Surface acoustic wave-assisted swing-angle spray: from mechanism investigation to deposition characteristics and <i>in vivo</i> wound healing.

Abstract

Wound care remains a significant global challenge, where delayed healing can lead to severe complications. While aerosol-based drug delivery offers a promising alternative to conventional treatments, its efficacy is often compromised by inconsistent atomization and poor distribution. Surface acoustic wave (SAW)-driven atomization can generate uniform micro-droplets but is fundamentally limited by the low propagation velocity of conventional surface mists and a fixed, unalterable spray direction. Here, we introduce a SAW-assisted swing-angle spray (SAW-SAS) strategy that overcomes these limitations. This method achieves effective, directionally adjustable spraying using only traveling SAWs, achieving targeted deposition while eliminating the need for external accelerating fields, and thereby transcending the conventional restriction of SAW atomization to the 22° Rayleigh angle. SAW-SAS produces a highly focused spray, enabling precise control over the deposition area and droplet size. We demonstrate that the swing-angle mechanism is governed by modulating the input frequency relative to the device's resonant frequency. This modulation alters the multi-modal acoustic waves in the device's edge region, which are shown by 2D simulations, shifts the internal acoustic streaming within the parent droplet and repositions the unstable oscillation point of the air-liquid interface. Deposition experiments confirmed that SAW-SAS provides excellent surface coverage with consistent droplet sizes across a range of spray angles. Furthermore, in a murine model, SAW-SAS-based drug delivery significantly accelerated skin wound healing. By using a narrow spray angle for deep drug penetration and a wider angle for broad surface coverage, our approach enables tailored drug delivery that matches the dosage to the wound's topography, thereby minimizing the risk of adverse effects from excessive drug application.