Schematic of pNIPMAm MP synthesis. The MP construct is a core-shell structure synthesized by preciptitation polymerization. The the shell consists of microgels composed of 68% NIPMAm, 2% BIS, 30% AAc Carboxylated-PS core particles were functionalized with 4-aminobenzophenone using EDC/NHS chemistry Microgel hetteroaggregates were prepared by mixing microgels functionalized core particles and exposing samples to UV. BMP4 loading and release from pNIPMAm MPs The hydrophilic nature of the microgels promotes immediate swelling upon exposure to water, subsequently imbibing growth factors present in the surrounding solution. Additionally, microgels are negatively charged due to their acrylic acid content, allowing for electrostatic interactions with positively charged BMP4 (pI = 8.97). The binding capacity of MPs for BMP4 was examined by measuring the depletion of BMP4 from solution, ranging in concentration from 2-2,000 ng protein per milligram of MP (Figure 3.2E). MP binding capacity of BMP4 increased with increasing concentrations of BMP4. Below 100 ng per mg of MP, the relationship between MP bound BMP4 and loading concentration of BMP4 was relatively linear (R2 = 0.998) with approximately 71.7% ± 16.9% of BMP4 bound to MPs. However, at BMP4 concentrations above 100 ng per mg MP, the efficiency of BMP4 binding decreased to approximately 45.0% ± 14.9%. Release of BMP4 from MPs was assessed at low (10 ng per mg of microparticles) and high (100 ng per mg of microparticles) concentrations of BMP4 at 37 °C. MPs loaded with the high concentration of BMP4 demonstrated a greater initial burst release within the first 3 hours (< 40%) and released a larger amount of BMP4 over 14 days than MPs loaded with a low concentration of BMP4 (Figure 3.2F). Independent of initial loading mass, MPs loaded with both low and high concentrations of BMP4 exhibited sustained release over the first 7 days. Overall, total release of BMP4 after 14 days was approximately 60% of loaded protein, indicating that the majority of the protein was released by the MPs during this time (Figure 3.2G).
