Iron oxide nanoparticles (IONPs, sometimes called superparamagnetic iron oxide nanoparticles or SPIONs) have already shown promising results for in vivo cell tracking using magnetic resonance imaging (MRI). To fully exploit the potential of these materials as contrast agents, there is still a need for a greater understanding of how they react to physiological conditions. A key aspect is the specific nature of the surface coating, which can affect important properties of the IONPs such as colloidal stability, toxicity, magnetism and labelling efficiency. Polymers are widely used as coatings for IONPs as they can increase colloidal stability in hydrophilic conditions, as well as protect the iron oxide core from degradation. In this tutorial review, we will examine the design and synthesis approaches currently being employed to produce polymer coated IONPs as cell tracking agents, and what considerations must be made. We will also give some perspective on the challenges and limitations that remain for polymer coated IONPs as MRI contrast agents for stem cell tracking.

Hydrogels prepared from low molecular weight gelators (LMWGs) are formed as a result of hierarchical intermolecular interactions between gelators to form fibres, and then further interactions between the self-assembled fibres via physical entanglements, as well as potential branching points. These interactions can allow hydrogels to recover quickly after a high shear rate has been applied. There are currently limited design rules describing which types of morphology or rheological properties are required for a LMWG hydrogel to be used as an effective, printable gel. By preparing hydrogels with different types of fibrous network structures, we have been able to understand in more detail the morphological type which gives rise to a 3D-printable hydrogel using a range of techniques, including rheology, small angle scattering and microscopy.

Regenerative medicine therapies hold enormous potential for a variety of currently incurable conditions with high unmet clinical need. Most progress in this field to date has been achieved with cell-based regenerative medicine therapies, with over a thousand clinical trials performed up to 2015. However, lack of adequate safety and efficacy data is currently limiting wider uptake of these therapies. To facilitate clinical translation, non-invasive in vivo imaging technologies that enable careful evaluation and characterisation of the administered cells and their effects on host tissues are critically required to evaluate their safety and efficacy in relevant preclinical models. This article reviews the most common imaging technologies available and how they can be applied to regenerative medicine research. We cover details of how each technology works, which cell labels are most appropriate for different applications, and the value of multi-modal imaging approaches to gain a comprehensive understanding of the responses to cell therapy in vivo.

Perylene bisimides (PBIs) are one example of useful p-conjugated molecules that can be used in optoelectronic devices as n-type materials with strong visible light absorption. PBIs can self-assemble into a range of structures, but it is rare to be able to control the packing such that the same PBI can form either H-type or J-type aggregates. This is important because the conductivity pathways and optoelectronic properties are directly affected by this packing. Here, we show that we can control the packing of a single PBI functionalized with an amino acid by a subtle change in pH. Under one set of conditions, H-type aggregates form a gel when the pH is decreased. At a slightly different set of starting conditions, J-type aggregates are formed, but they cannot form a gel when the pH is lowered. We show that films formed from the self-assembled structures have very different photoconductive properties.

Directional freezing and frozen UV initiated polymerization have been employed to prepare aligned porous stimuli-responsive hydrogels. Oligo-ethylene glycol methacrylates and dimethylamino ethyl methacrylate monomers are used to produce temperature and pH-responsive hydrogels respectively.The aqueous monomer mixtures are directionally frozen in liquid nitrogen and the frozen samples with dry ice are then polymerized by UV irradiation. Aligned porous morphologies are observed in both dry and hydrated states. The hydrogels exhibit stimuli-responsive behaviour in aqueous conditions and anisotropic compressive strength and diffusion behaviour with respect to freezing direction.