Ectopic bone formation in collagen sponge self-assembled peptide–amphiphile nanofibers hybrid scaffold in a perfusion culture bioreactor

Gene Therapy for Regenerative Medicine

The development of biological methods over the past decade has stimulated great interest in the possibility to regenerate human tissues. Advances in stem cell research, gene therapy, and tissue engineering have accelerated the technology in tissue and organ regeneration. However, despite significant progress in this area, there are still several technical issues that must be addressed, especially in the clinical use of gene therapy. The aims of gene therapy include utilising cells to produce a suitable protein, silencing over-producing proteins, and genetically modifying and repairing cell functions that may affect disease conditions. While most current gene therapy clinical trials are based on cell- and viral-mediated approaches, non-viral gene transfection agents are emerging as potentially safe and effective in the treatment of a wide variety of genetic and acquired diseases. Gene therapy based on viral vectors may induce pathogenicity and immunogenicity. Therefore, significant efforts are being invested in non-viral vectors to enhance their efficiency to a level comparable to the viral vector. Non-viral technologies consist of plasmid-based expression systems containing a gene encoding, a therapeutic protein, and synthetic gene delivery systems. One possible approach to enhance non-viral vector ability or to be an alternative to viral vectors would be to use tissue engineering technology for regenerative medicine therapy. This review provides a critical view of gene therapy with a major focus on the development of regenerative medicine technologies to control the in vivo location and function of administered genes.

Recycling protein selective adsorption on fluorine-modified surface through fluorine-fluorine interaction

Low surface energy materials with micro-nano structures have been widely developed to prevent non-specific adhesion of biomolecules. Herein we put forward a new approach based on the antifouling and self-assembly properties of fluorine components, to construct a non-specific protein resistance surface with selective protein adsorption property. Briefly, the antifouling surface (SN-F) was obtained by a simple one-step modification on silicon nanowire arrays (SiNWAs) with fluorine coupling agent 1 H,1 H,2 H,2 H-perfluorodecyltrimethoxysilane (FAS). And protein was fluorinated by conjugation with an amphiphilic fluoro-copolymer, produced from 2-methacrylamido glucopyranose (MAG) and trifluoroethyl methacrylate (TFEMA) via RAFT polymerization. The properties of the materials were characterized by ¹H nuclear magnetic resonance (¹H NMR), infrared spectroscopy (FTIR), water contact angle, and X-ray photoelectron spectroscopy (XPS) etc., and protein adsorption was investigated by protein content measurement, fluorescence detection, and electrophoresis. It was observed that the adsorption for native proteins on SN-F was at an extremely low level, while the adsorption for the fluoro-copolymer conjugated protein (PFG-BSA) was significantly increased. When the percentage of TFEMA in the fluoro-copolymer was as high as 52.0%, the fluorinated protein adsorbed on SN-F was more than 35 times of native proteins on the surface. Moreover, the platform could resist IgG adhesion in serum after the adsorption of fluorinated protein, and it could be recycled three times after 75% ethanol treatment. In conclusion, SN-F showed non-specific protein resistance through low surface energy and specific protein adsorption by fluorine-fluorine self-assembly. The fluorinated nanostructured platform has a great potential in controlling protein adsorption and release.

Supramolecular Peptide Nanofiber Hydrogels for Bone Tissue Engineering: From Multihierarchical Fabrications to Comprehensive Applications

Bone tissue engineering is becoming an ideal strategy to replace autologous bone grafts for surgical bone repair, but the multihierarchical complexity of natural bone is still difficult to emulate due to the lack of suitable biomaterials. Supramolecular peptide nanofiber hydrogels (SPNHs) are emerging biomaterials because of their inherent biocompatibility, satisfied biodegradability, high purity, facile functionalization, and tunable mechanical properties. This review initially focuses on the multihierarchical fabrications by SPNHs to emulate natural bony extracellular matrix. Structurally, supramolecular peptides based on distinctive building blocks can assemble into nanofiber hydrogels, which can be used as nanomorphology-mimetic scaffolds for tissue engineering. Biochemically, bioactive motifs and bioactive factors can be covalently tethered or physically absorbed to SPNHs to endow various functions depending on physiological and pharmacological requirements. Mechanically, four strategies are summarized to optimize the biophysical microenvironment of SPNHs for bone regeneration. Furthermore, comprehensive applications about SPNHs for bone tissue engineering are reviewed. The biomaterials can be directly used in the form of injectable hydrogels or composite nanoscaffolds, or they can be used to construct engineered bone grafts by bioprinting or bioreactors. Finally, continuing challenges and outlook are discussed.

Biophysical Stimuli as the Fourth Pillar of Bone Tissue Engineering

The repair of critical bone defects remains challenging worldwide. Three canonical pillars (biomaterial scaffolds, bioactive molecules, and stem cells) of bone tissue engineering have been widely used for bone regeneration in separate or combined strategies, but the delivery of bioactive molecules has several obvious drawbacks. Biophysical stimuli have great potential to become the fourth pillar of bone tissue engineering, which can be categorized into three groups depending on their physical properties: internal structural stimuli, external mechanical stimuli, and electromagnetic stimuli. In this review, distinctive biophysical stimuli coupled with their osteoinductive windows or parameters are initially presented to induce the osteogenesis of mesenchymal stem cells (MSCs). Then, osteoinductive mechanisms of biophysical transduction (a combination of mechanotransduction and electrocoupling) are reviewed to direct the osteogenic differentiation of MSCs. These mechanisms include biophysical sensing, transmission, and regulation. Furthermore, distinctive application strategies of biophysical stimuli are presented for bone tissue engineering, including predesigned biomaterials, tissue-engineered bone grafts, and postoperative biophysical stimuli loading strategies. Finally, ongoing challenges and future perspectives are discussed.

Current progress in hepatic tissue regeneration by tissue engineering

Liver, as a vital organ, is responsible for a wide range of biological functions to maintain homeostasis and any type of damages to hepatic tissue contributes to disease progression and death. Viral infection, trauma, carcinoma, alcohol misuse and inborn errors of metabolism are common causes of liver diseases are a severe known reason for leading to end-stage liver disease or liver failure. In either way, liver transplantation is the only treatment option which is, however, hampered by the increasing scarcity of organ donor. Over the past years, considerable efforts have been directed toward liver regeneration aiming at developing new approaches and methodologies to enhance the transplantation process. These approaches include producing decellularized scaffolds from the liver organ, 3D bio-printing system, and nano-based 3D scaffolds to simulate the native liver microenvironment. The application of small molecules and micro-RNAs and genetic manipulation in favor of hepatic differentiation of distinct stem cells could also be exploited. All of these strategies will help to facilitate the application of stem cells in human medicine. This article reviews the most recent strategies to generate a high amount of mature hepatocyte-like cells and updates current knowledge on liver regenerative medicine.

Biofunctionalized peptide nanofiber-based composite scaffolds for bone regeneration

Bone tissue had moderate self-healing capabilities, but biomaterial scaffolds were required for the repair of some defects such as large bone defects. Peptide nanofiber scaffolds demonstrated important potential in regenerative medicine. Functional modification and controlled release of signal molecules were two significant approaches to increase the bioactivity of biofunctionalized peptide nanofiber scaffolds, but peptide scaffolds were limited by insufficient mechanical strength. Thus, it was necessary to combine peptide scaffolds with other materials including polymers, hydroxyapatite, demineralized bone matrix (DBM) and metal materials based on the requirement of different bone defects. As the development of peptide-based composite scaffolds continued to evolve, ultimate translation to the clinical environment may allow for improved therapeutic outcomes for bone repair.

Influence of oriented nanofibrous PCL scaffolds on quantitative gene expression during neural differentiation of mouse embryonic stem cells

Neural differentiation of mouse embryonic stem cells in combination with three-dimensional electrospun nanofibers as an artificial extracellular matrix can be utilized to reconstruct a spinal cord defect. In this study, random and parallel-aligned nanofibrous poly ɛ-caprolactone was fabricated using electrospinning. Its hydrophobicity was modified by O2 plasma treatment to facilitate enhanced cell attachment. Embryoid bodies (EBs), which contain all three embryonic germ layers, were cultured on poly ɛ-caprolactone scaffolds to study the effect of fiber orientation on cell morphology and differentiation. Cell morphology and neuron-specific gene and protein expressions were, respectively, evaluated by scanning electron microscopy, real-time polymerase chain reaction, and immunocytochemistry. Although two types of nanofibrous scaffolds showed neural marker expression at the protein level, cells on randomly oriented scaffolds showed short-range topographical guidance and stretched across multiple directions, whereas cells on the parallel scaffolds exhibited long extension with enhanced neuron outgrowth along the fiber, producing oriented extracellular matrix, leading to direct cell migration and nerve regeneration. Quantitative real-time polymerase chain reaction showed that both aligned and random electrospun nanofibers downregulated the precursor neural marker Nestin compared with that in the control group, a gelatin-coated tissue culture plate (T). Analysis also showed higher expression of dorso-ventral neural markers (Isl1/2 and Lim1/2) than motor neuron progenitor markers (Pax6, Nkx6.1, and olig2) in aligned nanofibers than in the T group. Moreover, aligned nanofibers showed higher expression of mature neural specific markers such as β-tub and Map2 than those in the randomly oriented scaffolds. Therefore, we conclude that nanofibers with different orientations can support the neural lineage, but aligned nanofibrous scaffolds are superior candidates to promote the advancement of neural precursors to achieve maturity during the differentiation process.

Hierarchically biomimetic scaffold of a collagen-mesoporous bioactive glass nanofiber composite for bone tissue engineering

Mesoporous bioactive glass nanofibers (MBGNFs) were prepared by a sol-gel/electrospinning technique. Subsequently, a collagen-MBGNF (CM) composite scaffold that simultaneously possessed a macroporous structure and collagen nanofibers was fabricated by a gelation and freeze-drying process. Additionally, immersing the CM scaffold in a simulated body fluid resulted in the formation of bone-like apatite minerals on the surface. The CM scaffold provided a suitable environment for attachment to the cytoskeleton. Based on the measured alkaline phosphatase activity and protein expression levels of osteocalcin and bone sialoprotein, the CM scaffold promoted the differentiation and mineralization of MG63 osteoblast-like cells. In addition, the bone regeneration ability of the CM scaffold was examined using a rat calvarial defect model in vivo. The results revealed that CM is biodegradable and could promote bone regeneration. Therefore, a CM composite scaffold is a potential bone graft for bone tissue engineering applications.

Effect of graphitic layers encapsulating single-crystal apatite nanowire on the osteogenesis of human mesenchymal stem cells

An ideally designed scaffold for tissue engineering must be able to provide an environment that recapitulates the physiological conditions to control stem cell function. Here, we compared vertically aligned single-crystal apatite nanowires sheathed in graphitic layers (SANGs) with single-crystal apatite nanowires (SANs), which had the same geometric properties as--but differing nanotopographic surface chemistry than--SANGs, in order to evaluate the effect of the graphitic layer on the behavior of human mesenchymal stem cells (hMSCs). The difference in nanotopographic surface chemistry did not affect hMSC adhesion, growth, or morphology. However, hMSCs were more effectively differentiated into bone cells on SANGs through interaction with graphitic layers, which later degraded and thereby allowed the cells to continue differentiation on the bare apatite nanowires. Thus, SANGs provide an excellent microenvironment for the osteogenic differentiation of hMCS.

Development of 3D in vitro technology for medical applications

In the past few years, biomaterials technologies together with significant efforts on developing biology have revolutionized the process of engineered materials. Three dimensional (3D) in vitro technology aims to develop set of tools that are simple, inexpensive, portable and robust that could be commercialized and used in various fields of biomedical sciences such as drug discovery, diagnostic tools, and therapeutic approaches in regenerative medicine. The proliferation of cells in the 3D scaffold needs an oxygen and nutrition supply. 3D scaffold materials should provide such an environment for cells living in close proximity. 3D scaffolds that are able to regenerate or restore tissue and/or organs have begun to revolutionize medicine and biomedical science. Scaffolds have been used to support and promote the regeneration of tissues. Different processing techniques have been developed to design and fabricate three dimensional scaffolds for tissue engineering implants. Throughout the chapters we discuss in this review, we inform the reader about the potential applications of different 3D in vitro systems that can be applied for fabricating a wider range of novel biomaterials for use in tissue engineering.

Controlled surface morphology and hydrophilicity of polycaprolactone toward selective differentiation of mesenchymal stem cells to neural like cells

Differentiation of mesenchymal stem cells (MSCs) into neuron cells has great potential in therapy of damaged nerve tissue. It has been shown that three-dimensional biomaterials have great ability to up regulate the expression of neuronal proteins. In this study, O2 plasma technology was used to enhance hydrophilicity of poly (ε-caprolactone) (PCL) toward selective differentiation of MSCs into neural cells. Random and aligned PCL nanofibers scaffolds were fabricated by electrospinning method and their physicochemical and mechanical properties were carried out by scanning electron microscope (SEM), contact angle, and tensile measurements. Contact angle studies of PCL and plasma treated PCL (p-PCL) nanofibers revealed significant change on the surface properties PCL nanofibers from the view point of hydrophilicity. Physiochemical studies revealed that p-PCL nanofibers were extremely hydrophilic compared with untreated PCL nanofibers which were highly hydrophobic and nonabsorbent to water. Differentiation of MSCs were carried out by inducing growth factors including basic fibroblast growth factor, nerve growth factor, and brain derived growth factor, NT3, 3-isobutyl-1-methylxanthine (IBMX) in Dulbecco's modified Eagle's medium/F12 media. Differentiated MSCs on nanofibrous scaffold were examined by immunofluorescence assay and was found to express the neuronal proteins; β-tubulin III and Map2, on day 15 after cell culture. The real-time polymerase chain reaction (RT-PCR) analysis showed that p-PCL nanofibrous scaffold could upregulate expression of Map-2 and downregulate expression of Nestin genes in nerve cells differentiated from MSCs. This study indicates that mesenchymal stem cell cultured on nanofibrous scaffold have potential differentiation to neuronal cells on and could apply in nerve tissue repair.

Designer functionalised self-assembling peptide nanofibre scaffolds for cartilage tissue engineering

Owing to the limited regenerative capacity of cartilage tissue, cartilage repair remains a challenge in clinical treatment. Tissue engineering has emerged as a promising and important approach to repair cartilage defects. It is well known that material scaffolds are regarded as a fundamental element of tissue engineering. Novel biomaterial scaffolds formed by self-assembling peptides consist of nanofibre networks highly resembling natural extracellular matrices, and their fabrication is based on the principle of molecular self-assembly. Indeed, peptide nanofibre scaffolds have obtained much progress in repairing various damaged tissues (e.g. cartilage, bone, nerve, heart and blood vessel). This review outlines the rational design of peptide nanofibre scaffolds and their potential in cartilage tissue engineering.

IKVAV regulates ERK1/2 and Akt signalling pathways in BMMSC population growth and proliferation

Objectives

The molecular mechanism of bone marrow mesenchymal stem cell (BMMSC) population growth and proliferation, induced by Isoleucyl‐lysyl‐valyl‐alanyl‐valine (IKVAV), was explored in this study.

Materials and methods

IKVAV peptides were synthesized by the solid‐phase method. Influence of IKVAV on BMMSC population growth and proliferation were investigated by assays of CCK‐8, flow cytometry, real‐time PCR and western blotting.

Results

IKVAV peptide was found to induce proliferation and proliferating cell nuclear antigen (PCNA) synthesis of BMMSC in a dose‐ and time‐dependent manner. Cell cycle analysis showed that the proportion of IKVAV‐treated BMMSC in S phase in was higher than controls. Western blot results suggested that mitogen‐activated protein kinase/extracellular signal‐regulated kinase (MAPK/ERK) and phosphatidylinositol 3‐kinase/protein kinase B (PI3K/Akt) signalling pathways were activated by IKVAV by enhancing phosphorylation levels of ERK1/2 and Akt in the BMMSCs. Meanwhile, phosphorylation levels of ERK1/2 and Akt were partially blocked by ERK1/2 inhibitor (PD98059) and Akt inhibitor (wortmannin), respectively.

Conclusions

Our results demonstrated that IKVAV stimulated BMMSC population growth and proliferation by activating MAPK/ERK1/2 and PI3K/Akt signalling pathways. This study is the first to reveal an enhancement effect of IKVAV peptide on BMMSC at the signal transduction level, and the outcome could provide experimental evidence for application of IKVAV‐grafted scaffolds in the field of BMMSC‐based tissue engineering.

Nano/microfibrous polymeric constructs loaded with bioactive agents and designed for tissue engineering applications: a review

Nano/microfibrous polymeric constructs present various inherent advantages, such as highly porous architecture and high surface to volume ratio, making them attractive for tissue engineering purposes. Electrospinning is the most preferred technique for the fabrication of polymeric nanofibrous assemblies that can mimic the physical functions of native extracellular matrix greatly favoring cells attachment and thus influencing their morphology and activities. Different approaches have been developed to apply polymeric microfiber fabrication techniques (e.g. wet-spinning) for the obtainment of scaffolds with a three-dimensional network of micropores suitable for effective cells migration. Progress in additive manufacturing technology has led to the development of complex scaffold's shapes and microfibrous structures with a high degree of automation, good accuracy and reproducibility. Various loading methods, such as direct blending, coaxial electrospinning and microparticles incorporation, are enabling to develop customized strategies for the biofunctionalization of nano/microfibrous scaffolds with a tailored kinetics of release of different bioactive agents, ranging from small molecules, such as antibiotics, to protein drugs, such as growth factors, and even cells. Recent activities on the combination of different processing techniques and loading methods for the obtainment of biofunctionalized polymeric constructs with a complex multiscale structure open new possibilities for the development of biomimetic scaffolds endowed with a hierarchical architecture and a sophisticated release kinetics of different bioactive agents. This review is aimed at summarizing current advances in technologies and methods for manufacturing nano/microfibrous polymeric constructs suitable as tissue engineering scaffolds, and for their combination with different bioactive agents to promote tissue regeneration and therapeutic effects.

Use of perfusion bioreactors and large animal models for long bone tissue engineering

Tissue engineering and regenerative medicine (TERM) strategies for generation of new bone tissue includes the combined use of autologous or heterologous mesenchymal stem cells (MSC) and three-dimensional (3D) scaffold materials serving as structural support for the cells, that develop into tissue-like substitutes under appropriate in vitro culture conditions. This approach is very important due to the limitations and risks associated with autologous, as well as allogenic bone grafiting procedures currently used. However, the cultivation of osteoprogenitor cells in 3D scaffolds presents several challenges, such as the efficient transport of nutrient and oxygen and removal of waste products from the cells in the interior of the scaffold. In this context, perfusion bioreactor systems are key components for bone TERM, as many recent studies have shown that such systems can provide dynamic environments with enhanced diffusion of nutrients and therefore, perfusion can be used to generate grafts of clinically relevant sizes and shapes. Nevertheless, to determine whether a developed tissue-like substitute conforms to the requirements of biocompatibility, mechanical stability and safety, it must undergo rigorous testing both in vitro and in vivo. Results from in vitro studies can be difficult to extrapolate to the in vivo situation, and for this reason, the use of animal models is often an essential step in the testing of orthopedic implants before clinical use in humans. This review provides an overview of the concepts, advantages, and challenges associated with different types of perfusion bioreactor systems, particularly focusing on systems that may enable the generation of critical size tissue engineered constructs. Furthermore, this review discusses some of the most frequently used animal models, such as sheep and goats, to study the in vivo functionality of bone implant materials, in critical size defects.

Enhancement of bone regeneration by dual release of a macrophage recruitment agent and platelet-rich plasma from gelatin hydrogels

Macrophages play an important role in regulating inflammatory responses and tissue regeneration. In the present study, their effect on bone remodeling is investigated by the simultaneous application of a macrophage recruiting agent, SEW2871 of a sphingosine-1 phosphate agonist, and platelet-rich plasma (PRP). The non-water soluble SEW2871 was solubilized in water through micelles formation with l-lactic acid grafted gelatin, and the resulting micelles with PRP were incorporated into gelatin hydrogels. Mixed SEW2871-micelles and PRP were released from gelatin hydrogels in a controlled fashion both in vitro and in vivo. In vitro migration assay revealed that the presence of PRP synergistically promoted SEW2871-induced macrophages migration. When applied to a bone defect of rats, the hydrogels incorporating mixed SEW2871-micelles and PRP recruited a higher number of macrophages than those hydrogels incorporating either SEW2871-micelles or PRP. The hydrogels incorporating mixed SEW2871-micelles and PRP enhanced the level of tumor necrosis factor (TNF)-α of pro-inflammatory cytokine, 3 days after application, while pro-inflammatory responses coupled with a significant increase in the expression level of osteoprotegerin (OPG) and interleukin (IL)-10 and transforming growth factor (TGF)-β1 of anti-inflammatory cytokine were observed 10 days postoperatively. The hydrogels incorporating mixed SEW2871-micelles and PRP promoted bone regeneration to a significant great extent compared with those incorporating PBS and either SEW2871-micelles or PRP. It is concluded that macrophages recruitment contributed to PRP-induced bone regeneration.

In vivo bone regeneration using tubular perfusion system bioreactor cultured nanofibrous scaffolds

The use of bioreactors for the in vitro culture of constructs for bone tissue engineering has become prevalent as these systems may improve the growth and differentiation of a cultured cell population. Here we utilize a tubular perfusion system (TPS) bioreactor for the in vitro culture of human mesenchymal stem cells (hMSCs) and implant the cultured constructs into rat femoral condyle defects. Using nanofibrous electrospun poly(lactic-co-glycolic acid)/poly(ε-caprolactone) scaffolds, hMSCs were cultured for 10 days in vitro in the TPS bioreactor with cellular and acellular scaffolds cultured statically for 10 days as a control. After 3 and 6 weeks of in vivo culture, explants were removed and subjected to histomorphometric analysis. Results indicated more rapid bone regeneration in defects implanted with bioreactor cultured scaffolds with a new bone area of 1.23 ± 0.35 mm(2) at 21 days compared to 0.99 ± 0.43 mm(2) and 0.50 ± 0.29 mm(2) in defects implanted with statically cultured scaffolds and acellular scaffolds, respectively. At the 21 day timepoint, statistical differences (p<0.05) were only observed between defects implanted with cell containing scaffolds and the acellular control. After 42 days, however, defects implanted with TPS cultured scaffolds had the greatest new bone area with 1.72 ± 0.40 mm(2). Defects implanted with statically cultured and acellular scaffolds had a new bone area of 1.26 ± 0.43 mm(2) and 1.19 ± 0.33 mm(2), respectively. The increase in bone growth observed in defects implanted with TPS cultured scaffolds was statistically significant (p<0.05) when compared to both the static and acellular groups at this timepoint. This study demonstrates the efficacy of the TPS bioreactor to improve bone tissue regeneration and highlights the benefits of utilizing perfusion bioreactor systems to culture MSCs for bone tissue engineering.

Time-regulated drug delivery system based on coaxially incorporated platelet α-granules for biomedical use

Aim: Platelet derivatives serve as an efficient source of natural growth factors. In the current study, α-granules were incorporated into coaxial nanofibers. Materials & methods: A nanofiber scaffold containing α-granules was prepared by coaxial electrospinning. The biological potential of the nanofiber scaffold was evaluated in chondrocyte and mesenchymal stem cell cultivation studies. Additionally, the concentration of TGF-β1 was determined. Results: Microscopy studies showed that intact α-granules were incorporated into the coaxial nanofibers. The cultivation tests showed that the novel scaffold stimulated viability and extracellular matrix production of chondrocytes and mesenchymal stem cells. In addition, the concentration of growth factors necessary for the induction of cell proliferation significantly decreased. Conclusion: The system preserved α-granule bioactivity and stimulated cell viability and chondrogenic differentiation of mesenchymal stem cells. Core/shell nanofibers incorporating α-granules are a promising system for tissue engineering, particularly cartilage engineering.

Original submitted 21 March 2012; Revised submitted 8 August 2012; Published online 2 December 2012

Chemical–physical and in vivo evaluations of a self-assembling amphiphilic peptide as an injectable hydrogel scaffold for biomedical applications

The self-aggregation and gelation of an amphiphilic peptide (C17H35CONH–A4G3ERGD, peptide amphiphile) were studied by light scattering, viscometry, nuclear magnetic resonance diffusometry, and atomic force microscopy. The peptide amphiphile critical aggregation concentration was evaluated to be 16 and 60 µM by light scattering and viscometry, respectively. The observed difference was attributed to the larger sensitivity of the latter technique to the presence of long fibrils. The addition of one equivalent or more of divalent cations (Ca2+ and Mg2+) to peptide amphiphile formed dense incoherent hydrogels. Based on the atomic force microscopy and nanoindentation data, both the hydrogel morphology and stiffness were independent of the cation type and peptide amphiphile concentration. However, gel stiffness increased on increasing Ca2+/peptide amphiphile molar ratio while a parallel decrease in the apparent water diffusion rate was observed by nuclear magnetic resonance diffusometry. The dispersions of endothelial progenitor cells in the peptide amphiphile hydrogels were evaluated in vivo on a rat tissue hypoxia model. Significant capillary formation at the injection site was observed by tissue appearance and histological examination, which indicated endothelial progenitor cell/peptide amphiphile hydrogel-enhanced angiogenesis in ischemic tissue.

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.

Enhanced osteogenic differentiation with 3D electrospun nanofibrous scaffolds

AIM

Developing 3D scaffolds mimicking the nanoscale structure of the native extracellular matrix is important in tissue regeneration. In this study, we aimed to demonstrate the novelty of 3D nanofibrous scaffolds and compare their efficiency with 2D nanofibrous scaffolds.

MATERIALS & METHODS

The 2D poly(L-lactic acid)/collagen nanofibrous scaffolds were 2D meshes fabricated by the conventional electrospinning technique, whereas the 3D poly(L-lactic acid)/collagen nanofibrous scaffolds were fabricated by a modified electrospinning technique using a dynamic liquid support system. The morphology, proliferation and differentiation abilities of human mesenchymal stem cells in osteogenic medium on both scaffolds were investigated.

RESULTS & CONCLUSION

Compared with the 2D scaffolds, the 3D scaffolds significantly increased the expression of osteoblastic genes of the stem cells as well as the formation of bone minerals. In addition, the scanning electron microscopic and micro-computed tomographic images showed the dense deposition of bone minerals aligned along the nanofibers of the 3D scaffolds after 14 and 28 days cultured with the mesenchymal stem cells. As such, the 3D electrospun poly(L-lactic acid)/collagen nanofibrous scaffold is a novel bone graft substitute for bone tissue regeneration.

A nanofiber membrane maintains the quiescent phenotype of hepatic stellate cells

BACKGROUND

Hepatic stellate cells (HSC) play a major role in the progression of liver fibrosis.

AIM

The aim of our study was to investigate whether rat HSC cultured on a nanofiber membrane (NM) retain their quiescent phenotype during both short- and long-term culture and whether activated HSC revert to a quiescent form when re-cultured on NM.

METHODS

Rat HSC cultured for 1 day on plastic plates (PP) were used as quiescent HSC, while cells cultured for 1 week on PP were considered to be activated HSC. Quiescent or activated HSC were subsequently plated on PP or NM and cultured for an additional 4 days at which time their gene expression, stress fiber development, and growth factor production were determined. For long-term culture, HSC were grown on NM for 20 days and the cells then replated on PP and cultured for another 10 days.

RESULTS

Expression of marker genes for HSC activation, stress fiber development, and growth factor production were significantly lower in both quiescent and activated HSC cultured on NM than in those cultured on PP. After long-term culture on NM, activation marker gene expression and stress fiber development were still significantly lower in HSC than in PP, and HSC still retained the ability to activate when replated onto PP.

CONCLUSIONS

HSC cultured on NM retained quiescent characteristics after both short- and long-term culture while activated HSC reverted toward a quiescent state when cultured on NM. Cultures of HSC grown on NM are a useful in vitro model to investigate the mechanisms of activation and deactivation.

Ectopic study of calcium phosphate cement seeded with pBMP-2 modified canine bMSCs mediated by a non-viral PEI derivative

We have evaluated the ectopic new bone formation effects of CPC (calcium phosphate cement) seeded with pBMP-2 (plasmids containing bone morphogenetic protein-2 gene) transfected canine bMSCs (bone marrow stromal cells) mediated by a non-viral PEI (polyethylenimine) derivative (GenEscort™ II) in nude mice. Canine bMSCs were transfected with pBMP-2 or pEGFP (plasmids containing enhanced green fluorescent protein gene) mediated by GenEscort™ II in vitro, and the osteoblastic differentiation was explored by ALP (alkaline phosphatase) staining, ARS (alizarin red S) staining and RT-qPCR (real-time quantitative PCR) analysis. Ectopic bone formation effects of CPC/pBMP-2 transfected bMSCs were evaluated and compared with CPC/pEGFP transfected bMSCs or CPC/untransfected bMSCs through histological, histomorphological and immunohistochemical analysis 8 and 12 weeks post-operation in nude mice. Transfection efficiency was up ∼35% as demonstrated by EGFP (enhanced green fluorescent protein) expression. ALP and ARS staining were stronger with pBMP-2 gene transfection, and mRNA expression of BMP-2 (bone morphogenetic protein-2), Col 1 (collagen 1) and OCN (osteocalcin) in pBMP-2 group was significantly up-regulated at 6 and 9 days. Significantly higher NBV (new bone volume) was achieved in pBMP-2 group than in the control groups at 8 and 12 weeks (P<0.05). In addition, immunohistochemical analysis indicated higher OCN expression in pBMP-2 group (P<0.01). We conclude that CPC seeded with pBMP-2 transfected bMSCs mediated by GenEscort™ II could enhance ectopic new bone formation in nude mice, suggesting that GenEscort™ II mediated pBMP-2 gene transfer is an effective non-viral method and CPC is a suitable scaffold for gene enhanced bone tissue engineering.

Synergistic effect of scaffold composition and dynamic culturing environment in multilayered systems for bone tissue engineering

Bone extracellular matrix (ECM) is composed of mineralized collagen fibrils which support biological apatite nucleation that participates in bone outstanding properties. Understanding and mimicking bone morphological and physiological parameters at a biological scale is a major challenge in tissue engineering scaffolding. Using emergent (nano)technologies scaffold designing may be critically improved, enabling highly functional tissue substitutes for bone applications. This study aims to develop novel biodegradable composite scaffolds of tricalcium phosphate (TCPs) and electrospun nanofibers of poly(ϵ-caprolactone) (PCL), combining TCPs osteoconductivity with PCL biocompatibility and elasticity, mimicking bone structure and composition. We hypothesized that scaffolds with such structure/composition would stimulate the proliferation and differentiation of bone marrow stromal cells (BMSCs) towards the osteogenic phenotype. Composite scaffolds, developed by electrospining using consecutive stacked layers of PCL and TCPs, were characterized by FTIR spectroscopy, X-Ray diffraction and scanning electronic microscopy. Cellular behavior was assessed in goat BMSCs seeded onto composite scaffolds and cultured in static or dynamic conditions, using basal or osteogenic media during 7, 14 or 21 days. Cellular proliferation was quantified and osteogenic differentiation confirmed by alkaline phosphatase activity, alizarin red staining and immunocytochemistry for osteocalcin and collagen I. Results suggest that PCL-TCP scaffolds provide a 3D support for gBMSCs proliferation and osteogenic differentiation with production of ECM. TCPs positively stimulate the osteogenic process, especially under dynamic conditions, where PCL-TCP scaffolds are sufficient to promote osteogenic differentiation even in basal medium conditions. The enhancement of the osteogenic potential in dynamic conditions evidences the synergistic effect of scaffold composition and dynamic stimulation in gBMSCs osteogenic differentiation.

Nanofiber-reinforced biological conduit in cardiac surgery: preliminary report

Several options are available for right ventricular outflow tract reconstruction, including commercially available bovine jugular vein and cryo-preserved homografts. Homograft non-availability and the problems of commercially available conduits led us to develop indigenously processed bovine jugular vein conduits with competent valves. They were made completely acellular and strengthened by non-conventional cross-linking without disturbing the extracellular matrix, which improved the luminal surface characteristics for hemocompatibility. Biocompatibility in vitro and in vivo, along with thermal stability, matrix stability, and mechanical strength have been evaluated. Sixty-nine patients received these conduits for right ventricular outflow tract reconstruction. Seven conduits dilated and 4 required replacement. To counteract dilatation, biodegradable polymeric nanofibers in various combinations and in isolation (collagen, polycaprolactone, polylactic acid) were characterized and used to reinforce the conduit circumferentially. Physical validation by mechanical testing, scanning electron microscopy, and in-vitro cytotoxicity was conducted. Thermal stability, spectroscopy studies of the polymer, and preclinical studies of the coated bovine jugular vein in animals are in progress. The feasibility studies have been completed, and the final polymer selection depends on evaluation of the functional superiority of the coated bovine jugular vein.

Perfusion regulation of hMSC microenvironment and osteogenic differentiation in 3D scaffold

The combination of hMSCs with 3D scaffolds has become an important approach to creating functional bone constructs. Bioreactors are important tools to mitigate mass transfer limitations and to provide controlled physiochemical and biomechanical environments for the 3D bone construct development. Media flow in the bioreactor systems is generally controlled either parallel or transverse with respect to the 3D construct, creating different cellular and biomechanical microenvironments in the 3D constructs. In this study, a custom designed modular perfusion bioreactor system was operated under either the parallel or transverse flow. The influence of the flow patterns on the characteristics of the hMSCs' cellular microenvironment and subsequent construct development was investigated. The parallel flow configuration retained ECM proteins and mitogenic growth factors within the scaffold, effectively preserving hMSC progenicity and proliferation potential (e.g., CFU-F, proliferation, and OCT-4), whereas the transverse flow induced hMSC osteogenic differentiation with higher ALP activity and calcium deposition and up-regulation of osteogenic bone markers (e.g., BMP-2, ALP, RUNX2, OSX, and OC). These results demonstrate the regulatory role of the macroscopic flow on the cellular microenvironment of the 3D hMSC construct, and suggest configuring media flow as a strategy for directing hMSC fate and 3D bone construct development in the perfusion bioreactor.

Electrospun PLLA nanofiber scaffolds and their use in combination with BMP-2 for reconstruction of bone defects

INTRODUCTION

Adequate migration and differentiation of mesenchymal stem cells is essential for regeneration of large bone defects. To achieve this, modern graft materials are becoming increasingly important. Among them, electrospun nanofiber scaffolds are a promising approach, because of their high physical porosity and potential to mimic the extracellular matrix (ECM).

MATERIALS AND METHODS

The objective of the present study was to examine the impact of electrospun PLLA nanofiber scaffolds on bone formation in vivo, using a critical size rat calvarial defect model. In addition we analyzed whether direct incorporation of bone morphogenetic protein 2 (BMP-2) into nanofibers could enhance the osteoinductivity of the scaffolds. Two critical size calvarial defects (5 mm) were created in the parietal bones of adult male Sprague-Dawley rats. Defects were either (1) left unfilled, or treated with (2) bovine spongiosa, (3) PLLA scaffolds alone or (4) PLLA/BMP-2 scaffolds. Cranial CT-scans were taken at fixed intervals in vivo. Specimens obtained after euthanasia were processed for histology, histomorphometry and immunostaining (Osteocalcin, BMP-2 and Smad5).

RESULTS

PLLA scaffolds were well colonized with cells after implantation, but only showed marginal ossification. PLLA/BMP-2 scaffolds showed much better bone regeneration and several ossification foci were observed throughout the defect. PLLA/BMP-2 scaffolds also stimulated significantly faster bone regeneration during the first eight weeks compared to bovine spongiosa. However, no significant differences between these two scaffolds could be observed after twelve weeks. Expression of osteogenic marker proteins in PLLA/BMP-2 scaffolds continuously increased throughout the observation period. After twelve weeks osteocalcin, BMP-2 and Smad5 were all significantly higher in the PLLA/BMP-2 group than in all other groups.

CONCLUSION

Electrospun PLLA nanofibers facilitate colonization of bone defects, while their use in combination with BMP-2 also increases bone regeneration in vivo and thus combines osteoconductivity of the scaffold with the ability to maintain an adequate osteogenic stimulus.

Enhanced mechanical performance and biological evaluation of a PLGA coated β-TCP composite scaffold for load-bearing applications

Porous β-tricalcium phosphate (β-TCP) has been used for bone repair and replacement in clinics due to its excellent biocompatibility, osteoconductivity, and biodegradability. However, the application of β-TCP has been limited by its brittleness. Here, we demonstrated that an interconnected porous β-TCP scaffold infiltrated with a thin layer of poly (lactic-co-glycolic acid) (PLGA) polymer showed improved mechanical performance compared to an uncoated β-TCP scaffold while retaining its excellent interconnectivity and biocompatibility. The infiltration of PLGA significantly increased the compressive strength of β-TCP scaffolds from 2.90 MPa to 4.19 MPa, bending strength from 1.46 MPa to 2.41 MPa, and toughness from 0.17 MPa to 1.44 MPa, while retaining an interconnected porous structure with a porosity of 80.65%. These remarkable improvements in the mechanical properties of PLGA-coated β-TCP scaffolds are due to the combination of the systematic coating of struts, interpenetrating structural characteristics, and crack bridging. The in vitro biological evaluation demonstrated that rat bone marrow stromal cells (rBMSCs) adhered well, proliferated, and expressed alkaline phosphatase (ALP) activity on both the PLGA-coated β-TCP and the β-TCP. These results suggest a new strategy for fabricating interconnected macroporous scaffolds with significantly enhanced mechanical strength for potential load-bearing bone tissue regeneration.

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.

Proliferation and differentiation of mesenchymal stem cell on collagen sponge reinforced with polypropylene/polyethylene terephthalate blend fibers

Although tissue-engineered scaffolds made from collagen sponge are suitable for cell infiltrating, easily supplying oxygen and nutrients to cells, and removing the waste products, their mechanical properties are not satisfactory to be used as scaffold materials for tissue engineering applications. To improve mechanical properties of collagen, a novel porous scaffold for bone tissue engineering was prepared with collagen sponge reinforced by polypropylene/polyethylene terephthalate (PP/PET) fibers. Collagen solution (6.33 mg/mL) with PP/PET fibers (collagen/fiber ratio [w/w]: 1.27, 0.63, 0.42, 0.25) was freeze-dried, followed by cross-linking of combined dehydrothermal and glutaraldehyde. A scanning electron microscopy-based analysis of surface of the sponges demonstrated that the sponge with collagen/fiber <0.25 exhibited homogenous and interconnected pore structure with an average pore size of 200 μm. Incorporation of PP/PET fibers significantly enhanced the compressive strength of the collagen sponge. Proliferation and osteogenic differentiation of mesenchymal stem cell in collagen sponges reinforced with PP/PET fibers incorporation were significantly enhanced compared with collagen sponge without PP/PET incorporation. We conclude that incorporation of PP/PET fibers not only improves the mechanical properties of collagen sponge, but also enables mesenchymal stem cells to positively improve their proliferation and differentiation.

Collagen supramolecular and suprafibrillar organizations on osteoblasts long-term behavior: benefits for bone healing materials

This study compares the behavior of osteoblastic cells seeded on three structurally distinct collagen-based materials. Adhesion and long-term behavior were evaluated in vitro in regard to collagen scaffolds forming loose or dense fibrillar networks or exempt of fibrils. In this purpose collagen solutions at concentrations of 5 and 40 mg/mL were processed by freeze-drying or by sol/gel fibrillogenesis to form either sponges or hydrogels. Macroscopic and microscopic images of sponges showed a light material exhibiting large pores surrounded by dense collagen walls made of thin unstriated microfibrils of 20 nm in diameter. In comparison collagen hydrogels are more homogeneous materials, at 5 mg/mL the material consists of a regular network of cross-striated collagen fibrils of 100 nm in diameter. At 40 mg/mL the material appears stiffer, the ultrastructure exhibits cross-striated collagen fibrils packed in large bundles of 300-800 nm of width. Human osteoblastic cells seeded on top of the 5 mg/mL matrices exhibit a squared shaped osteoblast-like morphology over 28 days of culture and express both alkaline phosphatase and osteocalcin. Osteoblastic cells seeded on top of sponges or of 40 mg/mL matrices exhibit both flat and elongated resting-osteoblast morphology. Osteoblastic cells have mineralized the three collagen-based materials after 28 days of culture but collagen sponges spontaneously mineralized in absence of cells. These results highlight, in an in vitro cell culture approach, the benefit of fibrils and of dense fibrillar networks close to in vivo-like tissues, as positive criteria for new bone tissue repair materials.

Stem cells in bone tissue engineering

Bone tissue engineering has been one of the most promising areas of research, providing a potential clinical application to cure bone defects. Recently, various stem cells including embryonic stem cells (ESCs), bone marrow-derived mesenchymal stem cells (BM-MSCs), umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs), adipose tissue-derived stem cells (ADSCs), muscle-derived stem cells (MDSCs) and dental pulp stem cells (DPSCs) have received extensive attention in the field of bone tissue engineering due to their distinct biological capability to differentiate into osteogenic lineages. The application of these stem cells to bone tissue engineering requires inducing in vitro differentiation of these cells into bone forming cells, osteoblasts. For this purpose, efficient in vitro differentiation towards osteogenic lineage requires the development of well-defined and proficient protocols. This would reduce the likelihood of spontaneous differentiation into divergent lineages and increase the available cell source for application to bone tissue engineering therapies. This review provides a critical examination of the various experimental strategies that could be used to direct the differentiation of ESC, BM-MSC, UCB-MSC, ADSC, MDSC and DPSC towards osteogenic lineages and their potential applications in tissue engineering, particularly in the regeneration of bone.