Polymer-ceramic composite scaffold induces osteogenic differentiation of human mesenchymal stem cells

PLA/Hydroxyapatite scaffolds exhibit in vitro immunological inertness and promote robust osteogenic differentiation of human mesenchymal stem cells without osteogenic stimuli

Bone defects stand out as one of the greatest challenges of reconstructive surgery. Fused deposition modelling (FDM) allows for the printing of 3D scaffolds tailored to the morphology and size of bone damage in a patient-specific and high-precision manner. However, FDM still suffers from the lack of materials capable of efficiently supporting osteogenesis. In this study, we developed 3D-printed porous scaffolds composed of polylactic acid/hydroxyapatite (PLA/HA) composites with high ceramic contents (above 20%, w/w) by FDM. The mechanical properties of the PLA/HA scaffolds were compatible with those of trabecular bone. In vitro degradation tests revealed that HA can neutralize the acidification effect caused by PLA degradation, while simultaneously releasing calcium and phosphate ions. Importantly, 3D-printed PLA/HA did not induce the upregulation of activation markers nor the expression of inflammatory cytokines in dendritic cells thus exhibiting no immune-stimulatory properties in vitro. Evaluations using human mesenchymal stem cells (MSC) showed that pure PLA scaffolds exerted an osteoconductive effect, whereas PLA/HA scaffolds efficiently induced osteogenic differentiation of MSC even in the absence of any classical osteogenic stimuli. Our findings indicate that 3D-printed PLA scaffolds loaded with high concentrations of HA are most suitable for future applications in bone tissue engineering.

An ECM-Mimicking, Mesenchymal Stem Cell-Embedded Hybrid Scaffold for Bone Regeneration

While biologically feasible, bone repair is often inadequate, particularly in cases of large defects. The search for effective bone regeneration strategies has led to the emergence of bone tissue engineering (TE) techniques. When integrating electrospinning techniques, scaffolds featuring randomly oriented or aligned fibers, characteristic of the extracellular matrix (ECM), can be fabricated. In parallel, mesenchymal stem cells (MSCs), which are capable of both self-renewing and differentiating into numerous tissue types, have been suggested to be a suitable option for cell-based tissue engineering therapies. This work aimed to create a novel biocompatible hybrid scaffold composed of electrospun polymeric nanofibers combined with osteoconductive ceramics, loaded with human MSCs, to yield a tissue-like construct to promote in vivo bone formation. Characterization of the cell-embedded scaffolds demonstrated their resemblance to bone tissue extracellular matrix, on both micro- and nanoscales and MSC viability and integration within the electrospun nanofibers. Subcutaneous implantation of the cell-embedded scaffolds in the dorsal side of mice led to new bone, muscle, adipose, and connective tissue formation within 8 weeks. This hybrid scaffold may represent a step forward in the pursuit of advanced bone tissue engineering scaffolds.

Inferior In Vivo Osteogenesis and Superior Angiogenesis of Human Adipose‐Derived Stem Cells Compared with Bone Marrow‐Derived Stem Cells Cultured in Xeno‐Free Conditions

The possibility of using adipose tissue‐derived stromal cells (ATSC) as alternatives to bone marrow‐derived stromal cells (BMSC) for bone repair has garnered interest due to the accessibility, high cell yield, and rapid in vitro expansion of ATSC. For clinical relevance, their bone forming potential in comparison to BMSC must be proven. Distinct differences between ATSC and BMSC have been observed in vitro and comparison of osteogenic potential in vivo is not clear to date. The aim of the current study was to compare the osteogenesis of human xenofree‐expanded ATSC and BMSC in vitro and in an ectopic nude mouse model of bone formation. Human MSC were implanted with biphasic calcium phosphate biomaterials in subcutis pockets for 8 weeks. Implant groups were: BMSC, ATSC, BMSC and ATSC mixed together in different ratios, as well as MSC primed with either osteogenic supplements (250 μM ascorbic acid, 10 mM β‐glycerolphosphate, and 10 nM dexamethasone) or 50 ng/ml recombinant bone morphogenetic protein 4 prior to implantation. In vitro results show osteogenic gene expression and differentiation potentials of ATSC. Despite this, ATSC failed to form ectopic bone in vivo, in stark contrast to BMSC, although osteogenic priming did impart minor osteogenesis to ATSC. Neovascularization was enhanced by ATSC compared with BMSC; however, less ATSC engrafted into the implant compared with BMSC. Therefore, in the content of bone regeneration, the advantages of ATSC over BMSC including enhanced angiogenesis, may be negated by their lack of osteogenesis and prerequisite for osteogenic differentiation prior to transplantation. Stem Cells Translational Medicine2017;6:2160–2172

Nanomaterials for Tissue Engineering In Dentistry

The tissue engineering (TE) of dental oral tissue is facing significant changes in clinical treatments in dentistry. TE is based on a stem cell, signaling molecule, and scaffold triad that must be known and calibrated with attention to specific sectors in dentistry. This review article shows a summary of micro- and nanomorphological characteristics of dental tissues, of stem cells available in the oral region, of signaling molecules usable in TE, and of scaffolds available to guide partial or total reconstruction of hard, soft, periodontal, and bone tissues. Some scaffoldless techniques used in TE are also presented. Then actual and future roles of nanotechnologies about TE in dentistry are presented.

Tissue engineering: from research to dental clinics

Tissue engineering is an interdisciplinary field that combines the principles of engineering, material and biological sciences toward the development of therapeutic strategies and biological substitutes that restore, maintain, replace or improve biological functions. The association of biomaterials, stem cells, growth and differentiation factors has yielded the development of new treatment opportunities in most of the biomedical areas, including Dentistry. The objective of this paper is to present the principles underlying tissue engineering and the current scenario, the challenges and the perspectives of this area in Dentistry.

SIGNIFICANCE

The growth of tissue engineering as a research field has provided a novel set of therapeutic strategies for biomedical applications. Indeed, tissue engineering may lead to new strategies for the clinical management of patients with dental and craniofacial needs in the future.

Osteogenic differentiation of human bone marrow stromal cells in hydroxyapatite-loaded microsphere-based scaffolds

Calcium-based minerals have consistently been shown to stimulate osteoblastic behavior in vitro and in vivo. Thus, use of such minerals in biomaterial applications has become an effective method to enhance bone tissue engineered constructs. In the present study, for the first time, human bone marrow stromal cells (hBMSC) were osteogenically differentiated on scaffolds consisting only of hydroxyapatite (HAp)-loaded poly(D,L-lactic acid-co-glycolic acid) (PLGA) microspheres of high monodispersity. Scaffold formulations included 0, 5, 10, and 20 wt% Hap, and the hBMSC were cultured for 6 weeks. Results demonstrated suppression of some osteogenic genes during differentiation in the HAp group, but higher end-point glycosaminoglycan and collagen content in 10% and 20% HAp samples, as evidenced by biochemical tests, histology, and immunohistochemistry. After 6 weeks of culture, constructs with 0% and 5% HAp had average compressive moduli of 0.7 ± 0.2 and 1.5 ± 0.9 kPa, respectively, whereas constructs with 10% and 20% HAp had higher average moduli of 17.6 ± 4.6 and 18.9 ± 8.1 kPa, respectively. The results of this study indicate that HAp inclusion in microsphere-based scaffolds could be implemented as a physical gradient in combination with bioactive signal gradients seen in previous iterations of these microsphere-based scaffolds to enhance osteoconduction and mechanical integrity of a healing site.

New fabrication methods of bioactive and biodegradable scaffolds for bone tissue engineering

Bioceramic and polymers have been used as matrices for bone tissue engineering, and successful bone regeneration depends on cellular interaction with these matrices. The aim of this study was to fabricate polymer/ceramics composites with a novel sintering method. Also, we prepared homogenous porous poly(lactide-co-glycolide (PLGA) scaffolds in the supercritical CO2. These scaffolds had homogenous porous structure and high tensile and compressive mechanical properties compared to the scaffold prepared by conventional solvent casting method. This study revealed that generating bioactive and porous polymer scaffolds with novel sintering method or supercritical fluid technique could be useful for bone tissue engineering.

A model for tissue engineering applications: femoral critical size defect in immunodeficient mice

Animal models for preclinical functionality assays lie midway between in vitro systems such as cell culture and actual clinical trials. We have developed a novel external fixation device for femoral critical size defect (CSD) in the femurs of immunodeficient mice as an experimental model for studying bone regeneration and bone tissue engineering. The external fixation device comprises four pointed rods and dental acrylic paste. A segmental bone defect (2 mm) was created in the midshaft of the mouse femur. The CSD in the femur of the mice were either left untreated or treated with a bone allograft, a cell-scaffold construct, or a scaffold-only construct. The repair and healing processes of the CSD were monitored by digital x-ray radiography, microcomputed tomography, and histology. Repair of the femoral CSD was achieved with the bone allografts, and partial repair of the femoral CSD was achieved with the cell scaffold and the scaffold-only constructs. No repair of the nongrafted femoral CSD was observed. Our results establish the feasibility of this new mouse femoral model for CSD repair of segmental bone using a simple stabilized external fixation device. The model should prove especially useful for in vivo preclinical proof-of-concept studies that involve cell therapy-based technologies for bone tissue engineering applications in humans.

Osteogenic differentiation of mesenchymal stem cells on pregenerated extracellular matrix scaffolds in the absence of osteogenic cell culture supplements

This study utilized a full-factorial design to investigate the effect of four factors: presence of whole bone marrow cells, presence of in vitro-generated mineralized extracellular matrix (ECM), presence of dexamethasone, and variations in culture duration, on the proliferation and osteogenic differentiation of mesenchymal stem cells (MSCs) cultured on a polymer scaffold. Electrospun poly(epsilon-caprolactone) (PCL) fiber mesh scaffolds were seeded with rat MSCs and cultured in complete osteogenic medium for 12 days to generate constructs containing mineralized ECM. MSCs or MSCs and whole bone marrow cells were seeded onto decellularized ECM constructs (PCL/ECM) or plain PCL scaffolds and cultured statically for 4, 8, and 16 days in medium either with or without dexamethasone. After each culture period, the cell number was determined by DNA analysis, and the osteogenic differentiation state of the cells was determined by alkaline phosphatase activity and calcium assays. MSCs seeded onto PCL/ECM constructs and cultured in medium either with or without dexamethasone demonstrated similar amounts of calcium deposition after 16 days. A significant increase in cell number over time compared with all other groups was observed when whole bone marrow cells were cocultured with MSCs on PCL scaffolds in medium without dexamethasone. This study establishes that the osteogenic differentiation of MSCs seeded onto ECM-containing constructs is maintained even in the absence of dexamethasone and that the coculture of MSCs and whole bone marrow cells without dexamethasone and ECM enhances the proliferation of a cell population (or populations) present in the whole bone marrow.

Cytocompatibility of high strength non-oxide ceramics

Oxide ceramic materials like alumina (Al(2)O(3)) and zirconia (ZrO(2)) are frequently used for medical applications like implants and prostheses because of their excellent biocompatibility and high wear resistance. Unfortunately, oxide ceramics cannot be used for minimal invasive thin-walled implants like resurfacing hip prostheses because of their limited strength. The hypothesis of this study is that non-oxide ceramics like silicon nitride (Si(3)N(4)) and silicon carbide (SiC)-not previously used in the medical field-are not only high strength and mechanically reliable ceramic materials due to their high amount of covalent bonds, but also exhibit a suitable biocompatibility for use as medical implants and prostheses. Mechanical investigations and cell culture tests with mouse fibroblast cells (L929) and human mesenchymal stem cells (hMSC) were performed on the ceramics. An excellent cytocompatibility was demonstrated by live/dead stainings for both L929 cells and hMSC. HMSC were able to differentiate towards osteoblasts on all tested ceramics. The determined strength of silicon nitride and silicon carbide was shown as significantly higher than that of oxide ceramics. Our results indicate that the high strength non-oxide ceramics are material candidates in the future especially for highly loaded, thin-walled implants like ceramic resurfacing hip prostheses.

A tissue-like construct of human bone marrow MSCs composite scaffold support in vivo ectopic bone formation

Biocompatible and osteoconductive cell-scaffold constructs comprise the first and most important step towards successful in vivo bone repair. This study reports on a new cell-scaffold construct composed of gelatin-based hydrogel and ceramic (CaCO(3)/beta-TCP) particles loaded with human MSCs producing a tissue-like construct applied as a transplant for in vivo bone formation. Bone marrow-derived human MSCs were cultured in osteogenic induction medium. 5 x 10(5) (P(2)) cells were loaded on a mixture of hydrogel microspheres and ceramic particles, cultured in a rotating dynamic culture for up to 3 weeks. Both hydrogel microspheres and ceramic particles coalesced together to form a tissue-like construct, shown by histology to contain elongated spindle-like cells forming the new tissue between the individual particles. Cell proliferation and cell viability were confirmed by Alamar blue assay and by staining with CFDA, respectively. FACS analysis conducted before loading the cells, and after formation of the construct, revealed that the profile of cell surface markers remained unchanged throughout the dynamic culture. The osteogenic potential of the cells composing the tissue-like construct was further validated by subcutaneous transplants in athymic nude mice. After 8 weeks a substantial amount of new bone formation was observed in the cell-construct transplants, whereas no bone formation was observed in transplants containing no cells. This new cell construct provides a system for in vivo bone transplants. It can be tailored for a specific size and shape as needed for various transplant sites and for all aspects of regenerative medicine and biomaterial science.

Ability of polyurethane foams to support cell proliferation and the differentiation of MSCs into osteoblasts

In bone tissue reconstruction, the use of engineered constructs created by mesenchymal stem cells (MSCs) that differentiate and proliferate into three-dimensional porous scaffolds is an appealing alternative to autologous and heterologous bone grafts. Scaffolds considered in this work are represented by polyurethane (PU) foams. Two PU foams (EC-1 and EC-2) were synthesized and characterized for morphology, mechanical properties and in vitro interaction with the osteoblast-like cell line MG63 and MSCs from human bone marrow. EC-1 and EC-2 showed similar densities (0.20 g cm(-3)) with different morphologies: EC-1 showed a more homogeneous pore size (average Phi = 691 microm) and distribution, with a 35% open porosity, whereas EC-2 evidenced a wide range of pore dimension, with an average pore size of 955 microm and a 74% open porosity. The compressive properties of the two foams were similar in the dry condition and both showed a strong decrease in the wet condition. In vitro tests showed good MG63 cell proliferation, as confirmed by the results of the MTT assay and scanning electron microscopy (SEM) observations, with a higher cell viability on EC-2 foam 7 days post-seeding. In the experiments with MSCs, SEM observations showed the presence of an inorganic phase deposition starting day 7 onto EC-1, day 14 onto EC-2. The inorganic particles (CaP) deposition was much more evident onto the pore surface of both foams at day 30, indicating good differentiation of MSCs into osteoblasts. Both PU foams therefore appeared to stimulate cell adhesion and proliferation in vitro, sustaining the MSCs' growth and differentiation into osteoblasts.