Human mesenchymal stem cell position within scaffolds influences cell fate during dynamic culture

Early Osteogenic-Induced Adipose-Derived Stem Cells and Canine Bone Regeneration Potential Analyzed Using Biodegradable Scaffolds

The complex process of bone regeneration is influenced by factors such as inflammatory responses, tissue interactions, and progenitor cells. Currently, multiple traumas can interfere with fracture healing, causing the prolonging or failure of healing. In these cases, bone grafting is the most effective treatment. However, there are several drawbacks, such as morbidity at the donor site and availability of suitable materials. Advantages have been provided in this field by a variety of stem cell types. Adipose-derived stem cells (ASCs) show promise. In the radiological examination of this study, it was confirmed that the C/S group showed faster regeneration than the other groups, and Micro-CT also showed that the degree of bone formation in the defect area was highest in the C/S group. Compared to the control group, the change in cortical bone area in the defect area decreased in the sham group (0.874), while it slightly increased in the C/S group (1.027). An increase in relative vascularity indicates a decrease in overall bone density, but a weak depression filled with fibrous tissue was observed outside the compact bone. It was confirmed that newly formed cortical bone showed a slight difference in bone density compared to surrounding normal bone tissue due to increased distribution of cortical bone. In this study, we investigated the effect of bone regeneration by ADMSCs measured by radiation and pathological effects. These data can ultimately be applied to humans with important clinical applications in various bone diseases, regenerative, and early stages of formative differentiation.

Bioengineering of bone tissues using bioreactors for modulation of mechano-sensitivity in bone

Since the last decade, significant developments have been made in the area of bone tissue engineering associated with the emergence of novel biomaterials as well as techniques of scaffold fabrication. Despite all these developments, the translation from research findings to clinical applications is still very limited. Manufacturing the designed tissue constructs in a scalable manner remains the most challenging aspect. This bottleneck could be overcome by using bioreactors for the manufacture of these tissue constructs. In this review, a current scenario of bone injuries/defects and the cause of the translational gap between laboratory research and clinical use has been emphasized. Furthermore, various bioreactors being used in the area of bone tissue regeneration in recent studies have been highlighted along with their advantages and limitations. A vivid literature survey on the ideal attributes of bioreactors has been accounted, viz. dynamic, versatile, automated, reproducible and commercialization aspects. Additionally, the illustration of computational approaches that should be combined with bone tissue engineering experiments using bioreactors to simulate and optimize cellular growth in bone tissue constructs has also been done extensively.

Optical coherence tomography evaluation of the spatiotemporal effects of 3D bone marrow stromal cell culture using a bioreactor

Performing cell culture in a three-dimensional (3D) environment has various advantages. In cartilage tissue engineering, 3D in vitro cultures utilizing biomaterials and bioreactors can mimic the biological environment. However, the biggest drawback of these 3D culture systems is a limited ability to evaluate 3D cell distribution. Optical coherence tomography (OCT) has recently been used to evaluate 3D cellular morphology and structure in a timely manner. Here, we showed that OCT could be used to visually assess the distribution and the morphology of bone marrow stromal cells under chondrogenic 3D cultivation using alginate gels and rotary culture. In particular, OCT was able to visualize living cells embedded in alginate gels in a non-destructive and 3D manner, as well as quantitatively evaluate cell distribution and spheroid volume. We also found that cells were centralized in rotary culture but peripherally distributed in static culture, while rotary culture enhanced the hypertrophy of marrow stromal cells (MSCs) embedded in alginate gels. Together, our findings demonstrate that OCT can be used to evaluate the spatiotemporal effects of 3D cultivation using alginate gels and rotary culture. Therefore, this method may allow the observation of pre-cultured tissue over time and the optimization of culture conditions for regenerative tissue engineering.

Tympanic Membrane Collagen Expression by Dynamically Cultured Human Mesenchymal Stromal Cell/Star-Branched Poly(ε-Caprolactone) Nonwoven Constructs

The tympanic membrane (TM) primes the sound transmission mechanism due to special fibrous layers mainly of collagens II, III, and IV as a product of TM fibroblasts, while type I is less represented. In this study, human mesenchymal stromal cells (hMSCs) were cultured on star-branched poly(ε-caprolactone) (*PCL)-based nonwovens using a TM bioreactor and proper differentiating factors to induce the expression of the TM collagen types. The cell cultures were carried out for one week under static and dynamic conditions. Reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry (IHC) were used to assess collagen expression. A Finite Element Model was applied to calculate the stress distribution on the scaffolds under dynamic culture. Nanohydroxyapatite (HA) was used as a filler to change density and tensile strength of *PCL scaffolds. In dynamically cultured *PCL constructs, fibroblast surface marker was overexpressed, and collagen type II was revealed via IHC. Collagen types I, III and IV were also detected. Von Mises stress maps showed that during the bioreactor motion, the maximum stress in *PCL was double that in HA/*PCL scaffolds. By using a *PCL nonwoven scaffold, with suitable physico-mechanical properties, an oscillatory culture, and proper differentiative factors, hMSCs were committed into fibroblast lineage-producing TM-like collagens.

Aminated 3D Printed Polystyrene Maintains Stem Cell Proliferation and Osteogenic Differentiation

As 3D printing becomes more common and the technique is used to build culture platforms, it is imperative to develop surface treatments for specific responses. The advantages of aminating and oxidizing polystyrene (PS) for human mesenchymal stem cell (hMSC) proliferation and osteogenic differentiation are investigated. We find that ammonia (NH3) plasma incorporates amines while oxygen plasma adds carbonyl and carboxylate groups. Across 2D, 3D, and 3D dynamic culture, we find that the NH3- treated surfaces encouraged cell proliferation. Our results show that the NH3-treated scaffold was the only treatment allowing dynamic proliferation of hMSCs with little evidence of osteogenic differentiation. With osteogenic media, particularly in 3D culture, we find the NH3 treatment encouraged greater and earlier expression of RUNX2 and ALP. The NH3-treated PS scaffolds support hMSC proliferation without spontaneous osteogenic differentiation in static and dynamic culture. This work provides an opportunity for further investigations into shear profiling and coculture within the developed culture system toward developing a bone marrow niche model.

Development of surface functionalization strategies for 3D-printed polystyrene constructs

There is a growing interest in 3D printing to fabricate culture substrates; however, the surface properties of the scaffold remain pertinent to elicit targeted and expected cell responses. Traditional 2D polystyrene (PS) culture systems typically require surface functionalization (oxidation) to facilitate and encourage cell adhesion. Determining the surface properties which enhance protein adhesion from media and cellular extracellular matrix (ECM) production remains the first step to translating 2D PS systems to a 3D culture surface. Here we show that the presence of carbonyl groups to PS surfaces correlated well with successful adhesion of ECM proteins and sustaining ECM production of deposited human mesenchymal stem cells, if the surface has a water contact angle between 50° and 55°. Translation of these findings to custom-fabricated 3D PS scaffolds reveals carbonyl groups continued to enhance spreading and growth in 3D culture. Cumulatively, these data present a method for 3D printing PS and the design considerations required for understanding cell-material interactions. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2566-2578, 2019.

Trophoblast-endothelium signaling involves angiogenesis and apoptosis in a dynamic bioprinted placenta model

Trophoblast invasion and remodeling of the maternal spiral arteries are required for pregnancy success. Aberrant endothelium-trophoblast crosstalk may lead to preeclampsia, a pregnancy complication that has serious effects on both the mother and the baby. However, our understanding of the mechanisms involved in this pathology remains elementary because the current in vitro models cannot describe trophoblast-endothelium interactions under dynamic culture. In this study, we developed a dynamic three-dimensional (3D) placenta model by bioprinting trophoblasts and an endothelialized lumen in a perfusion bioreactor. We found the 3D printed perfusion bioreactor system significantly augmented responses of endothelial cells by encouraging network formations and expressions of angiogenic markers, cluster of differentiation 31 (CD31), matrix metalloproteinase-2 (MMP2), matrix metalloproteinase-9 (MMP9), and vascular endothelial growth factor A (VEGFA). Bioprinting favored colocalization of trophoblasts with endothelial cells, similar to in vivo observations. Additional analysis revealed that trophoblasts reduced the angiogenic responses by reducing network formation and motility rates while inducing apoptosis of endothelial cells. Moreover, the presence of endothelial cells appeared to inhibit trophoblast invasion rates. These results clearly demonstrated the utility and potential of bioprinting and perfusion bioreactor system to model trophoblast-endothelium interactions in vitro. Our bioprinted placenta model represents a crucial step to develop advanced research approach that will expand our understanding and treatment options of preeclampsia and other pregnancy-related pathologies.

A Fluidic Culture Platform for Spatially Patterned Cell Growth, Differentiation, and Cocultures

Stem cell cultures within perfusion bioreactors, while efficient in obtaining cell numbers, often lack the similarity to native tissues and consequently cell phenotype. We develop a three-dimensional (3D)-printed fluidic chamber for dynamic stem cell culture, with emphasis on control over flow and substrate curvature in a 3D environment, two physiologic features of native tissues. The chamber geometry, consisting of an array of vertical cylindrical pillars, facilitates actin-mediated localization of human mesenchymal stem cells (hMSCs) within ∼200 μm distance from the pillars, enabling spatial patterning of hMSCs and endothelial cells in cocultures and subsequent modulation of calcium signaling between these two essential cell types in the bone marrow microenvironment. Flow-enhanced osteogenic differentiation of hMSCs in growth media imposes spatial variations of alkaline phosphatase expression, which positively correlates with local shear stress. Proliferation of hMSCs is maintained within the chamber, exceeding the cell expansion in conventional static culture. The capability to manipulate cell spatial patterning, differentiation, and 3D tissue formation through geometry and flow demonstrates the culture chamber's relevant chemomechanical cues in stem cell microenvironments, thus providing an easy-to-implement tool to study interactions among substrate curvature, shear stress, and intracellular actin machinery in the tissue-engineered construct.

3D printing in cell culture systems and medical applications

3D printing plays an important role in various biomedical research applications including, but not limited to, culture systems and implantable devices. In this review, we discuss recent development in the applications of 3D printing technologies for clinically motivated research, particularly focusing on the fabrication of constructs subsequently incorporated with cells. Applications of this technology include pharmaceutical delivery, bioreactor culture platforms, acellular scaffolds, imaging modalities, and organ-on-a chip systems. Emphasis is placed on technological developments not possible without 3D printing technologies: where traditional manufacturing approaches would be cumbersome to demonstrate research objectives. The clinical applications of 3D printing are rapidly moving from the research to production phases and will certainly continue to grow, with ever increasing numbers of therapies becoming commercialized. The work discussed here holds promise for various applications in structural improvements, drug delivery, and physiology research.

A Perfusion Culture System for Assessing Bone Marrow Stromal Cell Differentiation on PLGA Scaffolds for Bone Repair

Biomaterials development for bone repair is currently hindered by the lack of physiologically relevant in vitro testing systems. Here we describe the novel use of a bi-directional perfusion bioreactor to support the long term culture of human bone marrow stromal cells (BMSCs) differentiated on polylactic co-glycolic acid (PLGA). Primary human BMSCs were seeded onto porous PLGA scaffolds and cultured in static vs. perfusion culture conditions for 21 days in osteogenic vs. control media. PLGA scaffolds were osteoconductive, supporting a mature osteogenic phenotype as shown by the upregulation of Runx2 and the early osteocyte marker E11. Perfusion culture enhanced the expression of osteogenic genes Osteocalcin and Osteopontin. Extracellular matrix deposition and mineralisation were spatially regulated within PLGA scaffolds in a donor dependant manner. This, together with the observed upregulation of Collagen type X suggested an environment permissive for the study of differentiation pathways associated with both intramembranous and endochondral ossification routes of bone healing. This culture system offers a platform to assess BMSC behavior on candidate biomaterials under physiologically relevant conditions. Use of this system may improve our understanding of the environmental cues orchestrating BMSC differentiation and enable fine tuning of biomaterial design as we develop tissue-engineered strategies for bone regeneration.

Segmental bone replacement via patient-specific, three-dimensional printed bioresorbable graft substitutes and their use as templates for the culture of mesenchymal stem cells under mechanical stimulation at various frequencies

The treatment of large segmental bone defects remains a challenge as infection, delayed union, and nonunion are common postoperative complications. A three-dimensional printed bioresorbable and physiologically load-sustaining graft substitute was developed to mimic native bone tissue for segmental bone repair. Fabricated from polylactic acid, this graft substitute is novel as it is readily customizable to accommodate the particular size and location of the segmental bone of the patient to be replaced. Inspired by the structure of the native bone tissue, the graft substitute exhibits a gradient in porosity and pore size in the radial direction and exhibit mechanical properties similar to those of the native bone tissue. The graft substitute can serve as a template for tissue constructs via seeding with stem cells. The biocompatibility of such templates was tested under in vitro conditions using a dynamic culture of human mesenchymal stem cells. The effects of the mechanical loading of cell-seeded templates under in vitro conditions were assessed via subjecting the tissue constructs to 28 days of daily mechanical stimulation. The frequency of loading was found to have a significant effect on the rate of mineralization, as the alkaline phosphatase activity and calcium deposition were determined to be particularly high at the typical walking frequency of 2 Hz, suggesting that mechanical stimulation plays a significant role in facilitating the healing process of bone defects. Utilization of such patient-specific and biocompatible graft substitutes, coupled with patient's bone marrow cells seeded and exposed to mechanical stimulation of 2 Hz have the potential of reducing significant volumes of cadaveric tissue required, improving long-term graft stability and incorporation, and alleviating financial burdens associated with delayed or failed fusions of long bone defects.

Cell Patterning Method on a Clinically Ubiquitous Culture Dish Using Acoustic Pressure Generated From Resonance Vibration of a Disk-Shaped Ultrasonic Transducer

Cell patterning methods have been previously reported for cell culture. However, these methods use inclusions or devices that are not used in general cell culture and that might affect cell functionality. Here, we report a cell patterning method that can be conducted on a general cell culture dish without any inclusions by employing a resonance vibration of a disk-shaped ultrasonic transducer located under the dish. A resonance vibration with a single nodal circle patterned C2C12 myoblasts into a circular shape on the dish with 10-min exposure of the vibration with maximum peak-peak amplitude of 10 μm[Formula: see text]. Furthermore, the relationship between the amplitude distribution of the transducer and the cell density in the patterned sample could be expressed as a linear function, and there was a clear threshold of amplitude for cell adhesion. To evaluate the cell function of the patterned cells, we conducted proliferation and protein assays at 120-h culture after patterning. Our results showed that the cell proliferation rate did not decrease and the expression of cellular proteins was unchanged. Thus, we conclude, this method can successfully pattern cells in the clinically ubiquitous culture dish, while maintaining cell functionality.

Looking into the Future: Toward Advanced 3D Biomaterials for Stem-Cell-Based Regenerative Medicine

Stem-cell-based therapies have the potential to provide novel solutions for the treatment of a variety of diseases, but the main obstacles to such therapies lie in the uncontrolled differentiation and functional engraftment of implanted tissues. The physicochemical microenvironment controls the self-renewal and differentiation of stem cells, and the key step in mimicking the stem cell microenvironment is to construct a more physiologically relevant 3D culture system. Material-based 3D assemblies of stem cells facilitate the cellular interactions that promote morphogenesis and tissue organization in a similar manner to that which occurs during embryogenesis. Both natural and artificial materials can be used to create 3D scaffolds, and synthetic organic and inorganic porous materials are the two main kinds of artificial materials. Nanotechnology provides new opportunities to design novel advanced materials with special physicochemical properties for 3D stem cell culture and transplantation. Herein, the advances and advantages of 3D scaffold materials, especially with respect to stem-cell-based therapies, are first outlined. Second, the stem cell biology in 3D scaffold materials is reviewed. Third, the progress and basic principles of developing 3D scaffold materials for clinical applications in tissue engineering and regenerative medicine are reviewed.

Imaging stem cell distribution, growth, migration, and differentiation in 3-D scaffolds for bone tissue engineering using mesoscopic fluorescence tomography

Regenerative medicine has emerged as an important discipline that aims to repair injury or replace damaged tissues or organs by introducing living cells or functioning tissues. Successful regenerative medicine strategies will likely depend upon a simultaneous optimization strategy for the design of biomaterials, cell-seeding methods, cell-biomaterial interactions, and molecular signaling within the engineered tissues. It remains a challenge to image three-dimensional (3-D) structures and functions of the cell-seeded scaffold in mesoscopic scale (>2 ∼ 3 mm). In this study, we utilized angled fluorescence laminar optical tomography (aFLOT), which allows depth-resolved molecular characterization of engineered tissues in 3-D to investigate cell viability, migration, and bone mineralization within bone tissue engineering scaffolds in situ.

Bioreactor culture duration of engineered constructs influences bone formation by mesenchymal stem cells

Perfusion culture of mesenchymal stem cells (MSCs) seeded in biomaterial scaffolds provides nutrients for cell survival, enhances extracellular matrix deposition, and increases osteogenic cell differentiation. However, there is no consensus on the appropriate perfusion duration of cellular constructs in vitro to boost their bone forming capacity in vivo. We investigated this phenomenon by culturing human MSCs in macroporous composite scaffolds in a direct perfusion bioreactor and compared their response to scaffolds in continuous dynamic culture conditions on an XYZ shaker. Cell seeding in continuous perfusion bioreactors resulted in more uniform MSC distribution than static seeding. We observed similar calcium deposition in all composite scaffolds over 21 days of bioreactor culture, regardless of pore size. Compared to scaffolds in dynamic culture, perfused scaffolds exhibited increased DNA content and expression of osteogenic markers up to 14 days in culture that plateaued thereafter. We then evaluated the effect of perfusion culture duration on bone formation when MSC-seeded scaffolds were implanted in a murine ectopic site. Human MSCs persisted in all scaffolds at 2 weeks in vivo, and we observed increased neovascularization in constructs cultured under perfusion for 7 days relative to those cultured for 1 day within each gender. At 8 weeks post-implantation, we observed greater bone volume fraction, bone mineral density, tissue ingrowth, collagen density, and osteoblastic markers in bioreactor constructs cultured for 14 days compared to those cultured for 1 or 7 days, and acellular constructs. Taken together, these data demonstrate that culturing MSCs under perfusion culture for at least 14 days in vitro improves the quantity and quality of bone formation in vivo. This study highlights the need for optimizing in vitro bioreactor culture duration of engineered constructs to achieve the desired level of bone formation.

Collagen hydrogel scaffold promotes mesenchymal stem cell and endothelial cell coculture for bone tissue engineering

The generation of functional, vascularized tissues is a key challenge for the field of tissue engineering. Before clinical implantations of such tissue engineered bone constructs can succeed, tactics to promote neovascularization need to be strengthened. We have previously demonstrated that the tubular perfusion system (TPS) bioreactor is an effective culturing method to augment osteogenic differentiation and maintain viability of human mesenchymal stem cells (hMSC). Here, we devised a strategy to address the need for a functional microvasculature by designing an in vitro coculture system that simultaneously cultures osteogenic differentiating hMSCs with endothelial cells (ECs). We utilized the TPS bioreactor as a dynamic coculture environment, which we hypothesize will encourage prevascularization of endothelial cells and early formation of bone tissue and could aid in anastomosis of the graft with the host vasculature after patient implantation. To evaluate the effect of different natural scaffolds for this coculture system, the cells were encapsulated in alginate and/or collagen hydrogel scaffolds. We discovered the necessity of cell-to-cell proximity between the two cell types as well as preference for the natural cell binding capabilities of hydrogels like collagen. We discovered increased osteogenic and angiogenic potential as seen by amplified gene and protein expression of ALP, BMP-2, VEGF, and PECAM. The TPS bioreactor further augmented these expressions, indicating a synergistic effect between coculture and applied shear stress. The development of this dynamic coculture platform for the prevascularization of engineered bone, emphasizing the importance of the construct microenvironments and will advance the clinical use of tissue engineered constructs. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1123-1131, 2017.

Approaches for building bioactive elements into synthetic scaffolds for bone tissue engineering

Bone tissue engineering (BTE) is emerging as a possible solution for regeneration of bone in a number of applications. For effective utilization, BTE scaffolds often need modifications to impart biological cues that drive diverse cellular functions such as adhesion, migration, survival, proliferation, differentiation, and biomineralization. This review provides an outline of various approaches for building bioactive elements into synthetic scaffolds for BTE and classifies them broadly under two distinct schemes; namely, the top-down approach and the bottom-up approach. Synthetic and natural routes for top-down approaches to production of bioactive constructs for BTE, such as generation of scaffold-extracellular matrix (ECM) hybrid constructs or decellularized and demineralized scaffolds, are provided. Similarly, traditional scaffold-based bottom-up approaches, including growth factor immobilization or peptide-tethered scaffolds, are provided. Finally, a brief overview of emerging bottom-up approaches for generating biologically active constructs for BTE is given. A discussion of the key areas for further investigation, challenges, and opportunities is also presented.

Hydroxyapatite-doped alginate beads as scaffolds for the osteoblastic differentiation of mesenchymal stem cells

This work investigates the role of an osteoblastic matrix component, hydroxyapatite (HA), in modular alginate scaffolds to support osteoblastic differentiation of human mesenchymal stem cells for the purpose of tissue engineered bone constructs. This system is first evaluated in a tubular perfusion bioreactor, which has been shown to improve osteoblastic differentiation over static culture conditions. HMSCs in alginate scaffolds that contain HA show increased osteoblastic gene expression compared to cells in pure alginate scaffolds, as well as significantly more matrix production and mineralization. The differentiated hMSCs and cell-laid matrix are ultimately evaluated in an in vivo site specific model. Implantation of these scaffolds with preformed matrix into the rat femoral condyle defects results in abundant bone growth and significant incorporation of the scaffold into the surrounding tissue. The developed mineralized matrix, induced in part by the HA component in the scaffold, could lead to increased tissue development in critically sized defects, and should be included in future implant strategies. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2325-2333, 2016.

In Vitro Endothelialization of Biodegradable Vascular Grafts Via Endothelial Progenitor Cell Seeding and Maturation in a Tubular Perfusion System Bioreactor

A critical challenge to the success of biodegradable vascular grafts is the establishment of a healthy endothelium. To establish this monolayer of endothelial cells (ECs), a variety of techniques have been developed, including cell seeding. Vascular grafts may be seeded with relevant cell types and allowed to mature before implantation. Due to the low proliferative ability of adult ECs and issues with donor site morbidity, there has been increasing interest in using endothelial progenitor cells (EPCs) for vascular healing procedures. In this work, we combined the proliferative and differentiation capabilities of a commercial cell line of early EPCs with an established bioreactor system to support the maturation of cell-seeded vascular grafts. All components of the vascular graft and bioreactor setup are commercially available and allow for complete customization of the scaffold and culturing system. This bioreactor setup enables the control of flow through the graft, imparting fluid shear stress on EPCs and affecting cellular proliferation and differentiation. Grafts cultured with EPCs in the bioreactor system demonstrated greatly increased cell populations and neotissue formation compared with grafts seeded and cultured in a static system. Increased expression of markers for mature endothelial tissues were also observed in bioreactor-cultured EPC-seeded grafts. These findings suggest the distinct advantages of a customizable bioreactor setup for the proliferation and maturation of EPCs. Such a strategy may be beneficial for utilizing EPCs in vascular tissue engineering applications.

3D Printed Vascular Networks Enhance Viability in High-Volume Perfusion Bioreactor

There is a significant clinical need for engineered bone graft substitutes that can quickly, effectively, and safely repair large segmental bone defects. One emerging field of interest involves the growth of engineered bone tissue in vitro within bioreactors, the most promising of which are perfusion bioreactors. Using bioreactor systems, tissue engineered bone constructs can be fabricated in vitro. However, these engineered constructs lack inherent vasculature and once implanted, quickly develop a necrotic core, where no nutrient exchange occurs. Here, we utilized COMSOL modeling to predict oxygen diffusion gradients throughout aggregated alginate constructs, which allowed for the computer-aided design of printable vascular networks, compatible with any large tissue engineered construct cultured in a perfusion bioreactor. We investigated the effect of 3D printed macroscale vascular networks with various porosities on the viability of human mesenchymal stem cells in vitro, using both gas-permeable, and non-gas permeable bioreactor growth chamber walls. Through the use of 3D printed vascular structures in conjunction with a tubular perfusion system bioreactor, cell viability was found to increase by as much as 50% in the core of these constructs, with in silico modeling predicting construct viability at steady state.

Endometrial mesenchymal stem cells as a cell based therapy for pelvic organ prolapse

Pelvic organ prolapse (POP) occurs when the pelvic organs (bladder, bowel or uterus) herniate into the vagina, causing incontinence, voiding, bowel and sexual dysfunction, negatively impacting upon a woman’s quality of life. POP affects 25% of all women and results from childbirth injury. For 19% of all women, surgical reconstructive surgery is required for treatment, often augmented with surgical mesh. The surgical treatment fails in up to 30% of cases or results in adverse effects, such as pain and mesh erosion into the bladder, bowel or vagina. Due to these complications the Food and Drug Administration cautioned against the use of vaginal mesh and several major brands have been recently been withdrawn from market. In this review we will discuss new cell-based approaches being developed for the treatment of POP. Several cell types have been investigated in animal models, including a new source of mesenchymal stem/stromal cells (MSC) derived from human endometrium. The unique characteristics of endometrial MSC, methods for their isolation and purification and steps towards their development for good manufacturing practice production will be described. Animal models that could be used to examine the potential for this approach will also be discussed as will a rodent model showing promise in developing an endometrial MSC-based therapy for POP. The development of a preclinical large animal model for assessing tissue engineering constructs for treating POP will also be mentioned.

Winner of the Young Investigator Award of the Society for Biomaterials at the 10th World Biomaterials Congress, May 17-22, 2016, Montreal QC, Canada: Microribbon-based hydrogels accelerate stem cell-based bone regeneration in a mouse critical-size cranial defect model

Stem cell-based therapies hold great promise for enhancing tissue regeneration. However, the majority of cells die shortly after transplantation, which greatly diminishes the efficacy of stem cell-based therapies. Poor cell engraftment and survival remain a major bottleneck to fully exploiting the power of stem cells for regenerative medicine. Biomaterials such as hydrogels can serve as artificial matrices to protect cells during delivery and guide desirable cell fates. However, conventional hydrogels often lack macroporosity, which restricts cell proliferation and delays matrix deposition. Here we report the use of injectable, macroporous microribbon (μRB) hydrogels as stem cell carriers for bone repair, which supports direct cell encapsulation into a macroporous scaffold with rapid spreading. When transplanted in a critical-sized, mouse cranial defect model, μRB-based hydrogels significantly enhanced the survival of transplanted adipose-derived stromal cells (ADSCs) (81%) and enabled up to three-fold cell proliferation after 7 days. In contrast, conventional hydrogels only led to 27% cell survival, which continued to decrease over time. MicroCT imaging showed μRBs enhanced and accelerated mineralized bone repair compared to hydrogels (61% vs. 34% by week 6), and stem cells were required for bone repair to occur. These results suggest that paracrine signaling of transplanted stem cells are responsible for the observed bone repair, and enhancing cell survival and proliferation using μRBs further promoted the paracrine-signaling effects of ADSCs for stimulating endogenous bone repair. We envision μRB-based scaffolds can be broadly useful as a novel scaffold for enhancing stem cell survival and regeneration of other tissue types. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1321-1331, 2016.

High Content Imaging of Early Morphological Signatures Predicts Long Term Mineralization Capacity of Human Mesenchymal Stem Cells upon Osteogenic Induction

Human bone marrow-derived multipotent mesenchymal stromal cells, often referred to as mesenchymal stem cells (MSCs), represent an attractive cell source for many regenerative medicine applications due to their potential for multi-lineage differentiation, immunomodulation, and paracrine factor secretion. A major complication for current MSC-based therapies is the lack of well-defined characterization methods that can robustly predict how they will perform in a particular in vitro or in vivo setting. Significant advances have been made with identifying molecular markers of MSC quality and potency using multivariate genomic and proteomic approaches, and more recently with advanced techniques incorporating high content imaging to assess high-dimensional single cell morphological data. We sought to expand upon current methods of high dimensional morphological analysis by investigating whether short term cell and nuclear morphological profiles of MSCs from multiple donors (at multiple passages) correlated with long term mineralization upon osteogenic induction. Using the combined power of automated high content imaging followed by automated image analysis, we demonstrated that MSC morphology after 3 days was highly correlated with 35 day mineralization and comparable to other methods of MSC osteogenesis assessment (such as alkaline phosphatase activity). We then expanded on this initial morphological characterization and identified morphological features that were highly predictive of mineralization capacities (>90% accuracy) of MSCs from additional donors and different manufacturing techniques using linear discriminant analysis. Together, this work thoroughly demonstrates the predictive power of MSC morphology for mineralization capacity and motivates further studies into MSC morphology as a predictive marker for additional in vitro and in vivo responses.

A single short session of media perfusion induces osteogenesis in hBMSCs cultured in porous scaffolds, dependent on cell differentiation stage

Perfusing culture media through porous cell-seeded scaffolds is now a common approach within many tissue engineering strategies. Human bone-marrow derived mesenchymal stem cells (hBMSC) are a clinically valuable source of osteoprogenitors that respond to mechanical stimuli. However, the optimal mechanical conditions for their osteogenic stimulation in vitro have not been defined. Whereas the effects of short durations of media fluid flow have been studied in monolayers of osteoblastic cells, in 3D culture continuous or repeated perfusion is usually applied. Here, we investigated whether a short, single perfusion session applied to hBMSCs cultured in 3D would enhance their osteogenesis in vitro. We cultured hBMSCs on gelatine-coated, porous polyurethane scaffolds with osteogenic supplements and stimulated them with a single 2-h session of unidirectional, steady, 2.5 mL/min media perfusion, at either early or late stages of culture in 3D. Some cells were pre-treated in monolayer with osteogenic supplements to advance cell differentiation, followed by 3D culture also with the osteogenic supplements. We report that this single, short session of media perfusion can markedly enhance the expression of bone-related transcription and growth factors, and matrix components, by hBMSCs but that it is more effective when cells reach the pre-osteoblast or osteoblast differentiation stage. These findings could aid in the optimization of 3D culture protocols for efficient bone tissue engineering. Biotechnol. Bioeng. 2016;113: 1814-1824. © 2016 Wiley Periodicals, Inc.

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.

Dynamic Bioreactor Culture of High Volume Engineered Bone Tissue

Within the field of tissue engineering and regenerative medicine, the fabrication of tissue grafts of any significant size--much less a whole organ or tissue--remains a major challenge. Currently, tissue-engineered constructs cultured in vitro have been restrained in size primarily due to the diffusion limit of oxygen and nutrients to the center of these grafts. Previously, we developed a novel tubular perfusion system (TPS) bioreactor, which allows the dynamic culture of bead-encapsulated cells and increases the supply of nutrients to the entire cell population. More interestingly, the versatility of TPS bioreactor allows a large range of engineered tissue volumes to be cultured, including large bone grafts. In this study, we utilized alginate-encapsulated human mesenchymal stem cells for the culture of a tissue-engineered bone construct in the size and shape of the superior half of an adult human femur (∼ 200 cm(3)), a 20-fold increase over previously reported volumes of in vitro engineered bone grafts. Dynamic culture in TPS bioreactor not only resulted in high cell viability throughout the femur graft, but also showed early signs of stem cell differentiation through increased expression of osteogenic genes and proteins, consistent with our previous models of smaller bone constructs. This first foray into full-scale bone engineering provides the foundation for future clinical applications of bioengineered bone grafts.

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.

Enhanced Viability of Endothelial Colony Forming Cells in Fibrin Microbeads for Sensor Vascularization

Enhanced vascularization at sensor interfaces can improve long-term function. Fibrin, a natural polymer, has shown promise as a biomaterial for sensor coating due to its ability to sustain endothelial cell growth and promote local vascularization. However, the culture of cells, particularly endothelial cells (EC), within 3D scaffolds for more than a few days is challenging due to rapid loss of EC viability. In this manuscript, a robust method for developing fibrin microbead scaffolds for long-term culture of encapsulated ECs is described. Fibrin microbeads are formed using sodium alginate as a structural template. The size, swelling and structural properties of the microbeads were varied with needle gauge and composition and concentration of the pre-gel solution. Endothelial colony-forming cells (ECFCs) were suspended in the fibrin beads and cultured within a perfusion bioreactor system. The perfusion bioreactor enhanced ECFCs viability and genome stability in fibrin beads relative to static culture. Perfusion bioreactors enable 3D culture of ECs within fibrin beads for potential application as a sensor coating.

Effect of decellularized adipose tissue particle size and cell density on adipose-derived stem cell proliferation and adipogenic differentiation in composite methacrylated chondroitin sulphate hydrogels

An injectable composite scaffold incorporating decellularized adipose tissue (DAT) as a bioactive matrix within a hydrogel phase capable of in situ polymerization would be advantageous for adipose-derived stem cell (ASC) delivery in the filling of small or irregular soft tissue defects. Building on previous work, the current study investigates DAT milling methods and the effects of DAT particle size and cell seeding density on the response of human ASCs encapsulated in photo-cross-linkable methacrylated chondroitin sulphate (MCS)-DAT composite hydrogels. DAT particles were generated by milling lyophilized DAT and the particle size was controlled through the processing conditions with the goal of developing composite scaffolds with a tissue-specific 3D microenvironment tuned to enhance adipogenesis. ASC proliferation and adipogenic differentiation were assessed in vitro in scaffolds incorporating small (average diameter of 38   ±   6 μm) or large (average diameter of 278   ±   3 μm) DAT particles in comparison to MCS controls over a period of up to 21 d. Adipogenic differentiation was enhanced in the composites incorporating the smaller DAT particles and seeded at the higher density of 5   ×   10(5) ASCs/scaffold, as measured by glycerol-3-phosphate dehydrogenase (GPDH) enzyme activity, semi-quantitative analysis of perilipin expression and oil red O staining of intracellular lipid accumulation. Overall, this study demonstrates that decellularized tissue particle size can impact stem cell differentiation through cell-cell and cell-matrix interactions, providing relevant insight towards the rational design of composite biomaterial scaffolds for adipose tissue engineering.

The role of mechanical stimuli in the vascular differentiation of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are among the most promising and suitable stem cell types for vascular tissue engineering. Substantial effort has been made to differentiate MSCs towards vascular cell phenotypes, including endothelial cells and smooth muscle cells (SMCs). The microenvironment of vascular cells not only contains biochemical factors that influence differentiation, but also exerts hemodynamic forces, such as shear stress and cyclic strain. Recent evidence has shown that these forces can influence the differentiation of MSCs into endothelial cells or SMCs. In this Commentary, we present the main findings in the area with the aim of summarizing the mechanisms by which shear stress and cyclic strain induce MSC differentiation. We will also discuss the interactions between these mechanical cues and other components of the microenvironment, and highlight how these insights could be used to maintain differentiation.

Development of a dynamic stem cell culture platform for mesenchymal stem cell adhesion and evaluation

The importance of providing a physiologically relevant environment for cell culture is well recognized. The combination of proper environmental cues which are provided in vivo by the bloodstream and extracellular matrix must be reproduced to properly examine cell response in vitro, and cannot be recapitulated using traditional culture on polystyrene. Here, we have developed a device, the dynamic stem cell culture platform (DSCCP), consisting of a biomimetic scaffold cultured within the dynamic environment of a perfusion bioreactor. By varying scaffold parameters including stiffness and protein inclusion at the material surface, we found that human mesenchymal stem cells (hMSCs) were able to adhere to modified substrates, while still maintaining multipotency. Culture in a perfusion bioreactor showed cell survival and proliferation, particularly on modified substrates. The DSCCP represents a complete platform for cell adhesion and subsequent evaluation, including the response of a cell population to drug treatment.

Use of perfusion bioreactors and large animal models for long bone tissue engineering

Tissue engineering and regenerative medicine (TERM) strategies for generation of new bone tissue includes the combined use of autologous or heterologous mesenchymal stem cells (MSC) and three-dimensional (3D) scaffold materials serving as structural support for the cells, that develop into tissue-like substitutes under appropriate in vitro culture conditions. This approach is very important due to the limitations and risks associated with autologous, as well as allogenic bone grafiting procedures currently used. However, the cultivation of osteoprogenitor cells in 3D scaffolds presents several challenges, such as the efficient transport of nutrient and oxygen and removal of waste products from the cells in the interior of the scaffold. In this context, perfusion bioreactor systems are key components for bone TERM, as many recent studies have shown that such systems can provide dynamic environments with enhanced diffusion of nutrients and therefore, perfusion can be used to generate grafts of clinically relevant sizes and shapes. Nevertheless, to determine whether a developed tissue-like substitute conforms to the requirements of biocompatibility, mechanical stability and safety, it must undergo rigorous testing both in vitro and in vivo. Results from in vitro studies can be difficult to extrapolate to the in vivo situation, and for this reason, the use of animal models is often an essential step in the testing of orthopedic implants before clinical use in humans. This review provides an overview of the concepts, advantages, and challenges associated with different types of perfusion bioreactor systems, particularly focusing on systems that may enable the generation of critical size tissue engineered constructs. Furthermore, this review discusses some of the most frequently used animal models, such as sheep and goats, to study the in vivo functionality of bone implant materials, in critical size defects.

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.

Evaluation of the in vitro cytotoxicity of cross-linked biomaterials

This study evaluated the in vitro cytotoxicity of poly(propylene fumarate) (PPF). PPF is an aliphatic biodegradable polymer that has been well characterized for use in bone tissue engineering scaffolds. Four different cell types, human mesenchymal stem cells (hMSC), fibroblasts (L929), preosteoblasts (MC3T3), and canine mesenchymal stem cells (cMSC), were used to evaluate the cytotoxicity of PPF. These cell types represent the tissues that PPF would interact with in vivo as a bone tissue scaffold. The sol fraction of the PPF films was measured and then utilized to estimate cross-linking density. Cytotoxicity was evaluated using XTT assay and fluorescence imaging. Results showed that PPF supported similar cell metabolic activities of hMSC, L929, MC3T3, and cMSC compared to the noncytotoxic control, high-density polyethylene (HDPE) and were statistically different than those cultured with the cytotoxic control, a polyurethane film containing 0.1% zinc diethyldithiocarbamate (ZCF). Results showed differing cellular responses to ZCF, the cytotoxic control. The L929 cells had the lowest cell metabolic activity levels after exposure to ZCF compared to the cell metabolic activity levels of the MC3T3, hMSC, or cMSC cells. Qualitative verification of the results using fluorescence imaging demonstrated no change in cell morphology, vacuolization, or detachment when cultured with PPF compared to HDPE or blank media cultures. Overall, the cytotoxicity response of the cells to PPF was demonstrated to be similar to the cytotoxic response of cells to known noncytotoxic materials (HDPE).

Critical size bone defect reconstruction by an autologous 3D osteogenic-like tissue derived from differentiated adipose MSCs

For critical size bone defects and bone non-unions, bone tissue engineering using osteoblastic differentiated adipose mesenchymal stem cells (AMSCs) is limited by the need for a biomaterial to support cell transplantation. An osteoblastic three-dimensional autologous graft made of AMSCs (3D AMSC) was developed to solve this issue. This autograft was obtained by supplementing the osteoblastic differentiation medium with demineralized bone matrix. Two surgical models were developed to assess the potential of this 3D osteogenic AMSC autograft. A four-level spinal fusion using polyetheretherketone cages was designed in six pigs to assess the early phase of ossification (8-12 weeks postimplantation). In each pig, four groups were compared: cancellous bone autograft, freeze-dried irradiated cancellous pig bone, 3D AMSC, and an empty cage. A critical size femoral defect (n = 4, bone non-union confirmed 6 months postoperatively) was used to assess the 3D AMSCs' ability to achieve bone fusion. Pigs were followed by CT scan and explanted specimens were analyzed for bone tissue remodeling by micro-CT scan, micro-radiography, and histology/histomorphometry. In the spine fusion model, bone formation with the 3D AMSC was demonstrated by a significant increase in bone content. In the critical-size femoral defect model, the 3D AMSC achieved new bone formation and fusion in a poorly vascularized fibrotic environment. This custom-made 3D osteogenic AMSC autograft is a therapeutic solution for bone non-unions and for critical-size defects.

Bioreactors to influence stem cell fate: augmentation of mesenchymal stem cell signaling pathways via dynamic culture systems

BACKGROUND

Mesenchymal stem cells (MSCs) are a promising cell source for bone and cartilage tissue engineering as they can be easily isolated from the body and differentiated into osteoblasts and chondrocytes. A cell based tissue engineering strategy using MSCs often involves the culture of these cells on three-dimensional scaffolds; however the size of these scaffolds and the cell population they can support can be restricted in traditional static culture. Thus dynamic culture in bioreactor systems provides a promising means to culture and differentiate MSCs in vitro.

SCOPE OF REVIEW

This review seeks to characterize key MSC differentiation signaling pathways and provides evidence as to how dynamic culture is augmenting these pathways. Following an overview of dynamic culture systems, discussion will be provided on how these systems can effectively modify and maintain important culture parameters including oxygen content and shear stress. Literature is reviewed for both a highlight of key signaling pathways and evidence for regulation of these signaling pathways via dynamic culture systems.

MAJOR CONCLUSIONS

The ability to understand how these culture systems are affecting MSC signaling pathways could lead to a shear or oxygen regime to direct stem cell differentiation. In this way the efficacy of in vitro culture and differentiation of MSCs on three-dimensional scaffolds could be greatly increased.

GENERAL SIGNIFICANCE

Bioreactor systems have the ability to control many key differentiation stimuli including mechanical stress and oxygen content. The further integration of cell signaling investigations within dynamic culture systems will lead to a quicker realization of the promise of tissue engineering and regenerative medicine. This article is part of a Special Issue entitled Biochemistry of Stem Cells.