Next-generation biomedical implants using additive manufacturing of complex, cellular and functional mesh arrays

In this paper, we examine prospects for the manufacture of patient-specific biomedical implants replacing hard tissues (bone), particularly knee and hip stems and large bone (femoral) intramedullary rods, using additive manufacturing (AM) by electron beam melting (EBM). Of particular interest is the fabrication of complex functional (biocompatible) mesh arrays. Mesh elements or unit cells can be divided into different regions in order to use different cell designs in different areas of the component to produce various or continually varying (functionally graded) mesh densities. Numerous design elements have been used to fabricate prototypes by AM using EBM of Ti-6Al-4V powders, where the densities have been compared with the elastic (Young) moduli determined by resonant frequency and damping analysis. Density optimization at the bone-implant interface can allow for bone ingrowth and cementless implant components. Computerized tomography (CT) scans of metal (aluminium alloy) foam have also allowed for the building of Ti-6Al-4V foams by embedding the digital-layered scans in computer-aided design or software models for EBM. Variations in mesh complexity and especially strut (or truss) dimensions alter the cooling and solidification rate, which alters the alpha-phase (hexagonal close-packed) microstructure by creating mixtures of alpha/alpha' (martensite) observed by optical and electron metallography. Microindentation hardness measurements are characteristic of these microstructures and microstructure mixtures (alpha/alpha') and sizes.

Ultrastructural evaluation of in vitro mineralized calcium phosphate phase on surface phosphorylated poly(hydroxy ethyl methacrylate-co-methyl methacrylate)

The in vitro functionality of surface phosphorylated poly(hydroxy ethyl methacrylate-co-methyl methacrylate), poly(HEMA-co-MMA) to induce bioinspired mineralization of calcium phosphate phase is evaluated. The primary nucleation of calcium phosphate on the surface phosphorylated copolymer occurs within 3 days of immersion when immersed in 1.5x simulated body fluid and the degree of mineralization is proportional to the hydroxy ethyl methacrylate content in the copolymer. The calcium phosphate phase is identified as hydroxyapatite by X-Ray diffraction analysis. The transmission electron microscopic evaluation combined with selected area diffraction pattern and energy dispersive analysis exemplified that the primary nuclei of amorphous calcium phosphate transforms to crystalline needle like calcium rich apatite, within a period of 3 days immersion in simulated body fluid. The atomic force microscopic results corroborate the c-axis growth of the crystals within 3 days immersion in SBF.

[Prevention of osseous defaults in the craneosinostosis surgery using calvarian cranial particulate bone]

It is considered that up to 20% of the craniosinostosis patients require secondary surgeries. Different techniques have been used in craneofacial surgery for the reconstruction of great osseous defects in pediatric patients for many years. This paper is about a new technique to obtain osseous graft for covering osseous cranial defects, using particulate bone, harvested from the patient calvarian using a hand-driven brace and covered with a fibrin adhesive. This is a very simple technique, which provides a great amount of bone from the patient himself, therefore producing a small morbidity. Since 2007 the authors have been using autologous particulate bone harvested from de patient calvarian for the reconstruction of different size osseous defects found in craneofacial surgery, especially in pediatrics patients. Although alloplastic materials and bone substitutes have been used for cranial reconstruction, the best option is the autogenous bone. In contrast to synthetic materials autologous grafts have a faster osteointegration, due to their osteogenic, osteoinductive and osteconductive properties. Harvesting the bone from the calvarian patient produces a minimal morbidity compared to the extraction of grafts from other donor sites such as rips or hip. The use of autologous particulate bone in craniosinostosis surgery reduces the risk of second interventions due to secondary ossifications defects. On the other hand, the harvest is easy and the supply of bone it is enough in pediatric patients.

Dipeptide-based polyphosphazene and polyester blends for bone tissue engineering

Polyphosphazene-polyester blends are attractive materials for bone tissue engineering applications due to their controllable degradation pattern with non-toxic and neutral pH degradation products. In our ongoing quest for an ideal completely miscible polyphosphazene-polyester blend system, we report synthesis and characterization of a mixed-substituent biodegradable polyphosphazene poly[(glycine ethyl glycinato)(1)(phenyl phenoxy)(1)phosphazene] (PNGEG/PhPh) and its blends with a polyester. Two dipeptide-based blends namely 25:75 (Matrix1) and 50:50 (Matrix2) were produced at two different weight ratios of PNGEG/PhPh to poly(lactic acid-glycolic acid) (PLAGA). Blend miscibility was confirmed by differential scanning calorimetry, Fourier transform infrared spectroscopy, and scanning electron microscopy. Both blends resulted in higher tensile modulus and strength than the polyester. The blends showed a degradation rate in the order of Matrix2<Matrix1<PLAGA in phosphate buffered saline at 37 degrees C over 12 weeks. Significantly higher pH values of degradation media were observed for blends compared to PLAGA confirming the neutralization of PLAGA acidic degradation by polyphosphazene hydrolysis products. The blend components PLAGA and polyphosphazene exhibited a similar degradation pattern as characterized by the molecular weight loss. Furthermore, blends demonstrated significantly higher osteoblast growth rates compared to PLAGA while maintaining osteoblast phenotype over a 21-day culture. Both blends demonstrated improved biocompatibility in a rat subcutaneous implantation model compared to PLAGA over 12 weeks.

Loading of VEGF to the heparin cross-linked demineralized bone matrix improves vascularization of the scaffold

Deficient vascularization is one of the prominent shortcomings of porous tissue-engineering scaffolds, which results in insufficient oxygen and nutrients transportation. Here, heparin cross-linked demineralized bone matrices (HC-DBM) pre-loaded with vascular endothelial growth factor (VEGF) were designed to promote cells and new microvessels invasion into the matrices. After being chemical crosslinked with heparin by N-hydroxysuccinimide and N-(3-di-methylaminopropyl)-N'-ethylcarbodiimide, the scaffold could bind more VEGF than the non-crosslinked one and achieve localized and sustained delivery. The biological activity of VEGF binding on heparinized collagen was demonstrated by promoting endothelial cells proliferation. Evaluation of the angiogenic potential of heparinized DBM loaded with VEGF was further investigated by subcutaneous implantation. Improved angiogenesis of heparinized DBM loaded with VEGF was observed from haematoxylin-eosin staining and immunohistochemistry examination. The results demonstrated that heparin cross-linked DBM binding VEGF could be a useful strategy to stimulate cells and blood vessels invasion into the scaffolds.

Silica xerogel-chitosan nano-hybrids for use as drug eluting bone replacement

Silica xerogel-chitosan hybrids containing vancomycin were fabricated by the sol-gel process at room temperature and their potential as a drug eluting bone replacement was evaluated in terms of their mechanical properties and drug release behaviors. Regardless of the content of chitosan, all of the prepared hybrids had a uniform mesoporous structure, which would allow the effectual loading of vancomycin. As the content of chitosan was increased, the strength, strain to failure, and work of fracture of the hybrids were significantly enhanced, while the elastic modulus was decreased. These changes in the mechanical properties were mainly attributed to the mitigation of the brittleness of the silica xerogel through its hybridization with the flexible chitosan phase. In addition, the initial burst-effect was remarkably reduced by increasing the content of chitosan. The hybrids with more than 30% chitosan could release the vancomycin for an extended period of time in a controlled manner.

Preparation of porous 45S5 Bioglass-derived glass-ceramic scaffolds by using rice husk as a porogen additive

Bioactive glass is currently regarded as the most biocompatible material in the bone regeneration field because of its bioactivity, osteoconductivity and even osteoinductivity. In the present work porous glass-ceramic scaffolds, which were prepared from the 45S5 Bioglass by foaming with rice husks and sintering at 1050 degrees C for 1 h, have been developed. The produced scaffolds were characterized for their morphology, properties and bioactivity. Micrographs taken using a scanning electron microscope (SEM) were used for analysis of macropores, mesopores and micropores, respectively. The bioactivity of the porous glass-ceramic scaffolds was investigated using simulated body fluid (SBF) and characterized by SEM, energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). A great potential scaffold that provides sufficient mechanical support temporarily while maintaining bioactivity, and that can biodegrade at later stages is achievable with the developed 45S5 Bioglass-derived scaffolds.

[Research on bioactivity of magnesium and its alloys]

Magnesium is an essential microelement which is not harmful to human body. As a light-weight metal with properties similar to natural bone, magnesium material possesses the characteristics of its degradability, little biotoxicity, as well as its regulatory strength and controllable degradation-speed. After the tissue has healed sufficiently, the burden of a second surgical procedure can be avoided. Therefore, there is need of investigation on the possible use of magnesium and its alloys as medical biomaterials, and the study of its bioactivity is the foundation of further application. This article reviews the bioactivity of magnesium and its alloys.

[Development of biodegradable magnesium-based biomaterials]

Magnesium is a macroelement which is indispensable to human bodies. As a lightweight metal with high specific strength and favorable biocompatibility, magnesium and its alloys have been introduced in the field of biomedical materials research and have a broad application prospect. It is possible to develop new type of biodegradable medical magnesium alloys by use of the poor corrosion resistance of magnesium. Bioabsorbable magnesium stents implanted in vivo could mechanically support the vessel in a short term, effectly prevent the acute coronary occlusion and in-stent restenosis, and then be gradully biodegraded and completely absorbed in a long term. Osteoconductive bioactivity in magnesium-based alloys could promote the apposition growth of bone tissue. This paper reviews the progress of magnesium and its alloys applied in bone tissue and cardiovascular stents, and the prospect of the future research of magnesium-based biomaterials is discussed.

[Animal implantation with a new type of chitosan microspheres/calcium phosphate cement]

OBJECTIVE

To investigate bioactivity, biodegradation, bone conductive properties, and clinical maneuverability of a novel injectable chitosan microspheres/calcium phosphate cement (CPC).

METHODS

The bone defect of pi x 4 mmx4 mmx6 mm was made at both thigh bones of 12 rabbits, and experimental material (chitosan microspheres/CPC) or control material (alpha-tricalcium phosphate cement, alpha-TCP) was injected into the defect respectively. The filling situation was evaluated by X-ray 3 days after operation. The rabbits were divided into three groups, four for each group. The samples with chitosan microspheres and the control with alpha-TCP were collected at 8, 16, 24 weeks after operation. Histological examination and scanning electron microscope (SEM) evaluation were performed.

RESULTS

The absorption of implants with chitosan microspheres was observed at 8 weeks, and became more apparent at 16 weeks. Different size of cavities were observed in CPC after the degradation of chitosan microspheres. The chitosan microspheres/CPC was dramatically degraded after 24 weeks with a few chitosan microspheres, and new bone replaced the degraded materials. The implants with alpha-TCP were absorbed slowly compared with the chitosan microspheres/CPC. The cavities in alpha-TCP were small.

CONCLUSION

The chitosan microspheres/calcium phosphate cement has the characters of good biocompatible and osteocombinative ability. Compared with the control material, adding chitosan microspheres into CPC could enhance its degradability and facilitate the new bone formation.

Potential effects of a low-molecular-weight fucoidan extracted from brown algae on bone biomaterial osteoconductive properties

In this work, we first tested the influence of low-molecular-weight (LMW) fucoidan extracted from pheophicae cell wall on bidimensional cultured normal human osteoblasts' behaviors. Second, by impregnation procedure with LMW fucoidan of bone biomaterial (Lubboc), we explored in this bone extracellular matrix context its capabilities to support human osteoblastic behavior in 3D culture. In bidimensionnal cultures, we evidenced that LMW fucoidan promotes human osteoblast proliferation and collagen type I expression and favors precocious alkaline phosphatase activity. Furthermore, with LMW fucoidan, von Kossa's staining was positive at 30 days and positive only at 45 days in the absence of LMW fucoidan. In our three-dimensional culture models with the biomaterial pretreated with LMW fucoidan, osteoblasts promptly overgrew the pretreated biomaterial. We also evidenced that osteoblasts increased proliferation with pretreated biomaterial when compared with untreated biomaterial. Osteoblasts secreted osteocalcin and expressed BMP2 receptor on control material as well as with LMW fucoidan impregnated biomaterial. In conclusion, in our experimental conditions, LMW fucoidan stimulated expression of osteoblastic markers differentiation such as alkaline phosphatase activity, collagen type I expression, and mineral deposition; furthermore, cell proliferation was favored. These findings suggest that fucoidan could be clinically useful for bone regeneration and bone substitute design.

Spatial and temporal patterns of bone formation in ectopically pre-fabricated, autologous cell-based engineered bone flaps in rabbits

Biological substitutes for autologous bone flaps could be generated by combining flap pre-fabrication and bone tissue engineering concepts. Here, we investigated the pattern of neotissue formation within large pre-fabricated engineered bone flaps in rabbits. Bone marrow stromal cells from 12 New Zealand White rabbits were expanded and uniformly seeded in porous hydroxyapatite scaffolds (tapered cylinders, 10-20 mm diameter, 30 mm height) using a perfusion bioreactor. Autologous cell-scaffold constructs were wrapped in a panniculus carnosus flap, covered by a semipermeable membrane and ectopically implanted. Histological analysis, substantiated by magnetic resonance imaging (MRI) and micro-computerized tomography scans, indicated three distinct zones: an outer one, including bone tissue; a middle zone, formed by fibrous connective tissue; and a central zone, essentially necrotic. The depths of connective tissue and of bone ingrowth were consistent at different construct diameters and significantly increased from respectively 3.1+/-0.7 mm and 1.0+/-0.4 mm at 8 weeks to 3.7+/-0.6 mm and 1.4+/-0.6 mm at 12 weeks. Bone formation was found at a maximum depth of 1.8 mm after 12 weeks. Our findings indicate the feasibility of ectopic pre-fabrication of large cell-based engineered bone flaps and prompt for the implementation of strategies to improve construct vascularization, in order to possibly accelerate bone formation towards the core of the grafts.

Bisphosphonate binding affinity as assessed by inhibition of carbonated apatite dissolution in vitro

Bisphosphonates (BPs), which display a high affinity for calcium phosphate surfaces, are able to selectively target bone mineral, where they are potent inhibitors of osteoclast-mediated bone resorption. The dissolution of synthetic hydroxyapatite (HAP) has been used previously as a model for BP effects on natural bone mineral. The present work examines the influence of BPs on carbonated apatite (CAP), which mimics natural bone more closely than does HAP. Constant composition dissolution experiments were performed at pH 5.50, physiological ionic strength (0.15M) and temperature (37 degrees C). Selected BPs were added at (0.5 x 10(-6)) to (50.0 x 10(-6))M, and adsorption affinity constants, K(L), were calculated from the kinetics data. The BPs showed concentration-dependent inhibition of CAP dissolution, with significant differences in rank order zoledronate > alendronate > risedronate. In contrast, for HAP dissolution at pH 5.50, the differences between the individual BPs were considerably smaller. The extent of CAP dissolution was also dependent on the relative undersaturation, sigma, and CAP dissolution rates increased with increasing carbonate content. These results demonstrate the importance of the presence of carbonate in mediating the dissolution of CAP, and the possible involvement of bone mineral carbonate in observed differences in bone affinities of BPs in clinical use.

[Biocompatibility of combined deproteinized bone coated with hepatocyte growth factor as scaffold for osteoblasts in vitro in fetal rabbits]

OBJECTIVE

To determine the cellular compatibility of combined deproteinized bone(DPB) coated with hepatocyte growth factor (HGF), and to observe the adherent effect of osteoblasts in response to HGF.

METHODS

Osteoblasts were isolated from fetal rabbits. Osteoblasts were cultured with DPB coated with HGF and deproteinized bone as experimental group and contral group, respectively. The proliferation and alkalinephosphatase activity were tested. Their growth was examined by inverted phase contrast microscope and scanning electronmicroscope.

RESULTS

The osteoblasts were attached to the outside and inside surfaces and grew well. HGF/DPB could stimulate the alkalinephosphatase activity of the osteoblasts and improve the proliferation of the osteoblasts.

CONCLUSION

HGF/DPB has good biocompatibility and bone induction. HGF could improve the adherent effect of DPB on osteoblasts, and it could be used as scaffold material for the bone tissue engineering.

The effect of simvastatin on bone formation and ceramic resorption in a peri-implant defect model

Experimental use of statins as stimulators of bone formation suggests they may have widespread applicability in the field of orthopaedics. With their combined effects on osteoblasts and osteoclasts, statins have the potential to enhance resorption of synthetic materials and improve bone ingrowth. In this study, the effect of oral and local administration of simvastatin to a beta tricalcium phosphate (betaTCP)-filled defect around an implant was compared with recombinant human bone morphogenetic protein 2 (rhBMP2). On hundred and sixty-two Sprague-Dawley rats were assigned to treatment groups: local application of 0.1, 0.9 or 1.7 mg of simvastatin, oral simvastatin at 5, 10 or 50 mg kg(-1) day(-1) for 20 days, local delivery of 1 or 10 microg of rhBMP2, or control. At 6 weeks rhBMP2 increased serum tartrate-resistant acid phosphatase 5b levels and reduced betaTCP area fraction, particle size and number compared with control, suggesting increased osteoclast activity. There was reduced stiffness and increased mechanical strength with this treatment. Local simvastatin resulted in a decreased mineral apposition rate at 6 weeks and increased fibrous area fraction, betaTCP area fraction, particle size and number at 26 weeks. Oral simvastatin had no effect compared with control. Local application of rhBMP2 increased resorption and improved mechanical strength whereas simvastatin was detrimental to healing. Oral simvastatin was ineffective at promoting either ceramic resorption or bone formation. The effect of statins on the repair of bone defects with graft substitute materials is influenced by its bioavailability. Thus, further studies on the optimal delivery system are needed.

Histological and histomorphometric investigations on bone integration of rapidly resorbable calcium phosphate ceramics

Resorbable ceramics can promote the bony integration of implants. Their rate of degradation should ideally be synchronized with bone regeneration. We report here the results of a histological study of implants with two resorbable calcium phosphate ceramic coatings: Ca(2)KNa(PO(4))(2)-(GB14) and Ca(10)[K/Na](PO(4))(7)-(602020). The results attained with these ceramic-coated implants show the benefits of these materials with regard to bioactive bone-healing stimulation, compared with uncoated implants. The GB14 ceramic coating exhibited greater bone regeneration and differentiation on its surface than the conventional hydroxyapatite coating and helped bone tissue achieve more extensive contact free of connective tissue. Not until the coating disintegrated did the histological features of GB14- and 602020-coated implants converge-both implant types were integrated into bone. Rapid disintegration of the coating material, as with 602020, supports osteoblast proliferation but has negative effects on bone mineralization. Both resorbable ceramics tested, GB14 and 602020, demonstrated bioactivity; even metal surfaces coated with these materials were populated by mature bone tissue without connective tissue after disintegration of their ceramic coating. The less rapidly degrading material, GB14, achieved better results. Degradable calcium phosphate coatings have the potential to stimulate bone regeneration. From the histological viewpoint, the resorbable ceramics examined here can be recommended as coating materials for clinical use.

[Morphological study of biocompatibility of the material on the bases of bone collagen saturated by sulphated glycosaminoglycans]

Results of the experimental study of material on the bases of bone undemineralized collagen saturated by sulphated glycosaminoglycans are described in the article. It was done in the experiment evaluation of its biocompatibility with surrounding tissues of the experimental animals. On the grounds of the received data it can be concluded that such material implantation into the bone defects would favour quick cell migration into the defect and implant's vascularization, that in its turn would create preconditions for new bone tissue development.

Formation of osteoclast-like cells on HA and TCP ceramics

An essential property of bone substitute materials is that they are integrated into the natural bone remodelling process, which involves the resorption by osteoclast cells and the formation by osteoblast cells. If monocyte cells adhere to a calcium phosphate surface (bone or bone substitute material), they can fuse together and form multinucleated osteoclast cells. In this study we show that osteoclast-like cells derived from a human leukoma monocytic lineage responded in a different way to tricalciumphosphate (TCP) than to hydroxyapatite (HA) ceramics. Both ceramics were degraded by resorbing cells; however, HA enhanced the formation of giant cells. The osteoclast-like cells on HA formed a more pronounced actin ring, and larger lacunas could be observed. TCP ceramics are medically used as bone substitute materials because of their high dissolution rate. On the other hand, highly soluble calcium phosphate ceramics like TCP seem to be inappropriate for osteoclast resorption because they produce a high calcium concentration in the osteoclast interface and in the environment.

Immunohistochemical in situ characterization of orthopedic implants on polymethyl metacrylate embedded cutting and grinding sections

When investigating the tissue reaction on orthopedic implants, the cellular activity at the bone-implant interface is of special interest. Preparation of undecalcified bone sections with methylmetacrylate (MMA)-based resins allows evaluation of the host tissue reactions with the implant in situ. However, the technical workup is demanding and few reports exist on the immunohistochemical characterization of these sections. Rat (R), sheep (S), and human (H) samples were investigated. R specimens contained intramedullary rods in the rat tibia. S specimens were sheep tibiae with an external fixator. H specimens were obtained from deceased patients. Specimens were embedded in MMA-based Technovit 9100N using cold polymerization. Sections of 10-15 microm thickness were obtained and prepared for immunohistochemical staining. Good morphological detail was preserved in all specimens providing information about mineralization, recent bone formation, and bone-implant contact. The following antibodies could reproducibly be detected specifically: Osteopontin (R, S, H), Osteonectin, Cathepsin D (R, S), von Willebrand factor (R, H), Osteocalcin, ED 1 (R), CD 3, CD 68, Keratin (H). Control procedures without adding primary antibodies showed no unspecific staining. Reliable detection of immunohistochemical markers of bone resorption, bone formation, inflammation, and angiogenesis at undecalcified sections with the implant in situ appears promising in enhancing our understanding of the cellular activity and cell-matrix interactions at the bone-implant interface.

Molded vascularized neo-ossicle formation in silicone chambers

Vascularized bone grafts generally achieve their aims but are not used frequently owing to donor site morbidity and limited supply. To bioengineer an alternate vascularized bone graft, we developed a novel silicone bone reactor capable of producing vascularized neo-ossicles when appropriate osteoprecursor elements are included in the implanted chambers. Requirements for ossicle production were assessed in the model, including osteoprogenitor cells (donor bone marrow), osteoinductive signals (rhBMP2 or demineralized bone matrix), and osteoconductive matrix (Collagraft). Ossicle production required patency of the vascular pedicle, and for samples not containing cancellous isograft, donor marrow viability and an osteoinductive signal. Ossicles were produced without the need for an implanted osteoinductive matrix. Bone production and maturation time course were similar in chambers containing cancellous isograft, marrow/rhBMP2, and marrow/demineralized bone matrix. The demineralized bone matrix group had delayed early bone production, and the rhBMP2 group had lower final bone area. All groups had central osteolysis in the vascularized neo-ossicles. We believe the approach is promising for selected applications.

Lateral alveolar ridge augmentation using a synthetic nano-crystalline hydroxyapatite bone substitution material (Ostim®). Preliminary clinical and histological results

OBJECTIVES

The purpose of this preliminary two-center clinical prospective study was to evaluate the tissue composition of augmented sites after the use of a nano-crystalline hydroxyapatite (ncHA) bone substitution material by clinical and histological examinations.

MATERIAL AND METHODS

A synthetic ncHA augmentation material was used without any additives in 14 patients requiring lateral ridge augmentation 6-7 months before (10 patients) or at implant placement (four patients). The ncHA material was covered by a titanium mesh for space maintenance. Clinical and radiographic parameters were evaluated and bone biopsy cores, obtained 6-7 months following augmentation, were assessed histologically and histomorphometrically.

RESULTS

One patient showed gingival swelling, redness and pain at the augmentation site requiring removal of the titanium mesh 6 weeks postoperatively. In seven patients, a premature exposure of the titanium mesh without any inflammatory symptoms was noted. The width of the fixed gingival and the alveolar ridge height did not change significantly at least 6 months following augmentation (P>0.5), whereas a significant gain in alveolar ridge width (P=0.01) was noted. After a median period of prosthetic loading of 24 months, no implant was considered to be a failure. Histology revealed ncHA remnants in peripheral and central parts of biopsy cores obtained from seven patients after at least 6 months without histological symptoms of inflammation, whereas histomorphometry of bone cores revealed no significant differences of the mean percentage area of ncHA in peripheral (23.4%) and central (15.1%) parts of biopsy cores (P=0.262). The mean percentage area of bone colonizing the defect was 52.3%.

CONCLUSIONS

Small amounts of ncHA were found after at least 6 months in bone biopsies. The former defect space was filled with bone. The alveolar ridge width gain was found to be significant after lateral augmentation utilizing ncHA, providing a quantitatively and qualitatively sufficient site for primary stable implant placement.

Repair of critical size defects in the rat cranium using ceramic-reinforced PLA scaffolds obtained by supercritical gas foaming

Bioresorbable scaffolds made of poly(L-lactic acid) (PLA) obtained by supercritical gas foaming were recently described as suitable for tissue engineering, portraying biocompatibility with primary osteoblasts in vitro and interesting mechanical properties when reinforced with ceramics. The behavior of such constructs remained to be evaluated in vivo and therefore the present study was undertaken to compare different PLA/ceramic composite scaffolds obtained by supercritical gas foaming in a critical size defect craniotomy model in Sprague-Dawley rats. The host-tissue reaction to the implants was evaluated semiquantitatively and similar tendencies were noted for all graft substitutes: initially highly reactive but decreasing with time implanted. Complete bone-bridging was observed 18 weeks after implantation with PLA/ 5 wt % beta-TCP (PLA/TCP) and PLA/5 wt % HA (PLA/HA) scaffolds as assessed by histology and radiography. We show here for the first time that this solvent-free technique provides a promising approach in tissue engineering demonstrating both the biocompatibility and osteoconductivity of the processed structures in vivo.

Cell morphology, markers, spreading, and proliferation on orthopaedic biomaterials. An innovative cellular model for the "in vitro" study

The aims of tissue engineering are the in vitro reconstruction of functionally active tissues, and the in vivo induction of their appropriate development. The great progresses in the fields of biology and biomaterials represent key events, which allowed the recent improvement of tissue engineering. In the orthopaedic perspective, tissue engineering is focused on the development of innovative materials, whose action consists in recruiting bone progenitor cells and in stimulating their proliferation. In this context, it should remind that these materials should not only allow cells adhesion and proliferation, but also ensure that attached cells maintain the cellular properties of the original tissue. In this study, a new cellular model, suitable for the rapid in vitro determination of the above parameters, is presented. The cell model derives from a human osteosarcoma cell line, Saos-2, which maintained the cytological features of the osteoblast cells. The cell line was genetically modified to express constitutively the enhanced green fluorescent protein. The engineered cell line Saos-eGFP represents a suitable in vitro mode for studying the biocompatibility, the cell adhesion, spreading, and proliferation on biomaterials developed for clinical applications.

In vitro degradation characteristics of photocrosslinked anhydride systems for bone augmentation applications

In the past decade, injectable biomaterials that are capable of in situ formation have garnered increased interest for use in restorative orthopedic procedures. In this study, the in vitro degradation of photocrosslinked polyanhydride matrices, derived from methacrylic anhydrides of 1,6-bis(p-carboxyphenoxy)hexane (MCPH) and sebacic acid (MSA) were evaluated over a 6-week period under physiological conditions. These matrices were augmented with two additives--the reactive diluent poly(ethylene glycol) diacrylate (PEGDA) and the buffering agent calcium carbonate (CaCO3). Disk shaped specimens were produced by crosslinking the components using both chemical and photoinitiators and exposure to visible light. The experimental variables studied included: MCPH:MSA ratio, PEGDA molecular weight and weight fraction, and incorporation of CaCO3. The effects of these variables on local pH, water uptake, mass loss, and mechanical properties were explored. Increasing the MCPH:MSA ratio decreased the mass loss and water uptake at predetermined endpoints, and decreased buffer acidity during degradation. Both PEGDA and CaCO3 were found to decrease acidity and to reduce water uptake during degradation. Incorporation of CaCO3 enabled maintenance of compressive modulus during degradation. These results demonstrate that incorporation of reactive diluents and nonreactive additives into networks of photocrosslinked anhydrides can improve system properties as a material for bone replacement.

Interaction of a blood coagulation factor on electrically polarized hydroxyapatite surfaces

Although the polarization treatment of hydroxyapatite (HA) remarkably enhances the osteoconductivity, the mechanisms have not yet been completely understood. The interaction of proteins in blood and tissue fluids with biomaterials are reportedly triggers for later cellular responses and played a major role in osteoconductive processes. Considering this, we disclosed the interaction of polarized HA surface with a coagulation factor, fibrin stabilizing factor XIII (FXIII). The HA activated FXIII even in Ca2+ free buffer, based on the SDS-PAGE detections of alpha-polymer and gamma-dimer bands assigned to stabilized fibrin. The Ca2+ ions, possibly released from the HA surfaces, were examined whether they initiate the activation of the FXIII. It was experimentally proved by ICP analysis that the induced large negative charges on the electrically polarized HA significantly increased the released Ca2+ concentration for the short pre-incubation time of 3 min. The more Ca2+ ions released from the negatively charged HA (N-HA) surfaces were more effective in the activation of the FXIII, resulting in the rapider disappearance of the gamma-chain bands in fibrin. The slightly lower Ca2+ concentration in the positively charged HA, compared to the nonpolarized HA activated the FXIII at an almost equal rate. The accelerated activation contributed to the stabilization of fibrin scaffold. Therefore, the polarity difference of the induced charges of the polarized HA surface altered the rate of the FXIII activation. The early stage interaction of the HA surfaces with blood proteins was considered to be an essential process of the accelerated new bone formation near implanted N-HA surface.