Microgels and microcapsules in peptide and protein drug delivery

Fabrication of uniform biodegradable microcages with predesigned shape printed from microarrays for sustained release of small hydrophilic molecules

Drug delivery vehicles have aroused increasing attention over the years due to their ability to protect and control the release of encapsulated cargo. However, several challenges significantly limit their wide applications including poor size distribution, uncontrollable size and shape, and leakage of loaded small hydrophilic cargos. This work introduces a novel and scalable microarray-based printing technique for preparing uniform biodegradable "microcages" with predesigned shapes for encapsulating and controlling the release of small hydrophilic molecules. The drugs encapsulated in the microcage are centrally located within solid microparticles without being exposed to the surface or dispersed throughout the polymer matrix. Here, 5(6)-carboxyfluorescein (CF) as a small and hydrophilic model drug are successfully loaded into polylactide acid (PLA) microcages with the dry loading method. Additionally, blending polycaprolactone (PCL) with PLA increases the permeability of the microcage polymer shells for controlled release. A higher PCL content results in a faster release rate of the encapsulated drug. Approximately 28 pg of CF particles can be encapsulated within individual microcages. This microcage printing technique provides a novel, scalable method for producing uniform biodegradable microcages, extending microprinting beyond microfilms and microparticles. A unique dry loading approach, independent of drug solubility, further broadens its utility for diverse biomedical applications.

NAC-Grafted ROS-Scavenging Polymer Nanoparticles for Modulation of Acute Lung Injury Microenvironment In Vivo

N-Acetyl cysteine (NAC) is an essential molecule that boosts acute lung injury (ALI) defense via its direct antioxidant capability. Nevertheless, the therapeutic use of NAC is limited due to its poor bioavailability and short half-life. In this study, NAC was grafted to the polyurethane consisting of poly(propylene fumarate), poly(thioketal), and 1,6-hexamethylene diisocyanate (PFTU) to reduce excessive oxidative stress and inflammatory factors in ALI. The NAC-grafted polymer nanoparticles (NPT@NPs) were prepared as a drug delivery system, which could effectively scavenge free radicals and reduce inflammation in vitro. The administration of NPT@NPs exhibited notable efficacy in ameliorating pulmonary edema, attenuating the presence of inflammatory cells, suppressing myeloperoxidase expression, diminishing the levels of pro-inflammatory cytokines, and reversing cell apoptosis in an ALI model induced by lipopolysaccharide (LPS). The NPT@NPs demonstrated significantly better efficacy compared to the free NAC in mitigating the deleterious effects of LPS on pulmonary tissue, thereby providing more effective protection against pulmonary inflammation.

Engineering poly(dehydroalanine)-based gels via droplet-based microfluidics: from bulk to microspheres

Biomedical applications such as drug delivery, tissue engineering, and functional surface coating rely on switchable adsorption and desorption of specialized guest molecules. Poly(dehydroalanine), a polyzwitterion containing pH-dependent positive and negative charges, shows promise for such reversible loading, especially when integrated into a gel network. Herein, we present the fabrication of poly(dehydroalanine)-derived gels of different size scales and evaluate them with respect to their practical use in biomedicine. Already existing protocols for bulk gelation were remodeled to derive suitable reaction conditions for droplet-based microfluidic synthesis. Depending on the layout of the microfluidic chip, microgels with a size of approximately 30 μm or 200 μm were obtained, whose crosslinking density can be increased by implementing a multi-arm crosslinker. We analyzed the effects of the crosslinker species on composition, permeability, and softness and show that the microgels exhibit advantageous properties inherent to zwitterionic polymer systems, including high hydrophilicity as well as pH- and ionic strength-sensitivity. We demonstrate pH-regulated uptake and release of fluorescent model dyes before testing the adsorption of a small antimicrobial peptide, LL-37. Quantification of the peptide accommodated within the microgels reveals the impact of size and crosslinking density of the microgels. Biocompatibility of the microgels was validated by cell tests.

Nanogels with Metal-Organic Cages as Functional Crosslinks

A dinuclear metal-organic cage with four acrylate side chains was prepared by self-assembly. Precipitation polymerization of the cage with N-isopropylacrylamide yielded a thermoresponsive nanogel. The host properties of the cage were retained within the gel matrix, endowing the nanogel with the capability to serve as a sorbent for chloride ions in water. Moreover, a heteroleptic cage with the drug abiraterone as co-ligand was integrated into a nanogel. The addition of chloride ions induced a structural rearrangement of the metal-ligand assembly, resulting in the gradual release of abiraterone.

Designing Tough Hydrogel Shells for Glucose Sensing

Conventional hydrogel microcapsules often suffer from inadequate mechanical stability, hindering their use. Here, water-cored double-network (DN) hydrogel shells are designed, formed by polyacrylamide and calcium alginate networks using triple-emulsion templates. These DN hydrogel shells offer robust mechanical stability, optical transparency, and a precisely-defined cut-off threshold. The feasibility of this platform is demonstrated through the development of a fluorometric glucose sensor. Glucose oxidase is enclosed within the water core, while a pH-responsive fluorescent dye is incorporated into the DN shells. Glucose diffuses into the core through the DN shells, where the glucose oxidase converts glucose into gluconic acid, leading to pH reduction and a subsequent decrease in fluorescence intensity of DN shells. Additionally, the pH-sensitive colorant dissolved in the medium enables visual pH assessment. Thus, glucose levels can be determined using both fluorometric and colorimetric methods. Notably, the DN shells exhibit exceptional stability, enduring intense mechanical stress and cycles of drying and rehydration without leakage. Moreover, the DN shells act as effective barriers, safeguarding glucose oxidase against proteolysis by large disruptive proteins, like pancreatin. This versatile DN shell platform extends beyond glucose oxidase encapsulation, serving as a foundation for various capsule sensors utilizing enzymes and heterogeneous catalysts.

Nanogel delivery systems for cationic peptides: More than a 'One Size Fits All' solution

Self-assembled hyaluronic acid-based nanogels are versatile drug carriers due to their biodegradable nature and gentle preparation conditions, making them particularly interesting for delivery of peptide therapeutics. This study aims to elucidate the relation between peptide structure and encapsulation in a nanogel. Key peptide properties that affect encapsulation in octenyl succinic anhydride-modified hyaluronic acid nanogels were identified as we explored the effect on nanogel characteristics using 12 peptides with varying charge and hydrophobicity. The size and surface properties of the microfluidics-assembled peptide-loaded nanogels were evaluated using dynamic light scattering, laser Doppler electrophoresis, and small angle neutron scattering. Additionally, the change in peptide secondary structure upon encapsulation in nanogels, their release from the nanogels, and the in vitro antimicrobial activity were assessed. In conclusion, the more hydrophobic peptides showed stronger binding to the nanogel carrier and localized internally rather than on the surface of the nanogel, resulting in more spherical nanogels with smoother surfaces and slower release profiles. In contrast, cationic and hydrophilic peptides localized at the nanogel surface resulting in fluffier nanogel structures and quick and more complete release in biorelevant medium. These findings emphasize that the advantages of nanogel delivery systems for different applications depend on the therapeutic peptide properties.

Oral peptide therapeutics for diabetes treatment: State-of-the-art and future perspectives

Diabetes, characterized by hyperglycemia, is a major cause of death and disability worldwide. Peptides, such as insulin and glucagon-like peptide-1 (GLP-1) analogs, have shown promise as treatments for diabetes due to their ability to mimic or enhance insulin's actions in the body. Compared to subcutaneous injection, oral administration of anti-diabetic peptides is a preferred approach. However, biological barriers significantly reduce the efficacy of oral peptide therapeutics. Recent advancements in drug delivery systems and formulation techniques have greatly improved the oral delivery of peptide therapeutics and their efficacy in treating diabetes. This review will highlight (1) the benefits of oral anti-diabetic peptide therapeutics; (2) the biological barriers for oral peptide delivery, including pH and enzyme degradation, intestinal mucosa barrier, and biodistribution barrier; (3) the delivery platforms to overcome these biological barriers. Additionally, the review will discuss the prospects in this field. The information provided in this review will serve as a valuable guide for future developments in oral anti-diabetic peptide therapeutics.

Injectable liposome-containing click hydrogel microparticles for release of macromolecular cargos

Hydrogel microparticles ranging from 0.1-100 μm, referred to as microgels, are attractive for biological applications afforded by their injectability and modularity, which allows facile delivery of mixed populations for tailored combinations of therapeutics. Significant efforts have been made to broaden methods for microgel production including via the materials and chemistries by which they are made. Via droplet-based-microfluidics we have established a method for producing click poly-(ethylene)-glycol (PEG)-based microgels with or without chemically crosslinked liposomes (lipo-microgels) through the Michael-type addition reaction between thiol and either vinyl-sulfone or maleimide groups. Unifom spherical microgels and lipo-microgels were generated with sizes of 74 ± 16 μm and 82 ± 25 μm, respectively, suggesting injectability that was further supported by rheological analyses. Super-resolution confocal microscopy was used to further verify the presence of liposomes within the lipo-microgels and determine their distribution. Atomic force microscopy (AFM) was conducted to compare the mechanical properties and network architecture of bulk hydrogels, microgels, and lipo-microgels. Further, encapsulation and release of model cargo (FITC-Dextran 5 kDa) and protein (equine myoglobin) showed sustained release for up to 3 weeks and retention of protein composition and secondary structure, indicating their ability to both protect and release cargos of interest.

Study of molecular interaction and texture characteristics of hydrocolloid-mixed alginate microspheres: As a shell to encapsulate multiphase oil cores

This work investigates the molecular interaction of hydrocolloids (xanthan gum (XG), hydroxyethyl cellulose (HEC), carbomer (CBM) and hymagic™-4D (HA)) with sodium alginate (SA) in microspheres in detail. The molecular interaction of hydrocolloids with SA are demonstrated by the rheological property analysis of the mixed solutions as well as the morphology structure and texture characteristics studies of the microspheres. It is found that the hydrocolloids (XG, HEC and CBM) with branches or capable to coil are able to form complex networks with SA through molecular interactions which hinders the free diffusion of calcium ions and changes the texture characteristics of microspheres. In addition, the mixed solutions (SA-XG and SA-HEC) with complex networks and do not have a chelating effect on calcium ions are used to form the shell of the microcapsules through droplet microfluidic technology, and stable with soft microcapsules encapsulating multiphase oil cores have been successfully prepared. At the same time, the textural properties of microcapsules are quantized, which are related to human sensory properties. The developed stable and soft microcapsules which have the properties of sensory comfort are expected to be applied in the personal care industry and a variety of fields.

Polyelectrolyte Brushes with Protein-Like Nanocolloids

Electrostatic interaction of ampholytic nanocolloidal particles (NPs), which mimic globular proteins, with polyelectrolyte brushes is analyzed within mean-field Poisson-Boltzmann approximation. In accordance with experimental findings, the theory predicts that an electrostatic driving force for the particle uptake by the brush may emerge when the net charge of the particle in the buffer and the charge of the brush are of the same sign. The origin of this driving force is change in the ionization state of weak cationic and anionic groups on the NP surface provoked by interaction with the brush. In experimental systems, the ionic interactions are complemented by excluded-volume, hydrophobic, and other types of interactions that all together control NP uptake by or expulsion from the brush. Here, we focus on the NP-brush ionic interactions. It is demonstrated that deviation between the buffer pH and the NP isoelectric point, considered usually as the key control parameter, does not uniquely determine the insertion free energy patterns. The latter depends also on the proportion of cationic and anionic groups in the NPs and their specific ionization constants as well as on salt concentration in the buffer. The analysis of the free energy landscape proves that a local minimum in the free energy inside the brush appears, provided the NP charge reversal occurs upon insertion into the brush. This minimum corresponds either to a thermodynamically stable or to a metastable state, depending on the pH offset from the IEP and salt concentration, and is separated from the bulk of the solution by a free energy barrier. The latter, being fairly independent of salt concentration in height, may strongly impede the NP absorption kinetically even when it is thermodynamically favorable. Hence, change reversal is a necessary but insufficient condition for the uptake of the NPs by similarly charged polyelectrolyte brushes.

Hydrogel Microparticles for Bone Regeneration

Hydrogel microparticles (HMPs) stand out as promising entities in the realm of bone tissue regeneration, primarily due to their versatile capabilities in delivering cells and bioactive molecules/drugs. Their significance is underscored by distinct attributes such as injectability, biodegradability, high porosity, and mechanical tunability. These characteristics play a pivotal role in fostering vasculature formation, facilitating mineral deposition, and contributing to the overall regeneration of bone tissue. Fabricated through diverse techniques (batch emulsion, microfluidics, lithography, and electrohydrodynamic spraying), HMPs exhibit multifunctionality, serving as vehicles for drug and cell delivery, providing structural scaffolding, and functioning as bioinks for advanced 3D-printing applications. Distinguishing themselves from other scaffolds like bulk hydrogels, cryogels, foams, meshes, and fibers, HMPs provide a higher surface-area-to-volume ratio, promoting improved interactions with the surrounding tissues and facilitating the efficient delivery of cells and bioactive molecules. Notably, their minimally invasive injectability and modular properties, offering various designs and configurations, contribute to their attractiveness for biomedical applications. This comprehensive review aims to delve into the progressive advancements in HMPs, specifically for bone regeneration. The exploration encompasses synthesis and functionalization techniques, providing an understanding of their diverse applications, as documented in the existing literature. The overarching goal is to shed light on the advantages and potential of HMPs within the field of engineering bone tissue.

Polyanhydride Microcapsules Exhibiting a Sharp pH Transition at Physiological Conditions for Instantaneous Triggered Release

Stimulus-responsive microcapsules pose an opportunity to achieve controlled release of the entire load instantaneously upon exposure to an external stimulus. Core-shell microcapsules based on the polyanhydride poly(bis(2-carboxyphenyl)adipate) as a shell were formulated in this work to encapsulate the model active substance pyrene and enable a pH-controlled triggered release. A remarkably narrow triggering pH interval was found where a change in pH from 6.4 to 6.9 allowed for release of the entire core content within seconds. The degradation kinetics of the shell were measured by both spectrophotometric detection of degradation products and mass changes by quartz crystal microbalance with dissipation monitoring and were found to correlate excellently with diffusion coefficients fitted to release measurements at varying pH values. The microcapsules presented in this work allow for an almost instantaneous triggered release even under mild conditions, thanks to the designed core-shell morphology.

Interaction of Polyanionic and Polycationic Brushes with Globular Proteins and Protein-like Nanocolloids

A large number of experimental studies have demonstrated that globular proteins can be absorbed from the solution by both polycationic and polyanionic brushes when the net charge of protein globules is of the same or of the opposite sign with respect to that of brush-forming polyelectrolyte chains. Here, we overview the results of experimental studies on interactions between globular proteins and polycationic or polyanionic brushes, and present a self-consistent field theoretical model that allows us to account for the asymmetry of interactions of protein-like nanocolloid particles comprising weak (pH-sensitive) cationic and anionic groups with a positively or negatively charged polyelectrolyte brush. The position-dependent insertion free energy and the net charge of the particle are calculated. The theoretical model predicts that if the numbers of cationic and anionic ionizable groups of the protein are approximately equal, then the interaction patterns for both cationic and anionic brushes at equal offset on the "wrong side" from the isoelectric point (IEP), i.e., when the particle and the brush charge are of the same sign, are similar. An essential asymmetry in interactions of particles with polycationic and polyanionic brushes is predicted when fractions of cationic and anionic groups differ significantly. That is, at a pH above IEP, the anionic brush better absorbs negatively charged particles with a larger fraction of ionizable cationic groups and vice versa.

Quantitative Elasticity Mapping of Submicron Silica Hollow Particles by PeakForce QNM AFM Mode

Silica hollow spheres with a diameter of 100-300 nm and a shell thickness of 8±2 nm were synthesized using a self-templating amphiphilic polymeric precursor, i.e., poly(ethylene glycol)-substituted hyperbranched polyethoxysiloxane. Their elastic properties were addressed with a high-frequency AFM indentation method based on the PeakForce QNM (quantitative nanomechanical mapping) mode enabling simultaneous visualization of the surface morphology and high-resolution mapping of the mechanical properties. The factors affecting the accuracy of the mechanical measurements such as a local slope of the particle surface, deformation of the silica hollow particles by a solid substrate, shell thickness variation, and applied force range were analysed. The Young's modulus of the shell material was evaluated as E=26±7 GPa independent of the applied force in the elastic regime of deformations. Beyond the elastic regime, the buckling instability was observed revealing a non-linear force-deformation response with a hysteresis between the loading and unloading force-distance curves and irreversible deformation of the shell at high applied forces. Thus, it was demonstrated that PeakForce QNM mode can be used for quantitative measurements of the elastic properties of submicon-sized silica hollow particles with nano-size shell thickness, as well as for estimation of the buckling behaviour beyond the elastic regime of shell deformations.

A novel all-organic microcapsule with excellent long-term antibacterial and anti-corrosion performances

This work successfully synthesized the salicylic acid@polyurea-formaldehyde (SA@PUF) microcapsules with PUF microcapsules as shell material and SA as core material. The loading content of SA in the PUF microcapsules was approximately 40 %. The SA@PUF microcapsules had excellent long-term antibacterial properties because the PUF microcapsules controlled the release of SA antifouling agents with the ability to induce reactive oxygen species generation and inactivate bacteria. The antibacterial efficiency of SA@PUF microcapsules after 35 days against Staphylococcus aureus and Pseudomonas aeruginosa remained at 80 % and 81 %, increased by 60 % and 62 % compared with pure SA, respectively. The impedance modulus at 0.01 Hz of the SA@PUF coating reached 5.51 GΩ cm², much higher than blank coating (2.55 GΩ cm²) and PUF coating (4.94 GΩ cm²), indicating that the anti-corrosion property of the SA@PUF coating was much better. This work would contribute to developing novel coatings with long-term antibacterial activity and excellent anti-corrosion performance.

Broad-temperature-range mechanically tunable hydrogel microcapsules for controlled active release

Here, we report PNIPAm-co-PEGDA hydrogel shelled microcapsules with a thin oil layer to achieve tunable thermo-responsive release of the encapsulated small hydrophilic actives. We use a microfluidic device integrated with a temperature-controlled chamber for consistent and reliable production of the microcapsules by utilizing triple emulsion drops (W/O/W/O) with a thin oil layer as capsule templates. The interstitial oil layer between the aqueous core and the PNIPAm-co-PEGDA shell provides a diffusion barrier for the encapsulated active until the temperature reaches a critical point above which the destabilization of interstitial oil layer occurs. We find that the destabilization of the oil layer with temperature increase is caused by outward expansion of the aqueous core due to volume increase and the radial inward compression from the deswelling of the thermo-responsive hydrogel shell. The copolymerization of NIPAm with PEGDA increases the biocompatibility of the resulting microcapsule while offering the ability to alter the compressive modulus in broad ranges by simply varying crosslinker concentrations thereby to precisely tune the onset release temperature. Based on this concept, we further demonstrate that the release temperature can be enhanced up to 62 °C by adjusting the shell thickness even without varying the chemical composition of the hydrogel shell. Moreover, we incorporate gold nanorods within the hydrogel shell to spatiotemporally regulate the active release from the microcapsules by illuminating with non-invasive near infrared (NIR) light.

Bovine Serum Albumin Interaction with Polyanionic and Polycationic Brushes: The Case Theoretical Study

We apply a coarse-grained self-consistent field Poisson-Boltzmann framework to study interaction between Bovine Serum Albumin (BSA) and a planar polyelectropyte brush. Both cases of negatively (polyanionic) and positively (polycationic) charged brushes are considered. Our theoretical model accounts for (1) re-ionization free energy of the amino acid residues upon protein insertion into the brush; (2) osmotic force repelling the protein globule from the brush; (3) hydrophobic interactions between non-polar areas on the globule surface and the brush-forming chains. We demonstrate that calculated position-dependent insertion free energy exhibits different patterns, corresponding to either thermodynamically favourable BSA absorption in the brush or thermodynamically or kinetically hindered absorption (expulsion) depending on the pH and ionic strength of the solution. The theory predicts that due to the re-ionization of BSA within the brush, a polyanionic brush can efficiently absorb BSA over a wider pH range on the "wrong side" of the isoelectric point (IEP) compared to a polycationic brush. The results of our theoretical analysis correlate with available experimental data and thus validate the developed model for prediction of the interaction patterns for various globular proteins with polyelectrolyte brushes.

Antimicrobial Peptides against Bacterial Pathogens: Innovative Delivery Nanosystems for Pharmaceutical Applications

The introduction of antibiotics has revolutionized the treatment and prevention of microbial infections. However, the global spread of pathogens resistant to available antibiotics is a major concern. Recently, the WHO has updated the priority list of multidrug-resistant (MDR) species for which the discovery of new therapeutics is urgently needed. In this scenario, antimicrobial peptides (AMPs) are a new potential alternative to conventional antibiotics, as they show a low risk of developing antimicrobial resistance, thus preventing MDR bacterial infections. However, there are limitations and challenges related to the clinical impact of AMPs, as well as great scientific efforts to find solutions aimed at improving their biological activity, in vivo stability, and bioavailability by reducing the eventual toxicity. To overcome some of these issues, different types of nanoparticles (NPs) have been developed for AMP delivery over the last decades. In this review, we provide an update on recent nanosystems applied to AMPs, with special attention on their potential pharmaceutical applications for the treatment of bacterial infections. Among lipid nanomaterials, solid lipid NPs and lipid nanocapsules have been employed to enhance AMP solubility and protect peptides from proteolytic degradation. In addition, polymeric NPs, particularly nanogels, are able to help in reducing AMP toxicity and also increasing AMP loading. To boost AMP activity instead, mesoporous silica or gold NPs can be selected due to their easy surface functionalization. They have been also used as nanocarriers for different AMP combinations, thus synergistically potentiating their action against pathogens.

Self-assembled polylactic acid (PLA): Synthesis, properties and biomedical applications

The surface morphology and topography of cell culture substrates play an important role in cell proliferation and growth. Regulation of the surface microstructure allows the development of tissue culture media suitable for different cells. Polylactic acid (PLA) is a biobased and biodegradable (under defined conditions) polymer with low immunogenicity, non-toxicity, and good mechanical properties, which have facilitated their pharmaceutical and biomedical applications. This review summarizes recent advances in the synthesis and self-assembly of surface microstructure based on PLA materials and discusses their biomedical applications such as cell culturing and tissue engineering.

Nanotechnology-based cell-mediated delivery systems for cancer therapy and diagnosis

The global prevalence of cancer is increasing, necessitating new additions to traditional treatments and diagnoses to address shortcomings such as ineffectiveness, complications, and high cost. In this context, nano and microparticulate carriers stand out due to their unique properties such as controlled release, higher bioavailability, and lower toxicity. Despite their popularity, they face several challenges including rapid liver uptake, low chemical stability in blood circulation, immunogenicity concerns, and acute adverse effects. Cell-mediated delivery systems are important topics to research because of their biocompatibility, biodegradability, prolonged delivery, high loading capacity, and targeted drug delivery capabilities. To date, a variety of cells including blood, immune, cancer, and stem cells, sperm, and bacteria have been combined with nanoparticles to develop efficient targeted cancer delivery or diagnosis systems. The review paper aimed to provide an overview of the potential applications of cell-based delivery systems in cancer therapy and diagnosis.

Polysaccharide-based hydrogels for drug delivery and wound management: a review

INTRODUCTION

Polysaccharide-based hydrogels (PBHs) offer several advantages over their synthetic counterparts. Their natural origin contributes to their nontoxicity, high biocompatibility, and in vivo biodegradability. Their properties can be tuned finely to obtain hydrogels with desired mechanical, structural, and chemical properties.

AREAS COVERED

Such versatile characteristics have potentiated the use of PBHs for the delivery of drugs, vaccines, protein and peptide therapeutics, genes, cells, probiotics, bacteriophages, and other therapeutic agents. Recent advances in hydrogel-based formulations such as nanogels, microgels, microneedles, hydrogel beads, nanocarrier-loaded hydrogels, and complexation hydrogels have enabled the precise delivery of a wide range of therapeutics. This review aims to give a holistic overview of hydrogels in the delivery of a variety of therapeutics through different routes.

EXPERT OPINION

PBHs have been used to enable the oral delivery of vaccines and other biologicals, thereby allowing self-administration of life-saving vaccines during public health emergencies. There is a lack of commercialized wound dressings for the treatment of chronic wounds. PBH-based wound dressings, especially those based on chitosan and loaded with actives and growth factors, have the potential to help in the long-term treatment of such wounds. Recent developments in the 3D printing of hydrogels can enable the quick and large-scale production of drug-loaded hydrogels.

Printed asymmetric microcapsules: Facile loading and multiple stimuli-responsiveness

Engineering of colloidal particles and capsules despite substantial progress is still facing a number of unsolved issues including low loading capacity, non-uniform size and shape of carriers, tailoring different functionalities and versatility to encapsulated cargo. In this work, we propose a method for defined-shaped functionally asymmetric polymer capsule fabrication based on a soft lithography approach. The developed capsules consist of two classes of polymers - the main part "cup" is made out of polyelectrolyte multilayers (PAH-PSS) and "lid" is made of biodegradable polyether (PLGA). Asymmetric capsules combine advantages from both traditional layer-by-layer capsules and recently developed printed "pelmeni" capsules. This combination provides stimuli-responsiveness due to polyelectrolyte multilayer properties differing from PLGA. The inner volume of capsules can be loaded with a variety of active compounds and the capsule's geometry is defined due to the soft-lithography method. Capsules have a core-shell structure and monodisperse size distribution. Three methods to trigger cargo release have been demonstrated, namely temperature treatment, ultrasonication and pH shift. Steroidal drug dexamethasone was used to illustrate the applicability of the systems for triggered drug release. The application of proposed asymmetric capsules includes but is not limited to pharmacology, diagnostics, sensors, micro- and nanoreactors and chemical actuators.

Microgels react to force: mechanical properties, syntheses, and force-activated functions

Microgels are colloidal polymer networks with high molar mass and properties between rigid particles, flexible macromolecules, and micellar aggregates. Their unique stimuli-responsiveness in conjunction with their colloidal phase behavior render them useful for many applications ranging from engineering to biomedicine. In many scenarios either the microgel's mechanical properties or its interactions with mechanical force play an important role. Here, we firstly explain microgel mechanical properties and how these are measured by atomic force microscopy (AFM), then we equip the reader with the synthetic background to understand how specific architectures and chemical functionalities enable these mechanical properties, and eventually we elucidate how the interaction of force with microgels can lead to the activation of latent functionality. Since the interaction of microgels with force is a multiscale and multidisciplinary subject, we introduce and interconnect the different research areas that contribute to the understanding of this emerging field in this Tutorial Review.

In-Line Characterization of the Temperature-Responsive Behavior of Surface-Bound Microgel Coatings by QCM-D: A Novel Strategy for Protein Repellence Evaluation

In this work, quartz crystal microbalance with dissipation monitoring (QCM-D) was used to develop a new method to evaluate the protein repellency of microgel coatings. Compared to traditional protocols for surface analysis, QCM has the advantage of a real-time quantitative approach with high sensitivity, allowing us to describe variations of the adsorbed mass with unprecedented accuracy. To enable the detectability of the film throughout the whole operational temperature interval, a poly(N-isopropylacrylamide-co-glycidyl methacrylate) p(NIPAm-co-GMA) microgel monolayer with defined thickness and rigidity was designed. Covalent adhesion of the film to the silica surface was achieved by epoxy-thiol click chemistry and tested for repeated temperature cycles, showing substantial reproducibility. Further functionalization of microgel surfaces by grafting polyzwitterionic chains remarkably improved the protein repellence leaving the strong surface adhesion unaltered. Before and after exposure to fluorescein-tagged bovine serum albumin (FITC-BSA), the coatings showed identical responsive behavior, proving the absence of protein deposition. In nonrepellent coatings, QCM monitoring instead displayed a characteristic shift in the volume phase transition (VPT), pointing out the effect of adsorbed proteins on the swelling behavior of pNIPAm. The combination of QCM-D and UV-visible (UV-vis) was used to evaluate the effect of increasing surface coverage, enabling to distinguish between the protein deposition occurring over the coated and the uncoated portion of the sensor.

Microencapsulation of functional ovalbumin and bovine serum albumin with polylysine-alginate complex for sustained protein vehicle's development

Overcoming harsh gastric environment is still a challenging to bioactive proteins, microencapsulation provides one strategy in designing this protection barrier. In this work, bovine serum albumin and ovalbumin were chosen as model proteins, while polylysine-alginate complex was fabricated for microencapsulation purpose. Both of the protein-loaded microcapsules had regular internal microstructures. The model protein's embedding increased the thermal stability of the microcapsules. Both of the protein-loaded microcapsules had a slow release rate in simulated gastric fluids (pH 3.0), while a sustained release profile in simulated intestinal fluids (pH 6.4), indicating an excellent tolerance to the acidic gastric environment. The microencapsulation process was mild and had no influence on the protein's molecular weight, while a slight peak shifting occurred in the secondary structure of the released proteins. The developed microcapsules could be explored as a kind of vehicle for bioactive proteins applied in functional foods, health care products and medical formulations.

Elastic modulus distribution in poly(N-isopopylacrylamide) and oligo(ethylene glycol methacrylate)-based microgels studied by AFM

The spatial elastic modulus distribution of microgel networks in presence and absence of bifunctional crosslinkers is studied by AFM. Thermoresponsive poly(N-isopopylacrylamide) (PNIPAM) and poly(2-(2-methoxyethoxy)ethyl methacrylate-co-oligo(ethylene glycol)methacrylate) (P(MEO2MA-co-OEGMA)) microgels are synthesized via precipitation polymerization above their lower critical solution temperature (LCST). High-resolution elastic modulus profiles are acquired using AFM force-indentation mapping of surface-deposited microgels at 25 °C. For both microgel systems, the use of a bifunctional crosslinker leads to a strong elastic modulus gradient with stiff microgel cores and soft networks toward the edge. In absence of a dedicated crosslinker (self-crosslinking), PNIPAM microgels show a homogeneous elastic modulus distribution, whereas self-crosslinked P(MEO2MA-co-OEGMA) microgels still show decreasing elastic moduli from the centre to the edge of the microgels. However, POEGMA microgels without comonomer showed no elastic modulus gradient suggesting that different incorporation rates of MEO2MA and OEGMA result in a radial variation of the polymer segment density. In addition, when varying the molecular weight of OEGMA the overall elastic modulus was affected, possibly due to molecular weight-dependent phase behavior and different reactivity. This shows that quite different microgel architectures can be obtained by the simple "one-pot" precipitation reaction of microgels which may open to new avenues toward advanced applications.

Recent Advances in Design of Functional Biocompatible Hydrogels for Bone Tissue Engineering

Bone related diseases have caused serious threats to human health owing to their complexity and specificity. Fortunately, owing to the unique 3D network structure with high aqueous content and functional properties, emerging hydrogels are regarded as one of the most promising candidates for bone tissue engineering, such as repairing cartilage injury, skull defect, and arthritis. Herein, various design strategies and synthesis methods (e.g., 3D‐printing technology and nanoparticle composite strategy) are introduced to prepare implanted hydrogel scaffolds with tunable mechanical strength, favorable biocompatibility, and excellent bioactivity for applying in bone regeneration. Injectable hydrogels based on biocompatible materials (e.g., collagen, hyaluronic acid, chitosan, polyethylene glycol, etc.) possess many advantages in minimally invasive surgery, including adjustable physicochemical properties, filling irregular shapes of defect sites, and on‐demand release drugs or growth factors in response to different stimuli (e.g., pH, temperature, redox, enzyme, light, magnetic, etc.). In addition, drug delivery systems based on micro/nanogels are discussed, and its numerous promising designs used in the application of bone diseases (e.g., rheumatoid arthritis, osteoarthritis, cartilage defect) are also briefed in this review. Particularly, several key factors of hydrogel scaffolds (e.g., mechanical property, pore size, and release behavior of active factors) that can induce bone tissue regeneration are also summarized in this review. It is anticipated that advanced approaches and innovative ideas of bioactive hydrogels will be exploited in the clinical field and increase the life quality of patients with the bone injury.

Proteins and Polyampholytes Interacting with Polyelectrolyte Brushes and Microgels: The Charge Reversal Concept Revised

Weak polyampholytes and globular proteins among them can be efficiently absorbed from solutions by polyelectrolyte brushes or microgels even if the net charge of the polyampholyte is of the same sign as that of the brush/microgel. We use a mean-field approach for calculating the free energy of insertion of a probe polyampholyte molecule into a polyelectrolyte brush/microgel. We anticipate that the insertion of the polyampholyte into similarly charged brush/microgel may be thermodynamically favorable due to the gain in the cumulative re-ionization free energy of the pH-sensitive acidic and basic residues. Importantly, we demonstrate that the polyampholyte (protein) charge sign inversion upon transfer from the bulk of the solution to the brush/microgel does not provide sufficient conditions to assure negative re-ionization free energy balance. Thus (in the absence of other driving or stopping mechanisms), charge sign inversion does not necessarily provoke spontaneous absorption of the polyampholyte into the brush/microgel.

Progress of Nanotechnology in Diabetic Retinopathy Treatment

Diabetic retinopathy (DR) is a chronic diabetes complication that progressively manifests itself as blurred vision, eye floaters, distorted vision, and even partial or total loss of vision as a result of retinal detachment in severe cases. Clinically, patients who have undergone variations in the microcirculation of the ocular fundus are treated with laser photocoagulation to improve the circulation of retina; but for patients with macular edema, anti-vascular endothelial growth factor (anti-VEGF) drugs are generally injected to eliminate macular edema and improve vision. The worst cases are patients with fundus hemorrhage or proliferative vitreoretinopathy, for whom vitrectomy has been performed. At present, these clinical treatment methods have widely been used, providing satisfactory results. However, considering the low bioavailability and potential side effects of drugs and the inevitable risks in major surgery, DR prevention, and treatment as well as nerve tissue regeneration in the later stage have always been the focus of research. In recent years, nanotechnology has been increasingly applied in the medical field, leading to new ideas for DR treatment. This study aims to systematically review the research progress of nanotechnology in DR treatment.

Peptide-Modified Biopolymers for Biomedical Applications

Polymeric biomaterials have been used in a variety of applications, like cargo delivery and tissue scaffolding, because they are easily synthesized and can be adapted to many systems. However, there is still a need to further enhance and improve their functions to progress their use in the biomedical field. A promising solution is to modify the polymer surfaces with peptides that can increase biocompatibility, cellular interactions, and receptor targeting. In recent years, peptide modifications have been used to overcome many challenges to polymer biomaterial development. This review discusses recent progress in developing peptide-modified polymers for therapeutic applications including cell-specific targeting and tissue engineering. Furthermore, we will explore some of the most frequently studied base components of these biomaterials.

Electrically controllable cargo delivery with dextran-rich droplets

The controllable delivery of cargo is of great importance in many areas, ranging from medicine and materials science to food and cosmetic industries. To fulfil the requirements in different areas, the development of new methods for cargo delivery in a controllable manner is always essential. A novel technique of cargo delivery controlled by electric pulse was developed in this paper. In an aqueous two-phase system, the dextran-rich droplets were fabricated as droplet carriers in a continuous polyethylene glycol-rich phase. The loading and releasing of model cargos (polystyrene particles) across the surface of the droplet carriers under electric pulses were demonstrated in microfluidic chips. By controlling the amplitude of the applied electric pulses, the cargos with designed sizes were sorted and loaded into the droplet carriers; hence, the targeted delivery of cargos by size can be achieved. The exchange of cargos between droplet carriers under reversed electric pulses was also investigated, and the results indicated the flexibility of this method in cargo delivery. Moreover, possible application of this method to biological cargos was demonstrated by controlling the loading and releasing of yeast cells under electric pulses. With the advantages of easy operation and fast response, this approach provides a novel route for controllable cargo delivery with droplets.

Camacho-Cruz L, Bucio E, Kadlubowski SS. An Updated Review of Macro, Micro, and Nanostructured Hydrogels for Biomedical and Pharmaceutical Applications

Hydrogels are materials with wide applications in several fields, including the biomedical and pharmaceutical industries. Their properties such as the capacity of absorbing great amounts of aqueous solutions without losing shape and mechanical properties, as well as loading drugs of different nature, including hydrophobic ones and biomolecules, give an idea of their versatility and promising demand. As they have been explored in a great number of studies for years, many routes of synthesis have been developed, especially for chemical/permanent hydrogels. In the same way, stimuli-responsive hydrogels, also known as intelligent materials, have been explored too, enhancing the regulation of properties such as targeting and drug release. By controlling the particle size, hydrogel on the micro- and nanoscale have been studied likewise and have increased, even more, the possibilities for applications of the so-called XXI century materials. In this paper, we aimed to produce an overview of the recent studies concerning methods of synthesis, biomedical, and pharmaceutical applications of macro-, micro, and nanogels.

Precise regulation of particle size of poly(N-isopropylacrylamide) microgels: Measuring chain dimensions with a "molecular ruler"

HYPOTHESIS

Poly(N-isopropylacrylamide) microgels are used extensively in the design of drug carriers, surfaces for control of cell adhesion, and optical devices. Particle size is a key factor and has a significant influence in many areas.

EXPERIMENTS

In this work, precise control of the particle size of poly(N-isopropylacrylamide) microgels was achieved by controlling the separation distance of the poly(N-isopropylacrylamide) chains. Dibromoalkanes of different size were used as an adjustable "molecular ruler" to measure molecular dimensions in poly(N-isopropylacrylamide) nanoaggregates at the critical crosslinking temperature.

FINDINGS

We find that the chain separation distance decreases as the temperature increases with a sharp decrease over the 55-to-65 °C interval. Based on the observed relationships between chain separation and crosslinker, the particle size of poly(N-isopropylacrylamide) microgels can be regulated by changing the length of the "molecular ruler" (crosslinker) at the same temperature. Furthermore, for partly crosslinked poly(N-isopropylacrylamide) microgels that contain free crosslinkable sites, the particle size can be reduced still more by further crosslinking ("re-crosslinking") with crosslinkers of different size. It is shown that the particle size can be regulated by adjusting the length of "molecular ruler" and the degree of crosslinking. This work provides a "molecular level" method for precise control of poly(N-isopropylacrylamide) microgel particle size.

Microgels and hydrogels as delivery systems for antimicrobial peptides

Due to rapid development of bacterial resistance against antibiotics, an emerging health crisis is underway, where 'simple' infections may no longer be treatable. Antimicrobial peptides (AMPs) constitute a class of substances attracting interest in this context. So far, research on AMPs has primarily focused on the identification of potent and selective peptides, as well as on the action mode of such peptides. More recently, there has been an increasing awareness that the delivery of AMPs is challenging due to their size, net positive charge, amphiphilicity, and proteolytic susceptibility. Hence, successful development of AMP therapeutics will likely require also careful design of efficient AMP delivery systems. In the present brief review, we discuss microgels, as well as related polyelectrolyte complexes and macroscopic hydrogels, as delivery systems for AMPs. In doing so, key factors for peptide loading and release are outlined and exemplified, together with consequences of this for functional performance relating to antimicrobial effects and cell toxicity.

Developing hyaluronic acid microgels for sustained delivery of platelet lysate for tissue engineering applications

Platelet lysate (PL), a blood product that contains high concentrations of growth factors (GFs), can be considered as a cost-effective source of multiple GFs. In this study, hyaluronic acid (HA) based microgels were developed for delivery of PL proteins. Spherical microgel were prepared using a water in oil emulsion method. First, hyaluronic acid was grafted with tyramine groups, after which prepared microdroplets were crosslinked via an enzymatic reaction in the presence of hydrogen peroxide and horseradish peroxidase. Because of electrostatic interactions, these microgels are promising carriers for positively charged proteins entrapment like most of the GFs. When microgels are incubated in PL solution, protein loading takes place which is mainly governed by nonspecific adsorption of plasma proteins. Although this hampered loading efficiency, loading could be increased by repeated washing and incubation steps. The loaded microgels presented a sustained release of PL growth factors for a period of two weeks. When PL enriched microgels were embedded in a HA bulk hydrogel, cell proliferation was higher compared to constructs without microgels. These findings suggest that the developed microgels are a potential candidate for sustained delivery of PL growth factors and present a solution to the issue of their short half-lives in vivo.

Biological Influence of Nonswelling Microgels on Cartilage Induction of Mouse Adipose-Derived Stem Cells

In cartilage tissue engineering, the target cells' functional performance depends on the biomaterials. However, it is difficult to develop an appropriate scaffold to differentiate mouse adipose-derived stem cells (mADSCs) into chondrocyte despite an increasing number of studies on biological scaffold materials. The purpose of this study was to create a novel scaffold for mADSC culture and chondrogenic differentiation with a new series of microgels based on polyethyleneimine (PEI), polyethylene glycol (PEG), and poly (L-lactic acid) (PLLA) and able to resist swelling with changes in temperature, pH, and polymer concentration. The biocompatibility and ability of the nonswelling microgels were then examined and served as scaffolds for cell culture and for cartilage differentiation. The results show that the new microgels are a novel biomaterial that both retains its nonswelling properties under various conditions and facilitates important scaffold functions such as cell adhesion, proliferation, and cartilage induction.

Bioactive nanoparticle embedded microcapsules for improving the efficacy of type I diabetes therapy

In order to overcome the side effects of pancreatic transplantation and insulin injection treatment for type I diabetes, we established a drug delivery system employing nanoparticle embedded microcapsules (NEMs). The system co-encapsulated chitosan nanoparticles with γ-aminobutyric acid and β-TC-6 cells for combined drug and cell therapy in diabetes mellitus (DM). The NEMs, which were formed via high-voltage electrostatic method, had an excellent sphericity with a smooth surface. The average size NEM was 245.52 ± 22.00 μm, which indicated a good size for cell encapsulation. Haemolysis rate of NEMs at concentrations of 100, 200 or 300 mg/mL were all below 5%. Relative viability rates of L929 cells with the same concentrations at 24, 48 or 72 h were all above 80%. We implanted bioactive NEMs into type 1 DM mice to evaluate the effect of the combined therapy. The level of blood glucose in the group receiving the combined therapy decreased during the first 2 weeks of treatment. During the next week, the level of blood glucose stayed in a safe range. Body weight continuously increased during the postoperative period after combined therapy group. Oral glucose tolerance test (OGTT) performed after 24 d showed that the level of blood glucose combined therapy reached the maximum peak of 13.04 mmol/L, lower than 16.56 mmol/L for the cell therapy group. This primary study indicated that microencapsulation technology and combined therapy are promising for the treatment of type I diabetes mellitus.

Complexation between antimicrobial peptides and polyelectrolytes

As a result of increasing bacterial resistance against antibiotics, we are facing an emerging health crisis, in which 'simple' infections may no longer be treatable. One class of molecules attracting interest in this context is antimicrobial peptides (AMPs), and considerable research efforts have been directed to identifying selective and potent AMPs. In addition, since in vivo delivery of AMPs is challenging, there is an emerging awareness that successful development of AMP therapeutics can be facilitated by careful design of AMPs delivery systems. In the present overview, we discuss polyelectrolyte complexation as a strategy to deliver AMPs. In doing so, key factors for AMP-polyelectrolyte complexation are illustrated for AMP-polyelectrolyte nanoparticle formation, as well as for AMP incorporation in polyelectrolyte microgels and multilayer structures, and consequences of these for functional performance exemplified.

Core-Shell-Shell Nanoparticles for NIR Fluorescence Imaging and NRET Swelling Reporting of Injectable or Implantable Gels

Injectable gels that support load are desirable for restoring the mechanical properties of degenerated load-bearing tissue. As these gels become increasingly sophisticated, the need to remotely image them and monitor their swelling increases. However, imaging such gels and monitoring their swelling using noninvasive means is challenging. Here, we use a very low concentration of near-infrared (NIR) core-shell-shell (CSS) reporter nanoparticles to both image and monitor swelling changes of two load-supporting gels. The load-supporting injectable gel consisted of covalently interlinked pH-responsive microgel (MG) particles. The latter gel was not cytotoxic and is termed a doubly cross-linked microgel (DX MG). Inclusion of a complementary fluorescent dye enabled ratiometric monitoring of gel swelling changes in response to pH via nonradiative resonance energy transfer (NRET). In addition, changes in the CSS nanoparticle emission intensity provided a NIR-only method that could also be used to monitor gel swelling. The gel was able to be imaged using NIR light, after being subcutaneously injected into a tissue model. To demonstrate versatility of our approach, CSS and the dye were included within a model implantable gel (poly(acrylamide/acrylic acid)) and fluorescent detection of swelling investigated. Because the concentrations of the reporting species were too low to affect the mechanical properties, our approach to remote gel imaging and swelling monitoring has good potential for application in injectable gels and implants.

Enhanced Nanoassembly-Incorporated Antibacterial Composite Materials

The rapid advancement of peptide- and amino-acid-based nanotechnology offers new approaches for the development of biomedical materials. The utilization of fluorenylmethyloxycarbonyl (Fmoc)-decorated self-assembling building blocks for antibacterial and anti-inflammatory purposes represents promising advancements in this field. Here, we present the antibacterial capabilities of the nanoassemblies formed by Fmoc-pentafluoro-l-phenylalanine-OH, their substantial effect on bacterial morphology, as well as new methods developed for the functional incorporation of these nanoassemblies within resin-based composites. These amalgamated materials inhibit and hinder bacterial growth and viability and are not cytotoxic toward mammalian cell lines. Importantly, due to the low dosage required to confer antibacterial activity, the integration of the nanoassemblies does not affect their mechanical and optical properties. This approach expands on the growing number of accounts on the intrinsic antibacterial capabilities of self-assembling building blocks and serves as a basis for further design and development of enhanced composite materials for biomedical applications.

Interaction of Proteins with Polyelectrolytes: Comparison of Theory to Experiment

We discuss recent investigations of the interaction of polyelectrolytes with proteins. In particular, we review our recent studies on the interaction of simple proteins such as human serum albumin (HSA) and lysozyme with linear polyelectrolytes, charged dendrimers, charged networks, and polyelectrolyte brushes. In all cases discussed here, we combined experimental work with molecular dynamics (MD) simulations and mean-field theories. In particular, isothermal titration calorimetry (ITC) has been employed to obtain the respective binding constants K_b and the Gibbs free energy of binding. MD simulations with explicit counterions but implicit water demonstrate that counterion release is the main driving force for the binding of proteins to strongly charged polyelectrolytes: patches of positive charges located on the surface of the protein become multivalent counterions of the polyelectrolyte, thereby releasing a number of counterions condensed on the polyelectrolyte. The binding Gibbs free energy due to counterion release is predicted to scale with the logarithm of the salt concentration in the system, which is verified by both simulations and experiment. In several cases, namely, for the interaction of proteins with linear polyelectrolytes and highly charged hydrophilic dendrimers, the binding constant could be calculated from simulations to very good approximation. This finding demonstrated that in these cases explicit hydration effects do not contribute to the Gibbs free energy of binding. The Gibbs free energy can also be used to predict the kinetics of protein uptake by microgels for a given system by applying dynamic density functional theory. The entire discussion demonstrates that the direct comparison of theory with experiments can lead to a full understanding of the interaction of proteins with charged polymers. Possible implications for applications, such as drug design, are discussed.

Interactions of NIPAM nanogels with model lipid multi-bilayers: A neutron reflectivity study

In dermal drug delivery, the influence of the chemical structure of the carriers on their penetration mechanisms is not yet fully understood. This is a key requirement in order to design highly efficient delivery systems. In this study, neutron reflectivity is used to provide insights into the interactions between thermoresponsive N-isopropylacrylamide based nanogels, cross-linked with 10%, 20% and 30% N,N'-methylenebisacrylamide, and skin lipid multi-bilayers models. Ceramide lipid multi-bilayers and ceramide/cholesterol/behenic acid mixed lipid multi-bilayers were used for this work. The results indicated that in both multi-bilayers the lipids were depleted by the nanogels mainly through hydrophobic interactions. The ability of nanogels to associate with skin lipids to form water-dispersible complexes was found to be a function of the percentage cross-linker. An enhanced depletion of lipids was further observed in the presence of benzyl alcohol, a well-known skin penetration enhancer.