Microfluidic Preparation of Gelatin Methacryloyl Microgels as Local Drug Delivery Vehicles for Hearing Loss Therapy

Droplet-based microfluidics for drug delivery applications

The microfluidic method primainly utilizes two incompatible liquids as continuous phase and dispersed phase respectively. It controls the formation of droplets by managing the microchannel structure and the flow rate ratio of the two phases. Droplet-based microfluidics is a rapidly expanding interdisciplinary research field encompassing physics, biochemistry, and Microsystems engineering. Droplet microfluidics offer a diverse and practical toolset that enables chemical and biological experiments to be conducted at high speeds and with greater efficiency compared to traditional instruments. The applications of droplet-based microfluidics are vast, including areas such as drug delivery, owing to its compatibility with numerous chemical and biological reagents and its ability to carry out various operations. This technology has been extensively researched due to its promising features. In this review, we delve into the materials used in droplet generation-based microfluidic devices, manufacturing techniques, methods for droplet generation in channels, and, finally, we summarize the applications of droplet generation-based microfluidics in drug delivery vectors, encompassing nanoparticles, microspheres, microcapsules, and hydrogel particles. We also discuss the challenges and future prospects of this technology across a wide array of applications.

Microfluidic-Assisted Pneumatic Droplet Generators Designed for Multiscenario Biomanufacturing with Favorable Biocompatibility and Extendibility

Droplets, tiny liquid compartments, are increasingly emerging in the biomedical and biomanufacturing fields due to their unique properties to serve as templates or independent reaction units. Currently, the straightforward and efficient generation of various functional droplets in a biofriendly manner remains challenging. Herein, a novel microfluidic-assisted pneumatic strategy is described for the customizable and high-throughput production of monodispersed droplets, and the droplet size can be precisely controlled via a simplified gas pressure regulation module. In particular, numerous uniform alginate microcarriers can be rapidly fabricated in an all-aqueous manner, wherein the encapsulated islet or liver cells exhibit favorable viability and biological functions. Furthermore, by changing the microchannel configuration, several fluid manipulation functions developed by microfluidic technology, such as mixing and laminar flow, can be successfully incorporated into this platform. The droplet generators with scalable functionality are demonstrated in many biomanufacturing scenarios, including on-demand distribution of cell-mimetic particles, continuous synthesis of biomedical metal-organic framework (MOF), controllable preparation of compartmental microgel, etc. These may provide sustainable inspiration for developing droplet generators and their applications in tissue and organ engineering, biomaterials design, bioprinting nozzles, and other fields.

Intratympanic injections of emulsion-like dispersions to augment cinnarizine amount in a healthy rabbit inner ear model

Aim: To investigate eutectic liquid-based emulsion-like dispersions for intratympanic injections to augment cinnarizine permeability across round window membrane in a healthy rabbit inner ear model.Methods: Two-tier systematic optimization was used to get the injection formula. The drug concentrations in perilymph and plasma were analyzed via. Ultra-performance liquid chromatography-tandem mass spectrometry method after 30-, 60-, 90- and 120-min post intratympanic injection time points in rabbits.Results: A shear-thinning behavior, immediate drug release (∼98.80%, 10 min) and higher cell viability (>97.86%, 24 h) were observed in dispersions. The cinnarizine level of 8168.57 ± 1236.79 ng/ml was observed in perilymph at 30 min post intratympanic injection in rabbits.Conclusion: The emulsion-like dispersions can augment drug permeability through round window membrane.

Micro/nanoengineered agricultural by-products for biomedical and environmental applications

Agriculturally derived by-products generated during the growth cycles of living organisms as secondary products have attracted increasing interest due to their wide range of biomedical and environmental applications. These by-products are considered promising candidates because of their unique characteristics including chemical stability, profound biocompatibility and offering a green approach by producing the least impact on the environment. Recently, micro/nanoengineering based techniques play a significant role in upgrading their utility, by controlling their structural integrity and promoting their functions at a micro and nano scale. Specifically, they can be used for biomedical applications such as tissue regeneration, drug delivery, disease diagnosis, as well as environmental applications such as filtration, bioenergy production, and the detection of environmental pollutants. This review highlights the diverse role of micro/nano-engineering techniques when applied on agricultural by-products with intriguing properties and upscaling their wide range of applications across the biomedical and environmental fields. Finally, we outline the future prospects and remarkable potential that these agricultural by-products hold in establishing a new era in the realms of biomedical science and environmental research.

Chondroitin sulfate-modified tragacanth gum-gelatin composite nanocapsules loaded with curcumin nanocrystals for the treatment of arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease of yet undetermined etiology that is accompanied by significant oxidative stress, inflammatory responses,  and damage to joint tissues. In this study, we designed chondroitin sulfate (CS)-modified tragacanth gum-gelatin composite nanocapsules (CS-Cur-TGNCs) loaded with curcumin nanocrystals (Cur-NCs), which rely on the ability of CS to target CD44 to accumulate drugs in inflamed joints. Cur was encapsulated in the form of nanocrystals into tragacanth gum-gelatin composite nanocapsules (TGNCs) by using an inborn microcrystallization method, which produced CS-Cur-TGNCs with a particle size of approximately 80 ± 11.54 nm and a drug loading capacity of 54.18 ± 5.17%. In an in vitro drug release assay, CS-Cur-TGNCs showed MMP-2-responsive properties. During the treatment of RA, CS-Cur-TGNCs significantly inhibited oxidative stress, promoted the polarization of M2-type macrophages to M1-type macrophages, and decreased the expression of inflammatory factors (TNF-α, IL-1β, and IL-6). In addition, it also exerted excellent anti-inflammatory effects, and significantly alleviated the swelling of joints during the treatment of gouty arthritis (GA). Therefore, CS-Cur-TGNCs, as a novel drug delivery system, could lead to new ideas for clinical therapeutic regimens for RA and GA.

Gelatin methacryloyl granular scaffolds for localized mRNA delivery

mRNA therapy is the intracellular delivery of messenger RNA (mRNA) to produce desired therapeutic proteins. Developing strategies for local mRNA delivery is still required where direct intra-articular injections are inappropriate for targeting a specific tissue. The mRNA delivery efficiency depends on protecting nucleic acids against nuclease-mediated degradation and safe site-specific intracellular delivery. Herein, we report novel mRNA-releasing matrices based on RGD-moiety-rich gelatin methacryloyl (GelMA) microporous annealed particle (MAP) scaffolds. GelMA concentration in aerogel-based microgels (μgels) produced through a microfluidic process, MAP stiffnesses, and microporosity are crucial parameters for cell adhesion, spreading, and proliferation. After being loaded with mRNA complexes, MAP scaffolds composed of 10 % GelMA μgels display excellent cell viability with increasing cell infiltration, adhesion, proliferation, and gene transfer. The intracellular delivery is achieved by the sustained release of mRNA complexes from MAP scaffolds and cell adhesion on mRNA-releasing scaffolds. These findings highlight that hybrid systems can achieve efficient protein expression by delivering mRNA complexes, making them promising mRNA-releasing biomaterials for tissue engineering.

Personalized Porous Gelatin Methacryloyl Sustained-Release Nicotinamide Protects Against Noise-Induced Hearing Loss

There are no Food and Drug Administration-approved drugs for treating noise-induced hearing loss (NIHL), reflecting the absence of clear specific therapeutic targets and effective delivery strategies. Noise trauma is demonstrated results in nicotinamide adenine dinucleotide (NAD+) downregulation and mitochondrial dysfunction in cochlear hair cells (HCs) and spiral ganglion neurons (SGNs) in mice, and NAD+ boosted by nicotinamide (NAM) supplementation maintains cochlear mitochondrial homeostasis and prevents neuroexcitatory toxic injury in vitro and ex vivo, also significantly ameliorated NIHL in vivo. To tackle the limited drug delivery efficiency due to sophisticated anatomical barriers and unique clearance pathway in ear, personalized NAM-encapsulated porous gelatin methacryloyl (PGMA@NAM) are developed based on anatomy topography of murine temporal bone by micro-computed tomography and reconstruction of round window (RW) niche, realizing hydrogel in situ implantation completely, NAM sustained-release and long-term auditory preservation in mice. This study strongly supports personalized PGMA@NAM as NIHL protection drug with effective inner ear delivery, providing new inspiration for drug-based treatment of NIHL.

Complete Restoration of Hearing Loss and Cochlear Synaptopathy via Minimally Invasive, Single-Dose, and Controllable Middle Ear Delivery of Brain-Derived Neurotrophic Factor-Poly(dl-lactic acid-co-glycolic acid)-Loaded Hydrogel

Noise-induced hearing loss (NIHL) often accompanies cochlear synaptopathy, which can be potentially reversed to restore hearing. However, there has been little success in achieving complete recovery of sensorineural deafness using nearly noninvasive middle ear drug delivery before. Here, we present a study demonstrating the efficacy of a middle ear delivery system employing brain-derived neurotrophic factor (BDNF)-poly-(dl-lactic acid-co-glycolic acid) (PLGA)-loaded hydrogel in reversing synaptopathy and restoring hearing function in a mouse model with NIHL. The mouse model achieved using the single noise exposure (NE, 115 dBL, 4 h) exhibited an average 20 dBL elevation of hearing thresholds with intact cochlear hair cells but a loss of ribbon synapses as the primary cause of hearing impairment. We developed a BDNF-PLGA-loaded thermosensitive hydrogel, which was administered via a single controllable injection into the tympanic cavity of noise-exposed mice, allowing its presence in the middle ear for a duration of 2 weeks. This intervention resulted in complete restoration of NIHL at frequencies of click, 4, 8, 16, and 32 kHz. Moreover, the cochlear ribbon synapses exhibited significant recovery, whereas other cochlear components (hair cells and auditory nerves) remained unchanged. Additionally, the cochlea of NE treated mice revealed activation of tropomyosin receptor kinase B (TRKB) signaling upon exposure to BDNF. These findings demonstrate a controllable and minimally invasive therapeutic approach that utilizes a BDNF-PLGA-loaded hydrogel to restore NIHL by specifically repairing cochlear synaptopathy. This tailored middle ear delivery system holds great promise for achieving ideal clinical outcomes in the treatment of NIHL and cochlear synaptopathy.

Modeling, applications and challenges of inner ear organoid

More than 6% of the world's population is suffering from hearing loss and balance disorders. The inner ear is the organ that senses sound and balance. Although inner ear disorders are common, there are limited ways to intervene and restore its sensory and balance functions. The development and establishment of biologically therapeutic interventions for auditory disorders require clarification of the basics of signaling pathways that control inner ear development and the establishment of endogenous or exogenous cell-based therapeutic methods. In vitro models of the inner ear, such as organoid systems, can help identify new protective or regenerative drugs, develop new gene therapies, and be considered as potential tools for future clinical applications. Advances in stem cell technology and organoid culture offer unique opportunities for modeling inner ear diseases and developing personalized therapies for hearing loss. Here, we review and discuss the mechanisms for the establishment and the potential applications of inner ear organoids.

Harnessing astaxanthin-loaded diselenium cross-linked apotransferrin nanoparticles for the treatment of secretory otitis media

Secretory otitis media (SOM) is a clinical condition characterized by the accumulation of fluids and oxidative stress in the middle ear, leading to hearing impairment and infection complications. One potential solution for mitigating oxidative stress associated with SOM is the use of antioxidants such as astaxanthin. However, its effectiveness is limited due to its poor bioavailability and rapid oxidation. Herein, we developed a novel diselenium-crosslinked apotransferrin enriched with astaxanthin (AST@dSe-AFT) nanoparticles to augment the transport of astaxanthin across biological membranes, resulting in increased bioavailability and reduced oxidative stress in SOM. Our research demonstrated that AST@dSe-AFT efficiently accumulated in the middle ear, allowing for controlled delivery of astaxanthin in response to reactive oxygen species and reducing oxidative stress. Additionally, AST@dSe-AFT stimulated macrophages to polarize towards M2 phenotype and neutrophils to polarize towards N2 phenotype, thereby facilitating an anti-inflammatory response and tissue restoration. Importantly, AST@dSe-AFT exhibited no toxicity or adverse effects, suggesting its potential for safety and future clinical translation. Our findings suggested that AST@dSe-AFT represents a promising approach for the treatment of secretory otitis media and other oxidative stress-related disorders.

Injectable dexamethasone-loaded peptide hydrogel for therapy of radiation-induced ototoxicity by regulating the mTOR signaling pathway

Radiation-induced ototoxicity is associated with inflammation response and excessive reactive oxygen species in the cochlea. However, the effectiveness of many drugs in clinical settings is limited due to anatomical barriers in the inner ear and pharmacokinetic instability. To address this issue, we developed an injectable hydrogel called RADA32-HRN-dexamethasone (RHD). The RHD hydrogel possesses self-anti-inflammatory properties and can self-assemble into nanofibrous structures, ensuring controlled and sustained release of dexamethasone in the local region. Flow cytometry analysis revealed that the uptake of FITC-conjugated RHD gel by hair cells increased in a time-dependent manner. Compared to free dexamethasone solutions, dexamethasone-loaded RHD gel achieved a longer and more controlled release profile of dexamethasone. Additionally, RHD gel effectively protected against the inflammatory response, reduced excessive reactive oxygen species production, and reversed the decline in mitochondrial membrane potentials induced by ionizing radiation, leading to attenuation of apoptosis and DNA damage. Moreover, RHD gel promoted the recovery of outer hair cells and partially restored auditory function in mice exposed to ionizing radiation. These findings validated the protective effects of RHD gel against radiation-induced ototoxicity in both cell cultures and animal models. Furthermore, RHD gel enhanced the activity of the mammalian target of rapamycin (mTOR) signaling pathway, which was inhibited by ionizing radiation, thereby promoting the survival of hair cells. Importantly, intratympanic injections of RHD gel exhibited excellent biosafety and do not interfere with the anti-tumor effects of radiotherapy. In summary, our study demonstrates the therapeutic potential of injectable dexamethasone-loaded RHD hydrogel for the treatment of radiation-induced hearing loss by regulating the mTOR signaling pathway.

Natural Multifunctional Silk Microcarriers for Noise-Induced Hearing Loss Therapy

Noise-induced hearing loss (NIHL) is a common outcome of excessive reactive oxygen species in the cochlea, and the targeted delivery of antioxidants to the inner ear is a potential therapeutic strategy. In this paper, a novel natural biomaterials-derived multifunctional delivery system using silk fibroin-polydopamine (PDA)-composited inverse opal microcarriers (PDA@SFMCs) is presented for inner ear drug delivery and NIHL therapy. Due to their large specific surface area and interpenetrating nanochannels, PDA@SFMCs can rapidly load active biomolecules making them a convenient medium for the storage and delivery of such molecules. In addition, surface modification of PDA enables the microcarriers to remain in the round window niche, thus facilitating the precise local and directed delivery of loaded drugs. Based on these features, it is demonstrated here that n-acetylcysteine-loaded silk microcarriers have satisfactory antioxidant properties on cells and can successfully prevent NIHL in guinea pigs. These results indicate that the natural multifunctional silk microcarriers are promising agents for local inner ear drug delivery in the clinic.

Photocrosslinked methacrylated natural macromolecular hydrogels for tissue engineering: A review

A hydrogel is a three-dimensional (3D) network structure formed through polymer crosslinking, and these have emerged as a popular research topic in recent years. Hydrogel crosslinking can be classified as physical, chemical, or enzymatic, and photocrosslinking is a branch of chemical crosslinking. Compared with other methods, photocrosslinking can control the hydrogel crosslinking initiation, crosslinking time, and crosslinking strength using light. Owing to these properties, photocrosslinked hydrogels have important research prospects in tissue engineering, in situ gel formation, 3D bioprinting, and drug delivery. Methacrylic anhydride modification is a common method for imparting photocrosslinking properties to polymers, and graft-substituted polymers can be photocrosslinked under UV irradiation. In this review, we first introduce the characteristics of common natural polysaccharide- and protein-based hydrogels and the processes used for methacrylate group modification. Next, we discuss the applications of methacrylated natural hydrogels in tissue engineering. Finally, we summarize and discuss existing methacrylated natural hydrogels in terms of limitations and future developments. We expect that this review will help researchers in this field to better understand the synthesis of methacrylate-modified natural hydrogels and their applications in tissue engineering.

Microfluidic Platform for Microparticle Fabrication and Release of a Cathepsin Inhibitor

Cathepsins are a family of cysteine proteases responsible for a variety of homeostatic functions throughout the body, including extracellular matrix remodeling, and have been implicated in a variety of degenerative diseases. However, clinical trials using systemic administration of cathepsin inhibitors have been abandoned due to side effects, so local delivery of cathepsin inhibitors may be advantageous. In these experiments, a novel microfluidic device platform was developed that can synthesize uniform, hydrolytically degradable microparticles from a combination of poly(ethylene glycol) diacrylate (PEGDA) and dithiothreitol (DTT). Of the formulations examined, the 10-polymer weight percentage 10 mM DTT formulation degraded after 77 days in vitro. A modified assay using the DQ Gelatin Fluorogenic Substrate was used to demonstrate sustained release and bioactivity of a cathepsin inhibitor (E-64) released from hydrogel microparticles over 2 weeks in vitro (up to ∼13 μg/mL released with up to ∼40% original level of inhibition remaining at day 14). Altogether, the technologies developed in this study will allow a small-molecule, broad cathepsin inhibitor E-64 to be released in a sustained manner for localized inhibition of cathepsins for a wide variety of diseases.

3D Bioprinting of a Bioactive Composite Scaffold for Cell Delivery in Periodontal Tissue Regeneration

Hydrogels have been widely applied to the fabrication of tissue engineering scaffolds via three-dimensional (3D) bioprinting because of their extracellular matrix-like properties, capacity for living cell encapsulation, and shapeable customization depending on the defect shape. However, the current hydrogel scaffolds show limited regeneration activity, especially in the application of periodontal tissue regeneration. In this study, we attempted to develop a novel multi-component hydrogel that possesses good biological activity, can wrap living cells for 3D bioprinting and can regenerate periodontal soft and hard tissue. The multi-component hydrogel consisted of gelatin methacryloyl (GelMA), sodium alginate (SA) and bioactive glass microsphere (BGM), which was first processed into hydrogel scaffolds by cell-free 3D printing to evaluate its printability and in vitro biological performances. The cell-free 3D-printed scaffolds showed uniform porous structures and good swelling capability. The BGM-loaded scaffold exhibited good biocompatibility, enhanced osteogenic differentiation, apatite formation abilities and desired mechanical strength. The composite hydrogel was further applied as a bio-ink to load with mouse bone marrow mesenchymal stem cells (mBMSCs) and growth factors (BMP2 and PDGF) for the fabrication of a scaffold for periodontal tissue regeneration. The cell wrapped in the hydrogel still maintained good cellular vitality after 3D bioprinting and showed enhanced osteogenic differentiation and soft tissue repair capabilities in BMP2- and PDGF-loaded scaffolds. It was noted that after transplantation of the cell- and growth factor-laden scaffolds in Beagle dog periodontal defects, significant regeneration of gingival tissue, periodontal ligament, and alveolar bone was detected. Importantly, a reconstructed periodontal structure was established in the treatment group eight weeks post-transplantation of the scaffolds containing the cell and growth factors. In conclusion, we developed a bioactive composite bio-ink for the fabrication of scaffolds applicable for the reconstruction and regeneration of periodontal tissue defects.