An overview of tissue engineered bone

Sub-confluent culture of human mesenchymal stromal cells on biodegradable polycaprolactone microcarriers enhances bone healing of rat calvarial defect

In the current emerging trend of using human mesenchymal stromal cell (MSCs) for cell therapy, large quantities of cells are needed for clinical testing. Current methods of culturing cells, using tissue culture flasks or cell multilayer vessels, are proving to be ineffective in terms of cost, space and manpower. Therefore, alternatives such as large-scale industrialized production of MSCs in stirred tank bioreactors using microcarriers (MCs) are needed. Moreover, the development of biodegradable MCs for MSC expansion can streamline the bioprocess by eliminating the need for enzymatic cell harvesting and scaffold seeding for bone-healing therapies. Our previous studies described a process of making regulated density (1.06 g/cm³) porous polycaprolactone biodegradable MCs Light Polycarprolactone (LPCL) (MCs), which were used for expanding MSCs from various sources in stirred suspension culture. Here, we use human early MSCs (heMSCs) expanded on LPCL MCs for evaluation of their osteogenic differentiation potential in vitro as well as their use in vivo calvarial defect treatment in a rat model. In summary, (i) in vitro data show that LPCL MCs can be used to efficiently expand heMSCs in stirred cultures while maintaining surface marker expression; (ii) LPCL MCs can be used as scaffolds for cell transfer for transplantation in vivo; (iii) 50% sub-confluency, mid-logarithmic phase, on LPCL MCs (50% confluent) exhibited higher secretion levels of six cytokines (interleukin [IL]-6, IL-8, Vascular endothelial growth factor (VEGF), Monocyte Chemoattractant Protein-1 (MCP-1), growth-regulated oncogene-α (GRO-α) and stromal cell-derived factor-1α (SDF-1α)) as compared with 100% confluent, stationary phase cultures (100% confluent); (iv) these 50% confluent cultures demonstrated better in vitro osteogenic differentiation capacity as compared with 100% confluent cultures (higher levels of calcium deposition and at earlier stage); the improved bone differentiation capacity of these 50% confluent cultures was also demonstrated at the molecular level by higher expression of early osteoblast genes Runt-related transcription factor 2 (RUNX2), Alkaline phosphatase (ALP), collagen type I, osterix and osteocalcin); and (v) in vivo implantation of biodegradable LPCL MCs covered with 50% heMSCs into rats with calvarial defect demonstrated significantly better bone formation as compared with heMSCs obtained from monolayer cultures (5.1 ± 1.6 mm³ versus 1.3 ± 0.7 mm³). Moreover, the LPCL MCs covered with 50% heMSCs supported better in vivo bone formation compared with 100% confluent culture (2.1 ± 1.3 mm³). Taken together, our study highlights the potential of implanting 50% confluent MSCs propagated on LPCL MCs as optimal for bone regeneration. This methodology allows for the production of large numbers of MSCs in a three-dimensional (3D) stirred reactor, while supporting improved bone healing and eliminating the need for a 3D matrix support scaffold, as traditionally used in bone-healing treatments.

The Impact of Hybrid Nano-Materials in Tooth Tissue Restoration

Tooth loss due to dental diseases, caries, and other related pathological conditions has plagued people and is the most prevalent cause of human organ failure. Billions of people have suffered from losing teeth and dental diseases so that generating natural dental tissues are more appreciated than artificial tooth implantation. The aspiration among the dentists to restore this loss biologically is the genesis of the tooth regeneration. Current trends initiate tissue engineering with a concept of functional restoration of tissue and organ defects by the triad of biomaterial scaffolds, growth factors, and stem cells (Rosa et al. 2012). This paper, therefore, focuses on the significance of nanostructured hybrid materials in the tooth regeneration through tissue engineering. For this purpose, literature was examined and studies on nanomorphological features of stem cells, dental tissues found within the oral area, the signaling molecules utilized in the tissue engineering, and the hybrid scaffolds that guide reconstructions of periodontal tissues were selected for the review. The nanodentistry has been potential, undoubtedly, to achieve almost perfect dental health in the nearest future. However, the success will largely be determined by human requirements and resource supply (technology, economy, and time). Finally, the future and actual potentials of nanotechnologies pertaining tissue engineering will be applied in dentistry (Mitziadis, Woloszyk, & Jimenez-Rojo, 2012).Keywords: Stem cells; scaffolds; nanomaterials; hybrid materials, tissue engineering; dentistry; signaling molecules.

Bioactive Nanocomposites for Tissue Repair and Regeneration: A Review

This review presents scientific findings concerning the use of bioactive nanocomposites in the field of tissue repair and regeneration. Bioactivity is the ability of a material to incite a specific biological reaction, usually at the boundary of the material. Nanocomposites have been shown to be ideal bioactive materials due the many biological interfaces and structures operating at the nanoscale. This has resulted in many researchers investigating nanocomposites for use in bioapplications. Nanocomposites encompass a number of different structures, incorporating organic-inorganic, inorganic-inorganic and bioinorganic nanomaterials and based upon ceramic, metallic or polymeric materials. This enables a wide range of properties to be incorporated into nanocomposite materials, such as magnetic properties, MR imaging contrast or drug delivery, and even a combination of these properties. Much of the classical research was focused on bone regeneration, however, recent advances have enabled further use in soft tissue body sites too. Despite recent technological advances, more research is needed to further understand the long-term biocompatibility impact of the use of nanoparticles within the human body.

Three dimensional printed macroporous polylactic acid/hydroxyapatite composite scaffolds for promoting bone formation in a critical-size rat calvarial defect model

We have explored the applicability of printed scaffold by comparing osteogenic ability and biodegradation property of three resorbable biomaterials. A polylactic acid/hydroxyapatite (PLA/HA) composite with a pore size of 500 μm and 60% porosity was fabricated by three-dimensional printing. Three-dimensional printed PLA/HA, β-tricalcium phosphate (β-TCP) and partially demineralized bone matrix (DBM) seeded with bone marrow stromal cells (BMSCs) were evaluated by cell adhesion, proliferation, alkaline phosphatase activity and osteogenic gene expression of osteopontin (OPN) and collagen type I (COL-1). Moreover, the biocompatibility, bone repairing capacity and degradation in three different bone substitute materials were estimated using a critical-size rat calvarial defect model in vivo. The defects were evaluated by micro-computed tomography and histological analysis at four and eight weeks after surgery, respectively. The results showed that each of the studied scaffolds had its own specific merits and drawbacks. Three-dimensional printed PLA/HA scaffolds possessed good biocompatibility and stimulated BMSC cell proliferation and differentiation to osteogenic cells. The outcomes in vivo revealed that 3D printed PLA/HA scaffolds had good osteogenic capability and biodegradation activity with no difference in inflammation reaction. Therefore, 3D printed PLA/HA scaffolds have potential applications in bone tissue engineering and may be used as graft substitutes in reconstructive surgery.

Modulating hydrogel crosslink density and degradation to control bone morphogenetic protein delivery and in vivo bone formation

Bone morphogenetic proteins (BMPs) show promise in therapies for improving bone formation after injury; however, the high supraphysiological concentrations required for desired osteoinductive effects, off-target concerns, costs, and patient variability have limited the use of BMP-based therapeutics. To better understand the role of biomaterial design in BMP delivery, a matrix metalloprotease (MMP)-sensitive hyaluronic acid (HA)-based hydrogel was used for BMP-2 delivery to evaluate the influence of hydrogel degradation rate on bone repair in vivo. Specifically, maleimide-modified HA (MaHA) macromers were crosslinked with difunctional MMP-sensitive peptides to permit protease-mediated hydrogel degradation and growth factor release. The compressive, rheological, and degradation properties of MaHA hydrogels were characterized as a function of crosslink density, which was varied through either MaHA concentration (1-5wt.%) or maleimide functionalization (10-40%f). Generally, the compressive moduli increased, the time to gelation decreased, and the degradation rate decreased with increasing crosslink density. Furthermore, BMP-2 release increased with either a decrease in the initial crosslink density or an increase in collagenase concentration (non-specific MMP degradation). Lastly, two hydrogel formulations with distinct BMP-2 release profiles were evaluated in a critical-sized calvarial defect model in rats. After six weeks, minimal evidence of bone repair was observed within defects left empty or filled with hydrogels alone. For hydrogels that contained BMP-2, similar volumes of new bone tissue were formed; however, the faster degrading hydrogel exhibited improved cellular invasion, bone volume to total volume ratio, and overall defect filling. These results illustrate the importance of coordinating hydrogel degradation with the rate of new tissue formation.

Low elastic modulus titanium-nickel scaffolds for bone implants

The superelastic nature of repeating the human bones is crucial to the ideal artificial biomedical implants to ensure smooth load transfer and foster the ingrowth of new bone tissues. Three dimensional interconnected porous TiNi scaffolds, which have the tailorable porous structures with micro-hole, were fabricated by slurry immersing with polymer sponge and sintering method. The crystallinity and phase composition of scaffolds were studied by X-ray diffraction. The pore morphology, size and distribution in the scaffolds were characterized by scanning electron microscopy. The porosity ranged from 65 to 72%, pore size was 250-500μm. Compressive strength and elastic modulus of the scaffolds were ~73MPa and ~3GPa respectively. The above pore structural and mechanical properties are similar to those of cancellous bone. In the initial cell culture test, osteoblasts adhered well to the scaffold surface during a short time, and then grew smoothly into the interconnected pore channels. These results indicate that the porous TiNi scaffolds fabricated by this method could be bone substitute materials.

A comparison of tissue-engineered bone from adipose-derived stem cell with autogenous bone repair in maxillary alveolar cleft model in dogs

This study was designed to compare bone regeneration of tissue-engineered bone from adipose-derived stem cell and autogenous bone graft in a canine maxillary alveolar cleft model. In this prospective clinical trial, mesenchymal stem cells (MSCs) were isolated from subcutaneous canine adipose tissue. Undifferentiated cells were incubated with a 3mm×3mm×3mm hydroxyapatite/beta-tricalcium phosphate scaffold, in specific osteogenic medium for 21 days. Four mongrel dogs were prepared by removal of two of the three incisors bilaterally and a 15mm defect in bone was created from crest to nasal floor. After healing, repair was followed by a tissue engineered bone graft from adipose-derived stem cells on one side and corticocancellous tibial auto graft on the other side. Bone regeneration was evaluated by histomorphometry on days 15 and 60 after implantation. The data were analysed with descriptive and t test methods (α=0.05). Bone formation on the autograft sides was higher than on the stem cell sides at 15 and 60 days, 45% and 96% versus 5% and 70%, respectively. Differences between the two groups at 15 and 60 days were significant (p=0.004 and 0.001, respectively). Although autograft is still the gold standard for bone regeneration, tissue engineered bone may provide an acceptable alternative.

Cryopreservation of cell/scaffold tissue-engineered constructs

The aim of this work was to study the effect of cryopreservation over the functionality of tissue-engineered constructs, analyzing the survival and viability of cells seeded, cultured, and cryopreserved onto 3D scaffolds. Further, it also evaluated the effect of cryopreservation over the properties of the scaffold material itself since these are critical for the engineering of most tissues and in particular, tissues such as bone. For this purpose, porous scaffolds, namely fiber meshes based on a starch and poly(caprolactone) blend were seeded with goat bone marrow stem cells (GBMSCs) and cryopreserved for 7 days. Discs of the same material seeded with GBMSCs were also used as controls. After this period, these samples were analyzed and compared to samples collected before the cryopreservation process. The obtained results demonstrate that it is possible to maintain cell viability and scaffolds properties upon cryopreservation of tissue-engineered constructs based on starch scaffolds and goat bone marrow mesenchymal cells using standard cryopreservation methods. In addition, the outcomes of this study suggest that the greater porosity and interconnectivity of scaffolds favor the retention of cellular content and cellular viability during cryopreservation processes, when compared with nonporous discs. These findings indicate that it might be possible to prepare off-the-shelf engineered tissue substitutes and preserve them to be immediately available upon request for patients' needs.

Bioactive and biodegradable nanocomposites and hybrid biomaterials for bone regeneration

Strategies for bone tissue engineering and regeneration rely on bioactive scaffolds to mimic the natural extracellular matrix and act as templates onto which cells attach, multiply, migrate and function. Of particular interest are nanocomposites and organic-inorganic (O/I) hybrid biomaterials based on selective combinations of biodegradable polymers and bioactive inorganic materials. In this paper, we review the current state of bioactive and biodegradable nanocomposite and O/I hybrid biomaterials and their applications in bone regeneration. We focus specifically on nanocomposites based on nano-sized hydroxyapatite (HA) and bioactive glass (BG) fillers in combination with biodegradable polyesters and their hybrid counterparts. Topics include 3D scaffold design, materials that are widely used in bone regeneration, and recent trends in next generation biomaterials. We conclude with a perspective on the future application of nanocomposites and O/I hybrid biomaterials for regeneration of bone.

Bone tissue engineering using bone marrow stromal cells and an injectable sodium alginate/gelatin scaffold

To investigate the potential application of bone marrow stromal cells (BMSCs) and an injectable sodium alginate/gelatin scaffold for bone tissue engineering (BTE). The phenotype of osteogenic BMSCs was examined by mineralized nodules formation and type I collagen expression. Cell proliferation was evaluated by MTT assay. The biocompatibility of scaffold and osteogenic cells were examined by hematoxylin and eosin (H&E) staining. Ectopic bone formation as well as closure of rabbit calvarial critical-sized defects following scaffold-cell implantation were analyzed by histological examination and computed tomography (CT) scanning. Spindle-shaped osteogenic cells of high purity were derived from BMSCs. The osteogenic cells and sodium alginate/gelatin (2:3) scaffold presented fine biocompatibility following cross-linking with 0.6% of CaCl(2). After implantation, the scaffold-cell construct promoted both ectopic bone formation and bone healing in the rabbit calvarial critical-sized defect model. Our data demonstrated that the sodium alginate/gelatin scaffold could be a suitable biomaterial for bone engineering, and the scaffold-osteogenic cells construct is a promising alternative approach for the bone healing process.

Evaluation of a biodegradable graft substitute in rabbit bone defect model

OBJECTIVE

To evaluate a new biodegradable copolymer calcium sulfate/poly amino acid (CS/PAA) as a graft substitute for the repair of the surgically created cancellous bone defects in rabbits and its biological properties in vivo.

MATERIALS AND METHODS

Cancellous bone defects were created by drilling holes in the unilateral lateral aspect of the femoral condyle of New Zealand white rabbits. Three groups were assigned: Group A rabbits were grafted with 80% CS/PAA and group B rabbits were grafted with 95% CS/PAA as two treatment groups; group C was sham-operation control group. To study the osteogenic capability in vivo, specimens were harvested at 4, 8, 12, and 16 weeks after implantation and were evaluated by gross assessment, X-ray, histological examination, and histomorphometry. In order to identify the molecular mechanism of bone defect repair, the expression of bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF) was detected using Western blot at 4 weeks.

RESULTS

Group A and group B showed more vigorous and rapid repair leading to regeneration of cancellous bone than sham-operation control group on gross observation, radiology, and histomorphometry. There was no significant difference between groups A and B. Morphological observation and histological examination showed that the copolymers degraded in sync with the new bone formation process. The expression of BMP-2 and VEGF in implantation groups was higher than that in control group by western blot.

CONCLUSION

These findings demonstrated that the novel biodegradable copolymers can repair large areas of cancellous bone defects. With its controllable degradation rate, it suggests that CS/PAA may be a series of useful therapeutic substitute for bone defects.

Osteoblasts in bone tissue engineering

Osteoblasts are integral to the development, growth, function, repair and maintenance of bone. The osteoblast forms organic, non-mineralized bone matrix and is involved in complex interactions with a variety of factors, mediators and cell types. Degeneration, pathology, and trauma cause disruption and destruction of the normal skeletal environment and may lead to bone loss.

There is a rise in active populations involved in trauma, elderly patients with fragility fractures and an overall increase in primary, revision and reconstructive bone and joint surgery. Despite the rapid evolution of implant technologies and bone grafting techniques, there is still a great demand for novel bone replacement strategies.

Bone tissue engineering is the state of the art science with the potential to regenerate bone with natural form and function. This review presents the biology of osteoblasts and their current applications in bone tissue engineering biotechnologies and role in stem cell, bioactive factor, recombinant signalling molecule and gene therapy research.

Bone Regeneration with BMP-2 Gene-modified Mesenchymal Stem Cells Seeded on Nano-hydroxyapatite/Collagen/ Poly(L-Lactic Acid) Scaffolds

In this study, the capacity of bone morphogenetic protein 2 (BMP-2) gene-transfected bone marrow-derived mesenchymal stem cells (MSCs) in combination with nano-hydroxyapatite/collagen/poly(L-lactic acid) (nHAC/ PLA) to improve the repair of bone defects in rabbit was explored. MSCs from New Zealand White rabbits were cultured and injected with pIRES2-EGFPhBMP-2 or pIRES2-EGFP by electroporation. After the transfer efficiency was determined through the expression of EGFP, the MSCs were seeded on scaffolds to generate an in vitro 3D cell/scaffold construct. The adhesion and proliferation of the MSCs cultured in the scaffold was assessed by SEM. The cellular constructs obtained were allografted into the 15 mm critical-sized segmental bone defects in the radius of New Zealand White rabbits for 12 weeks. The bone regeneration was assessed by radiographical and histological analyses. In vitro, nHAC/PLA facilitated MSC adhesion and proliferation on the scaffold, and gene transfer efficiency reached a maximum of 35.5 ± 3.8%. In vivo, the implantation of BMP-2 transfected MSCs/nHAC/PLA construct significantly enhanced the formation of new bone in the segmental defect, compared to the control groups. This novel 3D BMP-2 transfected MSCs/nHAC/PLA construct has the potential for bone repair by genetic tissue engineering approach.

Ectopic osteogenic ability of calcium phosphate scaffolds cultured with osteoblasts

Bone substitute materials can induce bone formation when combined with mesenchymal stem cells (MSC). The aim of the current study was to examine in vivo ectopic bone formation with MSC on tricalcium phosphate (TCP) ceramics. Osteoblasts isolated from bone marrow stromal cells (BMSCs) of New Zealand rabbits were cultured with TCP ceramics for 10 days, followed by implantation of the cultured TCP ceramics into the rabbit dorsum muscle. The cultured TCP and in vivo new bone formation with TCP biodegradation were evaluated histologically. Scanning electron microscopy showed that the surface of the cultured TCP ceramics was filled by osteoblasts with a cell-free zone in the central area. New bone was formed on the cultured TCP ceramics with signs of gradual degradation of TCP ceramics at 8 weeks of implantation, indicating that TCP could be a potential scaffold for seeding cells used for development of bioengineering tissues.

Comparative investigation of viability, metabolism and osteogenic capability of tissue-engineered bone preserved in sealed osteogenic media at 37 °C and 4 °C

Preservation of tissue-engineered (TE) bone is one of the key problems needed to be solved for its clinic application and industrialization. Traditional cryopreservation has been restricted because of the damages caused by ice formation and solution. Hypothermic preservation at 4 °C has been widely used for the preservation of transplanted organ despite potential negative effects on viability of cells and tissue. 37 °C is the best temperature for maintaining cellular bioactivities. However, 37 °C also has a potential negative effect on preserved cells due to consumption of nutrients and accumulation of by-products. No studies have reported which temperature is more suitable for the preservation of TE bone constructs. The current study explored the feasibility of preservation of TE bone constructs in sealed osteogenic media at 37 °C and 4 °C. Human bone marrow stromal cells (hBMSCs) were seeded into partially demineralized bone matrix (pDBM) scaffolds and cultured for 7 days to form TE bone constructs. The constructs were preserved in sealed osteogenic media at either 37 °C or 4 °C for 5, 7, 9 and 11 days, respectively. Growth kinetics, viability, metabolism and osteogenic capability were evaluated to explore the feasibility of preservation at 37 °C and 4 °C. The constructs cultured in osteogenic media at humidified 37 °C/5%CO2 served as the positive control. The results demonstrated that all the constructs preserved at 4 °C showed negative osteogenic capability at all time points with a much lower level of growth kinetics, viability and metabolism compared to the positive control. However, the constructs preserved at 37 °C showed good osteogenic capability within 7 days with a certain level of growth kinetics, viability and metabolism, although an obvious decrease in osteogenic capability was observed in the constructs preserved at 37 °C over 9 days. These results indicate that the preservation of TE bone constructs is feasible at 37 °C within 7 days in sealed osteogenic media.

Secondary repair of alveolar clefts using human mesenchymal stem cells

Recently tissue engineering has become available as a regenerative treatment for bone defects; however, little has been reported on the application of tissue engineering for regeneration of cleft defect tissues. Mesenchymal-derived stem cells were applied to different kinds of bone substitute and compared in different animal models, but their usage in human critical defects remained unclear. In this study we report 2 patients with unilateral alveolar cleft, treated with the composite scaffold of demineralized bone mineral and calcium sulphate (Osteoset) loaded with mesenchymal stem cells (MSCs). Computed tomograms showed 34.5% regenerated bone, extending from the cleft walls and bridging the cleft after 4 months in one case and in the other there was 25.6% presentation of bone integrity. The available data revealed the conventional bone substitute was not a suitable scaffold for the MSC-induced bone regeneration.

Ectopic bone formation in adipose-derived stromal cell-seeded osteoinductive calcium phosphate scaffolds

The phenomenon of osteoinduction by biomaterials has been proven and used in animals. However, whether the ability of a biomaterial to initiate bone formation in ectopic implantation sites improves the performance of such osteoinductive biomaterial as a scaffold for tissue-engineered (TE) bone remains unclear. In this study, we compared ectopic bone formation by combining autologous adipose-derived stromal cells (ADSCs) with an osteoinductive and a nonosteoinductive biphasic calcium phosphate (BCP) ceramic to create a tissue engineering construct in the muscle of dogs. Two groups of BCP scaffolds (BCP1 and BCP2) were prepared. In each group, ADSCs were seeded, and the scaffolds without seeded cells served as controls. All implants were implanted in the back muscle of 10 adult dogs for 8 weeks and 12 weeks. Microcomputed tomography (Micro-CT) analysis and histomorphometry were performed to evaluate and quantify ectopic bone formation. The results indicated that the osteoinductive BCP1 performed significantly better compared to the nonosteoinductive BCP2 in cell-based TE bone formation ectopically. The ADSCs had a significantly positive effect on the ectopic bone formation. In addition, the usefulness of Micro-CT for the efficient and nondestructive analysis of mineralized bone and calcium phosphate scaffold was confirmed.

Porosity and pore size of beta-tricalcium phosphate scaffold can influence protein production and osteogenic differentiation of human mesenchymal stem cells: an in vitro and in vivo study

The interaction of stem cells and ceramics in bone regeneration is still poorly understood. The aim of this study was to examine the influence of the porosity (25%, 65% and 75%) of beta-tricalcium phosphate (TCP) ceramics on osteogenic differentiation of mesenchymal stem cells (MSC) in vitro and in vivo. For the in vitro portion of the study, TCP scaffolds loaded with MSC were kept in osteogenic induction medium for 21 days. For the in vivo portion of the study, scaffolds loaded with undifferentiated MSC were implanted subcutaneously into SCID mice for 8 weeks and compared with similarly implanted controls that were not loaded with MSC. Measurements of total protein as well as specific alkaline phosphatase (ALP) activity were taken as indicators of growth/matrix production and osteogenic differentiation. An increase in the total protein concentration was noted from day 1 to day 21 on the in vitro TCP 65% and TCP 75% scaffolds (p<0.05) with no such increase noted in the TCP 25% specimens. However, the specific alkaline phosphatase activity increased from day 1 to day 21 in all three in vitro specimens (p<0.02) and reached similar levels in each specimen by day 21. In vivo, ALP activity of cell-loaded TCP 65% ceramics was higher when compared with both the TCP 25% and TCP 75% specimens (p<0.046), and higher in the TCP 75% than TCP 25% specimens (p=0.008). Histology revealed mineralization by human cells in the pores of the TCP ceramic scaffolds with a trend toward greater calcification in TCP 65% and 75%. In summary, a higher porosity of TCP scaffolds does not necessarily mean a higher ALP activity in vivo. The distribution and size of the pores, as well as the surface structure, might play an important role for osteogenic differentiation in vivo.

Efficacy of nano-hydroxyapatite prepared by an aqueous solution combustion technique in healing bone defects of goat

The present study was undertaken to evaluate porous hydroxyapatite (HAp), the powder of which was prepared by a novel aqueous solution combustion technique, as a bone substitute in healing bone defects in vivo, as assessed by radiologic and histopathologic methods, oxytetracycline labeling, and angiogenic features in Bengal goat. Bone defects were created in the diaphysis of the radius and either not filled (group I) or filled with a HAp strut (group II). The radiologic study in group II showed the presence of unabsorbed implants which acted as a scaffold for new bone growth across the defect, and the quality of healing of the bone defect was almost indistinguishable from the control group, in which the defect was more or less similar, although the newly formed bony tissue was more organized when HAp was used. Histologic methods showed complete normal ossification with development of Haversian canals and well-defined osteoblasts at the periphery in group II, whereas the control group had moderate fibro-collagenization and an adequate amount of marrow material, fat cells, and blood vessels. An oxytetracycline labeling study showed moderate activity of new bone formation with crossing-over of new bone trabeculae along with the presence of resorption cavities in group II, whereas in the control group, the process of new bone formation was active from both ends and the defect site appeared as a homogenous non-fluoroscent area. Angiograms of the animals in the control group showed uniform angiogenesis in the defect site with establishment of trans-transplant angiogenesis, whereas in group II there was complete trans-transplant shunting of blood vessel communication. Porous HAp ceramic prepared by an aqueous combustion technique promoted bone formation over the defect, confirming their biologic osteoconductive property.

Segmental bone tissue engineering by seeding osteoblast precursor cells into titanium mesh-coral composite scaffolds

The size and specific shape of bone grafts are important for jaw reconstruction. In this experiment, segmental bone grafts were engineered in a predetermined shape via seeding osteoblast precursor cells into titanium mesh-coral composite scaffolds. Titanium meshes were moulded into the shape of a column with length 12 mm and diameter 8mm. The column was filled with natural coral granules and the complex acted as a cell-seeding scaffold. About 4 x 10(7) osteoblast precursor cells in 200 microl cell-culture medium were seeded into each of six scaffolds and incubated in vitro for 2 days. Then, the composites were implanted subcutaneously into the backs of nude mice and incubated in vivo. Two months after implantation, the animals were killed and new bone formed in the scaffolds was investigated by gross inspection, X-ray examination, histological observation and mechanical testing. The results showed that newly formed tissue was red and presented the gross appearance of bone, and kept the original shape of the column. Titanium mesh was situated on the surface of the bone graft. An X-ray blocking shadow was observed in and around the titanium scaffolds; most of the coral granules had been absorbed. Histological observation demonstrated a large amount of new bone formed and integrated well with titanium mesh. Mechanical testing showed that new bone improved the mechanical property of the graft significantly. In conclusion, a titanium mesh-coral composite scaffold with osteoblast precursor cells is an efficient means to engineer segmental bone, possessing the desired shape and mechanical strength.

Modulations of 17-beta estradiol on osteogenic and adipogenic differentiations of human mesenchymal stem cells

Bone marrow mesenchymal stem cells (MSCs) are a promising cell source for tissue engineering and regenerative medicine applications. However, effective regulation to improve differentiation potentials of MSCs plays a critical role in promoting successful tissue formation. Because estrogen has been demonstrated to modulate tissue and organ development and differentiation, we hypothesized that adding estrogen could effectively improve the multiple differentiation potentials of human bone marrow MSCs in vitro. In the present study, 17-beta estradiol (E2) was investigated for in vitro osteogenic and adipogenic differentiations of MSCs isolated from a healthy male human donor. After MSCs were exposed to osteogenic differentiation medium supplemented with E2 at different concentrations, osteocalcin expression is upregulated and calcium deposition (21.0%) is significantly improved ( p < 0.01; n = 4). Under adipogenic stimulation, E2 increased 35.4% lipid accumulations more than that of the group without the E2 supplement ( p < 0.01; n = 4). Estrogen's effect on osteogenesis occurs via estrogen receptors (ER)-alpha and -beta, whereas the effect on adipogenesis is through ER-alpha. Estrogen's regulation of differentiations of MSCs is dose dependent. The present study indicated that estrogen could potentially improve the role of MSCs in tissue engineering and regeneration by serving as a modulator of differentiation.

Transplantation of mesenchymal stromal cells on mineralized collagen leads to ectopic matrix synthesis in vivo independently from prior in vitro differentiation

BACKGROUND

Tissue engineering using mesenchymal stromal cells (MSC) represents a promising approach for bone regeneration. Nevertheless, the optimal constructs have yet to be determined. It still remains unclear if there is a benefit of in vitro differentiation of MSC prior to transplantation or if undifferentiated MSC hold the optimal potential concerning new tissue formation.

METHODS

After isolation and in vitro expansion, MSC were seeded on mineralized collagen sponges and transplanted in a heterotopic SCID mice model (n=12). While group A contained undifferentiated MSC, in group B cells were cultivated for 14 days in vitro under osteogenic conditions prior to implantation. Results were compared with non-loaded scaffolds (group C). Animals were killed for investigation at 4 and at 8 weeks.

RESULTS

In situ hybridization demonstrated integration of MSC for up to 8 weeks in groups A and B. Histology revealed significantly more extracellular matrix synthesis in MSC-seeded scaffolds containing calcium phosphate and collagen type I at 4 and 8 weeks after transplantation compared with unloaded controls. At a biochemical level, higher levels of specific alkaline phosphatase expression were detected in MSC-loaded scaffolds (P<0.05). Scaffolds containing undifferentiated and differentiated MSC did not appear to differ in terms of matrix synthesis and protein expression, while the number of avital cells was significant higher in those probes loaded with differentiated MSC (P<0.01).

DISCUSSION

The integration of transplanted cells and MSC-associated matrix synthesis encourages the use of MSC-loaded mineralized collagen for tissue engineering of bone. Furthermore, our data suggest that in vitro differentiation of MSC does not have a positive influence in terms of improved matrix synthesis.

Introduction to Nanotechnology

Nanotechnology is a scientific movement that has the potential to transform the diagnosis and treatment of disease in the 21st century. The area of investigation is defined by the study, design, manipulation, manufacture, and control of materials or devices by physical or chemical means at resolutions on the order of one billionth of a meter. The potential for a wide range of clinical applications makes a basic understanding of nanotechnology important to physiatrists. This review presents an introduction to nanotechnology and discusses key developments in tissue engineering, drug delivery, imaging, diagnostics, surface texturing, and biointerfaces that could impact the practice of physiatry in the future.

Biodegradable polyurethane cancellous bone graft substitutes in the treatment of iliac crest defects

Porous scaffolds were produced from newly designed biodegradable, segmented aliphatic polyurethanes of various chemical compositions and hydrophilic-to-hydrophobic segment ratios. The scaffolds were implanted into monocortical defects in the iliac crest of healthy sheep for 6 months. The resected cortex was not repositioned. The ilium defects, which were not implanted with polyurethane scaffolds, were used as controls. In none of the control defects was there bone regeneration at the time of euthanasia. The defects implanted with porous scaffolds from polyurethanes were healed to varying extents with cancellous bone. The structure of the regenerated cancellous bone was radiographically denser than the structure of native bone. New bone that was formed in the scaffolds with a higher amount of hydrophilic component contained more calcium phosphate deposit than the bone formed in the scaffolds with a lower amount of the hydrophilic component. There was no new cortex formed over the defect, but a thin layer of soft tissue covered the newly formed cancellous bone.

Enhanced differentiation and mineralization of human fetal osteoblasts on PDLLA containing Bioglass® composite films in the absence of osteogenic supplements

This study investigates the cellular response of fetal osteoblasts to bioactive resorbable composite films consisting of a poly-D,L-lactide (PDLLA) matrix and bioactive glass 45S5 Bioglass (BG) particles at three different concentrations (0% (PDLLA), 5% (P/BG5), and 40% (P/BG40)). Using scanning electron microscopy (SEM) we observed that cells were less spread and elongated on PDLLA and P/BG5, whereas cells on P/BG40 were elongated but with multiple protrusions spreading over the BG particles. Vinculin immunostaining revealed similar distribution of focal adhesion contacts on all cells independent of substratum, indicating that all materials permitted cell adhesion. However, when differentiation and maturation of fetal osteoblasts was examined, incorporation of 45S5 BG within the PDLLA matrix was found to significantly (p < 0.05) enhance alkaline phosphatase enzymatic activity and osteocalcin protein synthesis compared to tissue culture polystyrene controls and PDLLA alone. Alizarin red staining indicated extracellular matrix mineralization on both P/BG5 and P/BG40, with significantly more bone nodules formed than on PDLLA. Real time RT-PCR revealed that expression of bone sialoprotein was also affected by the BG containing films compared to controls, whereas expression of Collagen Type I was not influenced. By performing these investigations in the absence of osteogenic factors it appears that the incorporation of BG stimulates osteoblast differentiation and mineralization of the extracellular matrix, demonstrating the osteoinductive capacity of the composite.

The use of tissue-engineered bone with human bone morphogenetic protein-4-modified bone-marrow stromal cells in repairing mandibular defects in rabbits

In this study, the capacity of hBMP-4 gene therapy combined with tissue-engineering techniques to improve the repair of mandibular osseous defects in rabbits was explored. A mammalian plasmid vector expressing enhanced green fluorescent protein-human bone morphogenetic protein-4 (pEGFP-hBMP-4) was initially constructed through subcloning techniques. Bone-marrow stromal cells (bMSCs) from New Zealand White rabbits were cultured and either transfected with pEGFP-hBMP-4 or pEGFP, or left untransfected in vitro. Once the transfer efficiency was determined through the expression of EGFP, cells from the three groups were combined with natural non-organic bone (NNB) at a concentration of 50 x 10(6)cells/ml and placed in 15 mm x 6 mm bilateral, full-thickness, mandibular defects surgically made in 12 rabbits. Together with NNB control, there were six samples per group. Four weeks after surgery, the implants were harvested and evaluated histomorphologically. Under optimal experimental conditions, gene transfer efficiency reached a maximum of 38.2+/-9.4%. While the percentage of new bone area in the NNB control group was 8.8+/-3.1%, in the untransfected bMSC group 22.5+/-8.2%, and in the pEGFP group 18.1+/-9.0%, a significantly higher amount of 32.5+/-6.1% was observed in the pEGFP-hBMP-4 group. These results suggest that transfection of bMSCs with hBMP-4 enhances their inherent osteogenic capacity for maxillofacial bone tissue-engineering applications.

The engineering of craniofacial tissues in the laboratory: a review of biomaterials for scaffolds and implant coatings

Tissue engineering is a rapidly growing interdisciplinary field that focuses on the interactions between cells, growth factors, and scaffolds to produce replacement tissue and organs. Recent developments in tissue engineering technology include refinements in isolation and differentiation of progenitor cells, 3-D printing technology to produce scaffolds, new biomaterials for scaffolds, and growth factor delivery systems. The purpose of this article is to review advances in biomaterials, scaffolds, and implant coatings for craniomaxillofacial (bone) tissue engineering.

Indirect selective laser sintering of an apatite-mullite glass-ceramic for potential use in bone replacement applications

The feasibility of using indirect selective laser sintering (SLS) to produce parts from glass-ceramic materials for bone replacement applications has been investigated. A castable glass based on the system SiO2 Al2O3 P2O5 CaO CaF2 that crystallizes to a glass-ceramic with apatite and mullite phases was produced, blended with an acrylic binder, and processed by SLS. Green parts with good structural integrity were produced using a wide range of processing conditions, allowing both monolayer and multilayer components to be constructed. Following SLS the parts were post-processed to remove the binder and to crystallize fully the material, evolving the apatite and mullite phases. The parts were heated to 1200O C using a number of different time-temperature profiles, following which the processed material was analysed by differential thermal analysis, X-ray diffraction, and scanning electron microscopy, and tested for flexural strength. An increase in strength was achieved by infiltrating the brown parts with a resorbable phosphate glass, although this altered the crystal phases present in the material.

Regeneration of bicortical defects in the iliac crest of estrogen-deficient sheep, using new biodegradable polyurethane bone graft substitutes

Porous scaffolds for cancellous bone graft substitutes were prepared from new experimental biodegradable aliphatic polyurethane elastomers with varying hydrophilicity. The ratios of the hydrophilic-to-hydrophobic content in the polymers were 30-70, 50-50, and 70-30%, respectively. The hydrophilic component consisted of poly(ethylene oxide) diol and the hydrophobic component of poly(epsilon-caprolactone) diol. To promote the materials' biological performance, the calcium complexing moiety, the polysaccharide, and vitamin D(3) were incorporated into the polymer chain upon synthesis. The scaffolds had an interconnected porous structure with an average pore size in the range of 300-2,000 microm and pore-to-volume ratios of (85 +/- 5)%. The bone substitutes were implanted (press-fit) in biocortical 10 x 10 mm(2) defects created in the tuber coxae of 21 skeletally mature Warhill ewes, which were ovariectomized 12 months prior to implantation. At the time of euthanasia at 18 and 25 months, all the defects in the ilium implanted with polyurethane bone substitutes had healed with new bone. The extent of bone healing depended on the chemical composition of the polymer from which the implant was made, although for the same material there were animal-related differences in healing. The structure of the newly formed cancellous bone was radiographically and histologically similar to the native bone. The implants from polymers with the incorporated calcium-complexing additive were the most effective promoters of bone healing, followed by those with vitamin D(3) and polysaccharide-containing polymer. There was no bone healing in the control defects.

Biodegradable porous polyurethane scaffolds for tissue repair and regeneration

Critical-size bone defects usually require the insertion of autogenous bone graft to heal. Harvesting of bone is traumatic and results in high morbidity at the donor site. A potential alternative to bone graft may be a bone substitute with adequate biocompatibility and biological properties produced from ceramics or bioresorbable/biodegradable polymers. In the present study, new elastomeric biodegradable polyurethanes with an enhanced affinity toward cells and tissues were synthesized using aliphatic diisocyanate, poly(epsilon-caprolactone) diol, and biologically active 1,4:3,6-dianhydro-D-sorbitol (isosorbide diol) as chain extender. The polymers were processed into 3D porous scaffolds by applying a combined salt leaching-phase inverse process. The critical parameters controlling pore size and geometry were the solvents and nonsolvents used for scaffold preparation and the sizes of the solid porogen crystals. Scaffolds prepared from the polymer solution in solvents such as dimethylsulfoxide or methyl-2-pyrrolidone did not have a homogenous pore structure. Many pores were interconnected, but numerous pores were closed. Irrespective of the high pore-to-volume ratio (75%), the scaffolds showed poor water permeability. The best solvent for the preparation of scaffolds from the polyurethane used in the study was dimethylformamide (DMF). The type of nonsolvent admixed to the polymer solution in DMF strongly affected the scaffolds' pore structure. The elastomeric polyurethane scaffold prepared from the optimal solvent-nonsolvent mixture had regular interconnected pores, high water permeability, and a pore-to-volume ratio of 90%. The osteoconductive properties of the 3D porous polyurethane scaffolds can be additionally promoted by loading them with calcium phosphate salts such as hydroxyapatite or tricalcium phosphate, thus making them promising candidates for bone graft substitutes.

Thein vitro growth and activity of sheep osteoblasts on three-dimensional scaffolds from poly(L/DL-lactide) 80/20%

Critical-size bone defects usually require the use of autogenous bone grafts to heal. Harvesting of bone is traumatic, and results in high morbidity of donor site. A potential alternative to bone graft may be a bone substitute with adequate biocompatibility and biological properties produced from ceramics and/or bioresorbable or biodegradable polymers. In the present study, sheep osteoblasts isolated from cancellous bone chips were seeded and cultured for 1, 2, and 3 weeks on porous poly(L/DL-lactide) 80/20% scaffolds. The cell morphology was assessed from rhodamine staining and scanning electron microscopy, cell growth, and activity from the measurements of DNA, alkaline phosphatase activity, and total protein amount in the cell lysate, and mineral deposits from EDAX and van Kossa staining. The cells attached firmly to the scaffold walls, grew deeply into the pores, and exhibited morphology typical of osteoblasts. Mineralized noduli with a Ca/P ratio of 1.4 to 1.8 found in the scaffold indicated that the cells had maintained their osteoblastic phenotype. The amount of DNA, alkaline phosphatase activity, and the total amount of proteins increased with time of culturing, although at 3 weeks the cells did not yet reach the contact inhibition. These results demonstrate that three-dimensional porous poly(L/DL-lactide) 80/20% scaffolds provide a suitable substrate for the attachment and growth of primary osteoblasts, and might potentially be used as bone defect fillers and in the design of tissue-engineered bone substitutes.

Three-dimensional composites manufactured with human mesenchymal cambial layer precursor cells as an alternative for sinus floor augmentation: an in vitro study

Bone tissue engineering is a promising approach for treatment of defective and lost bone in the maxillofacial region. Creating functional tissue for load bearing bone reconstruction using biocompatible and biodegradable scaffolds seeded with living cells is of crucial importance. The aim of our study was to compare the effects of poly-lactic-co-glycolic acid (PLGA) and hydroxyapatite (HA) ceramic granulae on growth, differentiation, mineralization and gene expression of mandibular mesenchymal cambial layer precursor cells (MCLPCs) cultured onto tissue engineered three-dimensional (3-D) composites in vitro. These 3-D composites were cultivated in a rotating cultivation system under osteogenic differentiation conditions for a maximum period of 21 days. After 6 and 21 days, histological examination was performed; scanning electron microscopy (SEM), alkaline phosphatase (ALP) activity and levels of DNA were investigated. Expression of bone-specific genes osteocalcin, osteonectin, osteopontin, ALP, core binding factor alpha 1 and collagen type I were investigated by using a reverse transcription-polymerase chain reaction (RT-PCR) method. After 6 and 21 days of incubation an initiation of mineralization and the presence of newly formed bone at the surface of the composites were shown after evaluation of ALP activity, DNA content, SEM and histological staining. Expression of bone-specific genes confirmed the bone-like character of these composites and different effects of PLGA or HA granulae on the osteogenic differentiation of human MCLPCs in vitro. The results of this study support the concept that substrate signals significantly influence MCLPCs growth, differentiation, mineralization and gene expression in vitro, and that the use of these cells in the manufacturing of 3-D cell/HA composites is a promising approach for load bearing bone reconstruction in the maxillofacial region in vivo.

Ectopic bone formation associated with mesenchymal stem cells in a resorbable calcium deficient hydroxyapatite carrier

Bone substitute materials can induce bone formation in combination with mesenchymal stem cells (MSC). The aim of the current study was to examine ectopic in vivo bone formation with and without MSC on a new resorbable ceramic, called calcium deficient hydroxyapatite (CDHA). Ceramic blocks characterized by a large surface (48 m2/g) were compared with beta-tricalcium phosphate (beta-TCP), hydroxyapatite (HA) ceramics (both ca. 0.5 m2/g surface) and demineralized bone matrix (DBM). Before implantation in the back of SCID mice carriers were freshly loaded with 2x10(5) expanded human MSC or loaded with cells and kept under osteogenic conditions for two weeks in vitro. Culture conditions were kept free of xenogenic supplements. Deposits of osteoid at the margins of ceramic pores occurred independent of osteogenic pre-induction, contained human cells, and appeared in 416 MSC/CDHA composites compared to 216 MSC/beta-TCP composites. ALP activity was significantly higher in samples with MSC versus empty controls (p<0.001). Furthermore, ALP was significantly (p<0.05) higher for all ceramics when compared to the DBM matrix. Compared to previous studies, overall bone formation appeared to be reduced possibly due to the strict human protocol. Ectopic bone formation in the novel biomaterial CDHA varied considerably with the cell pool and was at least equal to beta-TCP blocks.

Macroporous calcium phosphate glass-ceramic prepared by two-step pressing technique and using sucrose as a pore former

Macroporous calcium phosphate glass-ceramic with an initial glass composition of 60CaO.30P2O5.3TiO2.7Na2O in mol% was successfully prepared by sintering the mixture compact consisting of calcium phosphate glass and sucrose powders, which was formed using a two-step pressing technique. After burning off the sucrose phase, a 3D interconnected macroporous structure was formed in the sintered body, in which the skeleton consisting of the calcium phosphate glass-ceramic (including beta-calcium pyrophosphate and beta-tricalcium phosphate as the crystalline phases) was transformed from the initial glass during the sintering. The macropores with several hundred microns in diameter and the large interconnection size (approximately 100 microm), which result from the controllably large-sized sucrose particles and the hot-pressing at a little higher temperature than the sucrose's melting point, are believed to meet the requirements for cell adhesion and bone tissue regeneration well. Moreover, in vitro dissolution behavior study indicates that the calcium phosphate glass-ceramic is soluble to an acetic acid solution of pH 5-7. These, together with the simplicity and feasibility of the innovative fabrication method itself, show that the formed porous glass-ceramic has a promising potential for application to a scaffold for bone tissue engineering.

Osteoblastic Phenotype Expression of MC3T3-E1 Cells Cultured on Polymer Surfaces

BACKGROUND

Current efforts in bone tissue engineering have as one focus the search for a scaffold material that will support osteoblast proliferation, matrix mineralization, and, ultimately, bone formation. The goal is to develop a bone substitute that is functionally equivalent to autograft bone. Previously published reports have shown that osteoblasts exhibit varying rates and degrees of proliferation and mineralization when grown on different surfaces.

METHODS

This study presents a histologic and biomolecular analysis of MC3T3-E1 murine preosteoblast cells grown on poly(lactide-co-glycolide) (PLGA) versus poly(-caprolactone) (PCL), two commonly studied scaffold polymers. MC3T3-E1 cells were cultured on slides coated with either PLGA or PCL, and on uncoated glass slides as control, with six slides in each group. After 6 weeks in culture, the cells were stained for osteocalcin, alkaline phosphatase activity, and matrix mineralization. In addition, to assess the effects of the surface material on phenotypic expression at the molecular level, MC3T3-E1 cells were cultured on polymer-coated 24-well plates for 4 days, and analyzed by reverse transcription polymerase chain reaction for the expression of osteocalcin and alkaline phosphatase.

RESULTS

The results showed that three groups of slides stained positively for osteocalcin at 6 weeks. However, markedly less alkaline phosphatase activity and mineralization were observed on the cells grown on PCL. Real-time polymerase chain reaction assays subsequently revealed decreased expression of both markers by cells cultured on PCL compared with PLGA.

CONCLUSIONS

These results suggest that PCL does not support the full expression of an osteoblastic phenotype by MC3T3-E1 cells. PCL, therefore, is less desirable as a scaffold polymer in bone tissue engineering in so far as supporting bone formation is concerned. However, because PCL has favorable handling characteristics and strength, modifications of PCL may prompt further investigation.

Analysis of Cell-Seeded 3-Dimensional Bone Constructs Manufactured In Vitro With Hydroxyapatite Granules Obtained From Red Algae

PURPOSE

Bone tissue engineering is a promising approach for the treatment of defective or lost bone in the maxillofacial region. Biocompatible and biodegradable scaffolds seeded with living cells are used to create functional tissue for load-bearing bone reconstruction. The aim of this study was to manufacture cell-seeded 3-dimensional bone constructs based on hydroxyapatite ceramic granule calcified from red algae and mesenchymal cambial-layer precursor cells. The ability of these cells to grow on hydroxyapatite ceramic was quantitatively investigated to evaluate 3-dimensional bone constructs for their potential use in bone tissue engineering.

MATERIALS AND METHODS

Mesenchymal cambial-layer precursor cells were isolated from mandibular periosteum biopsy samples of 3 patients. To manufacture 72 bone constructs, these cells and hydroxyapatite ceramic granules (C GRAFT/Algipore; Clinician's Preference LLC, Golden, CO) were cultivated under osteogenic differentiation conditions in a rotating wall vessel system. After 6 and 21 days, histologic examination and scanning electron microscopy were performed. The absolute DNA content, protein synthesis, and alkaline phosphatase activity were also quantified. The osteoblastic phenotype of the constructs was confirmed by the expression of bone-specific genes (osteocalcin, osteonectin, osteopontin, and core binding factor alpha1) using semiquantitative reverse transcription-polymerase chain reaction and Western blot analysis.

RESULTS

Cells within the constructs showed good viability, which was evidenced by an increase in DNA content over the culture period. The decrease in alkaline phosphatase-specific activity could be an indicator of the maturation of cells and the induction of mineralization. The osteoblastic phenotype of the constructs was demonstrated on protein and at the RNA level over the entire culture period.

CONCLUSION

We observed a positive effect of hydroxyapatite ceramic granules on mesenchymal cambial-layer precursor cell behavior in cell-seeded 3-dimensional bone constructs, indicating the potential applicability of C GRAFT/Algipore composites in bone tissue engineering.

The microenvironment around total hip replacement prostheses

The metal stem of the totally replaced hip carries load and resists fatigue, but it is electrochemically corroded. Metallic atoms act as haptens, induce type 1 T-helper cells/Th1-type immune responses and enhance periprosthetic osteolysis. Stiff metal implants, which do not have the same elasticity as the surrounding bone, cause stress shielding. Cyclic loading and lack of ligamentous support lead to mechanical and ischemia reperfusion injury and particle formation from bone, polymethylmethacrylate, and porous implant surfaces, which accelerate third-body polyethylene wear. Surgical injury and micromotion induce the formation of a fibrous capsule interface. Type-B lining cells produce lubricin and surface-active phospholipids to promote solid-to-solid lubrication but may loosen the implant from bone. The pumping action of the cyclically loaded joint and synovial fluid pressure waves dissect the implant-host interface and transports polyethylene particles and pro-inflammatory mediators to the interface. Hyaluronan induces formation of a synovial lining like layer. Because of its localization close to bone, foreign body inflammation at the interface stimulates osteoclastogenesis and peri-implant bone loss. Metal-on-metal and ceramic-on-ceramic pairs might minimize third body wear, but can lead to high-impact load of the acetabulum. Diamond coating of a metal-on-polyethylene couple might solve both of these problems. The basic biomaterial solutions allow good mechanical performance and relatively long life in-service, but surface modifications (porous coating, hydroxyapatite, diamond, bioglass, and others) may facilitate performance of the implant and improve the biomaterial and body interfaces.

Biological and biophysical principles in extracorporal bone tissue engineering. Part III

Over the last decade extracorporal bone tissue engineering has moved from laboratory to clinical application. The restoration of maxillofacial bones from cell harvesting through product manufacture and end-use has benefited from innovations in the fields of biomechanical engineering, product marketing and transplant research. Cell/scaffold bone substitutes face a variety of unique clinical challenges which must be addressed. This overview summarises the recent state of the art and future anticipations in the transplantation of extracorporally fabricated bone tissues.

Exogenous Runx2 Expression Enhances in Vitro Osteoblastic Differentiation and Mineralization in Primary Bone Marrow Stromal Cells

Bone marrow stromal cells represent a promising cell source for cell-based therapeutic and bone tissue-engineering applications, but are restricted by a low frequency in healthy marrow, an age-related decrease in osteogenic capacity, and a propensity for dedifferentiation during in vitro expansion. To address these limitations, retroviral gene delivery was used to examine the effects of sustained and elevated expression of the Runx2 osteoblastic transcription factor on osteoblastic gene and protein expression and mineralization in primary rat bone marrow stromal cells. Runx2 overexpression upregulated several osteoblast-specific genes, including collagen type I and osteocalcin, and enhanced alkaline phosphatase activity and biological mineral deposition. Forced Runx2 expression in combination with dexamethasone increased matrix mineralization compared with exogenous Runx2 expression or dexamethasone treatment alone, whereas dexamethasone-free control cultures displayed minimal mineralization. These additive effects suggest complementary interactions between Runx2 and dexamethasone-responsive regulatory factors. Finally, Runx2 overexpression in stromal cell cultures undergoing considerable in vitro expansion resulted in higher matrix mineralization capacity compared with controls, which completely lost the ability to produce mineralized matrix even in the presence of dexamethasone. These findings provide a novel strategy for cell-based therapeutic applications requiring significant numbers of osteogenic cells to synthesize mineralized constructs for the treatment of large bone defects.

Effect of flow perfusion on the osteogenic differentiation of bone marrow stromal cells cultured on starch-based three-dimensional scaffolds

This study aims to investigate the effect of culturing conditions (static and flow perfusion) on the proliferation and osteogenic differentiation of rat bone marrow stromal cells seeded on two novel scaffolds exhibiting distinct porous structures. Specifically, scaffolds based on SEVA-C (a blend of starch with ethylene vinyl alcohol) and SPCL (a blend of starch with polycaprolactone) were examined in static and flow perfusion culture. SEVA-C scaffolds were formed using an extrusion process, whereas SPCL scaffolds were obtained by a fiber bonding process. For this purpose, these scaffolds were seeded with marrow stromal cells harvested from femoras and tibias of Wistar rats and cultured in a flow perfusion bioreactor and in 6-well plates for 3, 7, and 15 days. The proliferation and alkaline phosphatase activity patterns were similar for both types of scaffolds and for both culture conditions. However, calcium content analysis revealed a significant enhancement of calcium deposition on both scaffold types cultured under flow perfusion. This observation was confirmed by Von Kossa-stained sections and tetracycline fluorescence. Histological analysis and confocal images of the cultured scaffolds showed a much better distribution of cells within the SPCL scaffolds than the SEVA-C scaffolds, which had limited pore interconnectivity, under flow perfusion conditions. In the scaffolds cultured under static conditions, only a surface layer of cells was observed. These results suggest that flow perfusion culture enhances the osteogenic differentiation of marrow stromal cells and improves their distribution in three-dimensional, starch-based scaffolds. They also indicate that scaffold architecture and especially pore interconnectivity affect the homogeneity of the formed tissue.