Core–shell microgels as “smart” carriers for enzymes

Abstract

We present a thermodynamic study of the adsorption of lysozyme on a negatively charged core-shell microgel at pH 7.2. The carrier particles consist of a polystyrene core onto which a charged poly (N-isopropylacrylamide-co-acrylic acid) network is attached. Isothermal titration calorimetry (ITC) is used to investigate the temperature and salt dependence of lysozyme binding. Our ITC analysis unequivocally shows that the adsorption of lysozyme onto the charged gel is driven by entropy. The addition of salt strongly decreases the binding affinity, indicating significant electrostatic contributions to the adsorption process. However, at high salt concentrations, substantial protein binding with unaltered entropies is still observed pointing to large contributions from hydrophobic interactions. Furthermore, the calorimetric analysis suggests that protonation of lysozyme takes place upon binding. This is directly shown by analysis of the enzymatic activity of adsorbed lysozyme. It was found that the activity is enhanced about $3.5 times, indicating that lysozyme has taken up approximately one proton when entering the gel. The entire set of data demonstrates that core-shell microgels present ''smart'' colloidal carriers for lysozyme that enhance its activity.

Reaction rate of a composite core–shell nanoreactor with multiple nanocatalysts

“…(15). Recalling the definitions (19) and making use of known properties of solid spherical harmonics, it is easy to see that…”

“…Interestingly, we have shown that, as a general situation, increasing both the core and the nanocatalyst sizes either has a rather mild effect on the overall performances, or, more generally, causes a rate-boosting effect, with an increase of the overall rate constant of up to 40 % for values of the core size R S /R 0 0.7. In order to determine the unknown coefficients in the expansions (19), we have to express the solution in the local coordinates on every boundary (the N + 1 spherical surfaces ∂ Ω α ) and at the microgel-bulk interface ∂ Ω 0 , where we impose the pseudocontinuity conditions for the reactant density field. This can be accomplished by using known addition theorems for spherical harmonics [38,39].…”

“…Remarkably, a simple yet accurate analytical expression can be easily obtained in the monopole approximation (MOA), which corresponds to keeping only the = 0 term in the multipole expansions (19) [26,27]. In particular, it is interesting to compute the rate normalized to the Smoluchowski rate of an isolated sink of the same size as the whole nanoreactor in the bulk, i.e.…”

“…The rate-determining step proceeds at the surface of the nanoparticles and the mechanism is known [18]. The present theory, however, comprises also the nanoreactors in which enzymes are used as catalytic centers embedded in the network shell [19].…”

Theory, simulations and the design of functionalized nanoparticles for biomedical applications: A Soft Matter Perspective

“…131 Moreover, it has been shown that certain enzymes can remain functional once adsorbed, 132 which could be interesting to cure diseases related to the presence of a malfunctioning enzyme, or lack of a functional one. 133 Rather than being used to prevent proteins adsorption as in the case of brushes, with polymer gels, one aims to control it, as well as to control their release. Several models containing similar ingredients to that of Biesheuvel et al 123,127 have been developed to describe protein adsorption in gels.…”