Design of an Adhesive Film-Based Microfluidic Device for Alginate Hydrogel-Based Cell Encapsulation

Wound Tissue Regeneration by Microfluidic Generated Fibroblast Cell/CuO Nanosheet-Loaded Alginate Hydrogel on an Excisional Full-Thickness Rat Model

Chronic ulcers present numerous challenges in treatment such as prolonged inflammation, infections resistant to drugs, and the formation of scars. In this research, we developed a calcium ion (Ca2+) cross-linked alginate (Alg) hydrogel loaded with CuO nanosheet/fibroblast cells via a microfluidic system with substantial efficiency in accelerating healing and preventing infection. Initially, the soft lithography method was utilized to fabricate the microfluidic system, which was employed to produce alginate hydrogel incorporating nanosheets of copper oxide (CuO) and MEF cells. The properties of hydrogel and copper oxide nanosheets were analyzed by using FE-SEM, EDS/EDX, and elemental mapping to determine their physicochemical characteristics. The viability of mouse embryonic fibroblast cells (MEF) in alginate-CuO hydrogel was explored through cell viability assay, and the antibacterial properties were also studied using colony-forming assay. The healing abilities of the hydrogel were investigated using an excisional, full-thickness wound rat model. Our results revealed proper antimicrobial and angiogenic properties with slight cytotoxicity for CuO nanosheets at a concentration of 25 μg/mL. The alginate-CuO-cell-treated group exhibited a faster wound contraction and healing among all treatments. The results of the in vivo assay along with histology and gene expression indicate a synergistic cooperation between MEF and CuO, leading to enhanced re-epithelialization, angiogenesis, and matrix remodeling. In this research, a therapeutic hydrogel with qualities like microbicidal, angiogenic, immune system modulation, and promotion of ECM and epithelium regeneration, resulting in faster healing, was developed. Moreover, there was a synergic impact noticed between CuO nanosheets and MEF cells as well as improved formation of blood vessels and collagen accumulation. In conclusion, this biocompatible hydrogel offers a promising strategy for effective wound healing without the need for invasive procedures.

Droplet Microfluidics Powered Hydrogel Microparticles for Stem Cell-Mediated Biomedical Applications

Stem cell-related therapeutic technologies have garnered significant attention of the research community for their multi-faceted applications. To promote the therapeutic effects of stem cells, the strategies for cell microencapsulation in hydrogel microparticles have been widely explored, as the hydrogel microparticles have the potential to facilitate oxygen diffusion and nutrient transport alongside their ability to promote crucial cell-cell and cell-matrix interactions. Despite their significant promise, there is an acute shortage of automated, standardized, and reproducible platforms to further stem cell-related research. Microfluidics offers an intriguing platform to produce stem cell-laden hydrogel microparticles (SCHMs) owing to its ability to manipulate the fluids at the micrometer scale as well as precisely control the structure and composition of microparticles. In this review, the typical biomaterials and crosslinking methods for microfluidic encapsulation of stem cells as well as the progress in droplet-based microfluidics for the fabrication of SCHMs are outlined. Moreover, the important biomedical applications of SCHMs are highlighted, including regenerative medicine, tissue engineering, scale-up production of stem cells, and microenvironmental simulation for fundamental cell studies. Overall, microfluidics holds tremendous potential for enabling the production of diverse hydrogel microparticles and is worthy for various stem cell-related biomedical applications.

Effect of controlled release of HGF on extracellular vesicle secretion by urine-derived stem cells

Introduction

The hepatic growth factor (HGF) stimulates DNA synthesis and cell proliferation and plays a role in tissue protection and regeneration. In this study, we have examined the effect of incubation of HGF with urine-derived stem cells (USCs) on the secretion of small extracellular vesicles (sEV) by the cells.

Materials and Methods

HGF in the incubation medium was either a bolus administration or a controlled release of an equivalent amount from microbeads within the size range of 50-200 µm made with ultrapurified low-viscosity high-guluronic acid (UP-LVG) alginate. USCs were incubated with or without HGF for 3 days or 7 days before removal of the incubation media, followed by harvesting sEV by the precipitation method. The protein content of isolated sEV was measured by bicinchoninic acid assay (BCA) for these three groups: control (no HGF beads), bolus HGF, and HGF beads. We also performed nanoparticle tracking analysis (NTA), Western blot assay, and ELISA for the HGF content of samples.

Results

We found a significantly higher concentration of proteins in the HGF microbead group (control release group) compared to the bolus group and the control group after 7 days (p < 0.0017). The NTA data aligned with the BCA; they showed a significantly higher concentration of particles within the size range of sEV (<200 nm) in the group treated with HGF beads compared to the two other groups on day 7 (p < 0.0001).

Conclusion

We found that administration of HGF to USCs by controlled release of the growth factor significantly enhances the levels of sEV secretion during 7 days of incubation.

Challenges and Perspectives for Future Considerations in the Bioengineering of a Bioartificial Pancreas

There is an unrelenting interest in the development of a reliable bioartificial pancreas construct since the first description of this technology of encapsulated islets by Lim and Sun in 1980 because it promised to be a curative treatment for Type 1 Diabetes Mellitus (T1DM). Despite the promise of the concept of encapsulated islets, there are still some challenges that impede the full realization of the clinical potential of the technology. In this review, we will first present the justification for continued research and development of this technology. Next, we will review key barriers that impede progress in this field and discuss strategies that can be used to design a reliable construct capable of effective long-term performance after transplantation in diabetic patients. Finally, we will share our perspectives on areas of additional work for future research and development of the technology.

Fabrication of hydrogel microspheres via microfluidics using inverse electron demand Diels-Alder click chemistry-based tetrazine-norbornene for drug delivery and cell encapsulation applications

Microfluidic on-chip production of polymeric hydrogel microspheres (MPs) can be designed for the loading of different biologically active cargos and living cells. Among different gelation strategies, ionically crosslinked microspheres generally show limited mechanical properties, meanwhile covalently crosslinked microspheres often require the use of crosslinking agents or initiators with limited biocompatibility. Inverse electron demand Diels Alder (iEDDA) click chemistry is a promising covalent crosslinking method with fast kinetics, high chemoselectivity, high efficiency and no cross-reactivity. Herein, in situ gellable iEDDA-crosslinked polymeric hydrogel microspheres are developed via water-in-oil emulsification (W/O) glass microfluidics. The microspheres are composed of two polyethylene glycol precursors modified with either tetrazine or norbornene as functional moieties. Using a single co-flow glass microfluidic platform, homogenous MPs of sizes 200-600 μm are developed and crosslinked within 2 minutes. The rheological properties of iEDDA crosslinked bulk hydrogels are maintained with a low swelling degree and a slow degradation behaviour under physiological conditions. Moreover, a high-protein loading capacity can be achieved, and the encapsulation of mammalian cells is possible. Overall, this work provides the possibility of developing microfluidics-produced iEDDA-crosslinked MPs as a potential drug vehicle and cell encapsulation system in the biomedical field.

Hep3Gel: A Shape-Shifting Extracellular Matrix-Based, Three-Dimensional Liver Model Adaptable to Different Culture Systems

Drug-induced hepatotoxicity is a leading cause of clinical trial withdrawal. Therefore, in vitro modeling the hepatic behavior and functionalities is not only crucial to better understand physiological and pathological processes but also to support drug development with reliable high-throughput platforms. Different physiological and pathological models are currently under development and are commonly implemented both within platforms for standard 2D cultures and within tailor-made chambers. This paper introduces Hep3Gel: a hybrid alginate-extracellular matrix (ECM) hydrogel to produce 3D in vitro models of the liver, aiming to reproduce the hepatic chemomechanical niche, with the possibility of adapting its shape to different manufacturing techniques. The ECM, extracted and powdered from porcine livers by a specifically set-up procedure, preserved its crucial biological macromolecules and was embedded within alginate hydrogels prior to crosslinking. The viscoelastic behavior of Hep3Gel was tuned, reproducing the properties of a physiological organ, according to the available knowledge about hepatic biomechanics. By finely tuning the crosslinking kinetics of Hep3Gel, its dualistic nature can be exploited either by self-spreading or adapting its shape to different culture supports or retaining the imposed fiber shape during an extrusion-based 3D-bioprinting process, thus being a shape-shifter hydrogel. The self-spreading ability of Hep3Gel was characterized by combining empirical and numerical procedures, while its use as a bioink was experimentally characterized through rheological a priori printability evaluations and 3D printing tests. The effect of the addition of the ECM was evident after 4 days, doubling the survival rate of cells embedded within control hydrogels. This study represents a proof of concept of the applicability of Hep3Gel as a tool to develop 3D in vitro models of the liver.

Toward 3D-Bioprinted Models of the Liver to Boost Drug Development

The main problems in drug development are connected to enormous costs related to the paltry success rate. The current situation empowered the development of high-throughput and reliable instruments, in addition to the current golden standards, able to predict the failures in the early preclinical phase. Being hepatotoxicity responsible for the failure of 30% of clinical trials, and the 21% of withdrawal of marketed drugs, the development of complex in vitro models (CIVMs) of liver is currently one of the hottest topics in the field. Among the different fabrication techniques, 3D-bioprinting is emerging as a powerful ally for their production, allowing the manufacture of three-dimensional constructs characterized by computer-controlled and customized geometry, and inter-batches reproducibility. Thanks to these, it is possible to rapidly produce tailored cell-laden constructs, to be cultured within static and dynamic systems, thus reaching a further degree of personalization when designing in vitro models. This review highlights and prioritizes the most recent advances related to the development of CIVMs of the hepatic environment to be specifically applied to pharmaceutical research, with a special focus on 3D-bioprinting, since the liver is primarily involved in the metabolism of drugs.

Cell encapsulation in alginate-based microgels using droplet microfluidics; a review on gelation methods and applications

Cell encapsulation within the microspheres using a semi-permeable polymer allows the two-way transfer of molecules such as oxygen, nutrients, and growth factors. The main advantages of cell encapsulation technology include controlling the problems involved in transplanting rejection in tissue engineering applications and reducing the long-term need for immunosuppressive drugs following organ transplantation to eliminate the side effects. Cell-laden microgels can also be used in 3D cell cultures, wound healing, and cancerous clusters for drug testing. Since cell encapsulation is used for different purposes, several techniques have been developed to encapsulate cells. Droplet-based microfluidics is one of the most valuable techniques in cell encapsulating. This study aimed to review the geometries and the mechanisms proposed in microfluidic systems to precisely control cell-laden microgels production with different biopolymers. We also focused on alginate gelation techniques due to their essential role in cell encapsulation applications. Finally, some applications of these microgels and researches will be explored.

Preparation of alginate hydrogel microparticles by gelation introducing cross-linkers using droplet-based microfluidics: a review of methods

This review examines the preparation of alginate hydrogel microparticles by using droplet-based microfluidics, a technique widely employed for its ease of use and excellent control of physicochemical properties, with narrow size distribution. The gelation of alginate is realized "on-chip" and/or "off-chip", depending on where cross-linkers are introduced. Various strategies are described and compared. Microparticle properties such as size, shape, concentration, stability and mechanical properties are discussed. Finally, we consider future perspectives for the preparation of hydrogel microparticles and their potential applications.

Droplet Microfluidics for Tumor Drug-Related Studies and Programmable Artificial Cells

Anticancer drug development is a crucial step toward cancer treatment, that requires realistic predictions of malignant tissue development and sophisticated drug delivery. Tumors often acquire drug resistance and drug efficacy, hence cannot be accurately predicted in 2D tumor cell cultures. On the other hand, 3D cultures, including multicellular tumor spheroids (MCTSs), mimic the in vivo cellular arrangement and provide robust platforms for drug testing when grown in hydrogels with characteristics similar to the living body. Microparticles and liposomes are considered smart drug delivery vehicles, are able to target cancerous tissue, and can release entrapped drugs on demand. Microfluidics serve as a high-throughput tool for reproducible, flexible, and automated production of droplet-based microscale constructs, tailored to the desired final application. In this review, it is described how natural hydrogels in combination with droplet microfluidics can generate MCTSs, and the use of microfluidics to produce tumor targeting microparticles and liposomes. One of the highlights of the review documents the use of the bottom-up construction methodologies of synthetic biology for the formation of artificial cellular assemblies, which may additionally incorporate both target cancer cells and prospective drug candidates, as an integrated "droplet incubator" drug assay platform.

Crosslinking Strategies for the Microfluidic Production of Microgels

This article provides a systematic review of the crosslinking strategies used to produce microgel particles in microfluidic chips. Various ionic crosslinking methods for the gelation of charged polymers are discussed, including external gelation via crosslinkers dissolved or dispersed in the oil phase; internal gelation methods using crosslinkers added to the dispersed phase in their non-active forms, such as chelating agents, photo-acid generators, sparingly soluble or slowly hydrolyzing compounds, and methods involving competitive ligand exchange; rapid mixing of polymer and crosslinking streams; and merging polymer and crosslinker droplets. Covalent crosslinking methods using enzymatic oxidation of modified biopolymers, photo-polymerization of crosslinkable monomers or polymers, and thiol-ene “click” reactions are also discussed, as well as methods based on the sol−gel transitions of stimuli responsive polymers triggered by pH or temperature change. In addition to homogeneous microgel particles, the production of structurally heterogeneous particles such as composite hydrogel particles entrapping droplet interface bilayers, core−shell particles, organoids, and Janus particles are also discussed. Microfluidics offers the ability to precisely tune the chemical composition, size, shape, surface morphology, and internal structure of microgels by bringing multiple fluid streams in contact in a highly controlled fashion using versatile channel geometries and flow configurations, and allowing for controlled crosslinking.

Surface modification of neurotrophin-3 loaded PCL/chitosan nanofiber/net by alginate hydrogel microlayer for enhanced biocompatibility in neural tissue engineering

This study prepared a novel three-dimensional nanocomposite scaffold by the surface modification of PCL/chitosan nanofiber/net with alginate hydrogel microlayer, hoping to have the privilege of both nanofibers and hydrogels simultaneously. Bead free randomly oriented nanofiber/net (NFN) structure composed of chitosan and polycaprolactone (PCL) was fabricated by electrospinning method. The low surface roughness, good hydrophilicity, and high porosity were obtained from the NFN structure. Then, the PCL/chitosan nanofiber/net was coated with a microlayer of alginate containing neurotrophin-3 (NT-3) and conjunctiva mesenchymal stem cells (CJMSCs) as a new stem cell source. According to the cross-sectional FESEM, the scaffold shows a two-layer structure with interconnected pores in the range of 20 μm diameter. The finding revealed that the surface modification of nanofiber/net by alginate hydrogel microlayer caused lower inflammatory response and higher proliferation of CJMSCs than the unmodified scaffold. The initial burst release of NT-3 was 69% in 3 days which followed by a sustained release up to 21 days. The RT-PCR analysis showed that the expression of Nestin, MAP-2, and β-tubulin III genes were increased 6, 5.4, and 8.8-fold, respectively. The results revealed that the surface-modified biomimetic scaffold possesses enhanced biocompatibility and could successfully differentiate CJMSCs to the neuron-like cells.

Preparation of Bi-based hydrogel for multi-modal tumor therapy

Radiotherapy (RT) is becoming a pervasive therapeutic pattern in clinical cancer therapy. However, the hypoxic microenvironment of tumors has a strong resistance to radiotherapy and could lead to a potential recurrence and metastasis after the treatment. Therefore, the use of synergistic strategies for improving and supplementing the RT efficiency is important. Herein, a novel Bi2S3/alginate (ALG) hydrogel containing tirapazamine (TPZ) was designed for the effective suppression of tumor recurrence, by introducing Bi3+ into the ALG, Na2S and TPZ solution. In this formulation, Bi3+ was used to crosslink with the ALG to form the hydrogel and react with S2- to simultaneously form Bi2S3 nanoparticles in the hydrogel matrix. The resulting Bi2S3 nanoparticles not only exhibit the superb radiosensitization effect to boost the effective eradication of tumors during RT but also manifest an excellent photothermal transforming performance for tumor hyperthermia and computed tomography (CT) imaging capacity for tumor monitoring. Furthermore, the RT caused hypoxia could activate the reductive prodrug TPZ and enhance its therapeutic efficiency. The reported hydrogel system provides an efficient and safe therapeutic strategy for current local tumor therapy.

Multifunctional Calcium-Deficient Hydroxyl Apatite-Alginate Core-Shell-Structured Bone Substitutes as Cell and Drug Delivery Vehicles for Bone Tissue Regeneration

In this work, we fabricated unique coiled-structured bioceramics contained in hydrogel beads for simultaneous drug and cell delivery using a combination of bone cement chemistry and bioprinting and characterized them. The core of the calcium-deficient hydroxyl apatite (CDHA) contains quercetin, which is a representative phytoestrogen isolated from onions and apples, to control the metabolism of bone tissue regeneration through sustained release over a long period of time. The shell consists of an alginate hydrogel that includes preosteoblast MC3T3-E1 cells. Ceramic paste and hydrogel were simultaneously extruded to fabricate core-shell beads through the inner and outer nozzles, respectively, of a concentric nozzle system based on a material-extruding-based three-dimensional (3D) printing system. The formation of beads and the coiled ceramic core is related to both alginate concentration and printing conditions. The size of the microbeads and the thickness of the coiled structure could be controlled by adjusting the nozzle conditions. The whole process was carried out at physiological conditions (37 °C) to be gentle on the cells. The alginate shell undergoes solidification by cross-linking in CaCl₂ or monocalcium phosphate monohydrate (MCPM) solution, while the hardening and cementation of the α-tricalcium phosphate (α-TCP) core to CDHA are subsequently initiated by immersion in phosphate-buffered saline solution. This process replaces the typical sintering of ceramic processing to prevent damage to the hydrogel, cells, and drugs in the beads. The cell-loaded beads were then cultured in cell culture media where the cells could maintain good viability during the entire testing period, which was over 50 days. Cell growth and elongation were observed even in the alginate along the CDHA coiled structure over time. Sustained release of quercetin without any initial burst was also confirmed during a test period of 120 days. These novel structured microbeads with multibiofunctionality can be used as new bone substitutes for hard tissue regeneration in indeterminate defect sites.

Microfluidic Systems for Assisted Reproductive Technologies: Advantages and Potential Applications

Microfluidic technologies have emerged as a powerful tool that can closely replicate the in-vivo physiological conditions of organ systems. Assisted reproductive technology (ART), while being able to achieve successful outcomes, still faces challenges related to technical error, efficiency, cost, and monitoring/assessment. In this review, we provide a brief overview of the uses of microfluidic devices in the culture, maintenance and study of ovarian follicle development for experimental and therapeutic applications. We discuss existing microfluidic platforms for oocyte and sperm selection and maintenance, facilitation of fertilization by in-vitro fertilization/intracytoplastimc sperm injection, and monitoring, selection and maintenance of resulting embryos. Furthermore, we discuss the possibility of future integration of these technologies onto a single platform and the limitations facing the development of these systems. In spite of these challenges, we envision that microfluidic systems will likely evolve and inevitably revolutionize both fundamental, reproductive physiology/toxicology research as well as clinically applicable ART.

Fabrication and Characterization of a Low-Cost Microfluidic System for the Manufacture of Alginate-Lacasse Microcapsules

The development of microfluidics-based systems in the recent years has provided a rapid and controlled method for the generation of monodisperse microencapsulates for multiple applications. Here, we explore the design, manufacture and characterization of a low-cost microsystem for the encapsulation of the fungal laccase from Pycnoporus sanguineus CS43 in alginate microcapsules. Multiphysics simulations were used to overview the fluid behavior within the device and estimate the resulting capsule size. Polymethylmethacrylate (PMMA) sheets were used for final microsystem manufacture. Different flow rates of the continuous (Q_c) and discrete (Q_d) phases in the ranges of 83–293 mL/h and 1–5 mL/h, respectively, were evaluated for microcapsule fabrication. Universal Serial Bus (USB) microscope and image analysis was used to measure the final particle size. Laccase encapsulation was evaluated using spectrophotometry and with the aid of fluorescent dyes and confocal microscopy. Results showed microcapsule size was in the range of 203.13–716.00 μm and Q_c was found as the dominant parameter to control capsule size. There was an effective enzyme encapsulation of 65.94% with respect to the initial laccase solution.