two Monitoring and evaluation of the biological response to biomaterials in vivo
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Imaging biomaterial-associated inflammation
Sree Chitra Tirunal Institute for Medical Sciences and Technology, Thiruvananthapuram, Kerala, India
Tens of millions of people across the world live with implanted medical devices, with an estimated 25 million people living in the United States alone (Hanna et al., 2001). Furthermore, the US demand for such devices is estimated to grow 7.7% annually to $52 billion in 2015 (The Freedonia Group, 2012). These implantable medical devices primarily include reconstructive joint replacements, cardiac pacemakers, defibrillators, stents, valves, electrical leads/batteries, tissue-engineered constructs, and drug delivery systems (Domb and Khan, 2014). Although most implanted devices function optimally for years, implantation of biomaterials in general elicits a strong host inflammatory response that severely affects long-term performance and lifetime of the device in vivo (Anderson et al., 2008). Moreover, implant-associated inflammation is assessed using conventional histological methods and biochemical assays, which are all end-point measurements that involve repeated invasive surgical procedures for obtaining tissue biopsies for analysis. In addition, these methods are labor-intensive, time-consuming, and cost-prohibitive, which seriously affect the quality of lives of millions of patients each year. Furthermore, from a clinical perspective, conventional methods also deter noninvasive longitudinal monitoring of biomaterial-associated inflammation due to its inherent tissue-destructive characteristics. Hence, there is a compelling need for developing strategies to noninvasively monitor implant-associated aseptic inflammation. Such methodologies will allow for a simple, fast, reliable, accurate, and real-time assessment of device-related inflammation, which is crucial for initiating anti-inflammatory therapies to modulate the inflammatory response in a clinical scenario. This chapter reviews the different preclinical imaging modalities that are currently being explored for monitoring and assessing implant-associated inflammation in vivo.