PH-sensitive microgels

Different ionic monomers were copolymerized with NIPAAm or VCL to obtain pH- and temperature-sensitive microgels. Snowden et al. [65] reported preparation of aqueous microgels by copolymerization of NIPAAm and acrylic acid (AAc) in a precipitation polymerization process. The AAc content was 5wt%. Obtained microgels displayed pH and electrolyte sensitivity, as well as temperature sensitivity. 

Lyon s group prepared aqueous microgels by copolymerization of NIPAAm with hydrophobic [tert-butyl acrylamide (TBAm)] and pH-sensitive acrylic acid monomers [73],... 

Li et al. [100] synthesized core-shell microgels with temperature-sensitive PNIPAAm core and pH-sensitive poly(4-vinylpyridine) (P4VP) shell. Narrowly distributed microgel particles with core diameter of 95 nm and shell thickness of approximately 30 nm were obtained. 

Temperature- and pH-sensitive core-shell microgels consisting of a PNIPAAm core crosslinked with BIS and a polyvinylamine (PVAm) shell were synthesized by graft copolymerization in the absence of surfactant and stabilizer [106] The core-shell morphology of the microgels was confirmed by TEM and zeta-potential measurements. Other examples of core-shell microgel systems are PNIPAAm-g-P(NIPAM-co-styrene) colloids [107] or PS(core)-g-PNIPAAm (shell) particles [108],... 

Huo D, Li Y, Qian Q, Kobayashi T (2006) Temperature-pH sensitivity of bovine serum albumin protein-microgels based on cross-linked pol y(/V-i sopropylacrylamide-co-acrylic acid). Colloids Surf B Biointerfaces 50 36-42... 

Soppimath KS, Kulkarni AR, and Aminabhavi TM. Chemically modified polyacrylamide-g-guar gum-hased cross-linked anionic microgels as pH-sensitive dmg delivery systems Preparation and characterization. Journal of Controlled Release 2001 75 331-345. 

Soppimath, K.S. Kulkarni, A.R. Aminabhavi, T.M. Chemically modified polyacrylamide-g-guar gum-based crosslinked anionic microgels as pH-sensitive drug delivery systems preparation and characterization. J. Control. 

In previous work reported on PDMAEMA-based microgels, most of them are prepared using At//-dimethylaminoethyl methaciylate (DMAEMA) as the monomer, and with one or two other comonomers added in the preparation process. " Although these copolymerizations are reported to enhance the glass transition temperature (Tg) or generate multi-stimuli-responsive properties, the pH sensitivity of the prepared microgels is reduced to a certain extent in most cases. To overcome this problem, PDMAEMA... 

The sensitivities of microgels toward different physical parameters (temperature, pH) or chemical species provide enormous potential for their use as actors in microfluidic devices. The basic function of the microgel in microfluidic devices is to switch or regulate a microliquid flow. Numerous automatic hydrogel-based microvalves have been reported such as glucose-sensitive microvalve, pH-sensitive micro-valve, and T-sensitive microvalve. In contrast to automatic microvalves, the electronically controllable microvalves are imspedfic and usable in manifold applications. In... 

Influence of Comonomers on Microgel Properties. The overall physicochemical properties of a microgel depend not only on the cross-linker concentration, but also on the concentration of monomer/comonomers used in the synthesis. The addition of a small amount of comonomer (typically 1-5 wt% monomer) can have a dramatic effect on the overall properties of the resultant microgel particles. For example, a pH- and temperature-sensitive microgel can be prepared by copolymerizing poly(NIPAM) with acrylic acid. These spherical particles undergo... 

Biocompatible microgels for the delivery of protein and DNA biomolecules were developed using acrylamide monomer, a bisacrylamide acetal crosslinker and potassium persulphate initiator. Encapsulation was shown to provide protection from enzymatic degradation of the protein or DNA. These particles demonstrated pH sensitivity such that in an acidic environment, as in the lysosome, the polymeric carrier degraded and released the encapsulated biomolecule. 9 refs. 

Methacrylic acid polymers are well known for their pH sensitivity [74]. Incorporation of co-monomers containing acidic [75] or basic [76] functionalities into poly(NIPAM) microgels yields particles with pH driven swelling. For example, Snowden etaL, reported the... 

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