Development of a Perfusion Bioreactor Strategy for Human Adipose-Derived Stem Cell Expansion

Abstract

Developing an optimized growth environment for adipose-derived stems cells (ASCs) to obtain clinically useable cell quantities from relatively small tissue biopsies would significantly impact the field of tissue engineering. To date, ASCs have been differentiated into adipose, bone, cartilage, smooth muscle, endothelial, skeletal muscle, nervous, and cardiac tissue. Therefore, ASCs have potential for use in the treatment of a wide variety of clinical conditions ranging from myocardial infarction, to musculoskeletal disorders, and the repair of soft tissue defects. In this work, a custom-designed, 3-dimensional (3-D) scaffold-based perfusion bioreactor system was investigated in the culture of ASCs. Decellularized adipose tissue (DAT) was used to provide a 3-dimensional scaffold, as it possesses the native extracellular matrix (ECM) architecture and composition of human adipose tissue. The DAT had a permeability of 149 m2, based on a perfusion rate of 1.5 mL/min over a 200 mg DAT sample, and the culturing medium was evenly perfused throughout the DAT, thereby permitting possible cell growth within the central regions. Initial culturing studies of human ASCs on tissue culture polystyrene (TCPS) demonstrated that hypoxic (5% O2) conditions decreased the doubling time, and resulted in enhanced cell proliferation, as compared to normoxic (21% O2) conditions. The cell imaging and DNA quantification results showed that suspension seeding of the ASCs permitted cell attachment to the DAT scaffold, but did not support long-term ASC growth. In contrast, when the ASCs were seeded as multicellular aggregates, the cells attached and underwent measurable proliferation. The optimal seeding density observed was 1 x 106 ASCs/scaffold; or 50 aggregates (20,000 ASCs/aggregate) per scaffold. Based on the confocal imaging, the ASCs remained spherical in morphology during the entire culturing period. Moreover, results illustrated that the perfusion bioreactor provided an improved culturing environment for ASCs over traditional static culturing. Hypoxic (5% O2) conditions showed improved proliferation over normoxic (21% O2) conditions, within the bioreactor system. After a 14-day hypoxic culturing period in the perfusion bioreactor, the seeded ASCs retained the ability to undergo adipogenesis, as indicated by Glycerol-3-Phsophate Dehydrogenase (GPDH) enzymatic activity measurements, demonstrating the promise of this approach for soft tissue engineering applications