Controlled Degradation of Polycaprolactone Polymers through Ultrasound Stimulation

Abstract

This study describes the development of an ultrasound-responsive polymer system that provides on-demand degradation when exposed to high-intensity focused ultrasound (HIFU). Diels−Alder cycloadducts were used to crosslink polycaprolactone (PCL) polymers and underwent a retro Diels− Alder reaction when stimulated with HIFU. Two Diels−Alder polymer compositions were explored to evaluate the link between reverse reaction energy barriers and polymer degradation rates. PCL crosslinked with isosorbide was also used as a non-Diels− Alder-based control polymer. An increase of HIFU exposure time and amplitude correlated with an increase of PCL degradation for Diels−Alder-based polymers. Ultrasound imaging during HIFU allowed for real-time visualization of the on-demand degradation through cavitation-based mechanisms. The temperature surrounding the sample was monitored with a thermocouple during HIFU stimulation; a minimal increase in temperature was observed. PCL polymers were characterized using Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), optical profilometry, and mechanical testing. PCL degradation byproducts were identified by mass spectrometry, and their cytocompatibility was evaluated in vitro. Overall, this study demonstrated that HIFU is an effective image-guided, external stimulus to control the degradation of Diels− Alder-based PCL polymers on-demand.

Controlling the lifetime of biodegradable electronics: from dissolution kinetics to trigger acceleration

“…An ideal approach to actively accelerate the degradation of polymer encapsulation and substrate is to ensure the complete dissolution of implanted medical devices once they are no longer needed after the treatment ends. Recently, methods using ultrasonic waves to fragment polymer materials have been introduced, accelerating the decomposition rate of the polymer or limiting the device operation at a desired time [131,134,135] . Ultrasound frequencies around 20 kHz have the advantage of penetrating deepest inside the body and are used for destructive medical applications [136,137] .…”

“…Ultrasound frequencies around 20 kHz have the advantage of penetrating deepest inside the body and are used for destructive medical applications [136,137] . Studies utilizing this frequency to actively control the lifetime of polymers have been reported [131,134,135] . Lee et al utilized 20 kHz ultrasound for ondemand degradation control of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), serving as the encapsulation layer in TENGs [130] [Figure 6E].…”

“…This is primarily due to the impedance mismatch between PHBV and air [131] . Additionally, acoustic pressure intensifies in the pores created during PHBV fabrication, leading to the mechanical fracture of the polymer film [131,134] . This method proved effective in controlling polymer lifespan, as it induced almost 30% weight loss in the PHBV film within 3 h [Figure 6G], a process taking eight weeks without ultrasound [131] .…”