Geometric effect of matrix upon cell differentiation: BMP-induced osteogenesis using a new bioglass with a feasible structure

3D-Printing of Hierarchically Designed and Osteoconductive Bone Tissue Engineering Scaffolds

In Bone Tissue Engineering (BTE), autologous bone-regenerative cells are combined with a scaffold for large bone defect treatment (LBDT). Microporous, polylactic acid (PLA) scaffolds showed good healing results in small animals. However, transfer to large animal models is not easily achieved simply by upscaling the design. Increasing diffusion distances have a negative impact on cell survival and nutrition supply, leading to cell death and ultimately implant failure. Here, a novel scaffold architecture was designed to meet all requirements for an advanced bone substitute. Biofunctional, porous subunits in a load-bearing, compression-resistant frame structure characterize this approach. An open, macro- and microporous internal architecture (100 µm-2 mm pores) optimizes conditions for oxygen and nutrient supply to the implant's inner areas by diffusion. A prototype was 3D-printed applying Fused Filament Fabrication using PLA. After incubation with Saos-2 (Sarcoma osteogenic) cells for 14 days, cell morphology, cell distribution, cell survival (fluorescence microscopy and LDH-based cytotoxicity assay), metabolic activity (MTT test), and osteogenic gene expression were determined. The adherent cells showed colonization properties, proliferation potential, and osteogenic differentiation. The innovative design, with its porous structure, is a promising matrix for cell settlement and proliferation. The modular design allows easy upscaling and offers a solution for LBDT.

Biodegradable Mg-Cu alloys with enhanced osteogenesis, angiogenesis, and long-lasting antibacterial effects

A series of biodegradable Mg-Cu alloys is designed to induce osteogenesis, stimulate angiogenesis, and provide long-lasting antibacterial performance at the same time. The Mg-Cu alloys with precipitated Mg2Cu intermetallic phases exhibit accelerated degradation in the physiological environment due to galvanic corrosion and the alkaline environment combined with Cu release endows the Mg-Cu alloys with prolonged antibacterial effects. In addition to no cytotoxicity towards HUVECs and MC3T3-E1 cells, the Mg-Cu alloys, particularly Mg-0.03Cu, enhance the cell viability, alkaline phosphatase activity, matrix mineralization, collagen secretion, osteogenesis-related gene and protein expressions of MC3T3-E1 cells, cell proliferation, migration, endothelial tubule forming, angiogenesis-related gene, and protein expressions of HUVECs compared to pure Mg. The favorable osteogenesis and angiogenesis are believed to arise from the release of bioactive Mg and Cu ions into the biological environment and the biodegradable Mg-Cu alloys with osteogenesis, angiogenesis, and long-term antibacterial ability are very promising in orthopedic applications.

Functional role of inorganic trace elements in angiogenesis-Part II: Cr, Si, Zn, Cu, and S

Trace elements play critical roles in angiogenesis events. The effects of nitrogen, iron, selenium, phosphorus, gold, and calcium were discussed in part I. In part II, we evaluated the effect of chromium, silicon, zinc, copper, and sulfur on different aspects of angiogenesis, with critical roles in healing and regeneration processes, and undeniable roles in tumor growth and cancer therapy. This review is the second of series that serves as an overview of the role of inorganic elements in regulation of angiogenesis and vascular function. The methods of exposure, structure, mechanism, and potential activity of these trace elements are briefly discussed. An electronic search was performed on the role of these trace elements in angiogenesis from January 2005 to April 2014. The recent aspects of the relationship between five different trace elements and their role in regulation of angiogenesis, and homeostasis of pro- and anti-angiogenic factors were assessed. Many studies have investigated the effects and importance of these elements in angiogenesis events. Both stimulatory and inhibitory effects on angiogenesis are observed for the evaluated elements. Chromium can promote angiogenesis in pathological manners. Silicon as silica nanoparticles is anti-angiogenic, while in calcium silicate extracts and bioactive silicate glasses promote angiogenesis. Zinc is an anti-angiogenic agent acting on important genes and growth factors. Copper and sulfur compositions have pro-angiogenic functions by activating pro-angiogenic growth factors and promoting endothelial cells migration, growth, and tube formation. Thus, utilization of these elements may provide a unique opportunity to modulate angiogenesis under various setting.

Bioactive glasses beyond bone and teeth: emerging applications in contact with soft tissues

The applications of bioactive glasses (BGs) have to a great extent been related to the replacement, regeneration and repair of hard tissues, such as bone and teeth, and there is an extensive bibliography documenting the role of BGs as bone replacement materials and in bone tissue engineering applications. Interestingly, many of the biochemical reactions arising from the contact of BGs with bodily fluids, in particular the local increase in concentration of various ions at the glass-tissue interface, are also relevant to mechanisms involved in soft tissue regeneration. An increasing number of studies report on the application of BGs in contact with soft tissues, aiming at exploiting the well-known bioactive properties of BGs in soft tissue regeneration and wound healing. This review focuses on research, sometimes involving preliminary in vitro studies but also in vivo evidence, that demonstrates the suitability of BGs in contact with tissues outside the skeletal system, which includes studies investigating vascularization, wound healing and cardiac, lung, nerve, gastrointestinal, urinary tract and laryngeal tissue repair using BGs in various forms of particulates, fibers and nanoparticles with and without polymer components. Potentially active mechanisms of interaction of BGs and soft tissues based on the surface bioreactivity of BGs and on biomechanical stimuli affecting the soft tissue-BG collagenous bonding are discussed based on results in the literature.

Silicate bioceramics induce angiogenesis during bone regeneration

The capacity to induce rapid vascular ingrowth during new bone formation is an important feature of biomaterials that are to be used for bone regeneration. Akermanite, a Ca-, Mg- and Si-containing bioceramic, has been demonstrated to be osteoinductive and to promote bone repair. This study further demonstrates the ability of akermanite to promote angiogenesis and investigates the mechanism of this behavior. The akermanite ion extract predominantly caused Si-ion-stimulated proliferation of human aortic endothelial cells. The Si ion in the extract was the most important component for the effect and the most effective concentration was found to be 0.6-2 μg ml(-1). In this range of Si ion concentration, the stimulating effect of the ceramic ion extract was demonstrated by the morphology of cells at the primary, interim and late stages during in vitro angiogenesis using ECMatrix™. The akermanite ion extract up-regulated the expression of genes encoding the receptors of proangiogenic cytokines and also increased the expression level of genes encoding the proangiogenic downstream cytokines, such as nitric oxide synthase and nitric oxide synthesis. Akermanite implanted in rabbit femoral condyle model promoted neovascularization after 8 and 16 weeks of implantation, which further confirmed its stimulation effect on angiogenesis in vivo. These results indicate that akermanite ceramic, an appropriate Si ion concentration source, could induce angiogenesis through increasing gene expression of proangiogenic cytokine receptors and up-regulated downstream signaling. To our knowledge, akermanite ceramic is the first Si-containing ceramic demonstrated to be capable of inducing angiogenesis during bone regeneration.

Bioactive glass-based scaffolds for bone tissue engineering

Originally developed to fill and restore bone defects, bioactive glasses are currently also being intensively investigated for bone tissue engineering applications. In this chapter, we review and discuss current knowledge on porous bone tissue engineering scaffolds made from bioactive silicate glasses. A brief historical review and the fundamental requirements in the field of bone tissue engineering scaffolds will be presented, followed by a detailed overview of recent developments in bioactive glass-based scaffolds. In addition, the effects of ionic dissolution products of bioactive glasses on osteogenesis and angiogenic properties of scaffolds are briefly addressed. Finally, promising areas of future research and requirements for the advancement of the field are highlighted and discussed.

Bioactive Glass and Glass-Ceramic Scaffolds for Bone Tissue Engineering

Traditionally, bioactive glasses have been used to fill and restore bone defects. More recently, this category of biomaterials has become an emerging research field for bone tissue engineering applications. Here, we review and discuss current knowledge on porous bone tissue engineering scaffolds on the basis of melt-derived bioactive silicate glass compositions and relevant composite structures. Starting with an excerpt on the history of bioactive glasses, as well as on fundamental requirements for bone tissue engineering scaffolds, a detailed overview on recent developments of bioactive glass and glass-ceramic scaffolds will be given, including a summary of common fabrication methods and a discussion on the microstructural-mechanical properties of scaffolds in relation to human bone (structure-property and structure-function relationship). In addition, ion release effects of bioactive glasses concerning osteogenic and angiogenic responses are addressed. Finally, areas of future research are highlighted in this review.

Bioglass as a carrier for reindeer bone protein extract in the healing of rat femur defect

Bioactive glasses have been developed as scaffolds for bone tissue engineering but combination with reindeer bone protein extract has not been evaluated. We investigated the effects of bone protein extract implants (5-40 mg dosages) with bioglass (BG) carrier on the healing of rat femur defects. Bioglass implants and untreated defects served as controls. All doses of extract increased bone formation compared with the control groups, and bone union was enhanced with doses of 10 mg or more. In comparison with untreated defect, mean cross-sectional bone area at the defect site was greater when implants with BG + 15 mg of extract or bioglass alone were used, bone density at the defect site was higher in all bioglass groups with and without bone extract, and the BG + 15 mg extract dosage marginally increased bone torsional stiffness in mechanical testing. Bioglass performed well as a carrier candidate for reindeer bone protein extract.

Biocompatibility of osteogenic predifferentiated human cord blood stem cells with biomaterials and the influence of the biomaterial on the process of differentiation

Modern cell-based bone reconstruction therapies offer new therapeutic opportunities and tissue engineering represents a more biological-oriented approach to heal bone defects of the skeleton. Human unrestricted somatic stem cells (USSCs) derived form umbilical cord blood offer new promising aspects e.g., can differentiate into osteogenetic cells. Furthermore these cells have fewer ethical and legal restrictions compared to embryonic stem cells (ESCs). The purpose of this study was to evaluate the compatibility of osteogenic pre-differentiated USSCs with various biomaterials and to address the question, whether biomaterials influence the process of differentiation of the USSCs. After osteogenic differentiation with DAG USSCs were cultivated with various biomaterials. To asses the biocompatibility of USSCs the attachment and the proliferation of the cells on the biomaterial were measured by a CyQUANT(®) assay, the morphology was analyzed by scanning electron microscopy and the influence of the gene expression was analyzed by real time PCR. Our results provide evidence that insoluble collagenous bone matrix followed by β-tricalciumphosphate is highly suitable for bone tissue engineering regarding cell attachment and proliferation. The gene expression analysis indicates that biomaterials influence the gene expression of USSCs. These results are in concordance with our previous study with ESCs.

Compatibility of Embryonic Stem Cells with Biomaterials

Periodontal bone defects and atrophy of the jaws in an aging population are of special concern. Tissue engineering using embryonic stem cells (ESCs) and biomaterials may offer new therapeutic options. The purpose of this study is to evaluate the compatibility of ESCs with biomaterials and the influence of biomaterials on the osteogenic gene expression profile.

Therefore, ESCs are cultured with various biomaterials. The cytocompatibility of murine ESCs is measured regarding the proliferation of the cells on the materials by CyQUANT ® assay, the morphology by scanning electron microscopy, and the influence on the gene expression by real time PCR.

The results show that insoluble collagenous bone matrix, followed by β-tricalciumphosphate, is most suitable for bone tissue engineering regarding cell proliferation, and phenotype. The gene expression analysis indicates that biomaterials do influence the gene expression of ESCs.

Our results provide new insight into the cytocompatibility of ESCs on different scaffolds.

Morphogenetic activity of silica and bio-silica on the expression of genes controlling biomineralization using SaOS-2 cells

In a previous study (Schröder et al., J Biomed Mater Res B Appl Biomater 75:387-392, 2005) we demonstrated that human SaOS-2 cells, when cultivated on bio-silica matrices, respond with an increased hydroxyapatite deposition. In the present contribution we investigate if silica-based components (Na-silicate, tetraethyl orthosilicate [TEOS], silica-nanoparticles) (1) change the extent of biomineralization in vitro (SaOS-2 cells) and (2) cause an alteration of the expression of the genes amelogenin, ameloblastin, and enamelin, which are characteristic for an early stage of osteogenesis. We demonstrate that the viability of SaOS-2 cells was not affected by the silica-based components. If Na-silicate or TEOS was added together with ss-glycerophosphate, an organic phosphate donor, a significant increase in biomineralization was measured. Finally, expression levels of the amelogenin, ameloblastin, and enamelin genes were determined in SaOS-2 cells during exposure to the silica-based components. After exposure for 2 days, expression levels of amelogenin and enamelin strongly increased in response to the silica-based components, while no significant change was seen for ameloblastin. In contrast, exposure of SaOS-2 cells to ss-glycerophosphate resulted in increased expression of all three genes. We conclude that the levels of the structural molecules of the enamel matrix, amelogenin and enamelin, increase in the presence of silica-based components and substantially contribute to the extent of hydroxyapatite crystallite formation. These results demonstrate that silica-based components augment hydroxyapatite deposition in vitro and suggest that enzymatically synthesized bio-silica (via silicatein) might be a promising route for tooth reconstruction in vivo.

Ectopic bone formation in cell-seeded poly(ethylene oxide)/poly(butylene terephthalate) copolymer scaffolds of varying porosity

Scaffolds from poly(ethylene oxide) and poly(butylene terephthalate), PEOT/PBT, with a PEO molecular weight of 1,000 and a PEOT content of 70 weight% (1000PEOT70PBT30) were prepared by leaching salt particles (425-500 microm). Scaffolds of 73.5, 80.6 and 85.0% porosity were treated with a CO(2) gas plasma and seeded with rat bone marrow stromal cells (BMSCs). After in vitro culture for 7 days (d) in an osteogenic medium the scaffolds were subcutaneously implanted for 4 weeks in nude mice. Poly(D, L-lactide) (PDLLA) and biphasic calcium phosphate (BCP) scaffolds were included as references. After 4 weeks (wks) all scaffolds showed ectopic formation of bone and bone marrow. For the scaffolds of different porosities, no significant differences were observed in the relative amounts of bone (7-9%) and bone marrow (6-11%) formed, even though micro computed tomography (mu-CT) data showed considerable differences in accessible pore volume and surface area. 1000PEOT70PBT30 scaffolds with a porosity of 85% could not maintain their original shape in vivo. Surprisingly, 1000PEOT70PBT30 scaffolds with a porosity of 73.5% showed cartilage formation. This cartilage formation is most likely due to poorly accessible pores in the scaffolds, as was observed in histological sections. mu-CT data showed a considerably smaller accessible pore volume (as a fraction of the total volume) than in 1000PEOT70PBT30 scaffolds of 80.6 and 85.0% porosity. BMSC seeded PDLLA (83.5% porosity) and BCP scaffolds (29% porosity) always showed considerably more bone and bone marrow formation (bone marrow formation is approximately 40%) and less fibrous tissue ingrowth than the 1000PEOT70PBT30 scaffolds. The scaffold material itself can be of great influence. In more hydrophobic and rigid scaffolds like the PDLLA or BCP scaffolds, the accessibility of the pore structure is more likely to be preserved under the prevailing physiological conditions than in the case of hydrophilic 1000PEOT70PBT30 scaffolds. Scaffolds prepared from other PEOT/PBT polymer compositions, might prove to be more suited.

Gene activation by bioactive glasses

Bioactive glasses have been shown to regulate gene expression in both hard and soft tissue repair. New resorbable bioactive glass constructs are now being developed that can influence gene expression in the local environment by manipulating material properties such as the surface chemistry, topography and the release of dissolution ions. The success of these scaffolds, however, may depend upon a greater understanding of the bioactive glass stimulated gene expression pathways. This will allow the construction of tissue specific scaffolds with tailored surface chemistry, topography and ion release rates. This paper summarises the advances made in understanding gene expression in response to bioactive glasses and discusses the future steps required for further insights into these molecular mechanisms.

Porous silk fibroin 3-D scaffolds for delivery of bone morphogenetic protein-2 in vitro and in vivo

Bone morphogenetic protein-2 (BMP-2) plays a key role in osteogenesis. Biomaterials used for the sustained delivery of BMP-2 in vivo have shown therapeutic benefits. In the present study, BMP-2 was loaded in porous silk fibroin scaffolds derived from silkworm cocoons (2.4 +/- 0.14 microg per scaffold). The release profile of BMP-2 under dynamic culture conditions (spinner flasks) showed that after 1 week in culture 25% of the initial BMP-2 was retained adsorbed to the scaffold; up to 4 weeks no additional BMP-2 was released. BMP-2 induced human bone marrow stromal cells (hMSCs) to undergo osteogenic differentiation when the seeded scaffolds were cultured in medium supplemented with osteogenic stimulants for 4 weeks, based on elevated alkaline phosphatase activity, calcium deposition, and transcript levels for bone sialoprotein, osteopontin, osteocalcin, BMP-2, and cbfa-1. Micro-computed tomography revealed densely deposited mineral at the center of the scaffolds. In contrast, hMSCs cultured in control scaffolds (no BMP-2) exhibited limited osteogenesis. When implanted in critical sized cranial defects in mice, scaffolds loaded with BMP-2 and seeded with hMSCs resulted in significant bone ingrowth. These results were qualitatively similar to scaffolds loaded with BMP-2 but no hMSCs or with BMP-2 and hMSCs but not pregrown into bone-like tissue. Bone-related outcomes were improved when compared with the scaffold controls implanted without BMP-2. These studies illustrate the potential use of slow degrading silk fibroin 3-D scaffolds loaded with BMP-2, in combination with hMSCs, in osteogenesis studies in vitro and in vivo, and provide a new range of material properties for these applications.

Electrospun silk-BMP-2 scaffolds for bone tissue engineering

Silk fibroin fiber scaffolds containing bone morphogenetic protein 2 (BMP-2) and/or nanoparticles of hydroxyapatite (nHAP) prepared via electrospinning were used for in vitro bone formation from human bone marrow-derived mesenchymal stem cells (hMSCs). BMP-2 survived the aqueous-based electrospinnig process in bioactive form. hMSCs were cultured for up to 31 days under static conditions in osteogenic media on the scaffolds (silk/PEO/BMP-2, silk/PEO/nHAP, silk/PEO/nHAP/BMP-2) and controls (silk/PEO, silk/PEO extracted). Electrospun silk fibroin-based scaffolds supported hMSC growth and differentiation toward osteogenic outcomes. The scaffolds with the co-processed BMP-2 supported higher calcium deposition and enhanced transcript levels of bone-specific markers than in the controls, indicating that these nanofibrous electrospun silk scaffolds were an efficient delivery system for BMP-2. X-ray diffraction (XRD) analysis revealed that the apatite formed on the silk fibroin/BMP-2 scaffolds had higher crystallinity than on the silk fibroin scaffold controls. In addition, nHAP particles were incorporated into the electrospun fibrous scaffolds during processing and improved bone formation. The coexistence of BMP-2 and nHAP in the electrospun silk fibroin fibers resulted in the highest calcium deposition and upregulation of BMP-2 transcript levels when compared with the other systems. The results suggest that electrospun silk-fibroin-based scaffolds are potential candidates for bone tissue engineering. Furthermore, the mild aqueous process required to spin the fibers offers an important option for delivery of labile cytokines and other components into the system.

Cigarette smoke disrupts VEGF165-VEGFR-2 receptor signaling complex in rat lungs and patients with COPD: morphological impact of VEGFR-2 inhibition

VEGF is fundamental in the development and maintenance of the vasculature. VEGF(165) signaling through VEGF receptor (VEGFR)-2/kinase insert domain receptor (KDR) is a highly regulated process involving the formation of a tertiary complex with glypican (GYP)-1 and neuropilin (NRP)-1. Both VEGF and VEGFR-2 expression are reduced in emphysematous lungs; however, the mechanism of regulation of VEGF(165) signaling through the VEGFR-2 complex in response to cigarette smoke exposure in vivo, and in smokers with and without chronic obstructive pulmonary disease (COPD), is still unknown. We hypothesized that cigarette smoke exposure disrupts the VEGF(165)-VEGFR-2 complex, a potential mechanism in the pathogenesis of emphysema. We show that cigarette smoke exposure reduces NRP-1 and GYP-1 as well as VEGF and VEGFR-2 levels in rat lungs and that VEGF, VEGFR-2, GYP-1, and NRP-1 expression in the lungs of both smokers and patients with COPD are also reduced compared with nonsmokers. Moreover, our data suggest that specific inhibition of VEGFR-2 alone with NVP-AAD777 would appear not to result in emphysema in the adult rat lung. As both VEGF(165) and VEGFR-2 expression are reduced in emphysematous lungs, decreased GYP-1 and NRP-1 expression may yet further disrupt VEGF(165)-VEGFR-2 signaling. Whether or not this by itself is critical for inducing endothelial cell apoptosis and decreased vascularization of the lung seen in emphysema patients is still unclear at present. However, targeted therapies to restore VEGF(165)-VEGFR-2 complex may promote endothelial cell survival and help to ameliorate emphysema.

Effect of bone extracellular matrix synthesized in vitro on the osteoblastic differentiation of marrow stromal cells

Alternative materials for bone grafts are gaining greater importance in dentistry and orthopaedics, as the limitations of conventional methods become more apparent. We are investigating the generation of osteoinductive matrix in vitro by culturing cell/scaffold constructs for tissue engineering applications. The main strategy involves the use of a scaffold composed of titanium (Ti) fibers seeded with progenitor cells. In this study, we investigated the effect of extracellular matrix (ECM) laid down by osteoblastic cells on the differentiation of marrow stromal cells (MSCs) towards osteoblasts. Primary rat MSCs were harvested from bone marrow, cultured in dexamethasone containing medium and seeded directly onto the scaffolds. Constructs were grown in static culture for 12 days and then decellularized by rapid freeze-thaw cycling. Decellularized scaffolds were re-seeded with pre-cultured MSCs at a density of 2.5 x 10(5) cells/construct and osteogenicity was determined according to DNA, alkaline phosphatase, calcium and osteopontin analysis. DNA content was higher for cells grown on decellularized scaffolds with a maximum content of about 1.3 x 10(6) cells/construct. Calcium was deposited at a greater rate by cells grown on decellularized scaffolds than the constructs with only one seeding on day-16. The Ti/MSC constructs showed negligible calcium content by day-16, compared with 213.2 (+/- 13.6) microg/construct for the Ti/ECM/MSC constructs cultured without any osteogenic supplements after 16 days. These results indicate that bone-like ECM synthesized in vitro can enhance the osteoblastic differentiation of MSCs.

Vascular supplies differ in regenerating and nonregenerating amputated rodent digits

Bone regenerates following amputation through the level of the nail, but bone is capped following amputation through more proximal levels. Because osteogenesis requires an ample blood supply, we postulated that a restricted vascular supply might be correlated with restricted regenerative ability at proximal levels. More than 40 rats and mice were injected with ink or resin to visualize vascular supplies of intact, regenerating, and nonregenerating rat and mouse digits. Ink-injected specimens were viewed as histological sections or cleared whole mounts. Partially digested resin casts were viewed using scanning electron microscopy. Contrary to our hypothesis, prior to amputation, proximal sites are more vascular than distal sites. At both proximal and distal levels, endosteal and periosteal vascular systems are evident. However, in proximal phalanges, additional subcutaneous and dermal layers encircle the bone. Beneath the distal nail, these layers are absent, and a single layer of vessels provides both periosteal and cutaneous supplies. After amputation at both levels, new vessels sprout profusely in osteogenic areas of both endosteum and periosteum. However, at proximal levels, the additional hypodermal and dermal vessels contribute to a vascular plexus that, paradoxically, may impair bone regrowth by contributing to the formation of dermal scar rather than bone.

Immunolocalization of Vascular Endothelial Growth Factor During Heterotopic Bone Formation Induced From Grafted Periosteum

Vessel invasion is an important step in cartilage replacement that leads to bone formation, and vascular endothelial growth factor (VEGF) has been implicated as a key player in this process. Although grafted periosteum undergoes endochondral ossification, little is known about the role of VEGF in this process. In the current study the authors investigated by immunohistochemical, histochemical, and ultrastructural techniques the localization of VEGF during bone formation in periosteal grafts. At day 14 after grafting the tibias of Japanese white rabbits, periosteal cells in the grafted tissue had differentiated into chondrocytes to form cartilage. Some chondrocytes were immunopositive for VEGF expression, and subsequent vessel invasion occurred predominantly in these VEGF-positive areas. At day 45, the cartilage invaded by blood vessels had been replaced by newly formed bone. These findings suggest that VEGF is associated with the process of blood vessel invasion into cartilage before bone replacement in endochondral ossification from grafted periosteum.

Carrier dependent cell differentiation of bone morphogenetic protein-2 induced osteogenesis and chondrogenesis during the early implantation stage in rats

To evaluate the osteoinductive effects of recombinant human bone morphogenetic protein (rhBMP)-2 during the early stages of rat ectopic bone formation, we prepared two distinct carriers. Two carriers, insoluble bone matrix (IBM) and fibrous glass membrane (FGM) were combined with rhBMP-2 and implanted into the backs of rats to evaluate the osteoinductive effects of the two rhBMP-2 carrier systems. Insoluble bone matrix particle size was 320 to 620 microm. Fibrous glass membrane was constructed from unwoven glass fibers 1 microm in diameter. Alkaline phosphatase (ALP) activity and type II collagen were detected in IBM/rhBMP-2 at 5 days postimplantation. Calcium (Ca) was also detected in IBM/rhBMP-2 at 7 and 9 days postimplantation. In contrast, ALP and type II collagen were detected in FGM/rhBMP-2 at 7 days. Calcium was undetected, indicating that the bone formation in IBM/rhBMP-2 proceeded faster than in FGM/rhBMP-2 during the early stage of BMP-induced osteogenesis. In addition, mRNA expression level of KDR, a receptor for vascular endothelial growth factor, was also increased in IBM/rhBMP-2. To investigate the in vivo release profile of rhBMP-2, iodine 125 ((125)I)-labeled BMP-2-incorporating IBM and FGM implants were inserted into the back subcutis of mice. More than 60% of the rhBMP-2 was released from the IBM/rhBMP-2 carrier within 1 day after implantation, whereas 50% of the rhBMP-2 was released from the FGM/rhBMP-2 10 days postimplantation. These results indicated that osteo- and chondrogenesis depends highly upon the geometry of the carrier and the in situ retention of rhBMP-2 during the early stage of rhBMP-2 induced bone formation.

Polyvinylpyrrolidone modified bioactive glass fibers as tissue constructs: in vitro mesenchymal stem cell response

The sol-gel synthesis of a bioactive glass (BAG) sol with the incorporation of polyvinylpyrrolidone and the subsequent spraying of short, discontinuous fibers is reported. The incorporation of the polymer into the BAG sol allowed for increased control of the rheological properties and resulted in a more homogeneous fibrous material when sprayed through an air gun. Reaction kinetics and sol viscosity were monitored and analyzed during synthesis, and fibers were characterized using scanning electron microscopy and thermal analysis. Fibers were sintered at 900 degrees C and were examined for in vitro bioactivity in a simulated body fluid solution. The presence of hydroxyapatite crystals is confirmed by examination with scanning electron microscopy, energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Both the proliferation rate and cell density of rat mesenchymal stem cells cultured on BAG fiber constructs of varying porosities were shown to be dependent upon fiber spacing.

Geometry of artificial ECM: sizes of pores controlling phenotype expression in BMP-induced osteogenesis and chondrogenesis

This study aims to elucidate the feasible geometry of the scaffolds in bone and periodontal tissue engineering. Several biomaterials with different geometries are compared in terms of their patterns of ectopic BMP-induced chondrogenesis and osteogenesis. The materials include a honeycomb-shaped hydroxyapatite (HCHAP) with different tunnel sizes, a laser-perforated collagen membrane (LPM), and CPSA bioglass fibers. Implanted pellets were removed at 1-4 weeks and analyzed for bone and cartilage formation histologically and biochemically. Porous particles of hydroxyapatite (PPHAP), porous blocks of hydroxyapatite (PBHAP), and LPM did not induce detectable cartilage formation. In straight tunnel structures with various diameters in honeycomb-shaped hydroxyapatite (HCHAP), tunnels with smaller diameters (approximately 0.1 mm) induced cartilage followed by bone formation, while one with a larger diameter (0.35 mm) directly induced bone formation within the tunnels. It is concluded that the "vasculature-inducing geometry" of the carrier as an ECM is crucially important for osteogenesis.

Histological characterization of the early stages of bone morphogenetic protein-induced osteogenesis

On the basis of currently available knowledge, we hypothesize that the initial bone formation, as induced by bone morphogenetic protein (BMP), is influenced by the chemical composition and three-dimensional spatial configuration of the used carrier material. Therefore, in the current study, the osteoinductive properties of porous titanium (Ti) fiber mesh with a calcium phosphate (Ca-P) coating (Ti-CaP), insoluble bone matrix (IBM), fibrous glass membrane (FGM), and porous particles of hydroxy apatite (PPHAP) loaded with rhBMP-2 were compared in a rat ectopic assay model at short implantation periods. Twelve Ti-CaP, 12 IBM, 12 FGM, and 12 PPHAP implants, loaded with rhBMP-2, were subcutaneously placed in 16 Wistar King rats. The rats were sacrificed at 3, 5, 7, and 9 days post-operative, and the implants were retrieved. Histological analysis demonstrated that IBM and Ti-CaP had induced ectopic cartilage and bone formation by 5 and 7 days, respectively. However, in PPHAP, bone formation and cartilage formation were seen together at 7 days. At 9 days, in Ti-CaP, IBM, and PPHAP, cartilage was seen together with trabecular bone. At 9 days, in FGM, only cartilage was observed. Quantitative rating of the tissue response, using a scoring system, demonstrated that the observed differences were statistically significant (Wilcoxon rank sum test, p < 0.05). We conclude that IBM, CaP-coated Ti mesh, FGM, and PPHAP provided with rhBMP-2 can indeed induce ectopic bone formation with a cartilaginous phase in a rat model at short implantation periods. Considering the different chemical composition and three-dimensional spatial configuration of the carrier materials used, these findings even suggest that endochondral ossification is present in rhBMP-2-induced osteogenesis, even though the amount of cartilage may differ.