Shanglin Wu

Remote measurement of the deformation ratio and discrimination between tension and compression for injectable gels is demonstrated using photoluminescence and two types of fluorescent probe particles.

Near infra-red (NIR) fluorescence is a desirable property for probe particles because such deeply penetrating light enables remote reporting of the local environment in complex surroundings and imaging. Here, two NIR non-radiative energy transfer (NRET) fluorophores (Cy5 and Cy5.5) are coupled to preformed pH-responsive poly(ethylacrylate-methacrylic acid-divinylbenzene) microgel particles (PEA-MAA-5/5.5 MGs) to obtain new NIR fluorescent probes that are cytocompatible and swell strongly. NIR ratiometric photoluminescence (PL) intensity analysis enables reporting of pH-triggered PEA-MAA-5/5.5 MG particle swelling ratios over a very wide range (from 1–90). The dispersions have greatly improved colloidal stability compared to a reference temperature-responsive NIR MG based on poly(N-isopropylacrylamide) (PNP-5/5.5). We also show that the wavelength of maximum PL intensity (λ_max) is a second PL parameter that enables remote reporting of swelling for both PEA-MAA-5/5.5 and PNP-5/5.5 MGs. After internalization the PEA-MAA-5/5.5 MGs are successfully imaged in stem cells using NIR light. They are also imaged after subcutaneous injection into model tissue using NIR light. The new NIR PEA-MAA-5/5.5 MGs have excellent potential for reporting their swelling states (and any changes) within physiological settings as well as very high ionic strength environments (e.g., waste water).

The mesoporous (meso)-TiO₂ layer is a key component of high efficiency perovskite solar cells (PSCs). Herein, pore size controllable meso-TiO₂ layers are prepared using spin coating of commercial TiO₂ nanoparticle (NP) paste with added soft polymer templates (SPT) followed by removal of the SPT at 500 °C. The SPTs consist of swollen crosslinked polymer colloids (microgels, MGs) or a commercial linear polymer (denoted as LIN). The MGs and LIN were comprised of the same polymer, which was poly(N-isopropylacrylamide) (PNIPAm). Large (L-MG) and small (S-MG) MG SPTs were employed to study the effect of template size. The SPT approach enabled pore size engineering in one deposition step. The SPT/TiO₂ nanoparticle films had pore sizes > 100 nm; whereas, the average pore size was 37 nm for the control meso-TiO₂ scaffold. The largest pore sizes were obtained using L-MG. SPT engineering increased the perovskite grain size in the same order as the SPT sizes: LIN < S-MG < L-MG and these grain sizes were larger than obtained using the control. The power conversion efficiencies (PCEs) of the SPT/TiO₂-devices were ~ 20% higher than that for the control meso-TiO₂ device and the PCE of the champion S-MG device was 18.8%. This is the highest PCE reported for a PSC prepared using a pore-size engineered TiO₂ layer to our knowledge and is also one of the highest for PSCs prepared using ITO/meso-TiO₂. The PCE improvement is due to the increased grain size and more effective light harvesting of the SPT devices. The increased grain size was also responsible for the improved stability of the SPT/TiO₂ devices. The SPT method used here is simple, scalable and versatile and should also apply to other PSCs.

Fabrication strategies for programmed hydrogels that provide precise spatial control with predetermined responses to external stimuli are highly desirable. In this study, a partially reversible light‐driven assembly (PRLDA) method is introduced to construct multiresponsive hydrogels utilizing microgel (MG) particle building blocks (swollen diameter of 107 nm). No other material is required to prepare the gels beyond the MGs themselves. Facile preparation of multiresponsive hydrogels that are reversibly responsive to light, pH, and temperature using phototriggered covalent interlinking of coumarin‐based MGs is demonstrated. The gels have phototuneable moduli and swelling ratios and show light‐assisted healing and reshaping. Remarkably, the intrinsic fluorescence of the gels undergoes a reversible light‐triggered wavelength‐shift. The emission peak blueshifted from 420 to 390 nm upon irradiation with 365 nm light. The PRLDA gels can be constructed using either positive or negative photopatterning. It is shown that the gels can be exploited for multiresponsive cytocompatible actuators, grippers, and ON/OFF circuit components as well as anticounterfeit gels. The PRLDA method provides new insight into programmed gel property control and has excellent potential for biomaterial and optoelectronic applications.

Elastic physical gels are highly desirable because they can be conveniently prepared and readily shaped. Unfortunately, many elastic physical gels prepared in water require in situ free-radical polymerization during the gel formation stage. In contrast, complex coacervate gels are physical gels that can be prepared by simply mixing two pre-formed oppositely-charged polyelectrolytes. However, as far as we are aware, highly elastic complex coacervate gels have not yet been reported. Herein, we combine polyanionic microgel particles with a well-known commercially-available cationic polyelectrolyte to prepare polymer/microgel complex coacervate (PMCC) physical gels. This new family of gels requires annealing at only 37 °C and behaves like a covalent gel but does not form covalent bonds. Thermal reconfiguration of the dynamic ionic bonds transforms the shapeable pre-gel into a highly elastic gel that is super-stretchable, adhesive, self-healing, highly swellable and can be further toughened using Ca²⁺ as an ionic crosslinker. Our PMCC gels have excellent potential for applications as engineering gels and structural biomaterials, as well as for wound healing and water purification.

Low concentrations of new stimuli-responsive blue-green-fluorescent nanogel probes within four different gels and stem cells reversibly report five different stimuli: cations, degradation, pH, temperature and tensile strain.

Swellable crosslinked polymer colloid particles (microgels) which have a swollen size that can be reversibly changed using light are rare. We report the synthesis of four different triply responsive microgels with as-made diameters ranging from 25 to 124 nm. Each MG system is pH-, temperature- and photo-responsive. These poly(MEO₂MA-co-MAA-co-CMA) microgels were prepared using precipitation copolymerisation of 2-(2-methoxyethoxy)ethyl methacrylate (MEO₂MA), methacrylic acid (MAA) and 7-(2-methacryloyloxyethoxy)-4-methylcoumarin (CMA). This one-step synthesis method is scalable. The microgel systems were strongly pH- and temperature-responsive. They were also photo-switchable between highly crosslinked and de-crosslinked states using UV-irradiation. The effective crosslinker density was easily controlled by irradiation at wavelengths of 365 nm (photo-crosslinked state) and 254 nm (photo-de-crosslinked state). Interestingly, the particle volume ratio increase upon photo-de-crosslinking was found to be at least twice that reported for other nanoparticle-based systems. The strong photo-switching behaviour of the present microgels was shown to be due to a uniform incorporation of CMA within the particles. Unexpectedly, it was found that the extent of photo-induced dimerisation increased with a decrease in the as-made microgel size. The photo-induced swelling of the microgel was used to accelerate the release of the anti-cancer drug doxorubicin to demonstrate potential for future application for on-demand drug release.

Microgels (MGs) are swellable crosslinked polymer colloids. They can also be used as the only building block to construct nanostructured hydrogels which are denoted as doubly crosslinked microgels (DX MGs). Here, new triply responsive DX MGs comprised of interlinked MGs of oligo(ethylene glycol)methacrylate (OEGMA), 2-(2-methoxyethoxy)ethyl methacrylate (MEO₂MA), methacrylic acid (MAA) and a o-nitrobenzyl-based UV photocleavable crosslinker are investigated. The MGs swelled or collapsed in response to temperature and pH changes. These behaviours were rationalised with a generic model using Monte Carlo simulations. The MGs also degraded when UV irradiated due to photocleavage of nPh. DX MGs were assembled from the MGs to give injectable gels that were not cytotoxic to nucleus pulposus cells. Comparison of the responsive properties of the DX MGs and MGs showed that the temperature and pH responses of the former were mostly governed by the latter. However, two key differences were found. Firstly, whilst increasing the crosslinker mol% in the MG building blocks (x) did not change MG particle swelling, the compression modulus (E) and swelling of the DX MG gels were strongly affected by x. The E value for the gels was tuneable using x which is a potentially useful new observation for DX MGs. Secondly, UV irradiation of the DX MGs enhanced gel mechanical photostability in contrast to the behaviour of the MGs. We find that the properties of the DX MGs do not simply follow those of the parent MGs and propose mechanisms to account for the differences. The new family of multi-responsive DX MGs presented in this study have potential application for soft tissue repair as injectable gels or as gel implants which report sterilisation.

New Au-copolymer core–shell nanoparticles with thin pH-responsive polymer shells show explainable thickness dependent surface plasmonic behaviour, enhanced dispersion stability or reversible aggregation.

Blends of semiconducting nanocrystals and conjugated polymers continue to attract major research interest because of their potential applications in optoelectronic devices, such as solar cells, photodetectors and light-emitting diodes. In this study we investigate the surface structure, morphological and optoelectronic properties of multilayer films constructed from ZnO nanocrystals (NCs) and poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV). The effects of layer number and ZnO concentration (C_ZnO) used on the multilayer film properties are investigated. An optimised solvent blend enabled well-controlled layers to be sequentially spin coated and the construction of multilayer films containing six ZnO NC (Z) and MDMO-PPV (M) layers (denoted as (ZM)₆). Contact angle data showed a strong dependence on C_ZnO and indicated distinct differences in the coverage of MDMO-PPV by the ZnO NCs. UV-visible spectroscopy showed that the MDMO-PPV absorption increased linearly with the number of layers in the films and demonstrates highly tuneable light absorption. Photoluminescence spectra showed reversible quenching as well as a surprising red-shift of the MDMO-PPV emission peak. Solar cells were constructed to probe vertical photo-generated charge transport. The measurements showed that (ZM)₆ devices prepared using C_ZnO = 14.0 mg mL⁻¹ had a remarkably high open circuit voltage of ∼800 mV. The device power conversion efficiency was similar to that of a control bilayer device prepared using a much thicker MDMO-PPV layer. The results of this study provide insight into the structure–optoelectronic property relationships of new semiconducting multilayer films which should also apply to other semiconducting NC/polymer combinations.