In vitro generation of osteochondral differentiation of human marrow mesenchymal stem cells in novel collagen-hydroxyapatite layered scaffolds

Osteogenic potential of adipose stem cells on hydroxyapatite-functionalized decellularized amniotic membrane

Amniotic membrane (AM) is an attractive source for bone tissue engineering because of its low immunogenicity, contains biomolecules and proteins, and osteogenic differentiation properties. Hydroxyapatite is widely used as bone scaffolds due to its biocompatibility and bioactivity properties. The aim of this study is to design and fabricate scaffold based on hydroxyapatite-coated decellularized amniotic membrane (DAM-HA) for bone tissue engineering purpose. So human amniotic membranes were collected from healthy donors and decellularized (DAM). Then a hydroxyapatite-coating was created by immersion in 10X SBF, under variable parameters of pH and incubation time. Hydroxyapatite-coating was characterized and the optimal sample was selected. Human adipose-derived mesenchymal stem cell behaviors were assessed on control, amniotic membrane, and coated amniotic membrane. The results of the SEM, MTT assay, and Live-Dead staining showed that DAM and DAM-HA support cell adhesion, viability and proliferation. Osteogenic differentiation was evaluated by assessment of alkaline phosphatase activity and expression of osteogenic markers. Maximum gene expression values compared to control occurred in 14 days for alkalin phosphatase, while the highest values for osteocalcin and osteopontin in 21 days. These gene expression values in DAM and DAM-HA for alkalin phosphatase is 6.41 and 8.47, for osteocalcin is 3.95 and 5.94 and for osteopontin is 5.59 and 9.9 respectively. The results of this study indicated DAM supports the survival and growth of stem cells. Also, addition of hydroxyapatite component to DAM promotes osteogenic differentiation while maintaining viability. Therefore, hydroxyapatite-coated decellularized amniotic membrane can be a promising choice for bone tissue engineering applications.

Enhancing chondrogenic differentiation of mesenchymal stem cells through synergistic effects of cellulose nanocrystals and plastic compression in collagen-based hydrogel for cartilage formation

Collagen-based (COL) hydrogels could be a promising treatment option for injuries to the articular cartilage (AC) becuase of their similarity to AC native extra extracellular matrix. However, the high hydration of COL hydrogels poses challenges for AC's mechanical properties. To address this, we developed a hydrogel platform that incorporating cellulose nanocrystals (CNCs) within COL and followed by plastic compression (PC) procedure to expel the excessive fluid out. This approach significantly improved the mechanical properties of the hydrogels and enhanced the chondrogenic differentiation of mesenchymal stem cells (MSCs). Radially confined PC resulted in higher collagen fibrillar densities together with reducing fibril-fibril distances. Compressed hydrogels containing CNCs exhibited the highest compressive modulus and toughness. MSCs encapsulated in these hydrogels were initially affected by PC, but their viability improved after 7 days. Furthermore, the morphology of the cells and their secretion of glycosaminoglycans (GAGs) were positively influenced by the compressed COL-CNC hydrogel. Our findings shed light on the combined effects of PC and CNCs in improving the physical and mechanical properties of COL and their role in promoting chondrogenesis.

Articular cartilage and osteochondral tissue engineering techniques: Recent advances and challenges

In spite of the considerable achievements in the field of regenerative medicine in the past several decades, osteochondral defect regeneration remains a challenging issue among diseases in the musculoskeletal system because of the spatial complexity of osteochondral units in composition, structure and functions. In order to repair the hierarchical tissue involving different layers of articular cartilage, cartilage-bone interface and subchondral bone, traditional clinical treatments including palliative and reparative methods have showed certain improvement in pain relief and defect filling. It is the development of tissue engineering that has provided more promising results in regenerating neo-tissues with comparable compositional, structural and functional characteristics to the native osteochondral tissues. Here in this review, some basic knowledge of the osteochondral units including the anatomical structure and composition, the defect classification and clinical treatments will be first introduced. Then we will highlight the recent progress in osteochondral tissue engineering from perspectives of scaffold design, cell encapsulation and signaling factor incorporation including bioreactor application. Clinical products for osteochondral defect repair will be analyzed and summarized later. Moreover, we will discuss the current obstacles and future directions to regenerate the damaged osteochondral tissues.

Tissue-Engineered Hydroxyapatite Bone Scaffold Impregnated with Osteoprogenitor Cells Promotes Bone Regeneration in Sheep Model

BACKGROUND

Managing massive bone defects, a great challenge to orthopaedics reconstructive surgery. The problem arise is the supply of suitable bone is limited with many complications. Tissue-engineered hydroxyapatite bone (TEHB) scaffold impregnated with osteoprogenitor cells developed as an alternative to promote bone regeneration.

METHODS

This animal protocol has been approved by Universiti Kebangsaan Malaysia Animal Ethical Committee. The TEHB scaffold prepared from hydroxyapatite using gel casting method. A total of six adolescent female sheep were chosen for this study. Later, all the sheep were euthanized in a proper manner and the bone harvested for biomechanical study. Bone marrow was collected from iliac crest of the sheep and bone marrow stem cells (BMSCs) isolated and cultured. BMSCs then cultured in osteogenic medium for osteoprogenitor cells development and the plasma collected was seeded with osteoprogenitor cells mixed with calcium chloride. Bone defect of 3 cm length of tibia bone created from each sheep leg and implanted with autologous and TEHB scaffold in 2 different groups of sheep. Wound site was monitored weekly until the wound completely healed and conventional X-ray performed at week 1 and 24. Shear test was conducted to determine the shear force on the autologous bone and TEHB scaffold after implantation for 24 weeks.

RESULTS

All of the sheep survived without any complications during the study period and radiograph showed new bone formation. Later, the bone harvested was for biomechanical study. The highest shear force for the autologous group was 13 MPa and the lowest was 5 MPa while for the scaffold group, the highest was 10 MPa and the lowest was 3 MPa. Although, proximal and distal interface of autologous bone graft shows higher shear strength compared to the TEHB scaffold but there is no significant difference in both groups, p value > 0.05. Histologically in both proximal and distal interface in both arms shows bone healing and woven bone formation.

CONCLUSION

TEHB scaffold impregnated with osteoprogenitor cells has the potential to be developed as a bone substitute in view of its strength and capability to promote bone regeneration.

Gradient scaffolds for osteochondral tissue engineering and regeneration

The tissue engineering approach for repairing osteochondral (OC) defects involves the fabrication of a biological tissue scaffold that mimics the physiological properties of natural OC tissue (e.g., the gradient transition between the cartilage surface and the subchondral bone). The OC tissue scaffolds described in many research studies exhibit a discrete gradient (e.g., a biphasic or tri/multiphasic structure) or a continuous gradient to mimic OC tissue attributes such as biochemical composition, structure, and mechanical properties. One advantage of a continuous gradient scaffold over biphasic or tri/multiphasic tissue scaffolds is that it more closely mimics natural OC tissue since there is no distinct interface between each layer. Although research studies to this point have yielded good results related to OC regeneration with tissue scaffolds, differences between engineered scaffolds and natural OC tissue remain; due to these differences, current clinical therapies to repair OC defects with engineered scaffolds have not been successful. This paper provides an overview of both discrete and continuous gradient OC tissue scaffolds in terms of cell type, scaffold material, microscale structure, mechanical properties, fabrication methods, and scaffold stimuli. Fabrication of gradient scaffolds with three-dimensional (3D) printing is given special emphasis due to its ability to accurately control scaffold pore geometry. Moreover, the application of computational modeling in OC tissue engineering is considered; for example, efforts to optimize the scaffold structure, mechanical properties, and physical stimuli generated within the scaffold-bioreactor system to predict tissue regeneration are considered. Finally, challenges associated with the repair of OC defects and recommendations for future directions in OC tissue regeneration are proposed.

3D printed gelatin/hydroxyapatite scaffolds for stem cell chondrogenic differentiation and articular cartilage repair

The hUCB-MSC-laden 3D printed gelatin/HAP scaffold effectively repairs knee cartilage defects in a pig model.

Mesenchymal Stem Cells as a Promising Cell Source for Integration in Novel In Vitro Models

The human-relevance of an in vitro model is dependent on two main factors-(i) an appropriate human cell source and (ii) a modeling platform that recapitulates human in vivo conditions. Recent years have brought substantial advancements in both these aspects. In particular, mesenchymal stem cells (MSCs) have emerged as a promising cell source, as these cells can differentiate into multiple cell types, yet do not raise the ethical and practical concerns associated with other types of stem cells. In turn, advanced bioengineered in vitro models such as microfluidics, Organs-on-a-Chip, scaffolds, bioprinting and organoids are bringing researchers ever closer to mimicking complex in vivo environments, thereby overcoming some of the limitations of traditional 2D cell cultures. This review covers each of these advancements separately and discusses how the integration of MSCs into novel in vitro platforms may contribute enormously to clinical and fundamental research.

Polydopamine regulated hydroxyapatite microspheres grown in the three-dimensional honeycomb-like mollusk shell-derived organic template for osteogenesis

Layered osteochondral composite scaffolds are considered as a promising strategy for the treatment of osteochondral defects. However, the insufficient osseous support and integration of the subchondral bone layer frequently result in the failure of osteochondral repair. Therefore, it is essentially important to explore new subchondral bone constructs tailored to support bone integration and healing. In this study, a novel three-dimensional porous biomimetic construct (HA/pDA-OTMS) was successfully developed by polydopamine (pDA) regulating hydroxyapatite (HA) microspheres grown in the honeycomb-like mollusk shell-derived organic template (OTMS). The biomimetic OTMS had good mechanical properties, high toughness, biodegradability and excellent biocompatibility. Moreover, the long-range ordered cavity structure of OTMS allowed the smallest material to create the largest and most stable geometric space, endowing it high HA loading capacity. The modification of pDA on OTMS surface effectively promoted the mineral nucleation of HA in the micro-nano cavities of OTMS. The compression mechanical tests showed that the combination of inorganic HA and organic pDA-OTMS greatly improved the mechanical properties of the construct. Additionally, the HA/pDA-OTMS composite provided adequate 3-D support for osteoblast cell attachment, proliferation and differentiation, as well as significantly up-regulated the expression of osteogenesis-related genes. These results demonstrated that as-prepared HA/pDA-OTMS constructs with combined mechanical strength and excellent osteogenic activity show great application prospects in subchondral bone regeneration.

Biomimetic gradient scaffold of collagen–hydroxyapatite for osteochondral regeneration

Osteochondral defects remain a major clinical challenge mainly due to the combined damage to the articular cartilage and the underlying bone, and the interface between the two tissues having very different properties. Current treatment modalities have several limitations and drawbacks, with limited capacity of restoration; however, tissue engineering shows promise in improving the clinical outcomes of osteochondral defects. In this study, a novel gradient scaffold has been fabricated, implementing a gradient structure in the design to mimic the anatomical, biological and physicochemical properties of bone and cartilage as closely as possible. Compared with the commonly studied multi-layer scaffolds, the gradient scaffold has the potential to induce a smooth transition between cartilage and bone and avoid any instability at the interface, mimicking the natural structure of the osteochondral tissue. The scaffold comprises a collagen matrix with a gradient distribution of low-crystalline hydroxyapatite particles. Physicochemical analyses confirmed phase and chemical compositions of the gradient scaffold and the distribution of the mineral phase along the gradient scaffold. Mechanical tests confirmed the gradient of stiffness throughout the scaffold, according to its mineral content. The gradient scaffold exhibited good biological performances both in vitro and in vivo. Biological evaluation of the scaffold, in combination with human bone-marrow–derived mesenchymal stem cells, demonstrated that the gradient of composition and stiffness preferentially increased cell proliferation in different sub-regions of the scaffold, according to their high chondrogenic or osteogenic characteristics. The in vivo biocompatibility of the gradient scaffold was confirmed by its subcutaneous implantation in rats. The gradient scaffold was significantly colonised by host cells and minimal foreign body reaction was observed. The scaffold’s favourable chemical, physical and biological properties demonstrated that it has good potential as an engineered osteochondral analogue for the regeneration of damaged tissue.

Recent advances in biomaterials for 3D scaffolds: A review

Considering the advantages and disadvantages of biomaterials used for the production of 3D scaffolds for tissue engineering, new strategies for designing advanced functional biomimetic structures have been reviewed. We offer a comprehensive summary of recent trends in development of single- (metal, ceramics and polymers), composite-type and cell-laden scaffolds that in addition to mechanical support, promote simultaneous tissue growth, and deliver different molecules (growth factors, cytokines, bioactive ions, genes, drugs, antibiotics, etc.) or cells with therapeutic or facilitating regeneration effect. The paper briefly focuses on divers 3D bioprinting constructs and the challenges they face. Based on their application in hard and soft tissue engineering, in vitro and in vivo effects triggered by the structural and biological functionalized biomaterials are underlined. The authors discuss the future outlook for the development of bioactive scaffolds that could pave the way for their successful imposing in clinical therapy.

The influence of cyclic tensile strain on multi-compartment collagen-GAG scaffolds for tendon-bone junction repair

Background: Orthopedic injuries often occur at the interface between soft tissues and bone. The tendon-bone junction (TBJ) is a classic example of such an interface. Current clinical strategies for TBJ injuries prioritize mechanical reattachment over regeneration of the native interface, resulting in poor outcomes. The need to promote regenerative healing of spatially-graded tissues inspires our effort to develop new tissue engineering technologies that replicate features of the spatially-graded extracellular matrix and strain profiles across the native TBJ. Materials and Methods: We recently described a biphasic collagen-glycosaminoglycan (CG) scaffold containing distinct compartment with divergent mineral content and structural alignment (isotropic vs. anisotropic) linked by a continuous interface zone to mimic structural and compositional features of the native TBJ. Results: Here, we report application of cyclic tensile strain (CTS) to the scaffold via a bioreactor leads to non-uniform strain profiles across the spatially-graded scaffold. Further, combinations of CTS and matrix structural features promote rapid, spatially-distinct differentiation profiles of human bone marrow-derived mesenchymal stem cells (MSCs) down multiple osteotendinous lineages. CTS preferentially upregulates MSC activity and tenogenic differentiation in the anisotropic region of the scaffold. This work demonstrates a tissue engineering approach that couples instructive biomaterials with cyclic tensile stimuli to promote regenerative healing of orthopedic interfaces.

A biomimetic cartilage gradient hybrid scaffold for functional tissue engineering of cartilage

Osteochondral tissue has a complex layered structure that is not self-repairing after a cartilage defect. Therefore, constructing a biomimetic gradient scaffold that meets the specific structural requirements of osteochondral tissue is a major challenge in the field of cartilage tissue engineering. In this study, chitosan/Sodium β-glycerophosphate/Gelatin (Cs/GP/Gel) biomimetic gradient scaffolds were prepared by regulating the mass ratio of single layer raw materials. The same ratio of Cs/GP/Gel hybrid scaffold material was used as the control. Physical properties such as water absorption, porosity and the degradation rate of the material were compared to optimize the proportion of scaffold materials. P3 Bone Mesenchymal Stem Cells (BMSCs) were inoculated on the gradient and the control scaffolds to investigate its biocompatibility. Scanning electron microscopy (SEM) results show that 3:1:2, 6:1:3.5, 9:1:5, 12:1:6.5, 15:1:8 Cs/GP/Gel gradient scaffolds had excellent three-dimensional porous structures. Channels were also shown to have been interconnected, and the walls of the pores were folded. In the longitudinal dimension, gradient scaffolds had an obvious stratified structure and pore gradient gradualism, that effectively simulated the natural physiological stratified structure of real cartilage. The diameter of the pores in the control scaffold was uniform and without any pore gradient. Gradient scaffolds had good water absorption (584.24 ± 3.79˜677.47 ± 1.70%), porosity (86.34 ± 5.10˜95.20 ± 2.86%) and degradation (86.09 ± 2.46˜92.48 ± 3.86%). After considering the physical properties assessed, the Cs/GP/Gel gradient scaffold with a ratio of 9:1:5 was found to be the most suitable material to support osteochondral tissue. BMSCs were subsequently inoculated on the proportional gradient and hybrid scaffolds culture. These cells survived, distributed and extended well on the gradient and hybrid scaffold material. The biomimetic gradient scaffold designed and prepared in this study provides an important foundation for the development of new gradient composite biomedical materials for osteochondral repair.

3D Printed scaffolds with hierarchical biomimetic structure for osteochondral regeneration

Osteochondral defects resulting from trauma and/or pathologic disorders are critical clinical problems. The current approaches still do not yield satisfactory due to insufficient donor sources and potential immunological rejection of implanted tissues. 3D printing technology has shown great promise for fabricating customizable, biomimetic tissue matrices. The purpose of the present study is to investigate 3D printed scaffolds with biomimetic, biphasic structure for osteochondral regeneration. For this purpose, nano-hydroxyapatite and transforming growth factor beta 1 nanoparticles were synthesized and distributed separately into the lower and upper layers of the biphasic scaffold, which was fabricated using 3D stereolithography printer. Our results showed that this scaffold design successfully promoted osteogenic and chondrogenic differentiation of human bone marrow mesenchymal stem cells, as well as enhanced gene expression associated with both osteogenesis and chondrogenesis alike. The finding demonstrated that 3D printed osteochondral scaffolds with biomimetic, biphasic structure are excellent candidates for osteochondral repair and regeneration.

Bioactive scaffolds for osteochondral regeneration

Treatment for osteochondral defects remains a great challenge. Although several clinical strategies have been developed for management of osteochondral defects, the reconstruction of both cartilage and subchondral bone has proved to be difficult due to their different physiological structures and functions. Considering the restriction of cartilage to self-healing and the different biological properties in osteochondral tissue, new therapy strategies are essential to be developed. This review will focus on the latest developments of bioactive scaffolds, which facilitate the osteogenic and chondrogenic differentiation for the regeneration of bone and cartilage. Besides, the topic will also review the basic anatomy, strategies and challenges for osteochondral reconstruction, the selection of cells, biochemical factors and bioactive materials, as well as the design and preparation of bioactive scaffolds. Specifically, we summarize the most recent developments of single-type bioactive scaffolds for simultaneously regenerating cartilage and subchondral bone. Moreover, the future outlook of bioactive scaffolds in osteochondral tissue engineering will be discussed. This review offers a comprehensive summary of the most recent trend in osteochondral defect reconstruction, paving the way for the bioactive scaffolds in clinical therapy.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

This review summaries the latest developments of single-type bioactive scaffolds for regeneration of osteochondral defects. We also highlight a new possible translational direction for cartilage formation by harnessing bioactive ions and propose novel paradigms for subchondral bone regeneration in application of bioceramic scaffolds.

Immobilization of type I collagen/hyaluronic acid multilayer coating on enoxacin loaded titania nanotubes for improved osteogenesis and osseointegration in ovariectomized rats

Titania nanotubes (Ti-NTs) have been proven to be good drug carriers and can release drugs efficiently around implants. Enoxacin (EN) is a broad-spectrum antibiotic that has the ability of anti-osteoclastogenesis. Immobilization of extracellular matrix components on the surface of the material can greatly enhance the biological activity of the implant and slow down the release rate of the drug in Ti-NTs. In the present study, a material system that provided uniform drug release, promoted osteogenesis, and inhibited osteoclast was designed and developed. Scanning electron microscopy, X-ray photoelectron spectroscopy, and water contact angle measurements were used for material surface characterization. Enoxacin release was detected by high performance liquid chromatography. Alkaline phosphatase and Alizarin Red staining were used to evaluate the osteogenic differentiation of rat bone marrow mesenchymal stem cells. Tartrate-resistant acid phosphatase staining and bone absorption assay were applied to osteoclastogenesis experiments. A drug delivery system based on Ti-NTs and type I collagen /hyaluronic acid multilayer coating (Ti-NT+EN+Col/HyA) with predominant biocompatibility, osteogenic property, and anti-osteoclastogenesis ability was successfully constructed. These excellent biological properties were further validated in an ovariectomized rat model. The results of the study indicate that Ti-NT+EN+Col/HyA is a potential material for future orthopedic implants.

Improved osteogenic differentiation of human dental pulp stem cells in a layer-by-layer-modified gelatin scaffold

Dental pulp stem cell is a new type of mesenchymal stem cell that has a potential for tissue regeneration. Gelatin sponges are often used for hemostasis in dental surgery. In this study, we aimed to evaluate the dental pulp stem cells' proliferation and osteogenic differentiation in different layer-by-layer-modified gelatin sponge scaffolds including the G, G + P (gelatin sponge+ poly-l-lysine modification), G + M (gelatin sponge + mineralization modification), and G + M + P (gelatin sponge + mineralization modification + poly-l-lysine modification) groups in vitro and assessed them in vivo. The results showed that dental pulp stem cells had a great potential for osteogenic differentiation. In vitro, the G + M + P group not only enhanced the adhesion and proliferation of dental pulp stem cells but also facilitated their osteogenic differentiation. However, alkaline phosphatase activity was prohibited after modification. In vivo, both dental pulp stem cells and cells from nude mice grew well on the scaffold, and G + M and G + M + P groups could promote the mineralization deposit formation and the expression of osteocalcin in osteogenic differentiation of dental pulp stem cells. In conclusion, the combination of dental pulp stem cells and G + M + P scaffold has a great potential for bone tissue engineering.

Incorporating β-cyclodextrin into collagen scaffolds to sequester growth factors and modulate mesenchymal stem cell activity

The development of biomaterials for a range of tissue engineering applications increasingly requires control over the bioavailability of biomolecular cues such as growth factors in order to promote desired cell responses. While efforts have predominantly concentrated on covalently-bound or freely-diffusible incorporation of biomolecules in porous, three-dimensional biomaterials, opportunities exist to exploit transient interactions to concentrate growth factor activity over desired time frames. Here, we report the incorporation of β-cyclodextrin into a model collagen-GAG scaffold as a means to exploit the passive sequestration and release of growth factors via guest-host interactions to control mesenchymal stem cell differentiation. Collagen-GAG scaffolds that incorporate β-cyclodextrin show improved sequestration as well as extended retention and release of TGF-β1. We further show extended retention and release of TGF-β1 and BMP-2 from β-cyclodextrin modified scaffolds was sufficient to influence the metabolic activity and proliferation of mesenchymal stem cells as well as differential activation of Smad 2/3 and Smad 1/5/8 pathways associated with differential osteo-chondral differentiation. Further, gene expression analysis showed TGF-β1 release from β-cyclodextrin CG scaffolds promoted early chondrogenic-specific differentiation. Ultimately, this work establishes a novel method for the incorporation and display of growth factors within CG scaffolds via supramolecular interactions. Such a design framework offers opportunities to selectively alter the bioavailability of multiple biomolecules within a three-dimensional collagen-GAG scaffold to enhance cell activity for a range of musculoskeletal regenerative medicine applications.

STATEMENT OF SIGNIFICANCE

We describe the incorporation of β-cyclodextrin into a model CG-scaffold under development for musculoskeletal tissue engineering applications. We show β-cyclodextrin modified scaffolds promote the sequestration of soluble TGF-β1 and BMP-2 via guest-host interactions, leading to extended retention and release. Further, β-cyclodextrin modified CG scaffolds promote TGF-β1 or BMP-2 specific Smad signaling pathway activation associated with divergent osseous versus chondrogenic differentiation pathways in mesenchymal stem cells.

Mesenchymal Stem Cells and Calcium Phosphate Bioceramics: Implications in Periodontal Bone Regeneration

In orthopedic medicine, a feasible reconstruction of bone structures remains one of the main challenges both for healthcare and for improvement of patients' quality of life. There is a growing interest in mesenchymal stem cells (MSCs) medical application, due to their multilineage differentiation potential, and tissue engineering integration to improve bone repair and regeneration. In this review we will describe the main characteristics of MSCs, such as osteogenesis, immunomodulation and antibacterial properties, key parameters to consider during bone repair strategies. Moreover, we describe the properties of calcium phosphate (CaP) bioceramics, which demonstrate to be useful tools in combination with MSCs, due to their biocompatibility, osseointegration and osteoconduction for bone repair and regeneration. Also, we overview the main characteristics of dental cavity MSCs, which are promising candidates, in combination with CaP bioceramics, for bone regeneration and tissue engineering. The understanding of MSCs biology and their interaction with CaP bioceramics and other biomaterials is critical for orthopedic surgical bone replacement, reconstruction and regeneration, which is an integrative and dynamic medical, scientific and bioengineering field of research and biotechnology.

Concise Review: Biomimetic Functionalization of Biomaterials to Stimulate the Endogenous Healing Process of Cartilage and Bone Tissue

Musculoskeletal reconstruction is an ongoing challenge for surgeons as it is required for one out of five patients undergoing surgery. In the past three decades, through the close collaboration between clinicians and basic scientists, several regenerative strategies have been proposed. These have emerged from interdisciplinary approaches that bridge tissue engineering with material science, physiology, and cell biology. The paradigm behind tissue engineering is to achieve regeneration and functional recovery using stem cells, bioactive molecules, or supporting materials. Although plenty of preclinical solutions for bone and cartilage have been presented, only a few platforms have been able to move from the bench to the bedside. In this review, we highlight the limitations of musculoskeletal regeneration and summarize the most relevant acellular tissue engineering approaches. We focus on the strategies that could be most effectively translate in clinical practice and reflect on contemporary and cutting‐edge regenerative strategies in surgery. Stem Cells Translational Medicine2017;6:2186–2196

The Combined Influence of Hydrogel Stiffness and Matrix-Bound Hyaluronic Acid Content on Glioblastoma Invasion

Glioblastoma (GBM) is the most common and lethal form of brain cancer. Its high mortality is associated with its aggressive invasion throughout the brain. The heterogeneity of stiffness and hyaluronic acid (HA) content within the brain makes it difficult to study invasion in vivo. A dextran-bead assay is employed to quantify GBM invasion within HA-functionalized gelatin hydrogels. Using a library of stiffness-matched hydrogels with variable levels of matrix-bound HA, it is reported that U251 GBM invasion is enhanced in softer hydrogels but reduced in the presence of matrix-bound HA. Inhibiting HA-CD44 interactions reduces invasion, even in hydrogels lacking matrix-bound HA. Analysis of HA biosynthesis suggests that GBM cells compensate for a lack of matrix-bound HA by producing soluble HA to stimulate invasion. Together, a robust method is showed to quantify GBM invasion over long culture times to reveal the coordinated effect of matrix stiffness, immobilized HA, and compensatory HA production on GBM invasion.

Comparison of the osteogenic capability of rat bone mesenchymal stem cells on collagen, collagen/hydroxyapatite, hydroxyapatite and biphasic calcium phosphate

Collagen (COL), collagen/hydroxyapatite (COL/HA), HA and biphasic calcium phosphate were prepared as representative bone grafting materials with composition analogous to bone, and their structural characteristics were analyzed. The rat bone mesenchymal stem cells (BMSCs) were further seeded onto four groups of materials, and BMSCs grown in basic medium and standard osteogenic medium were set as controls of a reference model to show the basic and osteogenic behavior of cells without the intervention of materials. Cellular behaviors were characterized, including proliferation, spreading morphology and expression of osteogenesis factors. The rat BMSCs proliferated properly with time on four groups of materials as well on two groups of controls, and typical cuboidal, polygonal and extremely-elongated morphologies of cells were observed. According to the real-time polymerase chain reaction data, a higher osteogenic gene expression level was dependent upon the growing morphology but not the proliferation rate of cells, and the osteogenic differentiation capacity of cells onto four groups of materials varied in specific genes. In general, BMSCs exhibited the highest osteogenic capacity onto COL/HA, but the poorest onto HA. The growing behaviors of cells on materials were further discussed in comparison with the cases of OC and BC of the reference model. The present attempt to comparatively analyze cell experimental data with a reference model is expected to be useful for revealing the difference in the osteogenic capability of MSCs onto materials or even the bioactivity of materials.

Directing the osteoblastic and chondrocytic differentiations of mesenchymal stem cells: matrix vs. induction media

While both induction culture media and matrix have been reported to regulate the stem cell fate, little is known about which factor plays a more decisive role in directing the MSC differentiation lineage as well as the underlying mechanisms. To this aim, we seeded MSCs on HA-collagen and HA-synthetic hydrogel matrixes, which had demonstrated highly different potentials toward osteoblastic and chondrocytic differentiation lineages, respectively, and cultured them with osteogenic, chondrogenic and normal culture media, respectively. A systematic comparison has been carried out on the effects of induction media and matrix on MSC adhesion, cytoskeleton organization, proliferation, and in particular differentiation into the osteoblastic and chondrocytic lineages. The results demonstrated that the matrix selection had a much more profound effect on directing the differentiation lineage than the induction media did. The strong modulation effect on the transcription activities might be the critical factor contributing to the above observations in our study, where canonical Wnt-β-Catenin signal pathway was directly involved in the matrix-driven osteoblastic differentiation. Such findings not only provide a critical insight on natural cellular events leading to the osteoblastic and chondrocytic differentiations, but also have important implications in biomaterial design for tissue engineering applications.

In vitro proliferation and osteogenic differentiation of human dental pulp stem cells in injectable thermo-sensitive chitosan/β-glycerophosphate/hydroxyapatite hydrogel

Injectable thermo-sensitive hydrogels have a potential application in bone tissue engineering for their sensitivities and minimal invasive properties. Human dental pulp stem cells have been considered a promising tool for tissue reconstruction. The objective of this study was to investigate the proliferation and osteogenic differentiation of dental pulp stem cells in injectable thermo-sensitive chitosan/β-glycerophosphate/hydroxyapatite hydrogel in vitro. The chitosan /β-glycerophosphate hydrogel and chitosan/β-glycerophosphate/hydroxyapatite hydrogel were prepared using the sol-gel method. The injectability of chitosan /β-glycerophosphate hydrogel and chitosan/β-glycerophosphate/hydroxyapatite hydrogel was measured using a commercial disposable syringe. Scanning electron microscopy was used to observe the inner structure of hydrogels. Then dental pulp stem cells were seeded in chitosan /β-glycerophosphate hydrogel and chitosan/β-glycerophosphate/hydroxyapatite hydrogel, respectively. The growth of dental pulp stem cells was periodically observed under an inverted microscope. The proliferation of dental pulp stem cells was detected by using an Alamar Blue kit, while cell apoptosis was determined by using a Live/Dead Viability/Cytotoxicity kit. The osteogenic differentiations of dental pulp stem cells in chitosan /β-glycerophosphate hydrogel and chitosan/β-glycerophosphate/hydroxyapatite hydrogel were evaluated by alkaline phosphatase activity assay and mRNA expression of osteogenesis gene for 21 days in osteogenic medium. The results indicated that there was no significant difference between chitosan /β-glycerophosphate hydrogel and chitosan/β-glycerophosphate/hydroxyapatite hydrogel in injectability. Cells within the chitosan/β-glycerophosphate/hydroxyapatite hydrogel displayed a typical adherent cell morphology and rapid proliferation with high cellular viability after 14 days of culture. Dental pulp stem cells seeded in chitosan/β-glycerophosphate/hydroxyapatite hydrogels had a higher alkaline phosphatase activity and better up-regulation of gene expression levels of Runx-2, Collagen I, alkaline phosphatase and osteocalcin than in chitosan /β-glycerophosphate hydrogels after osteogenic differentiation. These results demonstrated that the chitosan/β-glycerophosphate/hydroxyapatite hydrogel had excellent cellular compatibility and the superiority in promoting dental pulp stem cells osteogenic differentiation in vitro, showing that the combination of dental pulp stem cells and chitosan/β-glycerophosphate/hydroxyapatite hydrogel has the potential to be used for bone tissue engineering.

Current View on Osteogenic Differentiation Potential of Mesenchymal Stromal Cells Derived from Placental Tissues

Mesenchymal stromal cells (MSC) isolated from human term placental tissues possess unique characteristics, including their peculiar immunomodulatory properties and their multilineage differentiation potential. The osteogenic differentiation capacity of placental MSC has been widely disputed, and continues to be an issue of debate. This review will briefly discuss the different MSC populations which can be obtained from different regions of human term placenta, along with their unique properties, focusing specifically on their osteogenic differentiation potential. We will present the strategies used to enhance osteogenic differentiation potential in vitro, such as through the selection of subpopulations more prone to differentiate, the modification of the components of osteo-inductive medium, and even mechanical stimulation. Accordingly, the applications of three-dimensional environments in vitro and in vivo, such as non-synthetic, polymer-based, and ceramic scaffolds, will also be discussed, along with results obtained from pre-clinical studies of placental MSC for the regeneration of bone defects and treatment of bone-related diseases.

Scaffold-Free Fabrication of Osteoinductive Cellular Constructs Using Mouse Gingiva-Derived Induced Pluripotent Stem Cells

Three-dimensional (3D) cell constructs are expected to provide osteoinductive materials to develop cell-based therapies for bone regeneration. The proliferation and spontaneous aggregation capability of induced pluripotent stem cells (iPSCs) thus prompted us to fabricate a scaffold-free iPSC construct as a transplantation vehicle. Embryoid bodies of mouse gingival fibroblast-derived iPSCs (GF-iPSCs) were seeded in a cell chamber with a round-bottom well made of a thermoresponsive hydrogel. Collected ball-like cell constructs were cultured in osteogenic induction medium for 30 days with gentle shaking, resulting in significant upregulation of osteogenic marker genes. The constructs consisted of an inner region of unstructured cell mass and an outer osseous tissue region that was surrounded by osteoblast progenitor-like cells. The outer osseous tissue was robustly calcified with elemental calcium and phosphorous as well as hydroxyapatite. Subcutaneous transplantation of the GF-iPSC constructs into immunodeficient mice contributed to extensive ectopic bone formation surrounded by teratoma tissue. These results suggest that mouse GF-iPSCs could facilitate the fabrication of osteoinductive scaffold-free 3D cell constructs, in which the calcified regions and surrounding osteoblasts may function as scaffolds and drivers of osteoinduction, respectively. With incorporation of technologies to inhibit teratoma formation, this system could provide a promising strategy for bone regenerative therapies.

Exogenous Heparan Sulfate Enhances the TGF-β3-Induced Chondrogenesis in Human Mesenchymal Stem Cells by Activating TGF-β/Smad Signaling

Heparan sulfate (HS) interacts with growth factors and has been implicated in regulating chondrogenesis. However, the effect of HS on TGF-β-mediated mesenchymal stem cell (MSC) chondrogenesis and molecular mechanisms remains unknown. In this study, we explored the effects of exogenous HS alone and in combination with TGF-β3 on chondrogenic differentiation of human MSCs and possible signal mechanisms. The results indicated that HS alone had no obvious effects on chondrogenic differentiation of human MSCs and TGF-β/Smad2/3 signal pathways. However, the combined TGF-β3/HS treatment resulted in a significant increase in GAG synthesis, cartilage matrix protein secretion, and cartilage-specific gene expression compared to cells treated with TGF-β3 alone. Furthermore, HS inhibited type III TGF-β receptors (TβRIII) expression and increased TGF-β3-mediated ratio of the type II (TβRII) to the type I (TβRI) TGF-β receptors and phosphorylation levels of Smad2/3. The inhibitor of the TGF-β/Smad signal, SB431542, not only completely inhibited HS-stimulated TGF-β3-mediated Smad2/3 phosphorylation but also completely inhibited the effects of HS on TGF-β3-induced chondrogenic differentiation. These results demonstrate exogenous HS enhances TGF-β3-induced chondrogenic differentiation of human MSCs by activating TGF-β/Smad2/3 signaling.

Effective Spatial Separation of PC12 and NIH3T3 Cells by the Microgrooved Surface of Biocompatible Polymer Substrates

Most organs and tissues are composed of more than one type of cell that is spatially separated and located in different regions. This study used a microgrooved poly(lactic-co-glycolic acid) (PLGA) substrate to guide two types of cocultured cells to two spatially separated regions. Specifically, PC12 pheochromocytoma cells are guided to the inside of microgrooves, whereas NIH3T3 fibroblasts are guided to the ridge area in between neighboring parallel microgrooves. In addition, the microgrooved structures can significantly promote the proliferation and neural differentiation of PC12 cells as well as the osteogenic differentiation of NIH3T3 cells. Therefore, the microgrooved PLGA surface with separated PC12 and NIH3T3 cells can serve as a potential model system for studying nerve reconstruction in bone-repairing scaffolds.

Fabrication of Biomimetic Bone Tissue Using Mesenchymal Stem Cell-Derived Three-Dimensional Constructs Incorporating Endothelial Cells

The development of technologies to promote vascularization of engineered tissue would drive major developments in tissue engineering and regenerative medicine. Recently, we succeeded in fabricating three-dimensional (3D) cell constructs composed of mesenchymal stem cells (MSCs). However, the majority of cells within the constructs underwent necrosis due to a lack of nutrients and oxygen. We hypothesized that incorporation of vascular endothelial cells would improve the cell survival rate and aid in the fabrication of biomimetic bone tissues in vitro. The purpose of this study was to assess the impact of endothelial cells combined with the MSC constructs (MSC/HUVEC constructs) during short- and long-term culture. When human umbilical vein endothelial cells (HUVECs) were incorporated into the cell constructs, cell viability and growth factor production were increased after 7 days. Furthermore, HUVECs were observed to proliferate and self-organize into reticulate porous structures by interacting with the MSCs. After long-term culture, MSC/HUVEC constructs formed abundant mineralized matrices compared with those composed of MSCs alone. Transmission electron microscopy and qualitative analysis revealed that the mineralized matrices comprised porous cancellous bone-like tissues. These results demonstrate that highly biomimetic bone tissue can be fabricated in vitro by 3D MSC constructs incorporated with HUVECs.

Recent Advances in Hydroxyapatite Scaffolds Containing Mesenchymal Stem Cells

Modern day tissue engineering and cellular therapies have gravitated toward using stem cells with scaffolds as a dynamic modality to aid in differentiation and tissue regeneration. Mesenchymal stem cells (MSCs) are one of the most studied stem cells used in combination with scaffolds. These cells differentiate along the osteogenic lineage when seeded on hydroxyapatite containing scaffolds and can be used as a therapeutic option to regenerate various tissues. In recent years, the combination of hydroxyapatite and natural or synthetic polymers has been studied extensively. Due to the interest in these scaffolds, this review will cover the wide range of hydroxyapatite containing scaffolds used with MSCs for in vitro and in vivo experiments. Further, in order to maintain a progressive scope of the field this review article will only focus on literature utilizing adult human derived MSCs (hMSCs) published in the last three years.

Osteogenesis and chondrogenesis of biomimetic integrated porous PVA/gel/V-n-HA/pa6 scaffolds and BMSCs construct in repair of articular osteochondral defect

A novel bi-layered osteochondral scaffold, including of PVA/Gel/V layer for the cartilage and n-HA/PA6 layer for the subchondral bone, has been proposed to evaluate the potential of the engineered of osteochondral grafts in repairing articular osteochondral defects in rabbits. The two different layers of the scaffolds were seeded with allogenic bone marrow-derived stem cells (BMSCs), which were chondrogenically and osteogenically induced respectively. The critical-size osteochondral defects were created in the knees of adult rabbits. The defects were treated with cell-bi-layered constructs (Group A), bi-layered constructs (Group B) and untreated group C as control group. The adhesion, proliferation and differentiation of BMSCs were demonstrated by immunohistochemical staining and scanning electron microscopy (SEM) in vitro. Cell survival was tracked via fluorescent labeling in vivo. Overall, the porous PVA/Gel/V-n-HA/PA6 scaffold was compatible and had no negative effects on the BMSCs in vitro culture. The cell-bi-layered scaffolds showed superior repair results as compared to the control group using gross examination and histological assessment. With BMSCs implantation, the two different layers of the composite biomimetic scaffolds provided a suitable environment for cells to form respective tissue. Simultaneously, the RT-PCR results confirmed the expression of specific extracellular matrix (ECM) markers for cartilaginous or osteoid tissue. This investigation showed that the porous PVA/Gel/V-n-HA/PA6 scaffold is a potential matrix for treatment of osteochondral defects, and the method of using chondrogenically and osteogenically differentiated BMSCs as seed cells on each layer might be a promising strategy in repair of articular osteochondral defect due to enhanced chondrogenesis and osteogenesis.

A new injectable biphasic hydrogel based on partially hydrolyzed polyacrylamide and nanohydroxyapatite as scaffold for osteochondral regeneration

Fabrication of an injectable biphasic hydrogel based on partially hydrolyzed polyacrylamide (HPAM), nanocrystalline hydroxyapatite (nHAp), and chromium acetate (Cr(iii)) as a novel scaffold for osteochondral repair has been attempted.

Integrated trilayered silk fibroin scaffold for osteochondral differentiation of adipose-derived stem cells

Repairing osteochondral defects (OCD) remains a formidable challenge due to the high complexity of native osteochondral tissue and the limited self-repair capability of cartilage. Osteochondral tissue engineering is a promising strategy for the treatment of OCD. In this study, we fabricated a novel integrated trilayered scaffold using silk fibroin and hydroxyapatite by combining paraffin-sphere leaching with a modified temperature gradient-guided thermal-induced phase separation (TIPS) technique. This biomimetic scaffold is characterized by three layers: a chondral layer with a longitudinally oriented microtubular structure, a bony layer with a 3D porous structure and an intermediate layer with a dense structure. Live/dead and CCK-8 tests indicated that this scaffold possesses good biocompatibility for supporting the growth, proliferation, and infiltration of adipose-derived stem cells (ADSCs). Histological and immunohistochemical stainings and real-time polymerase chain reaction (RT-PCR) confirmed that the ADSCs could be induced to differentiate toward chondrocytes or osteoblasts in vitro at chondral and bony layers in the presence of chondrogenic- or osteogenic-induced culture medium, respectively. Moreover, the intermediate layer could play an isolating role for preventing the cells within the chondral and bony layers from mixing with each other. In conclusion, the trilayered and integrated osteochondral scaffolds can effectively support cartilage and bone tissue generation in vitro and are potentially applicable for OC tissue engineering in vivo.

Surface engineering of titanium alloy substrates with multilayered biomimetic hierarchical films to regulate the growth behaviors of osteoblasts

Osseointegration is essential for the long-term survival of orthopedic implants. Inspired by the hierarchical structure of natural bone, we fabricated a hierarchical structure with osteoinduction potential on titanium alloy (Ti6Al7Nb) substrates via a spin-assisted layer-by-layer assembly technique, with hydroxyapatite nanofibers as the intercalated materials and gelatin and chitosan as the polycation and polyanion, respectively. The as-synthesized hydroxyapatite nanofibers were characterized using scanning electron microscopy (SEM), transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The change of water contact angle corresponding to different layers indicated the formation of a multilayered structure, since different components have their inherent wettability natures. The multilayered lamellar structure was revealed by the cross-sectional view of SEM, suggesting that the film was successfully deposited onto Ti6Al7Nb substrates. Osteoblasts cultured on the hierarchical structure deposited Ti alloy substrates displayed significantly higher cell viability (P<0.01) and better adhesion, a higher production level of alkaline phosphatase, mineralization, genes expressions of osteocalcin and osteopontin (P<0.01 or P<0.05) compared to those of native Ti6Al7Nb substrates after culture for 4, 7 or 14days. These results indicated that the lamellar structure was beneficial for the biological functions of osteoblasts, establishing the basis for osseointegration of a titanium alloy implant.

Structural and biochemical modification of a collagen scaffold to selectively enhance MSC tenogenic, chondrogenic, and osteogenic differentiation

Biomaterial approaches for engineering orthopedic interfaces such as the tendon-bone junction (TBJ) are limited by a lack of understanding of how insoluble (microstructure, composition) and soluble regulators of stem cell fate work in concert to promote bioactivity and differentiation. One strategy for regenerating the interface is to design biomaterials containing spatially graded structural properties sufficient to induce divergent mesenchymal stem cell (MSC) differentiation into multiple interface-specific phenotypes. This work explores the hypothesis that selective structural modification to a 3D collagen-glycosaminoglycan (CG) scaffold combined with biochemical supplementation can drive human bone-marrow-derived MSC differentiation down tenogenic, osteogenic, and chondrogenic lineages. Tenogenic differentiation is enhanced in geometrically anisotropic scaffolds versus a standard isotropic control. Notably, blebbistatin treatment abrogates this microstructurally driven effect. Further, enhanced osteogenic differentiation and new mineral synthesis are achieved by incorporation of a calcium phosphate mineral phase within the CG scaffold along with the use of osteogenic induction media. Finally, chondrogenic differentiation is optimally driven by combining chondrogenic induction media with a reduced density scaffold that promotes increased cellular condensation, significantly higher expression of chondrogenic genes, and increased GAG deposition. Together these data provide critical insight regarding design rules for elements of an integrated biomaterial platform for orthopedic interface regeneration.

The in vitro characterization of a gelatin scaffold, prepared by cryogelation and assessed in vivo as a dermal replacement in wound repair

A sheet gelatin scaffold with attached silicone pseudoepidermal layer for wound repair purposes was produced by a cryogelation technique. The resulting scaffold possessed an interconnected macroporous structure with a pore size distribution of 131 ± 17 μm at one surface decreasing to 30 ± 8 μm at the attached silicone surface. The dynamic storage modulus (G') and mechanical stability were comparable to the clinical gold standard dermal regeneration template, Integra®. The scaffolds were seeded in vitro with human primary dermal fibroblasts. The gelatin based material was not only non-cytotoxic, but over a 28 day culture period also demonstrated advantages in cell migration, proliferation and distribution within the matrix when compared with Integra®. When seeded with human keratinocytes, the neoepidermal layer that formed over the cryogel scaffold appeared to be more advanced and mature when compared with that formed over Integra®. The in vivo application of the gelatin scaffold in a porcine wound healing model showed that the material supports wound healing by allowing host cellular infiltration, biointegration and remodelling. The results of our in vitro and in vivo studies suggest that the gelatin based scaffold produced by a cryogelation technique is a promising material for dermal substitution, wound healing and other potential biomedical applications.

The use of physiological solutions or media in calcium phosphate synthesis and processing

This review examined the literature to spot uses, if any, of physiological solutions/media for the in situ synthesis of calcium phosphates (CaP) under processing conditions (i.e. temperature, pH, concentration of inorganic ions present in media) mimicking those prevalent in the human hard tissue environments. There happens to be a variety of aqueous solutions or media developed for different purposes; sometimes they have been named as physiological saline, isotonic solution, cell culture solution, metastable CaP solution, supersaturated calcification solution, simulated body fluid or even dialysate solution (for dialysis patients). Most of the time such solutions were not used as the aqueous medium to perform the biomimetic synthesis of calcium phosphates, and their use was usually limited to the in vitro testing of synthetic biomaterials. This review illustrates that only a limited number of research studies used physiological solutions or media such as Earle's balanced salt solution, Bachra et al. solutions or Tris-buffered simulated body fluid solution containing 27mM HCO3(-) for synthesizing CaP, and these studies have consistently reported the formation of X-ray-amorphous CaP nanopowders instead of Ap-CaP or stoichiometric hydroxyapatite (HA, Ca10(PO4)6(OH)2) at 37°C and pH 7.4. By relying on the published articles, this review highlights the significance of the use of aqueous solutions containing 0.8-1.5 mMMg(2+), 22-27mM HCO3(-), 142-145mM Na(+), 5-5.8mM K(+), 103-133mM Cl(-), 1.8-3.75mM Ca(2+), and 0.8-1.67mM HPO4(2-), which essentially mimic the composition and the overall ionic strength of the human extracellular fluid (ECF), in forming the nanospheres of X-ray-amorphous CaP.