number of implanted MSCs up to 1,000,000, beyond which no additional benefits were observed. No significant difference was observed in repair outcomes between different sources of MSCs (BMAC, allogenic, or expanded cells). The study also highlighted that a 'washing effect' was beneficial, particularly for larger-volume osteonecrosis when combined with core decompression. Partial bone repair was the more frequent event observed, while total bone repair of osteonecrosis was rare. The volume and stage of osteonecrosis, alongside the number of injected cells, significantly affected treatment outcomes. In summary, this study provides comprehensive insights into the effectiveness and variables influencing the use of mesenchymal stem cells in treating human hip osteonecrosis. It emphasizes the potential of cell therapy while acknowledging the complexity and variability of results based on factors such as age, cell count, and disease stage.

Prognosis of hip osteonecrosis after cell therapy with a calculator and artificial intelligence: ten year collapse-free survival prediction on three thousand and twenty one hips.

PURPOSE: Several reports have identified prognostic factors for hip osteonecrosis treated with cell therapy, but no study investigated the accuracy of artificial intelligence method such as machine learning and artificial neural network (ANN) to predict the efficiency of the treatment. We determined the benefit of cell therapy compared with core decompression or natural evolution, and developed machine-learning algorithms for predicting ten year collapse-free survival in hip osteonecrosis treated with cell therapy. Using the best algorithm, we propose a calculator for "prognosis hip osteonecrosis cell therapy (PHOCT)" accessible for clinical use. METHODS: A total of 3145 patients with 5261 osteonecroses without collapses were included in this study, comprising 1321 (42%) men and 1824 (58%) women, with a median age of 34 (12-62) years. Cell therapy was the treatment for 3021 hips, core decompression alone for 1374 hips, while absence of treatment was the control group of 764 hips. First, logistic regression and binary logistic regression analysis were performed to compare results of the three groups at ten years. Then an artificial neural network model was developed for ten year collapse-free survival after cell therapy. The models' performances were compared. The algorithms were assessed by calibration, and performance, and with c-statistic as measure of discrimination. It ranges from 0.5 to 1.0, with 1.0 being perfect discrimination and 0.5 poor (no better than chance at making a prediction). RESULTS: Among the 3021 hips with cell therapy, 1964 hips (65%) were collapse-free survival at ten years, versus 453 (33%) among those 1374 treated with core decompression alone, and versus 115 (15%) among 764 hips with natural evolution. We analyzed factors influencing the prediction of collapse-free period with classical statistics and artificial intelligence among hips with cell therapy. After selecting variables, a machine learning algorithm created a prognosis osteonecrosis cell therapy calculator (POCT). This calculator proved to have good accuracy on validation in these series of 3021 hip osteonecroses treated with cell therapy. The algorithm had a c-statistic of 0.871 suggesting good-to-excellent discrimination when all the osteonecroses were mixed. The c-statistics were calculated separately for subpopulations of categorical osteonecroses. It retained good accuracy, but underestimated ten year survival in some subgroups, suggesting that specific calculators could be useful for some subgroups. This study highlights the importance of multimodal evaluation of patient parameters and shows the degree to which the outcome is modified by some decisions that are within a surgeon's control, as the number of cells to aspirate, the choice of injecting in both the osteonecrosis and the healthy bone, the choice between unilateral or bilateral injection, and the possibility to do a repeat injection. CONCLUSION: Many disease conditions and the heterogeneities of patients are causes of variation of outcome after cell therapy for osteonecrosis. Predicting therapeutic effectiveness with a calculator allows a good discrimination to target patients who are most likely to benefit from this intervention.

T-cadherin is a novel regulator of pericyte function during angiogenesis.

Pericytes are mural cells that play an important role in regulation of angiogenesis and endothelial function. Cadherins are a superfamily of adhesion molecules mediating Ca2+-dependent homophilic cell-cell interactions that control morphogenesis and tissue remodeling. To date, classical N-cadherin is the only cadherin described on pericytes. Here, we demonstrate that pericytes also express T-cadherin (H-cadherin, CDH13), an atypical glycosyl-phosphatidylinositol (GPI)-anchored member of the superfamily that has previously been implicated in regulation of neurite guidance, endothelial angiogenic behavior, and smooth muscle cell differentiation and progression of cardiovascular disease. The aim of the study was to investigate T-cadherin function in pericytes. Expression of T-cadherin in pericytes from different tissues was performed by immunofluorescence analysis. Using lentivirus-mediated gain-of-function and loss-of-function in cultured human pericytes, we demonstrate that T-cadherin regulates pericyte proliferation, migration, invasion, and interactions with endothelial cells during angiogenesis in vitro and in vivo. T-cadherin effects are associated with the reorganization of the cytoskeleton, modulation of cyclin D1, α-smooth muscle actin (αSMA), integrin ß3, metalloprotease MMP1, and collagen expression levels, and involve Akt/GSK3ß and ROCK intracellular signaling pathways. We also report the development of a novel multiwell 3-D microchannel slide for easy analysis of sprouting angiogenesis from a bioengineered microvessel in vitro. In conclusion, our data identify T-cadherin as a novel regulator of pericyte function and support that it is required for pericyte proliferation and invasion during active phase of angiogenesis, while T-cadherin loss shifts pericytes toward the myofibroblast state rendering them unable to control endothelial angiogenic behavior.

Raman Spectroscopy in Skeletal Tissue Disorders and Tissue Engineering: Present and Prospective.

Musculoskeletal disorders are the most common reason of chronic pain and disability, representing an enormous socioeconomic burden worldwide. In this review, new biomedical application fields for Raman spectroscopy (RS) technique related to skeletal tissues are discussed, showing that it can provide a comprehensive profile of tissue composition in situ, in a rapid, label-free, and nondestructive manner. RS can be used as a tool to study tissue alterations associated to aging, pathologies, and disease treatments. The main advantage with respect to currently applied methods in clinics is its ability to provide specific information on molecular composition, which goes beyond other diagnostic tools. Being compatible with water, RS can be performed without pretreatment on unfixed, hydrated tissue samples, without any labeling and chemical fixation used in histochemical methods. This review first provides the description of the basic principles of RS as a biotechnology tool and is introduced into the field of currently available RS-based techniques, developed to enhance Raman signals. The main spectral processing, statistical tools, fingerprint identification, and available databases are mentioned. The recent literature has been analyzed for such applications of RS as tendon and ligaments, cartilage, bone, and tissue engineered constructs for regenerative medicine. Several cases of proof-of-concept preclinical studies have been described. Finally, advantages, limitations, future perspectives, and challenges for the translation of RS into clinical practice have been also discussed. Impact statement Raman spectroscopy (RS) is a powerful noninvasive tool giving access to molecular vibrations and characteristics of samples in a wavelength window of 600 to 3200 cm-1, thus giving access to a molecular fingerprint of biological samples in a nondestructive way. RS could not only be used in clinical diagnostics, but also be used for quality control of tissues and tissue-engineered constructs, reducing number of samples, time, and the variety of analysis required in the quality control chain before implantation.

Quality control methods in musculoskeletal tissue engineering: from imaging to biosensors.

Tissue engineering is rapidly progressing toward clinical application. In the musculoskeletal field, there has been an increasing necessity for bone and cartilage replacement. Despite the promising translational potential of tissue engineering approaches, careful attention should be given to the quality of developed constructs to increase the real applicability to patients. After a general introduction to musculoskeletal tissue engineering, this narrative review aims to offer an overview of methods, starting from classical techniques, such as gene expression analysis and histology, to less common methods, such as Raman spectroscopy, microcomputed tomography, and biosensors, that can be employed to assess the quality of constructs in terms of viability, morphology, or matrix deposition. A particular emphasis is given to standards and good practices (GXP), which can be applicable in different sectors. Moreover, a classification of the methods into destructive, noninvasive, or conservative based on the possible further development of a preimplant quality monitoring system is proposed. Biosensors in musculoskeletal tissue engineering have not yet been used but have been proposed as a novel technology that can be exploited with numerous advantages, including minimal invasiveness, making them suitable for the development of preimplant quality control systems.

Phenotypic Characterization of Bone Marrow Mononuclear Cells and Derived Stromal Cell Populations from Human Iliac Crest, Vertebral Body and Femoral Head.

(1) In vitro, bone marrow-derived stromal cells (BMSCs) demonstrate inter-donor phenotypic variability, which presents challenges for the development of regenerative therapies. Here, we investigated whether the frequency of putative BMSC sub-populations within the freshly isolated mononuclear cell fraction of bone marrow is phenotypically predictive for the in vitro derived stromal cell culture. (2) Vertebral body, iliac crest, and femoral head bone marrow were acquired from 33 patients (10 female and 23 male, age range 14-91). BMSC sub-populations were identified within freshly isolated mononuclear cell fractions based on cell-surface marker profiles. Stromal cells were expanded in monolayer on tissue culture plastic. Phenotypic assessment of in vitro derived cell cultures was performed by examining growth kinetics, chondrogenic, osteogenic, and adipogenic differentiation. (3) Gender, donor age, and anatomical site were neither predictive for the total yield nor the population doubling time of in vitro derived BMSC cultures. The abundance of freshly isolated progenitor sub-populations (CD45-CD34-CD73+, CD45-CD34-CD146+, NG2+CD146+) was not phenotypically predictive of derived stromal cell cultures in terms of growth kinetics nor plasticity. BMSCs derived from iliac crest and vertebral body bone marrow were more responsive to chondrogenic induction, forming superior cartilaginous tissue in vitro, compared to those isolated from femoral head. (4) The identification of discrete progenitor populations in bone marrow by current cell-surface marker profiling is not predictive for subsequently derived in vitro BMSC cultures. Overall, the iliac crest and the vertebral body offer a more reliable tissue source of stromal progenitor cells for cartilage repair strategies compared to femoral head.

In vitro simulation of the early proinflammatory phase in fracture healing reveals strong immunomodulatory effects of CD146-positive mesenchymal stromal cells.

The impact of microenvironmental cues and changes due to injury on the phenotype and fate of mesenchymal stromal cells (MSCs) is poorly understood. Here, we aimed to simulate the microenvironment associated with the early stage of bone healing in vitro and to study the regenerative response of MSCs. We enriched CD146+ MSCs from the human bone marrow. Different physiological and pathological microenvironments were simulated by using conditioned medium (CM) from human endothelial cells and osteoblasts (healthy bone), femoral head-derived bone fragments (injured bone), and activated platelets (platelet-rich plasma [PRP], injury). Cells were incubated in CM and analyzed with respect to proliferation, gene expression, migration, osteogenic differentiation, and their effect on polyclonally induced proliferation of peripheral blood mononuclear cells. CD146+ MSCs showed a specific response to different microenvironments. Cell proliferation was observed in all media with the highest values in PRP-CM and injured bone-CM. Gene expression analysis revealed the upregulation of chemokines, proinflammatory, proangiogenic, and genes involved in immunomodulation in cells stimulated with PRP- and injured bone-CM, suggesting strong paracrine activity. PRP-CM led to pronounced inhibition of lymphocyte proliferation by CD146+MSCs. Our results indicate that a microenvironment simulating bone injury elicits strong immunomodulatory and proangiogenic activity of CD146+ MSCs. This suggests that in the early stage of bone healing, the prime function of MSCs and their CD146+ subpopulation is in regulating the immune response and inducing neovascularization. Future studies will investigate the key components in CM driving this function, which might be potential targets to therapeutically stimulate the regenerative potential of MSCs.

Five Days Granulocyte Colony-Stimulating Factor Treatment Increases Bone Formation and Reduces Gap Size of a Rat Segmental Bone Defect: A Pilot Study.

Bone is an organ with high natural regenerative capacity and most fractures heal spontaneously when appropriate fracture fixation is provided. However, additional treatment is required for patients with large segmental defects exceeding the endogenous healing potential and for patients suffering from fracture non-unions. These cases are often associated with insufficient vascularization. Transplantation of CD34+ endothelial progenitor cells (EPCs) has been successfully applied to promote neovascularization of bone defects, however including extensive ex vivo manipulation of cells. Here, we hypothesized, that treatment with granulocyte colony-stimulating factor (G-CSF) may improve bone healing by mobilization of CD34+ progenitor cells into the circulation, which in turn may facilitate vascularization at the defect site. In this pilot study, we aimed to characterize the different cell populations mobilized by G-CSF and investigate the influence of cell mobilization on the healing of a critical size femoral defect in rats. Cell mobilization was investigated by flow cytometry at different time points after five consecutive daily G-CSF injections. In a pilot study, bone healing of a 4.5-mm critical femoral defect in F344 rats was compared between a saline-treated control group and a G-CSF treatment group. In vivo microcomputed tomography and histology were applied to compare bone formation in both treatment groups. Our data revealed that leukocyte counts show a peak increase at the first day after the last G-CSF injection. In addition, we found that CD34+ progenitor cells, including EPCs, were significantly enriched at day 1, and further increased at day 5 and day 11. Upregulation of monocytes, granulocytes and macrophages peaked at day 1. G-CSF treatment significantly increased bone volume and bone density in the defect, which was confirmed by histology. Our data show that different cell populations are mobilized by G-CSF treatment in cell specific patterns. Although in this pilot study no bridging of the critical defect was observed, significantly improved bone formation by G-CSF treatment was clearly shown.

Platelet-Rich Plasma as an Autologous and Proangiogenic Cell Delivery System.

Angiogenesis is a key factor in early stages of wound healing and is crucial for the repair of vascularized tissues such as the bone. However, supporting timely revascularization of the defect site still presents a clinical challenge. Tissue engineering approaches delivering endothelial cells or prevascularized constructs may overcome this problem. In the current study, we investigated platelet-rich plasma (PRP) gels as autologous, injectable cell delivery systems for prevascularized constructs. PRP was produced from human thrombocyte concentrates. GFP-expressing human umbilical vein endothelial cells (HUVECs) and human bone marrow-derived mesenchymal stem cells (MSCs) were encapsulated in PRP gels in different proportions. The formation of cellular networks was assessed over 14 days by time-lapse microscopy, gene expression analysis, and immunohistology. PRP gels presented a favorable environment for the formation of a three-dimensional (3D) cellular network. The formation of these networks was apparent as early as 3 days after seeding. Networks increased in complexity and branching over time but were only stable in HUVEC-MSC cocultures. The high cell viability together with the 3D capillary-like networks observed at early time points suggests that PRP can be used as an autologous and proangiogenic cell delivery system for the repair of vascularized tissues such as the bone.

ELKS1 localizes the synaptic vesicle priming protein bMunc13-2 to a specific subset of active zones.

Presynaptic active zones (AZs) are unique subcellular structures at neuronal synapses, which contain a network of specific proteins that control synaptic vesicle (SV) tethering, priming, and fusion. Munc13s are core AZ proteins with an essential function in SV priming. In hippocampal neurons, two different Munc13s-Munc13-1 and bMunc13-2-mediate opposite forms of presynaptic short-term plasticity and thus differentially affect neuronal network characteristics. We found that most presynapses of cortical and hippocampal neurons contain only Munc13-1, whereas ∼10% contain both Munc13-1 and bMunc13-2. Whereas the presynaptic recruitment and activation of Munc13-1 depends on Rab3-interacting proteins (RIMs), we demonstrate here that bMunc13-2 is recruited to synapses by the AZ protein ELKS1, but not ELKS2, and that this recruitment determines basal SV priming and short-term plasticity. Thus, synapse-specific interactions of different Munc13 isoforms with ELKS1 or RIMs are key determinants of the molecular and functional heterogeneity of presynaptic AZs.

An In Vitro Investigation of Platelet-Rich Plasma-Gel as a Cell and Growth Factor Delivery Vehicle for Tissue Engineering.

Platelet-rich plasma (PRP) has been used for different applications in human and veterinary medicine. Many studies have shown promising therapeutic effects of PRP; however, there are still many controversies regarding its composition, properties, and clinical efficacy. The aim of this study was to evaluate the influence of different platelet concentrations on the rheological properties and growth factor (GF) release profile of PRP-gels. In addition, the viability of incorporated bone marrow-derived human mesenchymal stem cells (MSCs) was investigated. PRP (containing 1000 × 10(3), 2000 × 10(3), and 10,000 × 10(3) platelets/µL) was prepared from human platelet concentrates. Platelet activation and gelification were achieved by addition of human thrombin. Viscoelastic properties of PRP-gels were evaluated by rheological studies. The release of GFs and inflammatory proteins was measured using a membrane-based protein array and enzyme-linked immunosorbent assay. MSC viability and proliferation in PRP-gels were assessed over 7 days by cell viability staining. Cell proliferation was examined using DNA quantification. Regardless of the platelet content, all tested PRP-gels showed effective cross-linking. A positive correlation between protein release and the platelet concentration was observed at all time points. Among the detected proteins, the chemokine CCL5 was the most abundant. The greatest release appeared within the first 4 h after gelification. MSCs could be successfully cultured in PRP-gels over 7 days, with the highest cell viability and DNA content found in PRP-gels with 1000 × 10(3) platelets/µL. The results of this study suggest that PRP-gels represent a suitable carrier for both cell and GF delivery for tissue engineering. Notably, a platelet concentration of 1000 × 10(3) platelets/µL appeared to provide the most favorable environment for MSCs. Thus, the platelet concentration is an important consideration for the clinical application of PRP-gels.

Endothelial Progenitor Cell Fraction Contained in Bone Marrow-Derived Mesenchymal Stem Cell Populations Impairs Osteogenic Differentiation.

In bone tissue engineering (TE) endothelial cell-osteoblast cocultures are known to induce synergies of cell differentiation and activity. Bone marrow mononucleated cells (BMCs) are a rich source of mesenchymal stem cells (MSCs) able to develop an osteogenic phenotype. Endothelial progenitor cells (EPCs) are also present within BMC. In this study we investigate the effect of EPCs present in the BMC population on MSCs osteogenic differentiation. Human BMCs were isolated and separated into two populations. The MSC population was selected through plastic adhesion capacity. EPCs (CD34(+) and CD133(+)) were removed from the BMC population and the resulting population was named depleted MSCs. Both populations were cultured over 28 days in osteogenic medium (Dex(+)) or medium containing platelet lysate (PL). MSC population grew faster than depleted MSCs in both media, and PL containing medium accelerated the proliferation for both populations. Cell differentiation was much higher in Dex(+) medium in both cases. Real-time RT-PCR revealed upregulation of osteogenic marker genes in depleted MSCs. Higher values of ALP activity and matrix mineralization analyses confirmed these results. Our study advocates that absence of EPCs in the MSC population enables higher osteogenic gene expression and matrix mineralization and therefore may lead to advanced bone neoformation necessary for TE constructs.

Strategies to Stimulate Mobilization and Homing of Endogenous Stem and Progenitor Cells for Bone Tissue Repair.

The gold standard for the treatment of critical-size bone defects is autologous or allogenic bone graft. This has several limitations including donor site morbidity and the restricted supply of graft material. Cell-based tissue engineering strategies represent an alternative approach. Mesenchymal stem cells (MSCs) have been considered as a source of osteoprogenitor cells. More recently, focus has been placed on the use of endothelial progenitor cells (EPCs), since vascularization is a critical step in bone healing. Although many of these approaches have demonstrated effectiveness for bone regeneration, cell-based therapies require time consuming and cost-expensive in vitro cell expansion procedures. Accordingly, research is becoming increasingly focused on the homing and stimulation of native cells. The stromal cell-derived factor-1 (SDF-1) - CXCR4 axis has been shown to be critical for the recruitment of MSCs and EPCs. Vascular endothelial growth factor (VEGF) is a key factor in angiogenesis and has been targeted in many studies. Here, we present an overview of the different approaches for delivering homing factors to the defect site by absorption or incorporation to biomaterials, gene therapy, or via genetically manipulated cells. We further review strategies focusing on the stimulation of endogenous cells to support bone repair. Finally, we discuss the major challenges in the treatment of critical-size bone defects and fracture non-unions.

CD34/CD133 enriched bone marrow progenitor cells promote neovascularization of tissue engineered constructs in vivo.

Vascularization is critical for 3D tissue engineered constructs. In large size implants the ingrowth of vessels often fails. The purpose of this study was to identify an easily accessible, clinically relevant cell source able to promote neovascularization in engineered implants in vivo and to establish an autologous culture method for these cells. MSCs (mesenchymal stem cells) and an endothelial progenitor containing cell (EPCC) population were obtained from human bone marrow aspirates. The expression of endothelial-markers, uptake of acetylated low density lipoprotein (acLDL) and tube-like structure formation capability of EPCCs were analyzed after expansion in endothelial growth medium or medium supplemented with autologous platelet lysate (PL). EPCCs were co-seeded with MSCs on hydroxyapatite-containing polyurethane scaffolds and then implanted subcutaneously in nude mice. Human EPCCs displayed typical characteristics of endothelial cells including uptake of acLDL and formation of tube-like structures on Matrigel™. In vivo, EPCCs cultured with PL triggered neovascularization. MSC/EPCC interactions promoted the maturation of newly formed luminal structures, which were detected deep within the scaffold and partly perfused, demonstrating a connection with the host vascular system. We demonstrate that this population of cells, isolated in a clinically relevant manner and cultured with autologous growth factors readily promoted neovascularization in tissue engineered constructs in vivo enabling a potential translation into the clinic.

Induction of osteogenic differentiation by nanostructured alumina surfaces.

Permanent orthopedic implants are becoming increasingly important due to the demographic development. Their optimal osseointegration is key in obtaining good secondary stability. For anchorage dependent cells, topographic features of a surface play an essential role for cell adhesion, proliferation, differentiation and biomineralization. We studied the topographical effect of nanostructured alumina surfaces prepared by chemical vapor deposition on osteogenic differentiation and growth of human osteoblasts. Chemical vapor deposition of the single source precursor (tBuOAIH2)2 led to synthesis of one dimensional alumina nanostructures of high purity with a controlled stoichiometry. We fabricated different topographic features by altering the distribution density of deposited one dimensional nanostructures. Although the topography differed, all surfaces exhibited identical surface chemistry, which is the key requirement for systematically studying the effect of the topography on cells. Forty-eight hours after seeding, cell density and cell area were not affected by the nanotopography, whereas metabolic activity was reduced and formation of actin-fibres and focal adhesions was impaired compared to the uncoated control. Induction of osteogenic differentiation was demonstrated via up-regulation of alkaline phosphatase, bone sialoprotein, osteopontin and Runx2 at the mRNA level, demonstrating the potential of nanostructured surfaces to improve the osseointegration of permanent implants.

Direct cell-cell contact between mesenchymal stem cells and endothelial progenitor cells induces a pericyte-like phenotype in vitro.

Tissue engineering techniques for the regeneration of large bone defects require sufficient vascularisation of the applied constructs to ensure a sufficient supply of oxygen and nutrients. In our previous work, prevascularised 3D scaffolds have been successfully established by coculture of bone marrow derived stem cells (MSCs) and endothelial progenitor cells (EPCs). We identified stabilising pericytes (PCs) as part of newly formed capillary-like structures. In the present study, we report preliminary data on the interactions between MSCs and EPCs, leading to the differentiation of pericyte-like cells. MSCs and EPCs were seeded in transwell cultures, direct cocultures, and single cultures. Cells were cultured for 10 days in IMDM 10% FCS or IMDM 5% FCS 5% platelet lysate medium. Gene expression of PC markers, CD146, NG2, αSMA, and PDGFR-ß, was analysed using RT-PCR at days 0, 3, 7, and 10. The upregulation of CD146, NG2, and αSMA in MSCs in direct coculture with EPCs advocates the MSCs' differentiation towards a pericyte-like phenotype in vitro. These results suggest that pericyte-like cells derive from MSCs and that cell-cell contact with EPCs is an important factor for this differentiation process. These findings emphasise the concept of coculture strategies to promote angiogenesis for cell-based tissue engineered bone grafts.

Evaluation of the in vitro cell-material interactions and in vivo osteo-integration of a spinal acrylic bone cement.

INTRODUCTION: Polymethylmethacrylate bone cements have proven performance in arthroplasty and represent a common bone filler, e.g. in vertebroplasty. However, acrylic cements are still subject to controversy concerning their exothermic reaction and osteo-integration potential. Therefore, we submitted a highly filled acrylic cement to a systematic investigation on the cell-material and tissue-implant response in vitro and in vivo. MATERIALS AND METHODS: Cured Vertecem V+ Cements were characterized by electron microscopy. Human bone marrow-derived mesenchymal stem cell morphology, growth and differentiation on the cured cement were followed for 28 days in vitro. The uncured cement was injected in an ovine cancellous bone defect and analysed 4 and 26 weeks post-implantation. RESULTS: The rough surface of the cement allowed for good stem cells adhesion in vitro. Up-regulation of alkaline phosphatase was detected after 8 days of incubation. No adverse local effects were observed macroscopically and microscopically following 4 and 26 weeks of implantation of the cement into drill-hole defects in ovine distal femoral epiphysis. Direct bone apposition onto the implant surface was observed resulting in extended signs of osteo-integration over time (35.2 ± 24.2% and 88.8 ± 8.8% at week 4 and 26, respectively). CONCLUSION: Contrary to the established opinion concerning bony tissue response to implanted acrylic bone cements, we observed an early cell-implant in vitro interaction leading to cell growth and differentiation and significant signs of osteo-integration for this acrylic cement using standardized methods. Few outlined limitations, such as the use of low cement volumes, have to be considered in the interpretation of the study results.