Synthesis of polyacid nanogels: pH-responsive sub-100 nm particles for functionalisation and fluorescent hydrogel assembly

Abstract

Nanogels are crosslinked polymer particles with a swollen size between 1 and 100 nm. They are of major interest for advanced surface coatings, drug delivery, diagnostics and biomaterials. Synthesising polyacid nanogels that show triggered swelling using a scalable approach is a key objective of polymer colloid chemistry. Inspired by the ability of polar surfaces to enhance nanoparticle stabilisation, we report the first examples of pH-responsive polyacid nanogels containing high -COOH contents prepared by a simple, scalable, aqueous method. To demonstrate their functionalisation potential, glycidyl methacrylate was reacted with the -COOH chemical handles and the nanogels were converted to macro-crosslinkers. The concentrated (functionalised) nanogel dispersions retained their pH-responsiveness, were shear-thinning and formed physical gels at pH 7.4. The nanogels were covalently interlinked via free-radical coupling at 37 °C to form transparent, ductile, hydrogels. Mixing of the functionalised nanogels with polymer dots enabled covalent assembly of fluorescent hydrogels.

Highly deformable hydrogels constructed by pH-triggered polyacid nanoparticle disassembly in aqueous dispersions

“…The breaking strain of this new hydrogel is much greater than any value reported for DX MGs. 24,33,34,50,56 Furthermore, Gel-MMA-10 showed excellent recovery as shown by a qualitative deformation test (Fig. 5(c)).…”

“…What is the origin of the high deformability of these gels? There are two key differences between the NPs used in the present study and the MGs reported previously: 33,34 (i) the omission of a crosslinking comonomer and (ii) the higher MAA contents of the NPs. The absence of any crosslinker should enable faster diffusion of the GMA reagent throughout the precursor NPs during the coupling reaction between GMA and a minor fraction of the carboxylic acid groups on the monomer repeat units (Scheme S1, ESI †).…”

“…33 Such MGs are typically lightly crosslinked colloidal particles that are usually prepared with a crosslinking comonomer and significant swelling occurs when the solution pH approaches the pK a of the constituent copolymer chains. 34 Macroscopic gels were prepared in the absence of any small molecule crosslinker by covalent interlinking of the pre-formed MGs to produce doubly-crosslinked microgels (DX MGs) 33 (see Scheme 1(a)). As discussed in detail elsewhere 35 this DX MG concept differs from gels constructed from small molecule monomers and MG particle macro-crosslinkers.…”

Using green emitting pH-responsive nanogels to report environmental changes within hydrogels: a nanoprobe for versatile sensing

“…Recently, a new family of polyelectrolyte hydrogels have been reported which are assembled by covalent interlinking of MAA-containing nanogel particles 39 . Those gels are termed doubly crosslinked nanogels (DX NGs) and are optically transparent 39 . We prepared such a gel by covalently interlinking NG-MAA GMA as depicted in Fig.…”

Facile approach to prepare pH and redox-responsive nanogels via Diels-Alder click reaction

“…Therefore, the nanogel samples prepared from the molar ratio of 1:1 were used to analyze the size distribution and morphology by TEM and DLS. The average size of crosslinked nanogels was smaller than 100 nm in drying regime (Figure 6a) and around 100 nm in swelling state (Figure 6b), which could be suitable for anticancer drug delivery [37,38]. The selected nanogels formed at the condition of 120 mg/mL, furan:maleimide molar ratio = 1:1 and 1.5 h was isolated by dilution with THF and precipitated in diethyl ether.…”