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INTRODUCTION: The surface modification of nanoparticles (NP) with a dense layer of polyethylene glycol (PEG) has been widely used to improve NP circulation time, bioavailability, and diffusion through biological barriers [e.g. extracellular matrix (ECM), mucus]. While linear PEG coatings are commonly used, branched PEG coatings have not been widely explored as a design parameter for NP drug delivery systems. METHODS: NPs were densely coated with either linear 2, 5, 10 kDa linear PEG or with 10 kDa star-shaped, 4-arm branched PEG. NP cellular uptake was evaluated in HEK-293T and A549 cells. NP stability was evaluated in fetal bovine serum over 24 h using dynamic light scattering. Diffusion of NPs within a Matrigel ECM model and sputum (mucus) collected from individuals with cystic fibrosis (CF) lung disease were analyzed through multiple particle tracking. RESULTS: PEG-coated NPs appeared more stable in serum compared to uncoated NPs, but the reduction in total protein adsorbed was most significant for branched PEG coated NP. All PEGylated NPs had similar cellular uptake in HEK-293T and A549 cells. Interestingly, branched-PEG coated NPs had the largest diffusion coefficient and moved most rapidly through Matrigel. However in CF mucus, linear 2 and 5 kDa PEG coated NPs had the largest fraction of rapidly diffusing particles while branched PEG coated NPs had less hindered mobility compared to linear 10 kDa PEG coated NPs. CONCLUSION: Branched PEGylation may have the potential to increase NP efficiency in reaching target cells based on an apparent increase in diffusion through an ECM model while maintaining NP stability and uptake in target cells comparable to their linear PEG counterparts.

Idiopathic pulmonary fibrosis is a chronic disease characterized by progressive lung scarring that inhibits gas exchange. Evidence suggests fibroblast-matrix interactions are a prominent driver of disease. However, available preclinical models limit our ability to study these interactions. We present a technique for synthesizing phototunable poly(ethylene glycol) (PEG)-based hybrid-hydrogels comprising healthy or fibrotic decellularized extracellular matrix (dECM) to decouple mechanical properties from composition and elucidate their roles in fibroblast activation. Here, we engineered and characterized phototunable hybrid-hydrogels using molecular techniques such as ninhydrin and Ellman’s assays to assess dECM functionalization, and parallel-plate rheology to measure hydrogel mechanical properties. These biomaterials were employed to investigate the activation of fibroblasts from dual-transgenic Col1a1-GFP and αSMA-RFP reporter mice in response to changes in composition and mechanical properties. We show that reacting functionalized dECM from healthy or bleomycin-injured mouse lungs with PEG alpha-methacrylate (αMA) in an off-stoichiometry Michael-addition reaction created soft hydrogels mimicking a healthy lung elastic modulus (4.99 ± 0.98 kPa). Photoinitiated stiffening increased the material modulus to fibrotic values (11.48 ± 1.80 kPa). Percent activation of primary murine fibroblasts expressing Col1a1 and αSMA increased by approximately 40% following dynamic stiffening of both healthy and bleomycin hybrid-hydrogels. There were no significant differences between fibroblast activation on stiffened healthy versus stiffened bleomycin-injured hybrid-hydrogels. Phototunable hybrid-hydrogels provide an important platform for probing cell-matrix interactions and developing a deeper understanding of fibrotic activation in pulmonary fibrosis. Our results suggest that mechanical properties are a more significant contributor to fibroblast activation than biochemical composition within the scope of the hybrid-hydrogel platform evaluated in this study. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12195-022-00726-y.