Bioreactor Microcarrier Cell Culture System (Bio-MCCS) for Large-Scale Production of Autologous Melanocytes

Current Trends in Gelatin-Based Drug Delivery Systems

Gelatin is a highly versatile natural polymer, which is widely used in healthcare-related sectors due to its advantageous properties, such as biocompatibility, biodegradability, low-cost, and the availability of exposed chemical groups. In the biomedical field, gelatin is used also as a biomaterial for the development of drug delivery systems (DDSs) due to its applicability to several synthesis techniques. In this review, after a brief overview of its chemical and physical properties, the focus is placed on the commonly used techniques for the development of gelatin-based micro- or nano-sized DDSs. We highlight the potential of gelatin as a carrier of many types of bioactive compounds and its ability to tune and control select drugs' release kinetics. The desolvation, nanoprecipitation, coacervation, emulsion, electrospray, and spray drying techniques are described from a methodological and mechanistic point of view, with a careful analysis of the effects of the main variable parameters on the DDSs' properties. Lastly, the outcomes of preclinical and clinical studies involving gelatin-based DDSs are thoroughly discussed.

Plant proteins as the functional building block of edible microcarriers for cell-based meat culture application

Edible microcarriers are essential for developing cell-based meat in large-scale cell cultures. As they are required to be embedded in the final products, the microcarriers should be edible, biocompatible, cost-effective, and pathogen-free. The invention of edible animal-free microcarriers would be a breakthrough for cell-based meat culture. We reviewed the fabrication techniques and the materials of microcarriers, and found that plant proteins, having diverse structures and composition, could possess the active domains that are hypnotized to replace the animal-based extracellular matrix (ECM) for meat culture applications. In addition, the bioactive peptides in plants have been reviewed and most of them were resulted from enzyme hydrolysis. Therefore, plant proteins with rich bioactive peptides have the potential in the development microcarriers. Our work provided some new trains of thought for developing plant-based biomaterials as ECM materials and advances the fabrication of microcarriers for meat culture.

Tissue Regeneration of Human Mesenchymal Stem Cells on Porous Gelatin Micro-Carriers by Long-Term Dynamic In Vitro Culture

Background

Tissue engineering is a multidisciplinary field which attracted much attention in recent years. One of the most important issue in tissue engineering is how to obtain high cell numbers and tissue regeneration while maintaining appropriate cellular characteristics in vitro for restoring damaged or dysfunctional body tissues and organs. These demands can be achieved by the use of three dimensional (3D) dynamic cultures of cells combined with cell-adhesive micro-carriers.

Method

In this study, human mesenchymal stem cells (hMSCs) were cultured in a wave-bioreactor system for up to 100 days, after seeding on Cultisphere-S porous gelatin micro-carriers. Cell counting was performed at the time points of 7, 12, 17, 31 days and compared to those of hMSCs cultured under static condition. Higher growth and proliferation rates was achieved in wave-type dynamic culture, when cell culture continued to day 31. A scanning electron microscope (SEM) photographs, both live and dead and MTT assays were taken to confirm the survival and distribution of cells on porous gelatin micro-carrier surfaces. The results of histological stains such as hematoxylin and eosin, Masson's trichrome, Alcian blue and Alizarin red S also showed improved proliferation and tissue regeneration of hMSCs on porous gelatin micro-carriers.

Conclusion

The experimental results demonstrated the effect and importance of both micro-carriers and bioreactor in hMSC expansion on cell proliferation and migration as well as extracellular matrix formation on the superficial and pore surfaces of the porous gelatin micro-carriers, and then their inter-connections, leading to tissue regeneration.

Feasibility of human hair follicle-derived mesenchymal stem cells/CultiSpher(®)-G constructs in regenerative medicine

The use of human mesenchymal stem cells (hMSCs) in cell therapies has increased the demand for strategies that allow efficient cell scale-up. Preliminary data on the three-dimensional (3D) spinner culture describing the potential use of microcarriers for hMSCs culture scale-up have been reported. We exploited a rich source of autologous stem cells (human hair follicle) and demonstrated the robust in vitro long-term expansion of human hair follicle-derived mesenchymal stem cells (hHF-MSCs) by using CultiSpher(®)-G microcarriers. We analyzed the feasibility of 3D culture by using hHF-MSCs/CultiSpher(®)-G microcarrier constructs for its potential applicability in regenerative medicine by comparatively analyzing the performance of hHF-MSCs adhered to the CultiSpher(®)-G microspheres in 3D spinner culture and those grown on the gelatin-coated plastic dishes (2D culture), using various assays. We showed that the hHF-MSCs seeded at various densities quickly adhered to and proliferated well on the microspheres, thus generating at least hundreds of millions of hHF-MSCs on 1 g of CultiSpher(®)-G within 12 days. This resulted in a cumulative cell expansion of greater than 26-fold. Notably, the maximum and average proliferation rates in 3D culture were significantly greater than that of the 2D culture. However, the hHF-MSCs from both the cultures retained surface marker and nestin expression, proliferation capacity and differentiation potentials toward adipocytes, osteoblasts and smooth muscle cells and showed no significant differences as evidenced by Edu incorporation, cell cycle, colony formation, apoptosis, biochemical quantification and qPCR assays.

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.

Functional Cells Cultured on Microcarriers for Use in Regenerative Medicine Research

Microcarriers have been successfully used for many years for growing anchorage-dependent cells and as a means of delivering cells for tissue repair. When cultured on microcarriers, the number of anchorage-dependent cells, including primary cells, can easily be scaled up and controlled to generate the quantities of cells necessary for therapeutic applications. Recently, stem cell technology has been recognized as a powerful tool in regenerative medicine, but adequate numbers of stem cells that retain their differentiation potential are still difficult to obtain. For anchorage-dependent stem cells, however, microcarrier-based suspension culture using various types of microcarriers has proven to be a good alternative for effective ex vivo expansion. In this article, we review studies reporting the expansion, differentiation, or transplantation of functional anchorage-dependent cells that were expanded with the microcarrier culture system. Thus, the implementation of technological advances in biodegradable microcarriers, the bead-to-bead transfer process, and appropriate stem cell media may soon foster the ability to produce the numbers of stem cells necessary for cell-based therapies and/or tissue engineering.

Agarose-gelatin conjugate membrane enhances proliferation of adherent cells enclosed in hollow-core microcapsules

Controlling growth of cells enclosed in hollow-core microcapsules is an important issue for the practical use of the device in biomedical and biopharmaceutical fields. In this study, we developed hollow-core microcapsules with a cell-adhesive agarose-gelatin conjugate (Aga-Ge) gel membrane for enhancement of adherent cell growth. We enclosed adherent feline kidney cells in these microcapsules and compared their growth profile and behavior with cells in microcapsules with an unmodified agarose membrane. The cells grew approx. 2-fold faster in microcapsules with the Aga-Ge membrane than in those with the unmodified agarose membrane. Fluorescence observation of the cellular skeleton clearly revealed that the enclosed cells adhered and spread on the inner surface of the Aga-Ge membrane but not on the unmodified agarose membrane. The maximum cell densities estimated on the basis of the cellular mitochondrial activities were independent of the cellular adhesiveness of the membrane. The mitochondrial activities per vehicle were similar for the two types of microcapsules. These results demonstrate that construction of microcapsule membranes from cell-adhesive materials is effective for enhancing cellular growth in these devices.

Stem cells bioprocessing: an important milestone to move regenerative medicine research into the clinical arena

Regenerative Medicine is a new, multidisciplinary field that combines expertise in biology, chemistry, engineering, materials, and medicine, to find solutions to some of the most challenging medical problems faced by humankind. Regenerative Medicine has the potential to impact the whole spectrum of health care, such as heart disease, emphysema, and diabetes. Regenerative Medicine employs various combinations of specially grown cells, tissues, and laboratory-made compounds to replace or amplify the body's natural healing process. The impact of Regenerative Medicine to the health care industry is likely to be comparable with that of antibiotics, vaccines and lately, monoclonal antibodies have had in clinical care. Regenerative Medicine is growing and maturing steadily; however, many challenges lie ahead. These include best cell source, most appropriate biomaterials, and reliable ways of expanding the cells and growing them in a three-dimensional environment (stem cell bioprocessing). This concise review deals with current achievements in the field, challenges that lie ahead and potential ways of having robust and reliable "off the shelf" cellular products.

Employing human keratinocytes cultured on macroporous gelatin spheres to treat full thickness-wounds: An in vivo study on athymic rats

Providing cutaneous wounds with sufficient epidermis to prevent infections and fluid loss is one of the most challenging tasks associated with surgical treatment of burns. Recently, application of cultured keratinocytes in this context has allowed this challenge to be met without several of the limitations connected with the use of split-thickness skin grafts. The continuous development of this novel approach has now revealed that transplantation of cultured autologous keratinocytes as single-cell suspensions exhibits several advantages over the use of cultured epidermal grafts. However, a number of methodological problems remain to be solved, primarily with regards to the complexity of culturing these cells; loss of viability and other negative effects during their preparation and transportation; the relatively long period of time required following transplantation to obtain a sufficiently protective epidermis. In the present investigation we attempted to eliminate these limitations by culturing the keratinocytes on macroporous gelatin spheres. Accordingly, the efficacies of normal human keratinocytes in single-cell suspension or growing on macroporous gelatin spheres, as well as of split-thickness skin grafts in healing wounds on athymic rats were compared. Human keratinocytes were found to adhere and proliferate efficiently both on the surface and within the pores of such spheres. Transplantation of such cells adherent to the spheres resulted in significantly more rapid formation of a stratified epidermis than did transplantation of single-cell suspensions or spheres alone. Twenty-three days after transplantation, the epidermis formed from the cells bound to the spheres was not as thick as the epidermis on wounds covered with split-thickness skin grafts, but significantly thicker than on wounds to which single-cell suspensions, spheres alone or no transplant at all was applied. Furthermore, fluorescence in situ hybridisation revealed that the transplanted keratinocytes, both those adherent to gelatin spheres and those in single-cell suspension, were components of the newly formed epidermis. These findings indicate that application of biodegradable macroporous spheres may prove to be of considerable value in designing cell-based therapies for the treatment of acute and persistent wounds.

A 3D collagen microsphere culture system for GDNF-secreting HEK293 cells with enhanced protein productivity

Mammalian cell culture technology has been used for decades in mass production of therapeutic proteins. However, unrestricted cell proliferation usually results in low-protein productivity. Controlled proliferation technologies such as metabolism intervention and genetic manipulation are therefore applied to enhance the productivity. Nevertheless, these strategies induced growth arrest with reduced viability and increased apoptosis. In this study, we report a new controlled proliferation technology by encapsulating human embryonic kidney (HEK) 293 cells over-expressing glial-derived neurotrophic factor (GDNF) in 3D collagen microspheres for extended culture. We investigated the viability, proliferation, cell cycle and GDNF productivity of HEK293 cells in microspheres as compared to monolayer culture. This system provides a physiologically relevant tissue-like environment for cells to grow and exerts proliferation control throughout the culture period without compromising the viability. A significant increase in the production rate of GDNF was found in the 3D microsphere system comparing with the monolayer culture. GDNF productivity was also significantly affected by the initial cell number and the serum concentration. The secreted GDNF was still bioactive as it induced neurite extension in PC12 cells. In summary, the 3D collagen microsphere system presents a cost-effective controlled growth technology for protein production in pharmaceutical manufacturing.

Assessment of an Automated Bioreactor to Propagate and Harvest Keratinocytes for Fabrication of Engineered Skin Substitutes

Engineered skin substitutes (ESS) composed of autologous fibroblasts and keratinocytes attached to collagen-glycosaminoglycan (GAG) scaffolds are effective adjuncts in the treatment of massive burns. The Kerator, an automated bioreactor for keratinocyte culture, could hypothetically reduce labor and material requirements, and increase availability of ESS. Human keratinocytes were cultured in the Kerator and also in tissue-culture flasks. It was found that keratinocyte confluence increased exponentially with time in both the Kerator (r2=0.99) and the flasks (r2=0.96). Confluence (mean+/-SEM) of keratinocytes in the flasks (28+/-2.3%) was significantly higher than in the Kerator (18+/-0.93%) at day 4. However, there was no difference in confluence at harvest. The colony forming efficiency (CFE) and population doublings (PD) per day of keratinocytes harvested from the Kerator were 67+/-4.7% and 0.80+/-0.06, respectively, and were not different from the corresponding values for keratinocytes from flasks. ESS fabricated with keratinocytes from the Kerator or from the flasks were comparable in vitro in terms of histological anatomy, cellular viability, and surface hydration. These findings show that there are no differences between keratinocytes from the Kerator and those from the flasks regarding (a) growth to confluence, (b) CFE and growth rate (PD/day), or (c) quality of ESS in vitro, suggesting that the Kerator can automate fabrication of ESS and increase its availability for treatment of skin wounds.

High yields of autologous living dermal equivalents using porcine gelatin microbeads as microcarriers for autologous fibroblasts

Permanent skin replacement requires a dermal component to ensure adequate long-term graft stability and to prevent wound contraction. This study was to construct a bioreactor microcarrier cell culture system (Bio-MCCS) to produce autologous living dermal equivalents on a large scale. Autologous fibroblasts were isolated from split-thickness skin biopsy from a leg ulcer patient, inoculated onto macroporous porcine gelatin microbeads, and incubated in a bioreactor (Cellspin) in serum-free fibroblast growth medium or in DMEM medium containing 10% fetal calf serum (FCS). Fibroblasts rapidly adhered to and actively proliferated on the microbeads in the bioreactor in both serum-free and serum-containing medium. MTT assay showed the number of fibroblasts on the microbeads reached up to 5.3- or 4.0-fold the cells seeded in DMEM medium containing 10% FCS or serum-free medium, respectively. When removed from Bio-MCCS and cultured under static conditions, fibroblasts were able to leave the microbeads and proliferate to confluence on the bottom of tissue culture flasks. When stored at room temperature in DMEM containing 10% FBS, fibroblast cultured on the microbeads retained highest viabilities for at least 3 weeks, up to 82% of originals. This Bio-MCCS using porcine gelatin microbeads as carriers for fibroblasts offers a new option of mass production of autologous living dermal equivalents.