Synthesis of smart core–shell polymer in supercritical carbon dioxide

Synthesis of core-shell polymer particles in supercritical carbon dioxide via iterative monomer addition

A new, robust methodology for the synthesis of polystyrene-poly(methyl methacrylate) (PS-PMMA) core-shell particles using seeded dispersion polymerisation in supercritical carbon dioxide is reported, where the core-shell ratio can be controlled predictably via manipulation of reagent stoichiometry. The key development is the application of an iterative addition of the MMA shell monomer to the pre-prepared PS core. Analysis of the materials with differing core-shell ratios indicates that all are isolated as single particle populations with distinct and controllable core-shell morphologies.

Phase transition and potential biomedical applications of thermoresponsive compositions based on polysaccharides, proteins and DNA: A review

Smart thermoresponsive polymers have long attracted attention as materials of a great potential for biomedical applications, mainly for drug delivery, tissue engineering and wound dressing, with a special interest to injectable hydrogels. Poly-N-isopropylacrylamide (PNIPAM) is the most important synthetic thermoresponsive polymer due to its physiologically relevant transition temperature. However, the use of unmodified PNIPAM encounters such problems as low biodegradability, low drug loading capacity, slow response to thermal stimuli, and insufficient mechanical robustness. The use of natural polysaccharides and proteins in combinations with PNIPAM, in the form of grafted copolymers, IPNs, microgels and physical mixtures, is aimed at overcoming these drawbacks and creating dual-functional materials with both synthetic and natural polymers' properties. When developing such compositions, special attention should be paid to preserving their key property, thermoresponsiveness. Addition of hydrophobic and hydrophilic fragments to PNIPAM is known to affect its transition temperature. This review covers various classes of natural polymers - polysaccharides, fibrous and non-fibrous proteins, DNA - used in combination with PNIPAM for the prospective biomedical purposes, with a focus on their phase transition temperatures and its relation to the natural polymer's structure.

Synthesis of two-phase polymer particles in supercritical carbon dioxide

A simple method to synthesise phase-separated microparticles avoiding any control agents and post-polymerisation drying steps.

Monolithic intercalated PNIPAm/starch hydrogels with very fast and extensive one-way volume and swelling responses to temperature and pH: prospective actuators and drug release systems

Remarkable monolithic (non-porous) hydrogels based on poly(NIPAm-co-sodium methacrylate) intercalated by starch were prepared, and were found to display very fast and extensive one-way solvent (water) release, induced by both pH and temperature. With centimeter-sized 3D specimens, the achieved response times were as short as 4 min (for 70% water release), in combination with very large volume responses (shrinking ratios up to 15). The response time can be tuned from minutes, over tens of minutes, up to hours. The pH-induced deswelling is always slower than the temperature-induced one, but at the highest starch content, ca. 5.5 min are needed for 70% completion of the pH-triggered process. Simultaneous temperature- and pH-stimuli expectedly also lead to very fast water release. The unique intercalated structure and the temperature-dependent hydrogen bridging between the intercalated phases, as well as between these phases and water, were found to play the key role in the ability of the gels to rapidly release water and shrink, which was deeper elucidated in this work. The hydrogels are of interest as soft actuators, but also for chemical release systems or for drug release applications. The latter was successfully tested with theophylline as the drug.

Sulindac encapsulation and release from functional poly(HEMA) microparticles prepared in supercritical carbon dioxide

Sulindac loaded poly(HEMA) cross-linked microparticles were synthesized via one-pot free-radical dispersion polymerisation in supercritical carbon dioxide (scCO₂) in presence of photocleavable diblock stabilisers based on polyethylene oxide (PEO) and poly(heptadecafluorodecyl acrylate) (PFDA) bearing a o-nitrobenzyl photosensitive junction (hv) (PEO-hv-PFDA), and ethylene glycol dimethacrylate (EGDMA) as cross-linker. Poly(HEMA) cross-linked microparticles either empty or sulindac loaded were obtained with well-defined spherical morphology with the sizes between 250 and 350 nm. Additionally, upon UV-photolysis the stabiliser on the surface was cleaved which permits to microparticles to be redispersed in water leading to water swollen microgels about 2.1-3.6 µm. Moreover, the release behaviour from obtained microgels indicated the sustained release of sulindac over 10 days. Besides, the surface modification after UV-photolysis was studied and proved that the particles can be functionalised with further chemistries.

Thermal-sensitive Starch-g-PNIPAM prepared by Cu(0) catalyzed SET-LRP at molecular level

Starch-g-PNIPAM with controlled graft chains and its hydrogels with rapid shrinking rate were preparedviaSET-LRP at molecular level.

Supercritical carbon dioxide: a solvent like no other

Supercritical carbon dioxide (scCO2) could be one aspect of a significant and necessary movement towards green chemistry, being a potential replacement for volatile organic compounds (VOCs). Unfortunately, carbon dioxide has a notoriously poor solubilising power and is famously difficult to handle. This review examines attempts and breakthroughs in enhancing the physicochemical properties of carbon dioxide, focusing primarily on factors that impact solubility of polar and ionic species and attempts to enhance scCO2 viscosity.