Mechanism and kinetics of enzymatic degradation of polyester microparticles using a shrinking particle-shrinking core model.

Generalized shrinking particle (SPM) and shrinking core (SCM) models were developed to the kinetics of heterogenous enzymatic degradation of polymer microparticles in a continuous microflow system. This enzymatic degradation was performed in a microfluidic device designed to both physically separate and immobilize the microparticles. Then time-resolved measurements were made using image processing of the physical changes of the particles during degradation. The kinetics of enzyme-polymer intermediate formation, enzymatic bond cleavage, and enzyme diffusion through the layer of degraded substrate (SCM only) were mathematically derived to predict the time-resolved degradation of the substrate. The proposed models were tested against the degradation of 15-25 µm particles of polycaprolactone (PCL) and poly (butylene adipate-co-terephthalate) (PBAT) by cutinase enzyme from Humicola insolens. Degradation of PCL microparticles followed the SPM model and its kinetics were found to be zero-order, while the SCM model applied to PBAT microparticles showed first-order kinetics. Further, the degradation of polybutylene succinate (PBS), and poly butylene-sebacate-co-terephthalate (PBSeT) microparticles demonstrated wide applicability of the method. The use of image processing simplifies the required analysis by eliminating the need to remove aliquots or concentrate effluent for additional analytical characterization.

A Robust Aqueous Core-Shell-Shell Coconut-like Nanostructure for Stimuli-Responsive Delivery of Hydrophilic Cargo.

Conventional delivery systems for hydrophilic material still face critical challenges toward practical applications, including poor retention abilities, lack of stimulus responsiveness, and low bioavailability. Here, we propose a robust encapsulation strategy for hydrophilic cargo to produce a wide class of aqueous core-shell-shell coconut-like nanostructures featuring excellent stability and multifunctionality. The numerous active groups (-SH, -NH2, and -COOH) of the protein-polysaccharide wall material enable the formation of shell-cross-linked nanocapsules enclosing a liquid water droplet during acoustic cavitation. A subsequent pH switch can trigger the generation of an additional shell through the direct deposition of non-cross-linked protein back onto the cross-linked surface. Using anthocyanin as a model hydrophilic bioactive, these nanocapsules show high encapsulation efficiency, loading content, tolerance to environmental stresses, biocompatibility, and high cellular uptake. Moreover, the composite double shells driven by both covalent bonding and electrostatics provide the nanocapsules with pH/redox dual stimuli-responsive behavior. Our approach is also feasible for any shell material that can be cross-linked via ultrasonication, offering the potential to encapsulate diverse hydrophilic functional components, including bioactive molecules, nanocomplexes, and water-dispersible inorganic nanomaterials. Further development of this strategy should hold promise for designing versatile nanoengineered core-shell-shell nanoplatforms for various applications, such as the oral absorption of hydrophilic drugs/nutraceuticals and the smart delivery of therapeutics.