Apatite nano-crystalline surface modification of poly(lactide-co-glycolide) sintered microsphere scaffolds for bone tissue engineering: implications for protein adsorption

A number of bone tissue engineering approaches are aimed at (i) increasing the osteconductivity and osteoinductivity of matrices, and (ii) incorporating bioactive molecules within the scaffolds. In this study we examined the growth of a nano-crystalline mineral layer on poly(lactide-co-glycolide) (PLAGA) sintered microsphere scaffolds for tissue engineering. In addition, the influence of the mineral precipitate layer on protein adsorption on the scaffolds was studied. Scaffolds were mineralized by incubation in simulated body fluid (SBF). Scanning electron microscopy (SEM) analysis revealed that mineralized scaffolds possess a rough surface with a plate-like nanostructure covering the surface of microspheres. The results of protein adsorption and release studies showed that while the protein release pattern was similar for PLAGA and mineralized PLAGA scaffolds, precipitation of the mineral layer on PLAGA led to enhanced protein adsorption and slower protein release. Mineralization of tissue-engineered surfaces provides a method for both imparting bioactivity and controlling levels of protein adsorption and release.     

Apatite nano-crystalline surface modification of poly(lactide-co-glycolide) sintered microsphere scaffolds for bone tissue engineering: implications for protein adsorption

A number of bone tissue engineering approaches are aimed at (i) increasing the osteconductivity and osteoinductivity of matrices, and (ii) incorporating bioactive molecules within the scaffolds. In this study we examined the growth of a nano-crystalline mineral layer on poly(lactide-co-glycolide) (PLAGA) sintered microsphere scaffolds for tissue engineering. In addition, the influence of the mineral precipitate layer on protein adsorption on the scaffolds was studied. Scaffolds were mineralized by incubation in simulated body fluid (SBF). Scanning electron microscopy (SEM) analysis revealed that mineralized scaffolds possess a rough surface with a plate-like nanostructure covering the surface of microspheres. The results of protein adsorption and release studies showed that while the protein release pattern was similar for PLAGA and mineralized PLAGA scaffolds, precipitation of the mineral layer on PLAGA led to enhanced protein adsorption and slower protein release. Mineralization of tissue-engineered surfaces provides a method for both imparting bioactivity and controlling levels of protein adsorption and release.     

Delivery of VEGF using collagen-coated polycaprolactone scaffolds stimulates angiogenesis

Establishing sufficient vascularization in scaffold remains a challenge for tissue-engineering. To improve angiogenesis, we incorporated vascular endothelial growth factor (VEGF) in collagen-coating over the porous polycaprolactone (PCL) scaffolds. The release kinetics of loaded VEGF from collagen-coated PCL (col-PCL) scaffolds was same as from scaffolds without the collagen. The bioactivity of VEGF delivered by the col-PCL scaffolds was confirmed by human umbilical vein endothelial cell (HUVEC) proliferation and chorioallantoic membrane (CAM) assay. The col-PCL scaffolds were implanted subcutaneously in mice for 7 and 14 days. At day 7, vascularization within scaffolds loaded with VEGF was superior to that in the scaffolds without VEGF. However, the vessel connectivity to host circulatory system was incomplete and restricted to the scaffold edges. At day 14, blood vessels in scaffolds reached density similar to the subcutaneous tissue and were perfusable throughout the implant thickness. Prewashing the scaffolds with saline to remove the unbound growth factor decreased the initial burst release and sustained the VEGF-mediated angiogenesis in vivo. In conclusion, our study demonstrates that physically adsorbed VEGF stimulated angiogenesis in collagen-coated PCL scaffolds.     

Coating of VEGF-releasing scaffolds with bioactive glass for angiogenesis and bone regeneration

Bioactive glasses are potentially useful as bone defect fillers, and vascular endothelial growth factor (VEGF) has demonstrated benefit in bone regeneration as well. We hypothesized that the specific combination of prolonged localized VEGF presentation from a matrix coated with a bioactive glass may enhance bone regeneration. To test this hypothesis, the capacity of VEGF-releasing polymeric scaffolds with a bioactive glass coating was examined in vitro and in vivo using a rat critical-sized defect model. In the presence of a bioactive glass coating, we did not detect pronounced differences in the differentiation of human mesenchymal stem cells in vitro. However, we observed significantly enhanced mitogenic stimulation of endothelial cells in the presence of the bioactive glass coating, with an additive effect with VEGF release. This trend was maintained in vivo, where coated VEGF-releasing scaffolds demonstrated significant improvements in blood vessel density at 2 weeks versus coated control scaffolds. At 12 weeks, bone mineral density was significantly increased in coated VEGF-releasing scaffolds versus coated controls, while only a slight increase in bone volume fraction was observed. The results of this study suggest that a bioactive glass coating on a polymeric substrate participates in bone healing through indirect processes which enhance angiogenesis and bone maturation and not directly on osteoprogenitor differentiation and bone formation. The mass of bioactive glass used in this study provides a comparable and potentially additive, response to localized VEGF delivery over early time points. These studies demonstrate a materials approach to achieve an angiogenic response formerly limited to the delivery of inductive growth factors.     

Extracellular matrix formation and mineralization on a phosphate-free porous bioactive glass scaffold using primary human osteoblast (HOB) cells

Sol-gel derived bioactive glasses of the 70S30C (70mol% SiO2, 30mol% CaO) composition have been foamed to produce 3D bioactive scaffolds with hierarchical interconnected pore morphologies similar to trabecular bone. The aim of this study was to investigate primary human osteoblast response to porous bioactive glass scaffolds. The scaffolds supported osteoblast growth and induced differentiation, within the 3-week culture period, as depicted by enhanced ALPase enzymatic activity, without the addition of supplementary factors such as ascorbic acid, beta-glycerophosphate and dexamethasone. This is the first time this has been observed on a bioactive glass that does not contain phosphate. Deposition of extracellular matrix was also confirmed by enhanced production of the extracellular matrix protein collagen type I. SEM showed indications of mineralized bone nodule formation without the addition of growth factors. The 70S30C bioactive glass scaffolds therefore fulfil many of the criteria for an ideal scaffold for bone tissue engineering applications.     

The enhancement of osteogenesis by nano-fibrous scaffolds incorporating rhBMP-7 nanospheres

It is advantageous to incorporate controlled growth factor delivery into tissue engineering strategies. The objective of this study was to develop a three-dimensional (3D) porous tissue engineering scaffold with the capability of controlled releasing recombinant human bone morphogenetic protein-7 (rhBMP-7) for enhancement of bone regeneration. RhBMP-7 was first encapsulated into poly(lactic-co-glycolic acid) (PLGA) nanospheres (NS) with an average diameter of 300nm. Poly(l-lactic acid) (PLLA) scaffolds with interconnected macroporous and nano-fibrous architectures were prepared using a combined sugar sphere template leaching and phase separation technique. A post-seeding technique was then utilized to immobilize rhBMP-7 containing PLGA nanospheres onto prefabricated nano-fibrous PLLA scaffolds with well-maintained 3D structures. In vitro release kinetics indicated that nanosphere immobilized scaffold (NS-scaffold) could release rhBMP-7 in a temporally controlled manner, depending on the chemical and degradation properties of the NS which were immobilized onto the scaffold. In vivo, rhBMP-7 delivered from NS-scaffolds induced significant ectopic bone formation throughout the scaffold while passive adsorption of rhBMP-7 into the scaffold resulted in failure of bone induction due to either the loss of rhBMP-7 biological function or insufficient duration within the scaffold. We conclude that the interconnected macroporous architecture and the sustained, prolonged delivery of bioactive rhBMP-7 from NS immobilized nano-fibrous scaffolds actively induced new bone formation throughout the scaffold. The approach offers a new delivery method of BMPs and a novel scaffold design for bone regeneration.     

Growth of continuous bonelike mineral within porous poly(lactide-co-glycolide) scaffolds in vitro

Strategies to engineer bone have focused on the use of natural or synthetic degradable materials as scaffolds for cell transplantation or as substrates to guide bone regeneration. The basic requirements of the scaffold material are biocompatibility, degradability, mechanical integrity, and osteoconductivity. A major design problem is satisfying each of these requirements with a single scaffold material. This study addresses this problem by describing an approach to combine the biocompatibility and degradability of a polymer scaffold with the osteoconductivity and mechanical reinforcement of a bonelike mineral film. We report the nucleation and growth of a continuous carbonated apatite mineral on the interior pore surfaces of a porous, degradable polymer scaffold via a one step, room temperature incubation process. A 3-dimensional, porous scaffold of the copolymer 85:15 poly(lactide-co-glycolide) was fabricated by a solvent casting, particulate leaching process. Fourier transform IR spectroscopy and scanning electron microscopy (SEM) analysis after different incubation times in a simulated body fluid (SBF) demonstrate the growth of a continuous bonelike apatite layer within the pores of the polymer scaffold. Quantification of phosphate on the scaffold displays the growth and development of the mineral film over time with an incorporation of 0.43 mg of phosphate (equivalent to 0.76 mg of hydroxyapatite) per scaffold after 14 days in SBF. The compressive moduli of polymer scaffolds increased fivefold with formation of a mineral film after a 16-day incubation time as compared to control scaffolds. In summary, this biomimetic treatment provides a simple, one step, room temperature method for surface functionalization and subsequent mineral nucleation and growth on biodegradable polymer scaffolds for tissue engineering.     

胶原多糖基纳米羟基磷灰石仿生骨支架材料的研制

目的依据仿生原理制备新型的胶原多糖基纳米羟基磷灰石（HA）复合骨支架材料,并与成骨细胞复合培养,检测其细胞相容性。方法以胶原分子与透明质酸钠的交联产物为模板,调制钙磷盐在液相中沉积其上,得到矿化胶原多糖基复合材料;采用液相分离法与少量聚乳酸复合进一步制备成为三维多孔支架,使用成骨细胞（Mc3T3-E1）接种于该支架上培养。用X—ray衍射、扫描电镜、万能材料测试机等对材料进行观察和测试分析;并用倒置相差显微镜、荧光显微镜、扫描电镜、CCK-8细胞计数试剂盒、碱性磷酸酶（ALP）活性测定等观察和分析细胞在支架材料中的生长、分化情况。结果胶原多糖基纳米HA仿生复合材料的晶粒度较低,晶体极为细小,与天然骨中羟基磷灰石的组装结构类似;该复合支架为多孔状,孔隙率约82％,孔径大小为200～650μm;抗压性能好,成骨细胞可在其上贴附、生长和繁殖,并表现出较高的成骨活性。结论所制备的胶原多糖基纳米HA仿生骨支架材料,无论从组分和结构上均与天然松质骨类似,与成骨细胞相容性好,可望成为较理想的骨组织工程支架材料。     

The effect of mesenchymal populations and vascular endothelial growth factor delivered from biodegradable polymer scaffolds on bone formation

The capacity to deliver, temporally, bioactive growth factors in combination with appropriate progenitor and stem cells to sites of tissue regeneration promoting angiogenesis and osteogenesis offers therapeutic opportunities in regenerative medicine. We have examined the bone regenerative potential of encapsulated vascular endothelial growth factor (VEGF(165)) biodegradable poly(DL-lactic acid) (PLA) scaffolds created using supercritical CO(2) fluid technology to encapsulate and release solvent-sensitive and thermolabile growth factors in combination with human bone marrow stromal cells (HBMSC) implanted in a mouse femur segmental defect (5 mm) for 4 weeks. HBMSC seeded on VEGF encapsulated PLA scaffolds showed significant bone regeneration in the femur segmental defect compared to the scaffold alone and scaffold seeded with HBMSC as analysed by indices of increased bone volume (BV mm(3)), trabecular number (Tb.N/mm) and reduced trabecular separation (Tb.Sp.mm) in the defect region using micro-computed tomography. Histological examination confirmed significant new bone matrix in the HBMSC seeded VEGF encapsulated scaffold group as evidenced by Sirius red/alcian blue and Goldner's trichrome staining and type I collagen immunocytochemistry expression in comparison to the other groups. These studies demonstrate the ability to deliver, temporally, a combination of VEGF released from scaffolds with seeded HBMSC to sites of bone defects, results in enhanced regeneration of a bone defect.     

Growth of osteoblast-like cells on biomimetic apatite-coated chitosan scaffolds

Porous scaffold materials that can provide a framework for the cells to adhere, proliferate, and create extracellular matrix are considered to be suitable materials for bone regeneration. Interconnected porous chitosan scaffolds were prepared by freeze-drying method, and were mineralized by calcium and phosphate solution by double-diffusion method to form nanoapatite in chitosan matrix. The mineralized chitosan scaffold contains hydroxyapatite nanocrystals on the surface and also within the pore channels of the scaffold. To assess the effect of apatite and porosity of the scaffolds on cells, human osteoblast (SaOS-2) cells were cultured on unmineralized and mineralized chitosan scaffolds. The cell growth on the mineralized scaffolds and on the pure chitosan scaffold shows a similar growth trend. The total protein content and alkaline phosphatase enzyme activity of the cells grown on scaffolds were quantified, and were found to increase over time in mineralized scaffold after 1 and 3 weeks of culture. The electron microscopy of the cell-seeded scaffolds showed that most of the outer macropores became sealed off by a continuous layer of cells. The cells spanned around the pore wall and formed extra cellular matrix, consisting mainly of collagen in mineralized scaffolds. The hydroxyproline content also confirmed the formation of the collagen matrix by cells in mineralized scaffolds. This study demonstrated that the presence of apatite nanocrystals in chitosan scaffolds does not significantly influence the growth of cells, but does induce the formation of extracellular matrix and therefore has the potential to serve for bone tissue engineering.     

A biodegradable polymer scaffold for delivery of osteotropic factors

Despite discoveries and developments in osteotropic factors, therapies exploiting these macromolecules have been limited due to a lack of suitable delivery vehicles and three dimensional (3D) scaffolds that promote bone regeneration. To address this limitation, an emulsion freeze-drying process was developed to fabricate biodegradable scaffolds with controlled microarchitecture, and the ability to incorporate and deliver bioactive macromolecules for bone regeneration. The effect of median pore size and protein loading on protein release kinetics was investigated using scaffolds with different protein loading and median pore sizes ranging from 7 to 70 μm. Graphs of protein release from scaffolds showed an initial burst followed by a slower sustained release. Release kinetics were characterized using an unsteady-state, diffusion-controlled model with an effective diffusivity that took tortuosity (τ) and partition coefficient for protein adsorption (K_p) onto the scaffold walls into account. Tortuosity and partition coefficient significantly reduced the protein diffusivity by a factor of 41±43 and 105±51 for 60 and 30-μm median pore-sized scaffolds, respectively. The activity of the protein released from these scaffolds was demonstrated by delivering rhBMP 2 and [A-4] (an amelogenin derived polypeptide) proteins from the scaffold and regenerating bone in a rat ectopic bone induction assay [Whang et al. J Biomed Mater Res 1998;42:491–9, Veis et al. J Bone Mineral Res, Submitted].     

Characterization of mineralized collagen-glycosaminoglycan scaffolds for bone regeneration

Mineralized collagen–glycosaminoglycan scaffolds designed for bone regeneration have been synthesized via triple co-precipitation in the absence of a titrant phase. Here, we characterize the microstructural and mechanical properties of these newly developed scaffolds with 50 and 75 wt.% mineral content. The 50 wt.% scaffold had an equiaxed pore structure with isotropic mechanical properties and a Ca–P-rich mineral phase comprised of brushite; the 75 wt.% scaffold had a bilayer structure with a pore size varying in the through-thickness direction and a mineral phase comprised of 67% brushite and 33 wt.% monetite. The compressive stress–strain response of the scaffolds was characteristic of low-density open-cell foams with distinct linear elastic, collapse plateau and densification regimes. The elastic modulus and strength of individual struts within the scaffolds were measured using an atomic force microscopy cantilevered beam-bending technique and compared with the composite response under indentation and unconfined compression. Cellular solids models, using the measured strut properties, overestimated the overall mechanical properties for the scaffolds; the discrepancy arises from defects such as disconnected pore walls within the scaffold. As the scaffold stiffness and strength decreased with increasing overall mineral content and were less than that of natural, mineralized collagen scaffolds, these microstructural/mechanical relations will be used to further improve scaffold design for bone regeneration applications.     

聚左旋乳酸/壳聚糖纳米纤维三维多孔支架复合骨髓间充质干细胞修复兔骨缺损**△

背景：骨髓间充质干细胞具有向多种间质细胞谱系分化的能力,且支架材料的性能对骨缺损的修复有重要影响。 目的：观察聚左旋乳酸/壳聚糖纳米纤维三维多孔支架复合骨髓间充质干细胞治疗骨缺损。 方法：对骨缺损模型兔分别采用空白植入、髂后上棘自体松质骨移植、聚左旋乳酸/壳聚糖纳米纤维多孔支架移植和复合了骨髓间充质干细胞的聚左旋乳酸/壳聚糖纳米纤维多孔支架移植修复缺损部位。 结果与结论：至移植12周,移植复合了骨髓间充质干细胞的聚左旋乳酸/壳聚糖纳米纤维多孔支架的实验兔的缺损处有骨组织生成,支架材料降解,已完成缺损修复,其修复情况接近松质骨组;髂后上棘自体松质骨移植的实验兔的缺损修复完好,新形成的骨组织较规则;只植入聚左旋乳酸/壳聚糖纳米纤维多孔支架的实验兔有少量骨组织形成,材料部分降解;空白植入的实验兔缺损处无新生骨组织生成,主要由纤维结缔组织填充。说明新型的生物支架材料聚左旋乳酸/壳聚糖纳米纤维三维多孔支架与来源于新西兰大白兔的骨髓间充质干细胞复合培养后,植入同种异体兔股骨髁缺损处,使骨缺损的修复速度加快,表现为较好的体内诱导成骨的作用。     

Effect of varied release kinetics of the osteogenic thrombin peptide TP508 from biodegradable, polymeric scaffolds on bone formation in vivo

This study was designed to assess the influence of varied release kinetics of the osteogenic thrombin peptide TP508 from osteoconductive poly(propylene fumarate)-based (PPF) composite scaffolds on bone formation in vivo. Four classes of scaffolds were constructed with different TP508 dosages (200, 100, or 0 microg) and release kinetics (large burst release, minimal burst release, or no release) and implanted in 15.0 mm segmental defects in rabbit radii. The animals were euthanized at 12 weeks and the implants were analyzed by light microscopy, histological scoring analysis, and histomorphometric analysis. Samples from all classes displayed bone growth within the pores of the scaffold near the edges of the defect. In areas where bone was not observed, the pores were filled with mostly fibrous tissue and exhibited minimal inflammatory response for all classes. In contrast to other scaffold classes, scaffolds containing a total dose of 200 microg TP508 and exhibiting a large burst release profile showed statistically more bone formation guided along the surface of the scaffold, with these scaffolds averaging 80% of the defect length bridged with bone compared to 10% or less bridged for the other scaffold classes. These results demonstrate that the extent of in vivo bone formation in response to controlled release from PPF-composite scaffolds is determined by the release kinetics of the incorporated osteogenic peptide.     

Temporally regulated delivery of VEGF in vitro and in vivo

The exposure duration and tissue distribution will likely dictate the success of vascular endothelial growth factor (VEGF) in therapeutic angiogenesis. We hypothesized that these variables can be regulated via the manner in which the VEGF is incorporated into polymer constructs (formed with a gas foaming technique) used for its delivery. VEGF was incorporated directly into poly(lactide-co-glycolide) (PLG) scaffolds or pre-encapsulated in PLG microspheres used to fabricate scaffolds. Protein release kinetics and tissue distribution were determined using iodinated VEGF. VEGF was positioned predominantly adjacent to scaffold pores when incorporated directly and was released rapidly (40-60% in 5 days). Pre-encapsulation led to the VEGF being more deeply embedded and resulted in a delayed release. Alterations in polymer composition, scaffold size, and matrix composition generated minor variations in release kinetics. In vivo, the released VEGF generated local protein concentrations above 10 ng/mL at distances up to 2 cm from the implant site for the 21 days of the experiment, with negligible release into the systemic circulation, and significantly enhanced local angiogenesis. These data indicate that VEGF can be administered in a sustained and localized fashion in vivo, and the timing of VEGF delivery can be altered with the mechanism of incorporation into polymer scaffolds used for its delivery.     

Controllable mineral coatings on PCL scaffolds as carriers for growth factor release

In this study, we have developed mineral coatings on polycaprolactone scaffolds to serve as templates for growth factor binding and release. Mineral coatings were formed using a biomimetic approach that consisted in the incubation of scaffolds in modified simulated body fluids (mSBF). To modulate the properties of the mineral coating, which we hypothesized would dictate growth factor release, we used carbonate (HCO₃) concentration in mSBF of 4.2 mm, 25 mm, and 100 mm. Analysis of the mineral coatings formed using scanning electron microscopy indicated growth of a continuous layer of mineral with different morphologies. X-ray diffraction analysis showed peaks associated with hydroxyapatite, the major inorganic constituent of human bone tissue in coatings formed in all HCO₃ concentrations. Mineral coatings with increased HCO₃ substitution showed more rapid dissolution kinetics in an environment deficient in calcium and phosphate but showed re-precipitation in an environment with the aforementioned ions. The mineral coating provided an effective mechanism for growth factor binding and release. Peptide versions of vascular endothelial growth factor (VEGF) and bone morphogenetic protein 2 (BMP2) were bound with efficiencies up to 90% to mineral mineral-coated PCL scaffolds. We also demonstrated sustained release of all growth factors with release kinetics that were strongly dependent in the solubility of the mineral coating.     

In vitro performance of 13-93 bioactive glass fiber and trabecular scaffolds with MLO-A5 osteogenic cells

This in vitro study was performed to evaluate the ability of two types of porous bioactive glass scaffolds to support the growth and differentiation of an established osteogenic cell line. The two scaffold types tested included 13-93 glass fiber and trabecular-like scaffolds seeded with murine MLO-A5 cells and cultured for intervals of 2 to 12 days. Culture in MTT-containing medium showed metabolically active cells both on the surface and within the interior of the scaffolds. Scanning electron microscopy revealed well-attached cells on both types of scaffolds with a continual increase in cell density over a 6-day period. Protein measurements also showed a linear increase in cell density during the incubation. Activity of alkaline phosphatase, a key indicator of osteoblast differentiation, increased about 10-fold during the 6-day incubation with both scaffold types. The addition of mineralization media to MLO-A5 seeded scaffolds triggered extensive formation of alizarin red-positive mineralized extracellular material, additional evidence of cell differentiation and completion of the final step of bone formation on the constructs. Collectively, the results indicate that the 13-93 glass fiber and trabecular scaffolds promote the attachment, growth, and differentiation of MLO-A5 osteogenic cells and could potentially be used for bone tissue engineering applications. ? 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A 100A: 2593-2601, 2012.     

Vascular endothelial growth factor-releasing scaffolds enhance vascularization and engraftment of hepatocytes transplanted on liver lobes

Hepatocyte transplantation within porous scaffolds (HT) is being explored as a treatment strategy for end-stage liver diseases and enzyme deficiencies. One of the main issues in this approach is the limited viability of transplanted cells because vascularization of the scaffold site is either too slow or insufficient. We now address this by enhancing scaffold vascularization before cell transplantation via sustained delivery of vascular endothelial growth factor (VEGF), and by examining the liver lobes as a platform for transplanting donor hepatocytes in close proximity to the host liver. The vascularization kinetics of unseeded VEGF-releasing scaffolds on rat liver lobes were evaluated by analyzing the microvascular density and tissue ingrowth in implants harvested on days 3, 7, and 14 postimplantation. Capillary density was greater at all times in VEGF-releasing scaffolds than in the control scaffold without VEGF supplementation; on day 14, it was 220 +/- 33 versus 139 +/- 23 capillaries/mm2 (p < 0.05). Furthermore, 35% of the newly formed capillaries in VEGF-releasing scaffolds were larger than 16 microm in diameter, whereas in control scaffolds only 10% exceeded this size. VEGF had no effect on tissue ingrowth into the scaffolds. HT onto the implanted VEGF-releasing or control scaffolds was performed after 1 week of prevascularization on the liver lobe in Lewis rats. Fifty implants were harvested on days 1, 3, 7, and 12 and the area of viable hepatocytes was evaluated. The enhanced vascularization improved hepatocyte engraftment; 12 days after HT, the intact hepatocyte area (136,910 microm2/cross-section) in VEGF-releasing scaffolds was 4.6 higher than in the control group. This study shows that sustained local delivery of VEGF induced vascularization of porous scaffolds implanted on liver lobes and improved hepatocyte engraftment.     

In vitro ossification and remodeling of mineralized collagen I scaffolds

A promising strategy of bone tissue engineering is to repair bone defects by implanting biodegradable scaffolds that can undergo remodeling and be replaced completely by autologous bone tissue. For this purpose, it is necessary to create scaffolds that can be degraded by osteoclasts and enable osteoblasts to build new mineralized bone matrix. In order to achieve this goal a new porous material has been developed using biomimetically mineralized collagen I. These scaffolds were co-cultured with osteoclast-like cells and osteoblasts in order to characterize the capacity of these cells to remodel the material in vitro. It was possible to show the development of biologically active osteoclast- like cells that were able to invade and degrade the scaffold. They degraded the scaffold by internalizing it as intracellular vesicles, thereby making room for osteoblasts to invade and build new bone matrix. In addition, it could be shown that osteoblasts proliferated, differentiated, and produced new mineralized extracellular matrix. Hence, it could be shown that co-culture of osteoclastlike cells and osteoblasts on biomimetically mineralized collagen I is a promising approach for bone tissue engineering. In addition, it can be applied to study the process of bone remodeling in vitro.