Self‐Healing Supramolecular Hydrogels for Tissue Engineering Applications

Self‐healing supramolecular hydrogels have emerged as a novel class of biomaterials that combine hydrogels with supramolecular chemistry to develop highly functional biomaterials with advantages including native tissue mimicry, biocompatibility, and injectability. These properties are endowed by the reversibly cross‐linked polymer network of the hydrogel. These hydrogels have great potential for realizing yet to be clinically translated tissue engineering therapies. This review presents methods of self‐healing supramolecular hydrogel formation and their uses in tissue engineering as well as future perspectives.     

Alginate/Polyoxyethylene and Alginate/Gelatin Hydrogels: Preparation,Characterization, and Application in Tissue Engineering

Hydrogels are attractive biomaterials for three-dimensional cell culture and tissue engineering applications. The preparation of hydrogels using alginate and gelatin provides cross-linked hydrophilic polymers that can swell but do not dissolve in water. In this work, we first reinforced pure alginate by using polyoxyethylene as a supporting material. In an alginate/PEO sample that contains 20 % polyoxyethylene, we obtained a stable hydrogel for cell culture experiments. We also prepared a stable alginate/gelatin hydrogel by cross-linking a periodate-oxidized alginate with another functional component such as gelatin. The hydrogels were found to have a high fluid uptake. In this work, preparation, characterization, swelling, and surface properties of these scaffold materials were described. Lyophilized scaffolds obtained from hydrogels were used for cell viability experiments, and the results were presented in detail.     

可注射水凝胶及其在再生医学领域的应用

近年来,由工程生物材料制成的可注射治疗剂正变得越来越流行,并推动传统的临床实践走向微创化.可注射水凝胶由于其可调控的物理及化学特性、可控的降解性能、高含水量以及在微创方式下实现递送的能力,在组织工程和药物递送领域中变得越来越重要.研究者们已开发出例如原位交联水凝胶、大孔水凝胶、水凝胶微粒、动态交联水凝胶等一系列性能独特的可注射水凝胶.通过调控水凝胶的固含量和交联密度,并引入适当的共价或非共价相互作用,例如静电相互作用、疏水相互作用等,这些水凝胶可在注射过程中实现生物活性分子的递送.同时,可注射水凝胶亦可用于细胞的递送,提供细胞培养所需的三维环境,并通过调控力学性能、化学修饰、生物功能化修饰等手段调控细胞黏附、增殖、分化等行为.本文旨在回顾近年来可注射水凝胶的设计和制备的相关进展,以及其在再生医学中的应用,并对该领域存在的挑战和潜力进行了展望.     

Injectable Hyaluronic Acid/Poly(γ-glutamic acid) Hydrogel with Step-by-step Tunable Properties for Soft Tissue Engineering

Injectable hydrogels as an important class of biomaterials have gained much attention in tissue engineering. However, their crosslinking degree is difficult to be controlled after being injected into body. As we all know, the crosslinking degree strongly influences the physicochemical properties of hydrogels. Therefore, developing an injectable hydrogel with tunable crosslinking degree in vivo is important for tissue engineering. Herein, we present a dual crosslinking strategy to prepare injectable hydrogels with step-by-step tunable crosslinking degree using Schiff base reaction and photopolymerization. The developed hyaluronic acid/poly(γ-glutamic acid)(HA/γ-PGA) hydrogels exhibit step-bystep tunable swelling behavior, enzymatic degradation behavior and mechanical properties. Mechanical performance tests show that the storage moduli of HA/γ-PGA hydrogels are all less than 2000 Pa and the compressive moduli are in kilopascal, which have a good match with soft tissue. In addition, NIH 3 T3 cells encapsulated in HA/γ-PGA hydrogel exhibit a high cell viability, indicating a good cytocompatibility of HA/γ-PGA hydrogel.Therefore, the developed HA/γ-PGA hydrogel as an injectable biomaterial has a good potential in soft tissue engineering.     

The Mechanical and Biological Performance of Photopolymerized Gelatin-Based Hydrogels as a Function of the Reaction Media

From the first experiments with biomaterials to mimic tissue properties, the mechanical and biochemical characterization has evolved extensively. Several properties can be described, however, what should be essential is to conduct a proper and physiologically relevant characterization. Herein, the influence of the reaction media (RM) and swelling media (SM)–phosphate buffered saline (PBS) and Dulbecco's modified Eagle's medium (DMEM) with two different glucose concentrations–is described in gelatin methacrylamide (GelMA) hydrogel mechanics and in the biological behavior of two tumoral cell lines (Caco-2 and HCT-116). All scaffolds are UV-photocrosslinked under identical conditions and evaluated for mass swelling ratio and stiffness. The results indicate that stiffness is highly susceptible to the RM, but not to the SM. Additionally, PBS-prepared hydrogels exhibited a higher photopolymerization degree according to high resolution magic-angle spinning (HR-MAS) NMR. These findings correlate with the biological response of Caco-2 and HCT-116 cells seeded on the substrates, which demonstrated flatter morphologies on stiffer hydrogels. Overall, cell viability and proliferation are excellent for both cell lines, and Caco-2 cells displayed a characteristic apical-basal polarization based on F-actin/Nuclei fluorescence images. These characterization experiments highlight the importance of conducting mechanical testing of biomaterials in the same medium as cell culture.     

Human Albumin-Based Hydrogels for Their Potential Xeno-Free Microneedle Applications

Nowadays, hydrogels-based microneedles (MNs) have attracted a great interest owing to their outstanding qualities for biomedical applications. For the fabrication of hydrogels-based microneedles as tissue engineering scaffolds and drug delivery carriers, various biomaterials have been tested. They are required to feature tunable physiochemical properties, biodegradability, biocompatibility, nonimmunogenicity, high drug loading capacity, and sustained drug release. Among biomaterials, human proteins are the most ideal biomaterials for fabrication of hydrogels-based MNs; however, they are mechanically weak and poorly processible. To the best of the knowledge, there are no reports of xeno-free human protein-based MNs so far. Here, human albumin-based hydrogels and microneedles for tissue engineering and drug delivery by using relatively new processible human serum albumin methacryloyl (HSAMA) are engineered. The resultant HSAMA hydrogels display tunable mechanical properties, biodegradability, and good biocompatibility. Moreover, the xeno-free HSAMA microneedles display a sustained drug release profile and significant mechanical strength to penetrate the model skin. In vitro, they also show good biocompatibility and anticancer efficacy. Sustainable processible human albumin-based biomaterials may be employed as a xeno-free platform in vivo for tissue engineering and drug delivery in clinical trials in the future.     

The rheological and structural properties of Fmoc-peptide-based hydrogels: the effect of aromatic molecular architecture on self-assembly and physical characteristics

Biocompatible hydrogels are of high interest as a class of biomaterials for tissue engineering, regenerative medicine, and controlled drug delivery. These materials offer three-dimensional scaffolds to support the growth of cells and development of hierarchical tissue structures. Fmoc-peptides were previously demonstrated as attractive building blocks for biocompatible hydrogels. Here, we further investigate the biophysical properties of Fmoc-peptide-based hydrogels for medical applications. We describe the structural and thermal properties of these Fmoc-peptides, as well as their self-assembly process. Additionally, we study the role of interactions between aromatic moieties in the self-assembly process and on the physical and structural properties of the hydrogels.     

Photo-crosslinkable hydrogel and its biological applications

In the past few years,photo-crosslinkable hydrogels have drawn a great attention in tissue engineering applications due to their high biocompatibility and extracellular matrix(ECM)-like structure.They can be easily biofabricated through exposure of a photosensitive system composed of photo-crosslinkable hydrogels,photo-initiators and other compounds such as cells and therapeutic molecules,to ultraviolet or visible light.With the development of biofabrication methods,ma ny resea rchers studied the biological applications of photo-crosslinkable hydrogels in tissue engineering,such as vascular,wound dressing and bone engineering.This review highlights the biomaterials for photo-crosslinkable hydrogels,bio fabrication techniques and their biological applications in tissue engineering.Meanwhile,the challenges and prospects of photo-crosslinkable hydrogels are discussed as well.     

Coating Strategies Using Layer‐by‐layer Deposition for Cell Encapsulation

The layer‐by‐layer (LbL) deposition technique is widely used to develop multilayered films based on the directed assembly of complementary materials. In the last decade, thin multilayers prepared by LbL deposition have been applied in biological fields, namely, for cellular encapsulation, due to their versatile processing and tunable properties. Their use was suggested as an alternative approach to overcome the drawbacks of bulk hydrogels, for endocrine cells transplantation or tissue engineering approaches, as effective cytoprotective agents, or as a way to control cell division. Nanostructured multilayered materials are currently used in the nanomodification of the surfaces of single cells and cell aggregates, and are also suitable as coatings for cell‐laden hydrogels or other biomaterials, which may later be transformed to highly permeable hollow capsules. In this Focus Review, we discuss the applications of LbL cell encapsulation in distinct fields, including cell therapy, regenerative medicine, and biotechnological applications. Insights regarding practical aspects required to employ LbL for cell encapsulation are also provided.     

Cell-Encapsulating Hydrogel Puzzle: Polyrotaxane-Based Self-Healing Hydrogels

Slide-ring hydrogels using polyrotaxanes have been developed as highly tough soft materials. However, they have never been used as biomaterials because of the lack of biocompatibility. Meanwhile, self-healing hydrogels are expected to improve fatigue resistance and extend the period of use. However, owing to the lack of high mechanical strength, they are limited in their use as biomaterials. Here we first developed a biocompatible self-healing/slide-ring hydrogel using glycol chitosan and a water-soluble polyrotaxane. We obtained excellent mechanical toughness and biocompatibility to promote the proliferation of human umbilical vein endothelial cells (HUVECs) encapsulated in the hydrogel. Owing to the rapid self-healing property, the cell-encapsulating gels adjusted arbitrarily, maintaining good cell proliferation function. Therefore, slide-ring hydrogels enable the use of biomaterials for soft-tissue engineering.     

Combination of integrin-binding peptide and growth factor promotes cell adhesion on electron-beam-fabricated patterns

Understanding and controlling cell adhesion on engineered scaffolds is important in biomaterials and tissue engineering. In this report we used an electron-beam (e-beam) lithography technique to fabricate patterns of a cell adhesive integrin ligand combined with a growth factor. Specifically, micron-sized poly(ethylene glycol) (PEG) hydrogels with aminooxy- and styrene sulfonate-functional groups were fabricated. Cell adhesion moieties were introduced using a ketone-functionalized arginine-glycine-aspartic acid (RGD) peptide to modify the O-hydroxylamines by oxime bond formation. Basic fibroblast growth factor (bFGF) was immobilized by electrostatic interaction with the sulfonate groups. Human umbilical vein endothelial cells (HUVECs) formed focal adhesion complexes on RGD- and RGD and bFGF-immobilized patterns as shown by immunostaining of vinculin and actin. In the presence of both bFGF and RGD, cell areas were larger. The data demonstrate confinement of cellular focal adhesions to chemically and physically well-controlled microenvironments created by a combination of e-beam lithography and "click" chemistry techniques. The results also suggest positive implications for addition of growth factors into adhesive patterns for cell-material interactions.     

Applications of Gelatin Methacryloyl (GelMA) Hydrogels in Microfluidic Technique-Assisted Tissue Engineering

In recent years, the microfluidic technique has been widely used in the field of tissue engineering. Possessing the advantages of large-scale integration and flexible manipulation, microfluidic devices may serve as the production line of building blocks and the microenvironment simulator in tissue engineering. Additionally, in microfluidic technique-assisted tissue engineering, various biomaterials are desired to fabricate the tissue mimicking or repairing structures (i.e., particles, fibers, and scaffolds). Among the materials, gelatin methacrylate (GelMA)-based hydrogels have shown great potential due to their biocompatibility and mechanical tenability. In this work, applications of GelMA hydrogels in microfluidic technique-assisted tissue engineering are reviewed mainly from two viewpoints: Serving as raw materials for microfluidic fabrication of building blocks in tissue engineering and the simulation units in microfluidic chip-based microenvironment-mimicking devices. In addition, challenges and outlooks of the exploration of GelMA hydrogels in tissue engineering applications are proposed.     

Alginate hydrogels as biomaterials

[Image: see text] Alginate hydrogels are proving to have a wide applicability as biomaterials. They have been used as scaffolds for tissue engineering, as delivery vehicles for drugs, and as model extracellular matrices for basic biological studies. These applications require tight control of a number of material properties including mechanical stiffness, swelling, degradation, cell attachment, and binding or release of bioactive molecules. Control over these properties can be achieved by chemical or physical modifications of the polysaccharide itself or the gels formed from alginate. The utility of these modified alginate gels as biomaterials has been demonstrated in a number of in vitro and in vivo studies.Micro-CT images of bone-like constructs that result from transplantation of osteoblasts on gels that degrade over a time frame of several months leading to improved bone formation.     

Polypyrrole/Alginate Hybrid Hydrogels: Electrically Conductive and Soft Biomaterials for Human Mesenchymal Stem Cell Culture and Potential Neural Tissue Engineering Applications

Electrically conductive biomaterials that can efficiently deliver electrical signals to cells or improve electrical communication among cells have received considerable attention for potential tissue engineering applications. Conductive hydrogels are desirable particularly for neural applications, as they can provide electrical signals and soft microenvironments that can mimic native nerve tissues. In this study, conductive and soft polypyrrole/alginate (PPy/Alg) hydrogels are developed by chemically polymerizing PPy within ionically cross‐linked alginate hydrogel networks. The synthesized hydrogels exhibit a Young's modulus of 20–200 kPa. Electrical conductance of the PPy/Alg hydrogels could be enhanced by more than one order of magnitude compared to that of pristine alginate hydrogels. In vitro studies with human bone marrow‐derived mesenchymal stem cells (hMSCs) reveal that cell adhesion and growth are promoted on the PPy/Alg hydrogels. Additionally, the PPy/Alg hydrogels support and greatly enhance the expression of neural differentiation markers (i.e., Tuj1 and MAP2) of hMSCs compared to tissue culture plate controls. Subcutaneous implantation of the hydrogels for eight weeks induces mild inflammatory reactions. These soft and conductive hydrogels will serve as a useful platform to study the effects of electrical and mechanical signals on stem cells and/or neural cells and to develop multifunctional neural tissue engineering scaffolds.

     

Self‐Assembled Gels for Biomedical Applications

Natural and synthetic gel‐like materials have featured heavily in the development of biomaterials for wound healing and other tissue‐engineering purposes. More recently, molecular gels have been designed and tailored for the same purpose. When mixed with, or conjugated to therapeutic drugs or bioactive molecules, these materials hold great promise for treating/curing life‐threatening and degenerative diseases, such as cancer, osteoarthritis, and neural injuries. This focus review explores the latest advances in this field and concentrates on self‐assembled gels formed under aqueous conditions (i.e., self‐assembled hydrogels), and critically compares their performance within different biomedical applications, including three‐dimensional cell‐culture studies, drug delivery, and tissue engineering. Although stability and toxicity issues still need to be addressed in more detail, it is clear from the work reviewed here that self‐assembled gels have a bright future as novel biomaterials.     

Generation of Large‐Scale DNA Hydrogels with Excellent Blood and Cell Compatibility

Hemocompatibility and cytocompatibility of biomaterials codetermine the success of tissue engineering applications. DNA, the natural component of our cells, is an auspicious biomaterial for the generation of designable scaffolds with tailorable characteristics. In this study, a combination of rolling circle amplification and multiprimed chain amplification is used to generate hydrogels at centimeter scale consisting solely of DNA. Using an in vitro rotation model and fresh human blood, the reaction of the hemostatic system on DNA hydrogels is analyzed. The measurements of hemolysis, platelets activation, and the activation of the complement, coagulation, and neutrophils using enzyme‐linked immunosorbent assays demonstrate excellent hemocompatibility. In addition, the cytocompatibility of the DNA hydrogels is tested by indirect contact (agar diffusion tests) and material extract experiments with L929 murine fibroblasts according to the ISO 10993‐5 specifications and no negative impact on the cell viability is detected. These results indicate the promising potential of DNA hydrogels as biomaterials for versatile applications in the field of regenerative medicine.

     

光控水凝胶的构筑及在生物医药领域的应用

水凝胶由于具有优越的保水性、良好的生物相容性和可降解性,被认为是最接近人体组织的生物医用材料。通过构建环境敏感水凝胶可以高度拟合生物组织的微环境,实现其在组织工程与再生医学领域的应用。由于光具有非物理接触和时空分辨等优势,利用光调控技术可实现水凝胶微环境的精确构筑与调控。本文重点介绍了近年来光控水凝胶的构筑,以及在生物医学和材料领域的应用进展。     

糖化温敏凝胶的制备及其与HepG2细胞相互作用研究

利用自由基聚合法合成了半乳糖糖化温敏凝胶(P(NIPAAm-co-GAC))和壳聚糖糖化温敏凝胶(P(NIPAAm-co-CSA)),对其温度响应性和溶胀性能进行了研究,结果表明,两种糖化温敏凝胶在水中和细胞培养基中均显示较好的温度响应性,以及比聚(N-异丙基丙烯酰胺)温敏凝胶(PNIPAAm)更好的溶胀性能.进一步研究人肝肿瘤细胞(HepG2)在凝胶表面的细胞行为发现,HepG2在P(NIPAAm-co-GAC)、PNIPAAm凝胶表面吸附量及活性较高,表现出良好的生长趋势,而在P(NIPAAm-co-CSA)凝胶表面吸附量和活性很低,其增殖受到抑制;通过降低环境温度,能使培养在P(NIPAAm-co-GAC)和PNIPAAm凝胶表面的HepG2细胞发生自动脱附,避免了酶解法对细胞功能造成的损伤,并且细胞片层比单个细胞表现出更快的脱附速率;研究细胞转载行为表明,通过温度诱导得到的细胞片层,其生物活性远远大于通过酶解法得到的细胞的生物活性.     

Superabsorbent hydrogels based on cellulose for smart swelling and controllable delivery

Novel superabsorbent hydrogels were prepared successfully from carboxymethylcellulose sodium (CMC) and cellulose in the NaOH/urea aqueous system by using epichlorohydrin (ECH) as cross-linker. The structure and morphology of the hydrogels were characterized by FT-IR spectroscope, thermogravimetric analysis and scanning electron microscope. The results revealed that the CMC contributed to the enhanced size of pore, whereas cellulose as a strong backbone in the hydrogel to support it for keeping its appearance. Their equilibrium swelling ratio in distilled water and different physiological fluids were evaluated, indicating the maximum swelling ratio in water reached an exciting level of 1000 as the hydrogels still keeping a steady appearance. Moreover, the hydrogels exhibited smart swelling and shrinking in NaCl or CaCl₂ aqueous solution, as well as the release behavior of bovine serum albumin (BSA) that could be controlled by changing CMC content. The cellulose-based hydrogels are promising for the applications in the biomaterials area.     

Facile preparation of self-assembled hydrogel-like GdPO4*H2O nanorods

Of the methods employed in the preparation of one-dimensional lanthanide phosphate (LnPO(4)) nanorods/nanowires, such as GdPO(4), the hydrothermal method has been mainly used as a synthetic route. In this study, we report a facile low-temperature solution approach to prepare GdPO 4*H(2)O nanorods by simply refluxing GdCl(3) and KH(2)PO(4) for only 15 min at 88 degrees C, an approach that can easily be scaled up by increasing the reagent amounts. We observed a highly viscous macroscopic hydrogel-like material when we mixed as-prepared GdPO(4)*H(2)O nanomaterials with H(2)O. Hydrogels are an important class of biomaterials. Their building blocks, normally formed from protein-, peptide-, polymer-, and lipid-based materials, offer three-dimensional scaffolds for drug delivery, tissue engineering, and biosensors. Our preliminary results showed that GdPO(4)*H(2)O hydrogels could be used for encapsulation and drug release, and that they were biocompatible, acting as scaffolds to foster cell proliferation. These findings suggested that they might have biomedical uses. Our findings may lead to the creation of other inorganic nanomaterial-based hydrogels apart from the organic and biomolecular protein-, peptide-, polymer-, and lipid-based building blocks.