Using gene expression for analysis of cell response to biomaterials
When first defined, biocompatibility referred to the properties of a material related to inflammation and foreign body response; initial materials were designed to be inert— to not elicit a response in a biological environment (Williams, 2003). While these materials did function to an extent in certain applications in certain tissues, their efficacy was limited by the fact that they could not be incorporated into the host tissues into which they were implanted.
Functional incorporation of any given biomaterial into a host tissue requires quantifying how cells respond to the basic chemical and topographical features of the material, ensuring that the material elicits an appropriate response from these cells (Lim and Donahue, 2007). Although certain materials, such as contact lenses, are designed to prevent cell attachment (Dutta et al., 2012), the vast majority of new generation biomaterials are bioactive, and they are functionalized to promote cell attachment and tissue integration (Sakiyama-Elbert and Hubbell, 2001). If we consider cell adhesion as the initial step toward alterations in gene expression, then what processes are altered and how can they be measured through mRNA analysis?
Gene functions can be assigned to different categories in all cell types. First are those that are active in all cell types related to adhesion, survival, and proliferation. The second classification reflects those genes specific to the differentiated function of each cell type, which are therefore much more restricted in expression. While mRNA analysis can be utilized to assess whether cells are dying or proliferating on a given material, this is a cumbersome and expensive way to analyze these types of processes. Complementary assays would need to be used to actually confirm that the mRNA activation could be linked to either cell death or cell division.
In the remainder of this chapter, we will illustrate how changes in gene expression can be accurately measured when cells are cultured on or in biomaterials, as well as the potential pitfalls that researchers can fall into. Specifically, we will discuss measuring gene expression in two tissue systems: in vitro analysis of bone formation/ osteogenesis and in vivo quantification of skin healing.