Differences between in vitro viability and differentiation and in vivo bone-forming efficacy of human mesenchymal stem cells cultured on PCL–TCP scaffolds

Concise Review: Multifaceted Characterization of Human Mesenchymal Stem Cells for Use in Regenerative Medicine

Mesenchymal stem cells (MSC) hold great potential for regenerative medicine because of their ability for self-renewal and differentiation into tissue-specific cells such as osteoblasts, chondrocytes, and adipocytes. MSCs orchestrate tissue development, maintenance and repair, and are useful for musculoskeletal regenerative therapies to treat age-related orthopedic degenerative diseases and other clinical conditions. Importantly, MSCs produce secretory factors that play critical roles in tissue repair that support both engraftment and trophic functions (autocrine and paracrine). The development of uniform protocols for both preparation and characterization of MSCs, including standardized functional assays for evaluation of their biological potential, are critical factors contributing to their clinical utility. Quality control and release criteria for MSCs should include cell surface markers, differentiation potential, and other essential cell parameters. For example, cell surface marker profiles (surfactome), bone-forming capacities in ectopic and orthotopic models, as well as cell size and granularity, telomere length, senescence status, trophic factor secretion (secretome), and immunomodulation, should be thoroughly assessed to predict MSC utility for regenerative medicine. We propose that these and other functionalities of MSCs should be characterized prior to use in clinical applications as part of comprehensive and uniform guidelines and release criteria for their clinical-grade production to achieve predictably favorable treatment outcomes for stem cell therapy. Stem Cells Translational Medicine 2017;6:2173-2185.

Mesenchymal stromal/stem cell separation methods: concise review

Mesenchymal stem (stromal) cells (MSCs) possess unique biological characteristics such as plasticity, long term self-renewal, secretion of various bioactive molecules and ability of active migration to the diseased tissues that make them unique tool for regenerative medicine, nowadays. Until now MSCs were successfully derived from many tissue sources including bone marrow, umbilical cord, adipose tissue, dental pulp etc. The crucial step prior to their in vitro expansion, banking or potential clinical application is their separation. This review article aims to briefly describe the main MSCs separations techniques currently available, their basic principles, as well as their advantages and limits. In addition the attention is paid to the markers presently applicable for immunoaffinity-based separation of MSCs from different tissues and organs.

In Vitro Maturation and In Vivo Integration and Function of an Engineered Cell-Seeded Disc-like Angle Ply Structure (DAPS) for Total Disc Arthroplasty

Total disc replacement with an engineered substitute is a promising avenue for treating advanced intervertebral disc disease. Toward this goal, we developed cell-seeded disc-like angle ply structures (DAPS) and showed through in vitro studies that these constructs mature to match native disc composition, structure, and function with long-term culture. We then evaluated DAPS performance in an in vivo rat model of total disc replacement; over 5 weeks in vivo, DAPS maintained their structure, prevented intervertebral bony fusion, and matched native disc mechanical function at physiologic loads in situ. However, DAPS rapidly lost proteoglycan post-implantation and did not integrate into adjacent vertebrae. To address this, we modified the design to include polymer endplates to interface the DAPS with adjacent vertebrae, and showed that this modification mitigated in vivo proteoglycan loss while maintaining mechanical function and promoting integration. Together, these data demonstrate that cell-seeded engineered discs can replicate many characteristics of the native disc and are a viable option for total disc arthroplasty.

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.

* Mimicking the Biochemical and Mechanical Extracellular Environment of the Endochondral Ossification Process to Enhance the In Vitro Mineralization Potential of Human Mesenchymal Stem Cells

Chondrogenesis and mechanical stimulation of the cartilage template are essential for bone formation through the endochondral ossification process in vivo. Recent studies have demonstrated that in vitro regeneration strategies that mimic these aspects separately, either chondrogenesis or mechanical stimulation, can promote mineralization to a certain extent both in vitro and in vivo. However, to date no study has sought to incorporate both the formation of the cartilage template and the application of mechanical stimulation simultaneously to induce osteogenesis. In this study, we test the hypothesis that mimicking both the biochemical and mechanical extracellular environment arising during endochondral ossification can enhance the in vitro mineralization potential of human mesenchymal stem cells (hMSCs). hMSC aggregates were cultured for 21 days under the following culture conditions; (1) Growth Medium - hydrostatic pressure (HP), (2) Chondrogenic Priming-HP, (3) Growth Medium + HP, and (4) Chondrogenic Priming +HP. Each group was then further cultured for another 21 days in the presence of osteogenic growth factors without HP. Biochemical (DNA, sulfate glycosaminoglycan, hydroxyproline, alkaline phosphatase activity, and calcium), histological (Alcian Blue and Alizarin Red), and immunohistological (Col I, II, and X, and BSP-2) analyses were conducted to investigate chondrogenic and osteogenic differentiation at various time points (14, 21, 35, and 42 days). Our results showed the application of HP-induced chondrogenesis similar to that of chondrogenic priming, but interestingly, there was a reduction in hypertrophy markers (collagen type X) by applying HP alone versus chondrogenic priming alone. Moreover, the results showed that both chondrogenic priming and HP in tandem during the priming period, followed by culture in osteogenic medium, accelerated the osteogenic potential of hMSCs.

Osteogenesis for postoperative temporal bone defects using human ear adipose-derived stromal cells and tissue engineering: An animal model study

Mastoidectomy, the removal of infected mastoid bones, is a common surgical procedure for the treatment of chronic otitis media. Persistent and recurrent otorrhea and accumulation of keratin debris following open cavity mastoidectomy are still bothersome issues for both patients and otologists. In this study, we used human ear adipose-derived stromal cells (hEASCs) in combination with polycaprolactone (PCL) scaffolds and osteogenic differentiation medium (ODM) to regenerate temporal bone defects. The hEASCs showed stem cell phenotypes, and these characteristics were maintained up to passage 5. Mastoid bulla and cranial bone defects were induced in Sprague-Dawley rats using AgNO₃ and burr hole drilling, respectively, and the rats were then divided into five groups: (1) control, (2) hEASCs, (3) hEASCs + ODM, (4) hEASCs + PCL scaffolds, and (5) hEASCs + PCL scaffolds + ODM. Osteogenesis was evaluated by micro-computed tomography and histology. Compared with the control group, the groups transplanted with hEASCs and PCL scaffolds had significantly higher bone formation along the periphery of the mastoid bulla area. Moreover, ODM synergistically enhanced bone formation in mastoid bulla defects. Our results suggest that combining hEASCs with PCL scaffolds represents a promising method for anatomical and functional reconstruction of postoperative temporal bone defects following mastoidectomy. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3493-3501, 2017.

* In Vivo Models for the Evaluation of the Osteogenic Potency of Bone Substitutes Seeded with Mesenchymal Stem Cells of Human Origin: A Concise Review

Research concerning bone substitutes is one of the most challenging fields in orthopedic research and has a high clinical relevance, especially since the currently available bone substitutes are limited in their osteostimulative capabilities. In vitro models for the evaluation of the properties of bone substitutes allow the use of human mesenchymal stem cells (hMSCs) seeded onto scaffolds, but suffer from the lack of a physiological environment for those cells. Most in vivo models include the use of non-hMSC and are therefore lacking in clinical relevance. To overcome these issues, in vivo models were created that allow the evaluation of hMSC-seeded bone substitutes, combining the advantages of the use of human cells with the physiological conditions of an organism in vivo. In brief, models usually aim for bone formation in immunocompromised rodents. The subcutaneous implantation of scaffolds is most widely performed, showing low complication rates along with good results, but suffering from inferior vascularization of the implants and the absence of the realistic structural and mechanical conditions of bone. Orthotopic implantation, for example in calvarian or long bone defects, provides the most appropriate surrounding for hMSC-seeded scaffolds. However, parallel host-induced bone formation is a major limitation. This review summarizes in vivo models for the evaluation of the osteogenic potency of bone substitutes seeded with mesenchymal stem cells of human origin.

3D biomimetic artificial bone scaffolds with dual-cytokines spatiotemporal delivery for large weight-bearing bone defect repair

It is a great challenge to prepare “functional artificial bone” for the repair of large segmental defect, especially in weight-bearing bones. In this study, bioactive HA/PCL composite scaffolds that possess anatomical structure as autogenous bone were fabricated by CT-guided fused deposition modeling technique. The scaffolds can provide mechanical support and possess osteoconduction property. Then the VEGF-165/BMP-2 loaded hydrogel was filled into biomimetic artificial bone spatially to introduce osteoinduction and angioinduction ability via sustained release of these cytokines. It has been revealed that the cytokine-loaded hydrogel possessed good biodegradability and could release the VEGF-165/BMP-2 sustainedly and steadily. The synergistic effect of these two cytokines showed significant stimulation on the osteogenic gene expresssion of osteoblast in vitro and ectopic ossification in vivo. The scaffolds were then implanted into the rabbit tibial defect sites (1.2 cm) for bone regeneration for 12 weeks, indicating the best repair of defect in vivo, which was superior to the pure hydrogel/scaffolds or one-cytokine loaded hydrogel/scaffolds and close to autogenous bone graft. The strategy to construct an “anatomy-structure-function” trinity system as functional artificial bone shows great potential in replacing autogenous bone graft and applying in large bone defect repair clinically in future.

Polymers for 3D Printing and Customized Additive Manufacturing

Additive manufacturing (AM) alias 3D printing translates computer-aided design (CAD) virtual 3D models into physical objects. By digital slicing of CAD, 3D scan, or tomography data, AM builds objects layer by layer without the need for molds or machining. AM enables decentralized fabrication of customized objects on demand by exploiting digital information storage and retrieval via the Internet. The ongoing transition from rapid prototyping to rapid manufacturing prompts new challenges for mechanical engineers and materials scientists alike. Because polymers are by far the most utilized class of materials for AM, this Review focuses on polymer processing and the development of polymers and advanced polymer systems specifically for AM. AM techniques covered include vat photopolymerization (stereolithography), powder bed fusion (SLS), material and binder jetting (inkjet and aerosol 3D printing), sheet lamination (LOM), extrusion (FDM, 3D dispensing, 3D fiber deposition, and 3D plotting), and 3D bioprinting. The range of polymers used in AM encompasses thermoplastics, thermosets, elastomers, hydrogels, functional polymers, polymer blends, composites, and biological systems. Aspects of polymer design, additives, and processing parameters as they relate to enhancing build speed and improving accuracy, functionality, surface finish, stability, mechanical properties, and porosity are addressed. Selected applications demonstrate how polymer-based AM is being exploited in lightweight engineering, architecture, food processing, optics, energy technology, dentistry, drug delivery, and personalized medicine. Unparalleled by metals and ceramics, polymer-based AM plays a key role in the emerging AM of advanced multifunctional and multimaterial systems including living biological systems as well as life-like synthetic systems.

Bioactive-glass ceramic with two crystalline phases (BioS-2P) for bone tissue engineering

We aimed to evaluate the in vitro osteogenic and osteoinductive potentials of BioS-2P and its ability to promote in vivo bone repair. To investigate osteogenic potential, UMR-106 osteoblastic cells were cultured on BioS-2P and Bioglass 45S5 discs in osteogenic medium. The osteoinductive potential was evaluated using mesenchymal stem cells (MSCs) cultured on BioS-2P, Bioglass 45S5 and polystyrene in non-osteogenic medium. Rat bone calvarial defects were implanted with BioS-2P scaffolds alone or seeded with MSCs. UMR-106 proliferation was similar for both materials, while alkaline phosphatase (ALP) activity and mineralization were higher for BioS-2P. Bone sialoprotein (BSP), RUNX2 and osteopontin (OPN) gene expression and BSP, OPN, ALP and RUNX2 protein expression were higher on BioS-2P. For MSCs, ALP activity was higher on Bioglass 45S5 than on BioS-2P and was lower on polystyrene. All genes were highly expressed on bioactive glasses compared to polystyrene. BioS-2P scaffolds promoted in vivo bone formation without differences in the morphometric parameters at 4, 8 and 12 weeks. After 8 weeks, the combination of BioS-2P with MSCs did not increase the quantity of new bone compared to the BioS-2P alone. To stimulate osteoblast activity, drive MSC differentiation and promote bone formation, BioS-2P is a good choice as a scaffold for bone tissue engineering.

A Versatile Protocol for Studying Calvarial Bone Defect Healing in a Mouse Model

Animal models are vital tools for the preclinical development and testing of therapies aimed at providing solutions for several musculoskeletal disorders. For bone tissue engineering strategies addressing nonunion conditions, rodent models are particularly useful for studying bone healing in a controlled environment. The mouse calvarial defect model permits evaluation of drug, growth factor, or cell transplantation efficacy, together with offering the benefit of utilizing genetic models to study intramembranous bone formation within defect sites. In this study, we describe a detailed methodology for creating calvarial defects in mouse and present our results on bone morphogenetic protein-2-loaded fibrin scaffolds, thus advocating the utility of this functional orthotopic mouse model for the evaluation of therapeutic interventions (such as growth factors or cells) intended for successful bone regeneration therapies.

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

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

Three-dimensional printed polycaprolactone-based scaffolds provide an advantageous environment for osteogenic differentiation of human adipose-derived stem cells

The capacity of bone grafts to repair critical size defects can be greatly enhanced by the delivery of mesenchymal stem cells (MSCs). Adipose tissue is considered the most effective source of MSCs (ADSCs); however, the efficiency of bone regeneration using undifferentiated ADSCs is low. Therefore, this study proposes scaffolds based on polycaprolactone (PCL), which is widely considered a suitable MSC delivery system, were used as a three-dimensional (3D) culture environment promoting osteogenic differentiation of ADSCs. PCL scaffolds enriched with 5% tricalcium phosphate (TCP) were used. Human ADSCs were cultured in osteogenic medium both on the scaffolds and in 2D culture. Cell viability and osteogenic differentiation were tested at various time points for 42 days. The expression of RUNX2, collagen I, alkaline phosphatase, osteonectin and osteocalcin, measured by real-time polymerase chain reaction was significantly upregulated in 3D culture. Production of osteocalcin, a specific marker of terminally differentiated osteoblasts, was significantly higher in 3D cultures than in 2D cultures, as confirmed by western blot and immunostaining, and accompanied by earlier and enhanced mineralization. Subcutaneous implantation into immunodeficient mice was used for in vivo observations. Immunohistological and micro-computed tomography analysis revealed ADSC survival and activity toward extracellular production after 4 and 12 weeks, although heterotopic osteogenesis was not confirmed - probably resulting from insufficient availability of Ca/P ions. Additionally, TCP did not contribute to the upregulation of differentiation on the scaffolds in culture, and we postulate that the 3D architecture is a critical factor and provides a useful environment for prior-to-implantation osteogenic differentiation of ADSCs. Copyright © 2016 John Wiley & Sons, Ltd.

Application of selected scaffolds for bone tissue engineering: a systematic review

PURPOSE

The current systematic review investigated the results of application of some of the most commonly used scaffolds in conjugation with stem cells and growth factors in animal and clinical studies.

METHODS

A comprehensive electronic search was conducted according to the PRISMA guidelines in NCBI PMC and PubMed from January 1970 to December 2015 limited to English language publications with available full texts. In vivo studies in relation to "bone healing," "bone regeneration," and at least one of the following items were investigated: allograft, β-tricalcium phosphate, deproteinized bovine bone mineral, hydroxyapetite/tricalcium phosphate, nanohydroxyapatite, and composite scaffolds.

RESULTS

A total of 1252 articles were reviewed, and 46 articles completely fulfilled the inclusion criteria of this study. The highest bone regeneration has been achieved when combination of all three elements, given scaffolds, mesenchymal stem cells, and growth factors, were used. Among studies being reported in this review, bone marrow mesenchymal stem cells are the most studied mesenchymal stem cells, β-tricalcium phosphate is the most frequently used scaffold, and platelet-rich plasma is the most commonly used growth factor.

CONCLUSION

The current review aimed to inform reconstructive surgeons of how combinations of various mesenchymal stem cells, scaffolds, and growth factors enhance bone regeneration. The highest bone regeneration has been achieved when combination of all three elements, given scaffolds, mesenchymal stem cells, and growth factors, were used.

Content-Dependent Osteogenic Response of Nanohydroxyapatite: An in Vitro and in Vivo Assessment within Collagen-Based Scaffolds

The use of collagen-based scaffolds in orthopedic applications has been limited due to poor mechanical properties, but this may be overcome by the introduction of a stiffer supporting phase. Thus, we developed a synthesis technique to produce nonaggregating, stable nanohydroxyapatite (nHA) particles, permitting the fabrication of biomimetic-inspired scaffolds through the combination of nanosized HA with collagen, as found in native bone. This study evaluates the mechanical and biological impact of incorporating increasing concentrations of these nanoparticles into porous collagen scaffolds (1:1 and 5:1 weight ratios of nHA/collagen). Mechanical assessment demonstrated that increasing nHA incorporation correlated with increasing Young's moduli, which could be further amplified using cross-linking treatments. Typically, the porosity of a scaffold is sacrificed to produce a stiffer material; however, through the use of nanosized particles the inclusion of up to 5:1 nHA/collagen content still preserved the high 99% porosity of the composite scaffold, allowing for maximum cell infiltration. Moreover, increasing nHA presence induced significant bioactive responses, achieving superior cellular attachment and enhanced osteogenesis, promoting earlier expression of bone markers and cell-mediated mineralization versus nHA-free collagen controls. Interestingly, these content-dependent results observed in vitro did not directly translate in vivo. Instead, similar levels of bone formation were achieved within critical-sized rat calvarial defects, independent of nHA content, following acellular implantation. The addition of nHA, both 1:1 and 5:1, induced significantly higher levels of mineralization and de novo bone ingrowth versus collagen controls as demonstrated by microcomputed tomography, histological, and histomorphometric analyses. Ultimately, these results demonstrate the immense osteoinductivity of nonaggregated nanoparticles of HA incorporated into collagen-composite scaffolds and emphasize the importance of in vivo-based evaluation of therapies intended for clinical use.

Using Stem Cells to Grow Artificial Tissue for Peripheral Nerve Repair

Peripheral nerve injury continues to pose a clinical hurdle despite its frequency and advances in treatment. Unlike the central nervous system, neurons of the peripheral nervous system have a greater ability to regenerate. However, due to a number of confounding factors, this is often both incomplete and inadequate. The lack of supportive Schwann cells or their inability to maintain a regenerative phenotype is a major factor. Advances in nervous system tissue engineering technology have led to efforts to build Schwann cell scaffolds to overcome this and enhance the regenerative capacity of neurons following injury. Stem cells that can differentiate along a neural lineage represent an essential resource and starting material for this process. In this review, we discuss the different stem cell types that are showing promise for nervous system tissue engineering in the context of peripheral nerve injury. We also discuss some of the biological, practical, ethical, and commercial considerations in using these different stem cells for future clinical application.

Physical characteristics and biocompatibility of the polycaprolactone-biphasic calcium phosphate scaffolds fabricated using the modified melt stretching and multilayer deposition

Physical properties and biocompatibility of polycaprolactone (PCL)-biphasic calcium phosphate (BCP) scaffolds fabricated by the modified melt stretching and multilayer deposition (mMSMD) technique were evaluated in vitro. The PCL-BCP scaffold specimens included group A; PCL: BCP (wt%) = 80:20 and group B; 70:30. Mechanical properties of the scaffolds were assessed using a universal testing machine. Degradation behaviors of the scaffolds were assessed over 60 days. The amount of calcium and phosphate ions released from the scaffolds was detected over 30 days. Attachment and growth of osteoblasts on the scaffolds and indirect cytocompatibility to those cells were evaluated. The results showed that the scaffolds of both groups could withstand compressive forces on their superior aspect very well; however, their lateral aspect could only withstand light forces. Degradation of the scaffolds over 2 months was low (group A = 1.92 ± 0.47% and group B = 2.9 ± 1.3%,p > 0.05). The concentrations of calcium and phosphate ions released from the scaffolds of both groups significantly increased on day 7 (p < 0.05). Growth of the cells seemed to relate to accumulative increase in those ions. All results between the two ratios of the scaffolds were not statistically different.

Establishing criteria for human mesenchymal stem cell potency

This study sought to identify critical determinants of mesenchymal stem cell (MSC) potency using in vitro and in vivo attributes of cells isolated from the bone marrow of age‐ and sex‐matched donors. Adherence to plastic was not indicative of potency, yet capacity for long‐term expansion in vitro varied considerably between donors, allowing the grouping of MSCs from the donors into either those with high‐growth capacity or low‐growth capacity. Using this grouping strategy, high‐growth capacity MSCs were smaller in size, had greater colony‐forming efficiency, and had longer telomeres. Cell‐surface biomarker analysis revealed that the International Society for Cellular Therapy (ISCT) criteria did not distinguish between high‐growth capacity and low‐growth capacity MSCs, whereas STRO‐1 and platelet‐derived growth factor receptor alpha were preferentially expressed on high‐growth capacity MSCs. These cells also had the highest mean expression of the mRNA transcripts TWIST‐1 and DERMO‐1. Irrespective of these differences, both groups of donor MSCs produced similar levels of key growth factors and cytokines involved in tissue regeneration and were capable of multilineage differentiation. However, high‐growth capacity MSCs produced approximately double the volume of mineralized tissue compared to low‐growth capacity MSCs when assessed for ectopic bone‐forming ability. The additional phenotypic criteria presented in this study when combined with the existing ISCT minimum criteria and working proposal will permit an improved assessment of MSC potency and provide a basis for establishing the quality of MSCs prior to their therapeutic application. Stem Cells2015;33:1878–1891

Open-Source Selective Laser Sintering (OpenSLS) of Nylon and Biocompatible Polycaprolactone

Selective Laser Sintering (SLS) is an additive manufacturing process that uses a laser to fuse powdered starting materials into solid 3D structures. Despite the potential for fabrication of complex, high-resolution structures with SLS using diverse starting materials (including biomaterials), prohibitive costs of commercial SLS systems have hindered the wide adoption of this technology in the scientific community. Here, we developed a low-cost, open-source SLS system (OpenSLS) and demonstrated its capacity to fabricate structures in nylon with sub-millimeter features and overhanging regions. Subsequently, we demonstrated fabrication of polycaprolactone (PCL) into macroporous structures such as a diamond lattice. Widespread interest in using PCL for bone tissue engineering suggests that PCL lattices are relevant model scaffold geometries for engineering bone. SLS of materials with large powder grain size (~500 μm) leads to part surfaces with high roughness, so we further introduced a simple vapor-smoothing technique to reduce the surface roughness of sintered PCL structures which further improves their elastic modulus and yield stress. Vapor-smoothed PCL can also be used for sacrificial templating of perfusable fluidic networks within orthogonal materials such as poly(dimethylsiloxane) silicone. Finally, we demonstrated that human mesenchymal stem cells were able to adhere, survive, and differentiate down an osteogenic lineage on sintered and smoothed PCL surfaces, suggesting that OpenSLS has the potential to produce PCL scaffolds useful for cell studies. OpenSLS provides the scientific community with an accessible platform for the study of laser sintering and the fabrication of complex geometries in diverse materials.

3D printed structures for delivery of biomolecules and cells: tissue repair and regeneration

This paper reviews the current approaches to using 3D printed structures to deliver bioactive factors (e.g., cells and biomolecules) for tissue repair and regeneration.

Membranes combining chitosan and natural-origin nanoliposomes for tissue engineering

Chitosan thin films, elaborated by solvent casting, were functionalized by incorporating nanoliposomes based on natural vegetable (soy based) and marine (salmon derived) lecithin.

Bone Marrow Aspirate Concentrate in Animal Long Bone Healing: An Analysis of Basic Science Evidence

OBJECTIVES

Long bone fractures that fail to heal or show a delay in healing can lead to increased morbidity. Bone marrow aspirate concentrate (BMAC) containing bone mesenchymal stem cells (BMSCs) has been suggested as an autologous biologic adjunct to aid long bone healing. The purpose of this study was to systematically review the basic science in vivo evidence for the use of BMAC with BMSCs in the treatment of segmental defects in animal long bones.

DATA SOURCES

The PubMed/MEDLINE and EMBASE databases were screened in July 14-25, 2014.

STUDY SELECTION

The following search criteria were used: [("bmac" OR "bone marrow aspirate concentrate" OR "bmc" OR "bone marrow concentrate" OR "mesenchymal stem cells") AND ("bone" OR "osteogenesis" OR "fracture healing" OR "nonunion" OR "delayed union")].

DATA EXTRACTION

Three authors extracted data and analyzed for trends. Quality of evidence score was given to each study.

DATA SYNTHESIS

Results are presented as Hedge G standardized effect sizes with 95% confidence intervals.

RESULTS

The search yielded 35 articles for inclusion. Of studies reporting statistics, 100% showed significant increase in bone formation in the BMAC group on radiograph. Ninety percent reported significant improvement in earlier bone healing on histologic/histomorphometric assessment. Eighty-one percent reported a significant increase in bone area on micro-computed tomography. Seventy-eight percent showed a higher torsional stiffness for the BMAC-treated defects.

CONCLUSION

In the in vivo studies evaluated, BMAC confer beneficial effects on the healing of segmental defects in animal long bone models when compared with a control. Proof-of-concept has been established for BMAC in the treatment of animal segmental bone defects.

Bone marrow-derived mesenchymal stem cells assembled with low-dose BMP-2 in a three-dimensional hybrid construct enhances posterolateral spinal fusion in syngeneic rats

BACKGROUND CONTEXT

The combination of potent osteoinductive growth factor, functional osteoblastic cells, and osteoconductive materials to induce bone formation is a well-established concept in bone tissue engineering. However, supraphysiological dose of growth factor, such as recombinant human bone morphogenetic protein 2 (rhBMP-2), which is necessary in contemporary clinical application, have been reported to result in severe side effects.

PURPOSE

We hypothesize that the synergistic osteoinductive capacity of low-dose bone morphogenetic protein 2 (BMP-2) combined with undifferentiated bone marrow-derived stromal cells (BMSCs) is comparable to that of osteogenically differentiated BMSCs when used in a rodent model of posterolateral spinal fusion.

STUDY DESIGN/SETTING

A prospective study using a rodent model of posterolateral spinal fusion was carried out.

PATIENT SAMPLE

Thirty-six syngeneic Fischer rats comprised the patient sample.

METHODS

Six groups of implants were evaluated as follows (n=6): (1) 10 µg BMP-2 with undifferentiated BMSCs; (2) 10 µg BMP-2 with osteogenic-differentiated BMSCs; (3) 2.5 µg BMP-2 with undifferentiated BMSCs; (4) 2.5 µg BMP-2 with osteogenic-differentiated BMSCs; (5) 0.5 µg BMP-2 with undifferentiated BMSCs; and (6) 0.5 µg BMP-2 with osteogenic-differentiated BMSCs. Optimal in vitro osteogenic differentiation of BMSCs was determined by quantitative real-time polymerase chain reaction (qRT-PCR) gene analysis whereas in vivo bone formation capacity was evaluated by manual palpation, micro-computed tomography, and histology.

RESULTS

Rat BMSCs cultured in fibrin matrix that was loaded into the pores of medical-grade poly epsilon caprolactone tricalcium phosphate scaffolds differentiated toward osteogenic lineage by expressing osterix, runt-related transcription factor 2, and osteocalcium mRNA when supplemented with dexamethasone, ascorbic acid, and β-glycerophosphate. Whereas qRT-PCR revealed optimal increase in osteogenic genes expression after 7 days of in vitro culture, in vivo transplantation study showed that pre-differentiation of BMSCs before transplantation failed to promote posterolateral spinal fusion when co-delivered with low-dose BMP-2 (1/6 or 17% fusion rate). In contrast, combined delivery of undifferentiated BMSCs with low-dose BMP-2 (2.5 µg) demonstrated significantly higher fusion rate (4/6 or 67%) as well as significantly increased volume of new bone formation (p<.05).

CONCLUSION

In summary, this study supports the combination of undifferentiated BMSCs and low-dose rhBMP-2 for bone tissue engineering construct.

Effects of in vitro endochondral priming and pre-vascularisation of human MSC cellular aggregates in vivo

Introduction

During endochondral ossification, both the production of a cartilage template and the subsequent vascularisation of that template are essential precursors to bone tissue formation. Recent studies have found the application of both chondrogenic and vascular priming of mesenchymal stem cells (MSCs) enhanced the mineralisation potential of MSCs in vitro whilst also allowing for immature vessel formation. However, the in vivo viability, vascularisation and mineralisation potential of MSC aggregates that have been pre-conditioned in vitro by a combination of chondrogenic and vascular priming, has yet to be established. In this study, we test the hypothesis that a tissue regeneration approach that incorporates both chondrogenic priming of MSCs, to first form a cartilage template, and subsequent pre-vascularisation of the cartilage constructs, by co-culture with human umbilical vein endothelial cells (HUVECs) in vitro, will improve vessel infiltration and thus mineral formation once implanted in vivo.

Methods

Human MSCs were chondrogenically primed for 21 days, after which they were co-cultured with MSCs and HUVECs and cultured in endothelial growth medium for another 21 days. These aggregates were then implanted subcutaneously in nude rats for 4 weeks. We used a combination of bioluminescent imaging, microcomputed tomography, histology (Masson’s trichrome and Alizarin Red) and immunohistochemistry (CD31, CD146, and α-smooth actin) to assess the vascularisation and mineralisation potential of these MSC aggregates in vivo.

Results

Pre-vascularised cartilaginous aggregates were found to have mature endogenous vessels (indicated by α-smooth muscle actin walls and erythrocytes) after 4 weeks subcutaneous implantation, and also viable human MSCs (detected by bioluminescent imaging) 21 days after subcutaneous implantation. In contrast, aggregates that were not pre-vascularised had no vessels within the aggregate interior and human MSCs did not remain viable beyond 14 days. Interestingly, the pre-vascularised cartilaginous aggregates were also the only group to have mineralised nodules within the cellular aggregates, whereas mineralisation occurred in the alginate surrounding the aggregates for all other groups.

Conclusions

Taken together these results indicate that a combined chondrogenic priming and pre-vascularisation approach for in vitro culture of MSC aggregates shows enhanced vessel formation and increased mineralisation within the cellular aggregate when implanted subcutaneously in vivo.

Effect of heparin on the biological properties and molecular signature of human mesenchymal stem cells

Chronic use of heparin as an anti-coagulant for the treatment of thrombosis or embolism invokes many adverse systemic events including thrombocytopenia, vascular reactions and osteoporosis. Here, we addressed whether adverse effects might also be directed to mesenchymal stem cells that reside in the bone marrow compartment. Harvested human bone marrow-derived mesenchymal stem cells (hMSCs) were exposed to varying doses of heparin and their responses profiled. At low doses (<200 ng/ml), serial passaging with heparin exerted a variable effect on hMSC proliferation and multipotentiality across multiple donors, while at higher doses (≥ 100 μg/ml), heparin supplementation inhibited cell growth and increased both senescence and cell size. Gene expression profiling using cDNA arrays and RNA-seq analysis revealed pleiotropic effects of low-dose heparin on signaling pathways essential to hMSC growth and differentiation (including the TGFβ/BMP superfamily, FGFs, and Wnts). Cells serially passaged in low-dose heparin possess a donor-dependent gene signature that reflects their altered phenotype. Our data indicate that heparin supplementation during the culturing of hMSCs can alter their biological properties, even at low doses. This warrants caution in the application of heparin as a culture supplement for the ex vivo expansion of hMSCs. It also highlights the need for careful evaluation of the bone marrow compartment in patients receiving chronic heparin treatment.

3D Printing of Scaffolds for Tissue Regeneration Applications

The current need for organ and tissue replacement, repair, and regeneration for patients is continually growing such that supply is not meeting demand primarily due to a paucity of donors as well as biocompatibility issues leading to immune rejection of the transplant. In order to overcome these drawbacks, scientists have investigated the use of scaffolds as an alternative to transplantation. These scaffolds are designed to mimic the extracellular matrix (ECM) by providing structural support as well as promoting attachment, proliferation, and differentiation with the ultimate goal of yielding functional tissues or organs. Initial attempts at developing scaffolds were problematic and subsequently inspired an interest in 3D printing as a mode for generating scaffolds. Utilizing three-dimensional printing (3DP) technologies, ECM-like scaffolds can be produced with a high degree of complexity, where fine details can be included at a micrometer level. In this Review, the criteria for printing viable and functional scaffolds, scaffolding materials, and 3DP technologies used to print scaffolds for tissue engineering are discussed. Creating biofunctional scaffolds could potentially help to meet the demand by patients for tissues and organs without having to wait or rely on donors for transplantation.

Bioinspired nanostructured hydroxyapatite/collagen three-dimensional porous scaffolds for bone tissue engineering

A needle punching and bioinspired mineralization strategy has been developed to fabricate a collagen/hydroxyapatite porous scaffold for bone tissue engineering.

Optimized cell survival and seeding efficiency for craniofacial tissue engineering using clinical stem cell therapy

Traumatic injuries involving the face are very common, yet the clinical management of the resulting craniofacial deficiencies is challenging. These injuries are commonly associated with missing teeth, for which replacement is compromised due to inadequate jawbone support. Using cell therapy, we report the upper jaw reconstruction of a patient who lost teeth and 75% of the supporting jawbone following injury. A mixed population of bone marrow-derived autologous stem and progenitor cells was seeded onto β-tricalcium phosphate (β-TCP), which served as a scaffold to deliver cells directly to the defect. Conditions (temperature, incubation time) to achieve the highest cell survival and seeding efficiency were optimized. Four months after cell therapy, cone beam computed tomography and a bone biopsy were performed, and oral implants were placed to support an engineered dental prosthesis. Cell seeding efficiency (>81%) of the β-TCP and survival during the seeding process (94%) were highest when cells were incubated with β-TCP for 30 minutes, regardless of incubation temperature; however, at 1 hour, cell survival was highest when incubated at 4°C. Clinical, radiographic, and histological analyses confirmed that by 4 months, the cell therapy regenerated 80% of the original jawbone deficiency with vascularized, mineralized bone sufficient to stably place oral implants. Functional and aesthetic rehabilitation of the patient was successfully completed with installation of a dental prosthesis 6 months following implant placement. This proof-of-concept clinical report used an evidence-based approach for the cell transplantation protocol used and is the first to describe a cell therapy for craniofacial trauma reconstruction.

3D artificial bones for bone repair prepared by computed tomography-guided fused deposition modeling for bone repair

The medical community has expressed significant interest in the development of new types of artificial bones that mimic natural bones. In this study, computed tomography (CT)-guided fused deposition modeling (FDM) was employed to fabricate polycaprolactone (PCL)/hydroxyapatite (HA) and PCL 3D artificial bones to mimic natural goat femurs. The in vitro mechanical properties, in vitro cell biocompatibility, and in vivo performance of the artificial bones in a long load-bearing goat femur bone segmental defect model were studied. All of the results indicate that CT-guided FDM is a simple, convenient, relatively low-cost method that is suitable for fabricating natural bonelike artificial bones. Moreover, PCL/HA 3D artificial bones prepared by CT-guided FDM have more close mechanics to natural bone, good in vitro cell biocompatibility, biodegradation ability, and appropriate in vivo new bone formation ability. Therefore, PCL/HA 3D artificial bones could be potentially be of use in the treatment of patients with clinical bone defects.

In vivo ectopic implantation model to assess human mesenchymal progenitor cell potential

Clinical interest on human mesenchymal progenitor cells (hMPC) relies on their potential applicability in cell-based therapies. An in vitro characterization is usually performed in order to define MPC potency. However, in vitro predictions not always correlate with in vivo results and thus there is no consensus in how to really assess cell potency. Our goal was to provide an in vivo testing method to define cell behavior before therapeutic usage, especially for bone tissue engineering applications. In this context, we wondered whether bone marrow stromal cells (hBMSC) would proceed in an osteogenic microenvironment. Based on previous approaches, we developed a fibrin/ceramic/BMP-2/hBMSCs compound. We implanted the compound during only 2 weeks in NOD-SCID mice, either orthotopically to assess its osteoinductive property or subcutaneously to analyze its adequacy as a cell potency testing method. Using fluorescent cell labeling and immunohistochemistry techniques, we could ascertain cell differentiation to bone, bone marrow, cartilage, adipocyte and fibrous tissue. We observed differences in cell potential among different batches of hBMSCs, which did not strictly correlate with in vitro analyses. Our data indicate that the method we have developed is reliable, rapid and reproducible to define cell potency, and may be useful for testing cells destined to bone tissue engineering purposes. Additionally, results obtained with hMPCs from other sources indicate that our method is suitable for testing any potentially implantable mesenchymal cell. Finally, we propose that this model could successfully be employed for bone marrow niche and bone tumor studies.

The osteogenesis of bone marrow stem cells on mPEG-PCL-mPEG/hydroxyapatite composite scaffold via solid freeform fabrication

The study described a novel bone tissue scaffold fabricated by computer-aided, air pressure-aided deposition system to control the macro- and microstructure precisely. The porcine bone marrow stem cells (PBMSCs) seeded on either mPEG-PCL-mPEG (PCL) or mPEG-PCL-mPEG/hydroxyapatite (PCL/HA) composite scaffold were cultured under osteogenic medium to test the ability of osteogenesis in vitro. The experimental outcomes indicated that both scaffolds possessed adequate pore size, porosity, and hydrophilicity for the attachment and proliferation of PBMSCs and the PBMSCs expressed upregulated genes of osteogensis and angiogenesis in similar manner on both scaffolds. The major differences between these two types of the scaffolds were the addition of HA leading to higher hardness of PCL/HA scaffold, cell proliferation, and VEGF gene expression in PCL/HA scaffold. However, the in vivo bone forming efficacy between PBMSCs seeded PCL and PCL/HA scaffold was different from the in vitro results. The outcome indicated that the PCL/HA scaffold which had bone-mimetic environment due to the addition of HA resulted in better bone regeneration and mechanical strength than those of PCL scaffold. Therefore, providing a bone-mimetic scaffold is another crucial factor for bone tissue engineering in addition to the biocompatibility, 3D architecture with high porosity, and interpored connection.

In vivo gene activity of human mesenchymal stem cells after scaffold-mediated local transplantation

Functional activation of stem cells after transplantation is a main concern in stem cell therapy. For local transplantation, mesenchymal stem cells (MSCs) are usually administered via scaffolds, either by direct implantation or after preculturing of cells, and it is unclear which is better for the activation of transplanted cells. In this study, we investigated the in vivo gene expression activity of human MSCs (hMSCs) transplanted into calvarial defects either directly post-seeding on collagen sponges (Group 1) or after overnight in vitro culturing post-seeding (Group 2). Real-time reverse transcription-polymerase chain reaction at days 7 and 14 after transplantation identified a time-dependent, rapid decrease in gene expression by the hMSCs, which in Group 1 was slightly more attenuated than in Group 2. Both groups exhibited a limited range of human-specific gene expression, which involved type I collagen (ColI), fibronectin, stromal cell-derived factor (SDF-1), and osteoprotegerin. Among these, ColI expression was the most efficient, with higher levels in Group 1 than Group 2. There was a lack of evidence for the expression of osteoblast differentiation-related markers or trophic factors, while resident cells showed clear expression of those genes. Rat-specific β-actin expression in Group 2 was least among the scaffold control, Group 1, and Group 2, and this pattern was repeated in the expression of other rat osteogenic genes. Group 1 transplants positively influenced the osteogenic process of the defect tissue in part, and rat IGF-1 expression was significantly increased in Group 1. This tendency of gene expression by hMSCs in a rat model was very similar to what was observed in transplantations using immunodeficient mice. The current study showed that a main gene expressed by transplanted hMSCs during the initial weeks following transplantation is ColI, with a lack of differentiation-related markers or growth factor expression by hMSCs. Our data suggest that direct transplantation of hMSCs loaded on a collagen sponge is more efficient for gene activation in transplanted hMSCs, and more favorable to the local host tissue than transplantation after preculturing of cells.

Combined effect of three types of biophysical stimuli for bone regeneration

Pretreatment using various types of biophysical stimuli could provide appropriate potential to cells during construction of the engineered tissue in vitro. We hypothesized that multiple combinations of these biophysical stimuli could enhance osteogenic differentiation in vitro and bone formation in vivo. Cyclic strain, an electromagnetic field, and ultrasound were selected and combined as effective stimuli for osteogenic differentiation using a developed bioreactor. Here we report the experimental evaluation of the osteogenic effects of various combinations of three different biophysical stimuli in vitro and in vivo using human adipose-derived stem cells (ASCs). Osteogenic differentiation of ASCs was accelerated by multiple-combination biophysical stimulation in vitro. However, both single stimulation and double-combination stimulation were sufficient to accelerate bone regeneration in vivo, while the osteogenic marker expression of those groups was not as high as that of triple-combination stimulation in vitro. We inferred from these data that ASCs appropriately differentiated into the osteogenic lineage by biophysical stimulation could be a better option for accelerating bone formation in vivo than relatively undifferentiated or completely differentiated ASCs. Although many questions remain about the mechanisms of combined effects of various biophysical stimuli, this approach could be a more powerful tool for bone tissue regeneration.

Concise review: cell-based strategies in bone tissue engineering and regenerative medicine

Cellular strategies play an important role in bone tissue engineering and regenerative medicine (BTE/RM). Variability in cell culture procedures (e.g., cell types, cell isolation and expansion, cell seeding methods, and preculture conditions before in vivo implantation) may influence experimental outcome. Meanwhile, outcomes from initial clinical trials are far behind those of animal studies, which is suggested to be related to insufficient nutrient and oxygen supply inside the BTE/RM constructs as some complex clinical implementations require bone regeneration in too large a quantity. Coculture strategies, in which angiogenic cells are introduced into osteogenic cell cultures, might provide a solution for improving vascularization and hence increasing bone formation for cell-based constructs. So far, preclinical studies have demonstrated that cell-based tissue-engineered constructs generally induce more bone formation compared with acellular constructs. Further, cocultures have been shown to enhance vascularization and bone formation compared with monocultures. However, translational efficacy from animal studies to clinical use requires improvement, and the role implanted cells play in clinical bone regeneration needs to be further elucidated. In view of this, the present review provides an overview of the critical procedures during in vitro and in vivo phases for cell-based strategies (both monoculture and coculture) in BTE/RM to achieve more standardized culture conditions for future studies, and hence enhance bone formation.

Developmental-like bone regeneration by human embryonic stem cell-derived mesenchymal cells

The in vivo osteogenesis potential of mesenchymal-like cells derived from human embryonic stem cells (hESC-MCs) was evaluated in vivo by implantation on collagen/hydroxyapatite scaffolds into calvarial defects in immunodeficient mice. This study is novel because no osteogenic or chondrogenic differentiation protocols were applied to the cells prior to implantation. After 6 weeks, X-ray, microCT, and histological analysis showed that the hESC-MCs had consistently formed a highly vascularized new bone that bridged the bone defect and seamlessly integrated with host bone. The implanted hESC-MCs differentiated in situ to functional hypertrophic chondrocytes, osteoblasts, and osteocytes forming new bone tissue via an endochondral ossification pathway. Evidence for the direct participation of the human cells in bone morphogenesis was verified by two separate assays: with Alu and by human mitochondrial antigen positive staining in conjunction with co-localized expression of human bone sialoprotein in histologically verified regions of new bone. The large volume of new bone in a calvarial defect and the direct participation of the hESC-MCs far exceeds that of previous studies and that of the control adult hMSCs. This study represents a key step forward for bone tissue engineering because of the large volume, vascularity, and reproducibility of new bone formation and the discovery that it is advantageous to not over-commit these progenitor cells to a particular lineage prior to implantation. The hESC-MCs were able to recapitulate the mesenchymal developmental pathway and were able to repair the bone defect semi-autonomously without preimplantation differentiation to osteo- or chondroprogenitors.

Bone Regeneration Based on Tissue Engineering Conceptions - A 21st Century Perspective

The role of Bone Tissue Engineering in the field of Regenerative Medicine has been the topic of substantial research over the past two decades. Technological advances have improved orthopaedic implants and surgical techniques for bone reconstruction. However, improvements in surgical techniques to reconstruct bone have been limited by the paucity of autologous materials available and donor site morbidity. Recent advances in the development of biomaterials have provided attractive alternatives to bone grafting expanding the surgical options for restoring the form and function of injured bone. Specifically, novel bioactive (second generation) biomaterials have been developed that are characterised by controlled action and reaction to the host tissue environment, whilst exhibiting controlled chemical breakdown and resorption with an ultimate replacement by regenerating tissue. Future generations of biomaterials (third generation) are designed to be not only osteoconductive but also osteoinductive, i.e. to stimulate regeneration of host tissues by combining tissue engineering and in situ tissue regeneration methods with a focus on novel applications. These techniques will lead to novel possibilities for tissue regeneration and repair. At present, tissue engineered constructs that may find future use as bone grafts for complex skeletal defects, whether from post-traumatic, degenerative, neoplastic or congenital/developmental "origin" require osseous reconstruction to ensure structural and functional integrity. Engineering functional bone using combinations of cells, scaffolds and bioactive factors is a promising strategy and a particular feature for future development in the area of hybrid materials which are able to exhibit suitable biomimetic and mechanical properties. This review will discuss the state of the art in this field and what we can expect from future generations of bone regeneration concepts.

Predicting the elastic properties of selective laser sintered PCL/β-TCP bone scaffold materials using computational modelling

This study assesses the ability of finite element (FE) models to capture the mechanical behaviour of sintered orthopaedic scaffold materials. Individual scaffold struts were fabricated from a 50:50 wt% poly-ε-caprolactone (PCL)/β-tricalcium phosphate (β-TCP) blend, using selective laser sintering. The tensile elastic modulus of single struts was determined experimentally. High resolution FE models of single struts were generated from micro-CT scans (28.8 μm resolution) and an effective strut elastic modulus was calculated from tensile loading simulations. Three material assignment methods were employed: (1) homogeneous PCL elastic constants, (2) composite PCL/β-TCP elastic constants based on rule of mixtures, and (3) heterogeneous distribution of micromechanically-determined elastic constants. In comparison with experimental results, the use of homogeneous PCL properties gave a good estimate of strut modulus; however it is not sufficiently representative of the real material as it neglects the β-TCP phase. The rule of mixtures method significantly overestimated strut modulus, while there was no significant difference between strut modulus evaluated using the micromechanically-determined elastic constants and experimentally evaluated strut modulus. These results indicate that the multi-scale approach of linking micromechanical modelling of the sintered scaffold material with macroscale modelling gives an accurate prediction of the mechanical behaviour of the sintered structure.

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

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