Tools and Technologies II
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.
Statement of Benefit to California:
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.
This proposal is focused on the development of a multimodal imaging platform for analysis of tissue microstructure, morphology, and mechanical properties in vitro and in vivo. These minimally invasive methods will be used to perform in vivo diagnostic of engineered tissues. The applicant proposes to combine three imaging modalities, two optical and one ultrasonic, to allow for non-destructive, minimally invasive, long-term imaging of tissue-engineered constructs. In specific Aim 1 they proposed to calibrate and optimize the multimodal imaging platform by comparing imaging measurements with the biochemical and biomechanical measurements obtained through conventional destructive assays; and in Aim 2 to test this platform on tissue-engineered constructs in vitro during cell differentiation, and following transplant into animal models. The reviewers agreed that this proposal addresses a significant translational bottleneck in tissue engineering research. Most current methods for analyzing engineered tissue are destructive, putting a strain on the tissue supply and making in vivo evaluation difficult. If the proposed combination of imaging modalities permitted non-destructive evaluation, it could have a major impact. However, reviewers did not find the proposal particularly innovative, since all three imaging modalities have been previously used alone but not in combination. Reviewers raised significant concerns about the feasibility of the research plan. They were concerned about the potential light scatter when imaging thick tissue such as bone and cartilage. They also questioned the specificity of the approach. They noted that while it will be feasible to correlate between imaging signals and conventional measures, it would be very challenging to ensure that the detected signal will have predictive power across samples, labs and patients. Reviewers would have appreciated some experiments designed to test the imaging platform’s predictive power, rather than focusing entirely on post-hoc analysis. While the aims for the most part do seem achievable, the success criteria are weak since most of the work seems to be to confirm technological feasibility rather than to specifically address a meaningful scientific or clinical outcome. Finally, the connection to stem cell biology is not very strong, as the primary focus of the applicants appears to be in tissue-engineered constructs where stem cells just happen to be a convenient approach to generate the constructs; the cartilage tissue application does not even use stem cells as a source. The reviewers described the Principal Investigator (PI) and research team as excellent. The PI is an expert in multimodal imaging and has assembled a multidisciplinary team with expertise in tissue engineering, stem cell biology, scaffolds and surgery. One concern with the research team was an apparent lack of experience in developing FDA-approved medical devices. Overall, while reviewers appreciated the significance of the translational bottleneck addressed by this proposal, they raised a number of issues with the research plan that caused them to doubt its feasibility.