| Understanding the complex intermolecular interactions between the host and the bioengineered substrate is critical to the field of bioengineering and drug delivery. Monocytes/macrophages are commonly observed at the biomaterial-tissue interface and their adhesion onto a biomaterial and the subsequent protein release represents a critical component of biocompatibility. Cell adhesion onto peptide sequences in the extracellular matrix (ECM) proteins such as arginine-glycine-aspartic acid (RGD) through integrin receptors and the subsequent protein release also play a significant role in wound healing.;By conjugating RGD onto a polyethylene glycol (PEG) tether and grafting the RGD-PEG onto a gelatin and PEG based semi-interpenetrating network (sIPN), monocyte adhesion was enhanced. In addition, we observed that beta1 and beta3 containing integrin receptors were critical in mediating monocyte adhesion and the subsequent matrixin and inflammatory protein expression in the presence of RGD grafted ECM-derived scaffolds. The density of the RGD presented on the sIPN surface was also observed to modulate monocyte adhesion and the expression of matrixin and inflammatory protein expression over time.;We further probed monocyte response to the sIPN in a more physiologically relevant environment by creating a monocyte-fibroblast co-culture system to study the direct influence of fibroblasts on monocyte interaction with the ECM-based substrata. Molecular mechanisms behind monocyte adhesion onto the ECM scaffold and expression of key wound healing factors in inflammation, matrix remodeling and regeneration were analyzed. We observed that fibroblasts decreased monocyte adhesion onto RGD-PEG grafted sIPN. However, fibroblasts did not decrease monocyte adhesion by decreasing monocyte viability on RGD-PEG grafted sIPN. Fibroblasts increased monocyte GM-CSF drastically except on RGD and PHSRN grafted sIPNs at later stages. Monocytes decreased initial fibroblast IL-1alpha and TGF-alpha, but drastically increased fibroblast MMP-2 and GM-CSF at selective time points on all surfaces, including ligand-PEG grafted sIPNs. When the ligand immobilized was RGD, monocyte TGF-alpha, MIP-1beta and VEGF expression was increased while monocyte GM-CSF was decreased at selected time points. These results showed a dynamic monocyte response to selected ECM components in the presence of fibroblasts and the interrelated role of regulation in modulating monocyte-fibroblast interaction in the presence of the ECM-derived matrix. |
