Photocrosslinkable hydrogel for myocyte cell culture and injection

Preparation of carboxymethyl chitosan/double-formaldehyde cellulose based hydrogel loaded with ginger essential oil nanoemulsion for meat preservation

An antibacterial nano-hydrogel (ginger essential oil nanoemulsion hydrogel, GEONH) based on Schiff base reaction was prepared using double-formaldehyde micro fibrillated cellulose (DAMFC) and carboxymethyl chitosan (CMCS) loaded with ginger essential oil nanoemulsion (GEON). It was found that when the mass ratio of DAMFC/CMCS/GEON was 1/9/270, the gel time, the water absorbency, gel strength, and morphology were the best. The results of X-ray diffraction and FT-IR confirmed that the aldehyde group on the DAMFC molecular chain formed a stable chemical crosslinking with the amino group on the CMCS molecular chain, resulting in a change in the crystal structure. GEONH showed excellent bactericidal activity against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. Simultaneously, the prepared GEONH decreased the total viable count, Malondialdehyde, and total sulfhydryl content and improved the taste in the storage of boiled salted duck. Therefore, GEONH film is a promising fresh-keeping packaging for storing meat products.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01437-4.

A dual-crosslinking electroactive hydrogel based on gelatin methacrylate and dibenzaldehyde-terminated telechelic polyethylene glycol for 3D bio-printing

Gelatin was widely used as scaffold materials in 3D bio-printing due to its excellent bioactivity and availability and especially that their arginine-glycine-aspartic acid (RGD) sequences could efficiently promote cell adhesion and proliferation. In this study, an electroactive and 3D bio-printable hydrogel was prepared through a two-step chemical cross-linking process. Specifically, residual free amino groups of methacrylated gelatin (GelMA) were cross-linked with the aldehyde groups of dibenzaldehyde-terminated telechelic polyethylene glycol (DF-PEG) via Schiff base bonds, forming a gel at 37 °C. During the subsequent 3D bio-printing process, GelMA underwent UV curing, forming a secondary cross-linked network to the mechanical strength and stability of the printed structure. The uniform dispersion of carbon nanotubes (CNTs) in the GelMA/DF-PEG composite hydrogel significantly increased its conductivity. The optimized GelMA/DF-PEG composite hydrogel, i.e., 30% GelMA and 25% DF-PEG (G30D25-CNTs), exhibited superior bio-printability. When the content of CNTs was above 4%, the conductivity of G30D25-CNTs hydrogel exceeded 10-2 S/m, which satisfied the needs of cells for micro-current stimulation. Furthermore, the pore microstructures, swelling behavior, degradation ability and cell toxicity of G30D25-CNTs electroactive hydrogels were thoroughly evaluated. Thus, the G30D25-CNTs hydrogel with 4% MWCNTs could be considered for further application in electrical stimulation of tissue regeneration such as muscle and cardiac nerve tissue repair.

Injectable, Shear-Thinning, Self-Healing, and Self-Cross-Linkable Benzaldehyde-Conjugated Chitosan Hydrogels as a Tissue Adhesive

Benzaldehyde-conjugated chitosan (CH-CBA) was synthesized by a coupling reaction between chitosan (CH) and carboxybenzaldehyde (CBA). The pH-sensitive self-cross-linking can be achieved through the Schiff base reaction. The degree of substitution (DS) of CH-CBA was controlled at 1.4-12.7% by optimizing the pH and reagent stoichiometry. The dynamic Schiff base linkages conferred strong shear-thinning and self-healing properties to the hydrogels. The viscosity of the 2 wt/v % CH-CBA hydrogel decreased from 5.3 × 107 mPa·s at a shear rate of 10-2 s-1 to 2.0 × 103 mPa·s at 102 s-1 at pH 7.4. The CH-CBA hydrogel exhibited excellent biocompatibility in vitro and in vivo. Moreover, the hydrogel adhered strongly to porcine small intestine, colon, and cecum samples, comparable to commercial fibrin glue, and exhibited effective in vivo tissue sealing in a mouse cecal ligation and puncture model, highlighting its potential as a biomaterial for application in tissue adhesives, tissue engineering scaffolds, etc.

Cross-Linked Alginate Dialdehyde/Chitosan Hydrogel Encompassing Curcumin-Loaded Bilosomes for Enhanced Wound Healing Activity

The current study aimed to fabricate curcumin-loaded bilosomal hydrogel for topical wound healing purposes, hence alleviating the poor aqueous solubility and low oral bioavailability of curcumin. Bilosomes were fabricated via the thin film hydration technique using cholesterol, Span® 60, and two different types of bile salts (sodium deoxycholate or sodium cholate). Bilosomes were verified for their particle size (PS), polydispersity index (PDI), zeta potential (ZP), entrapment efficiency (EE%), and in vitro drug release besides their morphological features. The optimum formulation was composed of cholesterol/Span® 60 (molar ratio 1:10 w/w) and 5 mg of sodium deoxycholate. This optimum formulation was composed of a PS of 246.25 ± 11.85 nm, PDI of 0.339 ± 0.030, ZP of -36.75 ± 0.14 mv, EE% of 93.32% ± 0.40, and the highest percent of drug released over three days (96.23% ± 0.02). The optimum bilosomal formulation was loaded into alginate dialdehyde/chitosan hydrogel cross-linked with calcium chloride. The loaded hydrogel was tested for its water uptake capacity, in vitro drug release, and in vivo studies on male Albino rats. The results showed that the loaded hydrogel possessed a high-water uptake percent at the four-week time point (729.50% ± 43.13) before it started to disintegrate gradually; in addition, it showed sustained drug release for five days (≈100%). In vivo animal testing and histopathological studies supported the superiority of the curcumin-loaded bilosomal hydrogel in wound healing compared to the curcumin dispersion and plain hydrogel, where there was a complete wound closure attained after the three-week period with a proper healing mechanism. Finally, it was concluded that curcumin-loaded bilosomal hydrogel offered a robust, efficient, and user-friendly dosage form for wound healing.

Global hotspots and emerging trends in 3D bioprinting research

Three-dimensional (3D) bioprinting is an advanced tissue engineering technique that has received a lot of interest in the past years. We aimed to highlight the characteristics of articles on 3D bioprinting, especially in terms of research hotspots and focus. Publications related to 3D bioprinting from 2007 to 2022 were acquired from the Web of Science Core Collection database. We have used VOSviewer, CiteSpace, and R-bibliometrix to perform various analyses on 3,327 published articles. The number of annual publications is increasing globally, a trend expected to continue. The United States and China were the most productive countries with the closest cooperation and the most research and development investment funds in this field. Harvard Medical School and Tsinghua University are the top-ranked institutions in the United States and China, respectively. Dr. Anthony Atala and Dr. Ali Khademhosseini, the most productive researchers in 3D bioprinting, may provide cooperation opportunities for interested researchers. Tissue Engineering Part A contributed the largest publication number, while Frontiers in Bioengineering and Biotechnology was the most attractive journal with the most potential. As for the keywords in 3D bioprinting, Bio-ink, Hydrogels (especially GelMA and Gelatin), Scaffold (especially decellularized extracellular matrix), extrusion-based bioprinting, tissue engineering, and in vitro models (organoids particularly) are research hotspots analyzed in the current study. Specifically, the research topics "new bio-ink investigation," "modification of extrusion-based bioprinting for cell viability and vascularization," "application of 3D bioprinting in organoids and in vitro model" and "research in personalized and regenerative medicine" were predicted to be hotspots for future research.

Methacrylated Fibrinogen Hydrogels for 3D Cell Culture and Delivery

Methacrylation was performed on fibrinogen to design a new biomedical hydrogel for 3D cell culture or as a biodegradable delivery matrix for in vivo implantation. The methacrylation of denatured fibrinogen in solution was performed using methacrylic anhydride (MAA). The extent of fibrinogen methacrylation was quantified by proton NMR and controlled using stochiometric quantities of MAA during the reaction. The methacrylated fibrinogen (FibMA) hydrogels were formed by light-activated free-radical polymerization in the presence of macromolecular cross-linking polymers made from acrylated poly(ethylene glycol) (PEG). The biocompatibility and biodegradability of the FibMA hydrogels were characterized by in vitro assays and in vivo implantation experiments using quantitative magnetic resonance imaging (MRI) of the implant volume. The FibMA supported the growth and metabolic activity of human dermal fibroblasts in both 2D and 3D cultures. The methacrylation did not alter important biological attributes of the fibrinogen, including the ability to support cell adhesion and 3D cell culture, as well as to undergo proteolysis. Animal experiments confirmed the biodegradability of the FibMA for potential use as a scaffold in tissue engineering, as a bioink for 3D printing, or as a biodegradable matrix for in vivo sustained delivery of bioactive factors. STATEMENT OF SIGNIFICANCE: : This paper describes methacrylated fibrinogen (FibMA) and the formation of a biomedical hydrogel from FibMA for cell culture and other biomedical applications. Inspired from methacrylated gelatin (GelMA), the FibMA is made from blood-derived fibrinogen which is more suitable for clinical use. Sharing similar properties to other hydrogels made from methacrylated proteins, the FibMA has yet to be reported in the literature. In this manuscript, we provide the methodology to produce the FibMA hydrogels, we document the mechanical versatility of this new biomaterial, and we show the biocompatibility using 3D cell culture studies and in vivo implantations.

Improvement of IgA Nephropathy and Kidney Regeneration by Functionalized Hyaluronic Acid and Gelatin Hydrogel

BACKGROUND

Immunoglobulin A (IgA) nephropathy (IgAN) is one of an important cause of progressive kidney disease and occurs when IgA settles in the kidney resulted in disrupts kidney's ability to filter waste and excess water. Hydrogels are promising material for medical applications owing to their excellent adaptability and filling ability. Herein, we proposed a hyaluronic acid/gelatin (CHO-HA/Gel-NH₂) bioactive hydrogel as a cell carrier for therapeutic kidney regeneration in IgAN.

METHODS

CHO-HA/Gel-NH₂ hydrogel was fabricated by Schiff-base reaction without any additional crosslinking agents. The hydrogel concentrations and ratios were evaluated to enhance adequate mechanical properties and biocompatibility for further in vivo study. High serum IgA ddY mice kidneys were treated with human urine-derived renal progenitor cells encapsulated in the hydrogel to investigate the improvement of IgA nephropathy and kidney regeneration.

RESULTS

The stiffness of the hydrogel was significantly enhanced and could be modulated by altering the concentrations and ratios of hydrogel. CHO-HA/Gel-NH₂ at a ratio of 3/7 provided a promising milieu for cells viability and cells proliferation. From week four onwards, there was a significant reduction in blood urea nitrogen and serum creatinine level in Cell/Gel group, as well as well-organized glomeruli and tubules. Moreover, the expression of pro-inflammatory and pro-fibrotic molecules significantly decreased in the Gel/Cell group, whereas anti-inflammatory gene expression was elevated compared to the Cell group.

CONCLUSION

Based on in vivo studies, the renal regenerative ability of the progenitor cells could be further increased by this hydrogel system.

Dual setting brushite—gelatin cement with increased ductility and sustained drug release

A novel dual setting brushite-gelatin cement was achieved by genip ininitiated cross-linking of gelatin during cement setting. Although the combination of an inorganic and organic phase resulted in a decrease of the compressive strength from about 10 MPa without polymeric phase to 3–6–MPa for gelatin modified composites, an increase in elastic properties due to the gelatin hydrogel with a concentration of 10.0 w/v% was achieved. For a powder-to-liquid ratio of 2.5 g*mL−1, a shift of initial maximum stress value during compression testing was observed up to 5% deformation and tested samples showed a pseudo-ductile fracture behavior. The obtained composites of the different formulations were characterized regarding phase composition, porosity as well as drug loading capacity with rifampicin and vancomycin. For the latter, a sustained and prolonged release was realized with a drug release profile according to the Higuchi model and a release exponent of n = 0.5 for the formulation with a PLR of 2.5 g*mL−1 and an incorporation of 10.0 w/v% gelatin.

RGD-pectin microfiber patches for guiding muscle tissue regeneration

Opportunely arranged microscaled fibers offer an attractive 3D architecture for tissue regeneration as they may enhance and stimulate specific tissue regrowth. Among different scaffolding options, encapsulating cells in degradable hydrogel microfibers appears as particularly attractive strategy. Hydrogel patches, in fact, offer a highly hydrated environment, allow easy incorporation of biologically active molecules, and can easily adapt to implantation site. In addition, microfiber architecture is intrinsically porous and can improve mass transport, vascularization, and cell survival after grafting. Anionic polysaccharides, as pectin or the more popular alginate, represent a particularly promising choice for the fabrication of cell-laden patches, due to their extremely mild gelation in the presence of divalent ions and widely accepted biocompatibility. In this study, to combine the favorable properties of hydrogel and fibrous architecture, a simple coaxial flow wet-spinning system was used to prepare cell-laden, 3D fibrous patches using RGD-modified pectin. Rapid fabrication of coherent self-standing patches, with diameter in the range of 100-200 μm and high cell density, was possible by accurate choice of pectin and calcium ions concentrations. Cells were homogeneously dispersed throughout the microfibers and remained highly viable for up to 2 weeks, when the initial stage of myotubes formation was observed. Modified-pectin microfibers appear as promising scaffold to support muscle tissue regeneration, due to their inherent porosity, the favorable cell-material interaction, and the possibility to guide cell alignment toward a functional tissue.

3D bioprinting of an electroactive and self-healing polysaccharide hydrogels

Polysaccharide hydrogels including alginate, agarose, hyaluronic acid and chitosan have been widely used as scaffolds in 3D bio-printing field. Konjac glucomannan (KGM) exhibits excellent properties of water solubility, biocompatibility and biodegradability. Herein composite hydrogels were prepared via schiff-base reaction between the aldehyde group of oxidized konjac glucomannan (OKGM) and the amino group of branched polyethyleneimine (PEI). The OKGM/PEI composite hydrogel displayed self-healing ability and pH sensitivity and showed shear thinning capability, which is suitable for 3D bio-printing technology. Furthermore, the OKGM/PEI electroactive composite hydrogel was obtained by adding carbon nanotubes (CNTs). Then the rheological behavior and morphology of OKGM/PEI electroactive hydrogels were thoroughly characterized. The conductivities of OKGM/PEI electroactive composite hydrogels increased with increasing the content of carbon nanotubes. The rheological behavior and 3D bio-printability of OKGM/PEI electroactive hydrogels were also tested. It was found that carbon nanotubes can also improve the bio-printability of OKGM/PEI electroactive hydrogels. Thus, the OKGM/PEI electroactive hydrogels could be employed as scaffolds for muscle and cardiac nerve tissue regeneration. This article is protected by copyright. All rights reserved.

Recapitulating Cardiac Structure and Function In Vitro from Simple to Complex Engineering

Cardiac tissue engineering aims to generate in vivo-like functional tissue for the study of cardiac development, homeostasis, and regeneration. Since the heart is composed of various types of cells and extracellular matrix with a specific microenvironment, the fabrication of cardiac tissue in vitro requires integrating technologies of cardiac cells, biomaterials, fabrication, and computational modeling to model the complexity of heart tissue. Here, we review the recent progress of engineering techniques from simple to complex for fabricating matured cardiac tissue in vitro. Advancements in cardiomyocytes, extracellular matrix, geometry, and computational modeling will be discussed based on a technology perspective and their use for preparation of functional cardiac tissue. Since the heart is a very complex system at multiscale levels, an understanding of each technique and their interactions would be highly beneficial to the development of a fully functional heart in cardiac tissue engineering.

Types of biomaterials useful in brain repair

Biomaterials is an emerging field in the study of brain tissue engineering and repair or neurogenesis. The fabrication of biomaterials that can replicate the mechanical and viscoelastic features required by the brain, including the poroviscoelastic responses, force dissipation, and solute diffusivity are essential to be mapped from the macro to the nanoscale level under physiological conditions in order for us to gain an effective treatment for neurodegenerative diseases. This research topic has identified a critical study gap that must be addressed, and that is to source suitable biomaterials and/or create reliable brain-tissue-like biomaterials. This chapter will define and discuss the various types of biomaterials, their structures, and their function-properties features which would enable the development of next-generation biomaterials useful in brain repair.

Decellularized Extracellular Matrix-based Bioinks for Engineering Tissue- and Organ-specific Microenvironments

Biomaterials-based biofabrication methods have gained much attention in recent years. Among them, 3D cell printing is a pioneering technology to facilitate the recapitulation of unique features of complex human tissues and organs with high process flexibility and versatility. Bioinks, combinations of printable hydrogel and cells, can be utilized to create 3D cell-printed constructs. The bioactive cues of bioinks directly trigger cells to induce tissue morphogenesis. Among the various printable hydrogels, the tissue- and organ-specific decellularized extracellular matrix (dECM) can exert synergistic effects in supporting various cells at any component by facilitating specific physiological properties. In this review, we aim to discuss a new paradigm of dECM-based bioinks able to recapitulate the inherent microenvironmental niche in 3D cell-printed constructs. This review can serve as a toolbox for biomedical engineers who want to understand the beneficial characteristics of the dECM-based bioinks and a basic set of fundamental criteria for printing functional human tissues and organs.

MMP-sensitive PEG hydrogel modified with RGD promotes bFGF, VEGF and EPC-mediated angiogenesis

Traumatic soft tissue defects such as bedsores, chronic skin ulcers, limb necrosis, osteonecrosis and other ischemic orthopedic diseases are the most clinically intractable and common problems in orthopedics due to unsatisfactory conventional treatments. The present study designed poly(ethylene glycol; PEG) hydrogels with covalently binded arginylglycylaspartic acid (RGD). Endothelial progenitor cells (EPCs) were encapsulated in the modified hydrogel along with vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF). Results demonstrated that the modified hydrogel displayed good mechanical properties appropriate for a sustained release carrier. RGD modification significantly promoted EPC biocompatibility. VEGF and bFGF encapsulation enhanced the adhesion of EPCs, promoted the production of extracellular matrix and facilitated EPC proliferation. In addition, bFGF and VEGF induced angiogenesis. The combination of growth factors and EPCs in the hydrogel displayed a strong synergy to improve biocompatibility. The present results provided a potential novel treatment approach for soft tissue defects such as bone exposure, chronic skin ulcers, bedsores, limb necrosis, osteonecrosis and other ischemic diseases.

Current research trends and challenges in tissue engineering for mending broken hearts

Cardiovascular disease (CVD) is among the leading causes of mortality worldwide. The shortage of donor hearts to treat end-stage heart failure patients is a critical problem. An average of 3500 heart transplant surgeries are performed globally, half of these transplants are performed in the US alone. Stem cell therapy is growing rapidly as an alternative strategy to repair or replace the damaged heart tissue after a myocardial infarction (MI). Nevertheless, the relatively poor survival of the stem cells in the ischemic heart is a major challenge to the therapeutic efficacy of stem-cell transplantation. Recent advancements in tissue engineering offer novel biomaterials and innovative technologies to improve upon the survival of stem cells as well as to repair the damaged heart tissue following a myocardial infarction (MI). However, there are several limitations in tissue engineering technologies to develop a fully functional, beating cardiac tissue. Therefore, the main goal of this review article is to address the current advancements and barriers in cardiac tissue engineering to augment the survival and retention of stem cells in the ischemic heart.

Local release of gemcitabine via in situ UV-crosslinked lipid-strengthened hydrogel for inhibiting osteosarcoma

Osteosarcoma is among the most common malignant bone tumors in human skeletal system. The conventional treatment of osteosarcoma mainly consists of combining neoadjuvant chemotherapy with surgical approach. However, it is crucial to design an artificial implant that possesses excellent biomechanical properties and is capable of sustaining local release of chemotherapeutics. In this study, we envision that the highly efficient combination of gemcitabine (GEM) hydrochloride loaded liposomes with gelatin methacryloyl (GelMA) of in situ photocrosslinkable hydrogel will lead to a multifunctional implant with unique antitumor, mechanical, and biodegradable properties. A sustained controlled release was observed; more specifically, the release of GEM in vitro lasted for 4 days long. Furthermore, its capability in killing MG63 cells was further explored by using the lixivium of GEM-Lip@Gel and GEM-GelMA hydrogel in vitro (composite hydrogel by GEM loaded liposomes blending with GelMA, short for GEM-Lip@Gel), which agreed with the drug release outcome. In addition, these hydrogel showed excellent ability in inhibiting osteosarcoma in vivo by Balb/c mice bearing MG63 cells. Therefore, GEM-loaded lipo-hydrogel certainly has presented itself as a promising strategy for the development of implant in the field of osteosarcoma treatment.

Natural hydrogels for cartilage regeneration: Modification, preparation and application

Hydrogels, consisting of hydrophilic polymers, can be used as films, scaffolds, nanoparticles and drug carriers. They are one of the hot research topics in material science and tissue engineering and are widely used in the field of biomedical and biological sciences. Researchers are seeking for a type of material that is similar to human tissues and can partially replace human tissues or organs. The hydrogel has brought possibility to solve this problem. It has good biocompatibility and biodegradability. After entering the body, it does not cause immune and toxic reactions. The degradation time can be controlled, and the degradation products are nontoxic and nonimmunogenic; the final metabolites can be excreted outside the body. Owing to the lack of blood vessels and poor migration ability of chondrocytes, the self-healing ability of damaged cartilage is limited. Tissue engineering has brought a new direction for the regeneration of cartilage. Drug carriers and scaffolds made of hydrogels are widely used in cartilage tissue engineering. The present review introduces the natural hydrogels, which are often used for cartilage tissue engineering with respect to synthesis, modification and application methods.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

This review introduces the natural hydrogels that are often used in cartilage tissue engineering with respect to synthesis, modification and application methods. Furthermore, the essential concepts and recent discoveries were demonstrated to illustrate the achievable goals and the current limitations. In addition, we propose the putative challenges and directions for the use of natural hydrogels in cartilage regeneration.

Cell-Surface Engineering for Advanced Cell Therapy

Stem cells opened great opportunity to overcome diseases that conventional therapy had only limited success. Use of scaffolds made from biomaterials not only helps handling of stem cells for delivery or transplantation but also supports enhanced cell survival. Likewise, cell encapsulation can provide stability for living animal cells even in a state of separateness. Although various chemical reactions were tried to encapsulate stolid microbial cells such as yeasts, a culture environment for the growth of animal cells allows only highly biocompatible reactions. Therefore, the animal cells were mostly encapsulated in hydrogels, which resulted in enhanced cell survival. Interestingly, major findings of chemistry on biological interfaces demonstrate that cell encapsulation in hydrogels have a further a competence for modulating cell characteristics that can go beyond just enhancing the cell survival. In this review, we present a comprehensive overview on the chemical reactions applied to hydrogel-based cell encapsulation and their effects on the characteristics and behavior of living animal cells.

Cross-Linked Hydrogel for Pharmaceutical Applications: A Review

Hydrogels are promising biomaterials because of their important qualities such as biocompatibility, biodegradability, hydrophilicity and non-toxicity. These qualities make hydrogels suitable for application in medical and pharmaceutical field. Recently, a tremendous growth of hydrogel application is seen, especially as gel and patch form, in transdermal drug delivery. This review mainly focuses on the types of hydrogels based on cross-linking and; secondly to describe the possible synthesis methods to design hydrogels for different pharmaceutical applications. The synthesis and chemistry of these hydrogels are discussed using specific pharmaceutical examples. The structure and water content in a typical hydrogel have also been discussed.

Engineering Biodegradable and Biocompatible Bio-ionic Liquid Conjugated Hydrogels with Tunable Conductivity and Mechanical Properties

Conventional methods to engineer electroconductive hydrogels (ECHs) through the incorporation of conductive nanomaterials and polymers exhibit major technical limitations. These are mainly associated with the cytotoxicity, as well as poor solubility, processability, and biodegradability of their components. Here, we describe the engineering of a new class of ECHs through the functionalization of non-conductive polymers with a conductive choline-based bio-ionic liquid (Bio-IL). Bio-IL conjugated hydrogels exhibited a wide range of highly tunable physical properties, remarkable in vitro and in vivo biocompatibility, and high electrical conductivity without the need for additional conductive components. The engineered hydrogels could support the growth and function of primary cardiomyocytes in both two dimentinal (2D) and three dimensional (3D) cultures in vitro. Furthermore, they were shown to be efficiently biodegraded and possess low immunogenicity when implanted subcutaneously in rats. Taken together, our results suggest that Bio-IL conjugated hydrogels could be implemented and readily tailored to different biomedical and tissue engineering applications.

Delivery of growth factor-based therapeutics in vascular diseases: Challenges and strategies

Either cardiovascular or peripheral vascular diseases have become the major cause of morbidity and mortality worldwide. Recently, growth factors therapeutics, whatever administrated in form of exogenous growth factors or their relevant genes have been discovered to be an effective strategy for the prevention and therapy of vascular diseases, because of their promoting angiogenesis. Besides, as an alternative, stem cell-based therapy has been also developed in view of their paracrine-mediated effect or ability of differentiation toward angiogenesis-related cells under assistance of growth factors. Despite of being specific and potent, no matter growth factors or stem cells-based therapy, their full clinical transformation is limited from bench to bedside. In this review, the potential choices of therapeutic modes based on types of different growth factors or stem cells were firstly summarized for vascular diseases. The confronted various challenges such as lack of non-invasive delivery method, the physiochemical challenge, the short half-life time, and poor cell survival, were carefully analyzed for these therapeutic modes. Various strategies to overcome these limitations are put forward from the perspective of drug delivery. The expertised design of a suitable delivery form will undoubtedly provide valuable insight into their clinical application in the regenerative medicine.

Electrically conductive hydrogel-based micro-topographies for the development of organized cardiac tissues

In this study, we developed conductive microgrooved tissue constructs, leading to the formation of highly packed and uniaxially oriented cardiac cytoarchitecture.

Hydrogels for therapeutic cardiovascular angiogenesis

Acute myocardial infarction (MI) caused by ischemia is the most common cause of cardiac dysfunction. While growth factor or cell therapy is promising, the retention of bioactive agents in the highly vascularized myocardium is limited and prevents sustained activation needed for adequate cellular responses. Various types of biomaterials with different physical and chemical properties have been developed to improve the localized delivery of growth factor and/or cells for therapeutic angiogenesis in ischemic tissues. Hydrogels are particularly advantageous as carrier systems because they are structurally similar to the tissue extracellular matrix (ECM), they can be processed under relatively mild conditions and can be delivered in a minimally invasive manner. Moreover, hydrogels can be designed to degrade in a timely fashion that coincides with the angiogenic process. For these reasons, hydrogels have shown great potential as pro-angiogenic matrices. This paper reviews a few of the hydrogel systems currently being applied together with growth factor delivery and/or cell therapy to promote therapeutic angiogenesis in ischemic tissues, with emphasis on myocardial applications.

Multi-Functional Macromers for Hydrogel Design in Biomedical Engineering and Regenerative Medicine

Contemporary biomaterials are expected to provide tailored mechanical, biological and structural cues to encapsulated or invading cells in regenerative applications. In addition, the degradative properties of the material also have to be adjustable to the desired application. Oligo- or polymeric building blocks that can be further cross-linked into hydrogel networks, here addressed as macromers, appear as the prime option to assemble gels with the necessary degrees of freedom in the adjustment of the mentioned key parameters. Recent developments in the design of multi-functional macromers with two or more chemically different types of functionalities are summarized and discussed in this review illustrating recent trends in the development of advanced hydrogel building blocks for regenerative applications.

Grafting Techniques towards Production of Peptide-Tethered Hydrogels, a Novel Class of Materials with Biomedical Interest

In recent years, new highly functional polymeric biomaterials are being developed to increase the therapeutic efficacy in tissue regeneration approaches. Peptides regulate most physiological processes and display several other biological activities. Therefore, their importance in the field of biomedical research and drug development is rapidly increasing. However, the use of peptides as therapeutic agents is restricted by some of their physicochemical properties. The development of improved routes of delivery of peptide-based therapeutics is crucial and is crucial and its biomedical value is expected to increase in the near future. The unique properties of hydrogels triggered their spreading as localized drug depots. Several strategies, such as the carbodiimide chemistry, have been used to successfully immobilize bioactive peptide sequences into the hydrogels backbone. Peptide tethering through the so-called "click" chemistry reactions is also a highly promising, yet underexplored, approach to the synthesis of hydrogels with varying dimensions and patterns. The present review focus on the approaches that are being used for the establishment of chemical bonds between peptides and non-peptidic hydrogels throughout the last decade.

Strategies for the chemical and biological functionalization of scaffolds for cardiac tissue engineering: a review

The development of biomaterials for cardiac tissue engineering (CTE) is challenging, primarily owing to the requirement of achieving a surface with favourable characteristics that enhances cell attachment and maturation. The biomaterial surface plays a crucial role as it forms the interface between the scaffold (or cardiac patch) and the cells. In the field of CTE, synthetic polymers (polyglycerol sebacate, polyethylene glycol, polyglycolic acid, poly-l-lactide, polyvinyl alcohol, polycaprolactone, polyurethanes and poly(N-isopropylacrylamide)) have been proven to exhibit suitable biodegradable and mechanical properties. Despite the fact that they show the required biocompatible behaviour, most synthetic polymers exhibit poor cell attachment capability. These synthetic polymers are mostly hydrophobic and lack cell recognition sites, limiting their application. Therefore, biofunctionalization of these biomaterials to enhance cell attachment and cell material interaction is being widely investigated. There are numerous approaches for functionalizing a material, which can be classified as mechanical, physical, chemical and biological. In this review, recent studies reported in the literature to functionalize scaffolds in the context of CTE, are discussed. Surface, morphological, chemical and biological modifications are introduced and the results of novel promising strategies and techniques are discussed.

RGD-mimetic poly(amidoamine) hydrogel for the fabrication of complex cell-laden micro constructs

The potential of the 3D cell culture approach for creating in vitro models for drug screening and cellular studies, has led to the development of hydrogels that are able to mimic the in vivo 3D cellular milieu. To this aim, synthetic polymer-based hydrogels, with which it is possible to fine-tune the chemical and biophysical properties of the cell microenvironment, are becoming more and more acclaimed. Of all synthetic materials, poly(amidoamine)s (PAAs) hydrogels are known to have promising properties. In particular, PAAs hydrogels containing the 2,2-bisacrylamidoacetic acid-agmatine monomeric unit are capable of enhancing cellular adhesion by interacting with the RGD-binding αVβ3 integrin. The synthesis of a new photocrosslinkable, biomimetic PAA-Jeffamine®-PAA triblock copolymer (PJP) hydrogel is reported in this paper with the aim of improving the optical, biocompatibility and cell-adhesion properties of previously studied PAA hydrogels and providing an inexpensive alternative to the RGD peptide based hydrogels. The physicochemical properties of PJP hydrogels are extensively discussed and the behavior of 2D and 3D cell cultures was analyzed in depth with different cell types. Moreover, cell-laden PJP hydrogels were patterned with perfusable microchannels and seeded with endothelial cells, in order to investigate the possibility of using PJP hydrogels for fabricating cell laden tissue-like micro constructs and microfluidic devices. Overall the data obtained suggest that PJP could ultimately become a useful tool for fabricating improved in vitro models in order to potentially enhance the effectiveness of drug screening and clinical treatments.

RoY peptide-modified chitosan-based hydrogel to improve angiogenesis and cardiac repair under hypoxia

Myocardial infarction (MI) still represents the "Number One Killer" in the world. The lack of functional vasculature of the infracted myocardium under hypoxia is one of the main problems for cardiac repair. In this study, a thermosensitive chitosan chloride-RoY (CSCl-RoY) hydrogel was developed to improve angiogenesis under hypoxia after MI. First, RoY peptides were conjugated onto the CSCl chain via amide linkages, and our data show that the conjugation of RoY peptide to CSCl does not interfere with the temperature sensitivity. Then, the effect of CSCl-RoY hydrogels on vascularization in vitro under hypoxia was investigated using human umbilical vein endothelial cells (HUVECs). Results show that CSCl-RoY hydrogels can promote the survival, proliferation, migration and tube formation of HUVECs under hypoxia compared with CSCl hydrogel. Further investigations suggest that CSCl-RoY hydrogels can modulate the expression of membrane surface GRP78 receptor of HUVECs under hypoxia and then activate Akt and ERK1/2 signaling pathways related to cell survival/proliferation, thereby enhancing angiogenic activity of HUVECs under hypoxia. To assess its therapeutic properties in vivo, a MI model was induced in rats by the left anterior descending artery ligation. CSCl or CSCl-RoY hydrogels were injected into the border of infracted hearts. The results demonstrate that the introduction of RoY peptide can not only improve angiogenesis at MI region but also improve the cardiac functions. Overall, we conclude that the CSCl-RoY may represent an ideal scaffold material for injectable cardiac tissue engineering.

The role of tissue engineering in cellular therapies for myocardial infarction: a review

Current medical treatments of myocardial infarction (MI) face a serious shortcoming in that they cannot reverse the detrimental effects of ischemia induced necrosis.

Biomaterials in myocardial tissue engineering

Cardiovascular disease is the leading cause of death in the developed world, and as such there is a pressing need for treatment options. Cardiac tissue engineering emerged from the need to develop alternative sources and methods of replacing tissue damaged by cardiovascular diseases, as the ultimate treatment option for many who suffer from end-stage heart failure is a heart transplant. In this review we focus on biomaterial approaches to augmenting injured or impaired myocardium, with specific emphasis on: the design criteria for these biomaterials; the types of scaffolds - composed of natural or synthetic biomaterials or decellularized extracellular matrix - that have been used to develop cardiac patches and tissue models; methods to vascularize scaffolds and engineered tissue; and finally, injectable biomaterials (hydrogels) designed for endogenous repair, exogenous repair or as bulking agents to maintain ventricular geometry post-infarct. The challenges facing the field and obstacles that must be overcome to develop truly clinically viable cardiac therapies are also discussed.

25th anniversary article: Designer hydrogels for cell cultures: a materials selection guide

Cell culturing, whether for tissue engineering or cell biology studies, always involves placing cells in a non-natural environment and no material currently exist that can mimic the entire complexity of natural tissues and variety of cell-matrix interactions that is found in vivo. Here, we review the vast range of hydrogels, composed of natural or synthetic polymers that provide a route to tailored microenvironments.

Hydrogel based injectable scaffolds for cardiac tissue regeneration

Tissue engineering promises to be an effective strategy that can overcome the lacuna existing in the current pharmacological and interventional therapies and heart transplantation. Heart failure continues to be a major contributor to the morbidity and mortality across the globe. This may be attributed to the limited regeneration capacity after the adult cardiomyocytes are terminally differentiated or injured. Various strategies involving acellular scaffolds, stem cells, and combinations of stem cells, scaffolds and growth factors have been investigated for effective cardiac tissue regeneration. Recently, injectable hydrogels have emerged as a potential candidate among various categories of biomaterials for cardiac tissue regeneration due to improved patient compliance and facile administration via minimal invasive mode that treats complex infarction. This review discusses in detail on the advances made in the field of injectable materials for cardiac tissue engineering highlighting their merits over their preformed counterparts.

Minimally invasive cell-seeded biomaterial systems for injectable/epicardial implantation in ischemic heart disease

Myocardial infarction (MI) is characterized by heart-wall thinning, myocyte slippage, and ventricular dilation. The injury to the heart-wall muscle after MI is permanent, as after an abundant cell loss the myocardial tissue lacks the intrinsic capability to regenerate. New therapeutics are required for functional improvement and regeneration of the infarcted myocardium, to overcome harmful diagnosis of patients with heart failure, and to overcome the shortage of heart donors. In the past few years, myocardial tissue engineering has emerged as a new and ambitious approach for treating MI. Several left ventricular assist devices and epicardial patches have been developed for MI. These devices and acellular/cellular cardiac patches are employed surgically and sutured to the epicardial surface of the heart, limiting the region of therapeutic benefit. An injectable system offers the potential benefit of minimally invasive release into the myocardium either to restore the injured extracellular matrix or to act as a scaffold for cell delivery. Furthermore, intramyocardial injection of biomaterials and cells has opened new opportunities to explore and also to augment the potentials of this technique to ease morbidity and mortality rates owing to heart failure. This review summarizes the growing body of literature in the field of myocardial tissue engineering, where biomaterial injection, with or without simultaneous cellular delivery, has been pursued to enhance functional and structural outcomes following MI. Additionally, this review also provides a complete outlook on the tissue-engineering therapies presently being used for myocardial regeneration, as well as some perceptivity into the possible issues that may hinder its progress in the future.

High-efficiency matrix modulus-induced cardiac differentiation of human mesenchymal stem cells inside a thermosensitive hydrogel

Mesenchymal stem cells (MSCs) experience an extremely low rate of cardiac differentiation after transplantation into infarcted hearts, in part due to the inability of stiff scar tissue to support differentiation. We hypothesized that delivering MSCs in a hydrogel with a modulus matched to that of native heart tissue should stimulate MSC differentiation into cardiac cells. We have developed a thermosensitive and injectable hydrogel suitable for the delivery of cells into the heart, and found that the appropriate gel modulus can differentiate MSCs into cardiac cells with high efficiency. The hydrogel was based on N-isopropylacrylamide, N-acryloxysuccinimide, acrylic acid and poly(trimethylene carbonate)-hydroxyethyl methacrylate. The hydrogel solution can be readily injected through needles commonly used for heart injection, and is capable of gelling within 7s at 37°C. The formed gels were highly flexible, with breaking strains (>300%) higher than that of native heart tissue and moduli within the range of native heart tissue (1-140 kPa). Controlling the concentration of the hydrogel solution resulted in hydrogels with three different moduli: 16, 45 and 65 kPa. The moduli were decoupled from the gel water content and oxygen diffusion, parameters that can also influence cell differentiation. MSCs survived in the hydrogels throughout the entire culture period, and it was observed that gel stiffness did not affect cell survival. After 14 days of culture, more than 76% of MSCs had differentiated into cardiac cells in the 45 and 65 kPa gels, as confirmed by the expression of cardiac markers at both the gene and protein levels. MSCs in the hydrogel with the 65 kPa modulus had the highest differentiation efficiency. The differentiated cells also developed calcium channels that imparted an electrophysiological property, and gap junctions for cell-cell communication. The efficiency of differentiation reported in this study was much higher than for the differentiation approaches described in the literature, such as chemical induction and co-culture of MSCs and cardiomyocytes. These results indicate that the novel hydrogel holds great promise for delivering MSCs into an infarcted heart for the generation of new heart tissue.

Minimally invasive injectable short nanofibers of poly(glycerol sebacate) for cardiac tissue engineering

Myocardial tissue lacks the ability to appreciably regenerate itself following myocardial infarction (MI) which ultimately results in heart failure. Current therapies can only retard the progression of disease and hence tissue engineering strategies are required to facilitate the engineering of a suitable biomaterial to repair MI. The aim of this study was to investigate the in vitro properties of an injectable biomaterial for the regeneration of infarcted myocardium. Fabrication of core/shell fibers was by co-axial electrospinning, with poly(glycerol sebacate) (PGS) as core material and poly-L-lactic acid (PLLA) as shell material. The PLLA was removed by treatment of the PGS/PLLA core/shell fibers with DCM:hexane (2:1) to obtain PGS short fibers. These PGS short fibers offer the advantage of providing a minimally invasive injectable technique for the regeneration of infarcted myocardium. The scaffolds were characterized by SEM, FTIR and contact angle and cell-scaffold interactions using cardiomyocytes. The results showed that the cardiac marker proteins actinin, troponin, myosin heavy chain and connexin 43 were expressed more on short PGS fibers compared to PLLA nanofibers. We hypothesized that the injection of cells along with short PGS fibers would increase cell transplant retention and survival within the infarct, compared to the standard cell injection system.

Cell-based therapy for prevention and reversal of myocardial remodeling

Although pharmacological and interventional advances have reduced the morbidity and mortality of ischemic heart disease, there is an ongoing need for novel therapeutic strategies that prevent or reverse progressive ventricular remodeling following myocardial infarction, the process that forms the substrate for ventricular failure. The development of cell-based therapy as a strategy to repair or regenerate injured tissue offers extraordinary promise for a powerful anti-remodeling therapy. In this regard, the field of cell therapy has made major advancements in the past decade. Accumulating data from preclinical studies have provided novel insights into stem cell engraftment, differentiation, and interactions with host cellular elements, as well as the effectiveness of various methods of cell delivery and accuracy of diverse imaging modalities to assess therapeutic efficacy. These findings have in turn guided rationally designed translational clinical investigations. Collectively, there is a growing understanding of the parameters that underlie successful cell-based approaches for improving heart structure and function in ischemic and other cardiomyopathies.

Direct cell encapsulation in biodegradable and functionalizable carboxybetaine hydrogels

Hydrogels provide three-dimensional (3D) frames with tissue-like elasticity and high water content for tissue scaffolds. They were commonly prepared from macromers such as poly(ethylene glycol) diacrylate (PEGDA) via free radical polymerization and used to encapsulate cells. Here, we report the direct encapsulation of cells into hydrogels using a low-toxic and water-soluble monomer, carboxybetaine methacrylate (CBMA), via redox polymerization. A disulfide-containing crosslinker was added to form a biodegradable carboxybetaine (CB) hydrogel, which can be self-degraded as cells grow or degraded in an accelerating way via adding of a cysteine-contained medium NIH-3T3 cells encapsulated in the CB hydrogel formed spherical aggregates that were recovered from hydrogel erosion. Furthermore, an RGD-containing peptide was also added to improve cell adhesion on the two-dimensional (2D) hydrogel surface and promote cell proliferation in the 3D hydrogel. The non-cytotoxic and biodegradable CB hydrogel with additional cell-adhesion moieties provides an excellent 3D environment for cell growth as tissue scaffolds.

Semi-interpenetrating network of polyethylene glycol and photocrosslinkable chitosan as an in-situ-forming nerve adhesive

An ideal adhesive for anastomosis of severed peripheral nerves should tolerate strains imposed on rejoined nerves. We use blends of photocrosslinkable 4-azidobenzoic acid-modified chitosan (Az-C) and polyethylene glycol (PEG) as a new in-situ-forming bioadhesive for anastomosing and stabilizing the injured nerves. Cryo-scanning electron microscopy suggests that the polymer blends form a semi-interpenetrating network (semi-IPN), where PEG interpenetrates the Az-C network and reinforces it. Az-C/PEG semi-IPN gels have higher storage moduli than Az-C gel alone and fibrin glue. Nerves anastomosed with an Az-C/PEG gel tolerate a higher force than those with fibrin glue prior to failure. A series of ex vivo and in vitro cell experiments indicate the Az-C/PEG gels are compatible with nerve tissues and cells. In addition, Az-C/PEG gels release PEG over a prolonged period, providing sustained delivery of PEG, a potential aid for nerve cell preservation through membrane fusion. Az-C/PEG semi-IPN gels are promising bioadhesives for repairing severed peripheral nerves not only because of their improved mechanical properties but also because of their therapeutic potential and tissue compatibility.

Hydrogels for protein delivery in tissue engineering

Tissue defects caused by diseases or trauma present enormous challenges in regenerative medicine. Recently, a better understanding of the biological processes underlying tissue repair led to the establishment of new approaches in tissue engineering which comprise the combination of biodegradable scaffolds and appropriate cells together with specific environmental cues, such as growth or adhesive factors. These factors (in fact proteins) have to be loaded and sustainably released from the scaffolds in time. This review provides an overview of the various hydrogel technologies that have been proposed to control the release of bioactive molecules of interest for tissue engineering applications. In particular, after a brief introduction on bioactive protein drugs that have remarkable relevance for tissue engineering, this review will discuss their release mechanisms from hydrogels, their encapsulation and immobilization methods and will overview the main classes of hydrogel forming biomaterials used in vitro and in vivo to release them. Finally, an outlook on future directions and a glimpse into the current clinical developments are provided.