Biointerface Properties of Core–Shell Poly(vinyl alcohol)-hyaluronic Acid Microgels Based on Chemoselective Chemistry

The Application of Hydrogels Based on Natural Polymers for Tissue Engineering

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Hydrogels are known as polymer-based networks with the ability to absorb water and other body fluids. Because of this, the hydrogels are used to preserve drugs, proteins, nutrients or cells. Hydrogels possess great biocompatibility, and properties like soft tissue, and networks full of water, which allows oxygen, nutrients, and metabolites to pass. Therefore, hydrogels are extensively employed as scaffolds in tissue engineering. Specifically, hydrogels made of natural polymers are efficient structures for tissue regeneration, because they mimic natural environment which improves the expression of cellular behavior.

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Producing natural polymer-based hydrogels from collagen, hyaluronic acid (HA), fibrin, alginate, and chitosan is a significant tactic for tissue engineering because it is useful to recognize the interaction between scaffold with a tissue or cell, their cellular reactions, and potential for tissue regeneration. The present review article is focused on injectable hydrogels scaffolds made of biocompatible natural polymers with particular features, the methods that can be employed to engineer injectable hydrogels and their latest applications in tissue regeneration.

Stimuli responsive Janus microgels with convertible hydrophilicity for controlled emulsion destabilization

Although the utilization of rigid particles can afford stable emulsions, some applications require eventual emulsion destabilization to release contents captured in the particle-covered droplet. This destabilizing effect is achieved when using stabilizers that respond to controlled changes in environment. Microgels can be synthesized as stimuli responsive polymeric gel networks that adsorb to oil/water interfaces and stabilize emulsions. These particles are commonly hydrogels that swell and collapse in water in response to environmental changes. However, amphiphilic functionality is desired to enhance the adsorption abilities of these hydrogels while maintaining their stimuli responsivity. Microfluidic techniques are used to synthesize Janus microgels with two opposing stimuli responsive hemispheres. The particles have a temperature responsive domain connected to a pH responsive network where each side changes its hydrophilicity in response to a change in temperature or pH, respectively. The Janus microgels are amphiphilic in acidic conditions at 19 °C and alkaline conditions at 40 °C, while the opposite conditions cause a reduction of the amphiphilicity. By stabilizing emulsions with these dual responsive microgels, "smart" droplets that respond to environmental cues are formed. Emulsion droplets remain stable with smaller diameters when aqueous solution conditions favor amphiphilic particles yet, coalesce to larger droplets upon changing pH or temperature. These responsive Janus microgels represent the advancing technology of responsive droplets and demonstrate the applicability of microgels as emulsion stabilizers.

Microgels in biomaterials and nanomedicines

Microgels are colloidal particles with crosslinked polymer networks and dimensions ranging from tens of nanometers to micrometers. Specifically, smart microgels are fascinating capable of responding to biological signals in vivo or remote triggers and making the possible for applications in biomaterials and biomedicines. Therefore, how to fundamentally design microgels is an urgent problem to be solved. In this review, we put forward our important fundamental opinions on how to devise the intelligent microgels for cancer therapy, biosensing and biological lubrication. We focus on the design ideas instead of specific implementation process by employing reverse synthesis analysis to programme the microgels at the original stage. Moreover, special insights will be, for the first time, as far as we know, dedicated to the particles completely composed of DNA or proteins into microgel systems. These are discussed in detail in this review. We expect to give readers a broad overview of the design criteria and practical methodologies of microgels according to the application fields, as well as to propel the further developments of highly interesting concepts and materials.

Cellular Uptake of Plain and SPION-Modified Microbubbles for Potential Use in Molecular Imaging

Introduction

Both diagnostic ultrasound (US) and magnetic resonance imaging (MRI) accuracy can be improved by using contrast enhancement. For US gas-filled microbubbles (MBs) or silica nanoparticles (SiNPs), and for MRI superparamagnetic or paramagnetic agents, contribute to this. However, interactions of MBs with the vascular wall and cells are not fully known for all contrast media.

Methods

We studied the in vitro interactions between three types of non-targeted air-filled MBs with a polyvinyl-alcohol shell and murine macrophages or endothelial cells. The three MB types were plain MBs and two types that were labelled (internally and externally) with superparamagnetic iron oxide nanoparticles (SPIONs) for US/MRI bimodality. Cells were incubated with MBs and imaged by microscopy to evaluate uptake and adhesion. Interactions were quantified and the MB internalization was confirmed by fluorescence quenching of non-internalized MBs.

Results

Macrophages internalized each MB type within different time frames: plain MBs 6 h, externally labelled MBs 25 min and internally labelled MBs 2 h. An average of 0.14 externally labelled MBs per cell were internalized after 30 min and 1.34 after 2 h; which was 113% more MBs than the number of internalized internally labelled MBs. The macrophages engulfed these three differently modified new MBs at various rate, whereas endothelial cells did not engulf MBs.

Conclusions

Polyvinyl-alcohol MBs are not taken up by endothelial cells. The MB uptake by macrophages is promoted by SPION labelling, in particular external such, which may be important for macrophage targeting.

Polysaccharide-based nanoparticles for theranostic nanomedicine

Polysaccharides are natural biological molecules that have numerous advantages for theranostics, the integrated approach of therapeutics and diagnostics. Their derivable reactive groups can be leveraged for functionalization with a nanoparticle-enabling conjugate, therapeutics (small molecules, proteins, peptides, photosensitizers) and/or diagnostic agents (imaging agents, sensors). In addition, polysaccharides are diverse in size and charge, biodegradable and abundant and show low toxicity in vivo. Polysaccharide-based nanoparticles are increasingly being used as platforms for simultaneous drug delivery and imaging and are therefore becoming popular theranostic nanoparticles. The review focuses on the method of nanoparticle formation (self-assembled, physical or chemical cross-linked) when engineering polysaccharide-based nanoparticles for theranostic nanomedicine. We highlight recent examples of polysaccharide-based theranostic systems from literature and their potential for use in the clinic, particularly chitosan- and hyaluronic acid-based NPs.

Hyaluronic acid for anticancer drug and nucleic acid delivery

Hyaluronic acid (HA) is widely used in anticancer drug delivery, since it is biocompatible, biodegradable, non-toxic, and non-immunogenic; moreover, HA receptors are overexpressed on many tumor cells. Exploiting this ligand-receptor interaction, the use of HA is now a rapidly-growing platform for targeting CD44-overexpressing cells, to improve anticancer therapies. The rationale underlying approaches, chemical strategies, and recent advances in the use of HA to design drug carriers for delivering anticancer agents, are reviewed. Comprehensive descriptions are given of HA-based drug conjugates, particulate carriers (micelles, liposomes, nanoparticles, microparticles), inorganic nanostructures, and hydrogels, with particular emphasis on reports of preclinical/clinical results.

Temperature-Tunable Nanoparticles for Selective Biointerface

Drugs can be delivered by a temperature change-driven shrinking of the nanocarrier followed by the cargo release. This paper describes a different structural response to temperature, performed by nanoparticles of poly(N-isopropylacrylamide) and hyaluronic acid. Around 35 °C, the hydrophobicity of the vinyl polymer drives a core-shell rearrangement with the acrylamide chains confined in the core and the polysaccharide moiety forming the shell. In this arrangement, the nanoparticles enable the active targeting of tumor cells, due to the specific interaction of hyaluronic acid with the CD44 receptors. When doxorubicin-loaded nanoparticles are up-taken, the polysaccharide part degrades in the cytoplasm and the cytotoxic effect of the anticancer drug in colon adenocarcinoma cells has a 2-fold increase with respect to healthy fibroblasts. These core-shell particles have hyaluronic acid as the key factor for the specific targeting of tumor cells and drug release with poly(N-isopropylacrylamide) driving the transition.

Using click chemistry to dial up the modulus of doubly crosslinked microgels through precise control of microgel building block functionalisation

Vinyl functionalisation of poly(2-vinylpyridine-propargylacrylate) microgels via click chemistry gives hydrogels of inter-linked microgels with tuneable modulus values.

Click hydrogels, microgels and nanogels: emerging platforms for drug delivery and tissue engineering

Hydrogels, microgels and nanogels have emerged as versatile and viable platforms for sustained protein release, targeted drug delivery, and tissue engineering due to excellent biocompatibility, a microporous structure with tunable porosity and pore size, and dimensions spanning from human organs, cells to viruses. In the past decade, remarkable advances in hydrogels, microgels and nanogels have been achieved with click chemistry. It is a most promising strategy to prepare gels with varying dimensions owing to its high reactivity, superb selectivity, and mild reaction conditions. In particular, the recent development of copper-free click chemistry such as strain-promoted azide-alkyne cycloaddition, radical mediated thiol-ene chemistry, Diels-Alder reaction, tetrazole-alkene photo-click chemistry, and oxime reaction renders it possible to form hydrogels, microgels and nanogels without the use of potentially toxic catalysts or immunogenic enzymes that are commonly required. Notably, unlike other chemical approaches, click chemistry owing to its unique bioorthogonal feature does not interfere with encapsulated bioactives such as living cells, proteins and drugs and furthermore allows versatile preparation of micropatterned biomimetic hydrogels, functional microgels and nanogels. In this review, recent exciting developments in click hydrogels, microgels and nanogels, as well as their biomedical applications such as controlled protein and drug release, tissue engineering, and regenerative medicine are presented and discussed.