Controlling fine touch sensations with polymer tacticity and crystallinity.

The friction generated between a finger and an object forms the mechanical stimuli behind fine touch perception. To control friction, and therefore tactile perception, current haptic devices typically rely on physical features like bumps or pins, but chemical and microscale morphology of surfaces could be harnessed to recreate a wider variety of tactile sensations. Here, we sought to develop a new way to create tactile sensations by relying on differences in microstructure as quantified by the degree of crystallinity in polymer films. To isolate crystallinity, we used polystyrene films with the same chemical formula and number averaged molecular weights, but which differed in tacticity and annealing conditions. These films were also sufficiently thin as to be rigid which minimized effects from bulk stiffness and had variations in roughness lower than detectable by humans. To connect crystallinity to human perception, we performed mechanical testing with a mock finger to form predictions about the degree of crystallinity necessary to result in successful discrimination by human subjects. Psychophysical testing verified that humans could discriminate surfaces which differed only in the degree of crystallinity. Although related, human performance was not strongly correlated with a straightforward difference in the degree of crystallinity. Rather, human performance was better explained by quantifying transitions in steady to unsteady sliding and the generation of slow frictional waves (r2 = 79.6%). Tuning fine touch with polymer crystallinity may lead to better engineering of existing haptic interfaces or lead to new classes of actuators based on changes in microstructure.

Dynamic Properties of Novel Excipient Suggest Mechanism for Improved Performance in Liquid Stabilization of Protein Biologics.

To improve liquid formulation stability, formulators employ various excipients designed to stabilize protein drugs, including buffers, salts, sugars, and surfactants. One of the roles of surfactants is to protect the protein drug from surface interactions that can destabilize the protein. Protein drug products formulated with surfactants usually contain either a polysorbate or poloxamer. Even in the presence of these surfactants, protein drug stability is often insufficient, particularly because of agitation-induced aggregation. FM1000 is one of a series of surfactants containing an alkyl chain, an amino acid, and a polyetheramine. The characterization of the dynamics of FM1000 at various water/hydrophobic interfaces was compared to Polysorbate 20, Polysorbate 80, and Poloxamer 188. FM1000 stabilizes an interface 1-2 orders of magnitude faster than all three of these surfactants, even in the presence of protein. The faster dynamics leads to improved stabilization of model protein biologic drugs IgG and abatacept against agitation-induced aggregation. These results provide mechanistic understanding of the key causes and drivers of protein aggregation.