Stem cell bioprocessing: fundamentals and principles.

In recent years, the potential of stem cell research for tissue engineering-based therapies and regenerative medicine clinical applications has become well established. In 2006, Chung pioneered the first entire organ transplant using adult stem cells and a scaffold for clinical evaluation. With this a new milestone was achieved, with seven patients with myelomeningocele receiving stem cell-derived bladder transplants resulting in substantial improvements in their quality of life. While a bladder is a relatively simple organ, the breakthrough highlights the incredible benefits that can be gained from the cross-disciplinary nature of tissue engineering and regenerative medicine (TERM) that encompasses stem cell research and stem cell bioprocessing. Unquestionably, the development of bioprocess technologies for the transfer of the current laboratory-based practice of stem cell tissue culture to the clinic as therapeutics necessitates the application of engineering principles and practices to achieve control, reproducibility, automation, validation and safety of the process and the product. The successful translation will require contributions from fundamental research (from developmental biology to the 'omics' technologies and advances in immunology) and from existing industrial practice (biologics), especially on automation, quality assurance and regulation. The timely development, integration and execution of various components will be critical-failures of the past (such as in the commercialization of skin equivalents) on marketing, pricing, production and advertising should not be repeated. This review aims to address the principles required for successful stem cell bioprocessing so that they can be applied deftly to clinical applications.

Bioadhesive hydrogel microenvironments to modulate epithelial morphogenesis.

Epithelial cells polarize and differentiate into organotypic cell aggregates in response to cell-cell and cell-matrix interactions. For example, Madin-Darby Canine Kidney (MDCK) cells form spherical cell aggregates (cysts) with distinct apical and basolateral polarity when cultured three dimensionally (embedded) in type I collagen gels. To investigate the effects of individual extracellular factors on epithelial morphogenesis, we engineered fast degrading protease-responsive polyethylene glycol (PEG) hydrogels functionalized with controlled densities of various bioligands (RGD peptide, laminin-1 (LN)) to allow 3D culturing of MDCK cells, cyst expansion, and morphogenesis/polarization. Cysts formed after 15 days of culture in these hydrogels were analyzed with multiphoton fluorescence microscopy for markers of apical and basolateral membrane domains. Epithelial cysts formed in bioadhesive ligand-functionalized PEG gels exhibited a higher frequency of central lumen and interior apical pole formation as well as basolateral polarization compared to those of unmodified PEG hydrogels. These results demonstrate that incorporation of specific bioadhesive motifs into synthetic hydrogels provides 3D culture environments that support epithelial morphogenesis. These microenvironments provide a flexible and controlled system for systematic investigations into normal and pathologic morphogenic behaviours as well as synthetic environments for promoting tissue morphogenesis for regenerative medicine applications.