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Nanoparticle cellular interactions are governed by nanoparticle surface chemistry and the surface display of functional (bio)molecules. To conjugate and display thiol-containing (bio)molecules on nanoparticle surfaces, reactions between thiols and functional maleimide groups are often exploited. However, current procedures for modifying nanoparticle surfaces with maleimide groups are complex and can result in nanoparticle aggregation. Here, we demonstrate a straightforward, fast (∼30 min), efficient, and robust one-step surface engineering protocol for modifying gold nanoparticles with functional maleimide groups. We designed a hetero-bifunctional poly(ethylene glycol)-based molecule that attaches efficiently to the gold nanoparticle surface in a single step via its orthopyridyl disulfide (OPSS) terminal end, leaving its maleimide functional group available for downstream reaction with thiols. Using this surface engineering approach, we fabricated gold nanoparticles with near neutral and positive surface charges, respectively. We demonstrate that nanoparticle cellular uptake efficiencies in model mouse breast cancer (4T1) cells, human breast cancer (MDA-MB-231) cells, and human umbilical vein endothelial (HUVEC) cells in tissue culture can be tuned by up to 3 orders of magnitude by adjusting nanoparticle surface chemistry. Our straightforward and efficient maleimide-based nanoparticle surface engineering protocol creates a platform technology for controlled covalent surface attachment of a variety of thiol-containing (bio)molecules to nanoparticles for rational design of nanomaterials with precise cellular interactions for widespread applications in bioanalysis and nanomedicine.

There is growing evidence indicating the need to combine the rehabilitation and regenerative medicine fields to maximize functional recovery after spinal cord injury (SCI), but there are limited methods to synergistically combine the fields. Conductive biomaterials may enable synergistic combination of biomaterials with electric stimulation (ES), which may enable direct ES of neurons to enhance axon regeneration and reorganization for better functional recovery; however, there are three major challenges in developing conductive biomaterials: (1) low conductivity of conductive composites, (2) many conductive components are cytotoxic, and (3) many conductive biomaterials are pre‐formed scaffolds and are not injectable. Pre‐formed, noninjectable scaffolds may hinder clinical translation in a surgical context for the most common contusion‐type of SCI. Alternatively, an injectable biomaterial, inspired by lessons from bioinks in the bioprinting field, may be more translational for contusion SCIs. Therefore, in the current study, a conductive hydrogel was developed by incorporating high aspect ratio citrate‐gold nanorods (GNRs) into a hyaluronic acid and gelatin hydrogel. To fabricate nontoxic citrate‐GNRs, a robust synthesis for high aspect ratio GNRs was combined with an indirect ligand exchange to exchange a cytotoxic surfactant for nontoxic citrate. For enhanced surgical placement, the hydrogel precursor solution (i.e., before crosslinking) was paste‐like, injectable/bioprintable, and fast‐crosslinking (i.e., 4 min). Finally, the crosslinked hydrogel supported the adhesion/viability of seeded rat neural stem cells in vitro. The current study developed and characterized a GNR conductive hydrogel/bioink that provided a refinable and translational platform for future synergistic combination with ES to improve functional recovery after SCI.

The potential chondroinductivity from cartilage matrix makes it promising for cartilage repair; however, cartilage matrix-based hydrogels developed thus far have failed to match the mechanical performance of native cartilage or be bioprinted without adding polymers for reinforcement. There is a need for cartilage matrix-based hydrogels with robust mechanical performance and paste-like precursor rheology for bioprinting/enhanced surgical placement. In the current study, our goals were to increase hydrogel stiffness and develop the paste-like precursor/printability of our methacryl-modified solubilized and devitalized cartilage (MeSDVC) hydrogels. We compared two methacryloylating reagents, methacrylic anhydride (MA) and glycidyl methacrylate (GM), and varied the molar excess (ME) of MA from 2 to 20. The MA-modified MeSDVCs had greater methacryloylation than GM-modified MeSDVC (20 ME). While GM and most of the MA hydrogel precursors exhibited paste-like rheology, the 2 ME MA and GM MeSDVCs had the best printability (i.e., shape fidelity, filament collapse). After crosslinking, the 2 ME MA MeSDVC had the highest stiffness (1.55 ± 0.23 MPa), approaching the modulus of native cartilage, and supported the viability/adhesion of seeded cells for 15 days. Overall, the MA (2 ME) improved methacryloylation, hydrogel stiffness, and printability, resulting in a stand-alone MeSDVC printable biomaterial. The MeSDVC has potential as a future bioink and has future clinical relevance for cartilage repair.