Advancements in stem cell technologies hold great promise for engineering tissues for the restoration of functional loss from trauma or disease. However, inherent cellular variability requires ongoing evaluation of neo-tissues during culture to ensure that a quality product is produced and implanted in patients. Challenges include: (a) Stem cell isolation and expansion can be expensive, and destructive assays for multi-time-point biological assays are costly and inefficient; (b) Destructive assays for differentiation can exacerbate the already difficult problem of obtaining sufficient numbers of cells; and (c) Long-term safety and efficacy of engineered tissues are hard to assess because implanted tissue cannot be removed, for example during a clinical study. These challenges represent significant bottlenecks to translating stem cell technologies to the clinic that require a non-destructive solution to monitor tissue composition, microstructure, and function. This application addresses these specific bottlenecks through research, development, and validation on stem cells-derived engineered tissues of a novel multimodal flexible tissue diagnostic platform that integrates optical and ultrasonic technologies. These are (1) Time-resolved fluorescence spectroscopy that enables characterization of the biochemical composition and extracellular matrix production of distinct tissues; (2) Fluorescence lifetime imaging microscopy that facilitates recording of large amounts of fluorescence lifetime information in an image format and may be combined with emission spectroscopy to evaluate biochemical heterogeneities in the bioengineered tissue; and (3) Ultrasound backscatter microscopy that provides structural information that can be correlated to tissue microstructure, morphology, and mechanical properties. Specifically, the proposed studies seek to 1) validate the ability of this multimodal diagnostic platform for non-destructive and non- or minimally-invasive characterization of engineered tissue composition and microstructure, and 2) construct a probe utilizing these technologies and validate this probe for in vivo characterization of engineered tissue. The proposed approach will enable monitoring of the quality of engineered tissues (including functional mechanical properties) in vitro prior- implantation and in vivo post-implantation and alleviate the need for destructive assays for multi-time-points, an approach that is costly, inefficient, or impractical in the clinical setting. Emphasis is placed on the evaluation of bioengineered musculoskeletal tissue (i.e., bone and cartilage) produced by adult stem cells derived from bone marrow (mesenchymal stem cells) and a dermis-derived sub-population termed dermis-isolated aggrecan-sensitive (DIAS) cells.
The overall objective of current project is to develop technologies that contribute to improved quality and functionality of bioengineered tissue implants. Consequently, the proposed study is expected to have impact on patient with major health problems such as congenital abnormalities, bone loss, degenerative joint disease, and defects resulting from trauma that impacts individuals including Californians across their lifespan. For example, it is estimated that 1 in 8 Californians over the age of 25 have clinically manifested osteoarthritis (OA) [Lawrence et al, Arthritis Rheum. 2008], making it one of the leading causes of disability in the states. In the US OA related costs exceed $65 billion per year in both medical costs and lost wages [Jackson et al, Clin Orthop. 2001], and California takes in its fair share. A significant source of costs is loss of productivity. Also, it is expected that, as the baby boomers age, concomitant rise in management and treatment costs for OA will rise. In addition, cartilage related problems are not limited to aging population. Cartilage lesions frequently occur in the youth, a population whose needs for long-term solutions are much greater than their elders. A need for stem cell therapies for cartilage injuries rises from the prevalence of joint injuries in California’s adolescents (e.g. the adolescent knee injuries has an incidence rate greater than 25% in sports participants [Louw et al, Br J Sports Med. 2008]). Moreover, conventional therapies for orthopaedic-related abnormalities commonly require the grafting of bone segments into the defect (more than 500,000 procedures annually), yet a lack of sufficient material often precludes such therapies. Also, greater than 10% of all bone defects are non-healing, with an even higher prevalence of nonunions in the elderly. Given that at least 20% of California’s population will be over the age of 65 by 2025, it is important that new approaches to the repair of osteochondral tissues are developed. Nevertheless, the benefits to the State of California extends beyond the potential impact of proposed technology on the earlier interventions to speed tissue repair, markedly reducing the need for repeated surgical procedures, and conceivably improve the quality of life for patients that require restoration of functional loss from trauma or disease. The versatile technology developed here will have applications to other tissue engineering approaches that could benefit the biotechnology companies of California investing in regenerative medicine. Exposure of students to novel stem cell-related research and technologies may provide an additional benefit to California by inspiring future leaders in science to pursue their research efforts within the state or develop products and therapies at California-based biotechnology companies.