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Xie C, Chen Y, Wang L, Liao K, Xue B, Han Y, Li L, Jiang Q. Recent research of peptide-based hydrogel in nervous regeneration. Bioact Mater 2024; 40:503-523. [PMID: 39040568 PMCID: PMC11261279 DOI: 10.1016/j.bioactmat.2024.06.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2024] [Revised: 06/02/2024] [Accepted: 06/07/2024] [Indexed: 07/24/2024] Open
Abstract
Neurological disorders exert significantly affect the quality of life for patients, necessitating effective strategies for nerve regeneration. Both traditional autologous nerve transplantation and emerging therapeutic approaches encounter scientific challenges due to the complex nature of the nervous system and the unsuitability of the surrounding environment for cell transplantation. Tissue engineering techniques offer a promising path for neurotherapy. Successful neural tissue engineering relies on modulating cell differentiation behavior and tissue repair by developing biomaterials that mimic the natural extracellular matrix (ECM) and establish a three-dimensional microenvironment. Peptide-based hydrogels have emerged as a potent option among these biomaterials due to their ability to replicate the structure and complexity of the ECM. This review aims to explore the diverse range of peptide-based hydrogels used in nerve regeneration with a specific focus on dipeptide hydrogels, tripeptide hydrogels, oligopeptide hydrogels, multidomain peptides (MDPs), and amphiphilic peptide hydrogels (PAs). Peptide-based hydrogels offer numerous advantages, including biocompatibility, structural diversity, adjustable mechanical properties, and degradation without adverse effects. Notably, hydrogels formed from self-assembled polypeptide nanofibers, derived from amino acids, show promising potential in engineering neural tissues, outperforming conventional materials like alginate, poly(ε-caprolactone), and polyaniline. Additionally, the simple design and cost-effectiveness of dipeptide-based hydrogels have enabled the creation of various functional supramolecular structures, with significant implications for nervous system regeneration. These hydrogels are expected to play a crucial role in future neural tissue engineering research. This review aims to highlight the benefits and potential applications of peptide-based hydrogels, contributing to the advancement of neural tissue engineering.
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Affiliation(s)
- Chunmei Xie
- State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, China
| | - Yueyang Chen
- State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, China
| | - Lang Wang
- State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, China
| | - Kin Liao
- Advanced Digital and Additive Manufacturing Center, Khalifa University of Science and Technology, Po Box 127788, Abu Dhabi, United Arab Emirates
| | - Bin Xue
- National Laboratory of Solid State Microstructures, Department of Physics, Nanjing University, Nanjing, China
| | - Yulong Han
- State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, China
| | - Lan Li
- State Key Laboratory of Pharmaceutical Biotechnology, Division of Sports Medicine and Adult Reconstructive Surgery, Department of Orthopedic Surgery, Drum Tower Hospital Affiliated to Medical School of Nanjing University, Nanjing, China
- Jiangsu Engineering Research Center for 3D Bioprinting, Nanjing, China
- Institute of Medical 3D Printing, Nanjing University, Nanjing, China
| | - Qing Jiang
- State Key Laboratory of Pharmaceutical Biotechnology, Division of Sports Medicine and Adult Reconstructive Surgery, Department of Orthopedic Surgery, Drum Tower Hospital Affiliated to Medical School of Nanjing University, Nanjing, China
- Jiangsu Engineering Research Center for 3D Bioprinting, Nanjing, China
- Institute of Medical 3D Printing, Nanjing University, Nanjing, China
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Chen T, Jiang Y, Huang JP, Wang J, Wang ZK, Ding PH. Essential elements for spatiotemporal delivery of growth factors within bio-scaffolds: A comprehensive strategy for enhanced tissue regeneration. J Control Release 2024; 368:97-114. [PMID: 38355052 DOI: 10.1016/j.jconrel.2024.02.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2023] [Revised: 01/28/2024] [Accepted: 02/07/2024] [Indexed: 02/16/2024]
Abstract
The precise delivery of growth factors (GFs) in regenerative medicine is crucial for effective tissue regeneration and wound repair. However, challenges in achieving controlled release, such as limited half-life, potential overdosing risks, and delivery control complexities, currently hinder their clinical implementation. Despite the plethora of studies endeavoring to accomplish effective loading and gradual release of GFs through diverse delivery methods, the nuanced control of spatial and temporal delivery still needs to be elucidated. In response to this pressing clinical imperative, our review predominantly focuses on explaining the prevalent strategies employed for spatiotemporal delivery of GFs over the past five years. This review will systematically summarize critical aspects of spatiotemporal GFs delivery, including judicious bio-scaffold selection, innovative loading techniques, optimization of GFs activity retention, and stimulating responsive release mechanisms. It aims to identify the persisting challenges in spatiotemporal GFs delivery strategies and offer an insightful outlook on their future development. The ultimate objective is to provide an invaluable reference for advancing regenerative medicine and tissue engineering applications.
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Affiliation(s)
- Tan Chen
- Stomatology Hospital, School of Stomatology, Zhejiang University School of Medicine, Zhejiang Provincial Clinical Research Center for Oral Diseases, Key Laboratory of Oral Biomedical Research of Zhejiang Province, Cancer Center of Zhejiang University, Hangzhou 310000, China
| | - Yao Jiang
- Stomatology Hospital, School of Stomatology, Zhejiang University School of Medicine, Zhejiang Provincial Clinical Research Center for Oral Diseases, Key Laboratory of Oral Biomedical Research of Zhejiang Province, Cancer Center of Zhejiang University, Hangzhou 310000, China
| | - Jia-Ping Huang
- Stomatology Hospital, School of Stomatology, Zhejiang University School of Medicine, Zhejiang Provincial Clinical Research Center for Oral Diseases, Key Laboratory of Oral Biomedical Research of Zhejiang Province, Cancer Center of Zhejiang University, Hangzhou 310000, China
| | - Jing Wang
- Stomatology Hospital, School of Stomatology, Zhejiang University School of Medicine, Zhejiang Provincial Clinical Research Center for Oral Diseases, Key Laboratory of Oral Biomedical Research of Zhejiang Province, Cancer Center of Zhejiang University, Hangzhou 310000, China
| | - Zheng-Ke Wang
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310058, China.
| | - Pei-Hui Ding
- Stomatology Hospital, School of Stomatology, Zhejiang University School of Medicine, Zhejiang Provincial Clinical Research Center for Oral Diseases, Key Laboratory of Oral Biomedical Research of Zhejiang Province, Cancer Center of Zhejiang University, Hangzhou 310000, China.
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Liu J, Mouradian MM. Pathogenetic Contributions and Therapeutic Implications of Transglutaminase 2 in Neurodegenerative Diseases. Int J Mol Sci 2024; 25:2364. [PMID: 38397040 PMCID: PMC10888553 DOI: 10.3390/ijms25042364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2023] [Revised: 02/07/2024] [Accepted: 02/13/2024] [Indexed: 02/25/2024] Open
Abstract
Neurodegenerative diseases encompass a heterogeneous group of disorders that afflict millions of people worldwide. Characteristic protein aggregates are histopathological hallmark features of these disorders, including Amyloid β (Aβ)-containing plaques and tau-containing neurofibrillary tangles in Alzheimer's disease, α-Synuclein (α-Syn)-containing Lewy bodies and Lewy neurites in Parkinson's disease and dementia with Lewy bodies, and mutant huntingtin (mHTT) in nuclear inclusions in Huntington's disease. These various aggregates are found in specific brain regions that are impacted by neurodegeneration and associated with clinical manifestations. Transglutaminase (TG2) (also known as tissue transglutaminase) is the most ubiquitously expressed member of the transglutaminase family with protein crosslinking activity. To date, Aβ, tau, α-Syn, and mHTT have been determined to be substrates of TG2, leading to their aggregation and implicating the involvement of TG2 in several pathophysiological events in neurodegenerative disorders. In this review, we summarize the biochemistry and physiologic functions of TG2 and describe recent advances in the pathogenetic role of TG2 in these diseases. We also review TG2 inhibitors tested in clinical trials and discuss recent TG2-targeting approaches, which offer new perspectives for the design of future highly potent and selective drugs with improved brain delivery as a disease-modifying treatment for neurodegenerative disorders.
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Affiliation(s)
| | - M. Maral Mouradian
- RWJMS Institute for Neurological Therapeutics and Department of Neurology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA;
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Eskandani M, Derakhshankhah H, Zare S, Jahanban-Esfahlan R, Jaymand M. Enzymatically crosslinked magnetic starch-grafted poly(tannic acid) hydrogel for "smart" cancer treatment: An in vitro chemo/hyperthermia therapy study. Int J Biol Macromol 2023; 253:127214. [PMID: 37797855 DOI: 10.1016/j.ijbiomac.2023.127214] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2023] [Revised: 09/24/2023] [Accepted: 10/01/2023] [Indexed: 10/07/2023]
Abstract
A novel strategy was designed and developed based of horseradish peroxidase (HRP)-mediated crosslinking of tyramine-functionalized starch (Tyr-St), tannic acid (TA) and phenolated-magnetic nanoparticles (Fe3O4-PhOH NPs), and simultaneous loading of doxorubicin hydrochloride (Dox) to afford a pH-responsive magnetic hydrogel-based drug delivery system (DDS) for synergistic in vitro chemo/hyperthermia therapy of human breast cancer (MCF-7) cells. The developed St-g-PTA/Fe3O4 magnetic hydrogel showed porous micro-structure with saturation magnetization (δs) value of 19.2 emu g-1 for Fe3O4 NPs content of ∼7.4 wt%. The pore sizes of the St-g-PTA/Fe3O4 hydrogel was calculated to be 2400 ± 200 nm-2. In vitro drug release experiments exhibited the developed DDS has pH-dependent drug release behavior, while at physiological pH (7.4) released only 30 % of the loaded drug after 100 h. Human serum albumin (HSA) adsorption capacities of the synthesized St/Fe3O4 and St-g-PTA/Fe3O4 magnetic hydrogels were obtained as 86 ± 2.2 and 77 ± 1.9 μgmg-1, respectively. The well-known MTT-assay approved the cytocompatibility of the developed St-g-PTA/Fe3O4 hydrogel, while the Dox-loaded system exhibited higher anti-cancer activity than those of the free Dox as verified by MTT-assay, and optical as well as florescent microscopies imaging. The synergistic chemo/hyperthermia therapy effect was also verified for the developed St-g-PTA/Fe3O4-Dox via hot water approach.
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Affiliation(s)
- Morteza Eskandani
- Research Center for Pharmaceutical Nanotechnology, Biomedicine Institute, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Hossein Derakhshankhah
- Pharmaceutical Sciences Research Center, Health Institute, Kermanshah University of Medical Sciences, Kermanshah, Iran
| | - Soheila Zare
- Student Research Committee, Kermanshah University of Medical Sciences, Kermanshah, Iran
| | - Rana Jahanban-Esfahlan
- Department of Medical Biotechnology, School of Advanced Medical Sciences, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Mehdi Jaymand
- Nano Drug Delivery Research Center, Health Technology Institute, Kermanshah University of Medical Sciences, Kermanshah, Iran.
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Li Z, Lu F, Liu Y. A Review of the Mechanism, Properties, and Applications of Hydrogels Prepared by Enzymatic Cross-linking. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2023. [PMID: 37390351 DOI: 10.1021/acs.jafc.3c01162] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/02/2023]
Abstract
Hydrogels, as biological materials, are widely used in food, tissue engineering, and biomedical applications. Nevertheless, many issues remain in the preparation of hydrogels by physical and chemical methods, such as low bioaffinity, weak mechanical properties, and unstable structures, which also limit their applications in other fields. However, the enzymatic cross-linking method has the advantages of high catalytic efficiency, mild reaction conditions, and the presence of nontoxic substances. In this review, we evaluated the chemical, physical, and biological methods of preparing hydrogels and introduced three common cross-linking enzymes and their principles for preparing hydrogels. This review introduced the applications and properties of hydrogels prepared by the enzymatic method and also provided some suggestions regarding the current situation and future development of hydrogels prepared by enzymatic cross-linking.
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Affiliation(s)
- Ziyuan Li
- Key Laboratory of Industrial Fermentation Microbiology, Ministry of Education, Tianjin Key Laboratory of Industrial Microbiology, The College of Biotechnology, Tianjin University of Science and Technology, Tianjin 300457, P. R. China
| | - Fuping Lu
- Key Laboratory of Industrial Fermentation Microbiology, Ministry of Education, Tianjin Key Laboratory of Industrial Microbiology, The College of Biotechnology, Tianjin University of Science and Technology, Tianjin 300457, P. R. China
| | - Yihan Liu
- Key Laboratory of Industrial Fermentation Microbiology, Ministry of Education, Tianjin Key Laboratory of Industrial Microbiology, The College of Biotechnology, Tianjin University of Science and Technology, Tianjin 300457, P. R. China
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Wu J, Shaidani S, Theodossiou SK, Hartzell EJ, Kaplan DL. Localized, on-demand, sustained drug delivery from biopolymer-based materials. Expert Opin Drug Deliv 2022; 19:1317-1335. [PMID: 35930000 PMCID: PMC9617770 DOI: 10.1080/17425247.2022.2110582] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2022] [Accepted: 08/03/2022] [Indexed: 11/04/2022]
Abstract
INTRODUCTION Local drug delivery facilitiates higher concentrations of drug molecules at or near the treatment site to enhance treatment efficiency and reduce drug toxicity and other systemic side effects. However, local drug delivery systems face challenges in terms of encapsulation, delivery, and controlled release of therapeutics. AREAS COVERED We provide an overview of naturally derived biopolymer-based drug delivery systems for localized, sustained, and on-demand treatment. We introduce the advantages and limitations of these systems for drug encapsulation, delivery, and local release, as well as recent applications. EXPERT OPINION Naturally derived biopolymers like cellulose, silk fibroin, chitosan, alginate, hyaluronic acid, and gelatin are good candidates for localized drug delivery because they are readily chemically modified, biocompatible, biodegradable (with the generation of metabolically compatible degradation products), and can be processed in aqueous and ambient environments to maintain the bioactivity of various therapeutics. The tradeoff between the effective treatment dosage and the response by local healthy tissue should be balanced during the design of these delivery systems. Future directions will be focused on strategies to design tunable and controlled biodegradation rates, as well as to explore commercial utility in substituting biopolymer-based systems for currently utilized synthetic polymers for implants for drug delivery.
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Affiliation(s)
- Junqi Wu
- Department of Biomedical Engineering, Tufts University, 4 Colby St., Medford, USA, 02155
| | - Sawnaz Shaidani
- Department of Biomedical Engineering, Tufts University, 4 Colby St., Medford, USA, 02155
| | - Sophia K. Theodossiou
- Department of Biomedical Engineering, Tufts University, 4 Colby St., Medford, USA, 02155
| | - Emily J. Hartzell
- Department of Biomedical Engineering, Tufts University, 4 Colby St., Medford, USA, 02155
| | - David L. Kaplan
- Department of Biomedical Engineering, Tufts University, 4 Colby St., Medford, USA, 02155
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Application Progress of Modified Chitosan and Its Composite Biomaterials for Bone Tissue Engineering. Int J Mol Sci 2022; 23:ijms23126574. [PMID: 35743019 PMCID: PMC9224397 DOI: 10.3390/ijms23126574] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2022] [Revised: 05/30/2022] [Accepted: 06/08/2022] [Indexed: 12/28/2022] Open
Abstract
In recent years, bone tissue engineering (BTE), as a multidisciplinary field, has shown considerable promise in replacing traditional treatment modalities (i.e., autografts, allografts, and xenografts). Since bone is such a complex and dynamic structure, the construction of bone tissue composite materials has become an attractive strategy to guide bone growth and regeneration. Chitosan and its derivatives have been promising vehicles for BTE owing to their unique physical and chemical properties. With intrinsic physicochemical characteristics and closeness to the extracellular matrix of bones, chitosan-based composite scaffolds have been proved to be a promising candidate for providing successful bone regeneration and defect repair capacity. Advances in chitosan-based scaffolds for BTE have produced efficient and efficacious bio-properties via material structural design and different modifications. Efforts have been put into the modification of chitosan to overcome its limitations, including insolubility in water, faster depolymerization in the body, and blood incompatibility. Herein, we discuss the various modification methods of chitosan that expand its fields of application, which would pave the way for future applied research in biomedical innovation and regenerative medicine.
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Lai E, Bao B, Zhu Y, Lin H. Transglutaminase-Catalyzed Bottom-Up Synthesis of Polymer Hydrogel. Front Bioeng Biotechnol 2022; 10:824747. [PMID: 35392400 PMCID: PMC8980521 DOI: 10.3389/fbioe.2022.824747] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Accepted: 03/04/2022] [Indexed: 11/13/2022] Open
Abstract
Enzyme catalysis has attracted increasing attention for application in the synthesis of polymer hydrogel due to the eco-friendly process and the devisable catalytic reaction. Moreover, bottom-up approaches combining enzyme catalysts and molecular self-assembly have been explored for synthesizing hydrogel with complex architectures. An enzyme widely distributed in nature, transglutaminase (TGase) has been confirmed to catalyze the formation of isopeptide bonds between proteins, which can effectively improve the gelation of proteins. In this mini-review, TGase-catalyzed synthesis of polymer hydrogels, including fibrin hydrogels, polyethylene glycol hydrogels, soy protein hydrogels, collagen hydrogels, gelatin hydrogels and hyaluronan hydrogels, has been reviewed in detail. The catalytic process and gel formation mechanism by TGase have also been considered. Furthermore, future perspectives and challenges in the preparation of polymer hydrogels by TGase are also highlighted.
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Vernerey FJ, Lalitha Sridhar S, Muralidharan A, Bryant SJ. Mechanics of 3D Cell-Hydrogel Interactions: Experiments, Models, and Mechanisms. Chem Rev 2021; 121:11085-11148. [PMID: 34473466 DOI: 10.1021/acs.chemrev.1c00046] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Hydrogels are highly water-swollen molecular networks that are ideal platforms to create tissue mimetics owing to their vast and tunable properties. As such, hydrogels are promising cell-delivery vehicles for applications in tissue engineering and have also emerged as an important base for ex vivo models to study healthy and pathophysiological events in a carefully controlled three-dimensional environment. Cells are readily encapsulated in hydrogels resulting in a plethora of biochemical and mechanical communication mechanisms, which recapitulates the natural cell and extracellular matrix interaction in tissues. These interactions are complex, with multiple events that are invariably coupled and spanning multiple length and time scales. To study and identify the underlying mechanisms involved, an integrated experimental and computational approach is ideally needed. This review discusses the state of our knowledge on cell-hydrogel interactions, with a focus on mechanics and transport, and in this context, highlights recent advancements in experiments, mathematical and computational modeling. The review begins with a background on the thermodynamics and physics fundamentals that govern hydrogel mechanics and transport. The review focuses on two main classes of hydrogels, described as semiflexible polymer networks that represent physically cross-linked fibrous hydrogels and flexible polymer networks representing the chemically cross-linked synthetic and natural hydrogels. In this review, we highlight five main cell-hydrogel interactions that involve key cellular functions related to communication, mechanosensing, migration, growth, and tissue deposition and elaboration. For each of these cellular functions, recent experiments and the most up to date modeling strategies are discussed and then followed by a summary of how to tune hydrogel properties to achieve a desired functional cellular outcome. We conclude with a summary linking these advancements and make the case for the need to integrate experiments and modeling to advance our fundamental understanding of cell-matrix interactions that will ultimately help identify new therapeutic approaches and enable successful tissue engineering.
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Affiliation(s)
- Franck J Vernerey
- Department of Mechanical Engineering, University of Colorado at Boulder, 1111 Engineering Drive, Boulder, Colorado 80309-0428, United States.,Materials Science and Engineering Program, University of Colorado at Boulder, 4001 Discovery Drive, Boulder, Colorado 80309-613, United States
| | - Shankar Lalitha Sridhar
- Department of Mechanical Engineering, University of Colorado at Boulder, 1111 Engineering Drive, Boulder, Colorado 80309-0428, United States
| | - Archish Muralidharan
- Materials Science and Engineering Program, University of Colorado at Boulder, 4001 Discovery Drive, Boulder, Colorado 80309-613, United States
| | - Stephanie J Bryant
- Materials Science and Engineering Program, University of Colorado at Boulder, 4001 Discovery Drive, Boulder, Colorado 80309-613, United States.,Department of Chemical and Biological Engineering, University of Colorado at Boulder, 3415 Colorado Avenue, Boulder, Colorado 80309-0596, United States.,BioFrontiers Institute, University of Colorado at Boulder, 3415 Colorado Avenue, Boulder, Colorado 80309-0596, United States
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Crosslinking Strategies for the Microfluidic Production of Microgels. Molecules 2021; 26:molecules26123752. [PMID: 34202959 PMCID: PMC8234156 DOI: 10.3390/molecules26123752] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2021] [Revised: 06/17/2021] [Accepted: 06/18/2021] [Indexed: 02/03/2023] Open
Abstract
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.
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