Expansion of human nasal chondrocytes on macroporous microcarriers enhances redifferentiation

The role of cells and their derivatives in otorhinolaryngologic diseases treatment

Otolaryngology is an important specialty in the field of surgery that deals with the diagnosis and treatment of the ear, nose, throat, trachea, as well as related anatomical structures. Various otolaryngological disorders are difficult to treat using established pharmacological and surgical approaches. The advent of molecular and cellular therapies led to further progress in this respect. This article reviews the therapeutic strategies of using stem cells, immune cells, and chondrocytes in otorhinolaryngology. As the most widely recognized cell derivatives, exosomes were also systematically reviewed for their therapeutic potential in head and neck cancer, otitis media, and allergic rhinitis. Finally, we summarize the limitations of stem cells, chondrocytes, and exosomes, as well as possible solutions, and provide an outlook on the future direction of cell- and derivative-based therapies in otorhinolaryngology, to offer a theoretical foundation for the clinical translation of this therapeutic modality.

Bio-Nanohybrid Gelatin/Quantum Dots for Cellular Imaging and Biosensing Applications

The bio-nanohybrid gelatin protein/cadmium sulfide (Gel/CdS) quantum dots (QDs) have been designed via a facile one-pot strategy. The amino acids group of gelatin chelate Cd2+ and grow CdS QDs without any agglomeration. The 1H NMR spectra indicate that during the above process there are no alterations of the gelatin protein structure conformation and chemical functionalities. The prepared Gel/CdS QDs were characterized and their potential as a system for cellular imaging and the electrochemical sensor for hydrogen peroxide (H2O2) detection applications were investigated. The obtained results demonstrate that the developed Gel/CdS QDs system could offer a simple and convenient operating strategy both for the class of contrast agents for cell labeling and electrochemical sensors purposes.

Freeze-Dried Curdlan/Whey Protein Isolate-Based Biomaterial as Promising Scaffold for Matrix-Associated Autologous Chondrocyte Transplantation-A Pilot In-Vitro Study

The purpose of this pilot study was to establish whether a novel freeze-dried curdlan/whey protein isolate-based biomaterial may be taken into consideration as a potential scaffold for matrix-associated autologous chondrocyte transplantation. For this reason, this biomaterial was initially characterized by the visualization of its micro- and macrostructures as well as evaluation of its mechanical stability, and its ability to undergo enzymatic degradation in vitro. Subsequently, the cytocompatibility of the biomaterial towards human chondrocytes (isolated from an orthopaedic patient) was assessed. It was demonstrated that the novel freeze-dried curdlan/whey protein isolate-based biomaterial possessed a porous structure and a Young's modulus close to those of the superficial and middle zones of cartilage. It also exhibited controllable degradability in collagenase II solution over nine weeks. Most importantly, this biomaterial supported the viability and proliferation of human chondrocytes, which maintained their characteristic phenotype. Moreover, quantitative reverse transcription PCR analysis and confocal microscope observations revealed that the biomaterial may protect chondrocytes from dedifferentiation towards fibroblast-like cells during 12-day culture. Thus, in conclusion, this pilot study demonstrated that novel freeze-dried curdlan/whey protein isolate-based biomaterial may be considered as a potential scaffold for matrix-associated autologous chondrocyte transplantation.

Cell Sources for Cartilage Repair-Biological and Clinical Perspective

Cell-based therapy represents a promising treatment strategy for cartilage defects. Alone or in combination with scaffolds/biological signals, these strategies open many new avenues for cartilage tissue engineering. However, the choice of the optimal cell source is not that straightforward. Currently, various types of differentiated cells (articular and nasal chondrocytes) and stem cells (mesenchymal stem cells, induced pluripotent stem cells) are being researched to objectively assess their merits and disadvantages with respect to the ability to repair damaged articular cartilage. In this paper, we focus on the different cell types used in cartilage treatment, first from a biological scientist’s perspective and then from a clinician’s standpoint. We compare and analyze the advantages and disadvantages of these cell types and offer a potential outlook for future research and clinical application.

A Paradigm Shift in Tissue Engineering: From a Top–Down to a Bottom–Up Strategy

Tissue engineering (TE) was initially designed to tackle clinical organ shortage problems. Although some engineered tissues have been successfully used for non-clinical applications, very few (e.g., reconstructed human skin) have been used for clinical purposes. As the current TE approach has not achieved much success regarding more broad and general clinical applications, organ shortage still remains a challenging issue. This very limited clinical application of TE can be attributed to the constraints in manufacturing fully functional tissues via the traditional top–down approach, where very limited cell types are seeded and cultured in scaffolds with equivalent sizes and morphologies as the target tissues. The newly proposed developmental engineering (DE) strategy towards the manufacture of fully functional tissues utilises a bottom–up approach to mimic developmental biology processes by implementing gradual tissue assembly alongside the growth of multiple cell types in modular scaffolds. This approach may overcome the constraints of the traditional top–down strategy as it can imitate in vivo-like tissue development processes. However, several essential issues must be considered, and more mechanistic insights of the fundamental, underpinning biological processes, such as cell–cell and cell–material interactions, are necessary. The aim of this review is to firstly introduce and compare the number of cell types, the size and morphology of the scaffolds, and the generic tissue reconstruction procedures utilised in the top–down and the bottom–up strategies; then, it will analyse their advantages, disadvantages, and challenges; and finally, it will briefly discuss the possible technologies that may overcome some of the inherent limitations of the bottom–up strategy.

Microcarrier Screening and Evaluation for Dynamic Expansion of Human Periosteum-Derived Progenitor Cells in a Xenogeneic Free Medium

An increasing need toward a more efficient expansion of adherent progenitor cell types arises with the advancements of cell therapy. The use of a dynamic expansion instead of a static planar expansion could be one way to tackle the challenges of expanding adherent cells at a large scale. Microcarriers are often reported as a biomaterial for culturing cells in suspension. However, the type of microcarrier has an effect on the cell expansion. In order to find an efficient expansion process for a specific adherent progenitor cell type, it is important to investigate the effect of the type of microcarrier on the cell expansion. Human periosteum-derived progenitor cells are extensively used in skeletal tissue engineering for the regeneration of bone defects. Therefore, we evaluated the use of different microcarriers on human periosteum-derived progenitor cells. In order to assess the potency, identity and viability of these cells after being cultured in the spinner flasks, this study performed several in vitro and in vivo analyses. The novelty of this work lies in the combination of screening different microcarriers for human periosteum-derived progenitor cells with in vivo assessments of the cells’ potency using the microcarrier that was selected as the most promising one. The results showed that expanding human periosteum-derived progenitor cells in spinner flasks using xeno-free medium and Star-Plus microcarriers, does not affect the potency, identity or viability of the cells. The potency of the cells was assured with an in vivo evaluation, where bone formation was achieved. In summary, this expansion method has the potential to be used for large scale cell expansion with clinical relevance.

Bioprocess Technologies that Preserve the Quality of iPSCs

Large-scale production of induced pluripotent stem cells (iPSCs) is essential for the treatment of a variety of clinical indications. However, culturing enough iPSCs for clinical applications is problematic due to their sensitive pluripotent state and dependence on a supporting matrix. Developing stem cell bioprocessing strategies that are scalable and meet clinical needs requires incorporating methods that measure and monitor intrinsic markers of cell differentiation state, developmental status, and viability in real time. In addition, proper cell culture modalities that nurture the growth of high-quality stem cells in suspension are critical for industrial scale-up. In this review, we present an overview of cell culture media, suspension modalities, and monitoring techniques that preserve the quality and pluripotency of iPSCs during initiation, expansion, and manufacturing.

In Situ Precipitation of Cluster and Acicular Hydroxyapatite onto Porous Poly(γ-benzyl-l-glutamate) Microcarriers for Bone Tissue Engineering

Bone tissue engineering scaffold based on microcarriers provides an effective approach for the repair of irregular bone defects. The implantation of microcarriers by injection can reduce surgical trauma and fill various irregular shaped bone defects. Microcarriers with porous structure and osteogenic properties have shown great potential in promoting the repair of bone defects. In this study, two kinds of hydroxyapatite/poly-(γ-benzyl-l-glutamate) (HA/PBLG) microcarriers were constructed by emulsion/in situ precipitation method and their structures and properties were studied. First, PBLG porous microcarriers were prepared by an emulsion method. Surface carboxylation of PBLG microcarriers was performed to promote the deposition of HA on PBLG microcarriers. Next, the modified porous PBLG microcarriers were used as the matrix, combined with the in situ precipitation method; the cluster HA and acicular HA were precipitated onto the surface of porous microcarriers in the presence of ammonia water and tri(hydroxymethyl)aminomethane (Tris) solution, respectively. The micromorphology, composition, and element distribution of the two kinds of microcarriers were characterized by TEM, SEM, and AFM. Adipose stem cells (ADSCs) were cultured on the cluster HA/PBLG and acicular HA/PBLG microcarriers, respectively. ADSCs could grow and proliferate normally on both kinds of microcarriers wherein the acicular HA/PBLG microcarriers were more favorable for early cell adhesion and showed a beneficial effect on mineralization and osteogenic differentiation of ADSCs. Successful healing of a rabbit femur defect verified the bone regeneration ability of acicular HA/PBLG microcarriers.

Biomimetic polyetheretherketone microcarriers with specific surface topography and self-secreted extracellular matrix for large-scale cell expansion

Reusable microcarriers with appropriate surface topography, mechanical properties, as well as biological modification through decellularization facilitating repeated cell culture are crucial for tissue engineering applications. Herein, we report the preparation of topological polyetheretherketone (PEEK) microcarriers via gas-driven and solvent exchange method followed by hydrothermal treatment at high temperature and pressure. After hydrothermal treated for 8 h, the resulting topological PEEK microcarriers exhibit walnut-like surface topography and good sphericity as well as uniform size distribution of 350.24 ± 19.44 µm. And the average width between ravine-patterned surface of PEEK microcarriers is 780 ± 290 nm. After repeated steam sterilization by autoclaving for three times, topological PEEK microcarriers show nearly identical results compared with previous ones indicating strong tolerance to high temperature and pressure. This is a unique advantage for large-scale cell expansion and clinical applications. Moreover, PEEK microcarriers with special topography possess higher protein adsorption efficiency. In addition, the reutilization and biofunctionalization with repeated decellularization of topological PEEK microcarriers show highly beneficial for cell adhesion and proliferation. Therefore, our study is of great importance for new generation microcarriers with micro-and nano-scale surface feature for a broad application prospect in tissue engineering.

Spatially confined induction of endochondral ossification by functionalized hydrogels for ectopic engineering of osteochondral tissues

Despite the various reported approaches to generate osteochondral composites by combination of different cell types and materials, engineering of templates with the capacity to autonomously and orderly develop into cartilage-bone bi-layered structures remains an open challenge. Here, we hypothesized that the embedding of cells inducible to endochondral ossification (i.e. bone marrow derived mesenchymal stromal cells, BMSCs) and of cells capable of robust and stable chondrogenesis (i.e. nasal chondrocytes, NCs) adjacent to each other in bi-layered hydrogels would develop directly in vivo into osteochondral tissues. Poly(ethylene glycol) (PEG) hydrogels were functionalized with TGFβ3 or BMP-2, enzymatically polymerized encapsulating human BMSCs, combined with a hydrogel layer containing human NCs and ectopically implanted in nude mice without pre-culture. The BMSC-loaded layers reproducibly underwent endochondral ossification and generated ossicles containing bone and marrow. The NC-loaded layers formed cartilage tissues, which (under the influence of BMP-2 but not of TGFβ3 from the neighbouring layer) remained phenotypically stable. The proposed strategy, resulting in orderly connected osteochondral composites, should be further assessed for the repair of osteoarticular defects and will be useful to model developmental processes leading to cartilage-bone interfaces.

Evaluation of Cartilage Specific Matrix Synthesis of Human Articular Chondrocytes after Extended Propagation on Microcarriers by Image Analysis

Background

Cell-based technologies for the repair of cartilage defects usually rely on the expansion of low numbers of chondrocytes isolated from biopsies of healthy cartilage. Proliferating chondrocytes are known to undergo dedifferentiation characterized by downregulation of collagen type II and proteoglycan production, and by upregulation of collagen type I synthesis. Re-expression of cartilage specific matrix components by expanded chondrocytes is therefore critical for successful cartilage repair.

Methods

Human articular chondrocytes were expanded on microcarriers Cytodex 3. The growth area was increased by adding empty microcarriers. Added microcarriers were colonized by bead-to-bead transfer of the cells. The chondrocytes were harvested from the microcarriers and characterized by their ability to synthesize collagen type II when cultivated in alginate beads using chondrogenic growth factors. A semi-automatic image analysis technique was developed to determine the fractions of collagen type II and type I positive cells.

Results

The expansion of human articular chondrocytes on microcarriers yielded high cell numbers and propagation rates compared to chondrocytes expanded in flask culture for one passage. The proportion of collagen type II positive cells compared to collagen type I synthesizing cells was increased compared to chondrocytes expanded using conventional methods. The matrix synthesis upon treatment with chondrogenic factors IGF-I and BMP-7 was enhanced whereas TGF-β had an inhibitory effect on microcarrier expanded chondrocytes.

Conclusions

Expanding human articular chondrocytes on microcarriers omitting subcultivation steps leads to superior ratios of collagen type II to type I forming cells compared to the expansion in conventional monolayer culture.

Tunable Volumetric Density and Porous Structure of Spherical Poly-ε-caprolactone Microcarriers, as Applied in Human Mesenchymal Stem Cell Expansion

Polymeric microspheres may serve as microcarrier (MC) matrices, for the expansion of anchorage-dependent stem cells. They require surface properties that promote both initial cell adhesion and the subsequent spreading of cells, which is a prerequisite for successful expansion. When implemented in a three-dimensional culture environment, under agitation, their suspension under low shear rates depends on the MCs having a modest negative buoyancy, with a density of 1.02-1.05 g/cm³. Bioresorbable poly-ε-caprolactone (PCL), with a density of 1.14 g/cm³, requires a reduction in volumetric density, for the microspheres to achieve high cell viability and yields. Uniform-sized droplets, from solutions of PCL dissolved in dichloromethane (DCM), were generated by coaxial microfluidic geometry. Subsequent exposure to ethanol rapidly extracted the DCM solvent, solidifying the droplets and yielding monodisperse microspheres with a porous structure, which was demonstrated to have tunable porosity and a hollow inner core. The variation in process parameters, including the molecular weight of PCL, its concentration in DCM, and the ethanol concentration, served to effectively alter the diffusion flux between ethanol and DCM, resulting in a broad spectrum of volumetric densities of 1.04-1.11 g/cm³. The solidified microspheres are generally covered by a smooth thin skin, which provides a uniform cell culture surface and masks their internal porous structure. When coated with a cationic polyelectrolyte and extracellular matrix protein, monodisperse microspheres with a diameter of approximately 150 μm and densities ranging from 1.05-1.11 g/cm³ are capable of supporting the expansion of human mesenchymal stem cells (hMSCs). Validation of hMSC expansion was carried out with a positive control of commercial Cytodex 3 MCs and a negative control of uncoated low-density PCL MCs. Static culture conditions generated more than 70% cell attachment and similar yields of sixfold cell expansion on all coated MCs, with poor cell attachment and growth on the negative control. Under agitation, coated porous microspheres, with a low density of 1.05 g/cm³, achieved robust cell attachment and resulted in high cell yields of ninefold cell expansion, comparable with those generated by commercial Cytodex 3 MCs.

Redifferentiation of High-Throughput Generated Fibrochondrocyte Micro-Aggregates: Impact of Low Oxygen Tension

In meniscus tissue engineering strategies, enhancing the matrix quality of the neomeniscal tissue is important. When the differentiated phenotype of fibrochondrocytes is lost, the quality of the matrix becomes compromised. The objective of this study was to produce uniform fibrochondrocyte micro-aggregates with desirable phenotype and tissue homogeneity in large quantities using a simple and reproducible method. Furthermore, we investigated if hypoxia could enhance the matrix quality. Porcine fibrochondrocytes were expanded at 21% oxygen until passage 3 (P3) and a gene expression profile was determined. P3 fibrochondrocytes were cultivated in chondrogenic medium at 5 and 21% oxygen in high-throughput agarose chips containing 2,865 microwells 200 µm in diameter. Evaluation included live/dead staining, histological examination, immunohistochemistry, dimethylmethylene blue assay and real-time reverse transcriptase quantitative polymerase chain reaction of the micro-aggregates. Gene expression analysis showed a drastic decline in collagen II and high expression of collagen I during monolayer culture. After 4 days, uniform and stable micro-aggregates could be produced. The redifferentiation and matrix quality of the hypoxic cultured micro-aggregates were enhanced relative to the normoxic cultures. Sulfated glycosaminoglycan synthesis was significantly higher, and collagen II expression and the collagen II/collagen I ratio were significantly upregulated in the hypoxic cultures. High-throughput production of uniform microtissues holds promise for the generation of larger-scale tissue engineering constructs or optimization of redifferentiation mechanisms for clinical applications.

Fabrication of uniform-sized poly-ɛ-caprolactone microspheres and their applications in human embryonic stem cell culture

The generation of liquefied poly-ɛ-caprolactone (PCL) droplets by means of a microfluidic device results in uniform-sized microspheres, which are validated as microcarriers for human embryonic stem cell culture. Formed droplet size and size distribution, as well as the resulting PCL microsphere size, are correlated with the viscosity and flow rate ratio of the dispersed (Q d) and continuous (Q c) phases. PCL in dichloromethane increases its viscosity with concentration and molecular weight. Higher viscosity and Q d/Q c lead to the formation of larger droplets, within two observed formation modes: dripping and jetting. At low viscosity of dispersed phase and Q d/Q c, the microfluidic device is operated in dripping mode, which generates droplets and microspheres with greater size uniformity. Solutions with lower molecular weight PCL have lower viscosity, resulting in a wider concentration range for the dripping mode. When coated with extracellular matrix (ECM) proteins, the fabricated PCL microspheres are demonstrated capable of supporting the expansion of human embryonic stem cells.

Nanostructured injectable cell microcarriers for tissue regeneration

Biodegradable polymer microspheres have emerged as cell carriers for the regeneration and repair of irregularly shaped tissue defects due to their injectability, controllable biodegradability and capacity for drug incorporation and release. Notably, recent advances in nanotechnology allowed the manipulation of the physical and chemical properties of the microspheres at the nanoscale, creating nanostructured microspheres mimicking the composition and/or structure of natural extracellular matrix. These nanostructured microspheres, including nanocomposite microspheres and nanofibrous microspheres, have been employed as cell carriers for tissue regeneration. They enhance cell attachment and proliferation, promote positive cell-carrier interactions and facilitate stem cell differentiation for target tissue regeneration. This review highlights the recent advances in nanostructured microspheres that are employed as injectable, biomimetic and cell-instructive cell carriers.

Tissue engineering strategies to study cartilage development, degeneration and regeneration

Cartilage tissue engineering has primarily focused on the generation of grafts to repair cartilage defects due to traumatic injury and disease. However engineered cartilage tissues have also a strong scientific value as advanced 3D culture models. Here we first describe key aspects of embryonic chondrogenesis and possible cell sources/culture systems for in vitro cartilage generation. We then review how a tissue engineering approach has been and could be further exploited to investigate different aspects of cartilage development and degeneration. The generated knowledge is expected to inform new cartilage regeneration strategies, beyond a classical tissue engineering paradigm.

Large-scale expansion of Wharton's jelly-derived mesenchymal stem cells on gelatin microbeads, with retention of self-renewal and multipotency characteristics and the capacity for enhancing skin wound healing

INTRODUCTION

Successful stem cell therapy relies on large-scale generation of stem cells and their maintenance in a proliferative multipotent state. This study aimed to establish a three-dimension culture system for large-scale generation of hWJ-MSC and investigated the self-renewal activity, genomic stability and multi-lineage differentiation potential of such hWJ-MSC in enhancing skin wound healing.

METHODS

hWJ-MSC were seeded on gelatin microbeads and cultured in spinning bottles (3D). Cell proliferation, karyotype analysis, surface marker expression, multipotent differentiation (adipogenic, chondrogenic, and osteogenic potentials), and expression of core transcription factors (OCT4, SOX2, NANOG, and C-MYC), as well as their efficacy in accelerating skin wound healing, were investigated and compared with those of hWJ-MSC derived from plate cultres (2D), using in vivo and in vitro experiments.

RESULTS

hWJ-MSC attached to and proliferated on gelatin microbeads in 3D cultures reaching a maximum of 1.1-1.30×10(7) cells on 0.5 g of microbeads by days 8-14; in contrast, hWJ-MSC derived from 2D cultures reached a maximum of 6.5 -11.5×10(5) cells per well in a 24-well plate by days 6-10. hWJ-MSC derived by 3D culture incorporated significantly more EdU (P<0.05) and had a significantly higher proliferation index (P<0.05) than those derived from 2D culture. Immunofluorescence staining, real-time PCR, flow cytometry analysis, and multipotency assays showed that hWJ-MSC derived from 3D culture retained MSC surface markers and multipotency potential similar to 2D culture-derived cells. 3D culture-derived hWJ-MSC also retained the expression of core transcription factors at levels comparable to their 2D culture counterparts. Direct injection of hWJ-MSC derived from 3D or 2D cultures into animals exhibited similar efficacy in enhancing skin wound healing.

CONCLUSIONS

Thus, hWJ-MSC can be expanded markedly in gelatin microbeads, while retaining MSC surface marker expression, multipotent differential potential, and expression of core transcription factors. These cells also efficiently enhanced skin wound healing in vivo, in a manner comparable to that of hWJ-MSC obtained from 2D culture.

Novel injectable porous poly(γ-benzyl-l-glutamate) microspheres for cartilage tissue engineering: preparation and evaluation

A novel injectable synthetic polypeptide of a poly(γ-benzyl-l-glutamate) macroporous microcarrier was developed for cartilage tissue engineering.

3D dynamic culture of rabbit articular chondrocytes encapsulated in alginate gel beads using spinner flasks for cartilage tissue regeneration

Cell-based therapy using chondrocytes for cartilage repair suffers from chondrocyte dedifferentiation. In the present study, the effects of an integrated three-dimensional and dynamic culture on rabbit articular chondrocytes were investigated. Cells (passages 1 and 4) were encapsulated in alginate gel beads and cultured in spinner flasks in chondrogenic and chondrocyte growth media. Subcutaneous implantation of the cell-laden beads was performed to evaluate the ectopic chondrogenesis. It was found that cells remained viable after 35 days in the three-dimensional dynamic culture. Passage 1 cells demonstrated a proliferative growth in both media. Passage 4 cells showed a gradual reduction in DNA content in growth medium, which was attenuated in chondrogenic medium. Deposition of glycosaminoglycans (GAG) was found in all cultures. While passage 1 cells generally produced higher amounts of GAG than passage 4 cells, GAG/DNA became similar on day 35 for both cells in growth media. Interestingly, GAG/DNA in growth medium was greater than that in chondrogenic medium for both cells. Based on GAG quantification and gene expression analysis, encapsulated passage 1 cells cultured in growth medium displayed the best ectopic chondrogenesis. Taken together, the three-dimensional and dynamic culture for chondrocytes holds great potential in cartilage regeneration.

Tissue-engineered cartilage: the crossroads of biomaterials, cells and stimulating factors

Damage to cartilage represents one of the most challenging tasks of musculoskeletal therapeutics due to its limited propensity for healing and regenerative capabilities. Lack of current treatments to restore cartilage tissue function has prompted research in this rapidly emerging field of tissue regeneration of functional cartilage tissue substitutes. The development of cartilaginous tissue largely depends on the combination of appropriate biomaterials, cell source, and stimulating factors. Over the years, various biomaterials have been utilized for cartilage repair, but outcomes are far from achieving native cartilage architecture and function. This highlights the need for exploration of suitable biomaterials and stimulating factors for cartilage regeneration. With these perspectives, we aim to present an overview of cartilage tissue engineering with recent progress, development, and major steps taken toward the generation of functional cartilage tissue. In this review, we have discussed the advances and problems in tissue engineering of cartilage with strong emphasis on the utilization of natural polymeric biomaterials, various cell sources, and stimulating factors such as biophysical stimuli, mechanical stimuli, dynamic culture, and growth factors used so far in cartilage regeneration. Finally, we have focused on clinical trials, recent innovations, and future prospects related to cartilage engineering.

Dynamic cell culture on calcium phosphate microcarriers for bone tissue engineering applications

Developing appropriate cell culturing techniques to populate scaffolds has become a great challenge in tissue engineering. This work describes the use of spinner flask dynamic cell cultures to populate hydroxyapatite microcarriers for bone tissue engineering. The microcarriers were obtained through the emulsion of a self-setting aqueous α-tricalcium phosphate slurry in oil. After setting, hydroxyapatite microcarriers were obtained. The incorporation of gelatin in the liquid phase of the α-tricalcium phosphate slurry allowed obtaining hybrid gelatin/hydroxyapatite-microcarriers. Initial cell attachment on the microcarriers was strongly influenced by the speed of the dynamic culture, achieving higher attachment at low speed (40 r/min) as compared to high speed (80 r/min). Under moderate culture speeds (40 r/min), the number of cells present in the culture as well as the number of microcarrier-containing cells considerably increased after 3 days, particularly in the gelatin-containing microcarriers. At longer culture times in dynamic culture, hydroxyapatite-containing microcarriers formed aggregates containing viable and extracellular matrix proteins, with a significantly higher number of cells compared to static cultures.

Isolation and ex vivo expansion of synovial mesenchymal stromal cells for cartilage repair

BACKGROUND AIMS

Hyaline articular cartilage is a highly specialized tissue that offers a low-friction and wear-resistant interface for weight-bearing surface articulation in diarthrodial joints, but it lacks vascularity. It displays an inherent inability to heal when injured in a skeletally mature individual. Joint-preserving treatment procedures such as mosaicplasty, débridement, perichondrium transplantation and autologous chondrocyte implantation have shown variable results, and the average long-term result is sub-standard. Because of these limitations of the treatment methods and lack of intrinsic repair capacity of mature cartilage tissue, an alternative treatment approach is needed, and synovial mesenchymal stromal cells (SMSCs) represent an attractive therapeutic alternative because of their ex vivo proliferation capacity, multipotency and ability to undergo chondrogenesis.

METHODS

SMSCs were isolated from tissues obtained by arthroscopy using two types of biopsies. Ex vivo cell expansion was accomplished under static and dynamic culture followed by characterization of cells according to the International Society for Cellular Therapy guidelines. Kinetic growth models and metabolite analysis were used for understanding the growth profile of these cells.

RESULTS

For the first time, SMSCs were expanded in stirred bioreactors and achieved higher cell density in a shorter period of time compared with static culture or with other mesenchymal stromal cell sources.

CONCLUSIONS

In this study we were able to achieve (8.8 ± 0.2) × 10(5) cells within <2 weeks in dynamic culture under complete xeno-free conditions. Our results also provided evidence that after dynamic culture these cells had an up-regulation of chondrogenic genes, which can be a potential factor for articular cartilage regeneration in clinical settings.

Marine collagen scaffolds for nasal cartilage repair: prevention of nasal septal perforations in a new orthotopic rat model using tissue engineering techniques

Autologous grafts are frequently needed for nasal septum reconstruction. Because they are only available in limited amounts, there is a need for new cartilage replacement strategies. Tissue engineering based on the use of autologous chondrocytes and resorbable matrices might be a suitable option. So far, an optimal material for nasal septum reconstruction has not been identified. The aim of our study was to provide the first evaluation of marine collagen for use in nasal cartilage repair. First, we studied the suitability of marine collagen as a cartilage replacement matrix in the context of in vitro three dimensional cultures by analyzing cell migration, cytotoxicity, and extracellular matrix formation using human and rat nasal septal chondrocytes. Second, we worked toward developing a suitable orthotopic animal model for nasal septum repair, while simultaneously evaluating the biocompatibility of marine collagen. Seeded and unseeded scaffolds were transplanted into nasal septum defects in an orthotopic rat model for 1, 4, and 12 weeks. Explanted scaffolds were histologically and immunohistochemically evaluated. Scaffolds did not induce any cytotoxic reactions in vitro. Chondrocytes were able to adhere to marine collagen and produce cartilaginous matrix proteins, such as collagen type II. Treating septal cartilage defects in vivo with seeded and unseeded scaffolds led to a significant reduction in the number of nasal septum perforations compared to no replacement. In summary, we demonstrated that marine collagen matrices provide excellent properties for cartilage tissue engineering. Marine collagen scaffolds are able to prevent septal perforations in an autologous, orthotopic rat model. This newly described experimental surgical procedure is a suitable way to evaluate new scaffold materials for their applicability in the context of nasal cartilage repair.

Microstructure and characteristic properties of gelatin/chitosan scaffold prepared by a combined freeze-drying/leaching method

A combined freeze-drying and particulate leaching method for scaffold synthesis showed an improvement in the horizontal microstructure of the gelatin/chitosan scaffolds. Type and concentration of the cross-linking agent, freezing temperature, concentration of the polymeric solution and gelatin/chitosan weight ratio were the variables affecting the scaffold properties. Assessment of the tensile properties of the scaffolds revealed that for a scaffold with 50% chitosan, glutaraldehyde, as a cross-linking agent, created much tighter polymeric network compared to N,N-(3-dimethylaminopropyl)-N'-ethyl carbodiimide (EDC). However, in the case of gelatin scaffolds, EDC was identified as the stronger cross-linker. Compressive behavior of the scaffolds satisfied formulations obtained from the theoretical modeling of the low-density, elastomeric foams. The investigation of the scaffold degradation indicated that the increase in the mechanical strength of the scaffolds would not always reduce their degradation rate.

Microcarrier culture for efficient expansion and osteogenic differentiation of human fetal mesenchymal stem cells

Stirred microcarrier (MC) culture has been suggested as the method of choice for supplying large volumes of mesenchymal stem cells (MSCs) for bone tissue engineering. In this study, we show that in addition to the improvement in cell expansion capacity, MSCs propagated and harvested from MC culture also demonstrate higher osteogenic potency when differentiated in vivo or in vitro in three-dimensional (3D) scaffold cultures as compared with traditional monolayer (MNL) cultures. Cytodex 3 microcarrier-expanded human fetal MSC (hfMSC) cultures (MC-hfMSCs) achieved 12- to 16-fold expansion efficiency (6×10⁵–8×10⁵ cells/mL) compared to 4- to 6-fold (1.2×10⁵–1.8×10⁵ cells/mL) achieved by traditional MNL-expanded hfMSC culture (MNL-hfMSCs; p<0.05). Both MC-hfMSCs and MNL-hfMSCs maintained similar colony-forming capacity, doubling times, and immunophenotype postexpansion. However, when differentiated under in vitro two-dimensional (2D) osteogenic conditions, MC-hfMSCs exhibited a 45-fold reduction in alkaline phosphatase level and a 37.5% decrease in calcium deposition compared with MNL-hfMSCs (p<0.05). Surprisingly, when MC-hfMSCs and MNL-hfMSCs were seeded on 3D macroporous scaffold culture or subcutaneously implanted into nonobese diabetic/severe combined immunodeficient mice, MC-hfMSCs deposited 63.5% (p<0.05) more calcium and formed 47.2% (p<0.05) more bone volume, respectively. These results suggest that the mode of hfMSC growth in the expansion phase affects the osteogenic potential of hfMSCs differently in various differentiation platforms. In conclusion, MC cultures are advantageous over MNL cultures in bone tissue engineering because MC-hfMSCs have improved cell expansion capacity and exhibit higher osteogenic potential than MNL-hfMSCs when seeded in vitro into 3D scaffolds or implanted in vivo.

The interplay between chondrocyte redifferentiation pellet size and oxygen concentration

Chondrocytes dedifferentiate during ex vivo expansion on 2-dimensional surfaces. Aggregation of the expanded cells into 3-dimensional pellets, in the presence of induction factors, facilitates their redifferentiation and restoration of the chondrogenic phenotype. Typically 1×10(5)-5×10(5) chondrocytes are aggregated, resulting in "macro" pellets having diameters ranging from 1-2 mm. These macropellets are commonly used to study redifferentiation, and recently macropellets of autologous chondrocytes have been implanted directly into articular cartilage defects to facilitate their repair. However, diffusion of metabolites over the 1-2 mm pellet length-scales is inefficient, resulting in radial tissue heterogeneity. Herein we demonstrate that the aggregation of 2×10(5) human chondrocytes into micropellets of 166 cells each, rather than into larger single macropellets, enhances chondrogenic redifferentiation. In this study, we describe the development of a cost effective fabrication strategy to manufacture a microwell surface for the large-scale production of micropellets. The thousands of micropellets were manufactured using the microwell platform, which is an array of 360×360 µm microwells cast into polydimethylsiloxane (PDMS), that has been surface modified with an electrostatic multilayer of hyaluronic acid and chitosan to enhance micropellet formation. Such surface modification was essential to prevent chondrocyte spreading on the PDMS. Sulfated glycosaminoglycan (sGAG) production and collagen II gene expression in chondrocyte micropellets increased significantly relative to macropellet controls, and redifferentiation was enhanced in both macro and micropellets with the provision of a hypoxic atmosphere (2% O2). Once micropellet formation had been optimized, we demonstrated that micropellets could be assembled into larger cartilage tissues. Our results indicate that micropellet amalgamation efficiency is inversely related to the time cultured as discreet microtissues. In summary, we describe a micropellet production platform that represents an efficient tool for studying chondrocyte redifferentiation and demonstrate that the micropellets could be assembled into larger tissues, potentially useful in cartilage defect repair.

Gelatin microparticles aggregates as three-dimensional scaffolding system in cartilage engineering

A three-dimensional (3D) scaffolding system for chondrocytes culture has been produced by agglomeration of cells and gelatin microparticles with a mild centrifuging process. The diameter of the microparticles, around 10 μ, was selected to be in the order of magnitude of the chondrocytes. No gel was used to stabilize the construct that maintained consistency just because of cell and extracellular matrix (ECM) adhesion to the substrate. In one series of samples the microparticles were charged with transforming growth factor, TGF-β1. The kinetics of growth factor delivery was assessed. The initial delivery was approximately 48 % of the total amount delivered up to day 14. Chondrocytes that had been previously expanded in monolayer culture, and thus dedifferentiated, adopted in this 3D environment a round morphology, both with presence or absence of growth factor delivery, with production of ECM that intermingles with gelatin particles. The pellet was stable from the first day of culture. Cell viability was assessed by MTS assay, showing higher absorption values in the cell/unloaded gelatin microparticle pellets than in cell pellets up to day 7. Nevertheless the absorption drops in the following culture times. On the contrary the cell viability of cell/TGF-β1 loaded gelatin microparticle pellets was constant during the 21 days of culture. The formation of actin stress fibres in the cytoskeleton and type I collagen expression was significantly reduced in both cell/gelatin microparticle pellets (with and without TGF-β1) with respect to cell pellet controls. Total type II collagen and sulphated glycosaminoglycans quantification show an enhancement of the production of ECM when TGF-β1 is delivered, as expected because this growth factor stimulate the chondrocyte proliferation and improve the functionality of the tissue.

Current concepts in stem cell therapy for articular cartilage repair

INTRODUCTION

Hyaline articular cartilage is the connective tissue responsible for frictionless joint movement. Its degeneration ultimately results in complete loss of joint function in the late stages of osteoarthritis. Intrinsic repair is compromised, and cartilage tissue regeneration is difficult. However, new options are available to repair cartilage tissue by applying ESCs, MSCs and CPCs.

AREAS COVERED

In this review, the authors shed light on the different concepts currently under investigation for cartilage repair.

EXPERT OPINION

So far, there is no way to derive a chondrogenic lineage from stem cells that forms functional hyaline cartilage tissue in vivo. One alternative might be to enhance the chondrogenic potential of repair cells, which are already present in diseased cartilage tissue. CPCs found in diseased cartilage tissue in situ are biologically driven toward the osteochondrogenic lineage and can be directed toward chondrogenesis at least in vitro.

Chondrogenic phenotype of different cells encapsulated in κ-carrageenan hydrogels for cartilage regeneration strategies

Engineering articular cartilage substitutes using hydrogels with encapsulated cells is an approach that has received increasing attention in recent years. Hydrogels based on κ-carrageenan (κC), a thermoreversible natural-origin polymer, have been recently proposed as new cell/growth factor delivery vehicles for regenerative medicine. In this work, we report the potential of such hydrogels encapsulating either human-adipose-derived stem cells (hASCs), human nasal chondrocytes (hNCs), or a chondrocytic cell line (ATDC5) for cartilage regeneration strategies. The in vitro cellular behavior of the encapsulated cells within κC hydrogel was analyzed after different culturing periods using biochemical assays and histological and real-time reverse-transcription PCR analysis. The three types of cells encapsulated in κC hydrogels showed good cellular viability and proliferation up to 21 days of culture, and the cell-laden hydrogels were positive for specific cartilage markers. In summary, the results demonstrate that hASCs embedded in κC hydrogels proliferate faster and exhibit higher expression levels of typical cartilage markers as compared with hNCs or ATDC5 cells. Based on these data, it is possible to conclude that κC hydrogel provides a good support for culture and differentiation of encapsulated cells and that hASCs may provide an advantageous alternative to primary chondrocytes, currently used in clinical treatments of cartilage defects/diseases.

Micro- and nanostructured hydroxyapatite-collagen microcarriers for bone tissue-engineering applications

Novel hydroxyapatite (HA)-collagen microcarriers (MCs) with different micro/nanostructures were developed for bone tissue-engineering applications. The MCs were fabricated via calcium phosphate cement (CPC) emulsion in oil. Collagen incorporation in the liquid phase of the CPC resulted in higher MC sphericity. The MCs consisted of a porous network of entangled hydroxyapatite crystals, formed as a result of the CPC setting reaction. The addition of collagen to the MCs, even in an amount as small as 0.8 wt%, resulted in an improved interaction with osteoblast-like Saos-2 cells. The micro/nanostructure and the surface texture of the MCs were further tailored by modifying the initial particle size of the CPC. A synergistic effect between the presence of collagen and the nanosized HA crystals was found, resulting in significantly enhanced alkaline phosphatase activity on the collagen-containing nanosized HA MCs.

Cell expansion of human articular chondrocytes on macroporous gelatine scaffolds-impact of microcarrier selection on cell proliferation

This study investigates human chondrocyte expansion on four macroporous gelatine microcarriers (CultiSpher) differing with respect to two manufacturing processes-the amount of emulsifier used during initial preparation and the gelatine cross-linking medium. Monolayer-expanded articular chondrocytes from three donors were seeded onto the microcarriers and cultured in spinner flask systems for a total of 15 days. Samples were extracted every other day to monitor cell viability and establish cell counts, which were analysed using analysis of variance and piecewise linear regression. Chondrocyte densities increased according to a linear pattern for all microcarriers, indicating an ongoing, though limited, cell proliferation. A strong chondrocyte donor effect was seen during the initial expansion phase. The final cell yield differed significantly between the microcarriers and our results indicate that manufacturing differences affected chondrocyte densities at this point. Remaining cells stained positive for chondrogenic markers SOX-9 and S-100 but extracellular matrix formation was modest to undetectable. In conclusion, the four gelatine microcarriers supported chondrocyte adhesion and proliferation over a two week period. The best yield was observed for microcarriers produced with low emulsifier content and cross-linked in water and acetone. These results add to the identification of optimal biomaterial parameters for specific cellular processes and populations.

The interplay between cell adhesion cues and curvature of cell adherent alginate microgels in multipotent stem cell culture

Cell-adherent microcarriers are increasingly used to expand multipotent stem cells on a large scale for therapeutic applications. However, the role of the microcarrier properties and geometry on the phenotypic activities of multipotent cells has not been well studied. This study presents a significant interplay of the number of cell adhesion sites and the curvature of the microcarrier in regulating cell growth and differentiation by culturing mesenchymal stem cells on alginate microgels chemically linked with oligopeptides containing the Arg-Gly-Asp (RGD) sequence. Interestingly, the cell growth rate and osteogenic differentiation level were increased with the RGD peptide density. At a given RGD peptide density, the cell growth rate was inversely related to the microgel diameter, whereas the osteogenic differentiation level was minimally influenced. The dependency of the cell growth rate on the microgel diameter was related to changes in shear stresses acting on cells according to simulation. Overall, this study identifies material variables key to regulating cellular activities on microcarriers, and these findings will be useful to designing a broad array of bioactive microcarriers.

Effects of oxygen and culture system on in vitro propagation and redifferentiation of osteoarthritic human articular chondrocytes

Regenerative medicine-based approaches for the repair of damaged cartilage rely on the ability to propagate cells while promoting their chondrogenic potential. Thus, conditions for cell expansion should be optimized through careful environmental control. Appropriate oxygen tension and cell expansion substrates and controllable bioreactor systems are probably critical for expansion and subsequent tissue formation during chondrogenic differentiation. We therefore evaluated the effects of oxygen and microcarrier culture on the expansion and subsequent differentiation of human osteoarthritic chondrocytes. Freshly isolated chondrocytes were expanded on tissue culture plastic or CultiSpher-G microcarriers under hypoxic or normoxic conditions (5% or 20% oxygen partial pressure, respectively) followed by cell phenotype analysis with flow cytometry. Cells were redifferentiated in micromass pellet cultures over 4 weeks, under either hypoxia or normoxia. Chondrocytes cultured on tissue culture plastic proliferated faster, expressed higher levels of cell surface markers CD44 and CD105 and demonstrated stronger staining for proteoglycans and collagen type II in pellet cultures compared with microcarrier-cultivated cells. Pellet wet weight, glycosaminoglycan content and expression of chondrogenic genes were significantly increased in cells differentiated under hypoxia. Hypoxia-inducible factor-3α mRNA was up-regulated in these cultures in response to low oxygen tension. These data confirm the beneficial influence of reduced oxygen on ex vivo chondrogenesis. However, hypoxia during cell expansion and microcarrier bioreactor culture does not enhance intrinsic chondrogenic potential. Further improvements in cell culture conditions are therefore required before chondrocytes from osteoarthritic and aged patients can become a useful cell source for cartilage regeneration.

Expansion and preservation of multipotentiality of rabbit bone-marrow derived mesenchymal stem cells in dextran-based microcarrier spin culture

The use of mesenchymal stem cells (MSCs) in tissue repair and regeneration despite their multipotentiality has been limited by their cell source quantity and decelerating proliferative yield efficiency. A study was thus undertaken to determine the feasibility of using microcarrier beads in spinner flask cultures for MSCs expansion and compared to that of conventional monolayer cultures and static microcarrier cultures. Isolation and characterization of bone marrow derived MSCs were conducted from six adult New Zealand white rabbits. Analysis of cell morphology on microcarriers and culture plates at different time points (D0, D3, D10, D14) during cell culture were performed using scanning electron microscopy and bright field microscopy. Cell proliferation rates and cell number were measured over a period of 14 days, respectively followed by post-expansion characterization. MTT proliferation assay demonstrated a 3.20 fold increase in cell proliferation rates in MSCs cultured on microcarriers in spinner flask as compared to monolayer cultures (p < 0.05). Cell counts at day 14 were higher in those seeded on stirred microcarrier cultures (6.24 ± 0.0420 cells/ml) × 10(5) as compared to monolayer cultures (0.22 ± 0.004 cells/ml) × 10(5) and static microcarrier cultures (0.20 ± 0.002 cells/ml) × 10(5). Scanning electron microscopy demonstrated an increase in cell colonization of the cells on the microcarriers in stirred cultures. Bead-expanded MSCs were successfully differentiated into osteogenic and chondrogenic lineages. This system offers an improved and efficient alternative for culturing MSCs with preservation to their phenotype and multipotentiality.

Adult human articular chondrocytes in a microcarrier-based culture system: expansion and redifferentiation

Expanding human chondrocytes in vitro while maintaining their ability to form cartilage remains a key challenge in cartilage tissue engineering. One promising approach to address this is to use microcarriers as substrates for chondrocyte expansion. While microcarriers have shown beneficial effects for expansion of animal and ectopic human chondrocytes, their utility has not been determined for freshly isolated adult human articular chondrocytes. Thus, we investigated the proliferation and subsequent chondrogenic differentiation of these clinically relevant cells on porous gelatin microcarriers and compared them to those expanded using traditional monolayers. Chondrocytes attached to microcarriers within 2 days and remained viable over 4 weeks of culture in spinner flasks. Cells on microcarriers exhibited a spread morphology and initially proliferated faster than cells in monolayer culture, however, with prolonged expansion they were less proliferative. Cells expanded for 1 month and enzymatically released from microcarriers formed cartilaginous tissue in micromass pellet cultures, which was similar to tissue formed by monolayer-expanded cells. Cells left attached to microcarriers did not exhibit chondrogenic capacity. Culture conditions, such as microcarrier material, oxygen tension, and mechanical stimulation require further investigation to facilitate the efficient expansion of clinically relevant human articular chondrocytes that maintain chondrogenic potential for cartilage regeneration applications. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:539-546, 2011.

Enhanced attachment, growth and migration of smooth muscle cells on microcarriers produced using thermally induced phase separation

Microcarriers are widely used for the expansion of cells in vitro, but also offer an approach for combining cell transplantation and tissue bulking for regenerative medicine in a minimally invasive manner. This could be beneficial in conditions associated with muscle damage or atrophy, such as faecal incontinence, where the use of bulking materials or cell transplantation alone has proven to be ineffective. Microcarriers currently available have not been designed for this purpose and are likely to be suboptimal due to their physical and biochemical properties. The aim of this study was to investigate macroporous microspheres of polylactide-co-glycolide (PLGA), prepared using a thermally induced phase separation technique, for their suitability as cell microcarriers for the transplantation of smooth muscle cells. Cell attachment, growth and migration were studied and compared with commercially available porcine gelatin microcarriers (Cultispher-S) in suspension culture. Smooth muscle cells attached more rapidly to the PLGA microcarriers, which also significantly enhanced the rate of cell growth compared with Cultispher-S microcarriers. The majority of smooth muscle cells attached to the PLGA microcarriers in suspension culture were able to migrate away over a 15 day period of static culture, unlike Cultispher-S microcarriers which retained the majority of cells. The ability of PLGA microcarriers to enhance cell growth combined with their capacity to release cells at the sites of delivery are features that make them ideally suited for use as a cell transplantation delivery device in tissue engineering and regenerative medicine.