Mitchell A. Winnik

Polymer coatings are widely used to suppress nonspecific protein adsorption and modulate nanoparticle–cell interactions. However, the biological outcomes of polymer-functionalized nanoparticles remain difficult to predict in complex biological environments because protein corona formation rapidly alters nanoparticle identity. This challenge is particularly pronounced when hydrophobic moieties are incorporated for imaging or therapeutic applications, as they can promote nonspecific interactions at the nano–bio interface. Herein, we establish a modular grafting-to platform based on cellulose nanocrystals (CNCs) that enables systematic comparison of polyethylene glycol (PEG)-based, zwitterionic, and acrylamide-based polymers with controlled grafting density and chain conformation on a common porphyrin-modified surface. We demonstrate that dense polymer brushes reduce nonspecific protein adsorption in single-protein assays. By contrast, all CNC surfaces form dynamic coronas upon exposure to serum proteins, while specific polymer coatings selectively enrich or suppress distinct protein populations. We further demonstrate that polymer-dependent immune cell interactions are substantially reduced following protein corona formation, although differences among polymer chemistries persist. Zwitterionic coatings broadly suppress immune cell interactions, whereas PEG-based coatings preferentially promote interactions with antigen-presenting cells. These findings establish design principles for polymer-functionalized nanoparticles with specific immune cell interaction profiles.

The construction of hierarchical architectures with precisely controlled dimensions and morphologies remains a key challenge in block copolymer self-assembly. Here we introduce hybrid self-seeding, a streamlined strategy that employs either the coassembly of a crystallizable homopolymer with two block copolymers or the direct self-seeding of mixed one-dimensional (1D) and two-dimensional (2D) seed fragments. By orchestrating sequential nucleation events where the homopolymer nucleates first, followed by block copolymers with decreasing propensity for 1D growth, we achieve precise morphological control in a single process. This method yields uniform scarf-like micelles (up to 34 μm), yucca flaccida-like architectures, and long ribbon-like morphologies. Electron diffraction confirms homoepitaxial growth across morphological domains, linking the structural memory effect to crystal lattice continuity. Our approach establishes a generalizable platform for higher-level soft matter.

Hydrogels derived from synthetic polypeptides hold promise as biomaterials for tissue engineering and cell culture; however, they lack a fibrillar structure characteristic for the native extracellular matrix. Here, we report a fibrillar hydrogel formed by aldehyde-modified cellulose nanocrystals and poly(γ-propargyl-l-glutamate) that was prepared by ring-opening polymerization of the N-carboxyanhydride monomer and functionalized with diethylene glycol groups and amino groups. In the hydrogel, the polymer retained the α-helical secondary structure of the polypeptide backbone. The mechanical properties of the hydrogel were varied by changing the aldehyde to amino group molar concentration ratio. Human dermal fibroblasts cultured on this hydrogel showed good adherence and metabolic activity. This work should stimulate further studies on the synthesis and applications of synthetic polypeptide-derived biomimetic fibrillar hydrogels.

The chain folding and packing of semicrystalline polymers are influenced by a complex interplay of thermodynamic and kinetic factors and present a significant challenge for achieving precise dimensional control of polymeric nanomaterials. This study addresses this challenge by demonstrating controlled chain folding, fine-tuning dimensions along the nongrowth direction, and subsequently fabricating uniform assemblies. While bulky groups are known to disrupt the ordered packing of polyethylene (PE) chains, their potential for precisely regulating crystallization to achieve custom-sized crystals has not been fully explored. In this work, we introduce cyclic units such as cyclohexane, phenyl, and naphthalene as defects within the PE backbone to manipulate chain packing. Our results show that ortho-disubstituted defects, when incorporated periodically, can dominate the chain folding process, resulting in consistently formed crystalline segments. By adjusting the spacing between these bulky substituents along the polymer chain, we were able to generate lamellae and single crystals with precisely tunable thickness. Notably, the crystal thickness exhibits a strictly linear dependence on defect spacing. This approach paves the way for the preparation of uniform nanomaterials with three-dimensional precision.

Polymer coatings are widely used to suppress nonspecific protein adsorption and modulate nanoparticle-cell interactions. However, in complex biological systems, the biological outcomes of polymer-functionalized nanoparticles often deviate from their intended design owing to rapid protein corona formation that alters nanoparticle identity. Compounding this challenge, there is currently no unified platform for systematic evaluation of polymer coatings under comparable surface functionalization and biologically relevant conditions. To address this limitation, we establish a modular grafting-to platform based on cellulose nanocrystals (CNCs) that enables systematic comparison of polyethylene glycol (PEG)-based, zwitterionic, and acrylamide-based polymers with independent control over grafting density and chain conformation. Using this CNC- based model system, we demonstrate that dense polymer brushes reduce nonspecific protein adsorption in single-protein assays. By contrast, all CNC surfaces form albumin-rich coronas upon exposure to complex mixtures of serum proteins, although specific polymer coatings selectively enrich or suppress distinct protein populations. We further demonstrate that polymer-dependent immune cell interactions observed under serum-free conditions are largely attenuated following protein corona formation. Nevertheless, differences among polymer chemistries persist, with zwitterionic coatings broadly suppressing immune cell interactions and PEG-based coatings selectively promoting interactions with antigen-presenting cells, such as B cells and conventional dendritic cells. These findings establish design principles for polymer-functionalized nanoparticles with defined immune cell interaction profiles.

Cellulose nanocrystals (CNCs) are promising nanomaterials for biomedical applications owing to their biocompatibility, low toxicity, and versatile surface chemistry. However, efficient surface modification of CNCs with hydrophobic moieties and functional polymers remains challenging under mild aqueous conditions. Herein, we present an aqueous-phase "grafting-to" strategy that enables orthogonal conjugation of meso-tetra(4-carboxyphenyl)porphine (TCPP) and polyethylene glycol (PEG)-based polymers using a heterobifunctional linker. Aldehyde-functionalized CNCs were modified with dibenzocyclooctyne (DBCO)-amine via reductive amination to introduce two key functionalities: a secondary amine for amide coupling and a strained alkyne for copper-free click chemistry. We hypothesize that the hydrophobic environment surrounding the DBCO-modified CNC surface facilitates the noncovalent association of hydrophobic TCPP molecules, thereby significantly enhancing the conjugation reaction in water via the hydrophobic effect. The resulting dual-functionalized CNCs exhibited >1 month colloidal stability in water, reduced nonspecific protein adsorption by over 86% after PEGylation, and presented a versatile platform for biological applications.

Mass cytometry (MC) is a high-throughput bioanalytical technique for single-cell biomarker detection. Metal-chelating polymer reagents for MC have been used to bind isotopes of soft metal ions, such as Pt. However, there are challenges of suppressing nonspecific binding (NSB) and achieving high signal-to-noise ratios in cell studies for these reagents. Recently, our group reported that ligand exchange of the Pt-Cl bond with glutathione (GSH), a strong sulfur nucleophile, reduced the NSB of a Pt-binding polymer. To further investigate the effects of ligand exchange, we investigated alternative sulfur-containing ligands─including thiourea, diethyldithiocarbamate, and sodium thiosulfate, for their ability to reduce NSB and increase the signal contrast in MC applications through Pt-Cl bond substitution. Here, we report a Pt-binding polymer in which thiosulfate groups were introduced by ligand exchange, achieving ultralow NSB and enhanced signal-to-noise ratios in both suspension and imaging MC compared to the GSH-modified Pt polymer. This demonstrates thiosulfate as a promising candidate for ligand exchange to develop new MCPs that bind to soft metal ions.

Mesoporous silica nanoparticles (MSNs) have garnered significant attention for diverse bioscience applications due to their tunable surface properties and high biocompatibility. Functionalization with hydrophilic polymers like poly(ethylene glycol) (PEG) via silane chemistry is commonly employed to reduce non-specific protein adsorption and enhance stability in physiological environments. However, characterizing surface ligands, particularly in aqueous environments, remains a key challenge. In this study, we utilized a comprehensive suite of nuclear magnetic resonance (NMR) techniques, including ¹H quantitative NMR (qNMR), diffusion-ordered spectroscopy (DOSY), and relaxation time measurements (T₁ and T₂), to investigate PEG chain dynamics and conformation on MSN surfaces. Our analysis revealed the relationship between PEG grafting density and chain mobility, demonstrating a transition to a dense brush conformation at higher densities. DOSY and T₂ experiments enabled the differentiation of covalently bound PEG from loosely adsorbed molecules. This approach provided a robust method for evaluating the efficacy of surface functionalization, ensuring the quality and consistency of PEGylated nanoparticles. Furthermore, we examined the relationship between NMR-derived parameters and protein adsorption resistance, demonstrating that densely packed PEG chains with a “dense brush” conformation can effectively reduce non-specific adsorption of human serum albumin. These findings provided valuable insights into the design of PEGylated MSNs, supporting improved quality, consistency, and functionality for biomedical applications.