Reversibly Assembled Electroconductive Hydrogel via a Host-Guest Interaction for 3D Cell Culture

Physical and Chemical Factors Influencing the Printability of Hydrogel-based Extrusion Bioinks

Bioprinting researchers agree that "printability" is a key characteristic for bioink development, but neither the meaning of the term nor the best way to experimentally measure it has been established. Furthermore, little is known with respect to the underlying mechanisms which determine a bioink's printability. A thorough understanding of these mechanisms is key to the intentional design of new bioinks. For the purposes of this review, the domain of printability is defined as the bioink requirements which are unique to bioprinting and occur during the printing process. Within this domain, the different aspects of printability and the factors which influence them are reviewed. The extrudability, filament classification, shape fidelity, and printing accuracy of bioinks are examined in detail with respect to their rheological properties, chemical structure, and printing parameters. These relationships are discussed and areas where further research is needed, are identified. This review serves to aid the bioink development process, which will continue to play a major role in the successes and failures of bioprinting, tissue engineering, and regenerative medicine going forward.

Polycyclodextrins: Synthesis, functionalization, and applications

Cyclodextrins (CDs) are cyclic oligosaccharides with unique conical structure enabling host-guest inclusion complexes. However, virgin CDs sufferfrom low solubility, lack of functional groups and its inability to strong complexation with the guests. One of the most efficient ways to improve the properties of cyclodextrins is the synthesis of polycyclodextrins. Generally, there are two types of polycyclodextrins: 1) polymers containing CD units as parts of the main backbone; and 2) polymers with CD units as side chains. These polycyclodextrins are produced (i) from direct copolymerization of virgin cyclodextrins or cyclodextrins derivatives with various monomers including isocyanates, epoxides, carboxylic acids, anhydrides, acrylates, acrylamides and fluorinated aromatic compounds, or (ii) by post-functionalization of other polymers with CDs or CD derivatives.. By selecting the proper derivatives of CDs and controlling the polymerization, polycyclodextrins with linear, hyperbranched, and crosslinked structures have been synthesized. Polycyclodextrins have found significant applications in numerous areas, as adsorbents for removal of organic pollutants, carriers in gene/drug delivery, and for preparation of supramolecular based hydrogels. The focus of this review paper is placed on the synthesis, characterization, and applications of CDs so as to highlight challenges as well as the promising features of the future ahead of material developments based on CDs.

Functional Polymers Structures for (Bio)Sensing Application-A Review

In this review we present polymeric materials for (bio)sensor technology development. We focused on conductive polymers (conjugated microporous polymer, polymer gels), composites, molecularly imprinted polymers and their influence on the design and fabrication of bio(sensors), which in the future could act as lab-on-a-chip (LOC) devices. LOC instruments enable us to perform a wide range of analysis away from the stationary laboratory. Characterized polymeric species represent promising candidates in biosensor or sensor technology for LOC development, not only for manufacturing these devices, but also as a surface for biologically active materials' immobilization. The presence of biological compounds can improve the sensitivity and selectivity of analytical tools, which in the case of medical diagnostics is extremely important. The described materials are biocompatible, cost-effective, flexible and are an excellent platform for the anchoring of specific compounds.

Alkaline Double-Network Hydrogels with High Conductivities, Superior Mechanical Performances, and Antifreezing Properties for Solid-State Zinc-Air Batteries

For the development of advanced flexible and wearable electronic devices, functional electrolytes with excellent conductivity, temperature tolerance, and desirable mechanical properties need to be engineered. Herein, an alkaline double-network hydrogel with high conductivity and superior mechanical and antifreezing properties is designed and promisingly utilized as the flexible electrolyte in all-solid-state zinc-air batteries. The conductive hydrogel is comprised of covalently cross-linked polyelectrolyte poly(2-acrylamido-2-methylpropanesulfonic acid potassium salt) (PAMPS-K) and interpenetrating methyl cellulose (MC) in the presence of concentrated alkaline solutions. The covalently cross-linked PAMPS-K skeleton and interpenetrating MC chains endow the hydrogel with good mechanical strength, toughness, an extremely rapid self-recovery capability, and an outstanding antifatigue property. Gratifyingly, the entrapment of a concentrated alkaline solution in the hydrogel matrix yields an extremely high ionic conductivity (105 mS cm^-1 at 25 °C) and an excellent antifreezing capacity. The hydrogel retains comparable conductivity and eligible strength to withstand various mechanical deformations at -20 °C. The all-solid-state zinc-air batteries using PAMPS-K/MC hydrogels as flexible alkaline electrolytes exhibit comparable values of specific capacity (764.7 mAh g^-1), energy capacity (850.2 mWh g^-1), cycling stability, and mechanical flexibility. The batteries still possess competitive electrochemical performances even when the operating temperature drops to -20 °C.

A review on recent advances in polymer and peptide hydrogels

In this review, we focus on the very recent developments on the use of the stimuli responsive properties of polymer hydrogels for targeted drug delivery, tissue engineering, and biosensing utilizing their different optoelectronic properties. Besides, the stimuli-responsive hydrogels, the conducting polymer hydrogels are discussed, with specific attention to the energy generation and storage behavior of the xerogel derived from the hydrogel. The electronic and ionic conducting gels have been discussed that have applications in various electronic devices, e.g., organic field effect transistors, soft robotics, ionic skins, and sensors. The properties of polymer hybrid gels containing carbon nanomaterials have been exemplified here giving attention to applications in supercapacitors, dye sensitized solar cells, photocurrent switching, etc. Recent trends in the properties and applications of some natural polymer gels to produce thermal and acoustic insulating materials, drug delivery vehicles, self-healing material, tissue engineering, etc., are discussed. Besides the polymer gels, peptide gels of different dipeptides, tripeptides, oligopeptides, polypeptides, cyclic peptides, etc., are discussed, giving attention mainly to biosensing, bioimaging, and drug delivery applications. The properties of peptide-based hybrid hydrogels with polymers, nanoparticles, nucleotides, fullerene, etc., are discussed, giving specific attention to drug delivery, cell culture, bio-sensing, and bioimaging properties. Thus, the present review delineates, in short, the preparation, properties, and applications of different polymer and peptide hydrogels prepared in the past few years.

Cytocompatible, Injectable, and Electroconductive Soft Adhesives with Hybrid Covalent/Noncovalent Dynamic Network

Synthetic conductive biopolymers have gained increasing interest in tissue engineering, as they can provide a chemically defined electroconductive and biomimetic microenvironment for cells. In addition to low cytotoxicity and high biocompatibility, injectability and adhesiveness are important for many biomedical applications but have proven to be very challenging. Recent results show that fascinating material properties can be realized with a bioinspired hybrid network, especially through the synergy between irreversible covalent crosslinking and reversible noncovalent self-assembly. Herein, a polysaccharide-based conductive hydrogel crosslinked through noncovalent and reversible covalent reactions is reported. The hybrid material exhibits rheological properties associated with dynamic networks such as self-healing and stress relaxation. Moreover, through fine-tuning the network dynamics by varying covalent/noncovalent crosslinking content and incorporating electroconductive polymers, the resulting materials exhibit electroconductivity and reliable adhesive strength, at a similar range to that of clinically used fibrin glue. The conductive soft adhesives exhibit high cytocompatibility in 2D/3D cell cultures and can promote myogenic differentiation of myoblast cells. The heparin-containing electroconductive adhesive shows high biocompatibility in immunocompetent mice, both for topical application and as injectable materials. The materials could have utilities in many biomedical applications, especially in the area of cardiovascular diseases and wound dressing.

Cell-Laden Electroconductive Hydrogel Simulating Nerve Matrix To Deliver Electrical Cues and Promote Neurogenesis

Natural nerve tissue is composed of nerve bundles with multiple aligned assembles, and matrix electroconductivity is beneficial to the transmission of intercellular electrical signals, or effectively deliver external electrical cues to cells. Herein, aiming at the biomimetic design of the extracellular matrix for neurons, we first synthesized electroconductive polypyrrole (PPy) nanoparticles with modified hydrophilicity to improve their uniformity in collagen hydrogel. Next, cell-laden collagen-PPy hybrid hydrogel microfibers with highly oriented microstructures were fabricated via a microfluidic chip. The hydrogel microfibers formed a biomimetic three-dimensional microenvironment for neurons, resulting from the native cell adhesion domains, oriented fibrous structures, and conductivity. The oriented fibrous microstructures enhanced neuron-like cells aligning with fibers' axon; the matrix conductivity improved cell extension and upregulated neural-related gene expression; moreover, external electrical stimulation further promoted the neuronal functional expression. This mechanism was attributed to the electroconductive matrix and its delivered electrical stimulation to cells synergistically upregulated the expression of an L-type voltage-gated calcium channel, resulting in an increase in the intracellular calcium level, which in turn promoted neurogenesis. This approach has potential in constructing the biomimetic microenvironment for neurogenesis.