Adjustable Mechanical Properties Research Articles

Highly Stretchable Double Network Ionogels for Monitoring Physiological Signals and Detecting Sign Language

At the heart of the non-implantable electronic revolution lies ionogels, which are remarkably conductive, thermally stable, and even antimicrobial materials. Yet, their potential has been hindered by poor mechanical properties. Herein, a double network (DN) ionogel crafted from 1-Ethyl-3-methylimidazolium chloride ([Emim]Cl), acrylamide (AM), and polyvinyl alcohol (PVA) was constructed. Tensile strength, fracture elongation, and conductivity can be adjusted across a wide range, enabling researchers to fabricate the material to meet specific needs. With adjustable mechanical properties, such as tensile strength (0.06–5.30 MPa) and fracture elongation (363–1373%), this ionogel possesses both robustness and flexibility. This ionogel exhibits a bi-modal response to temperature and strain, making it an ideal candidate for strain sensor applications. It also functions as a flexible strain sensor that can detect physiological signals in real time, opening doors to personalized health monitoring and disease management. Moreover, these gels’ ability to decode the intricate movements of sign language paves the way for improved communication accessibility for the deaf and hard-of-hearing community. This DN ionogel lays the foundation for a future in which e-skins and wearable sensors will seamlessly integrate into our lives, revolutionizing healthcare, human–machine interaction, and beyond.

N-type semiconducting hydrogel.

Hydrogels are an attractive category of biointerfacing materials with adjustable mechanical properties, diverse biochemical functions, and good ionic conductivity. Despite these advantages, their application in electronics has been restricted because of their lack of semiconducting properties, and they have traditionally only served as insulators or conductors. We developed single- and multiple-network hydrogels based on a water-soluble n-type semiconducting polymer, endowing conventional hydrogels with semiconducting capabilities. These hydrogels show good electron mobilities and high on/off ratios, enabling the fabrication of complementary logic circuits and signal amplifiers with low power consumption and high gains. We demonstrate that hydrogel electronics with good bioadhesive and biocompatible interface can sense and amplify electrophysiological signals with enhanced signal-to-noise ratios.

CQDs-Cross-Linked Conductive Collagen/PAA-Based Nanocomposite Organohydrogel Coupling Flexibility with Multifunctionality for Dual-Modal Sensing of Human Motions.

Conductive hydrogels are ideal materials for intelligent medical devices, human-machine interfaces, and flexible bioelectrodes due to their adjustable mechanical properties and electrical responsiveness, whereas it is still a great challenge to achieve the integration of excellent flexibility and biocompatibility into one hydrogel sensor while also incorporating self-healing, self-adhesion, environmental tolerance, and antimicrobial properties. Here, a nanocomposite conductive organohydrogel was constructed by using collagen (Col), alginate-derived carbon quantum dots (OSA-CQDs), poly(acrylic acid) (PAA), ethylene glycol reduced AgNPs, and Fe3+ ions. Depending on OSA-CQDs with multiple chemical binding sites and high specific surface area as cross-linkers, while coupling highly biologically active Col chains and PAA chains are serving as an energy dissipation module, the resulting organohydrogel exhibited excellent flexibility (795% of strain, 193 kPa of strength), high cell compatibility (>95% survival rate), self-healing efficiency (HE = 79.5%), antifreezing (-20 °C), moisturizing (>120 h), repeatable adhesion (strength >20 kPa, times >10), inhibitory activity against Escherichia coli and Staphylococcus aureus (9 and 21.5 cm2), conductivity, and strain sensitivity (σ = 1.34 S/m, gauge factor (GF) = 11.63). Based on the all-in-one integration of multifunction, the organohydrogel can collaboratively adapt to the multimode of strain sensing and electrophysiological sensing to realize wireless real-time monitoring of human activities and physiological health. Therefore, this work provides a new and common platform for the design and sensing of next-generation hydrogel-based smart wearable sensors.

Facile fabrication and characteristics of enzymatically crosslinked injectable tyramine-substituted egg white hydrogels

Protein-based materials have always been preferred because they can be engineered into a wide range of biomaterials with multiple excellent properties including low immunogenicity, tunable mechanical properties and promotion of cell adhesion and proliferation. Spectacularly, chicken egg white (EW) has drawn particular attention in the biomaterial field due to its high bioactivity, low production costs and easy handling. In this study, EW was firstly modified with tyramine (TA) and then enzymatically crosslinked to form injectable EW-TA hydrogels through horseradish peroxidase (HRP) and hydrogen peroxide (H2O2). The prepared EW-TA hydrogels demonstrated adjustable mechanical properties and degradation behavior. When co-cultured with NIH-3 T3 cells, the EW-TA hydrogels exhibited excellent biocompatibility. Based on the above results, the fabricated EW hydrogel, which has excellent performance, possesses promosing prospect for biomedical applications.

Ultra-stretchable and anti-freezing ionic conductive hydrogels as high performance strain sensors and flexible triboelectric nanogenerator in extreme environments

Conductive hydrogels have shown promising applications in a variety of portable smart wearable electronics and flexible sensors due to their high flexibility, stretchability, adjustable mechanical properties and excellent electrical conductivity. However, most of the current hydrogel-based flexible strain sensors and portable triboelectric nanogenerator (TENG) generally suffer from low stretchability/flexibility, poor mechanical properties, weak low-temperature tolerance and low power output. Herein, a multifunctional ionic conductive hydrogel (PPAVC-BA) with ultra-stretchability (∼1750%), high transparency (85%), high electrical conductivity (13.7 mS/cm), and outstanding anti-freezing properties (below −80°C without freezing). The strain sensor assembled from the PPAVC-BA hydrogel shows high sensitivity (GF=4.43) and ultra-wide sensing detection range (0%-1100%) as well as fast response time. Based on these properties, the PPAVC-BA hydrogel strain sensor can accurately recognize different joint movements of the human body as well as weak muscle beats. In addition, the PPAVC-BA hydrogel-based TENG (PPAVC-BA-TENG) exhibits excellent electrical output performance, with an open circuit voltage (Voc) of about 420 V, a short circuit current (Isc) of 23 μA, a short-circuit transfer charge (Qsc) of 112 nC and a maximum power density of 2246.03 mW/m2, which allows it to power small electronic devices. This PPAVC-BA-TENG also shows outstanding tensile performance and can output stable electrical signals at 200% strain. Impressively, the PPAVC-BA-TENG exhibits good electrical output performance even at low temperature of −50°C and high temperature of 80°C. The flexible strain sensors and stretchable TENG for high performance and multifunctionality reported in this work provide viable references in the development of motion detection, energy harvesting and self-powered electronic devices.

Multifunctional organohydrogels for on-demand controlled drug release

Controlled drug release has sparked much attention in the field of drug delivery by prolonging the duration of drug effectiveness and reducing drug toxicity. However, the development of controlled-release drug delivery systems remains a significant challenge, primarily due to inadequate drug compatibility, low biocompatibility, and low response sensitivity of the drug carriers. Herein, an innovative strategy for fabricating multifunctional organohydrogels as drug carrier systems is designed. 1-Tetradecanol/water emulsions, stabilized by cellulose acetoacetate (CAA), are initially prepared. The organohydrogels are fabricated by the ternary enzyme-mediated polymerization of the monomer- containing emulsion. The amphipathy of CAA ensures the stability of emulsions during polymerization, and CAA participates in polymerization as an initiator. Through the reversible crystallization-melting transition of 1-tetradecanol, the drug can be encapsulated in/released from the organohydrogel. Moreover, 1-tetradecanol enhances the bioavailability of water-insoluble drugs without any additional cosolvent. Therefore, biofriendly organohydrogels can serve as ideal dressings with adjustable mechanical properties, effective temperature regulation, and temperature-triggered drug release ability.

Fabrication of Si3N4 ceramics with adjustable microstructure and mechanical properties via Y2O3 contents in ZrN–AlN–Y2O3 ternary sintering additives

To adapt to the different application environments, Si3N4 ceramics are required to have different mechanical properties. Therefore, in this study, Si3N4 ceramics with adjustable mechanical properties were fabricated via using ZrN–AlN–Y2O3 ternary sintering additives and hot-pressing at 1650 °C for 30 min. Subsequently, the effect of the Y2O3 concentration on the phase assemblage, microstructure, mechanical properties, and crack propagation of Si3N4 ceramics was systematically investigated. The results demonstrated that Si3N4 ceramics presented adjustable microstructure and mechanical properties with the Y2O3 contents added in the range of 0∼8 wt%. With the increase of Y2O3 contents, the average aspect ratio of Si3N4 grains had an increase of 61.77%, increasing from 3.95 to 6.39. Besides, the Si3N4 grains and the formed YAG intergranular phase exhibited a fairly good combination at the nano-scale. Si3N4 grains and intergranular phase were the main influence factors on the mechanical properties of Si3N4 ceramics. As a result, the bending strength was from 700.99 ± 38.72 to 961.13 ± 36.84 MPa. The fracture toughness exhibited a range of 4.87 ± 0.11 to 6.10 ± 0.23 MPa⋅m1/2, while Vickers hardness achieved a high level of 16.09 ± 0.16 to 19.98 ± 0.39 GPa.

Dual crosslinking silk fibroin/pectin-based bioink development and the application on neural stem/progenitor cells spheroid laden 3D bioprinting

The human nervous system is an incredibly intricate physiological network, and neural cells lack the ability to repair and regenerate after a brain injury. 3-dimensional (3D) bioprinting technology offers a promising strategy for constructing biomimetic organ constructs and in vitro brain/disease models. The bioink serves as a pivotal component that emulates the microenvironment of biomimetic construct and exerts a profound influence on cellular behaviors.In this study, a series of mechanically adjustable and dual crosslinking bioinks were developed using photocrosslinkable methacrylated silk fibroin (SilMA) in combination with the ionic crosslinking material, pectin, or pectin methacryloyl (PecMA) with silk fibroin (SF) supplementation. SilMA/pectin exhibited superior properties, with SilMA providing biocompatibility and adjustable mechanical properties, while the addition of pectin enhanced printability. The porous structure supported neural cell growth, and 15 % SilMA/0.5 % pectin bioinks displayed excellent printability and shape fidelity. Neural stem/progenitor cells (NSPCs)-loaded bioinks were used to construct a 3D brain model, demonstrating sustained vitality and high neuronal differentiation without the need for growth factors. The SilMA/pectin bioinks demonstrated adjustable mechanical properties, favorable biocompatibility, and an environment highly conducive to neural induction, offering an alternative approach for neural tissue engineering applications or in vitro brain models.

In situ magnesium-doped calcium phosphate microtube-reinforced magnesium-doped hydroxyapatite composites with tunable mechanical properties and biodegradability

Hydroxyapatite, commonly employed in bone defect repair, demonstrates limitations in load-bearing applications due to its poor mechanical property and biodegradability. This research introduces an innovative bone substitute material, namely, in situ magnesium-doped calcium phosphate microtube (Mg-CaPMT)-reinforced magnesium-doped hydroxyapatite composites (Mg-CaPMT/Mg-HA) inspired by microtube material with outstanding mechanical property and capillary tube in a plant. The in situ Mg-CaPMT, with a ~7 μm diameter and 400-500nm wall thickness, was formed by pore-forming carbon fiber (CF) and the coating on it. These microtubes are uniformly distributed within Mg-HA matrix. The composites can meet load-bearing bone requirements, demonstrating compressive strength of 167.0±20.7MPa and fracture toughness of 2.04±0.13MPa·m1/2. Notably, it exhibits exceptional permeability and biodegradability, attributed to capillary action by the Mg-CaPMT structure. The adjustable mechanical and biological properties of Mg-CaPMT/Mg-HA, based on microtube dimensions, content, and composition, offer a versatile solution for repairing various bone defects in load-bearing areas.

Synthesis, characterization, and thermal pyrolysis mechanism of high temperature resistant phenolphthalein-based poly (arylene ether nitrile)

Phenolphthalein (PP) is usually used as a functional monomer to design novel high performance polymers with adjustable thermal, mechanical, and fluorescent properties. In this study, a soluble, amorphous, high temperature resistant PP-based poly (arylene ether nitrile) (PAEN) was synthesized and its corresponding thermal decomposition mechanism was reported via TGA/DTG, TGA/FTIR and TGA/MS analysis. PP-based PAEN showed a Tg of 250 °C a Tdmax of 503 °C and a char residue of 59.2% at 800 °C, respectively. According to Kissinger and Flynn–Wall–Ozawa model, the activation energy of thermal pyrolysis was calculated as 225±4 and 284±17 kJ/mol respectively, higher than those of other poly arylene ethers. PP-based PAEN showed a three-stage thermal pyrolysis mechanism. Its initial degradation happened before 400 °C and liberated the inherent moisture. The latter backbone decomposition between 400 and 600 °C involved multiple routes mainly from the C-O and C-C cleavages of lactone ring, resulting in a Ph2-CH-Ph-O-Ph intermediate by releasing HCHO, HCOOH, CO2, H2O, CH4, C6H6, and C6H5OH. The third carbonization stage over 600 °C included the transformation from biphenyl linkages to aromatic graphite by dehydrogenation. This study not only gives a comprehensive understanding of the thermal pyrolysis behavior of PP-based PAEN, but also provides valuable references for the thermal behaviors of other PP-containing polymers.

Acoustic emission of lattice structures under cycling loading relates process parameters with fatigue properties

Metamaterials, especially lattice structures, are of great interest for many application areas such as aerospace, automotive and medicine due to their adjustable mechanical properties and their low weight. Due to their complex geometry, lattice structures are usually manufactured additively, which causes a large variance in the manufacturing-related mechanical properties. In order to establish metamaterials in industrial applications under cyclic loading, the fatigue behavior needs to be investigated to evaluate the load capacity of these structures. Here we analyze the fatigue behavior of AlSi10Mg truss structures fabricated with L-PBF using a load increase test in combination with acoustic emission measurements. The acoustic signals are evaluated in terms of time-dependent amplitude signal and frequency spectrum. Increasing load and increasing specimen damage resulted in changes of the acoustic spectrum and the amplitude of the time signal. Based on the results, a correlation of specimen properties with build platform position in the manufacturing process could be established. Acoustic emission measurement as an in situ characterization method during cyclic loading is promising for surveillance of lattice structures in safety related applications.

Superlubricity Achieved by a Transparent Poly(vinylpyrrolidone) Composite Hydrogel with Glycerol Ethoxylate in Ocular Conditions.

Efficient and stable ocular lubrication is pivotal in safeguarding eye tissues from wear, especially under repetitive strain due to frequent blinking. Hydrogels have been reported to possess adjustable mechanical properties, biocompatibility, durability, and elevated water content and extensive utilization in medical fields. In this work, a kind of visible photo-cross-linking poly(vinylpyrrolidone) (PVP) hydrogel was designed and synthesized using 1-vinyl-2-pyrrolidone (NVP) and poly(ethylene glycol) diacrylate (PEGDA). To optimize the structure and improve the lubrication performance of hydrogels, we prepared and investigated glycerol ethoxylate (GE)-introduced composite hydrogels (GE/PVP). The results show that the addition of 3 wt % GE helped the hydrogel to form a uniform and dense porous matrix and reduce the frictional coefficient (COF) by over 50%, achieving superlubricity (COF ≈ 0.005). However, with the excessive increase of GE (6 wt %), the structure of the hydrogel is destroyed, inducing pore walls to thin and expand. After that, a lubrication mechanism of the GE/PVP composite hydrogel was proposed, in which the addition of GE reduced the surface tension of the hydrogel, enhanced the hydration ability of the hydrogel, and thus decreased the friction between sliding surfaces. Besides, the cytotoxicity tests show that the composite hydrogels possess good biocompatibility. Overall, the as-synthesized hydrogels hold great potential as lubricating medium for use in ocular applications.

Cover Image, Volume 62, Issue 6

The eutectogels find promising applications as flexible conductive materials. The study from Jianhua Zhang of Tianjin University reports a facile strategy to prepare poly(N‐acryloyl glycinamide) eutectogels by one‐step in situ photopolymerization of N‐acryloyl glycinamide without any crosslinkers in a deep eutectic solvent composed of choline chloride and ethylene glycol. The obtained poly(N‐acryloyl glycinamide) eutectogels exhibit concentration‐dependent and adjustable mechanical properties, high electrical conductivity, and self‐healing abilities as well as good anti‐drying and antifreezing properties. DOI: 10.1002/pol.20230603 image

Hydrogel Ink for 3D Printing with High and Widely Tunable Mechanical Properties via the Salting‐Out Effect

AbstractDue to the difficulty of simultaneously ensuring printability and controlling their mechanical properties, 3D printed hydrogels thus far have low modulus, far less than that of many biological tissues and organs. Therefore, their feasibility toward various biomimetic applications is currently limited. Herein, Direct‐Ink‐Writing (DIW) based 3D printable hydrogel ink with broadly adjustable mechanical properties is introduced. The salting‐out effect is utilized to effectively lower the gelation temperature of hydrogel inks with a wide range of modulus (0.193–1.072 MPa), making them all 3D printable. As a proof of concept, multi‐layered synthetic blood vessels that mimic the mechanical properties of biological blood vessels are printed, and their practicability toward surgical training is demonstrated. The versatility and simplicity of this technique make it highly promising for use in various 3D‐printed hydrogel biomaterials applications.

Advances of GelMA-Based Hydrogel in Nerve Repair and Regeneration

Nerve repair and regeneration are still challenging issues in the world, mainly due to the complex anatomic structure and limited regeneration ability of natural nerves. Tissue engineering provides a structure and function similar to nerve tissue through scaffold materials, seed cells, and active factors, which is a promising method to treat nerve injury. Gelatin methacrylate (GelMA) hydrogel is a kind of gelatin modified by methacrylamide, which possesses adjustable mechanical properties, convenient processability, and excellent biocompatibility, has been widely used in nerve tissue engineering. In this paper, the research progress of GelMA-based hydrogel in nerve repair and regeneration in recent five years is reviewed, with emphasis on the advanced manufacturing technologies of three-dimensional (3D) GelMA scaffold and the application systems that can effectively promote nerve repair and regeneration. We also evaluated the challenges and prospects of GelMA-based hydrogels in the field of nerve repair and regeneration, which is of guiding significance to the research of nerve tissue engineering.

Designing a bi-layer multifunctional hydrogel patch based on polyvinyl alcohol, quaternized chitosan and gallic acid for abdominal wall defect repair

In abdominal wall defect repair, surgical site infection (SSI) remains the primary cause of failure, while complications like visceral adhesions present significant challenges following patch implantation. We designed a Janus multifunctional hydrogel patch (JMP) with antibacterial, anti-inflammatory, and anti-adhesive properties. The patch comprises two distinct layers: a pro-healing layer and an anti-adhesion layer. The pro-healing layer was created by a simple mixture of polyvinyl alcohol (PVA), quaternized chitosan (QCS), and gallic acid (GA), crosslinked to form PVA/QCS/GA (PQG) hydrogels through GA's self-assembly effect and hydrogen bonding. Additionally, the PVA anti-adhesive layer was constructed using a drying-assisted salting method, providing a smooth and dense physical barrier to prevent visceral adhesion while offering essential mechanical support to the abdominal wall. The hydrogel patch demonstrates widely adjustable mechanical properties, exceptional biocompatibility, and potent antimicrobial properties, along with a sustained and stable release of antioxidants. In rat models of skin and abdominal wall defects, the JMP effectively promoted tissue healing by controlling infection, inhibiting inflammation, stimulating neovascularization, and successfully preventing the formation of visceral adhesions. These compelling results highlight the JMP's potential to improve the success rate of abdominal wall defect repair and reduce surgical complications.

Design of 3D-Photoprintable, Bio-, and Hemocompatible Nonisocyanate Polyurethane Elastomers for Biomedical Implants.

Polyurethanes (PUs) have adjustable mechanical properties, making them suitable for a wide range of applications, including in the biomedical field. Historically, these PUs have been synthesized from isocyanates, which are toxic compounds to handle. This has encouraged the search for safer and more environmentally friendly synthetic routes, leading today to the production of nonisocyanate polyurethanes (NIPUs). Among these NIPUs, polyhydroxyurethanes (PHUs) bear additional hydroxyl groups, which are particularly attractive for derivatizing and adjusting their physicochemical properties. In this paper, polyether-based NIPU elastomers with variable stiffness are designed by functionalizing the hydroxyl groups of a poly(propylene glycol)-PHU by a cyclic carbonate carrying a pendant unsaturation, enabling them to be post-photo-cross-linked with polythiols (thiol-ene). Elastomers with remarkable mechanical properties whose stiffness can be adjusted are obtained. Thanks to the unique viscous properties of these PHU derivatives and their short gel times observed by rheology experiments, formulations for light-based three-dimensional (3D) printing have been developed. Objects were 3D-printed by digital light processing with a resolution down to the micrometer scale, demonstrating their ability to target various designs of prime importance for personalized medicine. In vitro biocompatibility tests have confirmed the noncytotoxicity of these materials for human fibroblasts. In vitro hemocompatibility tests have revealed that they do not induce hemolytic effects, they do not increase platelet adhesion, nor activate coagulation, demonstrating their potential for future applications in the cardiovascular field.

Metal and metal oxides nanoparticles as nanofillers for biodegradable polymers.

Polymeric materials, despite their many undeniable advantages, nowadays are a major environmental challenge. Thus, in recent years biodegradable polymer matrices have been widely used in various sectors, including the medicinal, chemical, and packaging industry. Their widespread use is due to the properties of biodegradable polymer matrices, among which are their adjustable physicochemical and mechanical properties, as well as lower environmental impact. The properties of biodegradable polymers can be modified with various types of nanofillers, among which clays, organic and inorganic nanoparticles, and carbon nanostructures are most commonly used. The performance of the final product depends on the size and uniformity of the used nanofillers, as well as on their distribution and dispersion in the polymer matrix. This literature review aims to highlight new research results on advances and improvements in the synthesis, physicochemical properties and applications of biodegradable polymer matrices modified with metal nanoparticles and metal oxides.

3D printed modular Bouligand dissipative structures with adjustable mechanical properties for gradient energy absorbing

Three-dimensional (3D) printing allows for the creation of complex, layered structures with precise micro and macro architectures that are not achievable through traditional methods. By designing 3D structures with geometric precision, it is possible to achieve selective regulation of mechanical properties, enabling efficient dissipation of mechanical energy. In this study, a series of modular samples inspired by the Bouligand structure were designed and produced using a direct ink writing system, along with a classical printable polydimethylsiloxane ink. By altering the angles of filaments in adjacent layers (from 30° to 90°) and the filament spacing during printing (from 0.8 mm to 2.4 mm), the mechanical properties of these modular samples can be adjusted. Compression mechanical testing revealed that the 3D printed modular Bouligand structures exhibit stress-strain responses that enable multiple adjustments of the elastic modulus from 0.06 MPa to over 0.8 MPa. The mechanical properties were adjusted more than 10 times in printed samples prepared using uniform materials. The gradient control mechanism of mechanical properties during this process was analyzed using finite element analysis. Finally, 3D printed customized modular Bouligand structures can be assembled to create an array with Bouligand structures displaying various orientations and interlayer details tailored to specific requirements. By decomposing the original Bouligand structure and then assembling the modular samples into a specialized array, this research aims to provide parameters for achieving gradient energy absorption structures through modular 3D printing.

Facile preparation of self-healing hydrogels based on chitosan and PVA with the incorporation of curcumin-loaded micelles for wound dressings

The increased demand for improved strategies for wound healing has, in recent years, motivated the development of multifunctional hydrogels with favorable bio-compatibility and antibacterial properties. To this regard, the current study presented the design of a novel self-healing composite hydrogel that could perform as wound dressing for the promotion of wound healing. The composite hydrogels were composed of polyvinyl alcohol (PVA), borax and chitosan functionalized with sialic acid (SA-CS) and curcumin loaded pluronic F127 micelles. The hydrogels were formed through the boronic ester bond formation between PVA, SA-CS and borax under physiological conditions and demonstrated adjustable mechanical properties, gelation kinetics and antibacterial properties. When incubating with NIH3T3 cells, the hydrogels also demonstrated good biocompatibility. These aspects offer a promising foundation for their prospective applications in developing clinical materials for wound healing.