Characterization and osteoblast-like cell compatibility of porous scaffolds: bovine hydroxyapatite and novel hydroxyapatite artificial bone

Enhanced toughness and strength of 3D printed carbide-oxide composite for biomedical applications

Natural materials derived/extracted Ceramics is an excellent material for developing ceramic-based orthopedic implants. Recently, we have demonstrated an easily scalable, energy-efficient green method to extract ceramic particles from bio-waste i.e. chicken bone. Though the chicken bone extract (CBE) has good biocompatibility, it lacks good mechanical properties in the 3D printed condition as that of human bones. Here, we have reinforced CBE with different weight proportions of silicon carbide to improve the mechanical characteristics of the composite. The hybrid of CBE (oxide) and carbide (SiC) is sintered at different temperatures to understand the effect of the interface of the two ceramics. It is observed that temperature has minimal effect and composition has a noticeable effect on mechanical strength as well as bio-toxicity. The toughness (∼3.58 MJ/m3) and compressive strength (∼64.64 MPa) of the 90:10 composition sintered at 1250 °C show the maximum optimum values. A mathematical model has also been developed to predict and correlate the toughness with porosity, volumetric loading, and elastic modulus of the 3D-printed ceramic composite.

Development, physicochemical characterization and in-vitro biocompatibility study of dromedary camel dentine derived hydroxyapatite for bone repair

This study aimed to produce hydroxyapatite from the dentine portion of camel teeth using a defatting and deproteinizing procedure and characterize its physicochemical and biocompatibility properties. Biowaste such as waste camel teeth is a valuable source of hydroxyapatite, the main inorganic constituent of human bone and teeth which is frequently used as bone grafts in the biomedical field. Fourier Transform infrared (FTIR), and micro-Raman spectroscopy confirmed the functional groups as-sociated with hydroxyapatite. X-ray diffraction (XRD) studies showed camel dentine-derived hydroxyapatite (CDHA) corresponded with hydroxyapatite spectra. Scanning electron micros-copy (SEM) demonstrated the presence of dentinal tubules measuring from 1.69-2.91 µm. The inorganic phases of CDHA were primarily constituted of calcium and phosphorus, with trace levels of sodium, magnesium, potassium, and strontium, according to energy dispersive X-ray analysis (EDX) and inductively coupled plasma mass spectrometry (ICP-MS). After 28 days of incubation in simulated body fluid (SBF), the pH of the CDHA scaffold elevated to 9.2. in-vitro biocompatibility studies showed that the CDHA enabled Saos-2 cells to proliferate and express the bone marker osteonectin after 14 days of culture. For applications such as bone augmentation and filling bone gaps, CDHA offers a promising material. However, to evaluate the clinical feasibility of the CDHA, further in-vivo studies are required.

Comparison of Low and High Temperature Sintering for Processing of Bovine Bone as Block Grafts for Oral Use: A Biological and Mechanical In Vitro Study

Large oral bone defects require grafting of bone blocks rather than granules to give physically robust, biocompatible and osteoconductive regeneration. Bovine bone is widely accepted as a source of clinically appropriate xenograft material. However, the manufacturing process often results in both reduced mechanical strength and biological compatibility. The aim of this study was to assess bovine bone blocks at different sintering temperatures and measure the effects on mechanical properties and biocompatibility. Bone blocks were divided into four groups; Group 1: Control (Untreated); Group 2: Initial boil for 6 h; Group 3: Boil 6 h followed by sintering at 550 °C for 6 h; Group 4: Boil 6 h followed by sintering at 1100 °C for 6 h. Samples were assessed for their purity, crystallinity, mechanical strength, surface morphology, chemical composition, biocompatibility and clinical handling properties. Statistical analysis was performed using one-way ANOVA and post-hoc Tukey's tests for normally distributed and Friedman test for abnormally distributed quantitative data from compression tests and PrestoBlue™ metabolic activity tests. The threshold for statistical significance was set at p < 0.05. The results showed that higher temperature sintering (Group 4) removed all organic material (0.02% organic components and 0.02% residual organic components remained) and increased crystallinity (95.33%) compared to Groups 1-3. All test groups (Group 2-4) showed decreased mechanical strength (MPa: 4.21 ± 1.97, 3.07 ± 1.21, 5.14 ± 1.86, respectively) compared with raw bone (Group 1) (MPa: 23.22 ± 5.24, p <0.05), with micro-cracks seen under SEM in Groups 3 and 4. Group 4 had the highest biocompatibility (p < 0.05) with osteoblasts as compared to Group 3 at all time points in vitro. Clinical handling tests indicated that Group 4 samples could better withstand drilling and screw placement but still demonstrated brittleness compared to Group 1. Hence, bovine bone blocks sintered at 1100 °C for 6 h resulted in highly pure bone with acceptable mechanical strength and clinical handling, suggesting it is a viable option as a block grafting material.

In-vitro viability of bone scaffolds fabricated using the adaptive foam reticulation technique

The adaptive foam reticulation technique combines the foam reticulation and freeze casting methodologies of fabricating bone reparative scaffolds to offer a potential alternative to autografts. For the first time this paper studies the effect of processing on the mechanical properties and in-vitro cell growth of controllably generating a hierarchical structure of macro- (94 ± 6 to 514 ± 36 μm) and microporosity (2-30 μm) by the inclusion of camphene as a porogen during processing. Scaffolds were produced with porogen additions of 0-25 wt%. Porosity values of the structures of 85-96% were determined using the Archimedes technique and verified using X-ray Computed Tomography. The strength of the hydroxyapatite scaffolds, 5.70 ± 1.0 to 159 ± 61 kPa, correlated to theoretically determined values, 3.71 ± 0.8 to 134 ± 12 kPa, calculated by the novel incorporation of a shape factor into a standard equation. Fibroblast (3T3) and pre-osteoblast (MC3T3) cell growth was found to be significantly (P < 0.005) improved using 25 wt% porogen. This was supported by increased levels of alkaline phosphatase and was thought to result from greater dissolution as quantified by increased calcium levels in incubating media. The combination of these properties renders adaptive foam reticulation-fabricated scaffolds suitable for non-structural bone regenerative applications in non-load bearing bone defects.

Injectable eggshell-derived hydroxyapatite-incorporated fibroin-alginate composite hydrogel for bone tissue engineering

Tissue engineering is a promising approach to repair and regenerate damaged or lost tissues or organs. In dental aspect, reconstruction of the resorbed alveolar bone after tooth extraction plays an important role in the success of dental substitution, especially in dental implant treatment. The hydroxyapatite (HA)-incorporated fibroin-alginate composite injectable hydrogel was fabricated to be used as scaffold for bone regeneration. HA was synthesized from eggshell biowaste. Fibroin was extracted from Bombyx mori cocoon. The synthesized HA, fibroin and alginate hydrogel were characterized. HA-incorporated fibroin-alginate hydrogel had decreased pore size and porosity compared with pure alginate hydrogel. Thermal analysis showed that hydrogel had a degradation peak of approximately 250 °C. Hydrogel could absorb water, with a swelling ratio of around 300% at 24 h. Hydrogel was degraded as time passed and almost completely degraded at day 7. Its compressive Young's modulus was approximately 0.04 ± 0.02 N/mm² to 0.10 ± 0.02 N/mm². Primary cytotoxicity test indicated non-toxic potential of the fabricated hydrogel. Increased ALP activity was observed in MC3T3-E1 cultured in HA-incorporated fibroin-alginate hydrogel. Results suggested the potential use of injectable HA fibroin-alginate hydrogel as dental scaffolding material. Further studies including in vivo examinations are needed prior to its clinical application.

Structural and Biomedical Properties of Common Additively Manufactured Biomaterials: A Concise Review

Biomaterials are in high demand due to the increasing geriatric population and a high prevalence of cardiovascular and orthopedic disorders. The combination of additive manufacturing (AM) and biomaterials is promising, especially towards patient-specific applications. With AM, unique and complex structures can be manufactured. Furthermore, the direct link to computer-aided design and digital scans allows for a direct replicable product. However, the appropriate selection of biomaterials and corresponding AM methods can be challenging but is a key factor for success. This article provides a concise material selection guide for the AM biomedical field. After providing a general description of biomaterial classes—biotolerant, bioinert, bioactive, and biodegradable—we give an overview of common ceramic, polymeric, and metallic biomaterials that can be produced by AM and review their biomedical and mechanical properties. As the field of load-bearing metallic implants experiences rapid growth, we dedicate a large portion of this review to this field and portray interesting future research directions. This article provides a general overview of the field, but it also provides possibilities for deepening the knowledge in specific aspects as it comprises comprehensive tables including materials, applications, AM techniques, and references.

Advanced Biomaterials and Techniques for Oral Tissue Engineering and Regeneration-A Review

The reconstruction or repair of oral and maxillofacial functionalities and aesthetics is a priority for patients affected by tooth loss, congenital defects, trauma deformities, or various dental diseases. Therefore, in dental medicine, tissue reconstruction represents a major interest in oral and maxillofacial surgery, periodontics, orthodontics, endodontics, and even daily clinical practice. The current clinical approaches involve a vast array of techniques ranging from the traditional use of tissue grafts to the most innovative regenerative procedures, such as tissue engineering. In recent decades, a wide range of both artificial and natural biomaterials and scaffolds, genes, stem cells isolated from the mouth area (dental follicle, deciduous teeth, periodontal ligament, dental pulp, salivary glands, and adipose tissue), and various growth factors have been tested in tissue engineering approaches in dentistry, with many being proven successful. However, to fully eliminate the problems of traditional bone and tissue reconstruction in dentistry, continuous research is needed. Based on a recent literature review, this paper creates a picture of current innovative strategies applying dental stem cells for tissue regeneration in different dental fields and maxillofacial surgery, and offers detailed information regarding the available scientific data and practical applications.

Structural and chemical features of xenograft bone substitutes: A systematic review of in vitro studies

Xenograft bone substitutes are obtained from different species and prepared by various procedures including heat treatment, hydrazine, and chemical and hydrothermal methods. These grafts are utilized widely because of similar structure and properties to human bone, proper bone formation, and biocompatibility. The aim of this systematic review was to evaluate different xenografts from structural and chemical aspects. In vitro studies published in English language, which assessed xenografts' features, met the inclusion criteria. Electronic search of four databases including PubMed, Google Scholar, Scopus, and Web of Science and a hand search until September 2020 were performed. The irrelevant studies were the ones which focused on cell adhesion and effect of growth factors. Finally, 25 studies were included in the review. Nineteen studies used bovine xenografts, and 12 studies applied heat treatment as their preparation method. Particles showed various morphologies, and their largest size was observed at 5 mm. From 18 studies, it is found that the smallest pore size was 1.3 µm and the highest pore size was 1000 µm. There is large heterogeneity of porosity, crystallinity, Ca/P ratio, and osteogenesis based on the preparation method. Proper porosity and the connection between pores affect bone regeneration. Therefore, biomaterial selection and outcomes evaluation should be interpreted separately.

Comparison of Bone Regeneration between Porcine-Derived and Bovine-Derived Xenografts in Rat Calvarial Defects: A Non-Inferiority Study

The present study aimed to compare the bone-regeneration capacity of porcine-derived xenografts to bovine-derived xenografts in the rat calvarial defect model. The observation of surface morphology and in vitro cell studies were conducted prior to the animal study. Defects with a diameter of 8 mm were created in calvaria of 20 rats. The rats were randomly treated with porcine-derived (Bone-XP group) or bovine-derived xenografts (Bio-Oss group) and sacrificed at 4 and 8 weeks after surgery. The new bone regeneration was evaluated by micro-computed tomography (μCT) and histomorphometric analyses. In the cell study, the extracts of Bone-XP and Bio-Oss showed a positive effect on the regulation of osteogenic differentiation of human mesenchymal stem cells (hMSCs) without cytotoxicity. The new bone volume of Bone-XP (17.52 ± 3.78% at 4 weeks and 32.09 ± 3.51% at 8 weeks) was similar to that of Bio-Oss (11.6 ± 3.88% at 4 weeks and 25.89 ± 7.43% at 8 weeks) (p > 0.05). In the results of new bone area, there was no significant difference between Bone-XP (9.08 ± 5.47% at 4 weeks and 25.22 ± 13.56% at 8 weeks) and Bio-Oss groups (5.83 ± 2.56% at 4 weeks and 21.68 ± 11.11% at 8 weeks) (p > 0.05). It can be concluded that the porcine-derived bone substitute may offer a favorable cell response and bone regeneration similar to those of commercial bovine bone mineral.

Nanostructured Lipid Carriers of Pioglitazone Loaded Collagen/Chitosan Composite Scaffold for Diabetic Wound Healing

Diabetic wound is a major problem that often needs amputation of the concerned organ in patients suffering from diabetes. In diabetes, the prolonged phase of inflammation obstructs the further phases of healing which, in turn, lead to improper healing of the wounds in diabetes. Pioglitazone (Pio) hydrochloride is an antidiabetic drug with reported anti-inflammatory properties. The aim of this study was to develop a Pio-nanostructured lipid carrier (Pio-NLC)-loaded collagen/chitosan (COL-CS) scaffold and evaluate its healing ability in diabetic wounds. The results of characterization of composite scaffolds reveal that cross-linked scaffolds possess optimum porosity, low matrix degradation, and sustained drug release compared with noncross-linked scaffolds. The in vitro studies reveal that the Pio-NLC-COL-CS scaffold was biocompatible and enhanced cell growth compared with control and NLC-COL-CS. Using the streptozotocin-induced diabetic wound model, significantly (p < 0.001) higher rates of wound contraction in Pio-NLC-COL-CS scaffold-treated group were observed in comparison with that in control and NLC-COL-CS-treated group. The enzyme-linked immunosorbent assay results indicate a significant (p < 0.001) decrease of matrix metalloproteinases-9 levels in the Pio-NLC-COL-CS-treated group compared with those in control group. Use of nanostructured lipid carrier (Pio-NLC-COL-CS) scaffold can prove to be a promising strategy for local treatment for diabetic wounds.

Biomimetic matrix fabricated by LMP-1 gene-transduced MC3T3-E1 cells for bone regeneration

Bone healing is regulated by multiple microenvironmental signals provided by the extracellular matrix (ECM). This study aimed to mimic the native osteoinductive microenvironment by developing an ECM using gene-transduced cells. The LIM mineralization protein-1 (LMP-1) gene was transferred to murine pre-osteoblast cells (MC3T3-E1) using lentiviral vectors. Western blotting assay indicated that the MC3T3-E1 cells expressed an increased level of bone morphologic protein-2, -4 and -7 (BMP-2, -4 and -7) after LMP-1 gene transduction. The transduced cells were then seeded into calcined bovine bone scaffolds and cultured for 7, 14, and 21 days to construct ECMs on the scaffolds. The ECM-scaffold composites were then decellularized using the freeze-drying method. Scaffolds without ECM deposition were used as controls. The composites and controls were implanted into critical-sized bone defects created in the distal femurs of New Zealand rabbits. Twelve weeks after the surgery, both microcomputed tomography and histologic results indicated that the 7-day-cell-modified ECM-scaffold composites induced bone regeneration with significantly larger volume, trabecular thickness and connectivity than the controls. However, the 14- and 21-day-cell-modified ECM-scaffold composites triggered sustained inflammation response even at 12 weeks after the surgery and showed less bone ingrowth and integration than their 7-day-cell-modified counterparts. In conclusion, these results highlight the viable gene transfer techniques for manipulating cells in a constructed microenvironment of ECM for bone regeneration. However, the unresolved inflammation relating to the duration of ECM modification needs to be considered.

3D Printing of Calcium Phosphate Ceramics for Bone Tissue Engineering and Drug Delivery

Additive manufacturing, also known as 3D printing, has emerged over the past 3 decades as a disruptive technology for rapid prototyping and manufacturing. Vat polymerization, powder bed fusion, material extrusion, and binder jetting are distinct technologies of additive manufacturing, which have been used in a wide variety of fields, including biomedical research and tissue engineering. The ability to print biocompatible, patient-specific geometries with controlled macro- and micro-pores, and to incorporate cells, drugs and proteins has made 3D-printing ideal for orthopaedic applications, such as bone grafting. Herein, we performed a systematic review examining the fabrication of calcium phosphate (CaP) ceramics by 3D printing, their biocompatibility in vitro, and their bone regenerative potential in vivo, as well as their use in localized delivery of bioactive molecules or cells. Understanding the advantages and limitations of the different 3D printing approaches, CaP materials, and bioactive additives through critical evaluation of in vitro and in vivo evidence of efficacy is essential for developing new classes of bone graft substitutes that can perform as well as autografts and allografts or even surpass the performance of these clinical standards.

Fabrication and characterization of novel nano-biocomposite scaffold of chitosan-gelatin-alginate-hydroxyapatite for bone tissue engineering

A novel nano-biocomposite scaffold was fabricated in bead form by applying simple foaming method, using a combination of natural polymers-chitosan, gelatin, alginate and a bioceramic-nano-hydroxyapatite (nHAp). This approach of combining nHAp with natural polymers to fabricate the composite scaffold, can provide good mechanical strength and biological property mimicking natural bone. Environmental scanning electron microscopy (ESEM) images of the nano-biocomposite scaffold revealed the presence of interconnected pores, mostly spread over the whole surface of the scaffold. The nHAp particulates have covered the surface of the composite matrix and made the surface of the scaffold rougher. The scaffold has a porosity of 82% with a mean pore size of 112±19.0μm. Swelling and degradation studies of the scaffold showed that the scaffold possesses excellent properties of hydrophilicity and biodegradability. Short term mechanical testing of the scaffold does not reveal any rupturing after agitation under physiological conditions, which is an indicative of good mechanical stability of the scaffold. In vitro cell culture studies by seeding osteoblast cells over the composite scaffold showed good cell viability, proliferation rate, adhesion and maintenance of osteoblastic phenotype as indicated by MTT assay, ESEM of cell-scaffold construct, histological staining and gene expression studies, respectively. Thus, it could be stated that the nano-biocomposite scaffold of chitosan-gelatin-alginate-nHAp has the paramount importance for applications in bone tissue-engineering in future regenerative therapies.

In vitro and in vivo evaluation of carbonate apatite-collagen scaffolds with some cytokines for bone tissue engineering

Background:

Collagen is regarded as one of the most useful biomaterials. We tried to combine collagen and carbonate apatite (CA) with some cytokines in order to enhance bone formation ability. In this study, we found that CA-collagen sponge (CA-CS) was a possible candidate of newly graft material for bone formation.

Materials and Methods:

CA-CS was fabricated by the following procedure. One wt% of pig hide collagen solution (Nippon Meat Packers. Inc., Tokyo, Japan) was neutralized with 0.1 N NaOH, and then mixed immediately 243 mg apatite powder with 0.06 M carbonate contents. After centrifugation at 1500 rpm for 10 min, excess water was removed, and the mixture was packed into Teflon molds (5.0 mm × 2.0 mm). Each 10 µg of basic fibroblast growth factor (bFGF) and recombinant human bone morphogenetic protein-2 (rh-BMP2) were involved in these sponges. Then these scaffolds frozen at −80°C for 2 h and dried in a freeze dry machine for 24 h. CA-CS without cytokines were also prepared as a control. Mouse osteoblast-like cell (MC3T3-E1) proliferations in these scaffolds were investigated by 3-day in vitro cell culture using MTT assay examination. Ten New Zealand rabbits (weight: 3–3.5 kg) were used in this in vivo study. After 3 weeks of placement, the scaffolds, rabbits were sacrificed, and bone formation in the sockets was evaluated histologically and histomorphometrically.

Results and Conclusion:

By histological observation and measurement of bone area ratio, CA-CS with cytokines showed higher bone formation ability (bFGF/CA-CS: 50.7 ± 7.3%, rh-BMP2/CA-CS: 54.2 ± 5.0%) than other groups. From the limited results of this study, it is suggested that CA collagen scaffolds with some cytokines may become an attractive scaffold for bone regeneration.

Effects of structural properties of electrospun TiO2 nanofiber meshes on their osteogenic potential

Ideal outcomes in the field of tissue engineering and regenerative medicine involve biomaterials that can enhance cell differentiation and production of local factors for natural tissue regeneration without the use of systemic drugs. Biomaterials typically used in tissue engineering applications include polymeric scaffolds that mimic the three-dimensional structural environment of the native tissue, but these are often functionalized with proteins or small peptides to improve their biological performance. For bone applications, titanium implants, or more appropriately the TiO2 passive oxide layer formed on their surface, have been shown to enhance osteoblast differentiation in vitro and to promote osseointegration in vivo. In this study we evaluated the effect on osteoblast differentiation of pure TiO2 nanofiber meshes with different surface microroughness and nanofiber diameters, prepared by the electrospinning method. MG63 cells were seeded on TiO2 meshes, and cell number, differentiation markers and local factor production were analyzed. The results showed that cells grew throughout the entire surfaces and with similar morphology in all groups. Cell number was sensitive to surface microroughness, whereas cell differentiation and local factor production was regulated by both surface roughness and nanofiber diameter. These results indicate that scaffold structural cues alone can be used to drive cell differentiation and create an osteogenic environment without the use of exogenous factors.

A comparative study of thermal calcination and an alkaline hydrolysis method in the isolation of hydroxyapatite from Thunnus obesus bone

In the present study, hydroxyapatite (HAp) was isolated from Thunnus obesus bone using alkaline hydrolysis and thermal calcination methods. The obtained ceramic has been characterized by thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), powder x-ray diffraction analysis (XRD), field-emission scanning electron microscopy, energy-dispersive x-ray analysis, transmission electron microscopy (TEM), selected area diffraction analysis, cytotoxic analysis and cell proliferation analysis. The results indicate that there are significant differences between the ceramics and T. obesus bone. FT-IR and TGA results affirmed that the collagen and organic moieties have been eliminated by both the proposed methods. XRD results were in agreement with JCPDS data. TEM and selective area diffraction images have signified that the thermal calcination method produces good crystallinity with dimensions 0.3-1.0 µm, whereas the alkaline hydrolysis method produces nanostructured HAp crystals with 17-71 nm length and 5-10 nm width. Biocompatibility of HAp crystals was evaluated by cytotoxicity and cell proliferation with human osteoblast-like cell MG-63.

Biphasic calcium phosphate to repair nasal septum: the first in vitro and in vivo study

Our objective was to evaluate the cytocompatibility and biocompatibility of biphasic calcium phosphate (BCP) in the nasal respiratory airway. In vitro, the attachment rate was quantified on BCP disks with normal human epithelial cells at 1, 3 and 24 h by determining N-acetyl beta-D-hexosaminidase activity. Proliferative activity of cells was indirectly assessed by MTT assay at 3, 9, 15 and 21 days. Plastic surfaces were used as positive control. In vivo, 15 rabbits underwent anterior nasal septum perforation and 10 septa were repaired with BCP disks. Five non-implanted animals were sacrificed at 3 months. Two groups of five implanted animals were sacrificed at 1 and 2 months. The surface of new airway mucosa covering BCP disks was evaluated macroscopically. During both steps, light microscopy, immunohistochemistry and scanning electron microscopy were performed. Statistical analysis was performed with the Mann-Whitney U-test. In vitro, at 1 and 3 h, the attachment rates were significantly better than on the plastic surface (p < 10(-2)). Mitochondrial activity increased on both surfaces but began 6 days later than on plastic. After 21 days of culture, cells were confluent and formed a monolayer covering the implant even in the bottom of the pores. In vivo, no perforations in the control group closed spontaneously. The mean rate of closure was 63% in the 1 month group and 64% in the 2 month group (p > 0.05). Implants were invaded by inflammatory reaction covered by incomplete differentiated respiratory epithelium. Throughout the study, all immunohistochemical findings remained positive. These data suggest a good affinity between BCP and nasal epithelial cells. BCP could be used to rebuild nasal septa.

Development of an in vitro model on cellular adhesion on granular natural bone mineral under dynamic seeding conditions--a pilot study

Adhesion of osteogenic cells on biomaterials can be studied with static in vitro models, whereas models representing dynamic seeding conditions are rare. Herein, we present an in vitro model to study cell adhesion on granular biomaterials under dynamic seeding conditions. Radiolabeled osteogenic MC3T3-E1 cells were allowed to adhere to granules of natural bovine bone mineral (NBM) under constant rotation. Adhesion of MC3T3-E1 cells was determined by liquid scintillation counting, and cell morphology was visualized by scanning electron microscopy. Cell viability was determined by MTT assay under static and dynamic conditions, at room and body temperature, and in the presence or absence of serum. We show here that MC3T3-E1 cells rapidly adhere to NBM, reaching a peak 3 h after seeding. Attached cells display characteristic signs of spreading. Five to ten percent of total radioactivity remained on NBM after the removal of nonadherent cells. Viability is maintained at room temperature and under rotation for upto 3 h. This data suggests that the dynamic in vitro model presented here provides a tool to study cell adhesion on granular biomaterials.

Tissue-like self-assembly in cocultures of endothelial cells and osteoblasts and the formation of microcapillary-like structures on three-dimensional porous biomaterials

The survival and functioning of a bone biomaterial requires a rapid and stable vascularization after implantation. However, the mechanisms involved in the context of the complex healing microenvironment are poorly understood. To evaluate the vascularization potential of bone biomaterials, angiogenic stimuli were added to human dermal microvascular endothelial cells (HDMEC) growing on three-dimensional (3-D) bone biomaterials consisting of porous hydroxyapatite, porous calcium phosphate, porous nickel-titanium, successfully being used in humans, and also silk fibroin nets. HDMEC did not migrate to form microcapillary-like structures as they did on cell culture plastic. In cocultures of HDMEC and primary human osteoblast cells (HOS) or the human osteoblast-like cell line MG-63 on these biomaterials, a tissue-like self-assembly of cells occurred with time, with endothelial cells forming microcapillary-like structures containing a lumen and giving a strong PECAM-1 expression at cell interfaces. These microcapillary-like structures were intertwined between cell layers of osteoblasts and did not form when exogenous angiogenic stimuli were added to these cocultures. The life span of HDMEC was also significantly enhanced by coculture; with HDMEC being present for up to at least 42 days, compared to the monoculture where cells began to die rapidly after 1 week without passage. This coculture system may be applicable to a prevascularization strategy for biomaterials prior to implantation. Irrespective of this, the coculture model holds promise for studies to deepen our understanding of bone regeneration on 3-D substrates. Most importantly, these data raise important questions concerning the exact nature of pro-angiogenic drug- or gene-delivery systems to be incorporated into scaffolds. Our results underline the necessity to take into account the in situ production of growth factors by invading mesenchymal cells in the regenerative niche.