Composition options for tissue-engineered bone

Nanotechnology Assisted Targeted Drug Delivery for Bone Disorders: Potentials and Clinical Perspectives

Nanotechnology and its allied modalities have brought revolution in tissue engineering and bone healing. The research on translating the findings of the basic and preclinical research into clinical practice is ongoing. Advances in the synthesis and design of nanomaterials along with advances in genomics and proteomics, and tissue engineering have opened a bright future for bone healing and orthopedic technology. Studies have shown promising outcomes in the design and fabrication of porous implant substrates that can be exploited as bone defect augmentation and drug-carrier devices. However, there are dozens of applications in orthopedic traumatology and bone healing for nanometer-sized entities, structures, surfaces, and devices with characteristic lengths ranging from tens 10s of nanometers to a few micrometers. Nanotechnology has made promising advances in the synthesis of scaffolds, delivery mechanisms, controlled modification of surface topography and composition, and biomicroelectromechanical systems. This study reviews the basic and translational sciences and clinical implications of the nanotechnology in tissue engineering and bone diseases. Recent advances in NPs assisted osteogenic agents, nanocomposites, and scaffolds for bone disorders are discussed.

Three-Dimensional Porous Trabecular Scaffold Exhibits Osteoconductive Behaviors In Vitro

In the USA, approximately 500,000 bone grafting procedures are performed annually to treat injured or diseased bone. Autografts and allografts are the most common treatment options but can lead to adverse outcomes such as donor site morbidity and mechanical failure within 10 years. Due to this, tissue engineered replacements have emerged as a promising alternative to the biological options. In this study, we characterize an electrospun porous composite scaffold as a potential bone substitute. Various mineralization techniques including electrodeposition were explored to determine the optimal method to integrate mineral content throughout the scaffold. In vitro studies were performed to determine the biocompatibility and osteogenic potential of the nanofibrous scaffolds. The presence of hydroxyapatite (HAp) and brushite throughout the scaffold was confirmed using energy dispersive X-ray fluorescence, scanning electron microscopy, and ash weight analysis. The active flow of ions via electrodeposition mineralization led to a threefold increase in mineral content throughout the scaffold in comparison to static and flow mineralization. Additionally, a ten-layer scaffold was successfully mineralized and confirmed with an alizarin red assay. In vitro studies confirmed the mineralized scaffold was biocompatible with human bone marrow derived stromal cells. Additionally, bone marrow derived stromal cells seeded on the mineralized scaffold with embedded HAp expressed 30% more osteocalcin, a primary bone protein, than these cells seeded on non-mineralized scaffolds and only 9% less osteocalcin than mature pre-osteoblasts on tissue culture polystyrene. This work aims to confirm the potential of a biomimetic mineralized scaffold for full-thickness trabecular bone replacement.

Construction of vascularized tissue-engineered bone with a double-cell sheet complex

A double-cell sheet (DCS) complex composed of an osteogenic cell sheet and a vascular endothelial cell sheet with osteogenesis and blood vessel formation potential was developed in this study. The osteogenic and vascular endothelial cell sheets were obtained after induced culture of rabbit adipose-derived mesenchymal stem cells. The osteogenic cell sheet showed positive alizarin red, von Kossa, and alkaline phosphatase (ALP) staining. The vascular endothelial cell sheet exhibited visible W-P bodies in the cells, the expression of CD31 was positive, and a vascular mesh structure was spontaneously formed in a Matrigel matrix. The subcutaneous transplantation results for four groups of DCS and DCS-coral hydroxyapatite (CHA) complexes, and the CHA scaffold group in nude mice revealed mineralization of collagen fibers and vascularization in each group at 12 weeks, but the degrees of mineralization and vascularization showed differences among groups. The pattern involving endothelial cell sheets covered with osteogenic cell sheets, group B, exhibited the best results. In addition, the degree of mineralization of the DCS-CHA complexes was more mature than those of the same group of DCS complexes and the CHA scaffold, and the capillary number was greater than those of the same group of DCS complexes and the CHA scaffold. Therefore, the CHA scaffold strengthened the osteogenesis and blood vessel formation potential of the DCS complexes. Meanwhile, the DCS complexes also promoted the osteogenesis and blood vessel formation potential of the CHA scaffold. This study will provide a basis for building vascularized tissue-engineered bone for bone defect therapy.

STATEMENT OF SIGNIFICANCE

This study developed a double-cell sheet (DCS) complex composed of an osteogenic cell sheet and a vascular endothelial cell sheet with osteogenesis and blood vessel formation potential. Osteogenic and vascular endothelial cell sheets were obtained after induced culture of rabbit adipose-derived mesenchymal stem cells. The DCS complex and DCS-CHA complex exhibited osteogenic and blood vessel formation potential in vivo. CHA enhanced the osteogenesis and blood vessel formation abilities of the DCS complexes in vivo. Meanwhile, the DCS complexes also promoted the osteogenesis and blood vessel formation potential of the CHA scaffold. Group B of the DCS complexes and DCS-CHA complexes exhibited the best osteogenesis and blood vessel formation abilities.

Perfusion Enhances Solute Transfer into the Shell of Hollow Fiber Membrane Bioreactors for Bone Tissue Engineering

Preparation of tissue engineered (TE) 3D constructs to repair large bone defects is limited by the difficult supply of nutrients and oxygen to cells in the innermost regions of constructs cultured in bioreactors. Poor oxygenation negatively affects cell viability and function. Bioreactor design optimization may help relieve these limitations. Bioreactors in which cells are cultured outside bundles of hollow fiber membranes (HFMBs) are structurally similar to natural bone. HFMB operation in pure diffusion has been reported to suffice for fibroblasts, but is deemed insufficient for bone cells. In this paper, the effect of perfusion flows in the cell compartment on solute transfer was investigated in HFMBs differing in design and operating conditions. HFMBs were designed and operated using values of non-dimensional groups that ensured solutes transfer towards the cell compartment mainly by diffusion; in the presence of low to high Starling flows; in the presence of pulsatile radial flows obtained by periodically stopping the solution flow leaving the bioreactor using a pinch valve. Distribution of matter in cell-free HFMBs was evaluated with tracer experiments in an optimized apparatus. Effectiveness of solute transfer to cell compartment was assessed based on the bioreactor response in terms of the shell volume actively involved in mass transfer (VMTA) according to transport models developed specifically for the purpose. VMTA increased with increasing Starling flows. In the pulsatile radial flow mode, tracer concentration in the shell increased 3 times faster than at high Starling flows. This suggests that controlled perfusion flows in HFMBs might enable the engineering of large TE bone constructs.

Graphene Oxide Hybridized nHAC/PLGA Scaffolds Facilitate the Proliferation of MC3T3-E1 Cells

Biodegradable porous biomaterial scaffolds play a critical role in bone regeneration. In this study, the porous nano-hydroxyapatite/collagen/poly(lactic-co-glycolic acid)/graphene oxide (nHAC/PLGA/GO) composite scaffolds containing different amount of GO were fabricated by freeze-drying method. The results show that the synthesized scaffolds possess a three-dimensional porous structure. GO slightly improves the hydrophilicity of the scaffolds and reinforces their mechanical strength. Young's modulus of the 1.5 wt% GO incorporated scaffold is greatly increased compared to the control sample. The in vitro experiments show that the nHAC/PLGA/GO (1.5 wt%) scaffolds significantly cell adhesion and proliferation of osteoblast cells (MC3T3-E1). This present study indicates that the nHAC/PLGA/GO scaffolds have excellent cytocompatibility and bone regeneration ability, thus it has high potential to be used as scaffolds in the field of bone tissue engineering.

Investigating processing techniques for bovine gelatin electrospun scaffolds for bone tissue regeneration

Tissue engineering has emerged as a promising solution to tissue regeneration in the case of significant bone loss due to disease or injury. The ability to promote cellular attachment, migration, and differentiation into tissue is dependent on the scaffold's surface properties and composition. Bovine gelatin is a natural polymer commonly used as a scaffolding material for tissue engineering applications. Nonetheless, due to the hydrophilic behavior of gelatin, cross-linking and additives are necessary to maintain the scaffold's structure and overall strength in vivo. In this article, we discuss various processing techniques to determine the optimal electrospinning, cross-linking, sintering, and mineralization parameters necessary to yield a porous, mechanically enhanced scaffold. The scaffolds were evaluated quantitatively using compressive mechanical testing, and qualitatively using scanning electron microscopy (SEM). Mechanical data concluded the use of biocompatible microbial transglutaminase (mTG) as a cross-linking agent, led to increased compressive strength. SEM images confirmed the presence of individual gelatin and polymeric nanofibers woven into one scaffold. Sintering before leaching the scaffold yielded structured pores throughout the three-dimensional scaffold when compared to the scaffolds that were leached prior to sintering. The results presented in this article will provide novel information about processing techniques that can be utilized to develop a hybrid synthetic and biological based biomimetic mineralized scaffold for trabecular bone tissue regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1131-1140, 2017.

Nanotechnology in bone tissue engineering

Nanotechnology represents a major frontier with potential to significantly advance the field of bone tissue engineering. Current limitations in regenerative strategies include impaired cellular proliferation and differentiation, insufficient mechanical strength of scaffolds, and inadequate production of extrinsic factors necessary for efficient osteogenesis. Here we review several major areas of research in nanotechnology with potential implications in bone regeneration: 1) nanoparticle-based methods for delivery of bioactive molecules, growth factors, and genetic material, 2) nanoparticle-mediated cell labeling and targeting, and 3) nano-based scaffold construction and modification to enhance physicochemical interactions, biocompatibility, mechanical stability, and cellular attachment/survival. As these technologies continue to evolve, ultimate translation to the clinical environment may allow for improved therapeutic outcomes in patients with large bone deficits and osteodegenerative diseases.

FROM THE CLINICAL EDITOR

Traditionally, the reconstruction of bony defects has relied on the use of bone grafts. With advances in nanotechnology, there has been significant development of synthetic biomaterials. In this article, the authors provided a comprehensive review on current research in nanoparticle-based therapies for bone tissue engineering, which should be useful reading for clinicians as well as researchers in this field.

The effects of separating inferior alveolar neurovascular bundles on osteogenesis of tissue-engineered bone and vascularization

AIM

To evaluate the effects of autologous blood vessels and nerves on vascularization.

METHODS

A dog model of tissue-engineered bone vascularization was established by constructing inferior alveolar neurovascular bundles through the mandibular canal. Sixteen 12-month-old healthy beagles were randomly divided into two groups (n=8). Group A retained inferior alveolar neurovascular bundles, and Group B retained inferior alveolar nerves. Bone marrow mesenchymal stem cells were injected into β-tricalcium phosphate to prepare internal tissue-engineered bone scaffold. A personalized titanium mesh was then prepared by rapid prototyping and fixed by external titanium scaffold. Two dogs in each group were sacrificed on the 30th, 45th, 60th and 90th postoperative days respectively. The bone was visually examined, scanned by CT, and subjected to HE staining, immunohistochemical staining, vascular casting and PCR to detect the changes in osteogenesis and vascularization.

RESULTS

The two groups had similar outcomes in regard to osteogenesis and vascularization (P>0.05): both showed remarkable regenerative capacities.

CONCLUSIONS

The model of tissue-engineered bone vascularization is potentially applicable in clinical practice to allow satisfactory osteogenesis and vascularization.

Ethyl-3,4-dihydroxybenzoate with a dual function of induction of osteogenic differentiation and inhibition of osteoclast differentiation for bone tissue engineering

The current approach in biomaterial design of bone implants is to induce in situ regeneration of bone tissue, thus improving integration of the implants and reducing their failure. Therefore, ethyl-3,4-dihydroxybenzoate (EDHB), which stimulates differentiation of osteoblasts and the resultant bone formation, should be studied. In this study, the osteoinductive ability of EDHB in preosteoblasts and human mesenchymal stem cells was examined. EDHB for future use in bone tissue engineering was evaluated by examination of early markers of differentiation (such as alkaline phosphatase [ALP] activity and collagen type I expression) and late markers of osteoblast differentiation (bone nodule formation). As bone remodeling and implant osteointegration depend not only on osteoblast response but also on interaction of the biomaterial with bone-resorbing osteoclasts, differentiation of osteoclasts in response to the compounds was also observed. For in vivo study, alginate gel comprised of EDHB and cells was transplanted into the back subcutis of mice. Our results show that EDHB might have beneficial effects through regulation of both osteoblast and osteoclast differentiation. Therefore, we suggest that EDHB could be a strong candidate for dual regulation to increase osteoblast differentiation and decrease osteoclast differentiation.

Transplantation of human placenta-derived mesenchymal stem cells in a silk fibroin/hydroxyapatite scaffold improves bone repair in rabbits

The main requirements for successful tissue engineering of the bone are non-immunogenic cells with osteogenic potential and a porous biodegradable scaffold. The purpose of this study is to evaluate the potential of a silk fibroin/hydroxyapatite (SF/HA) porous material as a delivery vehicle for human placenta-derived mesenchymal stem cells (PMSCs) in a rabbit radius defect model. In this study, we randomly assigned 16 healthy adult New Zealand rabbits into two groups, subjected to transplantation with either SF/HA and PMSCs (experimental group) or SF/HA alone (control group). To evaluate fracture healing, we assessed the extent of graft absorption, the quantity of newly formed bone, and re-canalization of the cavitas medullaris using radiographic and histological tools. We performed flow cytometric analysis to characterize PMSCs, and found that while they express CD90, CD105 and CD73, they stain negative for HLA-DR and the hematopoietic cell surface markers CD34 and CD45. When PMSCs were exposed to osteogenic induction medium, they secreted calcium crystals that were identified by von Kossa staining. Furthermore, when seeded on the surface of SF/HA scaffold, they actively secreted extracellular matrix components. Here, we show, through radiographic and histological analyses, that fracture healing in the experimental group is significantly improved over the control group. This strongly suggests that transplantation of human PMSCs grown in an SF/HA scaffold into injured radius segmental bone in rabbits, can markedly enhance tissue repair. Our finding provides evidence supporting the utility of human placenta as a potential source of stem cells for bone tissue engineering.

Calcium phosphate deposition rate, structure and osteoconductivity on electrospun poly(l-lactic acid) matrix using electrodeposition or simulated body fluid incubation

Mineralized nanofibrous scaffolds have been proposed as promising scaffolds for bone regeneration due to their ability to mimic both nanoscale architecture and chemical composition of natural bone extracellular matrix. In this study, a novel electrodeposition method was compared with an extensively explored simulated body fluid (SBF) incubation method in terms of the deposition rate, chemical composition and morphology of calcium phosphate formed on electrospun fibrous thin matrices with a fiber diameter in the range ~200-1400 nm prepared using 6, 8, 10 and 12 wt.% poly(l-lactic acid) (PLLA) solutions in a mixture of dichloromethane and acetone (2:1 in volume). The effects of the surface modification using the two mineralization techniques on osteoblastic cell (MC3T3-E1) proliferation and differentiation were also examined. It was found that electrodeposition was two to three orders of magnitude faster than the SBF method in mineralizing the fibrous matrices, reducing the mineralization time from ~2 weeks to 1h to achieve the same amounts of mineralization. The mineralization rate also varied with the fiber diameter but in opposite directions between the two mineralization methods. As a general trend, the increase of fiber diameter resulted in a faster mineralization rate for the electrodeposition method but a slower mineralization rate for the SBF incubation method. Using the electrodeposition method, one can control the chemical composition and morphology of the calcium phosphate by varying the electric deposition potential and electrolyte temperature to tune the mixture of dicalcium phosphate dihydrate and hydroxyapatite (HAp). Using the SBF method, one can only obtain a low crystallinity HAp. The mineralized electrospun PLLA fibrous matrices from either method similarly facilitate the proliferation and osteogenic differentiation of preosteoblastic MC3T3-E1 cells as compared to neat PLLA matrices. Therefore, the electrodeposition method can be utilized as a fast and versatile technique to fabricate mineralized nanofibrous scaffolds for bone tissue engineering.

Accelerating the early angiogenesis of tissue engineering constructs in vivo by the use of stem cells cultured in matrigel

In tissue engineering research, generating constructs with an adequate extent of clinical applications remains a major challenge. In this context, rapid blood vessel ingrowth in the transplanted tissue engineering constructs is the key factor for successful incorporation. To accelerate the microvascular development in engineered tissues, we preincubated osteoblast-like cells as well as mesenchymal stem cells or a combination of both cell types in Matrigel-filled PLGA scaffolds before transplantation into the dorsal skinfold chambers of balb/c mice. By the use of preincubated mesenchymal stem cells, a significantly accelerated angiogenesis was achieved. Compared with previous studies that showed a decisive increase of vascularization on day 6 after the implantation, we were able to halve this period and achieve explicitly denser microvascular networks 3 days after transplantation of the tissue engineering constructs. Thereby, the inflammatory host tissue response was acceptable and low, comparable with former investigations. A co-incubation of osteoblast-like cells and stem cells showed no additive effect on the density of the newly formed microvascular network. Preincubation of mesenchymal stem cells in Matrigel is a promising approach to develop rapid microvascular growth into tissue engineering constructs. After the implantation into the host organism, scaffolds comprising stem cells generate microvascular capillary-like structures exceptionally fast. Thereby, transplanted stem cells likely differentiate into vessel-associated cells. For this reason, preincubation of mesenchymal stem cells in nutrient solutions supporting different steps of angiogenesis provides a technique to promote the routine use of tissue engineering in the clinic.

Combination of poly L-lactic acid nanofiber scaffold with omentum graft for bone healing in experimental defect in tibia of rabbits

PURPOSE: To investigate the osteoconductive properties and biological performance of Poly L-lactic acid (PLLA) with omentum in bone defects. METHODS: PLLA nanofiber scaffolds were prepared via electrospinning technique. Forty four New Zealand white female rabbits randomly divided into three groups of 18 rabbits each. Created defects in right tibias were filled in group I with omentum, in group II with PLLA nanofiber scaffold and in group III with combination of the omentum and PLLA. The same defects were created in left tibia of all groups but did not receive any treatment (control group). Histological and histomorphometric evaluations were performed at two, four and six weeks after the implantation. RESULTS: Histological changes on all groups along with the time course were scored and statistical analysis showed that the average scores in group III were significantly higher than the other groups. CONCLUSION: Histomorphometric analysis of bone healing was shown to be significantly improved by the combined PLLA with omentum compared with the other groups, suggesting this biomaterial promote the healing of cortical bone, presumably by acting as an osteoconductive scaffold.

Building bridges: leveraging interdisciplinary collaborations in the development of biomaterials to meet clinical needs

Our laboratory at Rice University has forged numerous collaborations with clinicians and basic scientists over the years to advance the development of novel biomaterials and the modification of existing materials to meet clinical needs. This review highlights collaborative advances in biomaterials research from our laboratory in the areas of scaffold development, drug delivery, and gene therapy, especially as related to applications in bone and cartilage tissue engineering.

Microfabricated biomaterials for engineering 3D tissues

Mimicking natural tissue structure is crucial for engineered tissues with intended applications ranging from regenerative medicine to biorobotics. Native tissues are highly organized at the microscale, thus making these natural characteristics an integral part of creating effective biomimetic tissue structures. There exists a growing appreciation that the incorporation of similar highly organized microscale structures in tissue engineering may yield a remedy for problems ranging from vascularization to cell function control/determination. In this review, we highlight the recent progress in the field of microscale tissue engineering and discuss the use of various biomaterials for generating engineered tissue structures with microscale features. In particular, we will discuss the use of microscale approaches to engineer the architecture of scaffolds, generate artificial vasculature, and control cellular orientation and differentiation. In addition, the emergence of microfabricated tissue units and the modular assembly to emulate hierarchical tissues will be discussed.

Projection printing of 3-dimensional tissue scaffolds

Our ability to create precise, predesigned, spatially patterned biochemical and physical microenvironments inside polymer scaffolds could provide a powerful tool in studying progenitor cell behavior and differentiation under biomimetic, three-dimensional (3D) culture conditions. The development of freeform fabrication technology has become a promising tool for the manufacturing of biological scaffolds for tissue regeneration and stem cell engineering. Freeform fabrication is a very promising technology due to the efficient and simple process for creating bona fide 3D microstructures, such as closed channels and cavities. It is also capable of encapsulating biomolecules and even living cells. This chapter describes direct projection printing of 3D tissue engineering scaffolds by using a digital micromirror-array device (DMD) in a layer-by-layer process. This simple and fast microstereolithography system consists of an ultraviolet (UV) light source, a digital micromirror masking device, imaging optics, and controlling devices. Images of UV light are projected onto the photocurable resin by creating the "dynamic photomask" design with graphic software. Multilayered scaffolds are microfabricated through a photopolymerization process.

Adipose-derived stem cells and BMP2: part 1. BMP2-treated adipose-derived stem cells do not improve repair of segmental femoral defects

Recombinant human bone morphogenetic protein-2 (rhBMP2) has been shown to induce both in vitro osteogenic differentiation and in vivo bone formation, with the capacity of rhBMP2 to elicit the repair of numerous bony defects (calvaria, spinal fusion, femora, and so on) well documented. In addition, rhBMP2 has been approved by the Food and Drug Administration (FDA) for selected human indications. Despite the fact that healing is often achieved, the challenge still remains to optimize the therapeutic use of rhBMP2. One avenue may be through the combination of rhBMP2 with stem cells capable of osteogenic differentiation. This study investigates the ability of rhBMP2 at various doses in combination with human adipose-derived stem cells (ASCs) to heal critical-sized rat segmental femoral defects. For this, different doses of rhBMP2 were incorporated with apatite-coated porous poly(l-lactide-co-dl-lactide) (70  :  30) (PLDLA) scaffolds, seeded with ASCs, and implanted into athymic rats. After 8 weeks, all implants were harvested and processed for bone formation using micro computed tomography (microCT) analysis and histology. Despite the findings that indicate no adverse effect of the apatite surface on ASC osteogenesis, no significant difference in bone formation could be qualitatively or quantitatively determined upon the implantation of ASC-seeded scaffolds absorbed to increasing doses of rhBMP2. Such results would suggest that the presence of ASCs within rhBMP2-absorbed scaffolds does not improve the bone-forming ability of the construct and that the formation of bone may be driven by the rhBMP2 alone. Based on these results, the addition of ASCs to rhBMP2-treated scaffolds may provide no significant advantage in terms of the ability to heal bone.

The role of nanostructured mesoporous silicon in discriminating in vitro calcification for electrospun composite tissue engineering scaffolds

The impact of mesoporous silicon (PSi) particles-embedded either on the surface, or totally encapsulated within electrospun poly (ε-caprolactone) (PCL) fibers-on its properties as a tissue engineering scaffold is assessed. Our findings suggest that the resorbable porous silicon component can sensitively accelerate the necessary calcification process in such composites. Calcium phosphate deposition on the scaffolds was measured via in vitro calcification assays both at acellular and cellular levels. Extensive attachment of fibroblasts, human adult mesenchymal stem cells, and mouse stromal cells to the scaffold were observed. Complementary cell differentiation assays and ultrastructural measurements were also carried out; the levels of alkaline phosphatase expression, a specific biomarker for mesenchymal stem cell differentiation, show that the scaffolds have the ability to mediate such processes, and that the location of the Si plays a key role in levels of expression.

The effect of pore size on tissue ingrowth and neovascularization in porous bioceramics of controlled architecture in vivo

The purpose of this study was to investigate the role of pore size on tissue ingrowth and neovascularization in porous bioceramics under the accurate control of the pore parameters. For that purpose, β-tricalcium phosphate (β-TCP) cylinders with four different macropore sizes (300-400, 400-500, 500-600 and 600-700 µm) but the same interconnection size (120 µm) and unchangeable porosity were implanted into fascia lumbodorsalis in rabbits. The fibrous tissues and blood vessels formed in scaffolds were observed histologically and histomorphometrically. The vascularization of the porous bioceramics was analyzed by single-photon emission computed tomography (SPECT). It is found that pore size as an important parameter of a porous structure plays an important role in tissue infiltration into porous biomaterial scaffolds. The amount of fibrous tissue ingrowth increases with the decrease of the pore size. In four kinds of scaffolds with different macropore sizes (300-400, 400-500, 500-600 and 600-700 µm) and a constant interconnection size of 120 µm, the areas of fibrous tissue (%) were 60.5%, 52.2%, 41.3% and 37.3%, respectively, representing a significant decrease at 4 weeks (P < 0.01). The pore size of a scaffold is closely related to neovascularization of macroporous biomaterials implanted in vivo. A large pore size is beneficial for the growth of blood vessels, and the diameter of a pore smaller than 400 µm limits the growth of blood vessels and results in a smaller blood vessel diameter.

Nanotechnology and bone healing

Nanotechnology and its attendant techniques have yet to make a significant impact on the science of bone healing. However, the potential benefits are immediately obvious with the result that hundreds of researchers and firms are performing the basic research needed to mature this nascent, yet soon to be fruitful niche. Together with genomics and proteomics, and combined with tissue engineering, this is the new face of orthopaedic technology. The concepts that orthopaedic surgeons recognize are fabrication processes that have resulted in porous implant substrates as bone defect augmentation and medication-carrier devices. However, there are dozens of applications in orthopaedic traumatology and bone healing for nanometer-sized entities, structures, surfaces, and devices with characteristic lengths ranging from 10s of nanometers to a few micrometers. Examples include scaffolds, delivery mechanisms, controlled modification of surface topography and composition, and biomicroelectromechanical systems. We review the basic science, clinical implications, and early applications of the nanotechnology revolution and emphasize the rich possibilities that exist at the crossover region between micro- and nanotechnology for developing new treatments for bone healing.

The use of silk fibroin/hydroxyapatite composite co-cultured with rabbit bone-marrow stromal cells in the healing of a segmental bone defect

In a rabbit model we investigated the efficacy of a silk fibroin/hydroxyapatite (SF/HA) composite on the repair of a segmental bone defect. Four types of porous SF/HA composites (SF/HA-1, SF/HA-2, SF/HA-3, SF/HA-4) with different material ratios, pore sizes, porosity and additives were implanted subcutaneously into Sprague-Dawley rats to observe biodegradation. SF/HA-3, which had characteristics more suitable for a bone substitite based on strength and resorption was selected as a scaffold and co-cultured with rabbit bone-marrow stromal cells (BMSCs). A segmental bone defect was created in the rabbit radius. The animals were randomised into group 1 (SF/HA-3 combined with BMSCs implanted into the bone defect), group 2 (SF/HA implanted alone) and group 3 (nothing implanted). They were killed at four, eight and 12 weeks for visual, radiological and histological study.

The bone defects had complete union for group 1 and partial union in group 2, 12 weeks after operation. There was no formation of new bone in group 3. We conclude that SF/HA-3 combined with BMSCs supports bone healing and offers potential as a bone-graft substitute.

Up-regulation of alkaline phosphatase expression in human primary osteoblasts by cocultivation with primary endothelial cells is mediated by p38 mitogen-activated protein kinase-dependent mRNA stabilization

For the regeneration of bone in tissue engineering applications, it is essential to provide cues that support neovascularization. This can be achieved by cell-based therapies using mature endothelial cells (ECs) or endothelial progenitor cells. In this context, ECs were used in various in vivo studies in combination with primary osteoblasts to enhance neovascularization of bone grafts. In a previous study, we have shown that cocultivation of human primary ECs and human primary osteoblasts (hOBs) leads to a cell contact-dependent up-regulation of alkaline phosphatase (ALP) expression in osteoblasts, indicating that cocultivated ECs may support osteogenic differentiation and osteoblastic cell functions. In the present study, we investigated this effect in more detail, revealing a time and cell number dependency of EC-mediated up-regulation of the early osteoblastic marker ALP, whereas osteocalcin, a late marker of osteogenesis, was down-regulated. The effect on ALP expression was bidirectional specific for both cell types. Functional inhibition of gap junctional communication between ECs and hOBs by 18alpha-glycyrrhetinic acid had only a weak suppressive effect on EC-mediated ALP up-regulation. In contrast, inhibition of p38 mitogen-activated protein kinase nearly completely prevented the EC-mediated stimulation of osteoblastic ALP expression. To investigate the molecular mechanism underlying the ALP up-regulation, we examined the effect of EC cocultivation on osteoblastic ALP promoter activity as well as mRNA stability. Cocultivation of ECs with hOBs significantly elevated the half-life of osteoblastic ALP mRNA without affecting its promoter activity. In summary, our data show that EC-mediated up-regulation of osteoblastic ALP expression is cell-type specific and is posttranscriptionally regulated via p38 mitogen-activated protein kinase-dependent mRNA turn-over.

Cell interactions in bone tissue engineering

Bone fractures, where the innate regenerative bone response is compromised, represent between 4 and 8 hundred thousands of the total fracture cases, just in the United States. Bone tissue engineering (TE) brought the notion that, in cases such as those, it was preferable to boost the healing process of bone tissue instead of just adding artificial parts that could never properly replace the native tissue. However, despite the hype, bone TE so far could not live up to its promises and new bottom-up approaches are needed. The study of the cellular interactions between the cells relevant for bone biology can be of essential importance to that. In living bone, cells are in a context where communication with adjacent cells is almost permanent. Many fundamental works have been addressing these communications nonetheless, in a bone TE approach, the 3D perspective, being part of the microenvironment of a bone cell, is as crucial. Works combining the study of cell-to-cell interactions in a 3D environment are not as many as expected. Therefore, the bone TE field should not only gain knowledge from the field of fundamental Biology but also contribute for further understanding the biology of bone. In this review, a summary of the main works in the field of bone TE, aiming at studying cellular interactions in a 3D environment, and how they contributed towards the development of a functional engineered bone tissue, is presented.

Effects of polycaprolactone-tricalcium phosphate, recombinant human bone morphogenetic protein-2 and dog mesenchymal stem cells on bone formation: pilot study in dogs

PURPOSE

The aim of this study was to evaluate the survival, proliferation, and bone formation of dog mesenchymal stem cells (dMSCs) in the graft material by using Polycaprolactone-tricalcium phosphate (PCL-TCP), auto-fibrin glue (AFG), recombinant human bone morphogenetic protein-2 (rhBMP-2), and dMSCs after a transplantation to the scapula of adult beagle dogs.

MATERIALS AND METHODS

The subjects were two beagle dogs. Total dose of rhBMP-2 on each block was 10 microg with 50 microg/mg concentration. The cortical bone of the scapula of the dog was removed which was the same size of PCL-TCP block (Osteopore International Pte, Singapore; 5.0x5.0x8.0 mm in size), and the following graft material then was fixed with orthodontic mini-implant, Dual-top (Titanium alloy, Jeil Co. Seoul, Korea). Four experimental groups were prepared for this study, Group 1: PCL-TCP + aFG; Group 2: PCL-TCP + aFG + dMSCs; Group 3: PCL-TCP + aFG + dMSCs + rhBMP-2; Group 4: PCL-TCP + aFG + dMSCs + rhBMP-2 + PCL membrane. The survival or proliferation of dMSCs cells was identified with an extracted tissue through a fluorescence microscope, H-E staining and Von-Kossa staining in two weeks and four weeks after the transplantation.

RESULTS

The survival and proliferation of dMSCs were identified through a fluorescence microscope from both Group 1 and Group 2 in two weeks and four weeks after the transplantation. Histological observation also found that the injected cells were proliferating well in the G2, G3, and G4 scaffolds.

CONCLUSION

This study concluded that bone ingrowth occurred in PCL-TCP scaffold which was transplanted with rhBMP-2, and MSCs did not affect bone growth. More sufficient healing time would be needed to recognize effects of dMSCs on bone formation.

In vivo engineering of a human vasculature for bone tissue engineering applications

The neovascularization of three-dimensional voluminous tissues, such as bone, represents an important challenge in tissue engineering applications. The formation of a preformed vascular plexus could maintain cell viability and promote vascularization after transplantation. We have developed a three-dimensional spheroidal coculture system consisting of human primary endothelial cells and human primary osteoblasts (hOBs) to improve angiogenesis in bone tissue engineering applications. In this study, we investigated the survival and vascularization of the engineered implants in vivo. Endothelial cell spheroids were cocultured with hOBs in fibrin and seeded into scaffolds consisting of processed bovine cancellous bone (PBCB). The cell-seeded scaffolds were evaluated for their angiogenic potential in two different in vivo assays: the chick embryo chorioallantoic membrane (CAM) model and the severe combined immunodeficiency disorder (SCID) mouse model. In both assays, the development of a complex three-dimensional network of perfused human neovessels could be detected. After subcutaneous implantation into immunodeficient mice, the newly formed human vasculature was stabilized by the recruitment of murine smooth muscle α-actin-positive mural cells and anastomoses with the mouse vasculature. We conclude that this endothelial cell spheroid system can be used to create a network of functional perfused blood vessels in vivo. The finding that this process takes place with high efficacy in the presence of co-implanted primary osteoblasts and in an osteoconductive environment provided by the PBCB scaffold, suggests that this system may be suitable for improving vascularization in bone tissue engineering.

The effect of type I collagen on osteochondrogenic differentiation in adipose-derived stromal cells in vivo

BACKGROUND

Recent studies have demonstrated that adipose-derived adult stromal cells (ADASCs) offer great promise for cell-based therapies due to their ability to differentiate towards bone, cartilage and fat [corrected] The objective of this study was to investigate whether type I collagen would elicit in vivo bone formation of passaged rat adipose-derived adult stromal cells (ADASC) placed extraskeletally.

METHODS

After expansion for 1-4 passages (P), cells were incubated in osteogenic medium containing dexamethasone, ascorbic acid and beta-glycerol phosphate for 2-4 weeks. Undifferentiated cells were maintained in Dulbecco's modified Eagle's medium (DMEM) with 10% fetal bovine serum (FBS). Osteogenic differentiation was evaluated by alkaline phosphatase (ALP) and von Kossa staining as well as by gene expression of ALP, osteopontin (OP), osteonectin (ON), osteocalcin (OC), collagen I (colI), collagen II (colII), bone sialoprotein (BSP), periostin (Postn), runx2, osterix (Osx), sox9, msx1 and msx2. Diffusion chambers were filled with 1x10(6) cells mixed with or without type I collagen gel and implanted subcutaneously into rats. Controls included chambers exposed to (1) undifferentiated cells (with or without collagen, (2) collagen without cells and (3) empty chambers (n=5 per group).

RESULTS

Four weeks after implantation, in vivo bone and cartilage formation was demonstrated in implants containing 4-week osteo-induced P1 and P4 cells wrapped in the collagen gel, as confirmed by Goldner's trichrome and Alcian blue staining, respectively. Newly formed bone stained positive for type I collagen. Control implants had no bone or cartilage and were primarily filled with fibrous tissue at that time interval.

DISCUSSION

Recent studies have demonstrated that ADASC offer great promise for cell-based therapies because of their ability to differentiate toward bone, cartilage and fat. However, the influence of different matrices on the in vivo osteogenic capability of ADASC is not fully understood. These findings suggest that type I collagen may support the survival and expression of osteogenic and chondrogenic phenotypes in passaged rat ADASC in vivo.

Osteogenic differentiation of mesenchymal stem cells in defined protein beads

There is a need to develop improved methods for directing and maintaining the differentiation of human mesenchymal stem cells (hMSC) for regenerative medicine. Here, we present a method for embedding cells in defined protein microenvironments for the directed osteogenic differentiation of hMSC. Composite matrices of collagen I and agarose were produced by emulsification and simultaneous polymerization in the presence of hMSC to produce 30-150 mum diameter hydrogel "beads." The proliferation, morphology, osteogenic gene expression, and calcium deposition of hMSC in bead environments were compared to other two- and three-dimensional culture environments over 14-21 days in culture. Cells embedded within 40% collagen beads exhibited equivalent proliferation rates to those in gel disks, but showed upregulation of bone sialoprotein and increased calcium deposition over 2D controls. Osteocalcin gene expression was not changed in 3D beads and disks, while collagen type I gene expression was downregulated relative to cells in 2D culture. The hydrogel bead format allows controlled cell differentiation and is a cell delivery vehicle that may also enhance vascular invasion and host incorporation. Our results indicate that the application of such beads can be used to promote the osteogenic phenotype in hMSC, which is an important step toward using them in bone repair applications.

Nanoparticle technology in bone tissue engineering

Nanotechnology has been increasingly utilized to enhance bone tissue engineering strategies. In particular, nanotechnology has been employed to overcome some of the current limitations associated with bone regeneration methods including insufficient mechanical strength of scaffold materials, ineffective cell growth and osteogenic differentiation at the defect site, as well as unstable and insufficient production of growth factors to stimulate bone cell growth. Among the tremendous technologies of nanoparticles in biological systems, we focus here on the three major nanoparticle research areas that have been developed to overcome these limitations and disadvantages: (a) the generation of nanoparticle-composite scaffolds to provide increased mechanical strength for bone graft, (b) the fabrication of nanofibrous scaffolds to support cell growth and differentiation through morphologically-favored architectures, and (c) the development of novel delivery and targeting systems of genetic material, especially those encoding osteogenic growth factors. These nanoparticle-based bone tissue engineering technologies possess a great potential to ensure the efficacy of clinical bone regeneration.

Collagen scaffolds for tissue engineering

There are two major approaches to tissue engineering for regeneration of tissues and organs. One involves cell-free materials and/or factors and one involves delivering cells to contribute to the regeneraion process. Of the many scaffold materials being investigated, collagen type I, with selective removal of its telopeptides, has been shown to have many advantageous features for both of these approaches. Highly porous collagen lattice sponges have been used to support in vitro growth of many types of tissues. Use of bioreactors to control in vitro perfusion of medium and to apply hydrostatic fluid pressure has been shown to enhance histogenesis in collagen scaffolds. Collagen sponges have also been developed to contain differentiating-inducing materials like demineralized bone to stimulate differentiation of cartilage tissue both in vitro and in vivo.

Laser-layered microfabrication of spatially patterned functionalized tissue-engineering scaffolds

Understanding cell behavior inside complex, three-dimensional (3D) microenvironments with controlled spatiotemporal patterning of physical and biochemical factors would provide significant insights into the basic biology of organ development and tissue functions. One of the fundamental limitations in studying such behavior has been the inability to create patterned microenvironments within 3D scaffold structures. Here a simple, layer-by-layer stereolithography (SL) method that can precisely pattern ligands, extracellular-matrix (ECM) components, and growth factors, as well as controlled release particles inside a single scaffold, has been developed. The process also allows fabrication of predesigned internal architectures and porosities. Photocrosslinkable poly(ethylene glycol) dimethacrylate (PEGDMA) was used as the basic structural component of these microfabricated scaffolds. PEG acrylates, covalently modified with the cell adhesive peptide arginine-glycine-aspartic acid (RGD) or the ECM component heparan sulfate, was incorporated within the scaffolds to facilitate cell attachment and to allow spatial sequestration of heparan-binding growth factors. Fluorescently labeled polymer microparticles and basic fibroblast growth factor (FGF-2) were chosen to illustrate the capability of SL to spatiotemporally pattern scaffolds. The results demonstrate that a precise, predesigned distribution of single or multiple factors within a single 3D structure can be created, and specific internal architectures can be fabricated. Functionalization of these scaffolds with RGD is demonstrated, and heparan sulfate allows efficient cell attachment and spatial localization of growth factors. Such patterned scaffolds might provide effective systems to study cell behavior in complex microenvironments and could eventually lead to engineering of complex, hybrid tissue structures through predesigned, multilineage differentiation of a single stem-cell population.

A review of materials, fabrication methods, and strategies used to enhance bone regeneration in engineered bone tissues

Over the last decade, bone engineered tissues have been developed as alternatives to autografts and allografts to repair and reconstruct bone defects. This article provides a review of the current technologies in bone tissue engineering. Factors used for fabrication of three-dimensional bone scaffolds such as materials, cells, and biomolecular signals, as well as required properties for ideal bone scaffolds, are reviewed. In addition, current fabrication techniques including rapid prototyping are elaborated upon. Finally, this review article further discusses some effective strategies to enhance cell ingrowth in bone engineered tissues; for example, nanotopography, biomimetic materials, embedded growth factors, mineralization, and bioreactors. In doing so, it suggests that there is a possibility to develop bone substitutes that can repair bone defects and promote new bone formation for orthopedic applications.

Reconstruction of Cranial Bone Defects Using a Compound of Bone Marrow Stromal Cells and Hydroxyapatite-Tricalcium Phosphate

Hydroxyapatite-tricalcium phosphate (HA-TCP) is a new kind of material which shows good biocompatibility, biological degradability, and porosity. This study aimed to determine the effectiveness of HA-TCP as a bone tissue engineering scaffold. In this study, critical size cranial defects were reconstructed with compounds of autogenous bone marrow stromal cells (BMSCs) and HA-TCP. The resulting grafts were examined by X-ray, histological examination, semi-quantitative analysis of osteogenesis, immunochemical examination (collagen type I and III), scanning electron microscopy and transmission electron microscopy. The results showed that HA-TCP is a good bone tissue engineering scaffold and BMSCs/HA-TCP is a promising technique for reconstruction of bone defects.

In vitro and in vivo effects of rat kidney vascular endothelial cells on osteogenesis of rat bone marrow mesenchymal stem cells growing on polylactide-glycoli acid (PLGA) scaffolds

It is well established that vascularization is critical for osteogenesis. However, adequate vascularization also remains one of the major challenges in tissue engineering of bone. This problem is further accentuated in regeneration of large volume of tissue. Although a complex process, vascularization involves reciprocal regulation and functional interaction between endothelial and osteoblast-like cells during osteogenesis. This prompted us to investigate the possibility of producing bone tissue both in vitro and ectopically in vivo using vascular endothelial cells because we hypothesized that the direct contact or interaction between vascular endothelial cells and bone marrow mesenchymal stem cells are of benefit to osteogenesis in vitro and in vivo. For that purpose we co-cultured rat bone marrow mesenchymal stem cells (MSC) and kidney vascular endothelial cells (VEC) with polylactide-glycolic acid scaffolds. In vitro experiments using alkaline phosphatase and osteocalcin assays demonstrated the proliferation and differentiation of MSC into osteoblast-like cells, especially the direct contact between VEC and MSC. In addition, histochemical analysis with CD31 and von-Willebrand factor staining showed that VEC retained their endothelial characteristics. In vivo implantation of MSC and VEC co-cultures into rat's muscle resulted in pre-vascular network-like structure established by the VEC in the PLGA. These structures developed into vascularized tissue, and increased the amount and size of the new bone compared to the control group (p < 0.05). These results suggest that the vascular endothelial cells could efficiently stimulate the in vitro proliferation and differentiation of osteoblast-like cells and promote osteogenesis in vivo by the direct contact or interaction with the MSC. This technique for optimal regeneration of bone should be further investigated.

The performance of a bone-derived scaffold material in the repair of critical bone defects in a rhesus monkey model

The efficacy and safety of a material derived from human bones in the repair of critical segmental bone defects are evaluated in a rhesus monkey model. Frozen human bones were chemically and physically processed into a partially demineralized and deproteinized material in blocks. The complete tissue-engineered (TE) bone was constructed of the material preseeded with allogeneic bone marrow mesenchymal stem cells (MSCs). The material alone and the TE bone were, respectively, implanted to bridge 2.5cm-long critical defects in right and left radii of 15 monkeys. At weeks 1, 2, 3, 6 and 12 post-implantation, the grafts were collected from three animals and assessed for the local expression of osteogenic markers, histological and roentgenographic features, and immune reactions. It was shown that defects were well repaired with both treatments whereas the bone defects in 2 additional untreated animals remained the same size after 12 weeks. In radii implanted with the TE bones, the repair processes were approximately 3 weeks faster and new bones were formed in a multipoint way. There was neither observable toxic effect nor overt immune rejection in any animals. Taken together, these observations suggest that the TE bone blocks composited of the allogeneic or xenogeneic bone-derived scaffold and allogeneic MSCs may provide an ideal method for repairing large segmental bone defects.

Comparison among Four Kinds of Bone Tissue Engineering Scaffold

Bone tissue engineering is a promising way to repair of bone defects. To choose a proper scaffold is still a disputable problem in bone tissue engineering. This study aimed to compare the effects of repairing critical calvarial defects with the compounds of autogenous bone marrow stromal cells (BMSCs) and coral hydroxyapatite(CHA), hydroxyapatite/ tricalcium phosphate (HA/TCP), poly(lactide-co-glycolide) (PLGA) and alginate (AG). The results showed that CHA and AG were satisfactory bone tissues engineering scaffolds among the four kinds of materials. BMSCs/CHA and BMSCs/AG are promising techniques for reconstruction of bone defects.

Gene Expression Profiling Reveals Platelet-Derived Growth Factor Receptor Alpha as a Target of Cell Contact-Dependent Gene Regulation in an Endothelial Cell–Osteoblast Co-culture Model

Angiogenesis plays an important role in bone development, repair, and remodelling. Neovascularization is furthermore a crucial step in bone tissue engineering because implantation of voluminous grafts without sufficient vascularity results in hypoxic cell death of the engineered tissue. We have previously described a co-cultivation system of human primary osteoblasts and human primary endothelial cells that was developed to improve neovascularization in bone tissue-engineering applications. In our present study, we have performed complementary deoxyribonucleic acid microarray analysis to analyze putative changes in osteoblastic gene expression upon co-cultivation of osteoblasts and endothelial cells. Transcriptional profiling revealed upregulation of 79 genes and downregulation of 62 genes in osteoblasts after co-cultivation with endothelial cells. To verify the microarray data, quantitative real-time reverse transcriptase polymerase chain reaction was carried out on selected genes. The expression of the platelet-derived growth factor receptor alpha gene in osteoblasts was analyzed in more detail, revealing that a cell contact-dependent mechanism, and not paracrine-acting diffusible factors, mediates the downregulation of this receptor in osteoblasts upon co-cultivation with endothelial cells. In summary, the data demonstrate complex gene-regulation mechanisms between endothelial cells and osteoblasts that are likely to play a role in bone morphogenesis.

Using Dihydropyridine-Release Strategies to Enhance Load Effects in Engineered Human Bone Constructs

We report on the development of a novel biodegradable scaffold capable of enhancing mechanical signals for tissue-engineering applications. It has been shown that mechanotransduction enhances bone formation in vitro and in vivo; in tissue-engineering applications, this phenomenon is exploited through the use of mechanical bioreactors to generate bone tissue. The dihydropyridine agonist Bay K8644 (Bay) acts to increase the opening time of mechanosensitive voltage-operated calcium channels (VOCCs), specifi- cally L-type VOCCs, which are known to play a fundamental role in the early mediation of mechanotransduction. We have produced porous 3-dimensional, Bay-encapsulated biodegradable poly(L-lactide) acid scaffolds using a solvent-casting and salt-leaching technique. The effects of the released Bay on osteoid production and mineralization in human bone cell-seeded constructs following incubation in a perfusion-compression bioreactor in vitro was investigated using Western blotting techniques and a calcium assay protocol developed in our lab. Our newly developed scaffolds act by slowly releasing the calcium channel agonist Bay K8644 as observed using ultraviolet spectroscopy, maintaining the open state of mechanosensitive VOCCs responding to load, which augments the load signal at sites of strain across the scaffold. Our results demonstrate that, in the presence of physiological loading regimes in vitro, release of Bay enhances collagen I protein production and osteoid calcification more than non-Bay control constructs do. Osteopontin and alpha2delta1 VOCC subunit protein levels were also higher as a result of perfusion-compression conditioning. These results indicate that Bay-encapsulated scaffolds can be used in the presence of load to enhance the production of load-bearing engineered tissue.

Biofabricated marine hydrozoan: a bioactive crystalline material promoting ossification of mesenchymal stem cells

This study introduces a novel three-dimensional biomatrix obtained from the marine hydrocoral Millepora dichotoma as a scaffold for hard tissue engineering. Millepora dichotoma was biofabricated under field and laboratory conditions. Three-dimensional biomatrices were made in order to convert mesenchymal stem cells (MSCs) to exemplify osteoblastic phenotype. We investigated the effect of the biomatrices on MSCs proliferation and differentiation at 2, 3, 4, 7, 10, 14, 21, 28, and 42 days. Different analyses were made: light microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), calcium incorporation to newly formed tissue (alizarin red), bone nodule formation (von Kossa), fat aggregate formation (oil red O), collagen type I immunofluorescence, DNA concentrations, alkaline phosphatase (ALP) activity, and osteocalcin concentrations. MSCs seeded on Millepora dichotoma biomatrices showed higher levels of calcium and phosphate incorporation and higher type I collagen levels than did control Porites lutea biomatrices. ALP activity revealed that MSCs seeded on M. dichotoma biomatrices are highly osteogenic compared to those on control biomatrices. The osteocalcin content of MSCs seeded on M. dichotoma remained constant up to 2 weeks before rising to surpass that of seeded P. lutea biomatrices after 28 days. Our study thus showed that M. dichotoma biomatrices enhance the differentiation of MSCs into osteoblast and hence have excellent potential as bioscaffold for hard tissue engineering.

Fabrication of cultured oral gingiva by tissue engineering techniques without materials of animal origin

BACKGROUND

Cultured gingival substitute has been found to be a useful graft material for treatment of gingival recession. However, such substitutes include xenograft derivative materials that involve concomitant risk of viral contamination. To eliminate this risk, we designed new gingival substitutes made of recombinant human collagen types I and III sponges and cultured these substitutes in animal-free media (HFDM-1).

METHODS

Gingival fibroblasts were seeded onto sponges of type I or III recombinant collagen. These sponges were cultured in Dulbecco's modified Eagle's medium (DMEM) with 10% fetal bovine serum (FBS), HFDM-1 with 2% human serum (HS), or HFDM-1. Fibroblast proliferation in these samples was compared using the cell-counting kit assay. Vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) released into the cultured media were examined by enzyme-linked immunosorbent assay.

RESULTS

The fibroblasts proliferated significantly in all six combinations of collagen and medium types. The fibroblast growth rate after 9 days of culture was equal between HFDM-1 with 2% HS and DMEM with 10% FBS. The type III collagen sponge showed a higher fibroblast growth rate than the type I sponge. VEGF concentrations in HFDM-1 with 2% HS were higher than those in other media. The highest HGF levels were detected in DMEM with 10% FBS.

CONCLUSIONS

The new cultured gingival substitute containing no animal-derived materials produced good cell proliferation and VEGF release. The results suggested that the substitute may provide a new tool for the treatment of gingival recession.