Cross-linking Ratio Research Articles

Improving flexible actuating behaviors of gel-based artificial muscles through chamomile polysaccharide crosslinking

Abstract The flexible actuating behaviors of gel-based artificial muscles (GBAMs) are contingent upon the properties of their hydrogel actuating membranes. While the current preparation system for these membranes is deemed flawless, the electromechanical characteristics are constrained by the inherent properties of the material. The majority of raw materials used in this process are chemically synthesized; however, Chinese herbal polysaccharides offer a convenient, environmentally friendly, and non-toxic alternative, making them a prime candidate for actuating membrane preparation. The biological activities of chamomile polysaccharide (CP) include anti-inflammatory, lipid-lowering, sugar-lowering, and OH- clearance properties. Therefore, the actuating membrane of GBAM was prepared by crosslinking sodium alginate (SA) with CP. The findings indicated that at a crosslinking ratio of 4:5 for CP-SA, the electrically actuated force density and response speed reached 20.12 mN/g and 0.09 mN/g·s, respectively. Additionally, the working life extended to 781 seconds, tremor frequency decreased by 47.67%, and tremor amplitude was 19.55% of the control group. The elastic modulus was measured at 15.44 MPa, specific capacitance reached 183.99 mF/g, and internal resistance decreased by 13.44%. Charge and discharge time was 5.73 seconds, maximum energy reached 2.7 J, and specific energy was 12.66 A·J/g, representing increases of 2.3 seconds, 64.63%, and 6.47 A·J/g compared to the control group. The deflection displacement of 6.62 mm in the CP-SA group at a crosslinking ratio of 4:5 was found to be 3.06 times greater than that of the control group. In conclusion, the actuating membrane of GBAM, synthesized through the cross-linking of CP with SA at a specific ratio, demonstrated superior properties. This innovation offers a novel perspective and direction for the advancement of GBAMs and is anticipated to significantly contribute to future developments in related fields.

Using a Supramolecular Monomer Formulation Approach to Engineer Modular, Dynamic Microgels, and Composite Macrogels.

Microgels show advantages over bulk hydrogels due to convenient control over microgel size and composition, and the ability to use microgels to modularly construct larger hierarchical scaffold hydrogel materials. Here, supramolecular chemistry is used to formulate supramolecular polymer, dynamic microgels solely held together by non-covalent interactions. Four-fold hydrogen bonding ureido-pyrimidinone (UPy) monomers with different functionalities are applied to precisely tune microgel properties in a modular way, via variations in monomer concentration, bifunctional crosslinker ratio, and the incorporation of supramolecular dyes and peptides. Functionalization with a bioactive supramolecular cell-adhesive peptide induced selectivity of cells toward the bioactive microgels over non-active, non-functionalized versions. Importantly, the supramolecular microgels can also be applied as microscale building blocks into supramolecular bulk macrogels with tunable dynamic behavior: a robust and weak macrogel, where the micro- and macrogels are composed of similar molecular building blocks. In a robust macrogel, microgels act as modular micro-building blocks, introducing multi-compartmentalization, while in a weak macrogel, microgels reinforce and enhance mechanical properties. This work demonstrates the potential to modularly engineer higher-length-scale structures using small molecule supramolecular monomers, wherein microgels serve as versatile and modular micro-building units.

Structural Analysis of Hyaluronic Acid Fillers Using Nuclear Magnetic Resonance: Implications for Quality Control and Clinical Performance.

Potential disruptions in the biocompatibility of hyaluronic acid (HA) fillers can arise with mono-linked 1,4-butanediol diglycidyl ether (BDDE) or unreacted (pendant) 1,4-butanediol di-(propan-2,3-diolyl) ether. Assessing the filler's degree of modification involves evaluating improperly cross-linked BDDE. This study analyzed commercially available HA fillers using nuclear magnetic resonance (NMR), focusing on key parameters, such as the degree of modification (MoD), the cross-linker ratio (CrR), and the degree of cross-linking. We assessed thirteen commercially available HA fillers using NMR. The samples were placed in an NMR instrument, and each sample was analyzed for 26 h, including MoD and CrR assessments. MoD 1H ranged from 17.065% to 2.239%, MoD 13C ranged from 12.567% to 1.947%, and CrR 13C ranged from 0.394 to 0.014. Significant distinctions were observed in the CrR 13C values when the MoD values of the products were similar. This study underscores the importance of considering the MoD and the CrR together to ensure optimal cross-linking and minimize the risks associated with residual BDDE impurities. Utilizing NMR for HA gel characterization provides valuable insights regarding product quality control, safety assessments, and clinical performance evaluations for esthetic interventions, contributing to filler product improvements. Further studies correlating NMR findings with real-world outcomes are essential for ensuring safety and efficacy.

Sodium alginate-g-polyacrylamide hydrogel for water retention and plant growth promotion in water-deficient soils

Natural polymer-based hydrogels are preferred as soil water retention agents due to their inherent biocompatibility and biodegradability. Generally, these natural polymers are chemically modified by graft polymerization of vinyl monomers to improve their water absorption and retention properties. Among the polysaccharides used to prepare natural hydrogels, those based on sodium alginate (Alg) stand out for their high-water absorption and retention capacity, as well as for their ability to promote plant growth. The main objective of this study was to develop a biodegradable alginate-based hydrogel as a water retainer to promote plant growth under water deficit conditions. The synthesis was achieved by grafting poly(acrylamide) (PAM) onto Alg backbone, using bisacrylamide as chemical crosslinker and different ratios of alginate:acrylamide (Ac). In addition, Eucalyptus nitens seedlings were used as a model plant to evaluate the effect of alginate-g-polyacrylamide (Alg:PAM) hydrogel application to the growing medium on plant survival, growth, and physiological responses under both well-watered and water-deficient soil conditions. The maximum degree of swelling (65 g/g) was obtained for the hydrogel prepared. The pseudo-second order model described the water uptake kinetics of the hydrogel. The degradability of Alg:PAM hydrogel reached up to 85 % in 5 weeks in soil and occurs by breaking the glycosidic bonds of the alginate. The E. nitens seedlings cultivated with different doses of Alg:PAM hydrogel (4:1 Alg:Ac) showed higher values of height and root diameter relative growth, survival and photosynthetic responses in comparison to non-treated plants. The results indicate that Alg:PAM hydrogel (4:1 Alg:Ac) has promising applications in forestry as a water retention and seedling growth promoter under water deficient conditions.

Smart Implantable Hydrogel for Large Segmental Bone Regeneration.

Large segmental bone defects often lead to nonunion and dysfunction, posing a significant challenge for clinicians. Inspired by the intrinsic bone defect repair logic of "vascularization and then osteogenesis", this study originally reports a smart implantable hydrogel (PDS-DC) with high mechanical properties, controllable scaffold degradation, and timing drug release that can proactively match different bone healing cycles to efficiently promote bone regeneration. The main scaffold of PDS-DC consists of polyacrylamide, polydopamine, and silk fibroin, which endows it with superior interfacial adhesion, structural toughness, and mechanical stiffness. In particular, the adjustment of scaffold cross-linking agent mixing ratio can effectively regulate the in vivo degradation rate of PDS-DC and intelligently satisfy the requirements of different bone defect healing cycles. Ultimately, PDS hydrogel loaded with free desferrioxamine (DFO) and CaCO3 mineralized ZIF-90 loaded bone morphogenetic protein-2 (BMP-2) to stimulate efficient angiogenesis and osteogenesis. Notably, DFO is released rapidly by free diffusion, whereas BMP-2 is released slowly by pH-dependent layer-by-layer disintegration, resulting in a significant difference in release time, thus matching the intrinsic logic of bone defect repair. In vivo and in vitro results confirm that PDS-DC can effectively realize high-quality bone generation and intelligently regulate to adapt to different demands of bone defects.

Combining machine learning and molecular dynamics to predict strength-toughness and energy dissipation mechanisms of hybrid double-crosslinked CNT networks

Cross-linking has a significant strengthening effect on the mechanical properties of carbon nanoparticles, but there are still great challenges in how to control their mechanical properties through precise cross-linking ratios. Therefore, we use coarse-grained molecular dynamics (CGMD) to simulate its mechanical properties as data samples and combine it with machine learning methods to predict the optimal strength and toughness of carbon nanotubes (CNTs) corresponding to optimal cross-linking conditions. We found that the cross-linking density range is 2.60 ∼ 2.75 × 10-4/nm3, and the strong and weak cross-linking ratio range is 91 % S+9% W∼95 % S+5% W, which is the optimal range to achieve the mechanical properties of CNTs. Excessively high cross-link density and strong bond ratios can reduce the total number of cross-link bond breaks, thus decreasing their toughness. Meanwhile, high cross-linking density has a greater impact on the shear and slip between CNTs, tending to make CNTs brittle. Our proposed new approach for extracting data from coarse-grained models can obtain substantial optimization results without requiring much simulation computation. Furthermore, these cross-linking strategies and machine learning algorithms proposed in this work can provide a theoretical basis for controlling the mechanical properties of CNT materials, and also open up a new way for functional network materials other than CNTs.

Engineering fully quaternized (Dimethylamino)ethyl methacrylate-based photoresins for 3D printing of biodegradable antimicrobial polymers

Nowadays, medical devices or implants are widely used in the medical field to treat different diseases. However, bacterial infections are one of the significant problems associated with medical devices and are recognized as a concern in healthcare worldwide. Addressing this problem has driven the exploration of new materials with potent antibacterial properties. In this regard, quaternary ammonium compounds (QACs), which are organic salts with an alkane chain and a charged part of quaternary ammonium groups, came up with a potent antibacterial activity. Herein, we report for the first-time dimethylamino ethyl methacrylate (DMAEM) derived quaternary ammonium monomer and crosslinker to prepare photoresins for DLP (Digital light processing) 3D printing. The structure of the synthesized monomer and crosslinker was confirmed via FTIR (Fourrier Transform Infrared) and 1H NMR (Hydrogen Nuclear Magnetic Resonance) while the physicochemical properties of the 3D printed polymer were investigated using TGA (Thermogravimetric Analysis), DSC (Differential Scanning Calorimeter) and UTM (Universal testing machine). By optimizing the printing conditions and monomer to crosslinker ratio, we can print high-resolution 3D-printed objects. Additionally, in vitro biodegradation, cytocompatibility, and hemocompatibility tests revealed that the printed polymers are biodegradable, cytocompatible, and hemocompatible in nature. More importantly, the printed polymers exhibited strong antibacterial activity against both gram-negative and gram-positive bacteria, suggesting their potential utility in personalized antibacterial medical devices.

Injectable bone cement based on magnesium potassium phosphate and cross-linked alginate hydrogel designed for minimally invasive orthopedic procedures

Bone cement based on magnesium phosphate has extremely favorable properties for its application as a bioactive bone substitute. However, further improvement is still expected due to difficult injectability and high brittleness. This paper reported the preparation of novel biocomposite cement, classified as dual-setting, obtained through ceramic hydration reaction and polymer cross-linking. Cement was composed of magnesium potassium phosphate and sodium alginate cross-linked with calcium carbonate and gluconolactone. The properties of the obtained composite material and the influence of sodium alginate modification on cement reaction were investigated. Our results indicated that proposed cements have several advantages compared to ceramic cement, like shortened curing time, diverse microstructure, increased wettability and biodegradability and improved paste cohesion and injectability. The magnesium phosphate cement with 1.50% sodium alginate obtained using a powder-to-liquid ratio of 2.5 g/mL and cross-linking ratio 90/120 of GDL/CC showed the most favorable properties, with no adverse effect on mechanical strength and osteoblasts cytocompatibility. Overall, our research suggested that this novel cement might have promising medical application prospects, especially in minimally invasive procedures.

A super-stretchable and anti-fatigue silicone gel by regulating chain entanglement and cross-link density

Applications of silicone gel in flexible devices and soft machines require it to maintain excellent stretchability and antifatigue. However, the reported fatigue threshold of traditional silicone gels is in the range of 1–100 J m−2 and the stretchability below 2000 %. Herein, we report a simple strategy for constructing soft polydimethylsiloxane gels, which possesses high stretchability up to 8300 %, and high fatigue resistance (321 J m−2). This is achieved by controlling the ratio of chemical crosslinking and physical entanglement in the polydimethylsiloxane gels. The symbiotic relationship of this combination includes: extending the polymer chains helps them unfold to increase softness and intrinsic toughness; controlling the physical entanglement and chemical cross-linking helps to further increase the tensile rate and fatigue threshold, and adding small-molecule dimethyl PDMS as a solvent further increases fatigue resistance and tensile properties. This work provides a facile approach for developing super-stretchable and anti-fatigue silicone gel, which promises wide range of applicant in flexible devices and soft machines.

Tuning Mechanical Properties, Swelling, and Enzymatic Degradation of Chitosan Cryogels Using Diglycidyl Ethers of Glycols with Different Chain Length as Cross-Linkers.

Cross-linking chitosan at room and subzero temperature using a series of diglycidyl ethers of glycols (DEs)-ethylene glycol (EGDE), 1,4-butanediol (BDDE), and poly(ethylene glycol) (PEGDE) has been investigated to demonstrate that DEs can be a more powerful alternative to glutaraldehyde (GA) for fabrication of biocompatible chitosan cryogels with tunable properties. Gelation of chitosan with DEs was significantly slower than with GA, allowing formation of cryogels with larger pores and higher permeability, more suitable for flow-through applications and cell culturing. Increased hydration of the cross-links with increased DE chain length weakened intermolecular hydrogen bonding in chitosan and improved cryogel elasticity. At high cross-linking ratios (DE:chitosan 1:4), the toughness and compressive strength of the cryogels decreased in the order EGDE > BDDE > PEGDE. By varying the DE chain length and concentration, permeable chitosan cryogels with elasticity moduli from 10.4 ± 0.8 to 41 ± 3 kPa, toughness from 2.68 ± 0.5 to 8.3 ± 0.1 kJ/m3, and compressive strength at 75% strain from 11 ± 2 to 33 ± 4 kPa were fabricated. Susceptibility of cryogels to enzymatic hydrolysis was identified as the parameter most sensitive to cross-linking conditions. Weight loss of cryogels increased with increased DE chain length, and degradation rate of PEGDE-cross-linked chitosan decreased 612-fold, when the cross-linker concentration increased 20-fold.

Structure, Property Optimization, and Adsorption Properties of N,N'-methylenebisacrylamide Cross-Linked Polyacrylic Acid Hydrogels under Different Curing Conditions.

In this study, polyacrylic acid hydrogels were prepared by modulating the cross-linking agent mass ratio using UV and heat curing methods. The structures and properties of the hydrogels were characterized and analyzed using Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The results showed that the mechanical properties of the hydrogels prepared through UV curing were better than those prepared through heat curing. The maximum mechanical tensile strength of 139 kPa was achieved at a cross-linking agent mass ratio of 3.85% with 20 min of UV curing, and the maximum mechanical compressive strength of 0.16 MPa was achieved at a cross-linking agent mass ratio of 2.91% with 20 min of UV curing. However, the hydrogels prepared by heat curing had a higher tensile strength than those prepared using the heat curing method. In addition, the thermally cured hydrogels had higher water absorption and adsorption properties. Moreover, the PAA hydrogels prepared at cross-linking agent mass ratios of 1.91 and 2.91% with 2 h of the heat curing method had the best swelling properties. Moreover, the increase in the cross-linker mass concentration led to a decrease in the pore size and porosity and to a more compact structure.

High value-added use of waste photosensitive polyimide to develop low-shrinkage UV-curable inks for digital light projection technology

In the mass industrial production process of polyimide photoresists, waste generation is inevitable due to unqualified molecular weights, inappropriate ionic content of resins, or storage expiration. Consequently, the recycling and reuse of waste photosensitive polyimide (w-PSPI) is a growing concern in both scientific and industrial communities. In this work, w-PSPI was explored to prepare photocurable, fully crosslinked inks for digital light projection technology (DLP). For this purpose, suitable photoactive solvents and crosslinking agents were first screened to overcome the issue of large shrinkage caused by solvent volatilization. The formation of cross-linked network structures during DLP processing and subsequent imidization was also investigated. As a result, a polyimide DLP ink with minimum size shrinkage (less than 5 %) was proposed. For a given active solvent, the mechanical behavior and heat resistance of DLP-formed objects were significantly influenced by the ratio of short-chain and long-chain crosslinkers and the imidization temperature. By optimizing ink composition and imidization temperature, the DLP-formed objects showed high heat resistance (Td5 > 385 °C, Tg > 150 °C) and balanced mechanical properties of strength and toughness (Modulus ≥1 GPa, elongation at break >5 %). This w-PSPI ink has been successfully utilized to manufacture several complex 3D structures and vertical 3D microarrays with 100-µm on a limited-resolution DLP printer. This study not only points the direction for the high-added utilization of w-PSPI but also demonstrates the potential for expanding PSPI application from 2D lithography to 3D micro-manufacturing.

Lignin-Based Antioxidant Hydrogel Patch for the Management of Atopic Dermatitis by Mitigating Oxidative Stress in the Skin.

Atopic dermatitis (AD), a chronic skin condition characterized by itching, redness, and inflammation, is closely associated with heightened levels of endogenous reactive oxygen species (ROS) in the skin. ROS can contribute to the onset and progression of AD through oxidative stress, which leads to the release of proinflammatory cytokines, T-cell differentiation, and the exacerbation of skin symptoms. In this study, we aim to develop a therapeutic antioxidant hydrogel patch for the potential treatment of AD using lignin, a biomass waste material. Lignin contains polyphenol groups that enable it to scavenge ROS and exhibit antioxidant properties. The lignin hydrogel patches, possessing optimized mechanical properties through the control of the lignin and cross-linker ratio, demonstrated high ROS-scavenging capabilities. Furthermore, the lignin hydrogel demonstrated excellent biocompatibility with the skin, exhibiting beneficial properties in protecting human keratinocytes under high oxidative conditions. When applied to an AD mouse model, the hydrogel patch effectively reduced epidermal thickness in inflamed regions, decreased mast cell infiltration, and regulated inflammatory cytokine levels. These findings collectively suggest that lignin serves as a therapeutic hydrogel patch for managing AD by modulating oxidative stress through its ROS-scavenging ability.

Decrease of boron cross-linking ratio and morphological change in tomato plants under boron deficiency

ABSTRACT In tomato (Solanum lycopersicum L.), morphological changes caused by boron (B) deficiency were investigated. The B cross-linking ratio in cell walls and accumulation of reactive oxygen species (ROS) were determined in organs where physiological disorders and necrosis occurred. Under B deficiency in tomato, leaf colour turned yellow, plant height and stem diameter were shorter, and the shoot apex or flower bud necrosis was observed. The morphologically abnormal fruits, such as uneven, uneven black, and corky fruits appeared. The B cross-linking ratio was significantly decreased in the leaves and those abnormal fruits, which caused growth inhibition under B deficiency. By anatomical observation, the surrounding thickened cell walls of collenchyma cells decreased, and the arrangement of cells in the cortical layer and cambium was disordered in the stem. Cell necrosis was observed around the vascular bundle and in the flower bud. B cross-linking ratio significantly reduced in the parts with morphological abnormalities, which may decrease the mechanical strength of the cell wall. ROS accumulated, and necrosis occurred in the flower bud due to B deficiency. It was considered that B deficiency inhibits B cross-linking in the cell wall and induces ROS accumulation, causing cell collapse and necrosis.

A new pavement crack repair sealant with two-way shape memory effect

To address the challenge of sealant debonding due to cyclic temperature variations, a new pavement crack repair sealant which can achieve two-way shape memory deformation is developed. The developed crack sealant is a shape memory liquid crystal elastomer (SMLCE), designed to exhibit the deformation characteristics of heat contraction and cold expansion. First, the material composition and preparation process of the developed SMLCE are given. Thermodynamic properties, phase transition temperatures and molecular structures are analyzed based on DSC and FITR. The effects of the crosslinker and chain extender ratios and the key preparation processes on the two-way shape memory deformation and mechanical performance of SMLCE are systematically analyzed. Based on the analysis, the optimum ratio of SMLCE is determined to be 1:15 and the optimum secondary crosslinking preparation process is 150% orientation stretching. Under the optimal solution, the developed SMLCE can achieve the multiple two-way shape memory reversible deformation with a maximum 46% deformation in the temperature range of -20°C∼120°C. At the same time, the developed SMLCE has excellent mechanical properties, with a tensile strength of 20.7Mpa and an elongation at break of 322%. It also exhibits good low-temperature deformation capabilities at -10°C and above. Finally, the suitability and application potential of the developed two-way SMLCE as a pavement crack sealant are assessed. The developed SMLCE has good adaptability in most climate zones, which indicates its great potential as a pavement crack sealant. This research provides a new way for the pavement crack repair.

Sdc4 deletion perturbs intervertebral disc matrix homeostasis and promotes early osteopenia in the aging mouse spine

Syndecan 4 (SDC4), a cell surface heparan sulfate proteoglycan, is known to regulate matrix catabolism by nucleus pulposus cells in an inflammatory milieu. However, the role of SDC4 in the aging spine has never been explored. Here we analyzed the spinal phenotype of Sdc4 global knockout (KO) mice as a function of age. Micro-computed tomography showed that Sdc4 deletion severely reduced vertebral trabecular and cortical bone mass, and biomechanical properties of vertebrae were significantly altered in Sdc4 KO mice. These changes in vertebral bone were likely due to elevated osteoclastic activity. The histological assessment showed subtle phenotypic changes in the intervertebral disc. Imaging-Fourier transform-infrared analyses showed a reduced relative ratio of mature collagen crosslinks in young adult nucleus pulposus (NP) and annulus fibrosus (AF) of KO compared to wildtype discs. Additionally, relative chondroitin sulfate levels increased in the NP compartment of the KO mice. Transcriptomic analysis of NP tissue using CompBio, an AI-based tool showed biological themes associated with prominent dysregulation of heparan sulfate GAG degradation, mitochondria metabolism, autophagy, endoplasmic reticulum (ER)-associated misfolded protein processes and ER to Golgi protein processing. Overall, this study highlights the important role of SDC4 in fine-tuning vertebral bone homeostasis and extracellular matrix homeostasis in the mouse intervertebral disc.

Refractive index tuning and birefringence effect in crosslinked siloxane-acrylate copolymers for optical waveguide applications

Tunability of refractive index of polymeric waveguide material could be made by controlling free volume as well as polarizability of constituent materials. Two acrylate-co-polysiloxane series of different crosslinking network were synthesised by utilizing different crosslinker and monomer feeding ratio. Using Claussius-Mossotti/Lorentz-Lorentz (CM/LL) model, fractional free volumes were calculated showing a decrease in the experimental (nexp) compared to theoretical (ni) refractive indices. Curing agent with asymmetrical configuration induce a crosslink network of higher birefringence. They were respectively fabricated into multimode channel waveguide whose core-clad refractive index differences (Δn) show values in the range 0.0049–0.0408.

Anti-bacterial PVA@Ag/PVDF NF membrane made by filtration-coating plus in-situ reduction of NPs for dye removal

In this study, a filtration-coating method was developed to create a PVA layer on a PVDF membrane, and then silver nanoparticles (Ag NPs) were introduced by in-situ reduction to form an antibacterial PVA@Ag/PVDF NF membrane. The relationship between the rejection of dye by the membrane, the morphology of the coated PVA layer and its coating process parameters, such as polymer concentration, crosslinking ratio, vacuum pressure, and time, was investigated. The filtration-coating method facilitated the infiltration of PVA molecules into the porous channel of PVDF membrane, thus improved the stability of coated PVA. Meanwhile, it was observed that high vacuum pressure (1 bar), high polymer concentration (2%), and short filtration time (5 min) have a similar effect to low polymer concentration (1%) and long filtration time (10 min), which results in the formation of a dense layer structure (2–5 μm) on the membrane surface and leads to a high rejection rate but low flux. While filtration at low vacuum pressure (0.1 bar) leads to a thin PVA layer (<0.2μm), and PVA turns to appear on the entrance and surface of pore channel of membrane. The coated membrane showed a stable performance during 72 hrs filtration. Furthermore, Ag NPs were incorporated into PVA layer by the in-situ reduction method, the obtained membrane showed an enhanced dye rejection (92% for methyl blue), and a low salt rejection (NaCl 18%) and moderate flux (17.2 L·m−2·h−1 at 1 bar). Moreover, the composite membrane demonstrated excellent antibacterial properties (Staphylococcus aureus and E. coli). Overall, this work may present a novel approach to prepare new NF membrane.

Characterisation and biocompatibility of crosslinked hyaluronic acid with BDDE and PEGDE for clinical applications

Hyaluronic acid (HA) is a versatile biomaterial frequently utilized in regenerative medicine due to its gel-like properties, making it well-suited for clinical applications. However, its linear form is susceptible to rapid enzymatic degradation, limiting its longevity within the body. To address this challenge, extensive research has focused on crosslinking mechanisms to enhance the durability of HA gels. One early approach involved crosslinking HA with 1,4-butanediol diglycidyl ether (BDDE) to create HA-BDDE, a clinically used product since the 1990s. However, the manufacturing process for HA-BDDE, primarily used in industry, lacks comprehensive documentation in the literature. More recently, poly(propylene glycol) diglycidyl ether (PEGDE) has emerged as an alternative to BDDE for crosslinking, offering improved gel elasticity and reduced cytotoxicity. In this study, we present the manufacturing process for producing both crosslinked gels, HA-BDDE and HA-PEGDE, with negligible residual crosslinkers, as confirmed by FTIR and NMR analysis. We characterize the crosslinking kinetics and the resulting formulations, revealing that HA-PEGDE gel exhibits comparable stiffness (G' = 60 Pa vs. 75 Pa) to HA-BDDE, despite a lower effective crosslinking ratio (CrR = 0.12 vs. 0.24). Intriguingly, our cytotoxicity testing demonstrates significantly greater cell viability for HA-PEGDE compared to HA-BDDE (151% versus 105%). Overall, both gels can be readily manufactured using a similar process and demonstrate excellent in vitro biocompatibility. This study elucidates why HA-BDDE is widely utilized in clinical settings and underscores the potential promise of HA-PEGDE as an emerging variant for clinical applications.

Water-in-oil emulsion templated polyurethanes with uniform porosity

Porous PU foams have been receiving great attention because of their low density, lightweight, and high surface area. However, preparing PU foams with controlled porosity, pore size, and pore morphology is often difficult with commonly used methods like gas blowing. Here, highly controllable porous PU with small, uniform pore morphology and tunable material properties have been synthesized using water-in-oil polymerized high internal phase emulsion (PolyHIPE) templating and photoinitiated thiol-ene reactions between vinyl-functionalized polyurethane prepolymers and thiol-functionalized crosslinkers. The PolyHIPEs exhibited highly interconnected open-cell structures with pore sizes ranging from 5 to 10 μm. The storage moduli and elastic moduli of PU polyHIPEs derived from flexible HDI-PUs were low compared to stiff IPDI-PU based polyHIPEs. Furthermore, the storage moduli of relatively soft HDI-PU polyHIPEs were affected by the stoichiometric ratio of thiol crosslinker and vinyl-PU whereas no considerable effect on the stiffer IPDI-PU based polyHIPEs. In summary, this work presents an approach to synthesize porous polyurethane polyHIPEs with potential applications in aerospace, automotive, and biomedical industries.