Predictive Shapes of Ellipsoid PPDL-PTHF Copolymer Particles Prepared by the Phantom Stretching Technique

Abstract

Ellipsoidal polymer particles can be prepared from spheres by unidirectional stretching at elevated temperatures, while the particles’ aspect ratios (AR) that result from this phantom stretching methodology are often not precisely predictable. Here, an elastic deformation model was exemplarily evaluated for ~50 µm spherical microparticles from PPDL-PTHF block copolymers. The prolate ellipsoidal particles, obtained by stretching in polyvinyl alcohol phantoms, differed in dimensions at identical relative phantoms elongations up to 150%, depending on the relative polymer composition and their systematically altered mechanical properties. Importantly, the resulting particle shapes within the studied range of AR up to ~4 matched the predictions of the elastic deformation model, which includes information of the elastic moduli of phantom and particle materials. These data suggest that the model may be applicable to predict the conditions needed to precisely prepare ellipsoids of desired AR and may be applicable to various deformable particle materials.

Opportunities and Challenges of Switchable Materials for Pharmaceutical Use

“…They are based on elastic polymer network structures, are available both as hydrophobic matrices and as hydrogels, and can comprise various molecular switches, including heat-sensitive domains [60]. The SMP technology was also transferred from the level of macroscopic implants to microsized particles [61][62][63], which can be prepared from spherical stock particles via stretching deformation to ellipsoids of predefined aspect ratios [64] and may be useful for vessel occlusion and drug delivery [65]. SMPs can be deformed to a secondary shape and fixed in this state by introducing temporary netpoints, such as crystalline domains, via cooling.…”

“…Shape-memory polymers (SMPs) are temperature-switchable polymers that retain a practically constant volume during switching They are based on elastic polymer network structures, are available both as hydrophobic matrices and as hydrogels, and can comprise various molecular switches, including heatsensitive domains [60]. The SMP technology was also transferred from the level of macroscopic implants to microsized particles [61][62][63], which can be prepared from spherical stock particles via stretching deformation to ellipsoids of predefined aspect ratios [64] and Several examples of amorphous and semi-crystalline SMP networks from copolyesters have been reported to provide a sustained drug release that is timely independent of the shape-memory function and hydrolytic degradation of these materials [69,70]. Drug release in such systems is affected, among other parameters, by the polymer composition, as seen for a series of AB copolyester networks, where increasing drug release was correlated with the amount of glycolide as the more hydrophilic repeating unit [69].…”