Collagen Type I Increases Bone Remodelling around Hydroxyapatite Implants in the Rat Tibia

Probing the role of methyl methacrylate release from spacer materials in induced membrane bone healing

In the induced membrane (IM) technique for bone reconstruction, a poly(methyl methacrylate) (PMMA) spacer is implanted to induce formation of a foreign body membrane around the defect site. Membrane development is essential for later bone grafting success, yet the mechanism by which the IM promotes bone regeneration remains unknown, as are the ways that spacer composition plays a role in the membrane's healing potential. This study investigated the impact of leached methyl methacrylate (MMA)-the major monomeric component of PMMA-on IM development. In vitro cell culture found that MMA elution did not impact endothelial cell or mesenchymal stem cell proliferation. For in vivo analysis, we advanced a streamlined rat femoral model to efficiently study the influence of spacer properties on IM characteristics. Comparison of membrane formation around polycaprolactone (PCL), MMA-eluting PCL (high-dose PCL-MMA and low-dose PCL-MMA), and surgical PMMA revealed robust membranes enveloped all groups after 4 weeks in vivo, with elevated expression of osteogenic bone morphogenetic protein-2 and angiogenic vascular endothelial growth factor compared with the surrounding muscle and bone tissues. Growth factor quantitation in IM tissue found no statistically significant difference between groups. New bone growth, vascularization, and CD163+ macrophage populations surrounding the polymer implants were also quantified; and blood vessel formation around high-dose PCL-MMA was found to be significantly decreased compared with PCL alone. To the best of our knowledge, these findings represent the first time that results have been obtained about the characteristics of membranes formed around PCL in the IM setting.

The Effect of Low-Processing Temperature on the Physicochemical and Mechanical Properties of Bovine Hydroxyapatite Bone Substitutes

Bovine bone grafts (BBX) require protein removal as part of the manufacturing process to reduce antigenicity and, in consequence, to be safely used in humans. Deproteinisation may have direct effects on the characteristics of the bone material and on in vivo material performance. This research aimed to comprehensively study the physicochemical and mechanical properties of BBX processed at low deproteinisation processing temperatures. Cubes of bovine bone (8 mm³) were treated with temperatures between 100 °C and 220 °C at 30 °C intervals and with pressures ranging from 1.01 to 24.58 Bar. The samples were characterised topographically and mechanically using scanning electron microscopy (SEM), atomic force microscopy (AFM), and uniaxial bending tests. The organic content and the chemical composition were determined using thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FTIR). X-ray diffraction (XRD) and FTIR were also used to quantitatively determine the specimen crystallinity. Increasing temperature/pressure was associated with decreasing protein levels and compressive strength and increasing surface irregularities and crystallinity. The findings suggest that low-temperature processed bone is likely to exhibit a rapid in vivo degradation rate. The deproteinisation temperature can be adjusted to tailor the graft properties for specific applications.

Extracellular matrix containing nanocomposite bone graft in periodontal regeneration - A randomized controlled clinical and radiographic evaluation

Background

The study aims to evaluate the effect of adding extracellular matrix (ECM) component - natural collagen to nanocrystalline hydroxyapatite (nHA) bone graft in the treatment of intrabony defect in chronic periodontitis patients.

Materials and Methods

Forty chronic periodontitis patients having at least one intrabony defect were treated surgically by open flap debridement and the defect grafted (Group A: 20 sites grafted with nHA with natural collagen and Group B: 20 sites grafted with nHA). Plaque index, gingival index, probing pocket depth (PPD), clinical attachment level (CAL), and radiographic defect depth (RDD) were evaluated.

Results

The mean PPD reduced from 7.6 ± 0.88 at baseline to 4.45 ± 0.69 and 2.60 ± 0.6 at 3 and 6 months, respectively, in Group A. In Group B, the mean PPD reduced from 7.5 ± 0.89 at baseline to 4.95 ± 0.60 and 2.65 ± 0.59 at 3 and 6 months, respectively. The mean CAL reduced from 7.75 ± 0.85 at baseline to 5.05 ± 0.76 and 3.6 ± 0.68 at 3 and 6 months, respectively, in Group A. In Group B, the mean CAL reduced from 7.70 ± 0.86 at baseline to 5.8 ± 0.7 and 3.75 ± 0.64 at 3 and 6 months, respectively. The mean RDD reduced from 8.13 ± 0.78 and 8.12 ± 0.83 at baseline to 4.27 ± 0.66 and 3.94 ± 0.5 after 6 months in Groups A and B, respectively. After 3 months, a statistically significant reduction in mean PPD and CAL values was noted in Group A while the results were comparable after 6 months.

Conclusion

The effectiveness of nHA composite during initial healing phase (3 months) can be attributed to the presence of ECM-collagen in bone graft matrix.

Physiochemical characterization and biological effect of anorganic bovine bone matrix and organic-containing bovine bone matrix in comparison with Bio-Oss in rabbits

Bovine origin matrix has been widely used in clinical applications and investigated by various research institutions. However, the potential factors that influence bone regeneration are still not thoroughly understood and need further investigations. In this study, bone regeneration properties of anorganic bovine bone matrix (ABBM), organic-containing bovine bone matrix (OBBM), and widely acknowledged anorganic bovine bone matrix (Bio-Oss) were compared. Besides, the correlations between physiochemical characterizations and bone regeneration properties of the three xenografts were also investigated. Physiochemical characterizations were measured by special instrumentations. In animal studies, the three xenografts were implanted into 8-mm-diameter cranial defects of 16 New Zealand white rabbits. The biological effects were evaluated by micro-computed tomography and histomorphometric analysis after 6 and 12 weeks of implantation. The physical characterizations showed that anorganic bovine bone matrix and Bio-Oss had more nanostructures, larger surface area, bigger pore volume, and bigger pore size than that of organic-containing bovine bone matrix. The chemical characterizations showed that anorganic bovine bone matrix and Bio-Oss had higher crystallinity than that of organic-containing bovine bone matrix, and organic-containing bovine bone matrix contained organic nitrogen (N) component. In vivo, anorganic bovine bone matrix and Bio-Oss possessed better bone regeneration properties than that of organic-containing bovine bone matrix. Taken together, nanostructures, larger surface area, bigger pore volume, and bigger pore size of xenografts played an active role in new bone formation. Besides, lower crystallinity and organic N element of xenografts produced a positive effect on graft degradation. The abovementioned findings could provide theoretical basis for better choice in clinical applications and better manufacturing hydroxyapatite-derived bone graft in the future.

Osseous response on linear and cyclic RGD-peptides immobilized on titanium surfaces in vitro and in vivo

Biomimetic surface modifications of titanium (Ti) implants using the Arg-Gly-Asp-sequence (RGD) are promising to accelerate bone healing in cases of medical implants. Therefore, we compared the impact of linear and cyclic RGD (l- and c-RGD) covalently coupled onto Ti surfaces on the osseous response in vitro and in vivo. In vitro, osteoblasts' behavior on different surfaces (unmodified, amino-silanized [APTES], l- and c-RGD) was analysed regarding adhesion (fluorescence microscopy), proliferation (resazurin stain) and differentiation (reverse transcription polymerase chain reaction on alkaline phosphatase and osteocalcin). In vivo, osteosynthesis screws (unmodified n = 8, l-RGD n = 8, c-RGD n = 8) were inserted into the proximal tibiae of 12 rabbits and evaluated for bone growth parameters (bone implant contact [%] and vertical bone apposition [VBA;%]) at 3 and 6 weeks. In vitro, c- as well as l-RGD surfaces stimulated osteoblasts' adherence, proliferation and differentiation in a similar manner, with only subtle evidence of superiority of the c-RGD modifications. In vivo, c-RGD-modifications led to a significantly increased VBA after 3 and 6 weeks. Thus, coating with c-RGD appears to play an important role influencing osteoblasts' behaviour in vitro but especially in vivo. These findings can be applied prospectively to implantable biomaterials with hypothetically improved survival and success rates. © 2017 Wiley Periodicals Inc. J Biomed Mater Res Part A: 106A: 419-427, 2018.

SEM-EDX Study of the Degradation Process of Two Xenograft Materials Used in Sinus Lift Procedures

Some studies have demonstrated that in vivo degradation processes are influenced by the material’s physico-chemical properties. The present study compares two hydroxyapatites manufactured on an industrial scale, deproteinized at low and high temperatures, and how physico-chemical properties can influence the mineral degradation process of material performance in bone biopsies retrieved six months after maxillary sinus augmentation. Residual biomaterial particles were examined by field scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) to determine the composition and degree of degradation of the bone graft substitute material. According to the EDX analysis, the Ca/P ratio significantly lowered in the residual biomaterial (1.08 ± 0.32) compared to the initial composition (2.22 ± 0.08) for the low-temperature sintered group, which also presented high porosity, low crystallinity, low density, a large surface area, poor stability, and a high resorption rate compared to the high-temperature sintered material. This demonstrates that variations in the physico-chemical properties of bone substitute material clearly influence the degradation process. Further studies are needed to determine whether the resorption of deproteinized bone particles proceeds slowly enough to allow sufficient time for bone maturation to occur.

Surface Functionalization of Orthopedic Titanium Implants with Bone Sialoprotein

Orthopedic implant failure due to aseptic loosening and mechanical instability remains a major problem in total joint replacement. Improving osseointegration at the bone-implant interface may reduce micromotion and loosening. Bone sialoprotein (BSP) has been shown to enhance bone formation when coated onto titanium femoral implants and in rat calvarial defect models. However, the most appropriate method of BSP coating, the necessary level of BSP coating, and the effect of BSP coating on cell behavior remain largely unknown. In this study, BSP was covalently coupled to titanium surfaces via an aminosilane linker (APTES), and its properties were compared to BSP applied to titanium via physisorption and untreated titanium. Cell functions were examined using primary human osteoblasts (hOBs) and L929 mouse fibroblasts. Gene expression of specific bone turnover markers at the RNA level was detected at different intervals. Cell adhesion to titanium surfaces treated with BSP via physisorption was not significantly different from that of untreated titanium at any time point, whereas BSP application via covalent coupling caused reduced cell adhesion during the first few hours in culture. Cell migration was increased on titanium disks that were treated with higher concentrations of BSP solution, independent of the coating method. During the early phases of hOB proliferation, a suppressive effect of BSP was observed independent of its concentration, particularly when BSP was applied to the titanium surface via physisorption. Although alkaline phosphatase activity was reduced in the BSP-coated titanium groups after 4 days in culture, increased calcium deposition was observed after 21 days. In particular, the gene expression level of RUNX2 was upregulated by BSP. The increase in calcium deposition and the stimulation of cell differentiation induced by BSP highlight its potential as a surface modifier that could enhance the osseointegration of orthopedic implants. Both physisorption and covalent coupling of BSP are similarly effective, feasible methods, although a higher BSP concentration is recommended.

Nanoparticulate mineralized collagen scaffolds induce in vivo bone regeneration independent of progenitor cell loading or exogenous growth factor stimulation

Current strategies for skeletal regeneration often require co-delivery of scaffold technologies, growth factors, and cellular material. However, isolation and expansion of stem cells can be time consuming, costly, and requires an additional procedure for harvest. Further, the introduction of supraphysiologic doses of growth factors may result in untoward clinical side effects, warranting pursuit of alternative methods for stimulating osteogenesis. In this work, we describe a nanoparticulate mineralized collagen glycosaminoglycan scaffold that induces healing of critical-sized rabbit cranial defects without addition of expanded stem cells or exogenous growth factors. We demonstrate that the mechanism of osteogenic induction corresponds to an increase in canonical BMP receptor signalling secondary to autogenous production of BMP-2 and -9 early and BMP-4 later during differentiation. Thus, nanoparticulate mineralized collagen glycosaminoglycan scaffolds may provide a novel growth factor-free and ex vivo progenitor cell culture-free implantable method for bone regeneration.

BIOMATERIAL IMPLANTS IN BONE FRACTURES PRODUCED IN RATS FIBULAS

To evaluate the importance of collagen and hydroxyapatite in the regeneration of fractures experimentally induced in the fibulas of rats. Method: 15 rats were used. These were subjected to surgery to remove a fragment from the fibula. This site then received a graft consisting of a silicone tubes filled with hydroxyapatite and collagen. Results: Little bone neoformation occurred inside the tubes filled with the biomaterials. There was more neoformation in the tubes with collagen. Conclusion: The biomaterials used demonstrated biocompatibility and osteoconductive capacity that was capable of stimulating osteogenesis, even in bones with secondary mechanical and morphological functions such as the fibula of rats.

Comparison of human mesenchymal stem cells proliferation and differentiation on poly(methyl methacrylate) bone cements with and without mineralized collagen incorporation

Poly(methyl methacrylate) bone cement is widely used in vertebroplasty, joint replacement surgery, and other orthopaedic surgeries, while it also exposed many problems on mechanical property and biocompatibility. Better performance in mechanical match and bone integration is highly desirable. Recently, there reported that incorporation of mineralized collagen into poly(methyl methacrylate) showed positive results in mechanical property and osteointegration ability in vivo. In the present study, we focused on the comparison of osteogenic behavior between mineralized collagen incorporated in poly(methyl methacrylate) and poly(methyl methacrylate). Human marrow mesenchymal stem cells are used in this experiment. Adhesion and proliferation were used to characterize biocompatibility. Activity of alkaline phosphatase was used to assess the differentiation of human marrow mesenchymal stem cells into osteoblasts. Real-time PCR was performed to detect the expression of osteoblast-related markers at messenger RNA level. The results show that osteogenic differentiation on mineralized collagen incorporated in poly(methyl methacrylate) bone cement is more than two times higher than that of poly(methyl methacrylate) after culturing for 21 days. Thus, important mechanism on mineralized collagen incorporation increasing the osteogenetic ability of poly(methyl methacrylate) bone cement may be understood in this concern.

Oxidized Titanium Implants Enhance Osseointegration via Mechanisms Involving RANK/RANKL/OPG Regulation

BACKGROUND

The role of implant surface properties for bone formation and bone remodeling, that is, the major events during osseointegration, are incompletely understood.

PURPOSE

This experimental study aimed to investigate the relation between molecular and morphological patterns at the bone interface for machined and oxidized implants.

MATERIALS AND METHODS

Machined and anodically oxidized titanium implants were inserted in rat tibiae. The implants and surrounding tissue were retrieved at 1, 3, 6, 14, or 28 days for gene expression, histology, histomorphometry, backscatter scanning electron microscopy, and transmission electron microscopy.

RESULTS

Compared with machined-surface implants, a higher degree of mineralized bone was found in contact with the oxidized-surface implants. After 3 days, cells adherent to the oxidized implants demonstrated a markedly higher expression of receptor activator of nuclear factor kappa-B (RANK), receptor activator of nuclear factor kappa-B ligand (RANKL), and osteoprotegerin (OPG). Whereas the OPG expression was higher at the machined implants at 6, 14, and 28 days, a higher RANKL/OPG ratio was detected at the oxidized implants. Between 3 and 14 days, both implants demonstrated a temporal increase in RANKL/OPG, corresponding to the remodeling phase at the bone-implant interface. For both implant types, the RANKL/OPG ratio sharply decreased to a low level after 28 days.

CONCLUSIONS

The present results show that oxidized implants rapidly promote a high degree of mineralized bone apposition to the surface. As determined by the gene expression data, the mechanisms involve an early induction of osteoclastic differentiation and subsequently more intensive bone remodeling, which accelerates the maturation of the bone-implant interface. The present study suggests that the RANKL/OPG ratio is a sensitive indicator for monitoring the remodeling process during osseointegration.

ECM inspired coating of embroidered 3D scaffolds enhances calvaria bone regeneration

Resorbable polymeric implants and surface coatings are an emerging technology to treat bone defects and increase bone formation. This approach is of special interest in anatomical regions like the calvaria since adults lose the capacity to heal large calvarial defects. The present study assesses the potential of extracellular matrix inspired, embroidered polycaprolactone-co-lactide (PCL) scaffolds for the treatment of 13 mm full thickness calvarial bone defects in rabbits. Moreover the influence of a collagen/chondroitin sulfate (coll I/cs) coating of PCL scaffolds was evaluated. Defect areas filled with autologous bone and empty defects served as reference. The healing process was monitored over 6 months by combining a novel ultrasonographic method, radiographic imaging, biomechanical testing, and histology. The PCL coll I/cs treated group reached 68% new bone volume compared to the autologous group (100%) and the biomechanical stability of the defect area was similar to that of the gold standard. Histological investigations revealed a significantly more homogenous bone distribution over the whole defect area in the PCL coll I/cs group compared to the noncoated group. The bioactive, coll I/cs coated, highly porous, 3-dimensional PCL scaffold acted as a guide rail for new skull bone formation along and into the implant.

Embroidered and surface coated polycaprolactone-co-lactide scaffolds: a potential graft for bone tissue engineering

Tissue engineering and regenerative techniques targeting bone include a broad range of strategies and approaches to repair, augment, replace or regenerate bone tissue. Investigations that are aimed at optimization of these strategies until clinical translation require control of systemic factors as well as modification of a broad range of key parameters.

This article reviews a possible strategy using a tissue engineering approach and systematically describes a series of experiments evaluating the properties of an embroidered and surface coated polycaprolactone-co-lactide scaffold being considered as bone graft substitute for large bone defects. The scaffold design and fabrication, the scaffolds properties, as well as its surface modification and their influence in vitro are evaluated, followed by in vivo analysis of the scaffolds using orthotopic implantation models in small and large animals.

Surface modification of implants in long bone

Coatings of orthopedic implants are investigated to improve the osteoinductive and osteoconductive properties of the implant surfaces and thus to enhance periimplant bone formation. By applying coatings that mimic the extracellular matrix a favorable environment for osteoblasts, osteoclasts and their progenitor cells is provided to promote early and strong fixation of implants. It is known that the early bone ongrowth increases primary implant fixation and reduces the risk of implant failure. This review presents an overview of coating titanium and hydroxyapatite implants with components of the extracellular matrix like collagen type I, chondroitin sulfate and RGD peptide in different small and large animal models. The influence of these components on cells, the inflammation process, new bone formation and bone/implant contact is summarized.

Uncemented primary total hip arthroplasty, presentation of pain, and expression of osteonectin

Osteonectin (ON) is an important matrix glycoprotein highly expressed in bone. In several in vitro and animal model studies, ON was used as indicator of the state of osseointegration of implanted devices. There are, however, no studies on ON expression in the synovial fluid of patients with total hip joint replacement (THJR). The purpose of our study was to determine the ON concentration in synovial fluid from three groups of patients: primary uncemented THJR with hip pain ("pain" group; n = 15) and without pain ("no-pain" group; n = 12), and patients with osteoarthitis scheduled to receive a primary THJR (control group; n = 5). For the prosthesized groups, the statistical nature of the correlation between ON concentration and patient age, in situ life of the THJR, presence of periprosthetic osteolysis, and presence of debris in the synovial fluid was individually investigated. ON concentration was determined using enzyme-linked immunosorbent assay, the presence of periprosthetic osteolysis was established using X-radiography and Engh's criteria, and the presence of debris was determined using digestion and EDX spectroscopy. ON concentration was significantly lower in the "pain" group compared with the "no-pain" one (median values 19.0 and 53.2 ng/mL, respectively). ON concentration in the control group (median value: 16.9 ng/mL) was comparable with that reported in the literature. In the prosthesized groups, ON concentration was not correlated with patient age, in situ life of the prosthesis, presence of periprosthetic osteolysis, or presence of debris in the synovial fluid. Our results suggest that cases of unexplained pain in THJR patients could be treated by paying special attention to the osseointegration status of the implant by using ON concentration as an early indicator of this status.

Healing properties of surface-coated polycaprolactone-co-lactide scaffolds: A pilot study in sheep

The aim of this pilot study was to evaluate the bioactive, surface-coated polycaprolactone-co-lactide scaffolds as bone implants in a tibia critical size defect model. Polycaprolactone-co-lactide scaffolds were coated with collagen type I and chondroitin sulfate and 30 piled up polycaprolactone-co-lactide scaffolds were implanted into a 3 cm sheep tibia critical size defect for 3 or 12 months ( n = 5 each). Bone healing was estimated by quantification of bone volume in the defects on computer tomography and microcomputer tomography scans, plain radiographs, biomechanical testing as well as by histological evaluations. New bone formation occurred at the proximal and distal ends of the tibia in both groups. The current pilot study revealed a mean new bone formation of 63% and 172% after 3 and 12 months, respectively. The bioactive, surface coated, highly porous three-dimensional polycaprolactone-co-lactide scaffold stack itself acted as a guide rail for new bone formation along and into the implant. These preliminary data are encouraging for future experiments with a larger group of animals.

The pore size of PLGA bone implants determines the de novo formation of bone tissue in tibial head defects in rats

PURPOSE

The influence of the pore size of biodegradable poly(lactic-co-glycolic acid) scaffolds on bone regeneration was investigated.

METHODS

Cylindrical poly(lactic-co-glycolic acid) scaffolds were implanted into a defect in the tibial head of rats. Pore sizes of 100-300, 300-500, and 500-710 μm were tested and compared to untreated defects as control. Two and four weeks after implantation, the specimens were explanted and defect regeneration and de novo extracellular matrix generation were investigated by MRI, quantitative solid-state NMR, and mass spectrometry.

RESULTS

The pore size of the scaffolds had a pronounced influence on the quantity of the extracellular matrix synthesized in the graft; most collagen was synthesized within the first 2 weeks of implantation, while the amount of hydroxyapatite increased in the second 2 weeks. After 4 weeks, the scaffolds contained large quantities of newly formed lamellar bone while the control defects were filled by inhomogenous woven bone. Best results were obtained for scaffolds of a pore size of 300-500 μm.

CONCLUSION

Our analysis showed that the structure and dynamics of the regenerated extracellular matrix was very similar to that of the native bone, suggesting that biomineralization was significantly enhanced by the choice of the most appropriate implant material.

31P and 13C solid-state NMR spectroscopy to study collagen synthesis and biomineralization in polymer-based bone implants

A combination of solid-state NMR spectroscopy and MRI was used to evaluate the formation of extracellular matrix in poly(D,L-lactide-co-glycolide) (PLGA) bone implants. Porous PLGA scaffolds were implanted into rat tibiae and analysed after 2, 4 or 8 weeks. MRI clearly delineated the implants within the cancellous bone. Differences in the trabecular structure of the implanted material and native bone were demonstrated. In addition, implants were analyzed by solid-state NMR spectroscopy under magic angle spinning. (13)C NMR spectra showed the unambiguous signature of collagen formed in the scaffolds, but also the characteristic signals of the PLGA matrix, indicating that resorption was not complete after 8 weeks. Furthermore, (31)P NMR spectroscopy detected the inorganic component of the matrix, which is composed of bioapatite. (31)P NMR spectra were quantified and this analysis revealed that the amount of inorganic extracellular matrix formed de novo was significantly lower than in native bone. This demonstrates that solid-state NMR spectroscopy, in particular in combination with MRI, can provide useful information on the composition and structure of the extracellular matrix, and serve as a tool to evaluate the quality of tissue engineering strategies.

Biomimetic composite coating on rapid prototyped scaffolds for bone tissue engineering

The objective of this present study was to improve the functional performance of rapid prototyped scaffolds for bone tissue engineering through biomimetic composite coating. Rapid prototyped poly(ε-caprolactone)/tri-calcium phosphate (PCL/TCP) scaffolds were fabricated using the screw extrusion system (SES). The fabricated PCL/TCP scaffolds were coated with a carbonated hydroxyapatite (CHA)-gelatin composite via biomimetic co-precipitation. The structure of the prepared CHA-gelatin composite coating was studied by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Compressive mechanical testing revealed that the coating process did not have any detrimental effect on the mechanical properties of the scaffolds. The cell-scaffold interaction was studied by culturing porcine bone marrow stromal cells (BMSCs) on the scaffolds and assessing the proliferation and bone-related gene and protein expression capabilities of the cells. Confocal laser microscopy and SEM images of the cell-scaffold constructs showed a uniformly distributed cell sheet and accumulation of extracellular matrix in the interior of CHA-gelatin composite-coated PCL/TCP scaffolds. The proliferation rate of BMSCs on CHA-gelatin composite-coated PCL/TCP scaffolds was about 2.3 and 1.7 times higher than that on PCL/TCP scaffolds and CHA-coated PCL/TCP scaffolds, respectively, by day 10. Furthermore, reverse transcription polymerase chain reaction and Western blot analysis revealed that CHA-gelatin composite-coated PCL/TCP scaffolds stimulate osteogenic differentiation of BMSCs the most, compared with PCL/TCP scaffolds and CHA-coated PCL/TCP scaffolds. These results demonstrate that CHA-gelatin composite-coated rapid prototyped PCL/TCP scaffolds are promising for bone tissue engineering.

Enhancement of peptide coupling to hydroxyapatite and implant osseointegration through collagen mimetic peptide modified with a polyglutamate domain

Hydroxyapatite (HA) is a widely-used biomaterial for bone repair due to its high degree of osteoconductivity. However, strategies for improving HA performance by functionalizing surfaces with bioactive factors are limited. In this study, we explored the use of a HA-binding domain (heptaglutamate, "E7") to facilitate coupling of the collagen mimetic peptide, DGEA, to two types of HA-containing materials, solid HA disks and electrospun polycaprolactone matrices incorporating nanoparticulate HA. We found that the E7 domain directed significantly more peptide to the surface of HA and enhanced peptide retention on both materials in vitro. Moreover, E7-modified peptides were retained in vivo for at least two months, highlighting the potential of this mechanism as a sustained delivery system for bioactive peptides. Most importantly, E7-DGEA-coupled HA, as compared with DGEA-HA, enhanced the adhesion and osteoblastic differentiation of mesenchymal stem cells, and also increased new bone formation and direct bone-implant contact on HA disks implanted into rat tibiae. Collectively, these results support the use of E7-DGEA peptides to promote osteogenesis on HA substrates, and further suggest that the E7 domain can serve as a universal tool for anchoring a wide variety of bone regenerative molecules to any type of HA-containing material.

Repair of large cranial defects by hBMP-2 expressing bone marrow stromal cells: comparison between alginate and collagen type I systems

Despite a wide range of available sources for bone repair, significant limitations persist. To bioengineer bone, we have previously transferred adenovirus-mediated human BMP-2 gene into autologous bone marrow stromal cells (MSC). We have successfully repaired large, full thickness, cranial defects using this approach. We report now the effectiveness of various hydrogels as the scaffold for this type of bone regeneration, comparing specifically alginate with Type I collagen. Cultured MSC of miniature swine were infected with BMP-2 or beta-gal adenovirus 7 days before implantation. These cells were mixed with alginate, ultrapure alginate, alginate-RGD, or type I collagen to fabricate the MSC/biomaterial constructs. The results of cranial bone regeneration were assessed by gross examination, histology, 3D CT, and biomechanical tests at 6 weeks and 3 months after implantation. We found that the BMP-2 MSC/collagen type I construct, but not the beta-gal control, effectively achieved nearly complete repair of the cranial defects. No bone regeneration was observed with the other hydrogels. Biomechanical testing showed that the new bone strength was very close and only slightly inferior to that of normal cranial bone. Controlling for the integration of stem cells and ex vivo gene transfer, the alginate scaffolds has a significant negative impact on the success of the construct. Our study demonstrates better bone regeneration by collagen type I over alginate. This may have therapeutic implications for tissue engineered bone repair.

Improvement on the performance of bone regeneration of calcium sulfate hemihydrate by adding mineralized collagen

Comparative investigations of bone regeneration performance for calcium sulfate hemihydrate (CaSO(4).(1/2)H(2)O; CSH) only and CSH with mineralized collagen are reported in this article. The mineralized collagen is the nanohydroxyapatite/collagen (nHAC). The investigations included biocompatibility in vitro and performance of bone repair in vivo. Quantitative and qualitative biocompatibility assays with bone stromal stem cells were performed. A critical box-shaped defect model in the mandible of the rabbit was used to evaluate the bone-remodeling ability of CSH and nHAC/CSH. Results in vitro indicated that the nHAC/CSH significantly improved bioactivity compared with that of CSH, especially in promoting cell adhesion. Further, a higher bone remodeling activity was observed around nHAC/CSH composite than the CSH, especially at the early stage of remodeling. This result means that nHAC/CSH could cause an earlier accelerator and better osseointegration for bone repair than CSH only.

Effects of crystalline phase on the biological properties of collagen-hydroxyapatite composites

The objective of this study was to investigate the effects of spatial structure and crystalline phase on the biological performance of collagen-hydroxyapatite (Col-HA) composite prepared by biomineralization crystallization. Two types of Col-HA composites were prepared using mineralization crystallization (MC composites) and pre-crystallization (PC composites), respectively. Structural characteristics were analyzed by scanning electron microscopy and transmission electron microscopy. Surface elemental compositions were measured by electron spectroscopy for chemical analysis (ESCA). These composites were used in in vivo repair of bone defects. The effects of the crystalline phase on the biological performance of Col-HA composites were investigated using radionuclide bone scan, histopathology and morphological observation. It was observed that in MC composites, HA was located on the surface of the collagen fibers and aggregated into crystal balls, whereas HA in PC composites was scattered among the collagen fibers. ESCA showed that phosphorus and calcium were 8.99% and 17.56% on MC composite surface, compared with 4.39% and 5.86% on the PC composite surface. In vivo bone defect repair experiments revealed that radionuclide uptake was significantly higher in the area implanted with the PC composite than in the contralateral area implanted with the MC composite. Throughout the whole repair process, the PC composite proved to be superior to the MC composite with regard to capillary-forming capacity and the amount of newly formed bone tissue. So it could be concluded that HA placement on collagen fibers affected the biological performance of Col-HA composites. Pre-crystallization made HA scattered among collagen fibers, creating a better structure for bone defect repair in comparison with MC Col-HA composites.

The effect on bone growth enhancement of implant coatings with hydroxyapatite and collagen deposited electrochemically and by plasma spray

Skeletal bone consists of hydroxyapatite (HA) [Ca(10)(PO(4))(6)(OH)(2)] and collagen type I, both of which are osseoconductive. The goal of osseointegration of orthopedic and dental implants is the rapid achievement of a mechanically stable long-lasting fixation between bone and an implant surface. In this study, we evaluated the mechanical fixation and tissue distribution surrounding implants coated with three surfaces: plasma-sprayed HA coating, thinner coating of electrochemical-assisted deposition of HA, and an identical thin coating with a top layer of mineralized collagen. Uncoated plasma-sprayed titanium (Ti-6Al-4V) served as negative control. The electrochemical-assisted deposition was performed near physiological conditions. We used a canine experimental joint replacement model with four cylindrical implants (one of each treatment group) inserted in the humeri cancellous metaphyseal bone in a 1 mm gap. Observation time was 4 weeks. The mechanical fixation was quantified by push-out test to failure, and the peri-implant tissue formation by histomorphometric evaluation. HA coatings deposited by plasma spray technique or electrochemically, increased the mechanical fixation and bone ongrowth, but there was no statistical difference between the individual HA applications. Addition of collagen to the mineralized phase of the coating to create a more bone natural surface did not improve the osseoconductive effect of HA.

Influence of different modifications of a calcium phosphate bone cement on adhesion, proliferation, and osteogenic differentiation of human bone marrow stromal cells

Collagen and noncollagenous proteins of the extracellular bone matrix are able to stimulate bone cell activities and bone healing. The modification of calcium phosphate bone cements used as temporary bone replacement materials with these proteins seems to be a promising approach to accelerate new bone formation. In this study, we investigated adhesion, proliferation, and osteogenic differentiation of human bone marrow stromal cells (hBMSC) on Biocement D/collagen composites which have been modified with osteocalcin and O-phospho-L-serine. Modification with osteocalcin was carried out by its addition to the cement precursor before setting as well as by functionalization of the cement samples after setting and sterilization. hBMSC were cultured on these samples for 28 days with and without osteogenic supplements. We found a positive impact especially of the phosphoserine-modifications but also of both osteocalcin-modifications on differentiation of hBMSC indicated by higher expression of the osteoblastic markers matrix metalloproteinase-13 and bone sialo protein II. For hBMSC cultured on phosphoserine-containing composites, an increased proliferation has been observed. However, in case of the osteocalcin-modified samples, only osteocalcin adsorbed after setting and sterilization of the cement samples was able to promote initial adhesion and proliferation of hBMSC. The addition of osteocalcin before setting results in a finer microstructure but the biological activity of osteocalcin might be impaired due to the sterilization process. Thus, our data indicate that the initial adhesion and proliferation of hBMSC is enhanced rather by the biological activity of osteocalcin than by the finer microstructure.

Mechanical performance and in vivo tests of an acrylic bone cement filled with bioactive sepia officinalis cuttlebone

To promote osteointegration, bioactive cuttlebone particles containing collagen were used to fill an acrylic cement, varying filler concentration (0-50 wt%). Cuttlebone was characterized by X-ray diffraction, plasma atomic emission and FT-IR. Mechanical properties of the filled cement were determined following ASTM procedures, included stress-strain, compression, bending, and fracture toughness tests. For in vivo tests, three groups of seven adult healthy rabbits were prepared to make an implant in the parietal bone of each one. For such groups (I-III), the amount of filler in the cement was 0, 10 and 30 wt%, respectively. Mechanical results for the composites complied with norm requirements. However, as mechanical performance for composite with 50 wt% of filler decreased significantly, for the in vivo tests, such composite was excluded. In vivo tests showed that three implants of group I were loosely attached to the parietal bone, whereas all the implants made with cement containing cuttlebone particles (groups II and III) were firmly attached to the parietal bone, indicating osteointegration. These results clearly show the potential of this type of bioactive filler to be used for medical applications.

Heparin modification of calcium phosphate bone cements for VEGF functionalization

A promising strategy to promote angiogenesis within an engineered tissue is the local and sustained delivery of an angiogenic factor by the substitute itself. Recently, we reported on functionalization of Biocement D (BioD) and several modifications of this calcium phosphate bone cement with vascular endothelial growth factor (VEGF). Maintenance of biological activity of VEGF after release from the cement was improved by modification of BioD with mineralized collagen type I (BioD/coll). However, BioD/coll composites showed a higher initial burst of VEGF release than do the unmodified BioD. In the present study, VEGF release from BioD/coll composites modified with different amounts of heparin was investigated. We found a distinct reduction of the initial burst of release by adding heparin in a concentration-dependent manner. Moreover, the heparin modification had a positive impact on the biological activity of released VEGF. An advancement of biological properties of BioD/coll by addition of heparin was further shown by improved adhesion of endothelial cells on the cement surface. Characterization of material properties of the heparin-modified BioD/coll composites revealed a finer microstructure with smaller HA-particles and a higher specific surface area than heparin-free BioD/coll. However, higher amounts of heparin resulted in a reduced compressive strength. The rheological properties of these cement pastes have been found to be favorable for good handling particularly with regard to their clinical application.

Effect of bone sialoprotein and collagen coating on cell attachment to TICER and pure titanium implant surfaces

To improve integration between implants and biological tissues, this study compared bone sialoprotein (BSP) as a surface-coating material against the major organic and inorganic components of bone, collagen type I and hydroxyapatite (TICER). The expression of osteocalcin, osteonectin and transforming growth factor ss was evaluated using immunohistochemical staining procedures. The distribution patterns of osteoblasts on the surface of pure titanium with a smooth machined surface and a rough surface (TICER) were determined by image processing using confocal laser scanning microscopy. The results compared to uncoated control materials showed that, at all times investigated, the number of cells on the surface of the TICER and pure titanium samples differed significantly (P<0.1), demonstrating the superiority of TICER over pure titanium in this respect. For pure titanium implants, collagen-precoated surfaces were not beneficial for the attachment of bone-derived cells with the exception of day 3 in vitro (P<0.01). BSP-precoated implant surfaces displayed non-significantly higher numbers of settled cells. BSP-precoated implant surfaces were beneficial for osteoinduction as revealed by osteocalcin and osteonectin expression. BSP precoating of the rough TICER implant surface enhanced the osteoinductive effect much more than did collagen precoating. These results contribute to the consideration of at least two distinct pathways of osseointegration.

Effect of chondroitin sulphate on material properties and bone remodelling around hydroxyapatite/collagen composites

Chondroitin sulphate (CS) has an anti-inflammatory effect and increases the regeneration ability of injured bone. The goal of this study was to characterize the material properties and osteoconductive potency of calcium phosphate bone cements modified with CS. The early interface reaction of cancellous bone to a nanokristalline hydroxyapatite cement containing type I collagen (HA/Coll) without and with CS (HA/Coll/CS) in a rat tibia model was evaluated. Cylindrical implants were inserted press-fit into defect of the tibial head. Six specimens per group were analyzed at 2, 4, 7, 14, and 28 days. HA/Coll/CS composite cylinders showed a 15% increase in compressive strength and by investigations with powder X-ray diffraction more nontransformed cement precursor was found. The microstructures of both types of implants were similar. A significantly higher average number of TRAP positive osteoclasts and ED1 positive mononuclear cells were observed in the interface around HA/Coll/CS implants on day 4 and 7 (p < 0.05). At 28 days the direct bone contact and the percentage of newly formed bone were significantly higher around HA/Coll/CS implants (p < 0.05). The addition of CS appears to enhance bone remodelling and new bone formation around HA/Coll composites in the early stages of bone healing. Possible mechanisms are discussed.

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.

In vivo effects of coating loaded and unloaded Ti implants with collagen, chondroitin sulfate, and hydroxyapatite in the sheep tibia

The in vivo effects of coating titanium implants with organic extracellular matrix molecules were examined in the sheep tibia. Titanium screws (5.0 mm) were coated with type I collagen (Ti/Coll) or type I collagen and chondroitin sulfate (Ti/Coll/CS) by biomimetic fibrillogenesis. Uncoated screws (Ti) and screws coated with hydroxyapatite (Ti/HA) served as control. Six adult female sheep received one screw of each type to stabilize a midshaft tibial fracture with external fixation. Four cylindrical implants of 4-mm outer diameter and 3.3-mm inner diameter with the same coatings were inserted into the tibial head. No pin track infections were seen at the time of implant retrieval 6 weeks after implantation. Extraction torque was greater for Ti/HA (1181 Nmm) and Ti/Coll/CS (1088 Nmm) compared to Ti/Coll (900 Nmm) and Ti (904 Nmm) [N.S.]. Newly formed bone was noted around all coated screws within the medullary cavity. Macrophage and osteoclast activity was significantly reduced around Ti/Coll/CS in both types of implants compared to uncoated controls (p < 0.05). Osteoblast activity was significantly increased around loaded Ti/Coll and Ti/Coll/CS screws compared to uncoated Ti screws (p < 0.05). Microtomographic evaluation (SRmicroCT) revealed no significant differences in new bone formation around the unloaded tibial head implants. Coating of external fixation devices with of type I collagen and chondroitin sulfate appears to have similar effects with respect to stability and bone healing as HA but with less osteoclast activity. These findings were more pronounced under loaded than unloaded conditions in the sheeptibia.

Calcium phosphate bone cements, functionalized with VEGF: release kinetics and biological activity

Calcium phosphate bone cements are of great interest for bone replacement since the nanocrystalline structure allows their remodelling into native bone tissue. A strategy to accelerate vascularization of the implant region is the functionalization with vascular endothelial growth factor (VEGF), which is known to mediate angiogenesis in vivo. In this study, the release of recombinant human VEGF (rhVEGF(165)) following physical adsorption to Biocement D (BioD) and several modifications were investigated. Our data demonstrate a high VEGF binding capacity of BioD and a sustained release with a moderate initial burst. A proliferation assay using endothelial cells revealed maintenance of biological activity of VEGF after release from BioD. Release behavior of BioD was not improved by modification with mineralized collagen type I, as well as with a combination of mineralized collagen with O-phospho-L-serine and sodium citrate, respectively. In contrast, a positive impact of these modifications on the activity of released VEGF was observed; in case of the phosphoserine- and sodium citrate-modified cements, the biological efficacy of released VEGF was even higher than that of nonreleased control VEGF. We conclude that the bone implant material BioD and, especially, the phosphoserine modification may support activation of angiogenesis by delivery of VEGF in a local and sustained manner.

Ceramic composites as matrices and scaffolds for drug delivery in tissue engineering

Ceramic composites and scaffolds are popular implant materials in the field of dentistry, orthopedics and plastic surgery. For bone tissue engineering especially CaP-ceramics or cements and bioactive glass are suitable implant materials due to their osteoconductive properties. In this review the applicability of these ceramics but also of ceramic/polymer composites for bone tissue engineering is discussed, and in particular their use as drug delivery systems. Overall, the high density and slow biodegradability of ceramics is not beneficial for tissue engineering purposes. To address these issues, macroporosity can be introduced often in combination with osteoinductive growth factors and cells. Ceramics are good carriers for drugs, in which release patterns are strongly dependent on the chemical consistency of the ceramic, type of drug and drug loading. Biodegradable polymers like polylactic acid, gelatin or chitosan are used as matrices for ceramic particles or as adjuvant to calcium phosphate cements. The use of these polymers can introduce a tailored biodegradation/drug release to the ceramic material.

Influence of recovering collagen with bioactive glass on osteoblast behavior

Bioactive ceramics have interesting properties from the biological standpoint, but their effects on cellular events remain partially unknown. In the current work, we investigated cellular viability, proliferation, and metabolic activity of rat primary osteoblasts in contact with four different samples: type I collagen, bioactive glass-coated collagen (GC), and both samples submitted to immersion for 5 days in a simulated body fluid. The bioactive glass coating was obtained from a sol-gel process. The cell viability, the alkaline phosphate, the collagen secretion, and the nitric oxide production by osteoblast were measured after 72 h of incubation in the presence of the samples. The GC that was immersed for 5 days in a simulated body fluid solution showed an increase in osteoblast viability and proliferation when it was compared with control and the other samples.

Coating of titanium implants with collagen, RGD peptide and chondroitin sulfate

Coating of orthopaedic implants with extracellular bone matrix components was performed to enhance bone healing. Titanium pins of 0.8mm diameter were coated with type I collagen (Ti/Coll), RGD peptide (Ti/RGD) or type I collagen and chondroitin sulfate (Ti/Coll/CS). Uncoated pins (Ti) served as control. The pins were inserted as intramedullary nails into the tibia of male adult Wistar rats. Six specimens of each group were retrieved at 4, 7, 14 and 28 days. All implants healed uneventfully without adverse reactions. ED 1-positive macrophages appeared in higher numbers around Ti/RGD at day 4 and around Ti at day 14 after implantation (p < 0.05). TRAP-positive osteoclasts and precursors were abundant around Ti/Coll/CS at day 7 (p < 0.05). A significant increase in osteopontin-positive osteoblasts was seen around Ti/Coll/CS implants at days 7 and 14, and around Ti/RGD at day 14 (p < 0.05). At day 28, 62% of Ti, 76% of Ti/Coll, 85%* of Ti/RGD and 89%* of Ti/CoIl/CS (*p < 0.05) implants were covered with newly formed lamellar bone. The addition of extracellular matrix components significantly enhances bone remodelling in the early stages of bone healing around Ti implants, eventually leading to increased new bone formation at the implant surface after 4 weeks.