Study of hydroxyapatite osteoinductivity with an osteogenic differentiation of mesenchymal stem cells

Improving osteointegration and osteogenesis of three-dimensional porous Ti6Al4V scaffolds by polydopamine-assisted biomimetic hydroxyapatite coating

Titanium alloys with various porous structures can be fabricated by advanced additive manufacturing techniques, which are attractive for use as scaffolds for bone defect repair. However, modification of the scaffold surfaces, particularly inner surfaces, is critical to improve the osteointegration of these scaffolds. In this study, a biomimetic approach was employed to construct polydopamine-assisted hydroxyapatite coating (HA/pDA) onto porous Ti6Al4V scaffolds fabricated by the electron beam melting method. The surface modification was characterized with the field emission scanning electron microscopy, energy dispersive spectroscopy, water contact angle measurement, and confocal laser scanning microscopy. Attachment and proliferation of MC3T3-E1 cells on the scaffold surface were significantly enhanced by the HA/pDA coating compared to the unmodified surfaces. Additionally, MC3T3-E1 cells grown on the HA/pDA-coated Ti6Al4V scaffolds displayed significantly higher expression of runt-related transcription factor-2, alkaline phosphatase, osteocalcin, osteopontin, and collagen type-1 compared with bare Ti6Al4V scaffolds after culture for 14 days. Moreover, microcomputed tomography analysis and Van-Gieson staining of histological sections showed that HA/pDA coating on surfaces of porous Ti6Al4V scaffolds enhanced osteointegration and significantly promoted bone regeneration after implantation in rabbit femoral condylar defects for 4 and 12 weeks. Therefore, this study provides an alternative to biofunctionalized porous Ti6Al4V scaffolds with improved osteointegration and osteogenesis functions for orthopedic applications.

High porous titanium scaffolds showed higher compatibility than lower porous beta-tricalcium phosphate scaffolds for regulating human osteoblast and osteoclast differentiation

We compared osteoblast and osteoclast differentiation when using beta-tricalcium phosphate (βTCP) and titanium scaffolds by investigating human mesenchymal stem cells (hMSCs) and osteoclast progenitor cell activities. hMSCs were cultured for 7, 14, and 21days on titanium scaffolds with 60%, 73%, and 87% porosity and on βTCP scaffolds with 60% and 75% porosity. Human osteoclast progenitor cells were cultured with osteoblast for 14 and 21days on 87% titanium and 75% βTCP scaffolds. Viable cell numbers with 60% and 73% titanium were higher than with 87% titanium and βTCP scaffolds (P<0.05). An 87% titanium scaffold resulted in the highest osteocalcin production with calcification on day 14 (P<0.01) in titanium scaffolds. All titanium scaffolds resulted in higher osteocalcin production on days 7 and 14 compared to βTCP scaffolds (P<0.01). Osteoblasts cultured on 87% titanium scaffolds suppressed osteoclast differentiation on day 7 but enhanced osteoclast differentiation on day 14 compared to 75% βTCP scaffolds (P<0.01). These findings concluded that high porosity titanium scaffolds could enhance progression of hMSC/osteoblast differentiation and regulated osteoclast differentiation cooperating with osteoblast differentiation for calcification as compared with lower porous βTCP.

Effect of different hydroxyapatite incorporation methods on the structural and biological properties of porous collagen scaffolds for bone repair

Scaffolds which aim to provide an optimised environment to regenerate bone tissue require a balance between mechanical properties and architecture known to be conducive to enable tissue regeneration, such as a high porosity and a suitable pore size. Using freeze-dried collagen-based scaffolds as an analogue of native ECM, we sought to improve the mechanical properties by incorporating hydroxyapatite (HA) in different ways while maintaining a pore architecture sufficient to allow cell infiltration, vascularisation and effective bone regeneration. Specifically we sought to elucidate the effect of different hydroxyapatite incorporation methods on the mechanical, morphological, and cellular response of the resultant collagen-HA scaffolds. The results demonstrated that incorporating either micron-sized (CHA scaffolds) or nano-sized HA particles (CnHA scaffolds) prior to freeze-drying resulted in moderate increases in stiffness (2.2-fold and 6.2-fold, respectively, vs. collagen-glycosaminoglycan scaffolds, P < 0.05, a scaffold known to support osteogenesis), while enabling good cell attachment, and moderate mesenchymal stem cell (MSC)-mediated calcium production after 28 days' culture (2.1-fold, P < 0.05, and 1.3-fold, respectively, vs. CG scaffolds). However, coating of collagen scaffolds with a hydroxyapatite precipitate after freeze-drying (CpHA scaffolds) has been shown to be a highly effective method to increase the compressive modulus (26-fold vs. CG controls, P < 0.001) of scaffolds while maintaining a high porosity (~ 98%). The coating of the ligand-dense collagen structure results in a lower cell attachment level (P < 0.05), although it supported greater cell-mediated calcium production (P < 0.0001) compared with other scaffold variants after 28 days' culture. The comparatively good mechanical properties of these high porosity scaffolds is obtained partially through highly crosslinking the scaffolds with both a physical (DHT) and chemical (EDAC) crosslinking treatment. Control of scaffold microstructure was examined via alterations in freezing temperature. It was found that the addition of HA prior to freeze-drying generally reduced the pore size and so the CpHA scaffold fabrication method offered increased control over the resulting scaffolds microstructure. These findings will help guide future design considerations for composite biomaterials and demonstrate that the method of HA incorporation can have profound effects on the resulting scaffold structural and biological response.

Fluorapatite-modified scaffold on dental pulp stem cell mineralization

In previous studies, fluorapatite (FA) crystal-coated surfaces have been shown to stimulate the differentiation and mineralization of human dental pulp stem cells (DPSCs) in two-dimensional cell culture. However, whether the FA surface can recapitulate these properties in three-dimensional culture is still unknown. This study examined the differences in behavior of human DPSCs cultured on electrospun polycaprolactone (PCL) NanoECM nanofibers with or without the FA crystals. Under near-physiologic conditions, the FA crystals were synthesized on the PCL nanofiber scaffolds. The FA crystals were evenly distributed on the scaffolds. DPSCs were cultured on the PCL+FA or the PCL scaffolds for up to 28 days. Scanning electron microscope images showed that DPSCs attached well to both scaffolds after the initial seeding. However, it appeared that more multicellular aggregates formed on the PCL+FA scaffolds. After 14 days, the cell proliferation on the PCL+FA was slower than that on the PCL-only scaffolds. Interestingly, even without any induction of mineralization, from day 7, the upregulation of several pro-osteogenic molecules (dmp1, dspp, runx2, ocn, spp1, col1a1) was detected in cells seeded on the PCL+FA scaffolds. A significant increase in alkaline phosphatase activity was also seen on FA-coated scaffolds compared with the PCL-only scaffolds at days 14 and 21. At the protein level, osteocalcin expression was induced only in the DPSCs on the PCL+FA surfaces at day 21 and then significantly enhanced at day 28. A similar pattern was observed in those specimens stained with Alizarin red and Von Kossa after 21 and 28 days. These data suggest that the incorporation of FA crystals within the three-dimensional PCL nanofiber scaffolds provided a favorable extracellular matrix microenvironment for the growth, differentiation, and mineralization of human DPSCs. This FA-modified PCL nanofiber scaffold shows promising potential for future bone, dental, and orthopedic regenerative applications.

Does translational symmetry matter on the micro scale? Fibroblastic and osteoblastic interactions with the topographically distinct poly(ε-caprolactone)/hydroxyapatite thin films

Material composition and topography of the cell-contacting material interface are important considerations in the design of biomaterials at the nano and micro scales. This study is one of the first to have assessed the osteoblastic response to micropatterned polymer-ceramic composite surfaces. In particular, the effect of topographic variations of composite poly(ε-caprolactone)/hydroxyapatite (PCL/HAp) films on viability, proliferation, migration and osteogenesis of fibroblastic and osteoblastic MC3T3-E1 cells was evaluated. To that end, three different micropatterned PCL/HAp films were compared: flat and textured, the latter of which included films comprising periodically arranged and randomly distributed oval topographic features 10 μm in diameter, 20 μm in separation and 10 μm in height, comparable to the dimensions of MC3T3-E1 cells. PCL/HAp films were fabricated by the combination of a bottom-up, soft chemical synthesis of the ceramic, nanoparticulate phase and a top-down, photolithographic technique for imprinting fine, microscale features on them. X-ray diffraction analysis indicated an isotropic orientation of both the polymeric chains and HAp crystallites in the composite samples. Biocompatibility tests indicated no significant decrease in their viability when grown on PCL/HAp films. Fibroblast proliferation and migration onto PCL/HAp films proceeded slower than on the control borosilicate glass, with the flat composite film fostering more cell migration activity than the films containing topographic features. The gene expression of seven analyzed osteogenic markers, including procollagen type I, osteocalcin, osteopontin, alkaline phosphatase, and the transcription factors Runx2 and TGFβ-1, was, however, consistently upregulated in cells grown on PCL/HAp films comprising periodically ordered topographic features, suggesting that the higher levels of symmetry of the topographic ordering impose a moderate mechanochemical stress on the adherent cells and thus promote a more favorable osteogenic response. The obtained results suggest that topography can be a more important determinant of the cell/surface interaction than the surface chemistry and/or stiffness as well as that the regularity of the distribution of topographic features can be a more important variable than the topographic features per se.

Blends and Nanocomposite Biomaterials for Articular Cartilage Tissue Engineering

This review provides a comprehensive assessment on polymer blends and nanocomposite systems for articular cartilage tissue engineering applications. Classification of various types of blends including natural/natural, synthetic/synthetic systems, their combination and nanocomposite biomaterials are studied. Additionally, an inclusive study on their characteristics, cell responses ability to mimic tissue and regenerate damaged articular cartilage with respect to have functionality and composition needed for native tissue, are also provided.

Effect of thickness of HA-coating on microporous silk scaffolds using alternate soaking technology

Hydroxyapatite (HA) can be coated on various materials surface and has the function of osteogenicity. Microporous silk scaffold has excellent biocompatibility. In this study, alternate soaking technology was used to coat HA on microporous silk scaffolds. However, the cell proliferation was found to decrease with the increasing thickness (cycles of soaking) of HA-coating. This study aims to determine the best thickness (cycles of soaking) of HA-coating on microporous silk scaffolds. The SEM observation showed that group with one cycle of alternate soaking (1C-HA) has the most optimal porosity like non-HA-modified microporous silk scaffolds. The proliferation of osteoblasts has no significant difference between noncoated HA (N-HA) and 1C-HA groups, which are both significantly higher than those in two cycles of soaking (2C-HA) and three cycles of soaking (3C-HA) groups. The transcription levels of specific genes (runx2 and osteonectin) in osteoblasts of 1C-HA group were significantly higher than those of N-HA group. Moreover, the levels showed no significant difference among 1C-HA, 2C-HA, and 3C-HA groups. In conclusion, microporous silk scaffold with 1 cycle of HA-coating can combine the biocompatibility of silk and osteogenicity of HA.

Biomimetic nanocomposites to control osteogenic differentiation of human mesenchymal stem cells

The design of biomimetic nanomaterials that can directly influence the behavior of cells and facilitate the regeneration of tissues and organs has become an active area of research. Here, the production of materials based on nano-hydroxyapatite composites in scaffolds with nanofibrous and nanoporous topographies, designed to mimic the native bone matrix for applications in bone tissue engineering, is reported. Human mesenchymal stem cells grown on these nanocomposites are stimulated to rapidly produce bone minerals in situ, even in the absence of osteogenic supplements in the cell-culture medium. Nanocomposites comprising type I collagen and nano-hydroxyapatite are found to be especially efficient at inducing mineralization. When subcutaneously implanted into nude mice, this biomimetic nanocomposite is able to form a new bone matrix within only two weeks. Furthermore, when the nanocomposite is enriched with human mesenchymal stem cells before implantation, development of the bone matrix is accelerated to within one week. To the best of the authors' knowledge, this study provides the first clear in vitro and in vivo demonstration of osteoinduction controlled by the material characteristics of a biomimetic nanocomposite. This approach can potentially facilitate the translation of de novo bone-formation technologies to the clinic.

Effects of novel hydroxyapatite-based 3D biomaterials on proliferation and osteoblastic differentiation of mesenchymal stem cells

The aim of this study was to examine the differential capacity of isolated dental pulp stem cells (SHED) cultured onto four different scaffold materials. The differential potential of isolated SHED was examined on the following scaffolds: porous hydroxyapatite (pHAP) alone or combined with three polymers [polylactic-co-glycolic acid (PLGA), alginate, and ethylene vinylacetate / ethylene vinylversatate (EVA/EVV)]. SHED were isolated by "outgrowth" method and characterized by the flow cytometry. Viability of cells grown with scaffolds was assessed by MTT and LDH assays. No significant cytotoxic effect of any of the tested materials was shown. Staining with alizarin red and estimated alkaline phosphatase activity to identify differentiation, demonstrated osteoblastic phenotype of SHED and newly deposited and mineralized extra cellular matrix (ECM) in presence of all tested scaffolds. The developed ECM seen at scanning electronic micrographs additionally confirmed the osteogenic differentiation and biocompatibility between cells and materials. In summary, all studied biomaterials are suitable carriers for proliferation and osteoblastic differentiation of dental pulp mesenchymal stem cells in vitro.

Hydroxyapatite coating affects the Wnt signaling pathway during peri-implant healing in vivo

Owing to its bio- and osteoconductivity, hydroxyapatite (HA) is a widely used implant material, but its osteogenic properties are only partly evaluated in vitro and in vivo. The present study focused on bone healing adjacent to HA-coated titanium (Ti) implants, with or without incorporated lithium ions (Li(+)). Special attention was given to the Wnt signaling pathway. The implants were inserted into rat tibia for 7 or 28 days and analyzed ex vivo, mainly by histomorphometry and quantitative real-time polymerase chain reaction (qPCR). HA-coated implants showed, irrespective of Li(+) content, bone-implant contact (BIC) and removal torque values significantly higher than those of reference Ti. Further, the expression of OCN, CTSK, COL1A1, LRP5/6 and WISP1 was significantly higher in implant-adherent cells of HA-coated implants, with or without Li(+). Significantly higher β-catenin expression and significantly lower COL2A1 expression were observed in peri-implant bone cells from HA with 14 ng cm(-2) released Li(+). Interestingly, Ti implants showed a significantly larger bone area (BA) in the threads than HA with 39 ng cm(-2) released Li(+), but had a lower BIC than any HA-coated implant. This study shows that HA, with or without Li(+), is a strong activator of the Wnt signaling pathway, and may to some degree explain its high bone induction capacity.

Combined usage of hydroxyapatite and cross-finger flap for fingertip reconstruction

Reconstruction for fingertip defects categorized as Type 3 and Type 4 in Allen's classification is challenging, because surgeons need to reconstruct not only the pulp but also great parts of the distal phalangeal bone. This paper introduces an original technique for the reconstruction of defects of these types. The defects of seven fingers (two small fingers and five index fingers) of seven patients (three males and four females; aged 14-44 years) were repaired. After the fingertip is divided in a fish-mouth fashion to expose the stump of the distal phalangeal bone, a curved block of hydroxyapatite is grafted to fill the phalangeal defect and straighten the nail bed. A rectangular flap is raised from the dorsal side of the neighbouring finger in the region between the PIP and DIP joints. Then the fish-mouth region carrying the grafted hydroxyapatite is covered with the rectangular flap to reconstruct the pulp. The rectangular cross-finger flap is separated 3-4 weeks postoperatively. In all seven cases, the flap survived completely. Infection developed in no case. In all cases, aesthetic appearance of the pulp and nail presented improvement, satisfying the patients. Combined usage of hydroxyapatite and a cross-finger flap from the neighbouring finger is an effective method for the reconstruction of type 3 and type 4 defects in Allen's classification.

Fabrication and evaluation of porous beta-tricalcium phosphate/hydroxyapatite (60/40) composite as a bone graft extender using rat calvarial bone defect model

Beta-tricalcium phosphate ( β -TCP) and hydroxyapatite (HA) are widely used as bone graft extenders due to their osteoconductivity and high bioactivity. This study aims to evaluate the possibility of using porous substrate with composite ceramics ( β -TCP: HA = 60% : 40%, 60TCP40HA) as a bone graft extender and comparing it with Bio-Oss. Interconnectivity and macroporosity of β -TCP porous substrate were 99.9% and 83%, respectively, and the macro-porosity of packed granule after crushing was 69%. Calvarial defect model with 8 mm diameter was generated with male Sprague-Dawley rats and 60TCP40HA was implanted. Bio-Oss was implanted for a control group and micro-CT and histology were performed at 4 and 8 weeks after implantation. The 60TCP40HA group showed better new bone formation than the Bio-Oss group and the bone formation at central area of bone defect was increased at 8 weeks in micro-CT and histology. The percent bone volume and trabecular number of the 60TCP40HA group were significantly higher than those of Bio-Oss group. This study confirms the usefulness of the porous 60TCP40HA composite as a bone graft extender by showing increased new bone formation in the calvarial defect model and improved bone formation both quantitatively and qualitatively when compared to Bio-Oss.

Nano-ceramic composite scaffolds for bioreactor-based bone engineering

BACKGROUND

Composites of biodegradable polymers and bioactive ceramics are candidates for tissue-engineered scaffolds that closely match the properties of bone. We previously developed a porous, three-dimensional poly (D,L-lactide-co-glycolide) (PLAGA)/nanohydroxyapatite (n-HA) scaffold as a potential bone tissue engineering matrix suitable for high-aspect ratio vessel (HARV) bioreactor applications. However, the physical and cellular properties of this scaffold are unknown. The present study aims to evaluate the effect of n-HA in modulating PLAGA scaffold properties and human mesenchymal stem cell (HMSC) responses in a HARV bioreactor.

QUESTIONS/PURPOSES

By comparing PLAGA/n-HA and PLAGA scaffolds, we asked whether incorporation of n-HA (1) accelerates scaffold degradation and compromises mechanical integrity; (2) promotes HMSC proliferation and differentiation; and (3) enhances HMSC mineralization when cultured in HARV bioreactors.

METHODS

PLAGA/n-HA scaffolds (total number = 48) were loaded into HARV bioreactors for 6 weeks and monitored for mass, molecular weight, mechanical, and morphological changes. HMSCs were seeded on PLAGA/n-HA scaffolds (total number = 38) and cultured in HARV bioreactors for 28 days. Cell migration, proliferation, osteogenic differentiation, and mineralization were characterized at four selected time points. The same amount of PLAGA scaffolds were used as controls.

RESULTS

The incorporation of n-HA did not alter the scaffold degradation pattern. PLAGA/n-HA scaffolds maintained their mechanical integrity throughout the 6 weeks in the dynamic culture environment. HMSCs seeded on PLAGA/n-HA scaffolds showed elevated proliferation, expression of osteogenic phenotypic markers, and mineral deposition as compared with cells seeded on PLAGA scaffolds. HMSCs migrated into the scaffold center with nearly uniform cell and extracellular matrix distribution in the scaffold interior.

CONCLUSIONS

The combination of PLAGA/n-HA scaffolds with HMSCs in HARV bioreactors may allow for the generation of engineered bone tissue.

CLINICAL RELEVANCE

In cases of large bone voids (such as bone cancer), tissue-engineered constructs may provide alternatives to traditional bone grafts by culturing patients' own MSCs with PLAGA/n-HA scaffolds in a HARV culture system.

Integrated bi-layered scaffold for osteochondral tissue engineering

Osteochondral tissue engineering poses the challenge of combining both cartilage and bone tissue engineering fundamentals. In this study, a sphere-templating technique was applied to fabricate an integrated bi-layered scaffold based on degradable poly(hydroxyethyl methacrylate) hydrogel. One layer of the integrated scaffold was designed with a single defined, monodispersed pore size of 38 μm and pore surfaces coated with hydroxyapatite particles to promote regrowth of subchondral bone while the second layer had 200 μm pores with surfaces decorated with hyaluronan for articular cartilage regeneration. Mechanical properties of the construct as well as cyto-compatibility of the scaffold and its degradation products were elucidated. To examine the potential of the biphasic scaffold for regeneration of osteochondral tissue the designated cartilage and bone layers of the integrated bi-layered scaffold were seeded with chondrocytes differentiated from human mesenchymal stem cells and primary human mesenchymal stem cells, respectively. Both types of cells were co-cultured within the scaffold in standard medium without soluble growth/differentiation factors over four weeks. The ability of the integrated bi-layered scaffold to support simultaneous matrix deposition and adequate cell growth of two distinct cell lineages in each layer during four weeks of co-culture in vitro in the absence of soluble growth factors was demonstrated.

Reinforcement of a new calcium phosphate cement with RGD-chitosan-fiber

Calcium phosphate cement (CPC) has been widely used in orthopedic and dental applications. A critical limitation of CPC is low strength and high susceptibility to severe fracture. Surgeons can use it only to reconstruct non-stress bearing bone, raising the need for a tougher new generation of CPC. Fibers have been used as a reinforcement of CPC to improve the strength of a pure CPC scaffold. The RGD peptides (Arg-Gly-Asp) have been used to improve the biocompatibility of the scaffold, via physical adsorption. The purpose of this study was to develop a novel CPC scaffold reinforced by RGD peptide-bearing chitosan fibers (RGD-fiber-CPC). Our data showed that the RGD-fiber-CPC scaffold had an increased flexural strength, and stimulated new bone formation in an animal model. The RGD-fiber-CPC is a novel bone graft substitute in orthopedic surgery.

Enhanced mechanical strength and biocompatibility of electrospun polycaprolactone-gelatin scaffold with surface deposited nano-hydroxyapatite

In this study for the first time, we compared physico-chemical and biological properties of polycaprolactone-gelatin-hydroxyapatite scaffolds of two types: one in which the nano-hydroxyapatite (n-HA) was deposited on the surface of electrospun polycaprolactone-gelatin (PCG) fibers via alternate soaking process (PCG-HAAS) and other in which hydroxyapatite (HA) powders were blended in electrospinning solution of PCG (PCG-HAB). The microstructure of fibers was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which showed n-HA particles on the surface of the PCG-HAAS scaffold and embedded HA particles in the interior of the PCG-HAB fibers. PCG-HAAS fibers exhibited the better Young's moduli and tensile strength as compared to PCG-HAB fibers. Biological properties such as cell proliferation, cell attachment and alkaline phosphatase activity (ALP) were determined by growing human osteosarcoma cells (MG-63) over the scaffolds. Cell proliferation and confocal results clearly indicated that the presence of hydroxyapatite on the surface of the PCG-HAAS scaffold promoted better cellular adhesion and proliferation as compared to PCG-HAB scaffold. ALP activity was also observed better in alternate soaked PCG scaffold as compared to PCG-HAB scaffold. Mechanical strength and biological properties clearly demonstrate that surface deposited HA scaffold prepared by alternate soaking method may find application in bone tissue engineering.

Effects of hydroxyapatite-containing composite nanofibers on osteogenesis of mesenchymal stem cells in vitro and bone regeneration in vivo

Among a variety of polymers, poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a microbial polyester, with biodegradable, nonantigenic, and biocompatible properties, is attracting more and more attention in tissue engineering. Hydroxyapatite (HA), similar to the mineral component of natural bone, is known to be osteoconductive, nontoxic, and noninflammatory. In this study, aligned and random-oriented PHBV nanofibrous scaffolds loaded with HA nanoparticles were fabricated through electrospinning technique. Mesenchymal stem cells (MSCs) derived from rat bone marrow were used to investigate the effects of HA and orientation of fibers on cell proliferation and differentiation in vitro. Cell proliferation tested with CCK-8 assay indicated that the MSCs attached and proliferated more favorably on random-oriented PHBV nanofibrous meshes without HA. After one, two and four weeks of cell seeding, osteogenic markers including alkaline phosphate (ALP), osteocalcin (OCN), and mineralized matrix deposits were detected, respectively. The results indicated that the introduction of HA could induce MSCs to differentiate into osteoblasts. Moreover, 3D PHBV/HA scaffolds made from aligned and random-oriented nanofibers were implanted into critical-sized rabbit radius defects and exhibited significant effects on the repair of critical bone defects, implying their promising applications in bone tissue engineering.

Osteogenic differentiation of bone marrow mesenchymal stem cells on the collagen/silk fibroin bi-template-induced biomimetic bone substitutes

Biomimetic bone substitutes of collagen-silk fibroin/hydroxyapatite (COL-SF/HA) were synthesized via a bi-template-induced coassembly strategy. Collagen-hydroxyapatite (COL-HA) and silk fibroin-hydroxyapatite (SF-HA) served as controls were prepared with similar method. The osteogenic differentiation ability of bone marrow mesenchymal stem cells (BMSCs) seeded onto the resulting materials was evaluated both in vitro and in vivo. The results suggested that the bi-template-induced biomimetic substitutes were able to support the growth and proliferation of BMSCs. We further demonstrated that BMSCs were stimulated to differentiate into the osteoblast cell lineage by evaluating several specific osteogenic markers including staining of alkaline phosphate (ALP) and calcium nodular and expression of osteogenic genes of osteocalcin (OCN) and osteonectin (ONN). The rat femoral defect model was used to assess the aforementioned biomimetic bone substitutes combined with BMSCs in vivo. Histological analysis indicated that the bi-template material exhibited good biocompatibility and strong ability of the new bone formation in comparison with the control of single-template material in vivo.

Osteoinductivity Assessment of BMP-2 Loaded Composite Chitosan-Nano-Hydroxyapatite Scaffolds in a Rat Muscle Pouch

The objective of this study was to evaluate the osteoinductivity of composite chitosan-nano-hydroxyapatite scaffolds in a rat muscle pouch model. Previous in vitro characterization demonstrated the ability of the scaffolds to promote bone regeneration and as a carrier for local delivery of BMP-2. Composite microspheres were prepared using a co-precipitation method, and scaffolds were fabricated using an acid wash to adhere beads together. To determine the in vivo osteoinductivity of the scaffolds, the following groups (n = 6) were implanted into muscle pouches created in the latissimus dorsi of Sprague Dawley rats: (A) lyophilized scaffolds without rhBMP-2, (B) lyophilized scaffolds with rhBMP-2, (C) non-lyophilized scaffolds with rhBMP-2, and (D) absorbable collagen sponge with rhBMP-2 (control). Groups B, C, and D were loaded with 4 mL of a 9.0 μg/mL solution of rhBMP-2 for 48 h. The rats were sacrificed after one month and samples were analyzed for amount of residual implant material, new bone, and osteoid. Although the experimental groups displayed minimal degradation after one month, all of the scaffolds contained small amounts of woven bone and considerable amounts of osteoid. Approximately thirty percent of the open space available for tissue ingrowth in the scaffolds contained new bone or osteoid in the process of mineralization. The ability of the composite scaffolds (with and without BMP-2) to promote ectopic bone growth in vivo was demonstrated.

Current trends in mesenchymal stem cell application in bone augmentation: a review of the literature

PURPOSE

The literature regarding mesenchymal stem cell (MSC)-based bone reconstruction techniques are sparse and no comprehensive review of current methods has been performed. The aim of this article was to provide a discussion of clinical and experimental reports of MSC application in the reconstruction of bony defects in live models.

MATERIALS AND METHODS

This search was executed using the PubMed database with various combinations of related keywords. Currently published English-language studies that had applied MSCs as a part of their treatment protocol for reconstruction of bony defects in rat, rabbit, dog, and human models were reviewed. The included studies had reported substantiation that the applied cells were of MSC origin as a part of the study design. Publications inclusive to February 1, 2010 were evaluated. Of review of 187 found abstracts and full texts, 25 articles met the inclusion criteria.

RESULT

Based on this review, tremendous differences exist among investigators for the application of MSCs in bone augmentation procedures. These differences include not only species uniqueness but also a plethora of other variances, such as stem cell source, defect sites and sizes, carriers and constructs, use of additional growth factors, measured parameters, and methods of data collection.

CONCLUSION

Because of the multitude of protocols, range of parameters, and data in the current English-language literature, this review did not reach any significant conclusion as to the "most predictable" model in stem cell reconstruction. However, it does "shed light" on the need for additional collaborated studies using similar homogenous designs and data analysis in advancing the science of bone reconstruction using MSCs.

Biomimetic Nanostructured Materials — Potential Regulators for Osteogenesis?

Nanostructured materials are gaining new impetus owing to the advancements in material fabrication techniques and their unique properties (their nanosize, high surface area-to-volume ratio, and high porosity). Such nanostructured materials mimic the subtleties of extracellular matrix (ECM) proteins, creating artificial microenvironments which resemble the native niches in the body. On the other hand, the isolation of mesenchymal stem cells (MSCs) from various tissue sources has resulted in the interest to study the multiple differentiation lineages for various therapeutic treatments. In this review, our focus is tailored towards the potential of biomimetic nanostructured materials as osteoinductive scaffolds for bone regeneration to differentiate MSCs towards osteoblastic cell types without the presence of soluble factors. In addition to mimicking the nanostructure of native bone, the supplement of collagen and hydroxyapatite which mimic the main components of the ECM also brings significant advantages to these materials. Key words: Biomaterials, Biomimetic, Bone, Hydroxyapatites, Nanomaterials, Stem cells, Tissue engineering

A novel nanoparticle-enhanced photoacoustic stimulus for bone tissue engineering

In this study, we introduce a novel nanoparticle-enhanced biophysical stimulus based on the photoacoustic (PA) effect. We demonstrate that the PA effect differentiates bone marrow-derived marrow stromal cells (MSCs) grown on poly(lactic-co-glycolic acid) (PLGA) polymer films toward osteoblasts. We further show that the osteodifferentiation of the MSCs due to PA stimulation is significantly enhanced by the presence of single-walled carbon nanotubes (SWCNTs) in the polymer. MSCs, without the osteogenic culture supplements (0.01 M β-glycerophosphate, 50 mg/L ascorbic acid, 10(-8) M dexamethasone), were seeded onto plain glass slides, glass slides coated with PLGA, or glass slides coated with SWCNT-PLGA films and photoacoustically stimulated by a 527 nm Nd:YLF pulse laser, with a 200 ns pulse duration, and 10 Hz pulse frequency for 10 min a day for 15 consecutive days. The study had four control groups; three baseline controls similar to the three experimental groups but without PA stimulation, and one positive control where MSCs were grown on glass slides without PA stimulation but with osteogenic culture supplements. The osteogenic differentiation of all the groups was evaluated using quantitative assays (alkaline phosphatase, calcium, osteopontin) and qualitative staining (alizarin red). After 15 days, the PA stimulated groups showed up to a 350% increase in calcium content when compared with the non-PA stimulated positive control. Further, within the PA stimulated group, the PLGA-SWCNT group had 130% higher calcium values than the PLGA film without SWCNTs. These results were further corroborated by the analysis of osteopontin secretion, alkaline phosphatase expression, and qualitative alizarin red staining of extracellular matrix calcification. The results indicate that PA stimulation holds promise for bone tissue engineering and that the nanomaterials which enhance the PA effect should allow the development of biophysical rather than biochemical strategies to induce osteoinductive properties into tissue engineering scaffolds.

Focal adhesions in osteoneogenesis

As materials technology and the field of tissue engineering advance, the role of cellular adhesive mechanisms, in particular, interactions with implantable devices, becomes more relevant in both research and clinical practice. A key tenet of medical device technology is to use the exquisite ability of biological systems to respond to the material surface or chemical stimuli in order to help to develop next-generation biomaterials. The focus of this review is on recent studies and developments concerning focal adhesion formation in osteoneogenesis, with an emphasis on the influence of synthetic constructs on integrin-mediated cellular adhesion and function.

Probing the osteoinductive effect of calcium phosphate by using an in vitro biomimetic model

The use of calcium phosphate (CaP)-based carriers in bone engineering is a promising approach to induce in vivo bone formation. However, the exact mechanism of osteoinduction by CaP is not known. Here, by mimicking the in vivo Ca(2+) and P(i)-enriched environment in an in vitro model, we assessed the effects of these ions on human periosteum-derived cells. We observed a significant Ca(2+) and P(i)-induced cell proliferation, which was found to be through the modulation of cell cycle progression, in a dose- and time-dependent manner. In addition, Ca(2+), P(i), and combined Ca-P upregulated osteogenic gene expression in a dose- and time-dependent manner. Encouragingly, both ions administered individually or in combination persistently and dose dependently upregulated bone morphogenetic protein-2 gene expression. This suggested a potential osteoinductive effect through an autonomous activation of the bone morphogenetic protein signaling pathway by released Ca(2+) and P(i), which may serve as an autocrine/paracrine osteoinduction loop that drives the cellularized CaP constructs toward effective bone formation in vivo. In conclusion, through an in vitro biomimetic model, we have partially probed the roles of the released Ca(2+) and P(i) on the osteoinductivity of CaP-based biomaterials.

The effect of novel fluorapatite surfaces on osteoblast-like cell adhesion, growth, and mineralization

There is increasing demand for biomedical implants to correct skeletal defects caused by trauma, disease, or genetic disorder. In this study, the MG-63 cells were grown on metals coated with ordered and disordered fluorapatite (FA) crystal surfaces to study the biocompatibility, initial cellular response, and the underlying mechanisms during this process. The long-term growth and mineralization of the cells were also investigated. After 3 days, the cell numbers on etched metal surface are significantly higher than those on the ordered and disordered FA surfaces, but the initial adherence of a greater number of cells did not lead to earlier mineral formation at the cell-implant interface. Of the 84 cell adhesion and matrix-focused pathway genes, an up- or down-regulation of a total of 15 genes such as integrin molecules, integrin alpha M and integrin alpha 7 and 8 was noted, suggesting a modulating effect on these adhesion molecules by the ordered FA surface compared with the disordered. Osteocalcin expression and the mineral nodule formation are most evident on the FA surfaces after osteogenic induction (OI) for 7 weeks. The binding of the ordered FA surfaces to the metal, with and without OI, was significantly higher than that of the disordered FA surfaces with OI. Most significantly, even without the OI supplement, the MG-63 cells grown on FA crystal surfaces start to differentiate and mineralize, suggesting that the FA crystal could be a simple and bioactive implant coating material.

Cell-derived matrix enhances osteogenic properties of hydroxyapatite

The study aimed to evaluate osteogenic properties of hydroxyapatite (HA) scaffold combined with extracellular matrix (ECM) derived in vitro from rat primary calvarial osteoblasts or dermal fibroblasts. The cellular viability, and the ECM deposited onto synthetic HA microparticles were assessed by MTT, Glycosaminoglycan, and Hydroxyproline assays as well as immunohistochemistry and scanning electron microscopy after 21 days of culture. The decellularized HA-ECM constructs were implanted in critical-sized calvarial defects of Sprague-Dawley rats, followed by bone repair and local inflammatory response assessments by histomorphometry and immunohistochemistry at 12 weeks postoperatively. We demonstrated that HA supported cellular adhesion, growth, and ECM production in vitro, and the HA-ECM constructs significantly enhanced calvarial bone repair (p<0.05, Mann-Whitney U-test), compared with HA alone, despite the significantly increased number of CD68+ macrophages, and foreign body giant cells (p<0.05, Mann-Whitney U-test). Selective accumulation of bone sialoprotein, osteopontin, and periostin was observed at the tissue-HA interfaces. In conclusion, in vitro-derived ECM mimics the native bone matrix, enhances the osteogenic properties of the HA microparticles, and might modulate the local inflammatory response in a bone repair-favorable way. Our findings highlight the ability to produce functional HA-ECM constructs for bone tissue engineering applications.

Nanohydroxyapatite-coated electrospun poly(l-lactide) nanofibers enhance osteogenic differentiation of stem cells and induce ectopic bone formation

A combination of calcium phosphates with nanofibrous scaffolds holds promising potential for bone tissue engineering applications. In this study, nanohydroxyapatite (n-HA) was coated on the plasma-treated surface of electrospun poly(l-lactide) (PLLA) nanofibers and the capacity of fabricated scaffolds for bone formation was investigated in vitro using human cord blood derived unrestricted somatic stem cells (USSC) under osteogenic induction and in vivo after subcutaneous implantation. PLLA and n-HA-coated PLLA (n-HA/PLLA) scaffolds exhibited a nanofibrous structure with interconnected pores and suitable mechanical properties. These scaffolds were also shown to support attachment, spreading, and proliferation of USSC, as shown by their flattened normal morphology and MTT assay. During osteogenic differentiation, significantly higher values of ALP activity, biomineralization, and bone-related gene expression were observed on n-HA/PLLA compared to PLLA scaffolds. Subsequently, these markers were measured in higher amounts in USSC on PLLA nanofibers compared to TCPS. According to the in vivo results, ossification and formation of trabeculi was observed in the n-HA/PLLA scaffold compared to PLLA. Taking together, it was shown that nanofibrous structure enhanced osteogenic differentiation of USSC. Furthermore, surface-coated n-HA stimulated the effect of nanofibers on the orientation of USSC toward osteolineage. In addition, the n-HA/PLLA electrospun scaffold showed the capacity for ectopic bone formation in the absence of exogenous cells.

Hydroxyapatite as a carrier for bone morphogenetic protein

Bone morphogenetic proteins (BMPs) can induce the formation of new bone in numerous orthopedic and dental applications in which loss of bone is the main issue. The combination of BMP with a biomaterial that can carry and deliver proteins has been demonstrated to maximize the therapeutic effects of BMPs. However, no ideal candidate with optimal characteristics as a carrier has emerged for clinical use of BMPs. Hydroxyapatite (HA) is a potential BMP carrier with its osteoconductive properties and desirable characteristics as a bone graft biomaterial. In this study, 3 different methods to load BMP into HA materials were characterized and compared based on the BMP uptake and release profile. BMP was loaded into HA in 3 ways: (1) incorporation of BMP during HA precipitation, (2) HA immersion in BMP solution, and (3) BMP incorporation during dicalcium phosphate dihydrate (DCPD) conversion to HA. The size of HA crystals decreased when BMP was loaded during HA precipitation and HA immersion in BMP solution; however, it did not change when BMP was loaded during DCPD-to-HA conversion. The highest BMP uptake was achieved using the immersion method followed by HA precipitation, and the lowest via DCPD conversion. It is interesting to note that BMP loading during HA precipitation resulted in sustained and prolonged BMP release compared with the 2 other BMP loading methods. In conclusion, BMP incorporation during HA precipitation revealed itself to be the best loading method.

A nondestructive method for evaluating in vitro osteoblast differentiation on biomaterials using osteoblast-specific fluorescence

Transgenic mice with a Col1a1-promoter-driven transgene pOBCol2.3GFP were previously developed to visually identify mature osteoblasts through fluorescent expression. Our goal was to determine if this technology could be used to nondestructively evaluate the in vitro differentiation of osteoprogenitor cells on biomaterials such as biomimetic carbonated hydroxyapatite (cHA). Primary osteoprogenitor cells were harvested from calvaria of neonatal Col2.3GFP transgenic mice and cultured on cHA and a tissue culture polystyrene (TCPS) control. The distribution of intensities and area percentage of green fluorescent protein (GFP)-positive cells were quantified using fluorimetry and image analysis of fluorescent microscopy. At 14 days, an increased area and higher mean intensity of GFP-positive cells was observed on cHA as compared to TCPS, indicating more rapid differentiation on cHA. Notably, there were large continuous regions of GFP-positive osteoblasts on cHA, in contrast to the sparse, nodules of osteoblasts on TCPS, implying that cHA provides an osteogenic cue to cells. Xylenol orange staining was capable of distinguishing osteoblast-initiated mineral from the cHA substrate. With this method the unique pattern of osteoblast differentiation on cHA was clearly observed for the first time. Importantly, the generalized method can be used for rapid, high-throughput, nondestructive screening of biomaterials intended to enhance osteogenic differentiation.

Direct and indirect effects of microstructured titanium substrates on the induction of mesenchymal stem cell differentiation towards the osteoblast lineage

Microstructured and high surface energy titanium substrates increase osseointegration in vivo. In vitro, osteoblast differentiation is increased, but effects of the surface directly on multipotent mesenchymal stem cells (MSCs) and consequences for MSCs in the peri-implant environment are not known. We evaluated responses of human MSCs to substrate surface properties and examined the underlying mechanisms involved. MSCs exhibited osteoblast characteristics (alkaline phosphatase, RUNX2, and osteocalcin) when grown on microstructured Ti; this effect was more robust with increased hydrophilicity. Factors produced by osteoblasts grown on microstructured Ti were sufficient to induce co-cultured MSC differentiation to osteoblasts. Silencing studies showed that this was due to signaling via alpha2beta1 integrins in osteoblasts on the substrate surface and paracrine action of secreted Dkk2. Thus, human MSCs are sensitive to substrate properties that induce osteoblastic differentiation; osteoblasts interact with these surface properties via alpha2beta1 and secrete Dkk2, which acts on distal MSCs.

Augmentation of bone growth onto the acetabular cup surface using bone marrow stromal cells in total hip replacement surgery

Aseptic loosening of acetabular components in total hip arthroplasty is the major cause of implant failure. Our hypothesis was that spraying autologous bone marrow-derived stromal cells (BMSCs) in fibrin glue onto the surface of hydroxyapatite-coated uncemented acetabular components would increase bone formation and contact in a caprine model. Ten million BMSCs were sprayed onto the acetabular cup at the time of surgery. Animals in the control group received fibrin glue only. Ground reaction force measurements were taken preoperatively and at 6 and 12 weeks postsurgery. After retrieval at 12 weeks new bone formation, bone-implant contact and fibrous tissue thickness adjacent to the cup were quantified. Viability and proliferation assays showed that the majority of the BMSCs survived spraying in fibrin glue at pressures of up to 1.5 atm. New bone growth adjacent to the bone implant interface in the BMSC-treated group (71.42 +/- 8.97%) was 30% greater than in control (54.22 +/- 16.56%) although this difference was not statistically significant. However, significantly increased new bone formation was measured at the periphery of the cup (zone 5) in the BMSC-treated group (71.97 +/- 10.91%) when compared with control (23.85 +/- 15.13%, p = 0.028). Bone-implant contact was significantly greater in the BMSC-treated group (20.03 +/- 4.64%) (control: 13.71 +/- 8.32%, p = 0.027); correspondingly, the average thickness of the fibrous tissue membrane where present was significantly reduced at the periphery of the cups in the BMSC-treated group (327.49 +/- 20.38 mum) when compared with control (887.21 +/- 158.89 mum) (p = 0.02). This study has clinical applications as greater bone contact at the cup surface will improve fixation and may decrease longer-term aseptic loosening by preventing wear debris-induced bone loss at the implant interface.

Bone morphogenetic proteins and tissue engineering: future directions

As long as bone repair and regeneration is considered as a complex clinical condition, the administration of more than one factor involved in fracture healing might be necessary. The effectiveness or not of bone morphogenetic proteins (BMPs) in association with other growth factors and with mesenchymal stem cells in bone regeneration for fracture healing and bone allograft integration is of great interest to the scientific community. In this study we point out possible future developments in BMPs, concerning research and clinical applications.

Poly-L-lactic acid/hydroxyapatite electrospun nanocomposites induce chondrogenic differentiation of human MSC

Cartilage and bone tissue engineering has been widely investigated but is still hampered by cell differentiation and transplant integration issues within the constructs. Scaffolds represent the pivotal structure of the engineered tissue and establish an environment for neo-extracellular matrix synthesis. They can be associated to signals to modulate cell activity. In this study, considering the well reported role of hydroxyapatite (HA) in cartilage repair, we focused on the putative chondrogenic differentiation of human mesenchymal stem cells (hMSCs) following culture on membranes of electrospun fibers of poly-L-lactic acid (PLLA) loaded with nanoparticles of HA. hMSCs were seeded on PLLA/HA and bare PLLA membranes and cultured in basal medium, using chondrogenic differentiation medium as a positive control. After 14 days of culture, SOX-9 positive cells could be detected in the PLLA/HA group. Cartilage specific proteoglycan immunostain confirmed the presence of neo-extracellular-matrix production. Co-expression of CD29, a typical surface marker of MSCs and SOX-9, suggested different degrees in the differentiation process. We developed a hydroxyapatite functionalized scaffold with the aim to recapitulate the native histoarchitecture and the molecular signaling of osteochondral tissue to facilitate cell differentiation toward chondrocyte. PLLA/HA nanocomposites induced differentiation of hMSCs in a chondrocyte-like phenotype with generation of a proteoglycan based matrix. This nanocomposite could be an amenable alternative scaffold for cartilage tissue engineering using hMSCs.