High-velocity micro-particle impact on gelatin and synthetic hydrogel

Optothermal Needle-Free Injection of Vaterite Nanocapsules

The propulsion and acceleration of nanoparticles with light have both fundamental and applied significance across many disciplines. Needle-free injection of biomedical nano cargoes into living tissues is among the examples. Here a new physical mechanism of laser-induced particle acceleration is explored, based on abnormal optothermal expansion of mesoporous vaterite cargoes. Vaterite nanoparticles, a metastable form of calcium carbonate, are placed on a substrate, underneath a target phantom, and accelerated toward it with the aid of a short femtosecond laser pulse. Light absorption followed by picosecond-scale thermal expansion is shown to elevate the particle's center of mass thus causing acceleration. It is shown that a 2 µm size vaterite particle, being illuminated with 0.5 W average power 100 fsec IR laser, is capable to overcome van der Waals attraction and acquire 15m sec-1 velocity. The demonstrated optothermal laser-driven needle-free injection into a phantom layer and Xenopus oocyte in vitro promotes the further development of light-responsive nanocapsules, which can be equipped with additional optical and biomedical functions for delivery, monitoring, and controllable biomedical dosage to name a few.

Next-generation protein-based materials capture and preserve projectiles from supersonic impacts

Extreme energy-dissipating materials are essential for a range of applications. The military and police force require ballistic armour to ensure the safety of their personnel, while the aerospace industry requires materials that enable the capture, preservation and study of hypervelocity projectiles. However, current industry standards display at least one inherent limitation, such as weight, breathability, stiffness, durability and failure to preserve captured projectiles. To resolve these limitations, we have turned to nature, using proteins that have evolved over millennia to enable effective energy dissipation. Specifically, a recombinant form of the mechanosensitive protein talin was incorporated into a monomeric unit and crosslinked, resulting in a talin shock-absorbing material (TSAM). When subjected to 1.5 km s-1 supersonic shots, TSAMs were shown to absorb the impact and capture and preserve the projectile.

Ballistic delivery of compounds to inner layers of the cornea is limited by tough mechanical properties of stromal tissue

The barrier characteristics of the cornea are interrogated using the impact of micro-particles into ex vivo porcine cornea. Using a commercial gene gun (BioRad; PDS1000), microparticles were accelerated and made to embed in target materials: either ballistic gelatin as a reference or corneal tissue. Statistical analysis of penetration of polydisperse spherical microparticles (5-22 μm dia.) with density of 2.5 g/cc, 4.2 g/cc, and 7.8 g/cc (soda-lime glass, barium-titanate glass and stainless steel; more limited examination of 1.1 g/cc polyethylene and 19.2 g/cc tungsten) spanned almost two decades in kinetic energy. Penetration profiles in ballistic gelatin show that the particle embedding depth is sensitive to particle size and density. In the cornea, penetration is a weak function of size and density, and the corneal stroma is an effective stopping medium for high velocity microparticles. Despite the high water content of corneal tissue (76% w/w) compared to the stratum corneum of skin (40% w/w), the resistance to penetration of the cornea is comparable to what is seen in previous research of penetration in skin tissue. Using low density polymer particles with a therapeutic agent payload, it is demonstrated that bulk material can be ballistically delivered to the central 1 cm² of the corneal epithelium in an even layer with high bioavailability of therapeutic compound.

Using microprojectiles to study the ballistic limit of polymer thin films

The dynamic impact between a particle and a planar material is important in many high impact events, and there is a growing need to characterize the mechanical properties of light-weight polymeric materials at dynamic loading conditions. Here, a laser-induced projectile impact test (LIPIT) is employed to investigate the ballistic limit (V0) and materials properties at impact velocities ranging from 40 m s-1 to 70 m s-1. An analytical expression describing the various energy dissipation mechanisms is established to estimate the yield stress and elasticity for polycarbonate thin films. This measurement approach demonstrates the utility of using low sample mass for discovery of materials for impact mitigation, as well as high-throughput mechanical characterization at dynamic loading rates.