Adhesion of mesenchymal stem cells to polymer scaffolds occurs via distinct ECM ligands and controls their osteogenic differentiation

Electrospun L-Lysine/Amorphous Calcium Phosphate Loaded Core-Sheath Nanofibers for Managing Oral Biofilm Infections and Promoting Periodontal Tissue Repairment

Introduction

Periodontitis, a chronic inflammatory disease prevalent worldwide, is primarily treated through GTR for tissue regeneration. The efficacy of GTR, however, remains uncertain due to potential infections and the intricate microenvironment of periodontal tissue. Herein, We developed a novel core-shell structure multifunctional membrane using a dual-drug-loaded coaxial electrospinning technique (Lys/ACP-CNF), contains L-lysine in the outer layer to aid in controlling biofilms after GTR regenerative surgery, and ACP in the inner layer to enhance osteogenic performance for accelerating alveolar bone repair.

Methods

The biocompatibility and cell adhesion were evaluated through CCK-8 and fluorescence imaging, respectively. The antibacterial activity was assessed using a plate counting assay. ALP, ARS, and RT-qPCR were used to examine osteogenic differentiation. Additionally, an in vivo experiment was conducted on a rat model with acute periodontal defect and infection. Micro-CT and histological analysis were utilized to analyze the in vivo alveolar bone regeneration.

Results

Structural and physicochemical characterization confirmed the successful construction of the core-shell fibrous structure. Additionally, the Lys/ACP-CNF showed strong antibacterial coaggregation effects and induced osteogenic differentiation of PDLSCs in vitro. The in vivo experiment confirmed that Lys/ACP-CNF promotes new bone formation.

Conclusion

Lys/ACP-CNF rapidly exhibited excellent antibacterial activity, protected PDLSCs from infection, and was conducive to osteogenesis, demonstrating its potential application for clinical periodontal GTR surgery.

Collagen type I-based recombinant peptide promotes bone regeneration in rat critical-size calvarial defects by enhancing osteoclast activity at late stages of healing

Introduction

We recently demonstrated the bone-forming potential of medium-cross-linked recombinant collagen peptide (mRCP) in animal models of bone defects. However, these studies were limited to a 4-week observation period; therefore, in the present study, we aimed to further evaluate mRCP as a suitable bone graft material for the alveolar cleft by analyzing its bone-forming potential, osteogenic-inducing ability, and biodegradation over an extended period of 12 weeks, using a rat critical-size calvarial defect model.

Methods

Using Sprague-Dawley rats, we created critical-size calvarial defects through a surgical procedure. The defects were then filled with 3 mg of mRCP (mRCP group) or 18 mg of Cytrans® (CA) granules, which has a carbonate apatite-based composition resembling natural bone, was used as a reference material (CA group). For negative control, the defects were left untreated. Bone volume, total bone volume (bone volume including CA granules), and bone mineral density (BMD) in the defect were assessed using micro-computed tomography (μ-CT) at 0, 4, 8, and 12 weeks after implantation. Using histomorphometric analyses of hematoxylin and eosin (H&E)-stained sections, we measured the amount of newly formed bone and total newly formed bone (new bone including CA granules) in the entire defect site, as well as the amount of newly formed bone in the central side, two peripheral sides (left and right), periosteal (top) side, and dura mater (bottom) side. In addition, we measured the amount of residual bone graft material in the defect. Osteoclasts and osteoblasts in the newly formed bone were detected using tartrate-resistant acid phosphatase (TRAP) and alkaline phosphatase (ALP) staining, respectively.

Results

Bone volume in the mRCP group increased over time and was significantly larger at 8 and 12 weeks after surgery than at 4 weeks. The bone volume in the mRCP group was greater than that of the CA and control groups at 4, 8, and 12 weeks after implantation, and while the total bone volume was greater in the CA group after 4 and 8 weeks, the mRCP group had comparable levels of total bone volume to that of the CA group at 12 weeks after implantation. The BMD of the mRCP group reached similar levels to native calvaria bone at the same time point. H&E-stained sections revealed a larger amount of newly formed bone 12 weeks after implantation in the mRCP group compared to that of the CA and control groups. The total newly formed bone at 12 weeks after implantation was on par with that in the CA group. Furthermore, at the defect site, the area of newly formed bone was larger on the peripheral and dura mater sides. Notably, the number of osteoclasts in the mRCP group was higher than in the CA and control groups and peaked 8 weeks after implantation, which coincided with the timing of the greatest resorption of mRCP. Although the ALP-positive area was greater in the mRCP group compared to other groups, we did not detect any significant changes in the number of osteoblasts over time.

Conclusion

This study demonstrated the bone-forming potential of mRCP over an extended period of 12 weeks, suggesting that mRCP sufficiently resists resorption to promote bone formation through induction of osteoclast activation in the late stages of the healing period.

Combined 3D bioprinting and tissue-specific ECM system reveals the influence of brain matrix on stem cell differentiation

We have previously shown that human and murine breast extracellular matrix (ECM) can significantly impact cellular behavior, including stem cell fate determination. It has been established that tissue-specific extracellular matrix from the central nervous system has the capacity to support neuronal survival. However, the characterization of its influence on stem cell differentiation and its adaptation to robust 3D culture models is underdeveloped. To address these issues, we combined our 3D bioprinter with hydrogels containing porcine brain extracellular matrix (BMX) to test the influence of the extracellular matrix on stem cell differentiation. Our 3D bioprinting system generated reproducible 3D neural structures derived from mouse embryonic stem cells (mESCs). We demonstrate that the addition of BMX preferentially influences 3D bioprinted mESCs towards neural lineages compared to standard basement membrane (Geltrex/Matrigel) hydrogels alone. Furthermore, we demonstrate that we can transplant these 3D bioprinted neural cellular structures into a mouse's cleared mammary fat pad, where they continue to grow into larger neural outgrowths. Finally, we demonstrate that direct injection of human induced pluripotent stem cells (hiPSCS) and neural stem cells (NSCs) suspended in pure BMX formed neural structures in vivo. Combined, these findings describe a unique system for studying brain ECM/stem cell interactions and demonstrate that BMX can direct pluripotent stem cells to differentiate down a neural cellular lineage without any additional specific differentiation stimuli.

Decellularised Cartilage ECM Culture Coatings Drive Rapid and Robust Chondrogenic Differentiation of Human Periosteal Cells

The control of cell behaviour in an effort to create highly homogeneous cultures is becoming an area of intense research, both to elucidate fundamental biology and for regenerative applications. The extracellular matrix (ECM) controls many cellular processes in vivo, and as such is a rich source of cues that may be translated in vitro. Herein, we describe the creation of cell culture coatings from porcine decellularised hyaline cartilage through enzymatic digestion. Surprisingly, heat-mediated sterilisation created a coating with the capacity to rapidly and robustly induce chondrogenic differentiation of human periosteal cells. This differentiation was validated through the alteration of cell phenotype from a fibroblastic to a cuboidal/cobblestone chondrocyte-like appearance. Moreover, chondrogenic gene expression further supported this observation, where cells cultured on heat sterilised ECM-coated plastic displayed higher expression of COL2A1, ACAN and PRG4 (p < 0.05) compared to non-coated plastic cultures. Interestingly, COL2A1 and ACAN expression in this context were sensitive to initial cell density; however, SOX9 expression appeared to be mainly driven by the coating independent of seeding density. The creation of a highly chondrogenic coating may provide a cost-effective solution for the differentiation and/or expansion of human chondrocytes aimed towards cartilage repair strategies.

Application of Alginate Hydrogels for Next-Generation Articular Cartilage Regeneration

The articular cartilage has insufficient intrinsic healing abilities, and articular cartilage injuries often progress to osteoarthritis. Alginate-based scaffolds are attractive biomaterials for cartilage repair and regeneration, allowing for the delivery of cells and therapeutic drugs and gene sequences. In light of the heterogeneity of findings reporting the benefits of using alginate for cartilage regeneration, a better understanding of alginate-based systems is needed in order to improve the approaches aiming to enhance cartilage regeneration with this compound. This review provides an in-depth evaluation of the literature, focusing on the manipulation of alginate as a tool to support the processes involved in cartilage healing in order to demonstrate how such a material, used as a direct compound or combined with cell and gene therapy and with scaffold-guided gene transfer procedures, may assist cartilage regeneration in an optimal manner for future applications in patients.

Improved cell adhesion to activated vapor silanization-biofunctionalized Ti-6Al-4V surfaces with ECM-derived oligopeptides

Titanium implants are widely used in traumatology and various orthopedic fields. Titanium and other metallic-based implants have limited structural and functional integration into the body, which translates into progressive prosthesis instability and the need for new surgical interventions that have enormous social and economic impacts. To enhance the biocompatibility of titanium implants, numerous biofunctionalization strategies have been developed. However, the problem persists, as more than 70% of implant failures are due to aseptic loosening. In this study we addressed the problem of improving the physiological engraftability and acceptability of titanium-based implants by applying a robust and versatile functionalization method based on the covalent immobilization of extracellular matrix (ECM)-derived oligopeptides on Ti-6Al-4V surfaces treated by activated vapor silanization (AVS). The feasibility of this technique was evaluated with two oligopeptides of different structures and compositions. These oligopeptides were immobilized on Ti-6Al-4V substrates by a combination of AVS and N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS) crosslinking chemistry. The immobilization was shown to be stable and resistant to chemical denaturing upon sodium dodecyl sulfate treatment. On Ti-6Al-4V surfaces both peptides increased the attachment, spreading, rearrangement and directional growth of mesenchymal stem and progenitor cells (MSC) with chondro- and osteo-regenerative capacities. We also found that this biofunctionalization method (AVS-EDC/NHS) increased the attachment capacity of an immortalized cell line of neural origin with poor adhesive properties, highlighting the versatility and robustness of this method in terms of potential oligopeptides that may be used, and cell lineages whose anchorage to the biomaterial may be enhanced. Collectively, this novel functionalization strategy can accelerate the development of advanced peptide-functionalized metallic surfaces, which, in combination with host or exogenously implanted stem cells, have the potential to positively affect the osteoregenerative and osteointegrative abilities of metallic-based prostheses.

Polylactide, Processed by a Foaming Method Using Compressed Freon R134a, for Tissue Engineering

Fabricating polymeric scaffolds using cost-effective manufacturing processes is still challenging. Gas foaming techniques using supercritical carbon dioxide (scCO₂) have attracted attention for producing synthetic polymer matrices; however, the high-pressure requirements are often a technological barrier for its widespread use. Compressed 1,1,1,2-tetrafluoroethane, known as Freon R134a, offers advantages over CO₂ in manufacturing processes in terms of lower pressure and temperature conditions and the use of low-cost equipment. Here, we report for the first time the use of Freon R134a for generating porous polymer matrices, specifically polylactide (PLA). PLA scaffolds processed with Freon R134a exhibited larger pore sizes, and total porosity, and appropriate mechanical properties compared with those achieved by scCO₂ processing. PLGA scaffolds processed with Freon R134a were highly porous and showed a relatively fragile structure. Human mesenchymal stem cells (MSCs) attached to PLA scaffolds processed with Freon R134a, and their metabolic activity increased during culturing. In addition, MSCs displayed spread morphology on the PLA scaffolds processed with Freon R134a, with a well-organized actin cytoskeleton and a dense matrix of fibronectin fibrils. Functionalization of Freon R134a-processed PLA scaffolds with protein nanoparticles, used as bioactive factors, enhanced the scaffolds' cytocompatibility. These findings indicate that gas foaming using compressed Freon R134a could represent a cost-effective and environmentally friendly fabrication technology to produce polymeric scaffolds for tissue engineering approaches.

Combinatorial effect of plasma treatment, fiber alignment and fiber scale of poly (ε-caprolactone)/collagen multiscale fibers in inducing tenogenesis in non-tenogenic media

Tendon being a hypocellular, low vascularized tissue often requires assistance for restoration after complete tear. Tendon tissue engineering aims in the development of suitable scaffold that could support the regeneration of tendon after damage. The success of such scaffolds is dependent on its integration with the native tissue which in turn is influenced by the cell-material interaction. In this work aligned poly(ε-caprolactone)/collagen (PCL/collagen) multiscale fibers were developed and plasma treatment using argon, nitrogen and its combination was accessed for inducing tenogenic differentiation in mesenchymal stem cells. The developed fibers mimicked tendon extracellular matrix (ECM) which upon plasma treatment maintained moderate hydrophilicity. Oxygen and nitrogen containing groups were observed to be incorporated after argon and nitrogen treatment respectively. Statistically significant (p < 0.001) enhancement was observed in average and root mean square (RMS) roughness after plasma treatment with the maximum in argon treated fibers. Vitronectin was competitively (statistically significant, p < 0.05) adsorbed after argon and combination treatment whereas nitrogen treatment led to the competitive adsorption of fibronectin (statistically significant, p < 0.05). Human mesenchymal stem cells (hMSCs) showed enhanced proliferation and attachment on plasma treated fibers. Increased porosity due to the presence of sacrificial collagen nanofibers improved cell infiltration which was further enhanced upon plasma treatment. RhoA activation was observed (statistically significant, p < 0.05) on aligned PCL/collagen multiscale fibers and PCL microfibers, which proved its impact on tenogenic differentiation. Further enhancement in rhoA expression was observed on argon (p < 0.01) and combination plasma (p < 0.05) treated fibers. Tenogenic differentiation of hMSCs was enhanced (statistically significant) on argon plasma treated aligned fibers which was confirmed by the expression of scleraxis, mohawk (early markers) and tenomodulin (late marker) at protein level and mohawk, collagen I, collagen III (early markers), thrombospondin 4 and tenascin C (late markers) at gene level. Thus argon plasma treatment on aligned fibers is an effective method to induce tenogenesis even in non-tenogenic media.

Effects of Chiral Molecule Modification on Surface Biosorption Behavior

Antifouling materials have many important applications in biomedical devices and marine coating. Oligo(ethylene glycol) (OEG) or poly(ethylene glycol) (PEG) exhibit promising antifouling properties and are widely used in biomedical engineering. Chiral selection is an important phenomenon in biological processes. Because of the influence of steric hindrance, the modification of chiral molecules with different chirality at interfaces will affect the intermolecular interaction at the interfaces and lead to different structures of interfacial molecules. The difference of surface structures such as surface hydration structure would impact the adsorption of biomolecules on the surface, thus causing different varieties of cell adhesion and cell growth. In this study, the influence on surface hydration and surface cell adhesion of OEG self-assembled monolayers (SAMs) modified with cysteine showing different chirality are explored. The water structure at the interfaces of OEG/water in different conditions was probed with sum frequency generation vibrational spectroscopy (SFG-VS). The results show that the interfacial water structure can change significantly with either d-cysteine or l-cysteine modification on OEG. Water molecules are more ordered at the OEG/water interface under the d-cysteine modification on OEG SAMs, which improves the protein adsorption resistance of the surface. In contrast, l-cysteine modification would make the water less ordered at the OEG/protein solution interface and enhance the protein adsorption. Additionally, optical micrographs indicate that l-cysteine can significantly promote the OEG SAMs cell adhesion and growth, while d-cysteine exhibits an inhibitory effect, which is consistent with the results of SFG-VS experiments.

Xeno-Free Bioreactor Culture of Human Mesenchymal Stromal Cells on Chemically Defined Microcarriers

Human mesenchymal stromal cells (hMSC), also called mesenchymal stem cells, are adult cells that have demonstrated their potential in therapeutic applications, highlighted by their ability to differentiate down different lineages, modulate the immune system, and produce biologics. There is a pressing need for scalable culture systems for hMSC due to the large number of cells needed for clinical applications. Most current methods for expanding hMSC fail to provide a reproducible cell product in clinically required cell numbers without the use of serum-containing media or harsh enzymes. In this work, we apply a tailorable, thin, synthetic polymer coating-poly(poly(ethylene glycol) methyl ether methacrylate-ran-vinyl dimethyl azlactone-ran-glycidyl methacrylate) (P(PEGMEMA-r-VDM-r-GMA), PVG)-to the surface of commercially available polystyrene (PS) microcarriers to create chemically defined three-dimensional (3D) surfaces for large-scale cell expansion. These chemically defined microcarriers provide a reproducible surface that does not rely on the adsorption of xenogeneic serum proteins to mediate cell adhesion, enabling their use in xeno-free culture systems. Specifically, this work demonstrates the improved adhesion of hMSC to coated microcarriers over PS microcarriers in xeno-free media and describes their use in a readily scalable, bioreactor-based culture system. Additionally, these surfaces resist the adsorption of media-borne and cell-produced proteins, which result in integrin-mediated cell adhesion throughout the culture period. This feature allows the cells to be efficiently passaged from the microcarrier using a chemical chelating agent (ethylenediaminetetraacetic acid (EDTA)) in the absence of cleavage enzymes, an improvement over other microcarrier products in the field. Bioreactor culture of hMSC on these microcarriers enabled the production of hMSC over 4 days from a scalable, xeno-free environment.

Characteristics and clinical potential of a cellularly modified gelatin sponge

BACKGROUND

Human umbilical cord mesenchymal stem cells (HuMSCs) injected directly have been proven effective for improving chronic wounds. However, HuMSCs largely die within 14 days. The aim of study is to establish a cellularly modified gelatin sponge and investigate its characteristics and clinical potential.

METHODS

HuMSCs were isolated, expanded and seeded in a poly-L-lysine (PLL)-coated gelatin sponge. Fabricated gelatin sponges were estimated through observation of morphological surface and ultrastructure, following confirmed by histology method. Supernatants were collected at different times for enzyme-linked immunosorbent assays (ELISAs) to measure growth factors. The cell embedded gelatin sponges were implanted subcutaneously on the backs of mice and the samples were harvested and studied histologically.

RESULTS

HuMSCs gradually modified the gelatin sponge by depositing collagen and hyaluronic acid, and degrading the structure of gelatin, resulting in a dense, and elastic structure. Compared with cells cultured in monolayer, the levels of growth factors increased remarkably when HuMSCs were cultivated in the gelatin sponge. Upon subcutaneous implantation in the backs of mice, the cellularized gelatin sponges persisted for up to 2 months and eventually integrated into the host tissue, while blank gelatin sponges degraded completely by the end of the second month.

CONCLUSION

Gelatin sponge is a clinically accessible scaffold for HuMSCs implantation to maintain short-term survival of the cells and high-level production of growth factors, which demonstrates good clinical potential for enhancing wound healing.

Bone formation potential of collagen type I-based recombinant peptide particles in rat calvaria defects

Introduction

This study aimed to examine the bone-forming ability of medium-cross-linked recombinant collagen peptide (mRCP) particles developedbased on human collagen type I, contains an arginyl-glycyl-aspartic acid-rich motif, fabricated as bone filling material, compared to that of the autologous bone graft.

Methods

Calvarial bone defects were created in immunodeficient rats though a surgical procedure. The rats were divided into 2 groups: mRCP graft and tibia bone graft (bone graft). The bone formation potential of mRCP was evaluated by micro-computed tomography and hematoxylin-eosin staining at 1, 2, 3, and 4 weeks after surgery, and the data were analyzed and compared to those of the bone graft.

Results

The axial volume-rendered images demonstrated considerable bony bridging with the mRCP graft, but there was no significant difference in the bone volume and bone mineral density between the mRCP graft and bone graft at 4 weeks. The peripheral new bone density was significantly higher than the central new bone density and the bottom side score was significantly higher than the top side score at early stage in the regenerated bone within the bone defects.

Conclusion

These results indicate that mRCP has a high potential of recruiting osteogenic cells, comparable to that of autologous bone chips.

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Bone formation potential of mRCP were comparable to that of autogenous bone.

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mRCP particles exhibit high new bone formation potential in the calvaria defect.

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Bone bridging was observed over the entire defect in mRCP graft at 4 weeks.

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mRCP has a high potential of recruiting osteogenic cells comparable to bone graft.

Hydrophilic Surface Functionalization of Electrospun Nanofibrous Scaffolds in Tissue Engineering

Electrospun polymer nanofibers have received much attention in tissue engineering due to their valuable properties such as biocompatibility, biodegradation ability, appropriate mechanical properties, and, most importantly, fibrous structure, which resembles the morphology of extracellular matrix (ECM) proteins. However, they are usually hydrophobic and suffer from a lack of bioactive molecules, which provide good cell adhesion to the scaffold surface. Post-electrospinning surface functionalization allows overcoming these limitations through polar groups covalent incorporation to the fibers surface, with subsequent functionalization with biologically active molecules or direct deposition of the biomolecule solution. Hydrophilic surface functionalization methods are classified into chemical approaches, including wet chemical functionalization and covalent grafting, a physiochemical approach with the use of a plasma treatment, and a physical approach that might be divided into physical adsorption and layer-by-layer assembly. This review discusses the state-of-the-art of hydrophilic surface functionalization strategies of electrospun nanofibers for tissue engineering applications. We highlighted the major advantages and drawbacks of each method, at the same time, pointing out future perspectives and solutions in the hydrophilic functionalization strategies.

Feeling Things Out: Bidirectional Signaling of the Cell-ECM Interface, Implications in the Mechanobiology of Cell Spreading, Migration, Proliferation, and Differentiation

Biophysical cues stemming from the extracellular environment are rapidly transduced into discernible chemical messages (mechanotransduction) that direct cellular activities-placing the extracellular matrix (ECM) as a potent regulator of cell behavior. Dynamic reciprocity between the cell and its associated matrix is essential to the maintenance of tissue homeostasis and dysregulation of both ECM mechanical signaling, via pathological ECM turnover, and internal mechanotransduction pathways contribute to disease progression. This review covers the current understandings of the key modes of signaling used by both the cell and ECM to coregulate one another. By taking an outside-in approach, the inherent complexities and regulatory processes at each level of signaling (ECM, plasma membrane, focal adhesion, and cytoplasm) are captured to give a comprehensive picture of the internal and external mechanoregulatory environment. Specific emphasis is placed on the focal adhesion complex which acts as a central hub of mechanical signaling, regulating cell spreading, migration, proliferation, and differentiation. In addition, a wealth of available knowledge on mechanotransduction is curated to generate an integrated signaling network encompassing the central components of the focal adhesion, cytoplasm and nucleus that act in concert to promote durotaxis, proliferation, and differentiation in a stiffness-dependent manner.

Biological responses of dental pulp cells to surfaces modified by collagen 1 and fibronectin

Collagen 1 (COL1) and fibronectin (FN) are extracellular matrix proteins that contribute in cell activity and involve in regulating dental pulp cells (DPCs). The purpose of this study was to investigate the effect of COL1 and FN on the behavior of DPCs. Here, DPCs were grown under three different conditions: COL1 coating, FN coating, and control group without coating. The proliferation and differentiation of DPCs were investigated. DPCs in osteogenic media were able to differentiate into osteoblastic phenotype. The morphological analysis revealed no obvious difference on the shape of cells. Cells had spread well on both coated and noncoated culture plates with slightly more spreading in the coated plates after 24 hr. The MTT analysis did not demonstrate a significant difference at 1 and 3 hr among the groups, but interestingly, the analysis disclosed more cells on the coated plates after longer cultures, which indicated a higher proliferative capacity in response to COL1 and FN. RT-PCR, Western Blotting and mineralization assays did not reveal significant differences between the coated and noncoated surfaces in relation to osteogenic differential potential. Our data suggested that the surface coating of COL1 and FN were able to promote cellular proliferation and the osteogenic differentiation tendency of DPCs was also observed in vitro.

Human Fat-Derived Mesenchymal Stem Cells Xenogenically Implanted in a Rat Model Show Enhanced New Bone Formation in Maxillary Alveolar Tooth Defects

BACKGROUND

Due to restorative concerns, bone regenerative therapies have garnered much attention in the field of human oral/maxillofacial surgery. Current treatments using autologous and allogenic bone grafts suffer from inherent challenges, hence the ideal bone replacement therapy is yet to be found. Establishing a model by which MSCs can be placed in a clinically acceptable bone defect to promote bone healing will prove valuable to oral/maxillofacial surgeons.

METHODS

Human adipose tissue-derived MSCs were seeded onto Gelfoam® and their viability, proliferation, and osteogenic differentiation was evaluated in vitro. Subsequently, the construct was implanted in a rat maxillary alveolar bone defect to assess in vivo bone healing and regeneration.

RESULTS

Human MSCs were adhered, proliferated, and uniformly distributed, and underwent osteogenic differentiation on Gelfoam®, comparable with the tissue culture surface. Data confirmed that Gelfoam® could be used as a scaffold for cell attachment and a delivery vehicle to implant MSCs in vivo. Histomorphometric analyses of bones harvested from rats treated with hMSCs showed statistically significant increase in collagen/early bone formation, with cells positive for osteogenic and angiogenic markers in the defect site. This pattern was visible as early as 4 weeks post treatment.

CONCLUSIONS

Xenogenically implanted human MSCs have the potential to heal an alveolar tooth defect in rats. Gelfoam®, a commonly used clinical biomaterial, can serve as a scaffold to deliver and maintain MSCs to the defect site. Translating this strategy to preclinical animal models provides hope for bone tissue engineering.

Tuning the biomimetic behavior of scaffolds for regenerative medicine through surface modifications

Tissue engineering and regenerative medicine rely extensively on biomaterial scaffolds to support cell adhesion, proliferation, and differentiation physically and chemically in vitro and in vivo. Changes to the surface characteristics of the scaffolds have the greatest impact on cell response. Here, we discuss five dominant surface modification approaches used to biomimetically improve the most common scaffolds for tissue engineering, those based on aliphatic polyesters. Scaffolds of aliphatic polyesters such as poly(l-lactic acid), poly(l-lactic-co-glycolic acid), and poly(ε-caprolactone) are often used in tissue engineering because they provide desirable, tunable properties such as ease of manufacturing, good mechanical properties, and nontoxic degradation products. However, cell-surface interactions necessary for tissue engineering are limited on these materials by their smooth postfabrication surfaces, hydrophobicity, and lack of recognizable biochemical binding sites. The surface modification techniques that have been developed for synthetic polymer scaffolds reduce initial barriers to cell adhesion, proliferation, and differentiation. Topographical modification, protein adsorption, mineral coating, functional group incorporation, and biomacromolecule immobilization each contribute through varying mechanisms to improving cell interactions with aliphatic polyester scaffolds. Furthermore, rational combination of methods from these categories can provide nuanced, specific environments for targeted tissue development.

Engineering a platform for nerve regeneration with direct application to nerve repair technology

The development of effective treatment options for repair of peripheral nerves is complicated by lack of knowledge concerning the interactions between cells and implants. A promising device, the multichannel scaffold, incorporates microporous channels, aligning glia and directing axonal growth across a nerve gap. To enhance clinical outcomes of nerve repair, a platform, representative of current implant technology, was engineered which 1) recapitulated key device features (porosity and linearity) and 2) demonstrated remyelination of adult neurons. The in vitro platform began with the study of Schwann cells on porous polycaprolactone (PCL) and poly(lactide co-glycolide) (PLGA) substrates. Surface roughness determined glial cell attachment, and an additional layer of topography, 40 μm linear features, aligned Schwann cells and axons. In addition, direct co-culture of sensory neurons with Schwann cells significantly increased neurite outgrowth, compared to neurons cultured alone (naive or pre-conditioned). In contrast to the control substrate (glass), on porous PCL substrates, Schwann cells differentiated into a mature myelinating phenotype, expressing Oct-6, MPZ and MBP. The direct applicability of this platform to nerve implants, including its response to physiological cues, allows for optimization of cell-material interactions, close observation of the regeneration process, and the study of therapeutics, necessary to advance peripheral nerve repair technology.

Petaloid recombinant peptide enhances in vitro cartilage formation by synovial mesenchymal stem cells

In vitro chondrogenesis of mesenchymal stem cells (MSCs) mimics in vivo chondrogenesis of MSCs. However, the size of the cartilage pellets that can be attained in vitro is limited by current methods; therefore, some modifications are required to obtain larger pellets. Petaloid pieces of recombinant peptide (petaloid RCP) have the advantage of creating spaces between cells in culture. The RCP used here is based on the alpha-1 sequence of human collagen type I and contains 12 Arg-Gly-Asp motifs. We examined the effect and mechanisms of adding petaloid RCP on the in vitro chondrogenesis of human synovial MSCs by culturing 125k cells with or without 0.125 mg petaloid RCP in chondrogenic medium for 21 days. The cartilage pellets were sequentially analyzed by weight, sulfated glycosaminoglycan content, DNA retention, and histology. Petaloid RCP significantly increased the weight of the cartilage pellets: The petaloid RCP group weighed 7.7 ± 1.2 mg (n = 108), whereas the control group weighed 5.3 ± 1.6 mg. Sulfated glycosaminoglycan and DNA contents were significantly higher in the petaloid RCP group than in the control group. Light and transmission electron microscopy images showed that the petaloid RCP formed the framework of the pellet at day 1, the framework was broken by production of cartilage matrix by the synovial MSCs at day 7, and the cartilage pellet grew larger, with diffuse petaloid RCP remaining, at day 21. Therefore, petaloid RCP formed a framework for the pellet, maintained a higher cell number, and promoted in vitro cartilage formation of synovial MSCs. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. J Orthop Res 37:1350-1357, 2019.

Incorporation of silica nanoparticles to PLGA electrospun fibers for osteogenic differentiation of human osteoblast-like cells

The development of bone tissue engineering scaffolds still remains a challenging field, although various biomaterials have been developed for this purpose. Electrospinning is a promising approach to fabricate nanofibers with an interconnected porous structure, which can support cell adhesion, guide cell proliferation and regulate cell differentiation. The aim of this study is to fabricate composite fibers composed of poly(lactic-co-glycolic acid) (PLGA) and silica nanoparticles (NPs) via electrospinning and investigate the effect of PLGA/SiO2 composite fibers on the cellular response of osteoblast-like cells (SaOS-2 cells). SEM and EDX analysis showed that silica NPs were homogenously dispersed in the composite fibers. The mechanical behavior of the fibers showed that silica NPs acted as reinforcements at concentrations of 2.5 and 5 mg/ml. The incorporation of silica NPs led to enhancement of cell attachment and spreading on PLGA/SiO2 composite fibers. SaOS-2 cells cultured on PLGA/SiO2 composite fibers exhibited increased alkaline phosphatase activity, collagen secretion and bone nodules formation. The bone nodules formation of SaOS-2 cells increased along with the amount of incorporated silica NPs. The present findings indicate that PLGA/SiO2 composite fibers can stimulate osteogenic differentiation of SaOS-2 cells and may be a promising candidate scaffold for bone tissue engineering.

The role of the micro-pattern and nano-topography of hydroxyapatite bioceramics on stimulating osteogenic differentiation of mesenchymal stem cells

The micro/nano hybrid structure is considered to be a biomaterial characteristic to stimulate osteogenesis by mimicking the three-dimensional structure of the bone matrix. However, the mechanism of the hybrid structure induced osteogenic differentiation of stem cells is still unknown. For elucidating the mechanisms, one of the challenge is to directly fabricate micro/nano hybrid structure on bioceramics because of its brittleness. In this study, hydroxyapatite (HA) bioceramics with the micro/nano hybrid structure were firstly fabricated via a hydrothermal treatment and template method, and the effect of the different surface structures on the expression of integrins, BMP2 signaling pathways and cell-cell communication was investigated. Interestingly, the results suggested that the osteogenic differentiation induced by micro/nano structures was modulated first through activating integrins and then further activating BMP2 signaling pathway and cell-cell communication, while activated BMP2 could in turn activate integrins and Cx43-related cell-cell communication. Furthermore, differences in activation of integrins, BMP2 signaling pathway, and gap junction-mediated cell-cell communication were observed, in which nanorod and micropattern structures activated different integrin subunits, BMP downstream receptors and Cx43. This finding may explain the synergistic effect of the micro/nano hybrid structure on the activation of osteogenic differentiation of BMSCs. Based on our study, we concluded that the different activation mechanisms of micro- and nano-structures led to the synergistic stimulatory effect on integrin activation and osteogenesis, in which not only the direct contact of cells on micro/nano structure played an important role, but also other surface characteristics such as protein adsorption might contribute to the bioactive effect.

STATEMENT OF SIGNIFICANCE

The micro/nano hybrid structure has been found to have synergistic bioactivity on osteogenesis. However, it is still a challenge to fabricate the hybrid structure directly on the bioceramics, and the role of micro- and nano-structure, in particular the mechanism of the micro/nano-hybrid structure induced stem cell differentiation is still unknown. In this study, we firstly fabricated hydroxyapatite bioceramics with the micro/nano hybrid structure, and then investigated the effect of different surface structure on expression of integrins, BMP2 signaling pathways and cell-cell communication. Interestingly, we found that the osteogenic differentiation induced by structure was modulated first through activating integrins and then further activating BMP2 signaling pathway and cell-cell communication, and activated BMP2 could in turn activate some integrin subunits and Cx43-related cell-cell communication. Furthermore, differences in activation of integrins, BMP2 signaling pathway, and gap junction-mediated cell-cell communication were observed, in which nanorod and micropattern structures activated different integrin subunits, BMP downstream receptors and Cx43. This finding may explain the synergistic effect of the micro/nano hybrid structure on the activation of osteogenic differentiation of BMSCs. Based on our study, we concluded that the different activation mechanisms of micro- and nano-structures led to the synergistic stimulatory effect on integrin activation and osteogenesis, in which not only the direct contact of cells on micro/nano structure played an important role, but also other surface characteristics such as protein adsorption might contribute to the bioactive effect.

Preparation of Decellularized Biological Scaffolds for 3D Cell Culture

The biggest challenge of designing and implementing an in vitro study is developing a microenvironment that most closely represents the interactions observed in vivo. Decellularization of tissues and organs has been shown to be an effective method for the removal of potentially immunogenic constituents while preserving essential growth factors and extracellular matrix (ECM ) proteins necessary for proper cell function. Enzymatic digestion of decellularized tissues allows these tissue-specific components to be reconstituted into bioactive hydrogels through a physical crosslinking of collagen. In the following protocol, we describe unique decellularization methods for both dermis and urinary bladder matrix (UBM) derived from porcine tissues. We then provide details for hydrogel formation and subsequent three-dimensional (3D) culture of two cell types: NIH 3T3 fibroblasts and C2C12 myoblasts .

A comparison study between electrospun polycaprolactone and piezoelectric poly(3-hydroxybutyrate-co-3-hydroxyvalerate) scaffolds for bone tissue engineering

In this study, bone scaffolds composed of polycaprolactone (PCL), piezoelectric poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and a combination of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and silicate containing hydroxyapatite (PHBV-SiHA) were successfully fabricated by a conventional electrospinning process. The morphological, chemical, wetting and biological properties of the scaffolds were examined. All fabricated scaffolds are composed of randomly oriented fibres with diameters from 800nm to 12μm. Fibre size increased with the addition of SiHA to PHBV scaffolds. Moreover, fibre surface roughness in the case of hybrid scaffolds was also increased. XRD, FTIR and Raman spectroscopy were used to analyse the chemical composition of the scaffolds, and contact angle measurements were performed to reveal the wetting behaviour of the synthesized materials. To determine the influence of the piezoelectric nature of PHBV in combination with SiHA nanoparticles on cell attachment and proliferation, PCL (non-piezoelectric), pure PHBV, and PHBV-SiHA scaffolds were seeded with human mesenchymal stem cells (hMSCs). In vitro study on hMSC adhesion, viability, spreading and osteogenic differentiation showed that the PHBV-SiHA scaffolds had the largest adhesion and differentiation abilities compared with other scaffolds. Moreover, the piezoelectric PHBV scaffolds have demonstrated better calcium deposition potential compared with non-piezoelectric PCL. The results of the study revealed pronounced advantages of hybrid PHBV-SiHA scaffolds to be used in bone tissue engineering.

A comparative study of the influence of two types of PHEMA stents on the differentiation of ASCs to myocardial cells

In the present study, subcutaneous fat was obtained from adult women that had undergone conventional liposuction surgery. A comparative study was performed to investigate the effect of transparent and white poly-β-hydroxyethyl methacrylate (PHEMA) stents, which have different surface and cross-sectional morphological characteristics, on the differentiation of adipose-derived stem cells (ASCs) into myocardial cells. The cell counting kit-8 assay revealed that cell growth increased at varying rates among the different treatment groups. The absorbance of the experimental transparent PHEMA treated group increased in a time-dependent manner with the duration of incubation. The highest levels of proliferation were observed in the transparent PHEMA group. In addition, the transparent PHEMA treated group exhibited the strongest cell adhesion ability, which was significantly different to that of the white PHEMA group (P<0.01 and P<0.05 for Matrigel and fibronectin assay, respectively). Comparisons between the two stent materials with the inducer control group revealed statistically significant differences in the rate of ASC differentiation (P<0.05). The level of differentiation was the greatest in the transparent PHEMA group, and was significantly different to the white PHEMA group (P<0.05) and the blank control group (P<0.01). The results suggest that the inducers 5-aza-2-deoxycytidin and laminin, and material microstructure stents effectively promote the proliferation, growth and adhesion of ASCs. However, the transparent material microstructure may be a more suitable candidate for ASC-associated injections. The present study provides further evidence that a PHEMA stent structure, comprised of a high number of matrixes and a low water content, induces a high level of ASC differentiation to myocardial cells.

Cationic osteogenic peptide P15-CSP coatings promote 3-D osteogenesis in poly(epsilon-caprolactone) scaffolds of distinct pore size

P15-CSP is a biomimetic cationic fusion peptide that stimulates osteogenesis and inhibits bacterial biofilm formation when coated on 2-D surfaces. This study tested the hypothesis that P15-CSP coatings enhance 3-D osteogenesis in a porous but otherwise hydrophobic poly-(ɛ-caprolactone) (PCL) scaffold. Scaffolds of 84 µm and 141 µm average pore size were coated or not with Layer-by-Layer polyelectrolytes followed by P15-CSP, seeded with adult primary human mesenchymal stem cells (MSCs), and cultured 10 days in proliferation medium, then 21 days in osteogenic medium. Atomic analyses showed that P15-CSP was successfully captured by LbL. After 2 days of culture, MSCs adhered and spread more on P15-CSP coated pores than PCL-only. At day 10, all constructs contained nonmineralized tissue. At day 31, all constructs became enveloped in a "skin" of tissue that, like 2-D cultures, underwent sporadic mineralization in areas of high cell density that extended into some 141 µm edge pores. By quantitative histomorphometry, 2.5-fold more tissue and biomineral accumulated in edge pores versus inner pores. P15-CSP specifically promoted tissue-scaffold integration, fourfold higher overall biomineralization, and more mineral deposits in the outer 84 µm and inner 141 µm pores than PCL-only (p < 0.05). 3-D Micro-CT revealed asymmetric mineral deposition consistent with histological calcium staining. This study provides proof-of-concept that P15-CSP coatings are osteoconductive in PCL pore surfaces with 3-D topography. Biomineralization deeper than 150 µm from the scaffold edge was optimally attained with the larger 141 µm peptide-coated pores. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2171-2181, 2017.

Carbon Nanofiber/Polycaprolactone/Mineralized Hydroxyapatite Nanofibrous Scaffolds for Potential Orthopedic Applications

Hydroxyapatite (Ca₁₀ (PO₄)₆(OH)₂, HAP), a multimineral substituted calcium phosphate is one of the most substantial bone mineral component that has been widely used as bone replacement materials because of its bioactive and biocompatible properties. However, the use of HAP as bone implants is restricted due to its brittle nature and poor mechanical properties. To overcome this defect and to generate suitable bone implant material, HAP is combined with biodegradable polymer (polycaprolactone, PCL). To enhance the mechanical property of the composite, carbon nanofibers (CNF) is incorporated to the composite, which has long been considered for hard and soft tissue implant due to its exceptional mechanical and structural properties. It is well-known that nanofibrous scaffold are the most-prominent material for the bone reconstruction. We have developed a new remarkable CNF/PCL/mineralized hydroxyapatite (M-HAP) nanofibrous scaffolds on titanium (Ti). The as-developed coatings were characterized by various techniques. The results indicate the formation and homogeneous distribution of components in the nanofibrous scaffolds. Incorporation of CNF into the PCL/M-HAP composite significantly improves the adhesion strength and elastic modulus of the scaffolds. Furthermore, the responses of human osteosarcoma (HOS MG63) cells cultured onto the scaffolds demonstrate that the viability of cells were considerably high for CNF-incorporated PCL/M-HAP than for PCL/M-HAP. In vivo analysis show the presence of soft fibrous tissue growth without any significant inflammatory signs, which suggests that incorporated CNF did not counteract the favorable biological roles of HAP. For load-bearing applications, research in various bone models is needed to substantiate the clinical availability. Thus, from the obtained results, we suggest that CNF/PCL/M-HAP nanofibrous scaffolds can be considered as potential candidates for orthopedic applications.

Differentiation behavior of iPS cells cultured on PLGA with osteoinduction medium

In the present report, we have generated osteoblast-like cells derived from mouse induced-pluripotent stem (iPS) cells on PLGA with osteoinduction medium in vitro and in vivo. The cell culture period was 2 weeks. At 2 weeks, mRNA level of type I collagen was significantly higher than at 1 week. Osteocalcin mRNA level at 2 weeks was tendency to increase compared with at 1 week. And the cells cultured on PLGA were positive for immunofluorescent staining of osteocalcin and alizarin red S staining. The scaffold and osteogenic-like cells induced in vitro were implanted subcutaneously into SCID mice. In resected teratoma, hard tissues resembling bone were observed mixed with other tissues on the scaffold. The sum of these findings suggests that PLGA does not disturb the osteogenesis of iPS cells.

Migration and Proliferative Activity of Mesenchymal Stem Cells in 3D Polylactide Scaffolds Depends on Cell Seeding Technique and Collagen Modification

We analyzed viability of mesenchymal stem cells seeded by static and dynamic methods to highly porous fibrous 3D poly-L-lactide scaffolds with similar physical and chemical properties, but different spatial organization modified with collagen. Standard collagen coating promoted protein adsorption on the scaffold surface and improved adhesive properties of 100 μ-thick scaffolds. Modification of 600-μ scaffolds with collagen under pressure increased proliferative activity of mesenchymal stem cells seeded under static and dynamic (delivery of 100,000 cells in 10 ml medium in a perfusion system at a rate of 1 ml/min) conditions by 47 and 648%, respectively (measured after 120-h culturing by MTT test). Dynamic conditions provide more uniform distribution of collagen on scaffold fibers and promote cell penetration into 3D poly-L-lactide scaffolds with thickness >600 μ.

Demineralized Bone Matrix Scaffolds Modified by CBD-SDF-1α Promote Bone Regeneration via Recruiting Endogenous Stem Cells

The reconstruction of bone usually depends on substitute transplantation, which has drawbacks including the limited bone substitutes available, comorbidity, immune rejection, and limited endogenous bone regeneration. Here, we constructed a functionalized bone substitute by combining application of the demineralized bone matrix (DBM) and collagen-binding stromal-cell-derived factor-1α (CBD-SDF-1α). DBM was a poriferous and biodegradable bone substitute, derived from bovine bone and consisting mainly of collagen. CBD-SDF-1α could bind to collagen and be controllably released from the DBM to mobilize stem cells. In a rat femur defect model, CBD-SDF-1α-modified DBM scaffolds could efficiently mobilize CD34⁺ and c-kit⁺ endogenous stem cells homing to the injured site at 3 days after implantation. According to the data from micro-CT, CBD-SDF-1α-modified DBM scaffolds could help the bone defects rejoin with mineralization accumulated and bone volume expanded. Interestingly, osteoprotegerin (OPG) and osteopontin (OPN) were highly expressed in CBD-SDF-1α group at an early time after implantation, while osteocalcin (OCN) was more expanded. H&E and Masson's trichrome staining showed that the CBD-SDF-1α-modified DBM scaffold group had more osteoblasts and that the bone defect rejoined earlier. The ultimate strength of the regenerated bone was investigated by three-point bending, showing that the CBD-SDF-1α group had superior strength. In conclusion, CBD-SDF-1α-modified DBM scaffolds could promote bone regeneration by recruiting endogenous stem cells.

The efficacy and safety of Collagen-I and hypoxic conditions in urine-derived stem cell ex vivo culture

Upper urinary tract-derived urine stem cells (USCs) are considered a valuable mesenchymal stem cell source for autologous cell therapy. However, the reported culture condition for USCs is not appropriate for large-quantity production, because cells can show limited replicativity, senescence, and undesirable differentiation during cultivation. These drawbacks led us to reconstitute a culture condition that mimics the natural stem cell niche. We selected extracellular matrix protein and oxygen tension to optimize the ex vivo expansion of USCs, and compared cell adhesion, proliferation, gene expression, chromosomal stability, differentiation capacity, immunity and safety. Culture on collagen type I (ColI) supported highly enhanced USC proliferation and retention of stem cell properties. In the oxygen tension analysis (with ColI), 5% O₂ hypoxia showed a higher cell proliferation rate, a greater proportion of cells in the S phase of the cell cycle, and normal stem cell properties compared to those observed in cells cultured under 20% O₂ normoxia. The established reconstituted condition (ColI/hypoxia, USCs^recon) was compared to the control condition. The expanded USCs^recon showed highly increased cell proliferation and colony forming ability, maintained transcription factors, chromosomal stability, and multi-lineage differentiation capacity (neuron, osteoblast, and adipocyte) compared to the control. In addition, USCs^recon retained their immune-privileged potential and non-tumorigenicity with in vivo testing at week 8. Therefore, reconstituted condition allows for expanded uUSC cell preparations that are safe and useful for application in stem cell therapy.

Controlled release of recombinant human cementum protein 1 from electrospun multiphasic scaffold for cementum regeneration

Periodontitis is a major cause for tooth loss, which affects about 15% of the adult population. Cementum regeneration has been the crux of constructing the periodontal complex. Cementum protein 1 (CEMP1) is a cementum-specific protein that can induce cementogenic differentiation. In this study, poly(ethylene glycol) (PEG)-stabilized amorphous calcium phosphate (ACP) nanoparticles were prepared by wet-chemical method and then loaded with recombinant human CEMP1 (rhCEMP1) for controlled release. An electrospun multiphasic scaffold constituted of poly(ε-caprolactone) (PCL), type I collagen (COL), and rhCEMP1/ACP was fabricated. The effects of rhCEMP1/ACP/PCL/COL scaffold on the attachment proliferation, osteogenic, and cementogenic differentiations of human periodontal ligament cells, (PDLCs) were systematically investigated. A critical size defect rat model was introduced to evaluate the effect of tissue regeneration of the scaffolds in vivo. The results showed that PEG-stabilized ACP nanoparticles formed a core-shell structure with sustained release of rhCEMP1 for up to 4 weeks. rhCEMP1/ACP/PCL/COL scaffold could suppress PDLCs proliferation behavior and upregulate the expression of cementoblastic markers including CEMP1 and cementum attachment protein while downregulating osteoblastic markers including osteocalcin and osteopontin when it was cocultured with PDLCs in vitro for 7 days. Histology analysis of cementum after being implanted with the scaffold in rats for 8 weeks showed that there was cementum-like tissue formation but little bone formation. These results indicated the potential of using electrospun multiphasic scaffolds for controlled release of rhCEMP1 for promoting cementum regeneration in reconstruction of the periodontal complex.

Bone engineering in dog mandible: Coculturing mesenchymal stem cells with endothelial progenitor cells in a composite scaffold containing vascular endothelial growth factor

We sought to assess the effects of coculturing mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) in the repair of dog mandible bone defects. The cells were delivered in β-tricalcium phosphate scaffolds coated with poly lactic co-glycolic acid microspheres that gradually release vascular endothelial growth factor (VEGF). The complete scaffold and five partial scaffolds were implanted in bilateral mandibular body defects in eight beagles. The scaffolds were examined histologically and morphometrically 8 weeks after implantation. Histologic staining of the decalcified scaffolds demonstrated that bone formation was greatest in the VEGF/MSC scaffold (63.42 ± 1.67), followed by the VEGF/MSC/EPC (47.8 ± 1.87) and MSC/EPC (45.21 ± 1.6) scaffolds, the MSC scaffold (34.59 ± 1.49), the VEGF scaffold (20.03 ± 1.29), and the untreated scaffold (7.24 ± 0.08). Hence, the rate of new bone regeneration was highest in scaffolds containing MSC, either mixed with EPC or incorporating VEGF. Adding both EPC and VEGF with the MSC was not necessary. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1767-1777, 2017.

Frequent mechanical stress suppresses proliferation of mesenchymal stem cells from human bone marrow without loss of multipotency

Mounting evidence indicated that human mesenchymal stem cells (hMSCs) are responsive not only to biochemical but also to physical cues, such as substrate topography and stiffness. To simulate the dynamic structures of extracellular environments of the marrow in vivo, we designed a novel surrogate substrate for marrow derived hMSCs based on physically cross-linked hydrogels whose elasticity can be adopted dynamically by chemical stimuli. Under frequent mechanical stress, hMSCs grown on our hydrogel substrates maintain the expression of STRO-1 over 20 d, irrespective of the substrate elasticity. On exposure to the corresponding induction media, these cultured hMSCs can undergo adipogenesis and osteogenesis without requiring cell transfer onto other substrates. Moreover, we demonstrated that our surrogate substrate suppresses the proliferation of hMSCs by up to 90% without any loss of multiple lineage potential by changing the substrate elasticity every 2nd days. Such “dynamic in vitro niche” can be used not only for a better understanding of the role of dynamic mechanical stresses on the fate of hMSCs but also for the synchronized differentiation of adult stem cells to a specific lineage.

Gradients in pore size enhance the osteogenic differentiation of human mesenchymal stromal cells in three-dimensional scaffolds

Small fractures in bone tissue can heal by themselves, but in case of larger defects current therapies are not completely successful due to several drawbacks. A possible strategy relies on the combination of additive manufactured polymeric scaffolds and human mesenchymal stromal cells (hMSCs). The architecture of bone tissue is characterized by a structural gradient. Long bones display a structural gradient in the radial direction, while flat bones in the axial direction. Such gradient presents a variation in bone density from the cancellous bone to the cortical bone. Therefore, scaffolds presenting a gradient in porosity could be ideal candidates to improve bone tissue regeneration. In this study, we present a construct with a discrete gradient in pore size and characterize its ability to further support the osteogenic differentiation of hMSCs. Furthermore, we studied the behaviour of hMSCs within the different compartments of the gradient scaffolds, showing a correlation between osteogenic differentiation and ECM mineralization, and pore dimensions. Alkaline phosphatase activity and calcium content increased with increasing pore dimensions. Our results indicate that designing structural porosity gradients may be an appealing strategy to support gradual osteogenic differentiation of adult stem cells.

Combined Chemical Groups and Topographical Nanopattern on the Poly(ε-Caprolactone) Surface for Regulating Human Foreskin Fibroblasts Behavior

Surface chemistry and substrate topography could contribute significantly to providing a biochemical and topographical cues for governing the fate of cells on the cell-material interface. However, the synergies between these two properties have not been exploited extensively for biomaterial design. Herein, we achieved spatial-controlled patterning of chemical groups on the poly(ε-caprolactone) (PCL) surface by elegant UV-nanoimprint lithography (UN-NIL). The introduction of chemical groups on the PCL surface was developed by our newly 6-benzyloxycarbonylmethyl-ε-caprolactone (BCL) monomer, which not only solved the lack of functional groups along the PCL chain but also retained the original favorable properties of PCL materials. The synergetic effect of the chemical groups and nanopatterns on the human foreskin fibroblasts (HFFs) behaviors was evaluated in detail. The results revealed that the patterned functional PCL surfaces could induce enhanced cell adhesion and proliferation, further trigger changes in HFFs morphology, orientation and collagen secretion. Taken together, this study provided a method for straightforward fabrication of reactive PCL surfaces with topographic patterns by one-step process, and they would facilitate PCL as potential candidate for cell cultivation and tissue engineering.

MiR-221-inhibited adipose tissue-derived mesenchymal stem cells bioengineered in a nano-hydroxy apatite scaffold

The repair of skeletal defects is the main goal of bone tissue engineering. Recent literature highlighted various regulatory roles of microRNAs in stem cell fate determination. In addition, the role of porous hydroxyapatite/polycaprolacton (nHA/PCL) as a bioactive scaffold which enhances adipose tissue-derived mesenchymal stem cells (AT-MSCs) growth and osteogenic differentiation has been proved. The aim of the present study was to investigate the synergistic potential of both down-regulating miR-221 and nHA/PCL scaffold seeding in osteogenic potential of AT-MSCs. After isolation and characterization of AT-MSCs, the transfection of anti-miR-221 was performed into the cells using lipofectamine 2000 and the transfected cells were seeded into a synthesized nHA/PCL scaffold. The DAPI staining confirmed the presence of AT-MSCs on nHA/PCL scaffold. Quantitative expression of osteoblast marker genes, Runx2, and osteocalcin of the transfected cells in the scaffold were evaluated. Interestingly, significant upregulation of transcribed Runx2 and osteocalcin genes (P < 0.01) were observed in miR-221-inhibited nHA/PCL seeded cells. Also, alkaline phosphatase activity (ALP) was significantly higher (P < 0.01) in miR-221-inhibited AT-MSCs seeded on nHA/PCL than those seeded on nHA/PCL or transfected with anti-miR-221, individually. The results of this combination suggest a valuable method for enhancing osteogenesis in AT-MSCs. This method could be applicable for gene-cell therapy of bone defects.

Bone Tissue Engineering: Past-Present-Future

Bone is one of the few tissues to display a true potential for regeneration. Fracture healing is an obvious example where regeneration occurs through tightly regulated sequences of molecular and cellular events which recapitulate tissue formation seen during embryogenesis. Still in some instances, bone regeneration does not occur properly (i.e. critical size lesions) and an appropriate therapeutic intervention is necessary. Successful replacement of bone by tissue engineering will likely depend on the recapitulation of this flow of events. In fact, bone regeneration requires cross-talk between microenvironmental factors and cells; for example, resident mesenchymal progenitors are recruited and properly guided by soluble and insoluble signaling molecules. Tissue engineering attempts to reproduce and to mimic this natural milieu by delivering cells capable of differentiating into osteoblasts, inducing growth factors and biomaterials to support cellular attachment, proliferation, migration, and matrix deposition. In the last two decades, a significant effort has been made by the scientific community in the development of methods and protocols to repair and regenerate tissues such as bone, cartilage, tendons, and ligaments. In this same period, great advancements have been achieved in the biology of stem cells and on the mechanisms governing "stemness". Unfortunately, after two decades, effective clinical translation does not exist, besides a few limited examples. Many years have passed since cell-based regenerative therapies were first described as "promising approaches", but this definition still engulfs the present literature. Failure to envisage translational cell therapy applications in routine medical practice evidences the existence of unresolved scientific and technical struggles, some of which still puzzle researchers in the field and are presented in this chapter.

Injectable dual-gelling cell-laden composite hydrogels for bone tissue engineering

The present work investigated the osteogenic potential of injectable, dual thermally and chemically gelable composite hydrogels for mesenchymal stem cell (MSC) delivery in vitro and in vivo. Composite hydrogels comprising copolymer macromers of N-isopropylacrylamide were fabricated through the incorporation of gelatin microparticles (GMPs) as enzymatically digestible porogens and sites for cellular attachment. High and low polymer content hydrogels with and without GMP loading were shown to successfully encapsulate viable MSCs and maintain their survival over 28 days in vitro. GMP incorporation was also shown to modulate alkaline phosphatase production, but enhanced hydrogel mineralization along with higher polymer content even in the absence of cells. Moreover, the regenerative capacity of 2 mm thick hydrogels with GMPs only, MSCs only, or GMPs and MSCs was evaluated in vivo in an 8 mm rat critical size cranial defect for 4 and 12 weeks. GMP incorporation led to enhanced bony bridging and mineralization within the defect at each timepoint, and direct bone-implant contact as determined by microcomputed tomography and histological scoring, respectively. Encapsulation of both GMPs and MSCs enabled hydrogel degradation leading to significant tissue infiltration and osteoid formation. The results suggest that these injectable, dual-gelling cell-laden composite hydrogels can facilitate bone ingrowth and integration, warranting further investigation for bone tissue engineering.