Four-ball tribometers are widely used to characterize the efficacy of lubricants in sliding contact. However, the standard apparatus requires 5 mL or more of fluid, which makes the characterization of biological fluids such as synovial fluid difficult. Here, we present a four-ball tribometer that requires less than a tenth of the sample volume and that is easy to replicate on any rheometer. An upper steel or polystyrene ball was attached to a parallel plate rheology geometry, then lowered onto three lower balls positioned and stabilized using an additively manufactured holder. Rheometer controls were then used to control axial force (contact pressure) and upper ball rotational velocity (sliding speed). The setup was validated on three well-characterized lubricant systems: motor oil, glycerol/water mixtures, and hyaluronic acid. Static and dynamic coefficients of Coulomb friction and wear “scar” test results were reproducible and consistent with trends from the literature. Simulated healthy and diseased synovial fluid was also characterized to demonstrate the setup’s utility in measuring lubrication by small volumes of biological samples. The tribo-rheology setup shows promise for quantifying the lubrication properties of small volumes of precious samples.

There is renewed interest in three-dimensional bioengineered models that replicate key aspects of the environment for the study of cellular behavior, with one key aspect being cell interactions with matrix interfaces. Here, we developed a dual-stiffness hydrogel-encapsulated glioblastoma (GBM) spheroid model to investigate GBM spreading along a stiffness interface. GBM is an aggressive brain cancer with a patient prognosis of 12-18 months, which is known to spread to distant brain regions by following stiffness interfaces. Our model consisted of a soft, 5% w/v, polyethylene glycol (PEG) hydrogel to mimic the native brain tissue and a stiff, 10% w/v, PEG hydrogel to replicate the stiffer GBM microenvironment. To ensure spheroids fall along the boundary, we adjusted the gelation time of the gel by varying the pH of the gel precursor solution. Encapsulated spheroids were assessed for infiltration and viability for up to 7 days. Spheroids exhibited high viability in all hydrogels. Spheroids showed a higher infiltration index in the soft hydrogel, and migration across the stiffness interface occurred only from the soft to the stiff hydrogel in the dual-stiffness gels. The developed model has a simple, robust design for studying GBM behavior , a high degree of imageability, requires no specialized equipment to prepare, and is compatible with a multiwell plate format for easy handling and analysis.

Self-assembled peptide-based biomaterials provide versatile platforms for biomedical uses, featuring customizable physicochemical properties, biocompatibility, and dynamic capabilities. This self-assembly process is primarily dictated by primary sequence features, such as hydrophobicity, length, and charge, leading to the formation of fibrils and hydrogels. Amphipathic peptides, with alternating polar and hydrophobic residues, are especially effective in forming supramolecular nanofibers stabilized by π-π interactions and hydrogen bonds. Chemical modifications on aromatic side chains are promising for controlling assembly morphology, stability, and biological activity. However, the influence of these substituents on peptide packing and immunogenicity remains relatively unexplored. Herein, we examine the effect of substituents on benzyl groups attached to short amphipathic peptides. By introducing different electron-donating and withdrawing groups at the para-position of benzyl rings and modifying the chain length connecting the backbone to the aromatic moiety, we observe notable effects on fibril formation, molecular packing, and immunogenicity both in vitro and in vivo. Our results show that subtle chemical modifications are practical tools for designing tailored peptide nanomaterials with promising potential in vaccine delivery, tissue engineering, and regenerative medicine.

Microgels are increasingly recognized as versatile building blocks for granular cell scaffolds, offering advantages over bulk hydrogels for a variety of biomedical applications. While existing methods for scaffold fabrication often require multistep processes involving separate microgel formation and assembly, here we introduce a streamlined, one-pot approach that achieves microgel formation and scaffold assembly in minutes. This developed method is robust, reproducible, user-friendly, and requires no specialized equipment, making it broadly accessible. Specifically, aqueous two-phase separation (ATPS) was utilized to form ~2 μm gelatin methacrylate (GelMA) microgels in sodium sulfate salt solution, which rapidly “clicked” to form macroporous scaffolds under UV light. Various parameters were modulated to observe the effect on scaffold formation including timing of UV exposure, salt concentration, photoinitiator concentration, and polymer concentration. Our results indicated a mechanically stable scaffold able to quickly imbibe water due to its interconnected macropores. U-87 glioblastoma, NIH 3T3 fibroblast, and ATDC5 chondrocyte cells were successfully encapsulated within these granular scaffolds and exhibited an elongated morphology at 24 h and > 90% viability over 14-21 days of culture. The ability to produce microgel scaffolds containing living cells in one step opens new routes to the production of cell-laden porous scaffolds.

Morquio A syndrome is a rare genetic disorder where deficiency in N-acetylgalactosamine-6-sulfate sulfatase (GALNS) enzyme prevents breakdown of glycosaminoglycans (GAGs). Recombinant human GALNS (rhGALNS) is currently administered by intravenous infusion, but the treatment is costly and time-consuming and provides limited efficacy. Patient quality of life could be improved by an injectable sustained rhGALNS release device that would eliminate weekly multi-hour infusions. Polyethylene glycol (PEG) hydrogels can be employed as a hydrophilic, tunable, non-toxic, and biodegradable drug delivery system for the sustained release of rhGALNS, as explored by us previously. Here, we investigated the stability of rhGALNS in various buffers mimicking the in vivo environment that would be encountered by the enzyme, inside of and outside the PEG hydrogels. rhGALNS activity was reduced 85% by reversible inhibition in phosphate-buffered saline (PBS), representing interstitial fluid and plasma. Buffer exchanging into acidic buffer representing the lysosome recovered this loss. However, incubation in PBS for 3 days resulted in an irreversible loss of 85%. There were no significant changes in rhGALNS hydrodynamic radius upon activity loss, suggesting structural integrity. Such activity loss makes sustained delivery impractical without additional stabilization, such as confinement within the hydrogel. rhGALNS activity was retained upon encapsulation, and the average specific activity of rhGALNS released from a hydrogel decreased only 20% over 7 days. These results show that the activity of rhGALNS was better retained within the hydrogel than in buffer alone, potentially enabling sustained release for rhGALNS or other enzymes unstable in physiological conditions with our hydrogel delivery device.