464254 Targeting and Altering In Vivo macrophage Responses with Modified Polymer Properties

Tuesday, November 15, 2016: 5:03 PM
Golden Gate 5 (Hilton San Francisco Union Square)
Kaitlin M. Bratlie, Chemical and Biological Engineering, Materials Science and Engineering, Iowa State University, Ames, IA

Targeting and altering in vivo macrophage responses with modified polymer properties

Kaitlin Bratlie

Departments of Materials Science & Engineering and Chemical & Biological Engineering, Iowa State University

Introduction: Two pathways for activating macrophages (MΦs) exist. One of these routes is termed the classically activated M1 pathway and is achieved through exposure to lipopolysaccharide (LPS). M1 MΦs are known as pro-inflammatory cells. The other pathway is reached through interleukin-4 (IL-4) and is known as the alternatively activated M2 pathway. M2 MΦ produce pro-angiogenic factors. Here, we successfully use in vivo imaging and histological analysis to identify the MΦ response and activation. We demonstrate the ability to induce various MΦ phenotypes with a change in material functionality as well as identify certain materials parameters that seem to correlate with each phenotype. This suggests the potential to develop materials for specific applications and predict the outcome of MΦ activation in response to new surface chemistries.













Figure 1. In vivo fluorescence images of cathepsin activity in response to implanted polymer nanoparticles. (Left) Fluorescence image of cathepsin activity 7 days after implantation of 600nm pNIPAm particles. (Right) Implantation scheme.

Figure 2. Ex vivo arginase:iNOS levels for modified pNIPAm particles.

Materials and Methods: The poly(N-isopropylacrylamide) (pNIPAm) (~600nm) particles were synthesized using established methods and modified through conjugation with surface modifiers through carbodiimide chemistry. MΦs were polarized to the M1 and M2 phenotypes and internalization of functionalized pNIPAm particles were measured. These materials were also subcutaneously injected in SKH1-E mice. Arginase:iNOS profiles have been consistently used as a measure of MΦ phenotype. Arginine activity was measured indirectly through a urea assay in which the lysate was activated, exposed to arginine, and conversion to urea was quantified. Nitrites were measured through a Griess reagent assay to indirectly determine the levels of inducible nitric oxide synthase (iNOS). Material properties of the modified particles including water contact angle, melting temperature, and zeta-potential were also measured.

Results and Discussion: SKH1-E mice were injected with the polymer particles and imaged for cathepsin activity (Figure 1). A range in cathepsin activity was observed for the different surface modifiers. The tissue sections from the mice in Figure 1 were excised and homogenized. The arginase:iNOS displayed a spectrum between the M1 and M2 phenotypes for different surface modifiers as shown in Figure 2.

Distinct material parameters influence MΦ phenotypes. For example, increasing the hydrogen bonding of polymeric particles can polarize MΦs towards the M1 phenotype. The induction of multiple MΦ phenotypes confirms the ability to control MΦ activation in vivo and suggests the importance of chemical properties in the biocompatibility of materials. The results obtained suggest that changing properties can result in opposite MΦ phenotypes.

Conclusions:  With this work, useful insight was gained about in vivo MΦ response to various material functionalities. Overall, this in vivo study was successful at drawing conclusions about the biomaterial parameters that will allow for tuning MΦ polarization responses to biomaterials and targeting MΦs.

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See more of this Session: Biomaterials for Immunological Applications
See more of this Group/Topical: Materials Engineering and Sciences Division