Cell immobilization in gelatin–hydroxyphenylpropionic acid hydrogel fibers

Polysaccharide-protein based scaffolds for cartilage repair and regeneration

Cartilage repair and regeneration have become a global issue that millions of patients from all over the world need surgical intervention to repair the articular cartilage annually due to the limited self-healing capability of the cartilage tissues. Cartilage tissue engineering has gained significant attention in cartilage repair and regeneration by integration of the chondrocytes (or stem cells) and the artificial scaffolds. Recently, polysaccharide-protein based scaffolds have demonstrated unique and promising mechanical and biological properties as the artificial extracellular matrix of natural cartilage. In this review, we summarize the modification methods for polysaccharides and proteins. The preparation strategies for the polysaccharide-protein based hydrogel scaffolds are presented. We discuss the mechanical, physical and biological properties of the polysaccharide-protein based scaffolds. Potential clinical translation and challenges on the artificial scaffolds are also discussed.

Recent progress and treatment strategy of pectin polysaccharide based tissue engineering scaffolds in cancer therapy, wound healing and cartilage regeneration

Natural polymers and its mixtures in the form of films, sponges and hydrogels are playing a major role in tissue engineering and regenerative medicine. Hydrogels have been extensively investigated as standalone materials for drug delivery purposes as they enable effective encapsulation and sustained release of drugs. Biopolymers are widely utilised in the fabrication of hydrogels due to their safety, biocompatibility, low toxicity, and regulated breakdown by human enzymes. Among all the biopolymers, polysaccharide-based polymer is well suited to overcome the limitations of traditional wound dressing materials. Pectin is a polysaccharide which can be extracted from different plant sources and is used in various pharmaceutical and biomedical applications including cartilage regeneration. Pectin itself cannot be employed as scaffolds for tissue engineering since it decomposes quickly. This article discusses recent research and developments on pectin polysaccharide, including its types, origins, applications, and potential demands for use in AI-mediated scaffolds. It also covers the materials-design process, strategy for implementation to material selection and fabrication methods for evaluation. Finally, we discuss unmet requirements and current obstacles in the development of optimal materials for wound healing and bone-tissue regeneration, as well as emerging strategies in the field.

Dynamic Stiffening Hydrogel with Instructive Stiffening Timing Modulates Stem Cell Fate In Vitro and Enhances Bone Remodeling In Vivo

Biomechanical stimuli derived from the extracellular matrix (ECM) extremely tune stem cell fate through 3D and spatiotemporal changes in vivo. The matrix stiffness is a crucial factor during bone tissue development. However, most in vitro models to study the osteogenesis of mesenchymal stem cells (MSCs) are static or stiffening in a 2D environment. Here, a dynamic and controllable stiffening 3D biomimetic model is created to regulate the osteogenic differentiation of MSCs with a dual-functional gelatin macromer that can generate a double-network hydrogel by sequential enzymatic and light-triggered crosslinking reactions. The findings show that these dynamic hydrogels allowed cells to spread and expand prior to the secondary crosslinking and to sense high stiffness after stiffening. The MSCs in the dynamic hydrogels, especially the hydrogel stiffened at the late period, present significantly elevated osteogenic ECM secretion, gene expression, and nuclear localization of Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ). In vivo evaluation of animal experiments further indicates that the enhancement of dynamic stiffening on osteogenesis of MSCs substantially promotes bone remodeling. Consequently, this work reveals that the 3D dynamic stiffening microenvironment as a critical biophysical cue not only mediates the stem cell fate in vitro, but also augments bone restoration in vivo.

Horseradish Peroxidase-Mediated Bioprinting via Bioink Gelation by Alternately Extruded Support Material

Horseradish peroxidase (HRP)-mediated extrusion bioprinting has a significant potential in tissue engineering and regenerative medicine. However, they often face challenges in terms of printing fidelity and structural integrity when using low-viscosity inks. To address this issue, a method that alternately extrudes bioinks and support material was developed in this study. The bioinks consisting of cells, HRP, and phenolated polymers, and the support material contained hydrogen peroxide (H2O2). The support material not only prevented the collapse of the constructs but also supplied H2O2 to facilitate the enzymatic reaction. 3D constructs with tall and complex shapes were successfully printed from a low-viscosity ink containing 10 U/mL HRP and 1.0% w/v phenolated hyaluronic acid (HA-Ph), with a support material containing 10 mM H2O2. Over 90% viability of mouse fibroblasts (10T1/2) was achieved following the printing process, along with a morphology and proliferation rate similar to that of nontreated cells. Furthermore, human hepatoblastoma (HepG2) cells showed an increased spheroid size over 14 days in the printed constructs. The 10T1/2 cells adhered and proliferated on the constructs printed from inks containing both phenolated gelatin and HA-Ph. These results demonstrate the great potential of this HRP-mediated extrusion bioprinting technique for tissue engineering applications.

Anatomy, molecular structures, and hyaluronic acid - Gelatin injectable hydrogels as a therapeutic alternative for hyaline cartilage recovery: A review

Cartilage damage caused by trauma or osteoarthritis is a common joint disease that can increase the social and economic burden in society. Due to its avascular characteristics, the poor migration ability of chondrocytes, and a low number of progenitor cells, the self-healing ability of cartilage defects has been significantly limited. Hydrogels have been developed into one of the most suitable biomaterials for the regeneration of cartilage because of its characteristics such as high-water absorption, biodegradation, porosity, and biocompatibility similar to natural extracellular matrix. Therefore, the present review article presents a conceptual framework that summarizes the anatomical, molecular structure and biochemical properties of hyaline cartilage located in long bones: articular cartilage and growth plate. Moreover, the importance of preparation and application of hyaluronic acid - gelatin hydrogels for cartilage tissue engineering are included. Hydrogels possess benefits of stimulating the production of Agc1, Col2α1-IIa, and SOX9, molecules important for the synthesis and composition of the extracellular matrix of cartilage. Accordingly, they are believed to be promising biomaterials of therapeutic alternatives to treat cartilage damage.

DNA hydrogels for bone regeneration

DNA-based biomaterials have been proposed for tissue engineering approaches due to their predictable assembly into complex morphologies and ease of functionalization. For bone tissue regeneration, the ability to bind Ca2+ and promote hydroxyapatite (HAP) growth along the DNA backbone combined with their degradation and release of extracellular phosphate, a known promoter of osteogenic differentiation, make DNA-based biomaterials unlike other currently used materials. However, their use as biodegradable scaffolds for bone repair remains scarce. Here, we describe the design and synthesis of DNA hydrogels, gels composed of DNA that swell in water, their interactions in vitro with the osteogenic cell lines MC3T3-E1 and mouse calvarial osteoblast, and their promotion of new bone formation in rat calvarial wounds. We found that DNA hydrogels can be readily synthesized at room temperature, and they promote HAP growth in vitro, as characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. Osteogenic cells remain viable when seeded on DNA hydrogels in vitro, as characterized by fluorescence microscopy. In vivo, DNA hydrogels promote the formation of new bone in rat calvarial critical size defects, as characterized by micro-computed tomography and histology. This study uses DNA hydrogels as a potential therapeutic biomaterial for regenerating lost bone.

Tuning Myogenesis by Controlling Gelatin Hydrogel Properties through Hydrogen Peroxide-Mediated Cross-Linking and Degradation

Engineering skeletal muscle tissue in vitro is important to study the mechanism of myogenesis, which is crucial for regenerating muscle cells. The physicochemical properties of the cellular microenvironment are known to govern various cell behaviours. Yet, most studies utilised synthetic materials to model the extracellular matrix that suffers from cytotoxicity to the cells. We have previously reported that the physicochemical property of hydrogels obtained from horseradish peroxidase (HRP)-catalysed cross-linking could be controlled by a simple adjustment to the exposure time to air containing H2O2. In this study, we evaluated the influence of physicochemical properties dynamics in the gelatin possessing phenol groups (Gelatin-Ph) hydrogel to regulate the myogenesis in vitro. We controlled the Young's modulus of the Gelatin-Ph hydrogel by tuning the air containing 16 ppm H2O2 exposure time for 15-60 min. Additionally, prolonged exposure to air containing H2O2 also induced Gelatin-Ph degradation. Myoblasts showed higher adhesion and myotube formation on stiff hydrogel (3.53 kPa) fabricated through 30 min of exposure to air containing H2O2 compared to those on softer hydrogel (0.77-2.79 kPa) fabricated through 15, 45, and 60 min of the exposure. These results demonstrate that the myogenesis can be tuned by changes in the physicochemical properties of Gelatin-Ph hydrogel mediated by H2O2.

Aqueous decomposition behavior of solid peroxides: Effect of pH and buffer composition on oxygen and hydrogen peroxide formation

The ability of solid peroxides to provide sustained release of both oxygen and hydrogen peroxide makes them potentially suitable for oxygen release or antibacterial applications. Most recent reports using solid peroxides to augment oxygen levels do so by compounding solid peroxide powders in polymers to retard the aqueous decomposition. Compounds with peroxidase activity may be added to reduce hydrogen peroxide toxicity. Peroxides are rarely pure and are mixed with oxide and themselves decompose to form hydroxides in water. Therefore, even if buffering strategies are used, locally the pH at the surface of aqueously immersed peroxide particles is inevitably alkaline. Since pH affects the decomposition of peroxides and hydrogen peroxide stability, this study compared for the first-time the aqueous decomposition products of hydrogen and inorganic peroxides that are in use or have been used for medical applications of have been evaluated preclinically; calcium peroxide (CaO₂), magnesium peroxide (MgO₂), zinc peroxide (ZnO₂), sodium percarbonate (Na₂CO₃.1.5H₂O₂) and hydrogen peroxide (H₂O₂). Since plasma can be approximated to be carbonate buffered phosphate solution, we maintained pH using carbonate and phosphate buffers and compared results with citrate buffers. For a given peroxide compound, we identified not only a strong effect of pH but also of buffer composition on the extent to which oxygen and hydrogen peroxide formation occurred. The influence of buffer composition was not previously appreciated, thereby establishing in vitro parameters for better design of intentional release of specific decomposition species. STATEMENT OF SIGNIFICANCE: This paper compares for the first time the aqueous decomposition products oxygen and hydrogen peroxide of solid peroxy compounds of metal cations, (calcium, magnesium, sodium and zinc) across a pH range that could feasibly be found in the body, (pH 5,7, 9) either physiologically or pathologically. We find that in addition to pH, buffer composition is also a critically important factor, making translation from in vitro models challenging. Cytotoxicity was related to hydrogen peroxide release, alkalinity and in the case of zinc peroxide to the cation itself. In vitro and preclinical studies generally report release data from polymer-peroxide composites and rarely compare peroxides with one another. Together our data provide guidance for oxygen and ROS delivery from these inorganic materials.

Recent Development of MOF-Based Photothermal Agent for Tumor Ablation

Metal-organic frameworks (MOFs) are 3D-architecture compounds of metal ions and organic molecules with sufficient and permanent porosity, showing great potential as a versatile platform to load various functional moieties to endow the hybrid materials with specific applications. Currently, a variety of photothermal nanometals have been embedded into organic ligands for integrating the unique photothermal effects with the merits of MOFs to improve their performances for cancer therapy. In this review, we have summarized a series of novel MOF-based photothermal materials for this unique therapeutic modality against tumors from three main aspects according to their chemical compositions and structures, i) metal-doped MOF, ii) organic-doped MOF, and iii) polymer-coated MOF. In addition, we have summarized the latest developments and characteristics of MOF-based photothermal agents, such as good biocompatibility, low toxicity, and responsive photothermal conversion without destroying the structure of hybrid photothermal agent. At last, we addressed the future perspectives of MOF-based photothermal agent in the field of phototherapy.

Freeform 3D Bioprinting Involving Ink Gelation by Cascade Reaction of Oxidase and Peroxidase: A Feasibility Study Using Hyaluronic Acid-Based Ink

Freeform bioprinting, realized by extruding ink-containing cells into supporting materials to provide physical support during printing, has fostered significant advances toward the fabrication of cell-laden soft hydrogel constructs with desired spatial control. For further advancement of freeform bioprinting, we aimed to propose a method in which the ink embedded in supporting materials gelate through a cytocompatible and rapid cascade reaction between oxidase and peroxidase. To demonstrate the feasibility of the proposed method, we extruded ink containing choline, horseradish peroxidase (HRP), and a hyaluronic acid derivative, cross-linkable by HRP-catalyzed reaction, into a supporting material containing choline oxidase and successfully obtained three-dimensional hyaluronic acid-based hydrogel constructs with good shape fidelity to blueprints. Cytocompatibility of the bioprinting method was confirmed by the comparable growth of mouse fibroblast cells, released from the printed hydrogels through degradation on cell culture dishes, with those not exposed to the printing process, and considering more than 85% viability of the enclosed cells during 10 days of culture. Owing to the presence of derivatives of the various biocompatible polymers that are cross-linkable through HRP-mediated cross-linking, our results demonstrate that the novel 3D bioprinting method has great potential in tissue engineering applications.

Micro/Nanopatterned Superhydrophobic Surfaces Fabrication for Biomolecules and Biomaterials Manipulation and Analysis

Superhydrophobic surfaces display an extraordinary repulsion to water and water-based solutions. This effect emerges from the interplay of intrinsic hydrophobicity of the surface and its morphology. These surfaces have been established for a long time and have been studied for decades. The increasing interest in recent years has been focused towards applications in many different fields and, in particular, biomedical applications. In this paper, we review the progress achieved in the last years in the fabrication of regularly patterned superhydrophobic surfaces in many different materials and their exploitation for the manipulation and characterization of biomaterial, with particular emphasis on the issues affecting the yields of the fabrication processes and the quality of the manufactured devices.

Dual Functionalization of Gelatin for Orthogonal and Dynamic Hydrogel Cross-Linking

Gelatin-based hydrogels are widely used in biomedical fields because of their abundance of bioactive motifs that support cell adhesion and matrix remodeling. Although inherently bioactive, unmodified gelatin exhibits temperature-dependent rheology and solubilizes at body temperature, making it unstable for three-dimensional (3D) cell culture. Therefore, the addition of chemically reactive motifs is required to render gelatin-based hydrogels with highly controllable cross-linking kinetics and tunable mechanical properties that are critical for 3D cell culture. This article provides a series of methods toward establishing orthogonally cross-linked gelatin-based hydrogels for dynamic 3D cell culture. In particular, we prepared dually functionalized gelatin macromers amenable for sequential, orthogonal covalent cross-linking. Central to this material platform is the synthesis of norbornene-functionalized gelatin (GelNB), which forms covalently cross-linked hydrogels via orthogonal thiol-norbornene click cross-linking. Using GelNB as the starting material, we further detail the methods for synthesizing gelatin macromers susceptible to hydroxyphenylacetic acid (HPA) dimerization (i.e., GelNB-HPA) and hydrazone bonding (i.e., GelNB-CH) for on-demand matrix stiffening. Finally, we outline the protocol for synthesizing a gelatin macromer capable of adjusting hydrogel stress relaxation via boronate ester bonding (i.e., GelNB-BA). The combination of these orthogonal chemistries affords a wide range of gelatin-based hydrogels as biomimetic matrices in tissue engineering and regenerative medicine applications.

Prediction of Viscoelastic Properties of Enzymatically Crosslinkable Tyramine-Modified Hyaluronic Acid Solutions Using a Dynamic Monte Carlo Kinetic Approach

The present study deals with the mathematical modeling of crosslinking kinetics of polymer-phenol conjugates mediated by the Horseradish Peroxidase (HRP)-hydrogen peroxide (H₂O₂) initiation system. More specifically, a dynamic Monte Carlo (MC) kinetic model is developed to quantify the effects of crosslinking conditions (i.e., polymer concentration, degree of phenol substitution and HRP and H₂O₂ concentrations) on the gelation onset time; evolution of molecular weight distribution and number and weight average molecular weights of the crosslinkable polymer chains and gel fraction. It is shown that the MC kinetic model can faithfully describe the crosslinking kinetics of a finite sample of crosslinkable polymer chains with time, providing detailed molecular information for the crosslinkable system before and after the gelation point. The MC model is validated using experimental measurements on the crosslinking of a tyramine modified Hyaluronic Acid (HA-Tyr) polymer solution reported in the literature. Based on the rubber elasticity theory and the MC results, the dynamic evolution of hydrogel viscoelastic and molecular properties (i.e., number average molecular weight between crosslinks, M_c, and hydrogel mesh size, ξ) are calculated.

Integrating biomaterials and food biopolymers for cultured meat production

Cultured meat has recently achieved mainstream prominence due to the emergence of societal and industrial interest. In contrast to animal-based production of traditional meat, the cultured meat approach entails laboratory cultivation of engineered muscle tissue. However, bioengineers have hitherto engineered tissues to fulfil biomedical endpoints, and have had limited experience in engineering muscle tissue for its post-mortem traits, which broadly govern consumer definitions of meat quality. Furthermore, existing tissue engineering approaches face fundamental challenges in technical feasibility and industrial scalability for cultured meat production. This review discusses how animal-based meat production variables influence meat properties at both the molecular and functional level, and whether current cultured meat approaches recapitulate these properties. In addition, this review considers how conventional meat producers employ exogenous biopolymer-based meat ingredients and processing techniques to mimic desirable meat properties in meat products. Finally, current biomaterial strategies for engineering muscle and adipose tissue are surveyed in the context of emerging constraints that pertain to cultured meat production, such as edibility, sustainability and scalability, and potential areas for integrating biomaterials and food biopolymer approaches to address these constraints are discussed. STATEMENT OF SIGNIFICANCE: Laboratory-grown or cultured meat has gained increasing interest from industry and the public, but currently faces significant impediment to market feasibility. This is due to fundamental knowledge gaps in producing realistic meat tissues via conventional tissue engineering approaches, as well as translational challenges in scaling up these approaches in an efficient, sustainable and high-volume manner. By defining the molecular basis for desirable meat quality attributes, such as taste and texture, and introducing the fundamental roles of food biopolymers in mimicking these properties in conventional meat products, this review aims to bridge the historically disparate fields of meat science and biomaterials engineering in order to inspire potentially synergistic strategies that address some of these challenges.

The effects of shock wave stimulation of mesenchymal stem cells on proliferation, migration, and differentiation in an injectable gelatin matrix for osteogenic regeneration

The treatment of a variety of defects in bony sites could benefit from mitogenic stimulation of osteoprogenitor cells, including endogenous bone marrow-derived mesenchymal stem cells (bMSCs), and from provision of such cells with a matrix permissive of their migration, proliferation, and osteogenic differentiation. That such MSC stimulation could result from treatment with noninvasive (extracorporeal) shock waves (ESWs), and the matrix delivered by injection could enable this therapeutic approach to be employed for applications in which preformed scaffolds and growth factor therapy are difficult to deploy. The objectives of the present study were to investigate focused ESWs for their effects on proliferation, migration, and osteogenic differentiation in an injectable gelatin (Gtn) matrix capable of undergoing covalent cross-linking in vivo. Gtn was conjugated with hydroxyphenyl propionic acid (HPA) in order to enable it to be covalently cross-linked with minute amounts of horseradish peroxidase and hydrogen peroxide. The results demonstrated that 500 shocks of 0.4-mJ/mm² energy flux density resulted in a twofold greater proliferation of bMSCs in the Gtn-HPA matrix after 14 days, compared with bMSCs grown with supplementation with platelet-derived growth factor (PDGF)-BB, a known mitogen for bMSCs. Moreover, SW treatment enhanced substantially osteogenic differentiation of bMSCs. The Gtn-HPA gel was permissive of MSC migration under the chemotactic influence of the growth factor, PDGF-BB, incorporated into and released by the gel. ESW treatment had no effect on the motility of the MSCs. The findings of the study warrant further investigation of this combined treatment modality for select bony defects.

In-situ crosslinked hydrogel based on amidated pectin/oxidized chitosan as potential wound dressing for skin repairing

Hydrogel can provide a favorable moisture environment for skin wound healing. In this study, a novel in-situ crosslinked injectable hydrogel was prepared using the water-soluble amidated pectin (AP) and oxidized chitosan (OC) through Schiff-base reaction without any chemical crosslinker. The influence of AP content on the properties of the hydrogel was systemically investigated. It showed that gelation time, pore structure, swelling capability and degradability of the hydrogel can be tuned by varying the content of amine and aldehyde groups from AP and OC. All the porous hydrogels with various AP contents (65%, 70%, and 80%) presented desirable gelation time, swelling property, high hemocompatibility and biocompatibility. Particularly, AP-OC-65 hydrogel presented superior swelling capability and better hemo- and bio-compatibility, owing to more residual amine sites in the hydrogel. Therefore, the injectable AP-OC-65 hydrogel has a greater potential for application to wound dressing or skin substitute.

Enzyme-Crosslinked Electrospun Fibrous Gelatin Hydrogel for Potential Soft Tissue Engineering

Soft tissue engineering has been seeking ways to mimic the natural extracellular microenvironment that allows cells to migrate and proliferate to regenerate new tissue. Therefore, the reconstruction of soft tissue requires a scaffold possessing the extracellular matrix (ECM)-mimicking fibrous structure and elastic property, which affect the cell functions and tissue regeneration. Herein, an effective method for fabricating nanofibrous hydrogel for soft tissue engineering is demonstrated using gelatin-hydroxyphenylpropionic acid (Gel-HPA) by electrospinning and enzymatic crosslinking. Gel-HPA fibrous hydrogel was prepared by crosslinking the electrospun fibers in ethanol-water solution with an optimized concentration of horseradish peroxidase (HRP) and H2O2. The prepared fibrous hydrogel held the soft and elastic mechanical property of hydrogels and the three-dimensional (3D) fibrous structure of electrospun fibers. It was proven that the hydrogel scaffolds were biocompatible, improving the cellular adhesion, spreading, and proliferation. Moreover, the fibrous hydrogel showed rapid biodegradability and promoted angiogenesis in vivo. Overall, this study represents a novel biomimetic approach to generate Gel-HPA fibrous hydrogel scaffolds which have excellent potential in soft tissue regeneration applications.

An injectable BMSC-laden enzyme-catalyzed crosslinking collagen-hyaluronic acid hydrogel for cartilage repair and regeneration

Articular cartilage has limited self-healing ability due to its lack of abundant nutrients and progenitor cells. In this study, an injectable hydrogel system consisting of collagen type I-tyramine (Col-TA) and hyaluronic acid-tyramine (HA-TA) was fabricated as the bone marrow mesenchymal stem cell (BMSC)-laden hydrogel system for cartilage regeneration. Next, the physiochemical properties of this hydrogel system were well characterized and optimized, including gelation time, stiffness, water absorption and degradability. Further, the proliferation and differentiation of BMSCs within the Col-HA hydrogel were evaluated, and the ability of in vivo cartilage repair was also examined in the presence of the transforming growth factor-β1 (TGF-β1). These results illustrate that this hydrogel can offer a great microenvironment for BMSC growth and cartilage differentiation both in vitro and in vivo, and the Col-HA hydrogel can serve as an ideal hydrogel for cartilage tissue regeneration.

Enzymatically crosslinked silk and silk-gelatin hydrogels with tunable gelation kinetics, mechanical properties and bioactivity for cell culture and encapsulation

Silk fibroin (SF) was enzymatically crosslinked with tyramine-substituted silk fibroin (SF-TA) or gelatin (G-TA) to fabricate hybrid hydrogels with tunable gelation kinetics, mechanical properties and bioactivity. Horseradish peroxidase (HRP)/hydrogen peroxide (H2O2) mediated crosslinking of SF in physiological buffers results in slow gelation and limited mechanical properties. Moreover, SF lacks cell attachment sequences, leading to poor cell-material interactions. These shortcomings can limit the uses of enzymatically crosslinked silk hydrogels in injectable tissue fillings, 3D bioprinting or cell microencapsulation, where rapid gelation and high bioactivity are desired. Here SF/SF-TA and SF/G-TA composite hydrogels were characterized for hydrogel properties and the influence of conjugated cyclic arginine-glycine-aspartic acid (RGD) peptide or G-TA content on bioactivity was explored. Both SF-TA and G-TA significantly increased gelation kinetics, improved mechanical properties and delayed enzymatic degradation in a concentration-dependent manner. β-Sheet formation and hydrogel stiffening were accelerated by SF-TA content but delayed by G-TA. Both cyclic RGD and G-TA significantly improved morphology and metabolic activity of human mesenchymal stem cells (hMSCs) cultured on or encapsulated in composite hydrogels. The hydrogel formulations introduced in this study provide improved control of gel formation and properties, along with biocompatible systems that can be utilized in tissue engineering and cell delivery applications.

Multifunctional Micro/Nanoscale Fibers Based on Microfluidic Spinning Technology

Superfine multifunctional micro/nanoscale fibrous materials with high surface area and ordered structure have attracted intensive attention for widespread applications in recent years. Microfluidic spinning technology (MST) has emerged as a powerful and versatile platform because of its various advantages such as high surface-area-to-volume ratio, effective heat transfer, and enhanced reaction rate. The resultant well-defined micro/nanoscale fibers exhibit controllable compositions, advanced structures, and new physical/chemical properties. The latest developments and achievements in microfluidic spun fiber materials are summarized in terms of the underlying preparation principles, geometric configurations, and functionalization. Variously architected structures and shapes by MST, including cylindrical, grooved, flat, anisotropic, hollow, core-shell, Janus, heterogeneous, helical, and knotted fibers, are emphasized. In particular, fiber-spinning chemistry in MST for achieving functionalization of fiber materials by in situ chemical reactions inside fibers is introduced. Additionally, the applications of the fabricated functional fibers are highlighted in sensors, microactuators, photoelectric devices, flexible electronics, tissue engineering, drug delivery, and water collection. Finally, recent progress, challenges, and future perspectives are discussed.

Experimental study on preparation of coaxial drug-loaded tissue-engineered bone scaffold by 3D printing technology

In order to combine the drug with the tissue-engineered bone scaffold and make the drugs on the scaffolds stable to achieve sustained-release stepwise function, a new method for preparing coaxial drug-loaded tissue engineering bone scaffolds using coaxial three-dimensional printing technology is proposed, in which inner layer material can carry drugs and the outer material can adjust the drug sustained-release rate. The coupling mechanism of both shape control and property control in the process of coaxial three-dimensional printing micro-structural unit is presented. Design-Expert software is introduced for experimental design. The influences of extrusion speed, filling speed, and delamination height on the forming quality are analyzed, and a coaxial gradient composite scaffold model with controllable micro-structure is established. The macro-structure, mechanical properties, in vitro degradation rate, and drug release rate of the scaffolds were analyzed. The experimental results show that the proposed forming technology and process parameter optimization can effectively improve the forming quality of the coaxial scaffold. At the same time, this design of the coaxial structure can effectively slow down the degradation rate of the scaffold and enables stable and long-time drug release. Furthermore, the presented method provides a new technical approach for the further implementation of implantable drug delivery systems for the effective treatment of bone tuberculosis.

Development and characterization of a suturable biomimetic patch for cardiac applications

3D scaffolds used to repair damaged tissues should be able to mimic both composition and functions of natural extracellular matrix, which is mainly composed of polysaccharides and proteins. In our previous research new biomimetic sponges, based on blends of alginate with gelatin, were produced and characterized for myocardial tissue engineering applications. It was observed that these scaffolds can potentially function as a promising cardiac extracellular matrix substitute, but a reinforcement is required to improve their suturing properties. Aim of the present work was the development of a suturable biomimetic patch by the inclusion of a synthetic mesh within an alginate/gelatin scaffold. The mesh, produced by dry spinning, was made of eight superimposed layers of polycaprolactone microfibers, each one rotated of 45° with respect to the adjacent one. Reinforced scaffolds were obtained through the use of a mold, specially designed to place the fibrous mesh exactly in the center of the sponge. Both the reinforcement mesh and the reinforced scaffold were characterized. A perfect integration between the mesh and the sponge was observed. The fibrous mesh reduced the capacity of the sponge to absorb water, but the degree of hydrophilicity of the material was still comparable with that of natural cardiac tissue. The reinforced system showed a suitable stability in aqueous environment and it resulted much more resistant to suturing than not reinforced scaffold and even than human arteries. Polycaprolactone mesh was not cytotoxic and the reinforced scaffold was able to support cardiomyocytes adhesion and proliferation. Overall, the obtained results confirmed that the choice to modify the alginate/gelatin sponges through the insertion of an appropriate reinforcement system turned out to be correct in view of their potential use in myocardial tissue engineering.

Silk Hydrogels Crosslinked by the Fenton Reaction

Here, the Fenton reaction is used to prepare silk hydrogels through oxidation of tyrosine residues in silk fibroin, leading to dityrosine crosslinking. At pH 5.7, gelation occurs rapidly within 30 s, and the resultant opaque gels show soft properties with a storage modulus of ≈100 Pa. The addition of ascorbic acid to the Fenton reaction increases the dityrosine bonds in the hydrogels but has little effect on the rheological or mechanical properties. The results indicate that Fe(III) ions significantly interacted with silk fibroin during the Fenton reaction, most likely binding to sites such as tyrosine, glutamate, and aspartate residues, triggering the formation of β-sheet structures that may impede dityrosine bond formation due to steric hindrance. The use of an iron chelator or the operation of the Fenton reaction at pH 9.2 enables control over the interaction of Fe(III) ions with silk fibroin, achieving a hydrogel with improved optical properties and enhanced dityrosine bond formation. Hydrogels prepared by the Fenton reaction are cytocompatible as L929 mouse fibroblasts remain viable and are proliferative when seeded on the hydrogels. The results offer a useful approach to generate chemically crosslinked silk fibroin hydrogels without the use of enzyme-catalyzed reactions for biomedical applications.

Response of soil bacterial community to bioaugmentation with a plant residue-immobilized bacterial consortium for crude oil removal

Both the crude oil removal efficiency of the Eichhornia crassipes dried straw-immobilized bacterial consortium and shifts in soil bacterial community in response to the bioaugmentation strategy were unmasked in this study. After 30 days of bioremediation, total petroleum hydrocarbon in soil was determined and immobilized consortium showed a removal percentage (51.7%) better than either Eichhornia crassipes dried powder (37.0%) or bacteria solution (36.0%) alone. Bacterial community and soil properties analyses demonstrated that the relative abundances of Cytophagales and Rhizobiales increased with increasing total organic carbon and total nitrogen contents because of the addition of Eichhornia crassipes dried powder. The genus Burkholderia which may play a key role in hydrocarbon degradation among the inoculated bacterial consortium proliferated when immobilized on the Eichhornia crassipes dried powder. Such a cell immobilization technology using plant residue materials as carriers helps to improve soil fertility and mitigate competition between indigenous and inoculated microorganisms for nutrients, which offers a promising way to enhance the removal of crude oil from contaminated soils.

In Situ Cross-linking Hydrogel as a Vehicle for Retinal Progenitor Cell Transplantation

One of the current limitations of retinal transplantation of stem cells as well as other cell types is the dispersion of cells from the injection site (including loss of cells into the vitreous chamber) and low survival after transplantation. Gelatin-hydroxyphenyl propionic acid (Gtn-HPA) conjugate is a biodegradable polymer that can undergo covalent cross-linking in situ, allowing for injection of incorporated cells through a small caliber needle followed by gel formation in vivo. We tested the hypothesis that Gtn-HPA hydrogel supports survival and integration of retinal progenitor cells (RPCs) post-transplantation. In vitro compatibility and in vivo graft survival were assessed by mixing an equal volume of Gtn-HPA conjugate and RPC suspension and triggering enzyme-mediated gelation, using minute amounts of horseradish peroxidase and peroxide. Immunocytochemistry showed >80% survival of cells and minimal apoptosis for cells incorporated into Gtn-HPA, equivalent to controls grown on fibronectin-coated flasks. RPCs undergoing mitosis were seen within the three-dimensional Gtn-HPA hydrogel, but the percentage of Ki-67-positive cells was lower compared with the monolayer controls. For in vivo studies, gel-cell mixture or cell suspension in saline was trans-sclerally injected into the left eye of female Long Evans rats immunosuppressed with cyclosporine A. Grafts survived at the 1 week time point of the study, with Gtn-HPA-delivered grafts showing less inflammatory response demonstrated by anti-leukocyte staining. More eyes in the gel-cell mixture group showed surviving cells in the subretinal space compared with saline-delivered controls, while the number of cells surviving per graft was not significantly different between the two groups. This work demonstrates an injectable in situ cross-linking hydrogel as a potential vehicle for stem cell delivery in the retina.

Fabrication of Kidney Proximal Tubule Grafts Using Biofunctionalized Electrospun Polymer Scaffolds

The increasing prevalence of end-stage renal disease and persistent shortage of donor organs call for alternative therapies for kidney patients. Dialysis remains an inferior treatment as clearance of large and protein-bound waste products depends on active tubular secretion. Biofabricated tissues could make a valuable contribution, but kidneys are highly intricate and multifunctional organs. Depending on the therapeutic objective, suitable cell sources and scaffolds must be selected. This study provides a proof-of-concept for stand-alone kidney tubule grafts with suitable mechanical properties for future implantation purposes. Porous tubular nanofiber scaffolds are fabricated by electrospinning 12%, 16%, and 20% poly-ε-caprolactone (PCL) v/w (chloroform and dimethylformamide, 1:3) around 0.7 mm needle templates. The resulting scaffolds consist of 92%, 69%, and 54% nanofibers compared to microfibers, respectively. After biofunctionalization with L-3,4-dihydroxyphenylalanine and collagen IV, 10 × 106 proximal tubule cells per mL are injected and cultured until experimental readout. A human-derived cell model can bridge all fiber-to-fiber distances to form a monolayer, whereas small-sized murine cells form monolayers on dense nanofiber meshes only. Fabricated constructs remain viable for at least 3 weeks and maintain functionality as shown by inhibitor-sensitive transport activity, which suggests clearance capacity for both negatively and positively charged solutes.

Bioactive hydrogels for bone regeneration

Bone self-healing is limited and generally requires external intervention to augment bone repair and regeneration. While traditional methods for repairing bone defects such as autografts, allografts, and xenografts have been widely used, they all have corresponding disadvantages, thus limiting their clinical use. Despite the development of a variety of biomaterials, including metal implants, calcium phosphate cements (CPC), hydroxyapatite, etc., the desired therapeutic effect is not fully achieved. Currently, polymeric scaffolds, particularly hydrogels, are of interest and their unique configurations and tunable physicochemical properties have been extensively studied. This review will focus on the applications of various cutting-edge bioactive hydrogels systems in bone regeneration, as well as their advantages and limitations. We will examine the composition and defects of the bone, discuss the current biomaterials for bone regeneration, and classify recently developed polymeric materials for hydrogel synthesis. We will also elaborate on the properties of desirable hydrogels as well as the fabrication techniques and different delivery strategies. Finally, the existing challenges, considerations, and the future prospective of hydrogels in bone regeneration will be outlined.

Design Principles and Multifunctionality in Cell Encapsulation Systems for Tissue Regeneration

Cell encapsulation systems are being increasingly applied as multifunctional strategies to regenerate tissues. Lessons afforded with encapsulation systems aiming to treat endocrine diseases seem to be highly valuable for the tissue engineering and regenerative medicine (TERM) systems of today, in which tissue regeneration and biomaterial integration are key components. Innumerous multifunctional systems for cell compartmentalization are being proposed to meet the specific needs required in the TERM field. Herein is reviewed the variable geometries proposed to produce cell encapsulation strategies toward tissue regeneration, including spherical and fiber-shaped systems, and other complex shapes and arrangements that better mimic the highly hierarchical organization of native tissues. The application of such principles in the TERM field brings new possibilities for the development of highly complex systems, which holds tremendous promise for tissue regeneration. The complex systems aim to recreate adequate environmental signals found in native tissue (in particular during the regenerative process) to control the cellular outcome, and conferring multifunctional properties, namely the incorporation of bioactive molecules and the ability to create smart and adaptative systems in response to different stimuli. The new multifunctional properties of such systems that are being employed to fulfill the requirements of the TERM field are also discussed.

Peroxidase-catalyzed microextrusion bioprinting of cell-laden hydrogel constructs in vaporized ppm-level hydrogen peroxide

Hydrogels were prepared by contacting air containing 10-50 ppm H₂O₂ with an aqueous solution containing polymer(s) possessing phenolic hydroxyl (Ph) moieties (polymer-Ph) and horseradish peroxidase (HRP). In this system, HRP catalyzes cross-linking of the Ph moieties by consuming H₂O₂ diffused from the air. The hydrogelation rate and mechanical properties of the resultant hydrogels can be tuned by controlling the H₂O₂ concentration in air, the exposure time of the air containing H₂O₂ to the solution containing polymer-Phs and HRP, and the HRP concentration. The shortest hydrogelation time of the solution stirred in air containing 16 ppm H₂O₂ was 6 s. Based on these findings, this hydrogelation system was applied to microextrusion bioprinting, in which bioink containing polymer-Phs, HRP, and cells were extruded into air containing H₂O₂. The superior cytocompatibility of the bioprinting method was confirmed by more than 90% viability, migration, and the spreading of mouse fibroblast 10T1/2 cells enclosed in the bioprinted hydrogels composed of derivatives of hyaluronic acid and gelatin, both possessing Ph moieties. These results demonstrate the great potency of HRP-catalyzed hydrogelation consuming H₂O₂ supplied in surrounding air for various biomedical applications, especially bioprinting.

Gelatin-Based Photocurable Hydrogels for Corneal Wound Repair

In this study, an injectable, photocurable gelatin system, consisting of acrylated gelatin and thiolated gelatin, with tunable mechanical, biodegradation, and biological properties was used as a potential cell-supportive scaffold for the repair of focal corneal wounds. The mechanical property of hydrogels can be readily modified (postcure shear modulus of between 0.3 and 22 kPa) by varying the ratio of acrylate to thiol groups, photointensity, and solid content, and the biodegradation times also varied with the change of solid content. More importantly, the generated hydrogels exhibited excellent cell viability in both cell seeding and cell encapsulation experiments. Furthermore, the hydrogels were found to be biocompatible with rabbit cornea and aided the regeneration of a new tissue under a focal corneal wound (exhibiting epithelial wound coverage in <3d), and ultraviolet irradiation did not have any obvious harmful effect on the cornea and posterior eye segment tissues. Along with their injectability and tunable mechanical properties, the photocurable thiol-acrylate hydrogels showed promise as corneal substitutes or substrates to construct a new corneal tissue.

Biomimetic and enzyme-responsive dynamic hydrogels for studying cell-matrix interactions in pancreatic ductal adenocarcinoma

The tumor microenvironment (TME) governs all aspects of cancer progression and in vitro 3D cell culture platforms are increasingly developed to emulate the interactions between components of the stromal tissues and cancer cells. However, conventional cell culture platforms are inadequate in recapitulating the TME, which has complex compositions and dynamically changing matrix mechanics. In this study, we developed a dynamic gelatin-hyaluronic acid hybrid hydrogel system through integrating modular thiol-norbornene photopolymerization and enzyme-triggered on-demand matrix stiffening. In particular, gelatin was dually modified with norbornene and 4-hydroxyphenylacetic acid to render this bioactive protein photo-crosslinkable (through thiol-norbornene gelation) and responsive to tyrosinase-triggered on-demand stiffening (through HPA dimerization). In addition to the modified gelatin that provides basic cell adhesive motifs and protease cleavable sequences, hyaluronic acid (HA), an essential tumor matrix, was modularly and covalently incorporated into the cell-laden gel network. We systematically characterized macromer modification, gel crosslinking, as well as enzyme-triggered stiffening and degradation. We also evaluated the influence of matrix composition and dynamic stiffening on pancreatic ductal adenocarcinoma (PDAC) cell fate in 3D. We found that either HA-containing matrix or a dynamically stiffened microenvironment inhibited PDAC cell growth. Interestingly, these two factors synergistically induced cell phenotypic changes that resembled cell migration and/or invasion in 3D. Additional mRNA expression array analyses revealed changes unique to the presence of HA, to a stiffened microenvironment, or to the combination of both. Finally, we presented immunostaining and mRNA expression data to demonstrate that these irregular PDAC cell phenotypes were a result of matrix-induced epithelial-mesenchymal transition (EMT).

Creating a 3D microenvironment for monocyte cultivation: ECM-mimicking hydrogels based on gelatine and hyaluronic acid derivatives

Macrophages play a critical role in the initial response to foreign materials in the body. As most biomaterial-based implantable devices would be treated as a foreign body by the immune system, there is a need for systems that can establish a favourable interaction between the implanted biomaterial and the host. Herein, we describe such a system that can be used as an ECM-like microenvironment for macrophage polarization. The hydrogel system was designed to provide a co-crosslinkable microenvironment containing both protein and glycosaminoglycan components, a hydroxyphenyl derivative of gelatine (GTN-HPA) and tyraminated hyaluronic acid (HA-TA). Both polymers can undergo a crosslinking reaction between polymer chains via the same polymerisation initiation system where the polymer network is formed by crosslinks between phenols in GTN-HPA and HA-TA. The mechanical properties and swelling of the hydrogel can be easily controlled as a function of the crosslinking mode and by the ratio of GTN-HPA and HA-TA compounds used. THP-1 monocytes were successfully encapsulated in the gels and cultured for up to 28 days. Cells exhibited higher metabolic activity when encapsulated in softer hydrogels (E ≈ 10 kPa) compared to stiffer (E ≈ 20 kPa) material in which monocytes tended to form large clusters. Encapsulation of monocytes in the material with HA-TA content enhanced the expression of macrophage-related genes. We demonstrated a co-crosslinkable GTN-HPA and HA-TA matrix microenvironment that is suitable for in vitro micro tissue model applications.

Horseradish peroxidase-catalyzed hydrogelation for biomedical applications

Hydrogels catalyzed by horseradish peroxidase (HRP) serve as an efficient and effective platform for biomedical applications due to their mild reaction conditions for cells, fast and adjustable gelation rate in physiological conditions, and an abundance of substrates as water-soluble biocompatible polymers.

Fast-forming BMSC-encapsulating hydrogels through bioorthogonal reaction for osteogenic differentiation

An injectable in situ fast-forming hydrogel was fabricated to encapsulate BMSCs for osteogenic differentiation through the inverse electron demand Diels–Alder click reaction between trans-cyclooctene-modified PEG and tetrazine-modified hyaluronic acid.

Differentiation potential of human adipose stem cells bioprinted with hyaluronic acid/gelatin-based bioink through microextrusion and visible light-initiated crosslinking

Bioprinting has a great potential to fabricate three-dimensional (3D) functional tissues and organs. In particular, the technique enables fabrication of 3D constructs containing stem cells while maintaining cell proliferation and differentiation abilities, which is believed to be promising in the fields of tissue engineering and regenerative medicine. We aimed to demonstrate the utility of the bioprinting technique to create hydrogel constructs consisting of hyaluronic acid (HA) and gelatin derivatives through irradiation by visible light to fabricate 3D constructs containing human adipose stem cells (hADSCs). The hydrogel was obtained from a solution of HA and gelatin derivatives possessing phenolic hydroxyl moieties in the presence of ruthenium(II) tris-bipyridyl dication and sodium ammonium persulfate. hADSCs enclosed in the bioprinted hydrogel construct elongated and proliferated in the hydrogel. In addition, their differentiation potential was confirmed by examining the expression of pluripotency marker genes and cell surface marker proteins, and differentiation to adipocytes in adipogenic differentiation medium. Our results demonstrate the great potential of the bioprinting method and the resultant hADSC-laden HA/gelatin constructs for applications in tissue engineering and regenerative medicine.

Fabrication of elastomeric silk fibers

Methods to generate fibers from hydrogels, with control over mechanical properties, fiber diameter, and crystallinity, while retaining cytocompatibility and degradability, would expand options for biomaterials. Here, we exploited features of silk fibroin protein for the formation of tunable silk hydrogel fibers. The biological, chemical, and morphological features inherent to silk were combined with elastomeric properties gained through enzymatic crosslinking of the protein. Postprocessing via methanol and autoclaving provided tunable control of fiber features. Mechanical, optical, and chemical analyses demonstrated control of fiber properties by exploiting the physical cross-links, and generating double network hydrogels consisting of chemical and physical cross-links. Structure and chemical analyses revealed crystallinity from 30 to 50%, modulus from 0.5 to 4 MPa, and ultimate strength 1-5 MPa depending on the processing method. Fabrication and postprocessing combined provided fibers with extensibility from 100 to 400% ultimate strain. Fibers strained to 100% exhibited fourth order birefringence, revealing macroscopic orientation driven by chain mobility. The physical cross-links were influenced in part by the drying rate of fabricated materials, where bound water, packing density, and microstructural homogeneity influenced cross-linking efficiency. The ability to generate robust and versatile hydrogel microfibers is desirable for bottom-up assembly of biological tissues and for broader biomaterial applications.

Macroporous Hydrogel Scaffolds for Three-Dimensional Cell Culture and Tissue Engineering

Hydrogels have been promising candidate scaffolds for cell delivery and tissue engineering due to their tissue-like physical properties and capability for homogeneous cell loading. However, the encapsulated cells are generally entrapped and constrained in the submicron- or nanosized gel networks, seriously limiting cell growth and tissue formation. Meanwhile, the spatially confined settlement inhibits attachment and spreading of anchorage-dependent cells, leading to their apoptosis. In recent years, macroporous hydrogels have attracted increasing attention in use as cell delivery vehicles and tissue engineering scaffolds. The introduction of macropores within gel scaffolds not only improves their permeability for better nutrient transport but also creates space/interface for cell adhesion, proliferation, and extracellular matrix deposition. Herein, we will first review the development of macroporous gel scaffolds and outline the impact of macropores on cell behaviors. In the first part, the advantages and challenges of hydrogels as three-dimensional (3D) cell culture scaffolds will be described. In the second part, the fabrication of various macroporous hydrogels will be presented. Third, the enhancement of cell activities within macroporous gel scaffolds will be discussed. Finally, several crucial factors that are envisaged to propel the improvement of macroporous gel scaffolds are proposed for 3D cell culture and tissue engineering.

Impact of immobilizing of low molecular weight hyaluronic acid within gelatin-based hydrogel through enzymatic reaction on behavior of enclosed endothelial cells

The hydrogels having the ability to promote migration and morphogenesis of endothelial cells (ECs) are useful for fabricating vascularized dense tissues in vitro. The present study explores the immobilization of low molecular weight hyaluronic acid (LMWHA) derivative within gelatin-based hydrogel to stimulate migration of ECs. The LMWHA derivative possessing phenolic hydroxyl moieties (LMWHA-Ph) was bound to gelatin-based derivative hydrogel through the horseradish peroxidase-catalyzed reaction. The motility of ECs was analyzed by scratch migration assay and microparticle-based cell migration assay. The incorporated LMWHA-Ph molecules within hydrogel was found to be preserved stably through covalent bonds during incubation. The free and immobilized LMWHA-Ph did not lose an inherent stimulatory effect on human umbilical vein endothelial cells (HUVECs). The immobilized LMWHA-Ph within gelatin-based hydrogel induced the high motility of HUVECs, accompanied by robust cytoskeleton extension, and cell subpopulation expressing CD44 cell receptor. In the presence of immobilized LMWHA-Ph, the migration distance and the number of existing HUVECs were demonstrated to be encouraged in dose-dependent and time-dependent manners. Based on the results obtained in this work, it was concluded that the enzymatic immobilization of LMWHA-Ph within gelatin-based hydrogel represents a promising approach to promote ECs' motility and further exploitation for vascular tissue engineering applications.

Encapsulating chromogenic reaction substrates with porous hydrogel scaffolds onto arrayed capillary tubes toward a visual and high-throughput colorimetric strategy for rapid occult blood tests

A porous hydrogel composite was used to encapsulate the chromogenic reaction substrates onto capillary tubes arrayed for visual and high-throughput occult blood test.

Hydrogel-Based Cell Therapies for Kidney Regeneration: Current Trends in Biofabrication and In Vivo Repair

Facing the problems of limited renal regeneration capacity and the persistent shortage of donor kidneys, dialysis remains the only treatment option for many end-stage renal disease patients. Unfortunately, dialysis is only a medium-term solution because large and protein-bound uremic solutes are not efficiently cleared from the body and lead to disease progression over time. Current strategies for improved renal replacement therapies (RRTs) range from whole organ engineering to biofabrication of renal assist devices and biological injectables for in vivo regeneration. Notably, all approaches coincide with the incorporation of cellular components and biomimetic micro-environments. Concerning the latter, hydrogels form promising materials as scaffolds and cell carrier systems due to the demonstrated biocompatibility of most natural hydrogels, tunable biochemical and mechanical properties, and various application possibilities. In this review, the potential of hydrogel-based cell therapies for kidney regeneration is discussed. First, we provide an overview of current trends in the development of RRTs and in vivo regeneration options, before examining the possible roles of hydrogels within these fields. We discuss major application-specific hydrogel design criteria and, subsequently, assess the potential of emergent biofabrication technologies, such as micromolding, microfluidics and electrodeposition for the development of new RRTs and injectable stem cell therapies.

Inkjetting Plus Peroxidase-Mediated Hydrogelation Produces Cell-Laden, Cell-Sized Particles with Suitable Characters for Individual Applications

The authors report a method to prepare cell-laden, cell-sized microparticles from various materials suitable for individual applications. The method includes a piezoelectric inkjetting technology and a horseradish peroxidase (HRP)-catalyzed crosslinking reaction. The piezoelectric inkjetting technology enables production of cell-laden, cell-sized (20-60 μm) droplets from a polymer aqueous solution. The HRP-catalyzed crosslinking of the polymer in the ejected solution enables production of spherical microparticles from various materials. Superior cytocompatibility of the microencapsulation method is confirmed from the viability and growth profiles of normal murine mammary gland epithelial cells.