A biaxial rotating bioreactor for the culture of fetal mesenchymal stem cells for bone tissue engineering

Sensor extended imaging workflow for creating fit for purpose models in basic and applied cell biology

While various engineering disciplines spent years on developing methods and workflows to increase their R&D efficiency, the field of cell biology has seen limited evolution in the fundamental approaches to interact with living cells. Perturbations are mostly of chemical nature, and physiologically relevant contexts and stimuli are left with limited attention, resulting in a solution space constrained within the boundaries of presently manageable perturbations. To predict in the laboratory how a drug will work in a human patient, cell biology must have a closer look at life and strive to mimic the human being in all his complexity. By implementing an iterative process from perturbation to measurement and vice versa, the authors suggest using a sensor-extended imaging workflow to implement product development practices to cell biology, opening a physiologically relevant solution space for the development of truly translational and predictive fit for purpose in vitro cell models.

Sinus augmentation with poly(ε)caprolactone-β tricalcium phosphate scaffolds, mesenchymal stem cells and platelet rich plasma for one-stage dental implantation in minipigs

PURPOSE

This study evaluated the efficacy of a tube-shaped poly(ε) caprolactone - β tricalcium phosphate (PCL-TCP) scaffold with the incorporation of human umbilical cord-derived mesenchymal stem cells (hUCMSCs) and platelet-rich plasma (PRP) for bone regeneration in the procedure of single-stage sinus augmentation and dental implantation in minipigs.

METHODS

Implants were placed in the bilateral sides of the maxillary sinuses of 5 minipigs and allocated to a PCL-TCP+hUCMSCs+PRP group (n=5), a PCL-TCP+PRP group (n=5), and a PCL-TCP-only group (n=6). After 12 weeks, bone regeneration was evaluated with soft X-rays, micro-computed tomography, fluorescence microscopy, and histomorphometric analysis.

RESULTS

Four implants failed (2 each in the PCL-TCP+hUCMSCs+PRP and PCL-TCP+hUCMSC groups). An analysis of the grayscale levels and bone-implant contact ratio showed significantly higher mean values in the PCL-TCP+hUCMSCs+PRP than in the PCL-TCP group (P=0.045 and P=0.016, respectively). In fluoromicroscopic images, new bone formation around the outer surfaces of the scaffolds was observed in the PCL-TCP+hUCMSCs+PRP group, suggesting a tenting effect of the specially designed scaffolds. Bone regeneration at the scaffold-implant interfaces was observed in all 3 groups.

CONCLUSIONS

Using a tube-shaped, honeycombed PCL-TCP scaffold with hUCMSCs and PRP may serve to enhance bone formation and dental implants' osseointegration in the procedure of simultaneous sinus lifting and dental implantation.

Significance of mechanical loading in bone fracture healing, bone regeneration, and vascularization

In 1892, J.L. Wolff proposed that bone could respond to mechanical and biophysical stimuli as a dynamic organ. This theory presents a unique opportunity for investigations on bone and its potential to aid in tissue repair. Routine activities such as exercise or machinery application can exert mechanical loads on bone. Previous research has demonstrated that mechanical loading can affect the differentiation and development of mesenchymal tissue. However, the extent to which mechanical stimulation can help repair or generate bone tissue and the related mechanisms remain unclear. Four key cell types in bone tissue, including osteoblasts, osteoclasts, bone lining cells, and osteocytes, play critical roles in responding to mechanical stimuli, while other cell lineages such as myocytes, platelets, fibroblasts, endothelial cells, and chondrocytes also exhibit mechanosensitivity. Mechanical loading can regulate the biological functions of bone tissue through the mechanosensor of bone cells intraosseously, making it a potential target for fracture healing and bone regeneration. This review aims to clarify these issues and explain bone remodeling, structure dynamics, and mechano-transduction processes in response to mechanical loading. Loading of different magnitudes, frequencies, and types, such as dynamic versus static loads, are analyzed to determine the effects of mechanical stimulation on bone tissue structure and cellular function. Finally, the importance of vascularization in nutrient supply for bone healing and regeneration was further discussed.

Preparation of Spheroids from Primary Pig Cells in a Mid-Scale Bioreactor Retaining Their Myogenic Potential

Three-dimensional cell culture techniques mimic the in vivo cell environment more adequately than flat surfaces. Spheroids are multicellular aggregates and we aimed to produce scaffold-free spheroids of myogenic origin, called myospheres, using a mid-scale incubator and bioreactor hybrid. For the first time, we obtained spheroids from primary porcine muscle cells (PMCs) with this technology and compared their morphology and growth parameters, marker expression, and myogenic potential to C2C12-derived spheroids. Both cell types were able to form round-shaped spheroids in the bioreactor already after 24 h. The mean diameter of the C2C12 spheroids (44.6 µm) was larger than that of the PMCs (32.7 µm), and the maximum diameter exceeded 1 mm. C2C12 cells formed less aggregates than PMCs with a higher packing density (cell nuclei/mm²). After dissociation from the spheroids, C2C12 cells and PMCs started to proliferate again and were able to differentiate into the myogenic lineage, as shown by myotube formation and the expression of F-Actin, Desmin, MyoG, and Myosin. For C2C12, multinucleated syncytia and Myosin expression were observed in spheroids, pointing to accelerated myogenic differentiation. In conclusion, the mid-scale incubator and bioreactor system is suitable for spheroid formation and cultivation from primary muscle cells while preserving their myogenic potential.

Impact of Fluid Dynamics on the Viability and Differentiation Capacity of 3D-Cultured Jaw Periosteal Cells

Perfused bioreactor systems are considered to be a promising approach for the 3D culturing of stem cells by improving the quality of the tissue-engineered grafts in terms of better cell proliferation and deeper penetration of used scaffold materials. Our study aims to establish an optimal perfusion culture system for jaw periosteal cell (JPC)-seeded scaffolds. For this purpose, we used beta-tricalcium phosphate (β-TCP) scaffolds as a three-dimensional structure for cell growth and osteogenic differentiation. Experimental set-ups of tangential and sigmoidal fluid configurations with medium flow rates of 100 and 200 µL/min were applied within the perfusion system. Cell metabolic activities of 3D-cultured JPCs under dynamic conditions with flow rates of 100 and 200 µL/min were increased in the tendency after 1, and 3 days of culture, and were significantly increased after 5 days. Significantly higher cell densities were detected under the four perfused conditions compared to the static condition at day 5. However, cell metabolic and proliferation activity under dynamic conditions showed flow rate independency in our study. In this study, dynamic conditions increased the expression of osteogenic markers (ALPL, COL1A1, RUNX2, and OCN) compared to static conditions and the tangential configuration showed a stronger osteogenic effect than the sigmoidal flow configuration.

Numerical and experimental simulation of a dynamic-rotational 3D cell culture for stratified living tissue models

Human tissues and organs are inherently heterogeneous, and their functionality is determined by the interplay between cell types, their secondary architecture, and gradients of signalling molecules and metabolites. To mimic the dynamics of native tissues, perfusion bioreactors and microfluidic devices are widely used, enhancing cell culture viability in the core of 3D constructs. Still, most in vitro methods for drug screening include cell or tissue exposure to constant and homogeneous compound concentrations over the testing period. Moreover, a prevalent issue inhibiting the large-scale adoption of microfluidics and bioreactors is the tubing dependence to induce a perfusion regime. Here, we propose a compartmentalized rotational (CR) bioreactor for stable control over gradient tissue culture conditions. Using the CR bioreactor, adjacent culture lanes are patterned by controlled flow dynamics to enable tissue stratification. Numerical and experimental models demonstrate cell seeding dynamics, as well as culture media rotational perfusion and gradient formations. Additionally, the developed system induces vertical and horizontal rotations, which increase medium exchange and homogeneous construct maturation, allowing both perfused tubing-based and tubing-free approaches. As a proof-of-concept, experiments are accompanied by a numerical model able to simulate the cellular inoculation, growth, and dynamic cell culture in 3D scaffolds and hydrogel. The examination of a blood-brain-barrier (BBB) model demonstrates the impact of a heterotypic culture on molecular permeability under mimetic dynamic conditions. Briefly, the present work discloses the simulation of 3D dynamic cultures, and a semi-automated platform for heterotypic tissues in vitro modelling, for broad tissue engineering and drug discovery/screening applications.

Silicon Nitride, a Bioceramic for Bone Tissue Engineering: A Reinforced Cryogel System With Antibiofilm and Osteogenic Effects

Silicon nitride (SiN [Si3N4]) is a promising bioceramic for use in a wide variety of orthopedic applications. Over the past decades, it has been mainly used in industrial applications, such as space shuttle engines, but not in the medical field due to scarce data on the biological effects of SiN. More recently, it has been increasingly identified as an emerging material for dental and orthopedic implant applications. Although a few reports about the antibacterial properties and osteoconductivity of SiN have been published to date, there have been limited studies of SiN-based scaffolds for bone tissue engineering. Here, we developed a silicon nitride reinforced gelatin/chitosan cryogel system (SiN-GC) by loading silicon nitride microparticles into a gelatin/chitosan cryogel (GC), with the aim of producing a biomimetic scaffold with antibiofilm and osteogenic properties. In this scaffold system, the GC component provides a hydrophilic and macroporous environment for cells, while the SiN component not only provides antibacterial properties and osteoconductivity but also increases the mechanical stiffness of the scaffold. This provides enhanced mechanical support for the defect area and a better osteogenic environment. First, we analyzed the scaffold characteristics of SiN-GC with different SiN concentrations, followed by evaluation of its apatite-forming capacity in simulated body fluid and protein adsorption capacity. We further confirmed an antibiofilm effect of SiN-GC against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as well as enhanced cell proliferation, mineralization, and osteogenic gene upregulation for MC3T3-E1 pre-osteoblast cells. Finally, we developed a bioreactor to culture cell-laden scaffolds under cyclic compressive loading to mimic physiological conditions and were able to demonstrate improved mineralization and osteogenesis from SiN-GC. Overall, we confirmed the antibiofilm and osteogenic effect of a silicon nitride reinforced cryogel system, and the results indicate that silicon nitride as a biomaterial system component has a promising potential to be developed further for bone tissue engineering applications.

Biophysical Stimuli as the Fourth Pillar of Bone Tissue Engineering

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

A practical guide for evaluating the osteoimmunomodulatory properties of biomaterials

Biomaterials offer a promising approach to repair bone defects. Whereas traditional studies predominantly focused on optimizing the osteogenic capacity of biomaterials, less focus has been on the immune response elicited by them. However, the immune and skeletal systems extensively interact, a concept which is referred to as 'osteoimmunology'. This realization has fuelled the development of biomaterials with favourable osteoimmunomodulatory (OIM) properties, aiming to modulate the immune response and to support bone regeneration, thereby affecting the success of an implant. Given the plethora of in vitro assays used to evaluate the OIM properties of biomaterials, it may be challenging to select the right methods to produce conclusive results. In this review, we aim to provide a comprehensive and practical guide for researchers interested in studying the OIM properties of biomaterials in vitro. After a concise overview of the concept of osteoimmunology, emphasis is put on the methodologies that are regularly used to evaluate the OIM properties of biomaterials. First, a description of the most commonly used cell types and cell culture media is provided. Second, typical experimental set-ups and their relevant characteristics are discussed. Third, a detailed overview of the generally used methodologies and readouts, including cell type-specific markers and time points of analysis, is given. Finally, we highlight the promise of advanced approaches, namely microarrays, bioreactors and microfluidic-based systems, and the potential that these may offer to the osteoimmunology field. STATEMENT OF SIGNIFICANCE: Osteoimmunology focuses on the connection and communication between the skeletal and immune systems. This interaction has been recognized to play an important role in the clinical success of biomaterials, which has resulted in an increasing amount of research on the osteoimmunomodulatory (OIM) properties of biomaterials. However, the amount of literature makes it challenging to extract the information needed to design experiments from beginning to end, and to compare obtained results to existing work. This article intends to serve as a guide for those aiming to learn more about the commonly used experimental approaches in the field. We cover early-stage choices, such as cell types and experimental set-ups, but also discuss specific assays, including cell markers and time points of analysis.

Bioreactor design and validation for manufacturing strategies in tissue engineering

The fields of regenerative medicine and tissue engineering offer new therapeutic options to restore, maintain or improve tissue function following disease or injury. To maximize the biological function of a tissue-engineered clinical product, specific conditions must be maintained within a bioreactor to allow the maturation of the product in preparation for implantation. Specifically, the bioreactor should be designed to mimic the mechanical, electrochemical and biochemical environment that the product will be exposed to in vivo. Real-time monitoring of the functional capacity of tissue-engineered products during manufacturing is a critical component of the quality management process. The present review provides a brief overview of bioreactor engineering considerations. In addition, strategies for bioreactor automation, in-line product monitoring and quality assurance are discussed.

Synergistic Effect of PVDF-Coated PCL-TCP Scaffolds and Pulsed Electromagnetic Field on Osteogenesis

Bone exhibits piezoelectric properties. Thus, electrical stimulations such as pulsed electromagnetic fields (PEMFs) and stimuli-responsive piezoelectric properties of scaffolds have been investigated separately to evaluate their efficacy in supporting osteogenesis. However, current understanding of cells responding under the combined influence of PEMF and piezoelectric properties in scaffolds is still lacking. Therefore, in this study, we fabricated piezoelectric scaffolds by functionalization of polycaprolactone-tricalcium phosphate (PCL-TCP) films with a polyvinylidene fluoride (PVDF) coating that is self-polarized by a modified breath-figure technique. The osteoinductive properties of these PVDF-coated PCL-TCP films on MC3T3-E1 cells were studied under the stimulation of PEMF. Piezoelectric and ferroelectric characterization demonstrated that scaffolds with piezoelectric coefficient d33 = -1.2 pC/N were obtained at a powder dissolution temperature of 100 °C and coating relative humidity (RH) of 56%. DNA quantification showed that cell proliferation was significantly enhanced by PEMF as low as 0.6 mT and 50 Hz. Hydroxyapatite staining showed that cell mineralization was significantly enhanced by incorporation of PVDF coating. Gene expression study showed that the combination of PEMF and PVDF coating promoted late osteogenic gene expression marker most significantly. Collectively, our results suggest that the synergistic effects of PEMF and piezoelectric scaffolds on osteogenesis provide a promising alternative strategy for electrically augmented osteoinduction. The piezoelectric response of PVDF by PEMF, which could provide mechanical strain, is particularly interesting as it could deliver local mechanical stimulation to osteogenic cells using PEMF.

Degradation Behavior of Polymers Used as Coating Materials for Drug Delivery-A Basic Review

The purpose of the work was to emphasize the main differences and similarities in the degradation mechanisms in the case of polymeric coatings compared with the bulk ones. Combined with the current background, this work reviews the properties of commonly utilized degradable polymers in drug delivery, the factors affecting degradation mechanism, testing methods while offering a retrospective on the evolution of the controlled release of biodegradable polymeric coatings. A literature survey on stability and degradation of different polymeric coatings, which were thoroughly evaluated by different techniques, e.g., polymer mass loss measurements, surface, structural and chemical analysis, was completed. Moreover, we analyzed some shortcomings of the degradation behavior of biopolymers in form of coatings and briefly proposed some solving directions to the main existing problems (e.g., improving measuring techniques resolution, elucidation of complete mathematical analysis of the different degradation mechanisms). Deep studies are still necessary on the dynamic changes which occur to biodegradable polymeric coatings which can help to envisage the future performance of synthesized films designed to be used as medical devices with application in drug delivery.

Tissue Engineering for Periodontal Ligament Regeneration: Biomechanical Specifications

The periodontal biomechanical environment is very difficult to investigate. By the complex geometry and composition of the periodontal ligament (PDL), its mechanical behavior is very dependent on the type of loading (compressive versus tensile loading; static versus cyclic loading; uniaxial versus multiaxial) and the location around the root (cervical, middle, or apical). These different aspects of the PDL make it difficult to develop a functional biomaterial to treat periodontal attachment due to periodontal diseases. This review aims to describe the structural and biomechanical properties of the PDL. Particular importance is placed in the close interrelationship that exists between structure and biomechanics: the PDL structural organization is specific to its biomechanical environment, and its biomechanical properties are specific to its structural arrangement. This balance between structure and biomechanics can be explained by a mechanosensitive periodontal cellular activity. These specifications have to be considered in the further tissue engineering strategies for the development of an efficient biomaterial for periodontal tissues regeneration.

Bioreactor cultivation condition for engineered bone tissue: Effect of various bioreactor designs on extra cellular matrix synthesis

Dynamic-based systems are bio-designed in order to mimic the micro-environments of the bone tissue. There is limited direct comparison between perfusion and perfusion-rotation forces in designing a bioreactor. Hence, in current study, we aimed to compare given bioreactors for bone regeneration. Two types of bioreactors including rotating & perfusion and perfusion bioreactors were designed. Mesenchymal stem cells derived from buccal fat pad were loaded on a gelatin/β-Tricalcium phosphate scaffold. Cell-scaffold constructs were subjected to different treatment condition and place in either of the bioreactors. Effect of different dynamic conditions on cellular behavior including cell proliferation, cell adhesion, and osteogenic differentiation were assessed. Osteogenic assessment of scaffolds after 24 days revealed that rotating & perfusion bioreactor led to significantly higher expression of OCN and RUNX2 genes and also greater amount of ALP and collagen I protein production compared to static groups and perfusion bioreactor. Observation of cellular sheets which filled the scaffold porosities in SEM images, approved the better cell responses to rotating & perfusion forces of the bioreactor. The outcomes demonstrated that rotating & perfusion bioreactor action on bone regeneration is much preferable than perfusion bioreactor. Therefore, it seems that exertion of multi-stimuli is more effective for bone engineering.

Role of offset and gradient architectures of 3-D melt electrowritten scaffold on differentiation and mineralization of osteoblasts

BACKGROUND

Cell-scaffold based therapies have the potential to offer an efficient osseous regenerative treatment and PCL has been commonly used as a scaffold, however its effectiveness is limited by poor cellular retention properties. This may be improved through a porous scaffold structure with efficient pore arrangement to increase cell entrapment. To facilitate this, melt electrowriting (MEW) has been developed as a technique able to fabricate cell-supporting scaffolds with precise micro pore sizes via predictable fibre deposition. The effect of the scaffold's architecture on cellular gene expression however has not been fully elucidated.

METHODS

The design and fabrication of three different uniform pore structures (250, 500 and 750 μm), as well as two offset scaffolds with different layout of fibres (30 and 50%) and one complex scaffold with three gradient pore sizes of 250-500 - 750 μm, was performed by using MEW. Calcium phosphate modification was applied to enhance the PCL scaffold hydrophilicity and bone inductivity prior to seeding with osteoblasts which were then maintained in culture for up to 30 days. Over this time, osteoblast cell morphology, matrix mineralisation, osteogenic gene expression and collagen production were assessed.

RESULTS

The in vitro findings revealed that the gradient scaffold significantly increased alkaline phosphatase activity in the attached osteoblasts while matrix mineralization was higher in the 50% offset scaffolds. The expression of osteocalcin and osteopontin genes were also upregulated compared to other osteogenic genes following 30 days culture, particularly in offset and gradient scaffold structures. Immunostaining showed significant expression of osteocalcin in offset and gradient scaffold structures.

CONCLUSIONS

This study demonstrated that the heterogenous pore sizes in gradient and fibre offset PCL scaffolds prepared using MEW significantly improved the osteogenic potential of osteoblasts and hence may provide superior outcomes in bone regeneration applications.

Identification of a prolonged action molecular GLP-1R agonist for the treatment of femoral defects

Poly-GLP-1 promotes angiogenesis to accelerate bone formationviaBMSC differentiation and M2 polarization.

Biomimetic open porous structured core-shell microtissue with enhanced mechanical properties for bottom-up bone tissue engineering

Background: Microtissues constructed with hydrogels promote cell expansion and specific differentiation by mimicking the microarchitecture of native tissues. However, the suboptimal mechanical property and osteogenic activity of microtissues fabricated by natural polymers need further improvement for bone reconstruction application. Core-shell designed structures are composed of an inner core part and an outer part shell, combining the characteristics of different materials, which improve the mechanical property of microtissues. Methods: A micro-stencil array chip was used to fabricate an open porous core-shell micro-scaffold consisting of gelatin as shell and demineralized bone matrix particles modified with bone morphogenetic protein-2 (BMP-2) as core. Single gelatin micro-scaffold was fabricated as a control. Rat bone marrow mesenchymal stem cells (BMSCs) were seeded on the micro-scaffolds, after which they were dynamic cultured and osteo-induced in mini-capsule bioreactors to fabricate microtissues. The physical characteristics, biocompatibility, osteo-inducing and controlled release ability of the core-shell microtissue were evaluated in vitro respectively. Then microtissues were tested in vivo via ectopic implantation and orthotopic bone implantation in rat model. Results: The Young's modulus of core-shell micro-scaffold was nearly triple that of gelatin micro-scaffold, which means the core-shell micro-scaffolds have better mechanical property. BMSCs rapidly proliferated and retained the highest viability on core-shell microtissues. The improved osteogenic potential of core-shell microtissues was evidenced by the increased calcification based on von kossa staining and osteo-relative gene expression. At 3months after transplantation, core-shell microtissue group formed the highest number of mineralized tissues in rat ectopic subcutaneous model, and displayed the largest amount of new bony tissue deposition in rat orthotopic cranial defect. Conclusion: The novel core-shell microtissue construction strategy developed may become a promising cell delivery platform for bone regeneration.

Development of a micro-tissue-mediated injectable bone tissue engineering strategy for large segmental bone defect treatment

BACKGROUND

Bone tissue engineering is not widely used in clinical treatment. Two main reasons hide behind this: (1) the seed cells are difficult to obtain and (2) the process of tissue engineering bone construction is too complex and its efficiency is still relatively low. It is foreseeable that in the near future, the problem of seed cell sources could be solved completely in tissue engineering bone repair. As for the complex process and low efficiency of tissue engineering bone construction, usually two strategies would be considered: (1) the construction strategy based on injectable bone tissue and (2) the construction strategy based on osteogenic cell sheets. However, the application of injectable bone tissue engineering (iBTE) strategy and osteogenic cell sheet strategy is limited and they could hardly be used directly in repairing defects of large segmental bone, especially load-bearing bone.

METHODS

In this study, we built an osteogenic micro-tissue with simple construction but with a certain structure and composition. Based on this, we established a new iBTE repair strategy-osteogenic micro-tissue in situ repair strategy, mainly targeting at solving the problem of large segmental bone defect. The steps are as follows: (1) Build the biodegradable three-dimensional scaffold based on the size of the defect site with 3D printing rapid prototyping technology. (2) Implant the three-dimensional scaffold into the defect site. This scaffold is considered as the "steel framework" that could provide both mechanical support and space for bone tissue growth. (3) Inject the osteogenic micro-tissue (i.e., the "cell-extracellular matrix" complex), which could be considered as "concrete," into the three-dimensional scaffold, to promote the bone tissue regeneration in situ. Meanwhile, the digested cells were injected as the compared group in this experiment. After 3 months, the effect of in situ bone defect repair of osteogenic micro-tissue and digested cells was compared.

RESULTS

It is confirmed that osteogenic micro-tissue could achieve a higher efficiency on cell usage and has a better repair effect than the digested cells.

CONCLUSIONS

Osteogenic micro-tissue repairing strategy would be a more promising clinical strategy to solve the problem of large segmental bone defect.

Enhancing effects of basic fibroblast growth factor and fibronectin on osteoblast adhesion to bone scaffolds for bone tissue engineering through extracellular matrix-integrin pathway

The present study aimed to investigate the effects of basic fibroblast growth factor (bFGF) and fibronectin (FN) on adhesion of osteoblasts seeded into bio-derived bone scaffolds. Rat calvarial osteoblasts were separated and their osteogenic phenotypes were determined by staining for alkaline phosphatase as well as alizarin red staining. The bio-derived bone scaffolds were prepared from the metaphysis of porcine femur and their physicochemical properties were assessed by scanning electron microscopy (SEM) and X-ray diffraction analysis. An MTT assay was used to detect the effects of bFGF and FN on osteoblast adhesion or proliferation on cell/scaffold constructs through blocking the extracellular matrix FN-integrin pathway by the Gly-Arg-Gly-Asp-Ser (GRGDS) peptide. Western blot analysis was used to measure the β1 integrin levels. Based on the adhesion of osteoblasts stimulated by various concentrations of bFGF (0.1, 1, 10 and 100 ng/ml) on bio-derived bone scaffolds modified by various concentrations of FN (0.1, 1, 10 and 100 µg/ml), the cell/scaffold constructs were divided into four groups: i) Control, non-stimulated and non-modified group; ii) 10 µg/ml FN-modified group; iii) 100 ng/ml bFGF-stimulated group; iv) 10 µg/ml FN + 100 ng/ml bFGF group. Cell proliferation curves acquired by MTT assay and micrographs obtained by SEM showed that the combination of bFGF and FN significantly improved cell adhesion, particularly in the 10 µg/ml FN + 100 ng/ml bFGF group vs. the other groups, and the effect on cell adhesion was inhibited by 1 mmol/l GRGDS peptide through the FN-integrin pathway. Western blot results showed that the combination of bFGF and FN significantly enhanced β1 integrin expression levels. These results suggested that osteoblasts stimulated by 100 ng/ml bFGF and bio-derived bone materials modified by 10 µg/ml FN should be combined to be applied in the bone tissue engineering.

In vitro evaluation of marrow clot enrichment on microstructure decoration, cell delivery and proliferation of porous titanium scaffolds by selective laser melting three-dimensional printing

Titanium alloy is a clinically approved material for bone substitution. Although three-dimensional printing (3DP) fabrication technique can build up porous Ti scaffolds with the designed shape and microstructure, the biomechanical performance of 3DP Ti scaffolds still need to be improved to increase the reliability of osseointegration capacity. To address this issue, rabbit bone marrow clot (MC) is used to modify 3DP Ti scaffolds by stem cell delivery and microenvironment decoration inside the pores of these scaffolds. Moreover, 3DP Ti scaffolds were built up using selective laser melting, and 3DP MC-Ti scaffolds were constructed through the enrichment of MC with Ti scaffolds in vitro. Results demonstrated that the obtained 3DP Ti scaffolds in current study has an average modulus of elasticity (ME) at 1294.48 MPa with average yield strength of 33.154 MPa. For MC-Ti scaffolds, MC enrichment obstructs the pores of 3DP scaffolds due to the large amount of fibrin and erythrocytes and leads to a decrease in ratio of live cells at 1-week culture. Cell proliferation and osteogenic differentiation performance of MC-Ti scaffolds were promoted with porous recanalization in the later 3 weeks. After 2 weeks in vitro culture, fivefold of cell number in MC-Ti scaffolds were observed than bone marrow-derived mesenchymal stem cell-seeded Ti scaffolds. Compared to Ti scaffolds, fourfold of deoxyribonucleic acid content, type I collagen-α1, osteocalcin, and alkaline phosphatase expression in MC-Ti scaffolds were observed after 4 weeks in vitro culture. Results suggested that the combination with MC is a highly efficient method that improves the biological performance of Ti scaffolds. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2245-2253, 2018.

In-vivo evaluation of subcutaneously implanted cell-loaded apatite microcarriers for osteogenic potency

Cell-loaded apatite microcarriers present as potential scaffolds for direct in-vivo delivery of cells post-expansion to promote bone regeneration. The objective of this study was to evaluate the osteogenic potency of human foetal mesenchymal stem cells (hfMSC)-loaded apatite microcarriers when implanted subcutaneously in a mouse model. This was done by examining for ectopic bone formation at 2 weeks, 1 month and 2 months, which were intended to coincide with the inflammation, healing and remodelling phases, respectively. Three histological examinations including haematoxylin and eosin staining to examine general tissue morphology, Masson's trichrome staining to identify tissue type, and Von Kossa staining to examine extent of tissue mineralisation were performed. In addition, immunohistochemistry assay of osteopontin was conducted to confirm active bone formation by the seeded hfMSCs. Results showed a high level of tissue organisation and new bone formation, with active bone remodelling being observed at the end of 2 months, and an increase in tissue density, organisation, and mineralisation could also be observed for hfMSC-loaded apatite microcarriers. Various cell morphology resembling that of osteoblasts and osteoclasts could be seen on the surfaces of the hfMSC-loaded apatite microcarriers, with presence of woven bone tissue formation being observed at the intergranular space. These observations were consistent with evidence of ectopic bone formation, which were absent in group containing apatite microcarriers only. Overall, results suggested that hfMSC-loaded apatite microcarriers retained their osteogenic potency after implantation, and provided an effective platform for bone tissue regeneration.

Review: bioreactor design towards generation of relevant engineered tissues: focus on clinical translation

In tissue engineering and regenerative medicine, studies that utilize 3D scaffolds for generating voluminous tissues are mostly confined in the realm of in vitro research and preclinical animal model testing. Bioreactors offer an excellent platform to grow and develop 3D tissues by providing conditions that mimic their native microenvironment. Aligning the bioreactor development process with a focus on patient care will aid in the faster translation of the bioreactor technology to clinics. In this review, we discuss the various factors involved in the design of clinically relevant bioreactors in relation to their respective applications. We explore the functional relevance of tissue grafts generated by bioreactors that have been designed to provide physiologically relevant mechanical cues on the growing tissue. The review discusses the recent trends in non-invasive sensing of the bioreactor culture conditions. It provides an insight to the current technological advancements that enable in situ, non-invasive, qualitative and quantitative evaluation of the tissue grafts grown in a bioreactor system. We summarize the emerging trends in commercial bioreactor design followed by a short discussion on the aspects that hamper the 'push' of bioreactor systems into the commercial market as well as 'pull' factors for stakeholders to embrace and adopt widespread utility of bioreactors in the clinical setting. Copyright © 2017 John Wiley & Sons, Ltd.

Effect of Rotation on Scaffold Motion and Cell Growth in Rotating Bioreactors

Efficient use of different bioreactor designs to improve cell growth in three-dimensional scaffolds requires an understanding of their mechanism of action. To address this for rotating wall vessel bioreactors, fluid and scaffold motion were investigated experimentally at different rotation speeds and vessel fill volumes. Low cost bioreactors with single and dual axis rotation were developed to investigate the effect of these systems on human osteoblast proliferation in free floating and constrained collagen-glycosaminoglycan porous scaffolds. A range of scaffold motions (free fall, periodic oscillation, and orbital motion) were observed at the rotation speeds and vessel fluid/air ratios used, with 85% fluid fill and an outer vessel wall velocity of ∼14 mm s⁻¹ producing a scaffold in a free fall state. The cell proliferation results showed that after 14 and 21 days of culture, this combination of fluid fill and speed of rotation produced significantly greater cell numbers in the scaffolds than when lower or higher rotation speeds (p < 0.002) or when the chamber was 60% or 100% full (p < 0.01). The fluid flow and scaffold motion experiments show that biaxial rotation would not improve the mass transfer of medium into the scaffold as the second axis of rotation can only transition the scaffold toward oscillatory or orbital motion and, hence, reduce mass transport to the scaffold. The cell culture results confirmed that there was no benefit to the second axis of rotation with no significant difference in cell proliferation either when the scaffolds were free floating or constrained (p > 0.05).

Fabrication of a silver octahedral nanoparticle-containing polycaprolactone nanocomposite for antibacterial bone scaffolds

Ag octahedral nanoparticle-containing PCL nanocomposite scaffolds exhibit successful osteogenic differentiation of stem cells and localized antibacterial effects.

In vitro cyclic compressive loads potentiate early osteogenic events in engineered bone tissue

Application of dynamic mechanical loads on bone and bone explants has been reported to enhance osteogenesis and mineralization. To date, published studies have incorporated a range of cyclic strains on 3D scaffolds and platforms to demonstrate the effect of mechanical loading on osteogenesis. However, most of the loading parameters used in these studies do not emulate the in vivo loading conditions. In addition, the scaffolds/platforms are not representative of the native osteoinductive environment of bone tissue and hence may not be entirely accurate to study the in vivo mechanical loading. We hypothesized that biomimicry of physiological loading will potentiate accelerated osteogenesis in bone grafts. In this study, we present a compression bioreactor system that applies cyclic compression to cellular grafts in a controlled manner. Polycaprolactone-β Tricalcium Phosphate (PCL-TCP) scaffolds seeded with Mesenchymal Stem Cells (MSC) were cyclically compressed in bioreactor for a period of 4 weeks at 1 Hz and physiological strain value of 0.22% for 4 h per day. Gene expression studies revealed increased expressions of osteogenesis-related genes (Osteonectin and COL1A1) on day 7 of cyclic loading group relative to its static controls. Cyclic compression resulted in a 3.76-fold increase in the activity of Alkaline Phosphatase (ALP) on day 14 when compared to its static group (p < 0.001). In addition, calcium deposition of cyclic loading group was found to attain saturation on day 14 (1.96 fold higher than its static scaffolds). The results suggested that cyclic, physiological compression of stem cell-seeded scaffolds generated highly mineralized bone grafts. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2366-2375, 2017.

Osteogenic Differentiation and Mineralization on Compact Multilayer nHA-PCL Electrospun Scaffolds in a Perfusion Bioreactor

BACKGROUND

Monolayer electrospun scaffolds have already been used in bone tissue engineering due to their high surface-tovolume ratio, interconnectivity, similarity to natural bone extracellular matrix (ECM), and simple production.

OBJECTIVES

The aim of this study was to evaluate the dynamic culture effect on osteogenic differentiation and mineralizationi into a compact cellular multilayer nHA-PCL electrospun construct. The dynamic culture was compared with static culture.

MATERIALS AND METHODS

The calcium content, alkaline phosphatase (ALP) activity and cell viability were investigated on days 3 and 7.

RESULTS

When the dynamic culture compared to static culture, the mineralization and ALP activity were increased in dynamic culture. After 7 days, calcium contents were 41.24 and 20.44 μg.(cm³)^-1, and also normalized ALP activity were 0.32 and 0.19 U.mg^-1 in dynamic and static culture, respectively. Despite decreasing the cell viability until day 7, the scanning electron microscopy (SEM) results showed that, due to higher mineralization, a larger area of the construct was covered with calcium deposition in dynamic culture.

CONCLUSIONS

The dynamic flow could improve ALP activity and mineralization into the compact cellular multilayer construct cultured in the perfusion bioreactor after 7 days. Fluid flow of media helped to facilitate the nutrients transportation into the construct and created uniform cellular construct with high mineralization. This construct can be applied for bone tissue engineering.

Emerging translational research on magnetic nanoparticles for regenerative medicine

Regenerative medicine, which replaces or regenerates human cells, tissues or organs, to restore or establish normal function, is one of the fastest-evolving interdisciplinary fields in healthcare. Over 200 regenerative medicine products, including cell-based therapies, tissue-engineered biomaterials, scaffolds and implantable devices, have been used in clinical development for diseases such as diabetes and inflammatory and immune diseases. To facilitate the translation of regenerative medicine from research to clinic, nanotechnology, especially magnetic nanoparticles have attracted extensive attention due to their unique optical, electrical, and magnetic properties and specific dimensions. In this review paper, we intend to summarize current advances, challenges, and future opportunities of magnetic nanoparticles for regenerative medicine.

Pre-implanted Sensory Nerve Could Enhance the Neurotization in Tissue-Engineered Bone Graft

In our previous study, it was found that implanting the sensory nerve tract into the tissue-engineered bone to repair large bone defects can significantly result in better osteogenesis effect than tissue-engineered bone graft (TEBG) alone. To study the behavior of the preimplanted sensory nerve in the TEBG, the TEBG was constructed by seeding bone mesenchymal stem cells into β-tricalcium phosphate scaffold with (treatment group) or without (blank group) implantation of the sensory nerve. The expression of calcitonin gene-related peptide (CGRP), which helps in the healing of bone defect in the treatment group was significantly higher than the blank group at 4, 8, and 12 weeks. The expression of growth-associated protein 43 (GAP43), which might be expressed during nerve healing in the treatment group, was significantly higher than the blank group at 4 and 8 weeks. The nerve tracts of the preimplanted sensory nerve were found in the scaffold by the nerve tracing technique. The implanted sensory nerve tracts grew into the pores of scaffolds much earlier than the vascular. The implanted sensory nerve tracts traced by Dil could be observed at 4 weeks, but at the same time, no vascular was observed. In conclusion, the TEBG could be benefited from the preimplanted sensory nerve through the healing behavior of the sensory nerve. The sensory nerve fibers could grow into the pores of the TEBG rapidly, and increase the expression of CGRP, which is helpful in regulating the bone formation and the blood flow.

Tunable osteogenic differentiation of hMPCs in tubular perfusion system bioreactor

The use of bioreactors for bone tissue engineering has been widely investigated. While the benefits of shear stress on osteogenic differentiation are well known, the underlying effects of dynamic culture on subpopulations within a bioreactor are less evident. In this work, we explore the influence of applied flow in the tubular perfusion system (TPS) bioreactor on the osteogenic differentiation of human mesenchymal progenitor cells (hMPCs), specifically analyzing the effects of axial position along the growth chamber. TPS bioreactor experiments conducted with unidirectional flow demonstrated enhanced expression of osteogenic markers in cells cultured downstream from the inlet flow. We utilized computational fluid dynamic modeling to confirm uniform shear stress distribution on the surface of the scaffolds and along the length of the growth chamber. The concept of paracrine signaling between cell populations was validated with the use of alternating flow, which diminished the differences in osteogenic differentiation between cells cultured at the inlet and outlet of the growth chamber. After the addition of controlled release of bone morphogenic protein-2 (BMP-2) into the system, osteogenic differentiation among subpopulations along the growth chamber was augmented, yet remained homogenous. These results allow for greater understanding of axial bioreactor cultures, their microenvironment, and how well-established parameters of osteogenic differentiation affect bone tissue development. With this work, we have demonstrated the capability of tuning osteogenic differentiation of hMPCs through the application of fluid flow and the addition of exogenous growth factors. Such precise control allows for the culture of distinct subpopulation within one dynamic system for the use of complex engineered tissue constructs. Biotechnol. Bioeng. 2016;113: 1805-1813. © 2016 Wiley Periodicals, Inc.

Toward Development of iMesenchymal Stem Cells for Immunomodulatory Therapy

Mesenchymal stem cells (MSC) are under development as an immunomodulatory therapy. The anticipated immunomodulatory effects of MSC are broad, from direct inhibition of lymphocyte proliferation, induction of regulatory T and B cells, to resetting the immune system via a hit-and-run principle. There are endless flavors of MSC. Differences between MSC are originating from donors variation, differences in tissue of origin, the effects of culture conditions, and expansion time. Even standard culture conditions change the properties of MSC dramatically and generate MSC that only remotely resemble their in vivo counterparts. Adjustments in culture protocols can further emphasize properties of interest in MSC, thereby generating cells fitted for specific purposes. Culture improved immunomodulatory MSC can be designed to target particular immune disorders. In this review, we describe the observed and the desired immunomodulatory effects of MSC and propose approaches how MSC with optimal immunomodulatory properties can be developed.

Chondrogenic regeneration using bone marrow clots and a porous polycaprolactone-hydroxyapatite scaffold by three-dimensional printing

Scaffolds play an important role in directing three-dimensional (3D) cartilage regeneration. Our recent study reported the potential advantages of bone marrow clots (MC) in promoting extracellular matrix (ECM) scaffold chondrogenic regeneration. The aim of this study is to build a new scaffold for MC, with improved characteristics in mechanics, shaping, and biodegradability, compared to our previous study. To address this issue, this study prepared a 3D porous polycaprolactone (PCL)-hydroxyapatite (HA) scaffold combined with MC (Group A), while the control group (Group B) utilized a bone marrow stem cell seeded PCL-HA scaffold. The results of in vitro cultures and in vivo implantation demonstrated that although an initial obstruction of nutrient exchange caused by large amounts of fibrin and erythrocytes led to a decrease in the ratio of live cells in Group A, these scaffolds also showed significant improvements in cell adhesion, proliferation, and chondrogenic differentiation with porous recanalization in the later culture, compared to Group B. After 4 weeks of in vivo implantation, Group A scaffolds have a superior performance in DNA content, Sox9 and RunX2 expression, cartilage lacuna-like cell and ECM accumulation, when compared to Group B. Furthermore, Group A scaffold size and mechanics were stable during in vitro and in vivo experiments, unlike the scaffolds in our previous study. Our results suggest that the combination with MC proved to be a highly efficient, reliable, and simple new method that improves the biological performance of 3D PCL-HA scaffold. The MC-PCL-HA scaffold is a candidate for future cartilage regeneration studies.

In vitro and in vivo bone formation potential of surface calcium phosphate-coated polycaprolactone and polycaprolactone/bioactive glass composite scaffolds

In this study, polycaprolactone (PCL)-based composite scaffolds containing 50wt% of 45S5 Bioglass(®) (45S5) or strontium-substituted bioactive glass (SrBG) particles were fabricated into scaffolds using an additive manufacturing technique for bone tissue engineering purposes. The PCL scaffolds were surface coated with calcium phosphate (CaP) to enable further comparison of the osteoinductive potential of different scaffolds: PCL (control), PCL/CaP-coated, PCL/50-45S5 and PCL/50-SrBG scaffolds. The PCL/50-45S5 and PCL/50-SrBG composite scaffolds were reproducibly manufactured with a morphology highly resembling that of PCL only scaffolds. However, 50wt% loading of the bioactive glass (BG) particles into the PCL bulk decreased the scaffold's compressive Young's modulus. Coating of PCL scaffolds with CaP had a negligible effect on the scaffold's porosity and compressive Young's modulus. When immersed in culture media, BG dissolution ions (Si and Sr) were detected for up to 10weeks in the immersion media and surface precipitates were formed on both PCL/50-45S5 and PCL/50-SrBG scaffolds' surfaces, indicating good in vitro bioactivity. In vitro cell studies were conducted using sheep bone marrow stromal cells (BMSCs) under non-osteogenic or osteogenic conditioned media, and under static or dynamic culture environments. All scaffolds were able to support cell adhesion, growth and proliferation. However, when cultured in non-osteogenic media, only PCL/CaP, PCL/50-45S5 and PCL/50-SrBG scaffolds showed an up-regulation of osteogenic gene expression. Additionally, under a dynamic culture environment, the rate of cell growth, proliferation and osteoblast-related gene expression was enhanced across all scaffold groups. Subsequently, PCL/CaP, PCL/50-45S5 and PCL/50-SrBG scaffolds, with or without seeded cells, were implanted subcutaneously into nude rats for the evaluation of osteoinductivity potential. After 8 and 16weeks, host tissue infiltrated well into the scaffolds, but no mature bone formation was observed in any scaffolds groups.

STATEMENT OF SIGNIFICANCE

This novelty of this research work is that it provide a comprehensive comparison, both in vitro and in vivo, between 3 different composite materials widely used in the field of bone tissue engineering for their bone regeneration capabilities. The materials used in this study include polycaprolactone, 45S5 Bioglass, strontium-substituted bioactive glass and calcium phosphate. Additionally, the composite materials were fabricated into the form of 3D scaffolds using additive manufacturing technique, a widely used technique in tissue engineering.

Non-invasive monitoring of the osteogenic differentiation of human mesenchymal stem cells on a polycaprolactone scaffold using Raman imaging

Raman imaging allows the non-invasive and label-free monitoring of the preferred osteogenic differentiation of human mesenchymal stem cells on the polycaprolactone scaffolds.

Effect of Dynamic Culture and Periodic Compression on Human Mesenchymal Stem Cell Proliferation and Chondrogenesis

We have recently developed a bioreactor that can apply both shear and compressive forces to engineered tissues in dynamic culture. In our system, alginate hydrogel beads with encapsulated human mesenchymal stem cells (hMSCs) were cultured under different dynamic conditions while subjected to periodic, compressive force. A customized pressure sensor was developed to track the pressure fluctuations when shear forces and compressive forces were applied. Compared to static culture, dynamic culture can maintain a higher cell population throughout the study. With the application of only shear stress, qRT-PCR and immunohistochemistry revealed that hMSCs experienced less chondrogenic differentiation than the static group. The second study showed that chondrogenic differentiation was enhanced by additional mechanical compression. After 14 days, alcian blue staining showed more extracellular matrix formed in the compression group. The upregulation of the positive chondrogenic markers such as Sox 9, aggrecan, and type II collagen were demonstrated by qPCR. Our bioreactor provides a novel approach to apply mechanical forces to engineered cartilage. Results suggest that a combination of dynamic culture with proper mechanical stimulation may promote efficient progenitor cell expansion in vitro, thereby allowing the culture of clinically relevant articular chondrocytes for the treatment of articular cartilage defects.

Enhanced in vitro osteogenic differentiation of human fetal MSCs attached to 3D microcarriers versus harvested from 2D monolayers

BACKGROUND

Mesenchymal stem cells (MSCs) are of great interest in bone regenerative medicine due to their osteogenic potential and trophic effects. However, challenges to large-scale production of MSCs can hinder the translation of MSC therapies. 3D Microcarrier (MC)-based MSC culture presents a scalable and cost-effective alternative to conventional methods of expansion in 2D monolayers. Furthermore, biodegradable MCs may allow for MC-bound MSC delivery without enzymatic harvest for selected applications such as bone healing. However, the effects of cell expansion on microcarriers and enzymatic cell harvest on MSC phenotype and osteogenic differential potential are not well understood. In this study, we characterized human fetal MSCs (hfMSCs) after expansion in 3D microcarrier spinner or 2D monolayer cultures. Following expansion, we compared osteogenic differentiation of cultures seeded with 3D MC-harvested, 3D MC-bound and conventional 2D monolayer (MNL)-harvested cells when cultured in osteogenic induction media on collagen-coated plates.

RESULTS

Fetal MSCs expanded on both 3D agitated Microcarriers (MC) and 2D Plastic static monolayer (MNL) cultures express high levels of MSC surface markers. MC-harvested hfMSCs displayed higher expression of early osteogenic genes but slower mineralization kinetics compared to MNL-harvested MSCs during osteogenic induction. However, in the comparison between MC-bound and MC-harvested hfMSCs, osteogenic genes were upregulated and mineralization kinetics was accelerated in the former condition. Importantly, 3D MC-bound hfMSCs expressed higher levels of osteogenic genes and displayed either higher or equivalent levels of mineralization, depending on the cell line, compared to the classical monolayer cultures use in the literature (MNL-harvested hfMSCs).

CONCLUSION

Beyond the processing and scalability advantages of the microcarrier culture, hfMSCs attached to MCs undergo robust osteogenic differentiation and mineralization compared to enzymatically harvested cells. Thus biodegradable/biocompatible MCs which can potentially be used for cell expansion as well as a scaffold for direct in vivo delivery of cells may have advantages over the current methods of monolayer-expansion and delivery post-harvest for bone regeneration applications.

Distribution and Viability of Fetal and Adult Human Bone Marrow Stromal Cells in a Biaxial Rotating Vessel Bioreactor after Seeding on Polymeric 3D Additive Manufactured Scaffolds

One of the conventional approaches in tissue engineering is the use of scaffolds in combination with cells to obtain mechanically stable tissue constructs in vitro prior to implantation. Additive manufacturing by fused deposition modeling is a widely used technique to produce porous scaffolds with defined pore network, geometry, and therewith defined mechanical properties. Bone marrow-derived mesenchymal stromal cells (MSCs) are promising candidates for tissue engineering-based cell therapies due to their multipotent character. One of the hurdles to overcome when combining additive manufactured scaffolds with MSCs is the resulting heterogeneous cell distribution and limited cell proliferation capacity. In this study, we show that the use of a biaxial rotating bioreactor, after static culture of human fetal MSCs (hfMSCs) seeded on synthetic polymeric scaffolds, improved the homogeneity of cell and extracellular matrix distribution and increased the total cell number. Furthermore, we show that the relative mRNA expression levels of indicators for stemness and differentiation are not significantly changed upon this bioreactor culture, whereas static culture shows variations of several indicators for stemness and differentiation. The biaxial rotating bioreactor presented here offers a homogeneous distribution of hfMSCs, enabling studies on MSCs fate in additive manufactured scaffolds without inducing undesired differentiation.

Bone-Forming Capacity and Biodistribution of Bone Marrow-Derived Stromal Cells Directly Loaded into Scaffolds: A Novel and Easy Approach for Clinical Application of Bone Regeneration

In the context of clinical applications of bone regeneration, cell seeding into scaffolds needs to be safe and easy. Moreover, cell density also plays a crucial role in the development of efficient bone tissue engineering constructs. The aim of this study was to develop and evaluate a simple and rapid cell seeding procedure on hydroxyapatite/ β-tricalcium phosphate (HA/βTCP), as well as define optimal cell density and control the biodistribution of grafted cells. To this end, human bone marrow-derived stromal cells (hBMSCs) were seeded on HA/βTCP scaffolds, and we have compared bone formation using an ectopic model. Our results demonstrated a significantly higher bone-forming capacity of hBMSCs directly loaded on HA/βTCP during surgery compared to hBMSCs preseeded for 7 days in vitro on HA/βTCP before ectopic implantation. The extent of new bone formation increases with increasing hBMSC densities quantitatively, qualitatively, and in frequency. Also, this study showed that grafted hBMSCs remained confined to the implantation site and did not spread toward other tissues, such as liver, spleen, lungs, heart, and kidneys. In conclusion, direct cell loading into a scaffold during surgery is more efficient for bone regeneration, as well as quick and safe. Therefore direct cell loading is suitable for clinical requirements and cell production control, making it a promising approach for orthopedic applications. Moreover, our results have provided evidence that the formation of a mature bone organ containing hematopoietic islets needs a sufficiently high local density of grafted hBMSCs, which should guide the optimal dose of cells for clinical use.

Physical and Biological Modification of Polycaprolactone Electrospun Nanofiber by Panax Ginseng Extract for Bone Tissue Engineering Application

Medicinal plants as a therapeutic agent with osteogenic properties can enhance fracture-healing process. In this study, the osteo-inductive potential of Asian Panax Ginseng root extract within electrospun polycaprolactone (PCL) based nanofibers has been investigated. Scanning electron microscopy images revealed that all nanofibers were highly porous and beadles with average diameter ranging from 250 to 650 nm. The incorporation of ginseng extract improved the physical characteristics (i.e., hydrophilicity) of PCL nanofibers, as well as the mechanical properties. Although ginseng extract increased the degradation rate of pure PCL nanofibers, the porous structure and morphology of fibers did not change significantly after 42 days. It was found that nanofibrous scaffolds containing ginseng extract had higher proliferation (up to ~1.5 fold) compared to the pristine PCL. The qRT-PCR analysis demonstrated the addition of ginseng extract into PCL nanofibers induced significant expression of osteogenic genes (Osteocalcin, Runx-2 and Col-1) in MSCs in a concentration dependent manner. Moreover, higher calcium content, alkaline phosphatase activity and higher mineralization of MSCs were observed compared to the pristine PCL fibers. Our results indicated the promising potential of ginseng extract as an additive to enhance osteo-inductivity, mechanical and physical properties of PCL nanofibers for bone tissue engineering application.

Natural-based nanocomposites for bone tissue engineering and regenerative medicine: a review

Tissue engineering and regenerative medicine has been providing exciting technologies for the development of functional substitutes aimed to repair and regenerate damaged tissues and organs. Inspired by the hierarchical nature of bone, nanostructured biomaterials are gaining a singular attention for tissue engineering, owing their ability to promote cell adhesion and proliferation, and hence new bone growth, compared with conventional microsized materials. Of particular interest are nanocomposites involving biopolymeric matrices and bioactive nanosized fillers. Biodegradability, high mechanical strength, and osteointegration and formation of ligamentous tissue are properties required for such materials. Biopolymers are advantageous due to their similarities with extracellular matrices, specific degradation rates, and good biological performance. By its turn, calcium phosphates possess favorable osteoconductivity, resorbability, and biocompatibility. Herein, an overview on the available natural polymer/calcium phosphate nanocomposite materials, their design, and properties is presented. Scaffolds, hydrogels, and fibers as biomimetic strategies for tissue engineering, and processing methodologies are described. The specific biological properties of the nanocomposites, as well as their interaction with cells, including the use of bioactive molecules, are highlighted. Nanocomposites in vivo studies using animal models are also reviewed and discussed.

Functionalization of polycaprolactone scaffolds with hyaluronic acid and β-TCP facilitates migration and osteogenic differentiation of human dental pulp stem cells in vitro

In this study, we sought to assess the osteogenic potential of human dental pulp stem cells (DPSCs) on three different polycaprolactone (PCL) scaffolds. The backbone structure of the scaffolds was manufactured by fused deposition modeling (PCL scaffold). The composition and morphology was functionalized in two of the scaffolds. The first underwent thermal induced phase separation of PCL infused into the pores of the PCL scaffold. This procedure resulted in a highly variable micro- and nanostructured porous (NSP), interconnected, and isotropic tubular morphology (NSP-PCL scaffold). The second scaffold type was functionalized by dip-coating the PCL scaffold with a mixture of hyaluronic acid and β-TCP (HT-PCL scaffold). The scaffolds were cylindrical and measured 5 mm in height and 10 mm in diameter. They were seeded with 1×10(6) human DPSCs, a cell type known to express bone-related markers, differentiate into osteoblasts-like cells, and to produce a mineralized bone-like extracellular matrix. DPSCs were phenotypically characterized by flow cytometry for CD90(+), CD73(+), CD105(+), and CD14(-). DNA, ALP, and Ca(2+) assays and real-time quantitative polymerase chain reaction for genes involved in osteogenic differentiation were analyzed on day 1, 7, 14, and 21. Cell viability and distribution were assessed on day 1, 7, 14, and 21 by fluorescent-, scanning electron-, and confocal microscopy. The results revealed that the DPSCs expressed relevant gene expression consistent with osteogenic differentiation. The NSP-PCL and HT-PCL scaffolds promoted osteogenic differentiation and Ca(2+) deposition after 21 days of cultivation. Different gene expressions associated with mature osteoblasts were upregulated in these two scaffold types, suggesting that the methods in which the scaffolds promote osteogenic differentiation, depends on functionalization approaches. However, only the HT-PCL scaffold was also able to support cell proliferation and cell migration resulting in even cell dispersion throughout the scaffold. In conclusion, DPSCs could be a possible alternate cell source for bone tissue engineering. The HT-PCL scaffold showed promising results in terms of promoting cell migration and osteogenic differentiation, which warrants future in vivo studies.

Synergistic effect of sustained release of growth factors and dynamic culture on osteoblastic differentiation of mesenchymal stem cells

Microparticles have been utilized as delivery vehicles of soluble factors to modify cellular behavior and therefore enhance tissue engineering regeneration. When incorporated into three-dimensional systems, microparticles can provide geometrical and temporal controlled release of bioactive agents, such as growth factors (GFs) to surrounding cells. This study investigates the effect of GFs release from biopolymer microparticles on osteoblastic differentiation of human mesenchymal stem cells (hMSCs) encapsulated in calcium (Ca)-alginate scaffolds while cultured in a tubular perfusion system bioreactor system. Empirical and deterministic models were used to demonstrate that poly(D,L-lactic-co-glycolic acid)-encapsulated GFs would result in a delayed release profile compared to GFs encapsulated into scaffolds directly. We hypothesized that the dual delivery of human bone-morphogenetic protein 2 (hBMP2) and human vascular endothelial growth factor to cells in dynamic culture would provide molecular and physical cues to promote differentiation. Results indicated that the exposures of hBMP2 and dynamic flow are sufficient in enhancing the osteoblastic differentiation pathway compared to no GF addition and static culture. The GF delivery system in a dynamic flow environment resulted in a synergistic effect on osteoblastic differentiation of hMSCs.