Development of a predictive cellular model to assess biomaterial-modulated immunoresponses of macrophages in vitro

Abstract

Biomaterials have become indispensable in medical practice. Implants and medical devices such as vascular grafts, heart valves, dental implants, or pacemakers and biosensors improve patients’ quality of life by replacing or substituting natural functions. Despite their broad and successful application in patients, implantation of medical products triggers inflammatory responses. Since the extend of the induced immune reactions significantly affects the long-term success of implants, it is of particular interest for the design and development of novel biomaterials to predict these host-material reactions. By employing in vitro tests based on human cells, a predictive statement can be made regarding the host responses following implantation. However, to date the assessment of immune reactions to biomaterials is mainly fulfilled by endpoint assays, which contradicts the spatial dynamic changes of inflammation in the human body. It is postulated that biomaterial surface properties not only affect the inflammatory phenotype of macrophages but that this phenotype is also reflected by the cellular morphology and cytoskeleton organization. In this dissertation, a macrophage model based on the monocytic cell line THP-1 was developed to assess biomaterial-induced responses. Upon chemical stimulation, the inflammatory macrophage phenotype was reflected by morphological changes. However, biomaterial-induced changes in macrophage morphology could not be linked to the inflammatory response. Nevertheless, employing a readout based on actin cytoskeleton formations a trend correlation to the cytokine secretion could be shown. To allow to trace these changes in living cells, the previously described actin-chromobody was stably introduced into THP-1 cells. For illustrating a possible application, the stable THP-1_actin-CB cell line was used to monitor the effect of hydrophobicity on the inflammatory response, macrophage morphology and cytoskeleton organization in living cells. Taken together, the THP-1 derived macrophage model provides a robust and sensitive tool to determine immune responses to biomaterials in vitro. While macrophage morphology does not seem to be directly related to the inflammatory phenotype, actin cytoskeleton organization indicated the macrophage polarization state. Replacement of cytokine measurement as well as the application of a high throughput approach are not possible.