Influence of Architecture on the Interaction of Negatively Charged Multisensitive Poly(N-isopropylacrylamide)-co-Methacrylic Acid Microgels with Oppositely Charged Polyelectrolyte: Absorption vs Adsorption

Abstract

Two sets of core-shell microgels composed of temperature-sensitive poly(N-isopropylacrylamide) (PNiPAM) with different spatial distribution of pH-sensitive methacrylic acid (MAA) groups were prepared. The cores consist of either PNiPAM (neutral core; nc) or PNiPAM-co-MAA (charged core; cc). A charged shell existing of PNiPAM-co-MAA was added to the neutral core (yielding neutral core-charged shell; nccs), on the charged core, on the other hand, a neutral shell of PNiPAM was added (charged core-neutral shell; ccns). Complexes of these microgels with positively charged poly(diallyldimethylammonium chloride) (PDADMAC) of different molar masses were prepared. The amount of bound polyelectrolyte was quantified, and the microgel-polyelectrolyte complexes were characterized with respect to electrophoretic mobility and hydrodynamic radius. The penetration of polyelectrolyte into the microgel was also monitored by means of lifetime analysis of a fluorescent dye covalently bound to poly(L-lysine) providing information on the probe's local environment. The architecture of the microgel has a significant influence on the interaction with oppositely charged polyelectrolyte. Complexes with microgel with the charged shell tend to flocculate at charge ratios of 1 and are thus similar to polyelectrolyte complexes with rigid colloidal particles. Complexes with microgels that consist of a charged core and a neutral shell show very different properties: They are still temperature sensitive and reveal an influence of the polyelectrolyte's chain length. Low molecular weight PDADMAC can penetrate through the neutral shell into the charged core, and thus nearly no charge reversal occurs. The high-MW polyelectrolyte does not penetrate fully and leads to charge reversal. The results demonstrate that microgels are able to absorb or adsorb polyelectrolytes depending on the polyelectrolyte's chain length and the microgels architecture. Complexes with different surface properties and different colloidal stability can be prepared, and polyelectrolytes can be encapsulated in the microgel core. Thus, multisensitive core-shell microgels combine permeability and compartmentalization on a nanometer length scale and provide unique opportunities for applications in controlled uptake and release.

Charged poly(N-isopropylacrylamide) nanogels for use as differential protein receptors in a turbidimetric sensor array

“…These results agree with our conclusions from the adsorption capacity experiments, that is, the high adsorption capacity of proteins to R1 and R2 (in both buffers), and R3 (in 0.1X PBS) was attributed to protein binding throughout the network while adsorption to R4 and R5 was attributed primarily to surface binding. Accordingly, for R4 and R5 , DLS results suggest the main factor causing the increased turbidity is surface binding leading to particle aggregation, 61 similar to standard particle-enhanced turbidimetric immunoassays. 59 For R1 - R3 , however, the increase in turbidity was primarily due to an increase in refractive index as a result of protein molecules filling the volumes of the nanogels.…”

Plastic deformation, wrinkling, and recovery in microgel multilayers

“…Additionally, film connectivity can be manipulated by changing the length of the PDADMAC used during assembly. The longer polymer chains associated with higher molecular weight polycation results in limited penetration into the microgel network, 34 as well as serving to cross-link neighboring microgels. As such, one would also anticipate that higher molecular weights would tend to lead to higher levels of microgel-to-microgel cross-linking within the films; shorter chains should result in poorer connectivity.…”

Temperature-Responsive Smart Nanocarriers for Delivery Of Therapeutic Agents: Applications and Recent Advances

“…Also, another example is when functional monomers have been used, and in these cases, it is possible to make either neutral shells with charged core or neutral core with charged shell. Richtering et al 120 developed core–shell microgels, utilizing temperature-sensitive PNIPAAm. Two different types of microgels could be produced, (a) neutral core and charged shell, and (b) charged core and neutral shell.…”