Translating Therapeutic Microgels into Clinical Applications

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.

Controlled release of therapeutic antibody using hydrolytically degradable microgels

Monoclonal antibodies have gained significant interest as potential therapeutics for treating various diseases. However, these therapies are not always effective due to poor treatment compliance associated with multiple administrations and drug resistance. Thus, there is a growing interest in developing advanced monoclonal antibody delivery systems that can customize pharmacokinetics to enhance therapeutic outcomes. This work aimed to engineer hydrolytic 4-arm PEG maleimide (PEG-4MAL) microgels for the controlled delivery of therapeutic antibodies, specifically anti-angiogenic bevacizumab, to overcome the limitations of current monoclonal antibody therapies. Through a PEGylation reaction with a thiol-terminated PEG linker, the antibody was covalently conjugated to the macromer backbone before microgel synthesis. The PEGylation reaction was simple, effective, and did not affect antibody bioactivity. Antibody release kinetics was tuned by changing the concentration of the hydrolytic linker (0-2 mM) and/or PEG-4MAL:protein molar ratio (1000:1, 2000:1, and 5000:1) in the macromer precursor solution during microgel fabrication. The bioactivity of the released antibody was assessed on human umbilical endothelial vascular cells (HUVEC), demonstrating that extracts from hydrolytic microgels reduced cell proliferation over time. Collectively, this study demonstrates the development of highly tunable delivery platform based on degradable PEG-4MAL microgels that can be adapted for therapeutic antibody-controlled release.

A multifunctional injectable, self-healing, and adhesive hydrogel-based wound dressing stimulated diabetic wound healing with combined reactive oxygen species scavenging, hyperglycemia reducing, and bacteria-killing abilities

The proficient handling of diabetic wounds, a rising issue coinciding with the global escalation of diabetes cases, poses significant clinical difficulties. A range of biofunctional dressings have been engineered and produced to expedite the healing process of diabetic wounds. This study proposes a multifunctional hydrogel dressing for diabetic wound healing, which is composed of Polyvinyl Alcohol (PVA) and N1-(4-boronobenzyl)-N3-(4-boronophenyl)-N1, N1, N3, N3-teramethylpropane-1, 3-diaminium (TSPBA), and a dual-drug loaded Gelatin methacryloyl (GM) microgel. The GM microgel is loaded with sodium fusidate (SF) and nanoliposomes (LP) that contain metformin hydrochloride (MH). Notably, adhesive and self-healing properties the hydrogel enhance their therapeutic potential and ease of application. In vitro assessments indicate that SF-infused hydrogel can eliminate more than 98% of bacteria within 24 h and maintain a sustained release over 15 days. Additionally, MH incorporated within the hydrogel has demonstrated effective glucose level regulation for a duration exceeding 15 days. The hydrogel demonstrates a sustained ability to neutralize ROS throughout the entire healing process, predominantly by electron donation and sequestration. This multifunctional hydrogel dressing, which integrated biological functions of efficient bactericidal activity against both MSSA and MRSA strains, blood glucose modulation, and control of active oxygen levels, has successfully promoted the healing of diabetic wounds in rats in 14 days. The hydrogel dressing exhibited significant effectiveness in facilitating the healing process of diabetic wounds, highlighting its considerable promise for clinical translation.

Mechanoactivation of Single Stem Cells in Microgels Using a 3D-Printed Stimulation Device

In this study, the novel 3D-printed pressure chamber for encapsulated single-cell stimulation (3D-PRESS) platform is introduced for the mechanical stimulation of single stem cells in 3D microgels. The custom-designed 3D-PRESS, allows precise pressure application up to 400 kPa at the single-cell level. Microfluidics is employed to encapsulate single mesenchymal stem cells within ionically cross-linked alginate microgels with cell adhesion RGD peptides. Rigorous testing affirms the leak-proof performance of the 3D-PRESS device up to 400 kPa, which is fully biocompatible. 3D-PRESS is implemented on mesenchymal stem cells for mechanotransduction studies, by specifically targeting intracellular calcium signaling and the nuclear translocation of a mechanically sensitive transcription factor. Applying 200 kPa pressure on individually encapsulated stem cells reveals heightened calcium signaling in 3D microgels compared to conventional 2D culture. Similarly, Yes-associated protein (YAP) translocation into the nucleus occurs at 200 kPa in 3D microgels with cell-binding RGD peptides unveiling the involvement of integrin-mediated mechanotransduction in singly encapsulated stem cells in 3D microgels. Combining live-cell imaging with precise mechanical control, the 3D-PRESS platform emerges as a versatile tool for exploring cellular responses to pressure stimuli, applicable to various cell types, providing novel insights into single-cell mechanobiology.

A review on Ag nanoparticles fabricated in microgels

In recent years, there has been growing interest in the composites of multi-responsive microgels and silver nanoparticles. This innovative hybrid system harnesses the responsive qualities of microgels while capitalizing on the optical and electronic attributes of silver nanoparticles. This combined system demonstrates a rapid response to minor changes in pH, temperature, ionic strength of the medium, and the concentration of specific biological substances. This review article presents an overview of the recent advancements in the synthesis, classification, characterization methods, and properties of microgels loaded with silver nanoparticles. Furthermore, it explores the diverse applications of these responsive microgels containing silver nanoparticles in catalysis, the biomedical field, nanotechnology, and the mitigation of harmful environmental pollutants.

Porous Hydrogels for Immunomodulatory Applications

Cancer immunotherapy relies on the insight that the immune system can be used to defend against malignant cells. The aim of cancer immunotherapy is to utilize, modulate, activate, and train the immune system to amplify antitumor T-cell immunity. In parallel, the immune system response to damaged tissue is also crucial in determining the success or failure of an implant. Due to their extracellular matrix mimetics and tunable chemical or physical performance, hydrogels are promising platforms for building immunomodulatory microenvironments for realizing cancer therapy and tissue regeneration. However, submicron or nanosized pore structures within hydrogels are not favorable for modulating immune cell function, such as cell invasion, migration, and immunophenotype. In contrast, hydrogels with a porous structure not only allow for nutrient transportation and metabolite discharge but also offer more space for realizing cell function. In this review, the design strategies and influencing factors of porous hydrogels for cancer therapy and tissue regeneration are first discussed. Second, the immunomodulatory effects and therapeutic outcomes of different porous hydrogels for cancer immunotherapy and tissue regeneration are highlighted. Beyond that, this review highlights the effects of pore size on immune function and potential signal transduction. Finally, the remaining challenges and perspectives of immunomodulatory porous hydrogels are discussed.

Dual growth factor methacrylic alginate microgels combined with chitosan-based conduits facilitate peripheral nerve repair

Treating severe peripheral nerve injuries is difficult. Nerve repair with conduit small gap tubulization is a treatment option but still needs to be improved. This study aimed to assess the use of microgels containing growth factors, along with chitosan-based conduits, for repairing nerves. Using the water-oil emulsion technique, microgels of methacrylic alginate (AlgMA) that contained vascular endothelial growth factor (VEGF) and brain-derived neurotrophic factor (BDNF) were prepared. The effects on rat Schwann cells (RSC96) and human umbilical vein endothelial cells (HUVECs) were evaluated. Chitosan-based conduits were fabricated and used in conjunction with microgels containing two growth factors to treat complete neurotmesis in rats. The results showed that the utilization of dual growth factor microgels improved the migration and decreased the apoptosis of RSC96 cells while promoting the growth and formation of tubes in HUVECs. The utilization of dual growth factor microgels and chitosan-based conduits resulted in notable advancements in the regeneration and myelination of nerve fibers, recovery of neurons, alleviation of muscle atrophy and recovery of neuromotor function and nerve conduction. In conclusion, the use of dual growth factor AlgMA microgels in combination with chitosan-based conduits has the potential to significantly improve the effectiveness of nerve repair.

Local Water Content in Polymer Gels Measured with Super-Resolved Fluorescence Lifetime Imaging

Water molecules play an important role in the structure, function, and dynamics of (bio-) materials. A direct access to the number of water molecules in nanoscopic volumes can thus give new molecular insights into materials and allow for fine-tuning their properties in sophisticated applications. The determination of the local water content has become possible by the finding that H2 O quenches the fluorescence of red-emitting dyes. Since deuterated water, D2 O, does not induce significant fluorescence quenching, fluorescence lifetime measurements performed in different H2 O/D2 O-ratios yield the local water concentration. We combined this effect with the recently developed fluorescence lifetime single molecule localization microscopy imaging (FL-SMLM) in order to nanoscopically determine the local water content in microgels, i.e. soft hydrogel particles consisting of a cross-linked polymer swollen in water. The change in water content of thermo-responsive microgels when changing from their swollen state at room temperature to a collapsed state at elevated temperature could be analyzed. A clear decrease in water content was found that was, to our surprise, rather uniform throughout the entire microgel volume. Only a slightly higher water content around the dye was found in the periphery with respect to the center of the swollen microgels.

Multiresponsive Core-Shell Microgels Functionalized by Nitrilotriacetic Acid

Stimuli-responsive microgels with ionizable functional groups offer versatile applications, e.g., by the uptake of oppositely charged metal ions or guest molecules such as drugs, dyes, or proteins. Furthermore, the incorporation of carboxylic groups enhances mucoadhesive properties, crucial for various drug delivery applications. In this work, we successfully synthesized poly{N-vinylcaprolactam-2,2'-[(5-acrylamido-1-carboxypentyl)azanediyl]diacetic acid} [p(VCL/NTAaa)] microgels containing varying amounts of nitrilotriacetic acid (NTA) using precipitation polymerization. We performed fundamental characterization by infrared (IR) spectroscopy and dynamic and electrophoretic light scattering. Despite their potential multiresponsiveness, prior studies on NTA-functionalized microgels lack in-depth analysis of their stimuli-responsive behavior. This work addresses this gap by assessing the microgel responsiveness to temperature, ionic strength, and pH. Morphological investigations were performed via NMR relaxometry, nanoscale imaging (AFM and SEM), and reaction calorimetry. Finally, we explored the potential application of the microgels by conducting cytocompatibility experiments and demonstrating the immobilization of the model protein cytochrome c in the microgels.

Polysaccharides and proteins-based bionanocomposites for microencapsulation of probiotics to improve stability and viability in the gastrointestinal tract: A review

Probiotics have recently received significant attention due to their various benefits, such as the modulation of gut flora, reduction of blood sugar and insulin resistance, prevention and treatment of digestive disorders, and strengthening of the immune system. One of the major issues concerning probiotics is the maintenance of their viability in the presence of digestive conditions and extended shelf life during storage. To address this concern, numerous techniques have been explored to achieve success. Among these methods, the microencapsulation of probiotics has been proposed as the most effective way to overcome this challenge. The combination of nanomaterials with biopolymer coating is considered a novel approach to improve its viability and effective delivery. The use of polysaccharides and proteins-based bionanocomposites for microencapsulation of probiotics has emerged as an efficient and promising approach for maintaining cell viability and targeted delivery. This review article aims to investigate the use of different bionanocomposites in microencapsulation of probiotics and their effect on cell survival in long-term storage and harsh conditions in the gastrointestinal tract.

1H-NMR studies on the volume phase transition of DNA-modified pNipmam microgels

DNA functionalized pNipmam microgels, which have recently been introduced, are examined at different concentrations of sodium chloride and in PBS solutions via temperature dependent 1H-NMR measurements and are compared to pure pNipmam microgels. We show that the DNA modification shifts the volume phase transition temperature towards lower temperatures and the addition of salt and PBS further supports this effect in both materials. Thermodynamic values, i.e. enthalpy, entropy and Gibbs free energy, are determined via a non-linear fit which can be applied directly to the measurement data without further linearization.

Biomimetic cell culture for cell adhesive propagation for tissue engineering strategies

Biomimetic cell culture, which involves creating a biomimetic microenvironment for cells in vitro by engineering approaches, has aroused increasing interest given that it maintains the normal cellular phenotype, genotype and functions displayed in vivo. Therefore, it can provide a more precise platform for disease modelling, drug development and regenerative medicine than the conventional plate cell culture. In this review, initially, we discuss the principle of biomimetic cell culture in terms of the spatial microenvironment, chemical microenvironment, and physical microenvironment. Then, the main strategies of biomimetic cell culture and their state-of-the-art progress are summarized. To create a biomimetic microenvironment for cells, a variety of strategies has been developed, ranging from conventional scaffold strategies, such as macroscopic scaffolds, microcarriers, and microgels, to emerging scaffold-free strategies, such as spheroids, organoids, and assembloids, to simulate the native cellular microenvironment. Recently, 3D bioprinting and microfluidic chip technology have been applied as integrative platforms to obtain more complex biomimetic structures. Finally, the challenges in this area are discussed and future directions are discussed to shed some light on the community.

Leveraging Microgels Prepared from Poly(ethylene glycol) Bisepoxide and Polyetheramine for Versatile Surface Structuring of Agarose Hydrogels

We demonstrate a macromer-type bisepoxide, poly(ethylene glycol) diglycidyl ether, polymerizing readily with a trifunctional polyetheramine Jeffamine T-403 in water to facilitate the development of a series of microgels abbreviated as PMG. Simply by varying the concentration of the as-prepared thermoresponsive intermediate prepolymer from 1 to 2 and 4%, hydrodynamic sizes of the resulting P1MG, P2MG, and P4MG are easily tuned in the submicrometer to micrometer range shown by the dynamic light scattering results. Besides size difference, these microgels also deform differently, where the drying-induced deformation effect is most severe for P1MG and least prominent for P4MG. Simple evaporative deposition of PMG into multilayer packing provides versatile and green options for microgel-mediated surface structuring of agarose hydrogels. Specifically, deformabile P1MG- and P2MG-derived coatings render agarose gel microwrinkle textures by buckling against swelling-induced surface instability. Conversely, stiffer P4MG microgels lead to a patchy patterned hierarchical coating on agarose, similar to the cracking effect in drying colloidal films. The straightforward microgel-on-macrogel strategy allows integration of both wrinkle and patchy patterns to generate Janus-type agarose gels, just by rationally arranging the coating sequence. Diversifying topographic features attainable through microgel-based coatings on hydrogels could potentially make the sustainable and biocompatible material of agarose a more compelling choice for bioapplications. Brief demonstrations of the broad applicability of P1MG toward wrinkling of proteinaceous and synthetic hydrogels further highlight promising prospects of the PMG microgel-on-macrogel functionalization strategy.

Compartmentalized Polyampholyte Microgels by Depletion Flocculation and Coacervation of Nanogels in Emulsion Droplets

In pH-responsive drug carriers, the distribution of charges has been proven to affect delivery efficiency but is difficult to control and verify. Herein, we fabricate polyampholyte nanogel-in-microgel colloids (NiM-C) and show that the arrangement of the nanogels (NG) can easily be manipulated by adapting synthesis conditions. Positively and negatively charged pH-responsive NG are synthesized by precipitation polymerization and labelled with different fluorescent dyes. The obtained NG are integrated into microgel (MG) networks by subsequent inverse emulsion polymerization in droplet-based microfluidics. By confocal laser scanning microscopy (CLSM), we verify that depending on NG concentration, pH value and ionic strength, NiM-C with different NG arrangements are obtained, including Janus-like phase-separation of NG, statistical distribution of NG, and core-shell arrangements. Our approach is a major step towards uptake and release of oppositely charged (drug) molecules.

The design and straightforward synthesis of multifunctional DNA microgels for the improved targeted delivery of antitumor drugs

Multifunctional drug delivery platforms represent ideal approaches to reliably targeting pharmacological agents of interest to the complex tumor microenvironment (TME), yet the complicated synthesis processes, high costs, and toxicities associated with these agents have hindered their clinical application to date. In this study, the properties of the TME are leveraged to develop a multifunctional pNAB/AS DNA microgel that is able to actively target tumors. This microgel is generated by a straightforward one-step free radical precipitation polymerization procedure, exhibiting extremely high drug encapsulation efficiency (∼90%), and is responsive to three environmental stimuli including temperature, reduction, and an acidic pH while showing minimal drug leakage under physiological conditions. Through a synergistic combination of appropriate size and aptamer recognition, this microgel is able to reliably facilitate intratumoral drug accumulation and nuclear drug delivery. Critically, pNAB/AS-Dox treatment is associated with specific antitumor activity in vitro and in vivo while retaining a good biosafety profile and causing lower levels of off-target toxicity as compared to free drug treatment. Together, these findings emphasize the potential value of this multifunctional pNAB/AS DNA microgel as a platform amenable to targeted drug delivery to the TME, providing a foundation for further efforts to readily develop multifunctional drug delivery systems.

Smart Targeted Delivery Systems for Enhancing Antitumor Therapy of Active Ingredients in Traditional Chinese Medicine

As a therapeutic tool inherited for thousands of years, traditional Chinese medicine (TCM) exhibits superiority in tumor therapy. The antitumor active components of TCM not only have multi-target treatment modes but can also synergistically interfere with tumor growth compared to traditional chemotherapeutics. However, most antitumor active components of TCM have the characteristics of poor solubility, high toxicity, and side effects, which are often limited in clinical application. In recent years, delivering the antitumor active components of TCM by nanosystems has been a promising field. The advantages of nano-delivery systems include improved water solubility, targeting efficiency, enhanced stability in vivo, and controlled release drugs, which can achieve higher drug-delivery efficiency and bioavailability. According to the method of drug loading on nanocarriers, nano-delivery systems can be categorized into two types, including physically encapsulated nanoplatforms and chemically coupled drug-delivery platforms. In this review, two nano-delivery approaches are considered, namely physical encapsulation and chemical coupling, both commonly used to deliver antitumor active components of TCM, and we summarized the advantages and limitations of different types of nano-delivery systems. Meanwhile, the clinical applications and potential toxicity of nano-delivery systems and the future development and challenges of these nano-delivery systems are also discussed, aiming to lay the foundation for the development and practical application of nano-delivery systems of TCM in clinical settings.

Microgels as Platforms for Antibody-Mediated Cytokine Scavenging

Therapeutic antibodies are the key treatment option for various cytokine-mediated diseases, such as rheumatoid arthritis, psoriasis, and inflammatory bowel disease. However, systemic injection of these antibodies can cause side effects and suppress the immune system. Moreover, clearance of therapeutic antibodies from the blood is limiting their efficacy. Here, water-swollen microgels are produced with a size of 25 µm using droplet-based microfluidics. The microgels are functionalized with TNFα antibodies to locally scavenge the pro-inflammatory cytokine TNFα. Homogeneous distribution of TNFα-antibodies is shown throughout the microgel network and demonstrates specific antibody-antigen binding using confocal microscopy and FLIM-FRET measurements. Due to the large internal accessibility of the microgel network, its capacity to bind TNFα is extremely high. At a TNFα concentration of 2.5 µg mL-1 , the microgels are able to scavenge 88% of the cytokine. Cell culture experiments reveal the therapeutic potential of these microgels by protecting HT29 colorectal adenocarcinoma cells from TNFα toxicity and resulting in a significant reduction of COX II and IL8 production of the cells. When the microgels are incubated with stimulated human macrophages, to mimic the in vivo situation of inflammatory bowel disease, the microgels scavenge almost all TNFα that is produced by the cells.

Multimodal Biomedical Implant with Plasmonic and Simulated Body Temperature Responses

This work presents a novel nanoparticle-based thermosensor implant able to reveal the precise temperature variations along the polymer filaments, as it contracts and expands due to changes in the macroscale local temperature. The multimodal device is able to trace the position and the temperature of a polypropylene mesh, employed in abdominal hernia repair, by combining plasmon resonance and Raman spectroscopy with hydrogel responsive system. The novelty relies on the attachment of the biocompatible nanoparticles, based on gold stabilized by a chitosan-shell, already charged with the Raman reporter (RaR) molecules, to the robust prosthesis, without the need of chemical linkers. The SERS enhanced effect observed is potentiated by the presence of a quite thick layer of the copolymer (poly(N-isopropylacrylamide)-co-poly(acrylamide)) hydrogel. At temperatures above the LCST of PNIPAAm-co-PAAm, the water molecules are expulsed and the hydrogel layer contracts, leaving the RaR molecules more accessible to the Raman source. In vitro studies with fibroblast cells reveal that the functionalized surgical mesh is biocompatible and no toxic substances are leached in the medium. The mesh sensor opens new frontiers to semi-invasive diagnosis and infection prevention in hernia repair by using SERS spectroscopy. It also offers new possibilities to the functionalization of other healthcare products.

Bone/cartilage targeted hydrogel: Strategies and applications

The skeletal system is responsible for weight-bearing, organ protection, and movement. Bone diseases caused by trauma, infection, and aging can seriously affect a patient's quality of life. Bone targeted biomaterials are suitable for the treatment of bone diseases. Biomaterials with bone-targeted properties can improve drug utilization and reduce side effects. A large number of bone-targeted micro-nano materials have been developed. However, only a few studies addressed bone-targeted hydrogel. The large size of hydrogel makes it difficult to achieve systematic targeting. However, local targeted hydrogel still has significant prospects. Molecules in bone/cartilage extracellular matrix and bone cells provide binding sites for bone-targeted hydrogel. Drug delivery systems featuring microgels with targeting properties is a key construction strategy for bone-targeted hydrogel. Besides, injectable hydrogel drug depot carrying bone-targeted drugs is another strategy. In this review, we summarize the bone-targeted hydrogel through application environment, construction strategies and disease applications. We hope this article will provide a reference for the development of bone-targeted hydrogels. We also hope this article could increase awareness of bone-targeted materials.

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Introducing the microenvironment and target molecules in different parts of long bones.

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Summarizing the construction strategy of micro/nanoparticle hydrogel with bone targeting properties.

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Summarizing the construction strategy of hydrogel based depot carrying bone-targeted drugs.

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Reporting the application and effect of bone targeting hydrogel in common bone diseases.

Enzymatically Crosslinked Collagen as a Versatile Matrix for In Vitro and In Vivo Co-Engineering of Blood and Lymphatic Vasculature

Adequate vascularization is required for the successful translation of many in vitro engineered tissues. This study presents a novel collagen derivative that harbors multiple recognition peptides for orthogonal enzymatic crosslinking based on sortase A (SrtA) and Factor XIII (FXIII). SrtA-mediated crosslinking enables the rapid co-engineering of human blood and lymphatic microcapillaries and mesoscale capillaries in bulk hydrogels. Whereas tuning of gel stiffness determines the extent of neovascularization, the relative number of blood and lymphatic capillaries recapitulates the ratio of blood and lymphatic endothelial cells originally seeded into the hydrogel. Bioengineered capillaries readily form luminal structures and exhibit typical maturation markers both in vitro and in vivo. The secondary crosslinking enzyme Factor XIII is used for in situ tethering of the VEGF mimetic QK peptide to collagen. This approach supports the formation of blood and lymphatic capillaries in the absence of exogenous VEGF. Orthogonal enzymatic crosslinking is further used to bioengineer hydrogels with spatially defined polymer compositions with pro- and anti-angiogenic properties. Finally, macroporous scaffolds based on secondary crosslinking of microgels enable vascularization independent from supporting fibroblasts. Overall, this work demonstrates for the first time the co-engineering of mature micro- and meso-sized blood and lymphatic capillaries using a highly versatile collagen derivative.

Hyaluronic acid-based multifunctional carriers for applications in regenerative medicine: A review

Hyaluronic acid (HA) is an important type of naturally derived carbohydrate polymer with specific polysaccharide macromolecular structures and multifaceted biological functions, including biocompatibility, low immunogenicity, biodegradability, and bioactivity. Specifically, HA hydrogels in a microscopic scale have been widely used for biomedical applications, such as drug delivery, tissue engineering, and medical cosmetology, considering their superior properties outperforming the more conventional monolithic hydrogels in network homogeneity, degradation profile, permeability, and injectability. Herein, we reviewed the recent progress in the preparation and applications of HA microgels in biomedical fields. We first summarized the fabrication of HA microgels by focusing on the different crosslinking/polymerization schemes for HA gelation and the miniaturized fabrication techniques for producing HA-based microparticles. We then highlighted the use of HA-based microgels for different applications in regenerative medicine, including cartilage repair, bioactive delivery, diagnostic imaging, modular tissue engineering. Finally, we discussed the challenges and future perspectives in bridging the translational gap in the utilization of HA-based microgels in regenerative medicine.

Microfluidic Manipulation for Biomedical Applications in the Central and Peripheral Nervous Systems

Physical injuries and neurodegenerative diseases often lead to irreversible damage to the organizational structure of the central nervous system (CNS) and peripheral nervous system (PNS), culminating in physiological malfunctions. Investigating these complex and diverse biological processes at the macro and micro levels will help to identify the cellular and molecular mechanisms associated with nerve degeneration and regeneration, thereby providing new options for the development of new therapeutic strategies for the functional recovery of the nervous system. Due to their distinct advantages, modern microfluidic platforms have significant potential for high-throughput cell and organoid cultures in vitro, the synthesis of a variety of tissue engineering scaffolds and drug carriers, and observing the delivery of drugs at the desired speed to the desired location in real time. In this review, we first introduce the types of nerve damage and the repair mechanisms of the CNS and PNS; then, we summarize the development of microfluidic platforms and their application in drug carriers. We also describe a variety of damage models, tissue engineering scaffolds, and drug carriers for nerve injury repair based on the application of microfluidic platforms. Finally, we discuss remaining challenges and future perspectives with regard to the promotion of nerve injury repair based on engineered microfluidic platform technology.

Hydrogels as promising platforms for engineered living bacteria-mediated therapeutic systems

The idea of using engineered bacteria as prospective living therapeutic agents for the treatment of different diseases has been raised. Nevertheless, the development of safe and effective treatment strategies remains essential to the success of living bacteria-mediated therapy. Hydrogels have presented great promise for the delivery of living bacterial therapeutics due to their tunable physicochemical properties, good bioactivities, and excellent protection of labile payloads. In this review, we summarize the hydrogel design strategies for living bacteria-mediated therapy and review the recent advances in hydrogel-based living bacterial agent delivery for the treatment of typical diseases, including those for digestive health, skin fungal infections, wound healing, vaccines, and cancer, and discuss the current challenges and future perspectives of these strategies in the field. It is believed that the importance of hydrogel-based living bacteria-mediated therapy is expected to further increase with the development of both synthetic biology and biomaterials science in the future.

Specific Binding of Ligand-Functionalized Thermoresponsive Microgels: Effect of Architecture, Ligand Density, and Hydrophobicity

The biomolecular interaction of ligand-presenting switchable microgels is studied with respect to the polymer type, composition, and structure of the microgels. Monodisperse microgels are prepared through precipitation polymerization of N-isopropylacrylamide (PNIPAM microgels) or oligo(ethylene glycol methacrylamide)s (POEGMA microgels) in the presence of crosslinkers or in their absence (self-crosslinked). Functionalization with mannose or biotin as model ligands and affinity measurements upon heating/cooling are conducted to obtain mechanistic insights into how the microgel phase transition affects the specific interactions. In particular, we are interested in adjusting the crosslinking, swelling degree, and ligand density of mannose-functionalized microgels to reversibly catch and release mannose binding Escherichia coli by setting the temperature below or above the microgels' volume phase transition temperature (VPTT). The increased mannose density for collapsed microgels above the VPTT results in stronger E. coli binding. Detachment of E. coli by reswelling the microgels below the VPTT is achieved only for self-crosslinked microgels showing a stronger decrease in ligand density compared to microgels with dedicated crosslinkers. Owing to a reduced mannose density in the shell of POEGMA microgels, their E. coli binding was lower compared to PNIPAM microgels, as supported by ultraresolution microscopy. Importantly, an inverse temperature-controlled binding of microgels decorated with hydrophilic mannose and hydrophobic biotin ligands is observed. This indicates that hydrophobic ligands are inaccessible in the collapsed hydrophobic network above the VPTT, whereas hydrophilic mannose units are then enriched at the microgel-water interface and thus are more accessible.