Two-Photon Polymerized Poly(2-Ethyl-2-Oxazoline) Hydrogel 3D Microstructures with Tunable Mechanical Properties for Tissue Engineering.

As the cornerstone of tissue engineering and regeneration medicine research, developing a cost-effective and bionic extracellular matrix (ECM) that can precisely modulate cellular behavior and form functional tissue remains challenging. An artificial ECM combining polysaccharides and fibrillar proteins to mimic the structure and composition of natural ECM provides a promising solution for cardiac tissue regeneration. In this study, we developed a bionic hydrogel scaffold by combining a quaternized β-chitin derivative (QC) and fibrin-matrigel (FM) in different ratios to mimic a natural ECM. We evaluated the stiffness of those composite hydrogels with different mixing ratios and their effects on the growth of human umbilical vein endothelial cells (HUVECs). The optimal hydrogels, QCFM1 hydrogels were further applied to load HUVECs into nude mice for in vivo angiogenesis. Besides, we encapsulated human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) into QCFM hydrogels and employed 3D bioprinting to achieve batch fabrication of human-engineered heart tissue (hEHT). Finally, the myocardial structure and electrophysiological function of hEHT were evaluated by immunofluorescence and optical mapping. Designed artificial ECM has a tunable modulus (220-1380 Pa), which determines the different cellular behavior of HUVECs when encapsulated in these. QCFM1 composite hydrogels with optimal stiffness (800 Pa) and porous architecture were finally identified, which could adapt for in vitro cell spreading and in vivo angiogenesis of HUVECs. Moreover, QCFM1 hydrogels were applied in 3D bioprinting successfully to achieve batch fabrication of both ring-shaped and patch-shaped hEHT. These QCFM1 hydrogels-based hEHTs possess organized sarcomeres and advanced function characteristics comparable to reported hEHTs. The chitin-derived hydrogels are first used for cardiac tissue engineering and achieve the batch fabrication of functionalized artificial myocardium. Specifically, these novel QCFM1 hydrogels provided a reliable and economical choice serving as ideal ECM for application in tissue engineering and regeneration medicine.

Tissue engineering has emerged as a viable approach to treat disease or repair damage in tissues and organs. One of the key elements for the success of tissue engineering is the use of a scaffold serving as artificial extracellular matrix (ECM). The ECM hosts the cells and improves their survival, proliferation, and differentiation, enabling the formation of new tissue. Here, we propose the development of a class of protein/polysaccharide-based porous scaffolds for use as ECM substitutes in cardiac tissue engineering. Scaffolds based on blends of a protein component, collagen or gelatin, with a polysaccharide component, alginate, were produced by freeze-drying and subsequent ionic and chemical crosslinking. Their morphological, physicochemical, and mechanical properties were determined and compared with those of natural porcine myocardium. We demonstrated that our scaffolds possessed highly porous and interconnected structures, and the chemical homogeneity of the natural ECM was well reproduced in both types of scaffolds. Furthermore, the alginate/gelatin (AG) scaffolds better mimicked the native tissue in terms of interactions between components and protein secondary structure, and in terms of swelling behavior. The AG scaffolds also showed superior mechanical properties for the desired application and supported better adhesion, growth, and differentiation of myoblasts under static conditions. The AG scaffolds were subsequently used for culturing neonatal rat cardiomyocytes, where high viability of the resulting cardiac constructs was observed under dynamic flow culture in a microfluidic bioreactor. We therefore propose our protein/polysaccharide scaffolds as a viable ECM substitute for applications in cardiac tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 769-781, 2018.

Electrically conductive biomaterials based on natural polysaccharides: Challenges and applications in tissue engineering

Development of Flexible Nanocomposites Based on Poly(ε-caprolactone) for Tissue Engineering Application: The Contributing Role of Poly(glycerol succinic acid) and Polypyrrole

The effects of inulin with three different degrees of polymerization (DP) on microbial dietary fiber fermentation were compared in an in vitro simulator of the porcine large bowel. The three inulin isolates had a DP of 15 (from chicory grown in Hokkaido, Japan), and 10 and 24 (from Orafti, Belgium), while cellulose was used as a control. The Lactobacillus level in the DP 10 group at 48 h and bifidobacteria levels in the DP 15 and DP 24 groups at 24 and 48 h were significantly higher than in the carbohydrate-free and cellulose groups. The SCFA concentrations in all the inulin groups were significantly higher than in the carbohydrate-free and cellulose groups at 24 and 48 h. Ammonia nitrogen concentrations in all the inulin groups were significantly lower than those in the carbohydrate-free and cellulose groups at 24 and 48 h. The three different inulin types were fermentable by gut microbiota as indicated by substantial increases in SCFA. In particular, inulin DP 15 exhibited a clear potential to be used as a prebiotic with significant increases in Lactobacillus and Bifidobacterium populations, and concomitantly propionate and butyrate productions than cellulose at the early incubation time. There was a negative correlation between SCFA and ammonia nitrogen concentrations. These results indicate DP 15 product has similar potential as a prebiotic to DP 10 or DP 24 product and showed substantial equivalence to DP 10 and DP 24 products.

In this work, a versatile and simple strategy to build an injectable interpenetrating polymer network (IPN) hydrogel with tunable mechanical properties and self‐healing ability is reported. The gelation time and mechanical properties can be tuned by pH or the solid content. Due to the exchange of acylhydrazone and boronate ester bonds formed between functionalized prepolymers, the hydrogels can self‐heal at either acidic or basic condition. Furthermore, the pH‐induced IPN to semi‐IPN reversible transition endows the hydrogels with tunable pore structure and mechanical properties. It is hoped that this novel strategy will provide new opportunities in design and preparation of 3D‐printable IPN hydrogels, fostering their use in a wide range of applications such as controlled drug release and tissue engineering.

Ionogels, with wide applications in tissue engineering, soft robotics, and flexible iontronic devices, require tunable optical, mechanical, and electrical properties for advanced functionality applications. Here, a facile strategy is reported to tune a set of properties of ionogels via tuning the redox states of the added polyoxometalate (POM) clusters. Upon external electrical stimuli, the POM clusters in the ionogels can be reversibly tuned from a transparent, oxidized state to a blue, reduced state. The redox states of the POM anions influence the POM‐polymer interactions, which promotes the in situ modulation of the ionogel properties reversibly over a large window: optical transparency from 91% to 7%, dissipated energy from 0.9 to 3.1 MJ m−3, elastic modulus from 1.5 to 2 MPa, conductivity from 1.6 × 10−4 to 2.2 × 10−4 S cm−1. Meanwhile, the sensory properties of the ionogels can be modulated simultaneously. For strain sensing and pressure sensing, the GF can be tuned from 2.3 to 7.2, and the sensitivity can be tuned from 0.8 to 1.2 kPa−1. Such an ionogel with tunable optical, mechanical, and electrical properties may find a variety of applications meeting specific demands. The POM functionalization strategy may also bring new insights into the design of the stimuli‐responsive ionogels.

ABSTRACTIntroduction: The applications of naturally obtained polymers are tremendously increased due to them being biocompatible, biodegradable, environmentally friendly and renewable in nature. Among them, polyhydroxyalkanoates are widely studied and they can be utilized in many areas of human life research such as drug delivery, tissue engineering, and other medical applications.Areas covered: This review provides an overview of the polyhydroxyalkanoates biosynthesis and their possible applications in drug delivery in the range of micro- and nano-size. Moreover, the possible applications in tissue engineering are covered considering macro- and microporous scaffolds and extracellular matrix analogs.Expert commentary: The majority of synthetic plastics are non-biodegradable so, in the last years, a renewed interest is growing to develop alternative processes to produce biologically derived polymers. Among them, PHAs present good properties such as high immunotolerance, low toxicity, biodegradability, so, they are promisingly using as biomaterials in biomedical applications.

Collagen peptide (COP) is water soluble, bioactive, and tends to be a promising alternative to collagen for tissue regeneration. However, its low viscosity and lack of readily polymerizable groups hinder its bioprinting and limit its wide applications in tissue engineering. In this study, methacrylated collagen peptide‐xanthan gum (COPMA‐XG) bioinks with interpenetrating networks are developed for bioprinting stable constructs, followed by stem cell differentiation. First, self‐healing COPMA hydrogels are developed with rapid UV‐curing and tunable mechanical properties. To increase the printability and the mechanical properties of COPMA, XG is mixed to create a set of COPMA‐XG bioinks. COPMA‐XG hydrogels show self‐healing properties, optimal printability, and stable morphology in the medium. The bioprinted human bone marrow mesenchymal stem cells (hMSCs) laden COPMA‐XG constructs are biocompatible and bioactive, with increased production of extracellular matrix, collagen type I, and scleraxis over 28 days. Overall, bioprinted COPMA‐XG constructs are versatile matrices to support hMSCs proliferation and differentiation with potential for ligament tissue engineering.

The successful engineering of synthetic hydrogels that exhibit key features of the natural extracellular matrices has led to significant advances in the field of tissue engineering. Various chemical and physical approaches have been developed for hydrogel synthesis. While the chemical methods rely on the presence of readily addressable functional groups for the formation of covalent bonds at the crosslinking points, the physical approaches utilize weak and reversible interactions for gelation purposes. In many cases, physical gels need to be covalently stabilized for their long term applications in tissue engineering. Over the past decade, hydrogels have evolved from passive scaffolding materials to bioactive and cell-responsive matrices that play a defining role in the regulation of cellular functions and tissue growth. Novel hydrogels with tunable microstructures, mechanical properties, and degradation rates have been engineered. Biological motifs or soluble factors have been successfully incorporated in the hydrogel matrices to allow for a higher level of cell-matrix communication. These synthesis methods have resulted in the production of a wide variety of functional hydrogels that support the growth of many different tissue types. The development of the next generation biomimetic hydrogels relies on parallel advancements in materials chemistry, cell biology and developmental biology.

Matrikines for therapeutic and biomedical applications

Scaffold‐guided tissue engineering based on synthetic and natural occurring polymers has gained many interests in recent year. In this study, the development of a chitosan‐heparin artificial extracellular matrix (AECM) is reported. Three‐dimensional, macroporous composite AECMs composed of heparin (Hep) and chitosan (Chito) were prepared by an interpolyelectrolyte complex/lyophilization method. The Chito‐Hep composite AECMs were, respectively, crosslinked with glutaraldehyde, as well as cocrosslinked with N,N‐(3‐dimethylaminopropyl)‐N′‐ethyl carbodiimide (EDC/NHS) and N‐hydroxysuccinimide (NHS). The crosslinking reactions were examined by FT‐IR analysis. In physiological buffer solution (PBS), the EDC/NHS‐crosslinked Chito‐Hep composite AECM showed a relative lower water retention ratio than its glutaraldehyde‐crosslinked counterparts. The EDC/NHS‐crosslinked Chito‐Hep composite AECMs showed excellent biocompatibility, according to the results of the in vitro cytotoxic test. This result suggested that the EDC/NHS‐crosslinked Chito‐Hep composite AECMs might be a potential biomaterial for scaffold‐guided tissue engineering applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Hydrogels have the capability to absorb large amounts of water or biological fluids into their three-dimensional hydrophilic polymer networks. These attractive materials are used to develop food additives, superabsorbents, wound dressing compounds, pharmaceuticals, and biomedical implants and also applied in tissue engineering, regenerative medicines, and controlled-release process. Hydrogels can be obtained from synthetic and/or natural resources. Synthetic hydrogels exhibit high water absorption capacities and proper mechanical strengthMechanical strength, although their applications are being limited because of low biocompatibility and biodegradability as well as the toxicity arisen from unreacted monomers remained in the gel structure. Natural hydrogels are often derived from polysaccharides and proteins. Protein-based hydrogels have substantial advantages such as biocompatibility, biodegradability, tunable mechanical properties, molecular binding abilities, and intelligent responses to external stimuli such as pH, ionic strength, and temperature. Therefore, this kind of hydrogels is known as smart biomaterials for controlled release, tissue engineering, regenerative medicine, and other applications. Protein can be converted to hydrogel using physical, chemical, or enzymatic treatments. To improve their mechanical properties, hybrid hydrogels are synthesized by combining natural polymers with synthetic ones. The main approach to obtain hybrid hydrogels is grafting natural polymers with synthetic one and vice versa. This chapter intends to look over protein-based hydrogels. After brief introduction of protein and its structure, the properties of proteins and peptides used to develop hydrogels, as well as their preparation methods are discussed. The potential applications of these polypeptide-based hydrogels in the fields of superabsorbent development, tissue engineering, and controlled release are reported. Characterization methods for protein-based hydrogels are covered in the final section to determine rheological properties, morphology, and thermal stability.

The eggshell membrane (ESM) is usually regarded as an agricultural byproduct waste, even though it has unique properties as a biomaterial. In particular, the ESM has a flexible and highly pure microfibrous network structure that can be used as an artificial extracellular matrix (ECM) platform for engraftment or as a tissue-engineered scaffold. In this study, flexible and functional scaffolds were constructed using an ESM and graphene, and their applicability for stem cell and tissue engineering was analyzed. The graphene-layered ESM (GEM) scaffolds show enhanced characteristics, such as ECM-like hierarchical micro- and nanostructures and better mechanical and hydrophilic properties than those of a raw ESM. The GEM scaffolds can control the adhesion properties of stem cells, enhancing the proliferation and osteogenic properties of the cells compared with the effects of a raw ESM. Additionally, the GEM scaffolds can improve the secretion of growth factors from stem cells, possibly through enhanced cell-substrate interactions, thereby promoting the proliferation and differentiation of these cells.

SummaryChitooligosaccharides (COS) with different degree of polymerisation (DP) have different physiological activities such as anti‐tumour and anti‐hyperlipidemia activities. However, the digestive process might lead to the change of DP of COS as well as cause the change of physiological activities in vivo. In this study, two in vitro digestion models (static and dynamic) were used to investigate digestion behaviours of COS and the influencing factors during digestion with or without food matrix. The results showed that COS with DP 2–5 were indigestible and COS with DP 6–10 degraded with time during gastric and intestinal digestion. Pepsin, pancreatin and lipase were the main factors leading to degradation. Food matrix could protect COS with DP 6–10 from degradation during gastric digestion. However, the degradation of COS with DP 6–10 accelerated and the degradation of COS with DP 5 occurred during intestinal digestion with food matrix due to pancreatin, lipase and bile salt.