Bioengineered human bone tissue using autogenous osteoblasts cultured on different biomatrices

Platelet rich fibrin as a bioactive matrix with proosteogenic and proangiogenic properties on human healthy primary cells in vitro

Blood concentrates like platelet rich fibrin (PRF) have been established as a potential autologous source of cells and growth factors with regenerative properties in the field of dentistry and regenerative medicine. To further analyze the effect of PRF on bone tissue regeneration, this study investigated the influence of liquid PRF matrices on human healthy primary osteoblasts (pOB) and co-cultures composed of pOB and human dermal vascular endothelial cells (HDMEC) as in vitro model for bone tissue regeneration. Special attention was paid to the PRF mediated influence on osteoblastic differentiation and angiogenesis. Based on the low-speed centrifugation concept, cells were treated indirectly with PRF prepared with a low (44 g) and high relative centrifugal force (710 g) before the PRF mediated effect on osteoblast proliferation and differentiation was assessed via gene and protein expression analyses and immunofluorescence. The results revealed a PRF-mediated positive effect on osteogenic proliferation and differentiation accompanied by increased concentration of osteogenic growth factors and upregulated expression of osteogenic differentiation factors. Furthermore, it could be shown that PRF treatment resulted in an increased formation of angiogenic structures in a bone tissue mimic co-culture of endothelial cells and osteoblasts induced by the PRF mediated increased release of proangiogenic growth factors. The effects on osteogenic proliferation, differentiation and vascularization were more evident when low RCF PRF was applied to the cells. In conclusion, PRF possess proosteogenic, potentially osteoconductive as well as proangiogenic properties, making it a beneficial tool for bone tissue regeneration.

Three Milliliters of Peripheral Blood Is Sufficient for Preparing Liquid Platelet-Rich Fibrin (PRF): An In Vitro Study

Platelet-rich fibrin (PRF) has assumed an important role in supporting tissue regeneration in different fields. To date, the standard protocol for liquid PRF requires at least 10 mL of peripheral blood. The present study aimed to analyze the composition, growth factor release, and effects on the cell proliferation of PRF samples produced using 3 mL vs. 10 mL of peripheral blood in vitro. Peripheral venous blood from six healthy donors was used to prepare liquid PRF using either 3 mL or 10 mL tubes. Three different centrifugation protocols were used according to the low-speed centrifugation concept. The cellular distribution was evaluated using immunohistology and automated cell count. ELISA was used to determine the release of different growth factors (EGF, TGF-β1, and PDGF) and interleukin 8 at different time points. Primary human osteoblasts (pOBs) were cultivated for 7 days using PRF-conditioned media acquired from either 3 mL or 10 mL of peripheral blood. The results showed that 3 mL of peripheral blood is sufficient to produce a liquid PRF concentrate similar to that acquired when using 10 mL blood. The concentrations of platelets and leukocytes were comparable regardless of the initial blood volume (3 mL vs. 10 mL). Similarly, the release of growth factors (EGF, TGF-β1, and PDGF) and interleukin 8 was often comparable in both groups over 7 days. The cultivation of pOBs using PRF-conditioned media showed a similar proliferation rate regardless of the initial blood volume. This proliferation rate was also similar to that of pOBs treated with 20% FBS-conditioned media. These findings validated the use of 3 mL of peripheral blood to generate liquid PRF matrices according to the low-speed centrifugation concept, which may open new application fields for research purposes such as in vivo experiments and clinical applications such as pediatric surgery.

Sound-based assembly of three-dimensional cellularized and acellularized constructs

Herein we show an accessible technique based on Faraday waves that assist the rapid assembly of osteoinductive β-Tricalcium phosphate (β-TCP) particles as well as human osteoblast pre-assembled in spheroids. The hydrodynamic forces originating at 'seabed' of the assembly chamber can be used to tightly aggregate inorganic and biological entities at packing densities that resemble those of native tissues. Additionally, following a layer-by-layer assembly procedure, centimeter scaled osteoinductive three-dimensional and cellularized constructs have been fabricated. We showed that the intimate connection between biological building blocks is essential in engineering living system able of localized mineral deposition. Our results demonstrate, for the first time, the possibility to obtain three-dimensional cellularized and acellularized anisotropic constructs using Faraday waves.

A Compilation of Study Models for Dental Pulp Regeneration

Efforts to heal damaged pulp tissue through tissue engineering have produced positive results in pilot trials. However, the differentiation between real regeneration and mere repair is not possible through clinical measures. Therefore, preclinical study models are still of great importance, both to gain insights into treatment outcomes on tissue and cell levels and to develop further concepts for dental pulp regeneration. This review aims at compiling information about different in vitro and in vivo ectopic, semiorthotopic, and orthotopic models. In this context, the differences between monolayer and three-dimensional cell cultures are discussed, a semiorthotopic transplantation model is introduced as an in vivo model for dental pulp regeneration, and finally, different animal models used for in vivo orthotopic investigations are presented.

Cellular Response of Human Osteoblasts to Different Presentations of Deproteinized Bovine Bone

Objectives: This study evaluated the cellular response of primary osteoblasts exposed to two different presentations of a low-temperature non-sintered deproteinized bovine bone matrix (DBBM). Materials and methods: Six different baths of a commercially available DBBM block (Bonefill^® Porous Block) and one of DBBM granule (Bonefill^® Porous) were evaluated to identify the mineral structure and organic or cellular remnants. Samples of the same baths were processed in TRIZOL for RNA extraction and quantification. For the immunologic cell reaction assay, primary human osteoblasts (pOB) were exposed to DBMM block (pOB + B) or granules (pOB + G), or none (control) for 1, 3, or 7 days of cell cultivation. Expression of proinflammatory cytokines by pOB was evaluated by crosslinked ELISA assay. In addition, total DNA amount, as well as cell viability via LDH evaluation, was assessed. Results: Organic remnants were present in DBBM blocks; 45.55% (±7.12) of osteocytes lacunae presented cellular remnants in blocks compared to 17.31% (±1.31) in granules. In three of five batches of blocks, it was possible to isolate bovine RNA. The highest concentration of TGF-β1 was found in supernatants of pOB + G on day 7 (218.85 ± 234.62 pg/mL) (p < 0.05), whereas pOB + B presented the lowest amount of TGF-β1 secretion at the end of evaluation (30.22 ± 14.94 pg/mL, p < 0.05). For IL-6 and OPG, there was no statistical difference between groups, while pOB + G induced more IL-8 secretion than the control (3.03 ± 3.38 ng/mL, p < 0.05). Considering the kinetics of cytokine release during the study period, all groups presented a similar pattern of cytokines, estimated as an increasing concentration for IL-6, IL-8, and OPG during cultivation. Adherent cells were observed on both material surfaces on day 7, according to H&E and OPN staining. Conclusion: Neither tested material induced a pronounced inflammatory response upon osteoblast cultivation. However, further studies are needed to elucidate the potential influence of organic remnants in bone substitute materials on the regeneration process.

Effect of Hydroxyapatite Nanoparticles and Nitrogen Plasma Treatment on Osteoblast Biological Behaviors of 3D-Printed HDPE Scaffold for Bone Tissue Regeneration Applications

The need for the repair of bone defects has been increasing due to various causes of loss of skeletal tissue. High density polyethylenes (HDPE) have been used as bone substitutes due to their excellent biocompatibility and mechanical strength. In the present study, we investigated the preosteoblast cell proliferation and differentiation on the adding nano-hydroxyapatite (n-HAp) particles into HDPE scaffold and treating HDPE/n-HAp scaffolds with nitrogen (N₂) plasma. The three-dimensional (3D) HDPE/n-HAp scaffolds were prepared by fused modeling deposition 3D printer. The HDPE/n-HAp was blended with 10 wt% of n-HAp particle. The scaffold surface was reactive ion etched with nitrogen plasma to improve the preosteoblast biological response in vitro. After N₂ plasma treatment, surfaces characterizations were investigated using Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy. The proliferation and differentiation of preosteoblast (MC3T3-E1) cells were evaluated by MTT assay and alkaline phosphatase (ALP) activity. The incorporation of n-HAp particles and N₂ plasma surface treatment showed the improvement of biological responses of MC3T3-E1 cells in the HDPE scaffolds.

A standardized g-force allows the preparation of similar PRF qualities regardless of rotor angle

Platelet rich fibrin (PRF) is an autologous blood concentrate, that supports tissue regeneration. The effect of the centrifuge rotor angle in the fabrication of PRF is still not fully elucidated. The hypothesis of this study is: When applying the same g-force {relative centrifugal force (RCF)} and centrifugation time, PRF components and bioactivity are not modified using either a swing-out or fixed angle rotor. For this purpose, peripheral blood samples (five donors )were used to gain solid matrices (710 xg, 8 minutes) and liquid (44 xg, 8 minutes) PRF matrices using three different centrifuges (one fixed angle as a control; and two different swingout rotor centrifuges). The physical characteristics of the solid PRF were measured to evaluate the clot formation and cellular distribution. Liquid PRF was used to evaluate the cell number, bioactivity and influence on primary human osteoblasts and fibroblasts in vitro. Solid PRF clots were significantly larger in the group of fixed rotor centrifuges compared to either of the two evaluated swing-out rotor centrifuges. No differences were observed when evaluating the cellular distribution within the solid No statistically significant differences were documented in the cell's density in liquid PRF samples (platelets, lymphocytes, neutrophils, eosinophils, and basophils) among the differently gained PRF samples. No statistically significant differences were documented for the released growth factors (VEGF, EGF, TGF-β1) over 7 days. Primary human osteoblasts (pOBs) and primary human fibroblasts (pHFs) viability after treatment with PRF conditioned media showed no statistically significant differences between the evaluated groups. However, the number of adherent cells treated with PRF obtained with the use of the fixed angle rotor was significantly higher when compared to those treated with PRF obtained by using the swing-out rotors. The presented results confirmed that regardless of the centrifuge rotor used, the components and bioactivity of solid and liquid PRF matrices are modified by the applied RCF and centrifugation time. These findings are of great importance for highlighting the essential role of adapting the centrifugation protocols when using different centrifuges and to correctly report the used centrifugation protocols in scientific research to allow for reproducible results.

The shape-effect of calcium phosphate nanoparticle based films on their osteogenic properties

Calcium phosphates (CaPs) in the form of hydroxyapatite (HA) have been extensively studied in the context of bone regeneration due to their chemical similarity to natural bone mineral. While HA is known to promote osteogenic differentiation, the structural properties of the ceramic have been shown to affect the extent of this effect; several studies have suggested that nanostructured HA can improve the bioactivity. However, the role shape plays in the osteogenic potential is more elusive. Here we studied the effect of HA nanoparticle shape on the ability to induce osteogenesis in human mesenchymal stromal cells (hMSCs) by developing nanoparticle films using needle-, rice- and spherical-shaped HA. We showed that the HA films made from all three shapes of nanoparticles induced increased levels of osteogenic markers (i.e. runt-related transcription factor 2 (RUNX2), bone morphogenetic protein 2 (BMP2), alkaline phosphatase (ALP), osteopontin (OPN), osteocalcin (OCN) on protein and gene level in comparison to hMSCs cultured on cover glass slides. Furthermore, their expression levels and profiles differed significantly as a function of nanoparticle shape. We also showed that nanoparticle films were more efficient in inducing osteogenic gene expression in hMSCs compared to adding nanoparticles to hMSCs in culture media. Finally, we demonstrated that hMSC morphology upon adhesion to the HA nanoparticle films is dependent on nanoparticle shape, with hMSCs exhibiting a more spread morphology on needle-shaped nanoparticle films compared to hMSCs seeded on rice- and spherical-shaped nanoparticle films. Our data suggests that HA nanoparticle films are efficient in inducing hMSC osteogenesis in basic cell culture conditions and that nanoparticle shape plays a vital role in cell adhesion and morphology and extent of induction of osteogenic differentiation.

Biologization of Pcl-Mesh Using Platelet Rich Fibrin (Prf) Enhances Its Regenerative Potential In Vitro

INTRODUCTION

Resorbable synthetic scaffolds are promising for different indications, especially in the context of bone regeneration. However, they require additional biological components to enhance their osteogenic potential. In addition to different cell types, autologous blood-derived matrices offer many advantages to enhance the regenerative capacity of biomaterials. The present study aimed to analyze whether biologization of a PCL-mesh coated using differently centrifuged Platelet rich fibrin (PRF) matrices will have a positive influence on primary human osteoblasts activity in vitro. A polymeric resorbable scaffold (Osteomesh, OsteoporeTM (OP), Singapore) was combined with differently centrifuged PRF matrices to evaluate the additional influence of this biologization concept on bone regeneration in vitro. Peripheral blood of three healthy donors was used to gain PRF matrices centrifuged either at High (710× g, 8 min) or Low (44× g, 8 min) relative centrifugal force (RCF) according to the low speed centrifugation concept (LSCC). OP-PRF constructs were cultured with pOBs. POBs cultured on the uncoated OP served as a control. After three and seven days of cultivation, cell culture supernatants were collected to analyze the pOBs activity by determining the concentrations of VEGF, TGF-β1, PDGF, OPG, IL-8, and ALP- activity. Immunofluorescence staining was used to evaluate the Osteopontin expression of pOBs. After three days, the group of OP+PRFLow+pOBs showed significantly higher expression of IL-8, TGF-ß1, PDGF, and VEGF compared to the group of OP+PRFHigh+pOBs and OP+pOBs. Similar results were observed on day 7. Moreover, OP+PRFLow+pOBs exhibited significantly higher activity of ALP compared to OP+PRFHigh+pOBs and OP+pOBs. Immunofluorescence staining showed a higher number of pOBs adherent to OP+PRFLow+pOBs compared to the groups OP+PRFHigh+pOBs and OP+pOBs. To the best of our knowledge, this study is the first to investigate the osteoblasts activity when cultured on a PRF-coated PCL-mesh in vitro. The presented results suggest that PRFLow centrifuged according to LSCC exhibits autologous blood cells and growth factors, seem to have a significant effect on osteogenesis. Thereby, the combination of OP with PRFLow showed promising results to support bone regeneration. Further in vivo studies are required to verify the results and carry out potential results for clinical translation.

An Image-Guided Intrascaffold Cell Assembly Technique for Accurate Printing of Heterogeneous Tissue Constructs

For tissue engineering and regenerative medicine, creating thick and heterogeneous scaffold-based tissue constructs requires deep and precise multicellular deposition. Traditional cell seeding strategies lack the ability to create multicellular tissue constructs with high cell penetration and distribution, while emerging strategies aim to simultaneously combine cell-laden tissue segments with scaffold fabrication. Here we describe a technique that allows for three-dimensional (3D) intrascaffold cell assembly in which scaffolds are prefabricated and pretreated, followed by accurate cell distribution within the scaffold using an image-guided technique. This two-step process yields less limitation in scaffold material choice as well as additional treatments, provides accurate cell distribution, and has less potential to harm cells. The image processing technique captures a 2D geometric image of the scaffold, followed by a series of processes, mainly including grayscale transformation, threshold segmentation, and boundary extraction, to ultimately locate scaffold macropore centroids. Coupled with camera calibration data, accurate 3D cell assembly pathway plans can be made. Intrascaffold assembly parameter optimization and complex intrascaffold gradient, multidirectional, and vascular structure assembly were studied. Demonstration was also made with path planning and cell assembly experiments using NIH3T3-cell-laden hydrogels and collagen-coated poly(lactic-co-glycolic acid) (PLGA) scaffolds. Experiments with CellTracker fluorescent monitoring, live/dead staining, and phalloidin-F-actin/DAPI immunostaining and comparison with two control groups (bioink manual injection and cell suspension static surface pipetting) showed accurate cell distribution and positioning and high cell viability (>93%). The PrestoBlue assay showed obvious cell proliferation over seven culture days in vitro. This technique provides an accurate method to aid simple and complex cell colonization with variant depth within 3D-scaffold-based constructs using multiple cells. The modular method can be used with any existing printing platform and shows potential in facilitating direct spatial organization and hierarchal 3D assembly of multiple cells and/or drugs within scaffolds for further tissue engineering studies and clinical applications.

In vitro evaluation of a biomaterial-based anticancer drug delivery system as an alternative to conventional post-surgery bone cancer treatment

Patients diagnosed with osteosarcoma are currently treated with intravenous injections of anticancer agents after tumor resection. However, due to remaining neoplastic cells at the site of tumor removal, cancer recurrence often occurs. Successful bone regeneration combined with the control of residual cancer cells presents a challenge for tissue engineering. Cyclodextrins loaded with chemotherapeutic drugs reversibly release the drugs over time. Hydroxyapatite bone biomaterials coated with doxorubicin-loaded cyclodextrin should release the drug with time after implantation directly at the original tumor site and may be a way to eliminate residual neoplastic cells. In the present study, we have carried out in vitro studies to evaluate such a drug-delivery system and have shown that doxorubicin released from cyclodextrin-coated hydroxyapatite retained biological activity and exhibited longer and higher cytotoxic effects on both cancer (osteosarcoma cells) and healthy cells (primary osteoblasts and endothelial cells) compared to biomaterials without cyclodextrin loaded with doxorubicin. Furthermore, doxorubicin released from biomaterials with cyclodextrin moderately induced the expression of tumor suppressor protein p53 whereas p21 expression was similar to control cells. In addition, hypoxic conditions, which occur after implantation until blood-flow to the area is regenerated, protected endothelial cells and primary osteoblasts from doxorubicin-induced cytotoxicity. This chemo-protective effect was far less prominent for the osteosarcoma cells. These findings indicate that a hydroxyapatite-cyclodextrin-doxorubicin chemotherapeutic strategy may enhance the drug-targeting effect on tumor cells while protecting the more sensitive healthy cells for a period of time after implantation. A successful integration of such a drug delivery system might allow healthy cells to initially survive during the doxorubicin exposure period, while eliminating residual neoplastic cells.

Platelet-rich fibrin-based matrices to improve angiogenesis in an in vitro co-culture model for bone tissue engineering

In the context of prevascularization strategies for tissue‐engineering purposes, co‐culture systems consisting of outgrowth endothelial cells (OECs) and primary osteoblasts (pOBs) have been established as a promising in vitro tool to study regeneration mechanisms and to identify factors that might positively influence repair processes such as wound healing or angiogenesis. The development of autologous injectable platelet‐rich fibrin (PRF), which can be generated from peripheral blood in a minimal invasive procedure, fulfils several requirements for clinically applicable cell‐based tissue‐engineering strategies. During this study, the established co‐culture system of OECs and pOBs was mixed with injectable PRF and was cultivated in vitro for 24 h or 7 days. The aim of this study was to analyse whether PRF might have a positive effect on wound healing processes and angiogenic activation of OECs in the co‐culture with regard to proinflammatory factors, adhesion molecules and proangiogenic growth factor expression. Histological cell detection revealed the formation of lumina and microvessel‐like structures in the PRF/co‐culture complexes after 7 days of complex cultivation. Interestingly, the angiogenic activation of OECs was accompanied by an upregulation of wound healing‐associated factors, as well as by a higher expression of the proangiogenic factor vascular endothelial growth factor, which was evaluated both on the mRNA level as well as on the protein level. Thus, PRF might positively influence wound healing processes, in particular angiogenesis, in the in vitro co‐culture, making autologous PRF‐based matrices a beneficial therapeutic tool for tissue‐engineering purposes by simply profiting from the PRF, which contains blood plasma, platelets and leukocytes.

Influence of different calcium phosphate ceramics on growth and differentiation of cells in osteoblast-endothelial co-cultures

Strategies for improvement of angiogenesis and vasculogenesis using different cells and materials are paramount aims in the field of bone tissue engineering. Thereby, the interaction between different cell types and scaffold materials is crucial for growth, differentiation, and long-term outcomes of tissue-engineered constructs. In this study, we evaluated the interaction of osteoblasts and endothelial cells in three-dimensional tissue-engineered constructs using beta tricalciumphosphate (β-TCP, [ß-Ca₃ (PO₄ )₂ ]) and calcium-deficient hydroxyapatite (CDHA, [Ca₉ (PO₄ )₅ (HPO₄ )OH]) ceramics as scaffolds. We focused on initial cell organization, cell proliferation, and differential expression of osteoblastic and endothelial markers employing monocultures and co-cultures of endothelial cells of two different origins [human umbilical vein endothelial cells (HUVECs) and outgrowth endothelial cells (OECs)] with primary human osteoblasts (hOBs). Despite different chemical and physical characteristics of CDHA and β-TCP ceramics, similar patterns in cell growth, differentiation, and gene expression were detected in tissue-engineered constructs consisting of hOB, HUVEC, and HUVEC/hOB-co-cultures. Under dynamic cell culture conditions we found proliferation of these cells with stable endothelial and osteoblastic differentiation patterns. Both material types are highly biocompatible with these cells providing a promising perspective for the future research. In this study, both materials did not support growth and differentiation of OEC. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1950-1962, 2017.

Interactions between osteopontin and vascular endothelial growth factor: Implications for skeletal disorders

Osteopontin (OPN) and vascular endothelial growth factor (VEGF) are characterized by a convergence in function for maintaining the homeostasis of the skeletal and renal systems (the bone-renal-vascular axis regulates bone metabolism). The two cytokines contribute to bone remodeling, dental healing, kidney function, and the adjustment to microgravity. Often, they are co-expressed or one molecule induces the other, however, in some settings OPN-associated pathways and VEGF-associated pathways are distinct. In bone remodeling, OPN and VEGF are regulated under the influence of growth factors and hormones, hypoxia and inflammation, the micro-environment, and various physical forces. Their abundance can be affected by drug treatment. OPN and VEGF are variably associated with kidney disease. Their balanced levels are critical for restoring endothelial cell function and ameliorating the adverse effects of microgravity. Here, we review the relevant 83 papers of 257 articles published, and listed in PubMed under the key words OPN and VEGF.

Interactions between osteopontin and vascular endothelial growth factor: Implications for cancer

For this comprehensive review, 257 publications with the keywords "osteopontin" or "OPN" and "vascular endothelial growth factor" or "VEGF" in PubMed were screened (time frame from year 1996 to year 2014). 37 articles were excluded because they were not focused on the interactions between these molecules, and papers relevant for transformation-related phenomena were selected. Osteopontin (OPN) and vascular endothelial growth factor (VEGF) are characterized by a convergence in function for regulating cell motility and angiogenesis, the response to hypoxia, and apoptosis. Often, they are co-expressed or one molecule induces the other, however, in some settings OPN-associated pathways and VEGF-associated pathways are distinct. Their relationships affect the pathogenesis in cancer, where they contribute to progression and angiogenesis and serve as markers for poor prognosis. The inhibition of OPN may reduce VEGF levels and suppress tumor progression. In vascular pathologies, these two cytokines mediate remodeling, but may also perpetuate inflammation and narrowing of the arteries. OPN and VEGF are elevated and contribute to vascularization in inflammatory diseases.

Biomechanical forces in the skeleton and their relevance to bone metastasis: biology and engineering considerations

Bone metastasis represents the leading cause of breast cancer related-deaths. However, the effect of skeleton-associated biomechanical signals on the initiation, progression, and therapy response of breast cancer bone metastasis is largely unknown. This review seeks to highlight possible functional connections between skeletal mechanical signals and breast cancer bone metastasis and their contribution to clinical outcome. It provides an introduction to the physical and biological signals underlying bone functional adaptation and discusses the modulatory roles of mechanical loading and breast cancer metastasis in this process. Following a definition of biophysical design criteria, in vitro and in vivo approaches from the fields of bone biomechanics and tissue engineering that may be suitable to investigate breast cancer bone metastasis as a function of varied mechano-signaling will be reviewed. Finally, an outlook of future opportunities and challenges associated with this newly emerging field will be provided.

Cell communication in a coculture system consisting of outgrowth endothelial cells and primary osteoblasts

Bone tissue is a highly vascularized and dynamic system with a complex construction. In order to develop a construct for implant purposes in bone tissue engineering, a proper understanding of the complex dependencies between different cells and cell types would provide further insight into the highly regulated processes during bone repair, namely, angiogenesis and osteogenesis, and might result in sufficiently equipped constructs to be beneficial to patients and thereby accomplish their task. This study is based on an in vitro coculture model consisting of outgrowth endothelial cells and primary osteoblasts and is currently being used in different studies of bone repair processes with special regard to angiogenesis and osteogenesis. Coculture systems of OECs and pOBs positively influence the angiogenic potential of endothelial cells by inducing the formation of angiogenic structures in long-term cultures. Although many studies have focused on cell communication, there are still numerous aspects which remain poorly understood. Therefore, the aim of this study is to investigate certain growth factors and cell communication molecules that are important during bone repair processes. Selected growth factors like VEGF, angiopoietins, BMPs, and IGFs were investigated during angiogenesis and osteogenesis and their expression in the cultures was observed and compared after one and four weeks of cultivation. In addition, to gain a better understanding on the origin of different growth factors, both direct and indirect coculture strategies were employed. Another important focus of this study was to investigate the role of “gap junctions,” small protein pores which connect adjacent cells. With these bridges cells are able to exchange signal molecules, growth factors, and other important mediators. It could be shown that connexins, the gap junction proteins, were located around cell nuclei, where they await their transport to the cell membrane. In addition, areas in which two cells formed gap junctions were found.

Biomechanical and antibacterial properties of Tobramycin loaded hydroxyapatite coated fixation pins

The present study investigates the use of nanoporous, biomimetic hydroxyapatite (HA) coatings deposited on TiO₂ coated fixation pins as functional implant surfaces for the local release of Tobramycin in order to prevent bacterial colonization. The impact of HA-coating thickness, coating morphology and biomechanical forces during insertion into synthetic bone on the drug loading and release properties are analyzed. The coatings are shown to exhibit bactericidal effects against Staphylococcus aureus in agar medium for a duration of 6 days after loading by adsorption with Tobramycin for only 5 min at elevated temperature and pressure. Furthermore, high performance liquid chromatography analysis shows a drug release in phosphate buffered saline for 8 days with antibiotic concentration remaining above the minimal inhibitory concentration for S. aureus during the entire release period. Biomechanical insertion tests into synthetic bone and conventional scratch testing demonstrate adhesive strength at the HA/TiO₂ interface. Biocompatibility is verified by cell viability tests. Outgrowth endothelial cells, as well as primary osteoblasts, are viable and firmly attached to both HA and TiO₂ surfaces. The results presented are encouraging and support the concept of functional HA coatings as local drug delivery vehicles for biomedical applications to treat as well as to prevent post-surgical infections.

Mild heat stress enhances angiogenesis in a co-culture system consisting of primary human osteoblasts and outgrowth endothelial cells

The repair and regeneration of large bone defects, including the formation of functional vasculature, represents a highly challenging task for tissue engineering and regenerative medicine. Recent studies have shown that vascularization and ossification can be stimulated by mild heat stress (MHS), which would offer the option to enhance the bone regeneration process by relatively simple means. However, the mechanisms of MHS-enhanced angiogenesis and osteogenesis, as well as potential risks for the treated cells are unclear. We have investigated the direct effect of MHS on angiogenesis and osteogenesis in a co-culture system of human outgrowth endothelial cells (OECs) and primary osteoblasts (pOBs), and assessed cytotoxic effects, as well as the levels of various heat shock proteins (HSPs) synthesized under these conditions. Enhanced formation of microvessel-like structures was observed in co-cultures exposed to MHS (41°C, 1 h), twice per week, over a time period of 7-14 days. As shown by real-time polymerase chain reaction (PCR), the expression of vascular endothelial growth factor (VEGF), angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), and tumor necrosis factor-alpha was up-regulated in MHS-treated co-cultures 24 h post-treatment. At the protein level, significantly elevated VEGF and Ang-1 concentrations were observed in MHS-treated co-cultures and pOB mono-cultures compared with controls, indicating paracrine effects associated with MHS-induced angiogenesis. MHS-stimulated co-cultures and OEC mono-cultures released higher levels of Ang-2 than untreated cultures. On the other hand MHS treatment of co-cultures did not result in a clear effect regarding osteogenesis. Nevertheless, real-time PCR demonstrated that MHS increased the expression of mitogen-activated protein kinase, interleukin-6, and bone morphogenetic protein 2, known as HSP-related molecules in angiogenic and osteogenic regulation pathways. In agreement with these observations, the expression of some selected HSPs also increased at both the mRNA and protein levels in MHS-treated co-cultures.

Development of a novel microfluidic device for long-term in situ monitoring of live cells in 3-dimensional matrices

Using the latest innovations in microfabrication technology, 3-dimensional microfluidic cell culture systems have been developed as an attractive alternative to traditional 2-dimensional culturing systems as a model for long-term microscale cell-based research. Most microfluidic systems are based on the embedding of cells in hydrogels. However, physiologically realistic conditions based on hydrogels are difficult to obtain and the systems are often too complicated. We have developed a microfluidic cell culture device that incorporates a biodegradable rigid 3D polymer scaffold using standard soft lithography methods. The device permits repeated high-resolution fluorescent imaging of live cell populations within the matrix over a 4 week period. It was also possible to track cell development at the same spatial location throughout this time. In addition, human primary periodontal ligament cells were induced to produce quantifiable calcium deposits within the system. This simple and versatile device should be readily applicable for cell-based studies that require long-term culture and high-resolution bioimaging.

Reaming debris as a novel source of autologous bone to enhance healing of bone defects

Reaming debris is formed when bone defects are stabilized with an intramedullary nail, and contains viable osteoblast-like cells and growth factors, and might thus act as a natural osteoinductive scaffold. The advantage of using reaming debris over stem cells or autologous bone for healing bone defects is that no extra surgery is needed to obtain the material. To assess the clinical feasibility of using reaming debris to enhance bone healing, we investigated whether reaming debris enhances the healing rate of a bone defect in sheep tibia, compared to an empty gap. As golden standard the defect was filled with iliac crest bone. Bones treated with iliac crest bone and reaming debris showed larger callus volume, increased bone volume, and decreased cartilage volume in the fracture gap, and increased torsional toughness compared to the empty gap group at 3 weeks postoperative. In addition, bones treated with reaming debris showed increased torsional stiffness at 6 weeks postoperatively compared to the empty defect group, while bending stiffness was marginally increased. These results indicate that reaming debris could serve as an excellent alternative to iliac crest bone for speeding up the healing process in bone defects that are treated with an intramedullary nail.

Rapid vascularization of starch-poly(caprolactone) in vivo by outgrowth endothelial cells in co-culture with primary osteoblasts

The successful integration of in vitro-generated tissues is dependent on adequate vascularization in vivo. Human outgrowth endothelial cells (OECs) isolated from the mononuclear cell fraction of peripheral blood represent a potent population of circulating endothelial progenitors that could provide a cell source for rapid anastomosis and scaffold vascularization. Our previous work with these cells in co-culture with primary human osteoblasts has demonstrated their potential to form perfused vascular structures within a starch-poly(caprolactone) biomaterial in vivo. In the present study, we demonstrate the ability of OECs to form perfused vascular structures as early as 48 h following subcutaneous implantation of the biomaterial in vivo. The number of OEC-derived vessels increased throughout the study, an effect that was independent of the OEC donor. This finding of rapid and thorough OEC-mediated scaffold vascularization demonstrates the great potential for OEC-based strategies to promote vascularization in tissue engineering. OECs have the potential to contribute to host-derived scaffold vascularization, and formed vascular structures at a similar density as those arising from the host. Additionally, immunohistochemical evidence demonstrated the close interaction between OECs and the co-cultured osteoblasts. In addition to the known paracrine activity osteoblasts have in modulating angiogenesis of co-cultured OECs, we demonstrate the potential of osteoblasts to provide additional structural support for OEC-derived vessels, perhaps acting in a pericyte-like role.

Influence of polymer content in Ca-deficient hydroxyapatite-polycaprolactone nanocomposites on the formation of microvessel-like structures

Calcium phosphate (CaP) ceramics are widely used in bone tissue engineering due to their good osteoconductivity. The mechanical properties of CaP can be modified by the addition of small volume fractions of biodegradable polymers such as polycaprolactone (PCL). Nevertheless, it is also important to evaluate how the polymer content influences cell-material or cell-cell interactions because of potential consequences for bone regeneration and vascularization. In this study we assessed the general biocompatibilty of Ca-deficient hydroxyapatite (CDHA)-PCL disks containing nominally 11 and 24% polycaprolactone using human umbilical vein endothelial cells and human primary osteoblasts. Confocal microscopy showed that both CDHA-PCL variants supported the growth of both cell types. In terms of the endothelial cells grown on CDHA-PCL nanocomposites with 24% PCL, an increased expression of the endothelial marker vWF compared to CDHA-PCL with 11% PCL was observed in real-time polymerase chain reaction analysis. In addition to monocultures, co-cultures of outgrowth endothelial cells, derived from peripheral blood, and primary osteoblasts were assessed as an example of a more complex test system for bone regeneration and vascularization. Constructs based on CDHA with different PCL contents were investigated with regard to the formation of microvessel-like structures induced by the co-culture process using confocal microscopy and quantitative image analysis. Furthermore, the osteogenic differentiation of the co-culture was assessed. As a result, more pre-vascular structures were observed after 1 week on the CDHA-PCL disks with 24% PCL, whereas after 4 weeks of culture the extent of microvessel-like structure formation was slightly higher on the CDHA with 11% PCL. In contrast to this, variation of PCL content had no effect on the osteogenic differentiation in the co-culture.

Sonic hedgehog promotes angiogenesis and osteogenesis in a coculture system consisting of primary osteoblasts and outgrowth endothelial cells

A number of previous studies documented the angiogenic potential of outgrowth endothelial cells in vitro and in vivo and provided evidence that therapeutic success could depend on coculture or coimplantation strategies. Thus, deeper insight into the molecular mechanisms underlying this pro-angiogenic effect of cocultures might provide new translational options for tissue engineering and regenerative medicine. One promising signaling pathway in bone repair involved in neoangiogenesis and bone formation is the sonic hedgehog (Shh) pathway. In this article, we focus on the effect of Shh on the formation of microvessel-like structures and osteoblastic differentiation in cocultures of primary osteoblasts and outgrowth endothelial cells. Already after 24 h of treatment, Shh leads to a massive increase in microvessel-like structures compared with untreated cocultures. Increased formation of angiogenic structures seems to correlate with the upregulation of vascular endothelial growth factor or angiopoietins (Ang-1 and Ang-2) studied at both the mRNA and protein levels. In addition, treatment with cyclopamine, an inhibitor of hedgehog signaling, blocked the formation of microvessel-like structures in the cocultures. However, exogenous Shh also resulted in the upregulation of several osteogenic differentiation markers in real-time polymerase chain reaction, as well as in an increased mineralization and alkaline phosphatase activity. The present data highlight the central role of the Shh pathway in bone regeneration and vascularization. Further, Shh might have the potential to improve both angiogenesis and osteogenesis in clinical applications in the future.

Study of hydroxyapatite osteoinductivity with an osteogenic differentiation of mesenchymal stem cells

Osteoinductivity of hydroxyapatite (HA) was investigated using uncommitted pluripotent mouse stem cells, C3H10T1/2 in an in vitro differentiation assay. For comparative analysis, the cells were cultured on substrates made of osteoinductive HA, with biocompatible titanium and plastics as the negative control. HA exhibited the ability to induce expression of osteo-specific genes in C3H10T1/2, including alkaline phosphatase (ALP), type I collagen, and osteocalcin; compared with its insignificant up-regulation of the same genes in osteoblast-like cells, Saos-2. HA osteoinductivity exhibited in C3H10T1/2 was comparable to that of a bone morphogenetic protein (BMP) with reference to the up-regulation of osteo-specific genes except the core binding factor 1 (Cbfa1, Runx). This result implies a difference in osteogenic induction pathway initiated by HA and BMP. Using this mesenchymal stem cells (MSC) culture assay, osteoinductivity was also demonstrated to be present in the conditioned medium derived from MSC cultured on HA substrates. This conditioned medium exhibited excellent ability to up-regulate ALP in the absence of HA and BMP. The results suggest that the HA can interact with the cells and generate potent inductive substance released into the medium. Such substance in turn is able to induce uncommitted cells to differentiate into the osteolineage.

Method to analyze three-dimensional cell distribution and infiltration in degradable scaffolds

Effective cell seeding throughout the tissue scaffold often determines the success of tissue-engineering products, although most current methods focus on determining the total number, not the distribution, of the cells associated with tissue-engineering constructs. The purpose of this investigation was to establish a quick, convenient, and efficient method to quantify cell survival, distribution, and infiltration into degradable scaffolds using a combination of fluorescence cell staining and cryosectioning techniques. After cell seeding and culture for different periods of time, seeded scaffolds were stained with a live cell dye and then cryosectioned. Cryosectioned scaffolds were then recompiled into a three-dimensional (3D) image to visualize cell behavior after seeding. To test the effectiveness of this imaging method, four common seeding methods, including static surface seeding, cell injection, orbital shaker seeding, and centrifuge seeding, were investigated for their seeding efficacy. Using this new method, we were able to visualize the benefits and drawbacks of each seeding method with regard to the cell behavior in 3D within the scaffolds. This method is likely to provide useful information to assist the development of novel materials or cell-seeding methods for producing full-thickness tissue grafts.

Dynamic processes involved in the pre-vascularization of silk fibroin constructs for bone regeneration using outgrowth endothelial cells

For successful bone regeneration tissue engineered bone constructs combining both aspects, namely a high osteogenic potential and a rapid connection to the vascular network are needed. In this study we assessed the formation of pre-vascular structures by human outgrowth endothelial cells (OEC) from progenitors in the peripheral blood and the osteogenic differentiation of primary human osteoblasts (pOB) on micrometric silk fibroin scaffolds. The rational was to gain more insight into the dynamic processes involved in the differentiation and functionality of both cell types depending on culture time in vitro. Vascular tube formation by OEC was assessed quantitatively at one and 4 weeks of culture. In parallel, we assessed the temporal changes in cell ratios by flow cytometry and in the marker profiles of endothelial and osteogenic markers by quantitative real-time PCR. In terms of OEC, we observed an increase in tube length, tube area, number of nodes and number of vascular meshes within a culture period of 4 weeks, but a decrease in endothelial markers in real-time PCR. At the same time early osteogenic markers were downregulated, while marker expression associated with progressing mineralized matrix was upregulated in later stages of the culture. In addition, deposition of matrix components, such as collagen type I, known as a pro-angiogenic substrate for endothelial cells, appeared to increase with time indicated by immunohistochemistry. In summary, the study suggests a progressing maturation of the tissue construct with culture time which seems to be not effected by culture conditions mainly designed for outgrowth endothelial cells.

Cultivation of human bone marrow stromal cells on three-dimensional scaffolds of mineralized collagen: influence of seeding density on colonization, proliferation and osteogenic differentiation

In this study human bone marrow stromal cells (hBMSCs) were cultured on three-dimensional porous scaffolds of biomimetically mineralized collagen type I developed for bone engineering. Three different cell numbers were used for seeding of the nanocomposites, and the impact of the seeding density on proliferation and osteogenic differentiation of hBMSCs was investigated. In addition, the effect of the seeding cell number on seeding efficiency and distribution of the cells within the scaffolds was studied. Our data revealed that the open and interconnecting porosity of the mineralized collagen scaffolds allows a very efficient seeding for all seeding densities tested. Although penetration of the cells into the interior of the scaffolds was demonstrated for all seeding densities, the application of higher cell numbers resulted in a better colonization also of the deeper scaffold regions. A substantial influence of the seeding density was observed on proliferation and osteogenic differentiation of hBMSCs. Thus, the highest proliferation rate and specific alkaline phosphatase activity was found for the cell matrix constructs seeded with the lowest density. RT-PCR analyses revealed a higher expression of alkaline phosphatase and bone sialoprotein II at lower seeding densities; however, expression of osteopontin was unaffected by the seeding cell number. Our results demonstrated that the seeding density might be an important factor for the development of optimal cell matrix constructs for bone tissue engineering.

MC3T3-E1 cell adhesion to hydroxyapatite with adsorbed bone sialoprotein, bone osteopontin, and bovine serum albumin

Native bone tissue is composed of a complex matrix of collagen, non-collagenous proteins, and hydroxyapatite (HAP). Bone sialoprotein (BSP) and bone osteopontin (OPN) are members of the non-collagenous protein family termed the SIBLING (small integrin-binding ligand, N-linked glycoproteins) proteins, which are primarily found in mineralized tissues. Previously, OPN was shown to exhibit a preferential orientation for MC3T3-E1 cell adhesion when it was specifically bound to collagen, while the MC3T3-E1 cell adhesion was shown to be dependant on the conformational flexibility of BSP specifically bound to collagen. Additionally, OPN was shown to play a greater role than BSP for cell binding to collagen. In this work, the orientations and conformations of BSP and OPN specifically bound to HAP are probed under similar conditions. Radiolabeled adsorption isotherms were obtained for BSP and OPN on HAP formed from a simulated body fluid, and the results show that HAP has the capacity to bind significantly more BSP than OPN. An in vitro MC3T3-E1 cell adhesion assay was then performed to compare the cell binding ability of adsorbed BSP and OPN specifically bound to HAP. It was found that there is a preference for cell binding to HAP with adsorbed BSP as compared to OPN, but not to a statistically significant level. However, the maximum cell binding was observed on HAP substrates with adsorbed heat denatured bovine serum albumin (BSA). The influence of BSA on cell binding was shown to be concentration dependant and it is believed that the adsorbed BSA modulates the proliferation state of the bound cells.

Microvessel-Like Structures from Outgrowth Endothelial Cells from Human Peripheral Blood in 2-Dimensional and 3-Dimensional Co-Cultures with Osteoblastic Lineage Cells

Tissue regeneration involves complex processes in the interaction between different cell types that control the process of neo-vascularization. In bone, osteoblasts and bone marrow stem cells provide cue elements for the proliferation of endothelial cells, differentiation of endothelial precursors, and the maturation of a vascular network. In this study, we investigated outgrowth endothelial cells (OECs), a potential source of autologous endothelial cells derived from human peripheral blood, in direct 2-dimensional (2-D) and 3-D co-culture systems with cells relevant for the regeneration of bone tissue, such as osteoblasts. In the co-cultures, OECs were evaluated in terms of their stability as an endothelial population at the single cell level using flow cytometry and their ability to establish a pre-vascular network at the light-microscopical and ultra-structural level. In co-cultures with the osteoblast cell line MG63 and with human primary osteoblasts (pOBs), OECs, in contrast to human umbilical vein endothelial cells, formed highly organized microvessel-like structures. These microvessel-like structures included the formation of a vascular lumen with tight junctional complexes at intercellular contacts of endothelial cells. In the co-culture, the formation of this vascular network was achieved in the standard growth medium for OECs. Furthermore, using a rotating culture vessel system, 3-D co-cultures consisting of OECs and pOBs were generated. Based on these observations, we conclude that OECs could provide a valuable source of autologous endothelial cells for the generation of complex tissue-engineered tissues.

Pre-culture period of mesenchymal stem cells in osteogenic media influences their in vivo bone forming potential

The objective of this study was to investigate if the in vitro pre-culture period in osteogenic media of rat mesenchymal stem cells (MSCs), influences their ability to regenerate bone when implanted in a critical size cranial defect. MSCs were harvested from the bone marrow of 6-8 weeks old male Fisher rats and expanded in vitro in osteogenic media for different time periods (4, 10, and 16 days) in tissue culture plates (TCP), seeded on sintered titanium fiber meshes without the extracellular matrix (ECM) generated in vitro, and implanted in the rat cranium after 12 h. Thirty two adult Fisher rats received the implants, divided in four groups. Three groups were implanted with cells cultured for 4, 10, or 16 days in osteogenic media and at that time their alkaline phosphatase activity and mineral deposition denoted that they were at different stages of their osteoblastic maturation (undifferentiated MSC, committed, and mature Osteoblasts, respectively). MSCs cultured without osteogenic media for 6 days were used as controls. The constructs were retrieved 4 weeks later and processed for histomorphometric analysis. Implants seeded with cells that have been cultured with osteogenic media for only 4 days revealed the highest bone formation. The lowest bone formation was obtained with the implants seeded with MSCs cultured for 16 days in the presence of osteogenic media. The results of this study suggested that the in vitro pre-culture period of MSCs is a critical factor for their ability to regenerate bone when implanted to an orthotopic site.

Human mesenchymal stem cell proliferation and osteogenic differentiation in fibrin gels in vitro

This study analyzed human mesenchymal stem cell (hMSC) behavior in a fibrin sealant. hMSC morphology, proliferation, and osteogenic differentiation were analyzed after up to 28 days of incubation in eight different formulations of fibrin gels (Tisseel) prepared with various concentrations of fibrinogen complex (FC) and thrombin. Cell morphology and distribution within the gels were observed by fluorescence microscopy after cell staining with calcein dye. Cell proliferation was assessed by measuring the fluorescence intensity of the cell suspension stained with calcein dye after dissolution of the gels. A standard alkaline phosphatase (ALP) assay, von Kossa staining, and real-time reverse transcriptase-polymerase chain reaction (RT-PCR) were used to analyze hMSC osteogenic differentiation. Cell behavior varied depending on the gel formulation. Proliferation was higher in the formulations containing a low FC concentration, but ALP activity was higher in the formulations containing a high FC concentration. Variations in thrombin concentration had a lesser effect. Small nodules of mineralization were observed at days 21 and 28 in a formulation containing a high FC concentration, in addition to a marked increase in bone sialoprotein (BSP) gene expression level as well as a lower increase in ALP and osteopontin (OPN) levels. However, there was no significant increase in osteocalcin (OCN) expression, a late marker of osteogenic differentiation, up to day 28. In conclusion, this study demonstrated that hMSC morphology, proliferation, and osteogenic differentiation in fibrin gels depended on the FC/thrombin ratio. hMSCs appeared to undergo osteogenic differentiation when seeded in Tisseel fibrin sealant containing a high FC concentration, but they did not fully differentiate into mature osteoblasts.

Intervariability and intravariability of bone morphogenetic proteins in commercially available demineralized bone matrix products

STUDY DESIGN

Enzyme-linked immunosorbent assay was used to detect bone morphogenetic proteins (BMPs) 2, 4, and 7 in 9 commercially available ("off the shelf") demineralized bone matrix (DBM) product formulations using 3 different manufacturer's production lots of each DBM formulation.

OBJECTIVES

To evaluate and compare the quantity of BMPs among several different DBM formulations (inter-product variability), as well as examine the variability of these proteins in different production lots within the same DBM formulation (intra-product variability).

SUMMARY OF BACKGROUND DATA

DBMs are commonly used to augment available bone graft in spinal fusion procedures. Surgeons are presented with an ever-increasing variety of commercially available human DBMs from which to choose. Yet, there is limited information on a specific DBM product's osteoinductive efficacy, potency, and constancy.

METHODS

There were protein extracts from each DBM sample separately dialyzed 4 times against distilled water at 4 degrees C for 48 hours. The amount of BMP-2, BMP-4, and BMP-7 was determined using enzyme-linked immunosorbent assay. RESULTS.: The concentrations of detected BMP-2 and BMP-7 were low for all DBM formulations, only nanograms of BMP were extracted from each gram of DBM (20.2-120.6 ng BMP-2/g DBM product; 54.2-226.8 ng BMP-7/g DBM). The variability of BMP concentrations among different lots of the same DBM formulation, intra-product variability, was higher than the variability of concentrations among different DBM formulations, inter-product variability (coefficient of variation range BMP-2 [16.34% to 76.01%], P < 0.01; BMP-7 [3.71% to 82.08%], P < 0.001). BMP-4 was undetectable.

CONCLUSIONS

The relative quantities of BMPs in DBMs are low, in the order of 1 x 10(-9) g of BMP/g of DBM. There is higher variability in concentration of BMPs among 3 different lots of the same DBM formulation than among different DBM formulations. This variability questions DBM products' reliability and, possibly, efficacy in providing consistent osteoinduction.

Pham Q, Sharma U, Sikavitsas VI, Jansen JA, Mikos AG. In vitro generated extracellular matrix and fluid shear stress synergistically enhance 3D osteoblastic differentiation

This study instituted a unique approach to bone tissue engineering by combining effects of mechanical stimulation in the form of fluid shear stresses and the presence of bone-like extracellular matrix (ECM) on osteodifferentiation. Rat marrow stromal cells (MSCs) harvested from bone marrow were cultured on titanium (Ti) fiber mesh discs for 12 days in a flow perfusion system to generate constructs containing bone-like ECM. To observe osteodifferentiation and bone-like matrix deposition, these decellularized constructs and plain Ti fiber meshes were seeded with MSCs (Ti/ECM and Ti, respectively) and cultured in the presence of fluid shear stresses either with or without the osteogenic culture supplement dexamethasone. The calcium content, alkaline phosphatase activity, and osteopontin secretion were monitored as indicators of MSC differentiation. Ti/ECM constructs demonstrated a 75-fold increase in calcium content compared with their Ti counterparts after 16 days of culture. After 16 days, the presence of dexamethasone enhanced the effects of fluid shear stress and the bone-like ECM by increasing mineralization 50-fold for Ti/ECM constructs; even in the absence of dexamethasone, the Ti/ECM constructs exhibited approximately a 40-fold increase in mineralization compared with their Ti counterparts. Additionally, denatured Ti/ECM* constructs demonstrated a 60-fold decrease in calcium content compared with Ti/ECM constructs after 4 days of culture. These results indicate that the inherent osteoinductive potential of bone-like ECM along with fluid shear stresses synergistically enhance the osteodifferentiation of MSCs with profound implications on bone-tissue-engineering applications.

Low oxygen tension enhances chondroinduction by demineralized bone matrix in human dermal fibroblasts in vitro

Endochondral bone formation is induced by demineralized bone powder (DBP) when DBP is implanted subcutaneously in rodents. Previously, we developed an in vitro model of this process, wherein human dermal fibroblasts (hDFs) differentiate to chondrocytes when cultured in a three-dimensional porous collagen sponge containing DBP. In other studies, medium perfusion was beneficial in maintaining phenotype and viability of many cell types in plain porous collagen sponges, including fibroblasts, bone marrow stromal cells, osteoblasts, and epidermal cells. In contrast, medium perfusion inhibited chondrogenesis by articular chondrocytes; reduction of oxygen tension to 5%, however, restored chondrogenesis. These observations are consistent with the fact that in vivo cartilage is avascular and relatively hypoxic compared with other vascularized tissues. In this study, we tested the hypothesis that low oxygen tension (hypoxia, 5% oxygen) would enhance induced chondrogenesis in hDFs cultured with DBP. As expected, hypoxia upregulated hypoxia-inducible factor-1alpha in hDFs in all conditions (i.e. +/- perfusion, +/- DBP). Hypoxia increased accumulation of cartilage-specific matrix chondroitin 4-sulfate in hDFs, but only in the presence of DBP (165%, compared to normoxia, p < 0.05). Hypoxia did not appear to have detrimental effects on cell viability and proliferation. In sum, hypoxia enhanced cartilage matrix accumulation by hDFs cultured with DBP. These defined conditions can optimize the use of dermal fibroblasts for cartilage tissue engineering.

Repair of mandible defect with tissue engineering bone in rabbits

BACKGROUND

The aim of the present study was to investigate the effect of tissue engineering bone composed of bone marrow-derived osteoblasts and demineralized bone in repairing mandible defect.

METHODS

Bone marrow-derived osteoblasts of 20 rabbits were cultured and seeded into scaffold of allogeneic demineralized bone to construct tissue engineering bone graft in vitro, which was used to repair the 10 x 5-mm bone defect made in the same rabbit mandible edge. Implant of demineralized bone alone was as the control. Rabbits were killed according to the schedule: five after 2 weeks, five after 4 weeks, five after 8 weeks, five after 12 weeks, and the implants were harvested for gross, radiographic, and histological observation.

RESULTS

New bone formation at the margin region of defect and osteogenesis at the centre were observed in the implant of tissue engineering bone, and the bone formation pattern included osteogenesis, osteoconduction, and osteoinduction. In the implant of demineralized bone alone, the major bone formation pattern was 'creeping substitute'.

CONCLUSIONS

The tissue engineering bone graft constructed by autogenous bone marrow-derived osteoblasts and allogeneic demineralized bone was better than demineralized bone alone in bone formation capability, which might be an ideal graft for bone defect repair.

The enhancement of osteoblast growth and differentiation in vitro on a peptide hydrogel-polyHIPE polymer hybrid material

The objective of this study was to investigate the effect of combining two biomaterials on osteoblast proliferation, differentiation and mineralised matrix formation in vitro. The first biomaterial has a well-defined architecture and is known as PolyHIPE polymer (PHP). The second biomaterial is a biologically inspired self-assembling peptide hydrogel (RAD16-I, also called PuraMatrix) that produces a nanoscale environment similar to native extracellular matrix (ECM). Our work investigates the effect of combining RAD16-I with two types of PHP (HA (Hydroxyapatite)-PHP and H (Hydrophobic)-PHP) and evaluates effects on osteoblast growth and differentiation. Results demonstrated successful incorporation of RAD16-I into both types of PHP. Osteoblasts were observed to form multicellular layers on the combined biomaterial surface and also within the scaffold. Dynamic cell seeding and culturing techniques were compared to static seeding methods and produced a more even distribution of cells throughout the constructs. Cells were found to penetrate the scaffold to a maximum depth of 3 mm after 35 days in culture. There was a significant increase in cell number in H-PHP constructs coated with RAD16-I compared to H-PHP alone. Our results show that RAD16-I enhances osteoblast differentiation and indicates that the incorporation of this peptide provides a more permissive environment for osteoblast growth. We have developed a microcellular polymer containing a nanoscale environment to enhance cell: biomaterial interactions and promote osteoblast growth in vitro.

The influence of bone allograft processing on osteoblast attachment and function

In order to assess the influence of eight different sterilisation and disinfection methods for bone allografts on adhesion, proliferation, and differentiation of human bone marrow stromal cells (BMSC), cells were grown in culture and then plated onto pieces of human bone allografts. Following processing methods were tested: autoclavation (AUT), low-temperature-plasma sterilisation of demineralised allografts (D-LTP), ethylene oxide sterilisation (EtO), fresh frozen bone (FFB), 80 degrees C-thermodisinfection (80 degrees C), gamma-irradiation (Gamma), chemical solvent disinfection (CSD), and Barrycidal-disinfection (BAR). The seeding efficiency was determined after one hour to detect the number of attached cells before mitosis started. The cell viability was determined after 3, 7, and 21 days. Tests to confirm the osteoblastic differentiation included histochemical alkaline phosphatase staining and RT-PCR for osteocalcin. Human BMSC showed greatest attachment affinities for D-LTP-, 80 degrees C-, and CSD-allografts, whereas less cells were found attached to AUT-, EtO-, FFB-, Gamma-, and BAR-probes. Cell viability assays at day 3 revealed highest proliferation rates within the FFB- and 80 degrees C-groups, whereas after 21 days most viable cells were found in D-LTP-, 80 degrees C-, CSD-, and Gamma-groups. BAR-treatment showed a considerably toxic effect and therefore was excluded from all further experiments. Highest AP-activity and gene expression of osteocalcin were detected in the D-LTP-group in comparison with all other groups. In summary, our results demonstrate that cell adhesion, final population, and function of BMSC are influenced by different disinfection and sterilisation methods. Therefore, processing-related alterations of BMSC-function may be important for the success of bone grafting. The experimental setup used in the present work may be useful for further optimisation of bone allograft processing.

Cement lines of secondary osteons in human bone are not mineral-deficient: New data in a historical perspective

Using qualitative backscattered electron (BSE) imaging and quantitative energy dispersive X-ray (EDX) spectroscopy, some investigators have concluded that cement (reversal) lines located at the periphery of secondary osteons are poorly mineralized viscous interfaces with respect to surrounding bone. This conclusion contradicts historical observations of apparent highly mineralized (or collagen-deficient) cement lines in microradiographs. Such conclusions, however, may stem from unrecognized artifacts that can occur during scanning electron microscopy. These include specimen degradation due to high-energy beams and the sampling of electron interaction volumes that extend beyond target locations during EDX analysis. This study used quantitative BSE imaging and EDX analysis, each with relatively lower-energy beams, to test the hypothesis that cement lines are poorly mineralized. Undemineralized adult human femoral diaphyses (n = 8) and radial diaphyses (n = 5) were sectioned transversely, embedded in polymethyl methacrylate, and imaged in a scanning electron microscope for BSE and EDX analyses. Unembedded samples were also evaluated. Additional thin embedded samples were stained and evaluated with light microscopy and correlated BSE imaging. BSE analyses showed the consistent presence of a bright line (higher atomic number) coincident with the classical location and description of the cement line. This may represent relative hypermineralization or, alternatively, collagen deficiency with respect to surrounding bone. EDX analyses of cement lines showed either higher Ca content or equivalent Ca content when compared to distant osteonal and interstitial bone. These data reject the hypothesis that cement lines of secondary osteons are poorly mineralized.