Mechanical Properties Of Gels Research Articles

Physical Properties and Biochemical Composition of Extracellular Matrix-Derived Hydrogels Dictate Vascularization Potential in an Organ-Dependent Fashion.

The inherent extracellular matrix (ECM) originating from a specific tissue impacts the process of vascularization, specifically vascular network formation (VNF) orchestrated by endothelial cells (ECs). The specific contribution toward these processes of ECM from highly disparate organs such as the skin and lungs remains a relatively unexplored area. In this study, we compared VNF and ECM remodeling mediated by microvascular ECs within gel, lung, and combinations thereof (hybrid) ECM hydrogels. Irrespective of the EC source, the skin-derived ECM hydrogel exhibited a higher propensity to drive and support VNF compared to both lung and hybrid ECM hydrogels. There were distinct disparities in the physical properties of the three types of hydrogels, including viscoelastic properties and complex architectural configurations, including fiber diameter, pore area, and numbers among the fibers. The hybrid ECM hydrogel properties were unique and not the sum of the component ECM parts. Furthermore, cellular ECM remodeling responses varied with skin ECM hydrogels promoting matrix metalloproteinase 1 (MMP1) secretion, while hybrid ECM hydrogels exhibited increased MMP9, fibronectin, and collagen IV deposition. Principal component analysis (PCA) indicated that the influence of a gel's mechanical properties on VNF was stronger than the biochemical composition. These data indicate that the organ-specific properties of an ECM dictate its capacity to support VNF, while intriguingly showing that ECs respond to more than just the biochemical constituents of an ECM. The study suggests potential applications in regenerative medicine by strategically selecting ECM origin or combinations to manipulate vascularization, offering promising prospects for enhancing wound healing through pro-regenerative interventions.

Preparation and Properties of Epoxy Adhesives with Fast Curing at Room Temperature and Low-Temperature Resistance.

Developing a highly efficient multifunctional epoxy adhesive is still an enormous challenge, which can rapidly cure at room temperature and has excellent low-temperature resistance performance and is crucial for the epoxy adhesive and electrical sealing fields during severe cold seasons. Herein, diglycidyl phthalate (DP) was synthesized with phthalic anhydride (PA) and epichlorohydrin (ECH) to enhance the curing rate and low-temperature resistance of bisphenol A diglycidyl ether (DGEBA) adhesive. The modified DP/DGEBA adhesives were systematically analyzed by gel time, mechanical properties, and aging resistance (time, temperature, and dry/wet treatment). The results showed that DP with highly active ester groups significantly accelerates the curing speed of DP/DGEBA. DP's rigid aromatic ring-benzene ring and flexible group-ester group gave the adhesive better low-temperature resistance. When the addition of DP was 10 wt % (based on the mass of DGEBA), the gel time of DP/DGEBA epoxy adhesives was reduced by 58 min compared to unmodified DGEBA epoxy adhesive, and after aging at low temperature (-20 °C) for 7 days, the tensile shear strengths of polyvinyl chloride (PVC) and aluminum plate increased by 76.2 and 80.6%, respectively. The results of non-isothermal curing kinetics and dynamic mechanical analysis suggested that when the amount of DP was 10 wt %, the reaction activation energy of DP/DGEBA epoxy adhesive decreased by 4.0%, and the cross-linking density increased by 8.9%. Moreover, the toughness of the modified adhesive was also improved. This study opens up a feasible way for the development of a low temperature-resistant epoxy adhesive cured rapidly at room temperature in practical application.

Stretchable, self-adhesion and durable polyacrylamide/polyvinylalcohol dual-network hydrogel for flexible supercapacitor and wearable sensor

Conductive hydrogels show great promise in the field of flexible electronics, but traditional hydrogels have some problems such as poor environmental tolerance, being easy to damage and not being durable. In this work, polyacrylamide (PAM) was used as the main network, and polyvinylalcohol (PVA) was added to construct a dual network hydrogel. Simultaneously, LiTFSI was added to improve hydrogel ionic conductivity, and multiple interionic and intermolecular interactions formed within the gel, significantly improving the gel's mechanical properties and durability. The area specific capacitance of the hydrogel-based supercapacitor is 383.4 mF cm−2, and it still maintains a high cycle life of 90.35 % after 10,000 cycles. The hydrogel-based strain sensor shows fatigue resistance, rapid recovery after 400 stretches, high sensitivity (GF = 3.83 at 300–400 %), and the ability to detect human motion. Therefore, the multi-functional properties of PAM/PVA/LiTFSI hydrogels are expected to play a demonstration role in a new generation of flexible electronic products.

Tough Hydro-Aerogels with Cation Specificity Enabled Ultra-High Stability for Multifunctional Sensing and Quasi-Solid-State Electrolyte Applications.

The anion-specific effects of the salting-in and salting-out phenomena are extensively observed in hydrogels, whereas the cation specificity of hydrogels is rarely reported. Herein, a multi-step strategy including borax pre-gelation, saline soaking, freeze-drying, and rehydrating is developed to fabricate polyvinyl alcohol gels with cation specificity, exhibiting the specific ordering of effects on the mechanical properties of gels as Ca2+ > Li+ > Mg2+ >> Fe3+ > Cu2+ >> Co2+ ≈ Ni2+ ≈ Zn2+. The multiple effects of the fabrication strategy, including the electrostatic repulsion among cations, skeleton support function of graphene oxide nanosheets, and water absorption and retention of ions, endow the gels with the dual characteristics of hydrogels and aerogels (i.e., hydro-aerogels). The hydro-aerogels prepared with the cationic salting-out effect display attractive pressure sensing performance with excellent stability over 90 days and enable continuous monitoring of ambient humidity in real-time and effective work in seawater to detect various parameters (e.g., depth, salinity, and temperature). The hydro-aerogels prepared without borax pretreatment or using the cationic salting-in effect can serve as quasi-solid-state electrolytes in supercapacitors, with 99.59% capacitance retention after 10000 cycles. This study realizes cation specificity in hydrogels and designs multifunctional hydro-aerogels for promising applications in various fields.

One‐Step Solvent‐Free Synthesis of Dimer Diamine‐Based Autocatalytic Polyol for the Preparation of Polyurethane Foams

AbstractHerein, this work reports the facile synthesis of a dimer diamine‐based autocatalytic polyol (ACP) and its use in polyurethane foam preparation. The ACP, namely TETRAOL is synthesized in one step, without using solvent, and with 100% atom economy. Additionally, a phosphorous‐modified polyol is synthesized by using 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and castor oil. In this study, all of the polyol components of the foams are of vegetable oil origin, and amine or tin‐based auxiliary catalysts are not used. The structures of the synthesized autocatalytic polyol as well as other bio‐polyols are characterized by Fourier‐transform infrared (FTIR) and Nuclear magnetic resonance (NMR) spectroscopies. The densities, rise and gel time values, and thermal and mechanical properties of the foams are determined and compared to foams prepared by using a petroleum‐based commercial ACP. The bio‐based TETRAOL‐containing foams display comparable densities and improve thermal properties but longer rise and gel time values concerning the foam prepared by using the commercial ACP.

Effects of concentration of hydrophobic component and swelling in saline solutions on mechanical properties of a stretchable hydrogel.

An elastic biopolymer, resilin possesses exceptional qualities such as high stretchability and resilience. Such attributes are utilized in nature by many species for mechanical energy storage to facilitate movement. The properties of resilin are attributed to the balanced combination of hydrophilic and hydrophobic segments. To mimic the properties of resilin, we developed a hydrogel system composed of hydrophilic acrylic acid (AAc) and methacrylamide (MAM) chains and hydrophobic poly(propylene glycol diacrylate) (PPGDA) chains. The gel was produced through free-radical polymerization in 0.8 M NaCl solutions using KPS as an initiator. In these gels, AAc and MAM can form hydrogen bonds, whereas the association between PPGDA chains can lead to hydrophobic domains. The PPGDA concentration affects the level of hydrogen bonding and gel mechanical properties. Tensile experiments revealed that the elastic modulus increased with a higher PPGDA concentration. Retraction experiments demonstrated increased velocity and acceleration when released from a stretched state with increasing PPGDA concentration. Swelling and deswelling of gels in saline solutions led to a change in mechanical properties and retraction behavior. This study shows that the stretchability and resilience of these hydrogels can be adjusted by changing the concentration of hydrophobic components.

Custom-engineered hydrogels for delivery of human iPSC-derived neurons into the injured cervical spinal cord

Cervical damage is the most prevalent type of spinal cord injury clinically, although few preclinical research studies focus on this anatomical region of injury. Here we present a combinatorial therapy composed of a custom-engineered, injectable hydrogel and human induced pluripotent stem cell (iPSC)-derived deep cortical neurons. The biomimetic hydrogel has a modular design that includes a protein-engineered component to allow customization of the cell-adhesive peptide sequence and a synthetic polymer component to allow customization of the gel mechanical properties. In vitro studies with encapsulated iPSC-neurons were used to select a bespoke hydrogel formulation that maintains cell viability and promotes neurite extension. Following injection into the injured cervical spinal cord in a rat contusion model, the hydrogel biodegraded over six weeks without causing any adverse reaction. Compared to cell delivery using saline, the hydrogel significantly improved the reproducibility of cell transplantation and integration into the host tissue. Across three metrics of animal behavior, this combinatorial therapy significantly improved sensorimotor function by six weeks post transplantation. Taken together, these findings demonstrate that design of a combinatorial therapy that includes a gel customized for a specific fate-restricted cell type can induce regeneration in the injured cervical spinal cord.

Interactions between pea protein and gellan gum for the development of plant-based structures

Plant-based analogs have been developed to mimic foods from animal sources by using ingredients from vegetable sources. Among the strategies to produce plant-based structures is the gelation of mixtures between plant proteins and polysaccharides. In this study, our aim was to investigate gels of pea proteins and gellan gum with high protein concentration and the addition of salt (potassium and sodium chloride). In the first step, a qualitative mapping was performed to select pea protein and gellan gum concentrations to produce self-sustainable gels. After that, the effect of salt addition was investigated for the formulations containing 10–15 % (wt) pea protein and 0.5–1 % (wt) gellan gum. The results showed that the gels containing potassium ions were more rigid and less deformable, with lesser water loss by syneresis. The morphological analysis showed a spatial exclusion of pea protein from the gel network mainly structured by the gellan gum. While potassium ions led to a more compact network, calcium ions promoted higher pores in the structure. Depending on the composition, the mechanical properties of gels were similar to some products from animal sources. So, the information obtained from these gels can be applied to the structuring of formulations in the development of plant-based analogs.

Development of Film-Forming Gel Formulations Containing Royal Jelly and Honey Aromatic Water for Cosmetic Applications.

This study aimed to develop a film-forming gel containing honey aromatic water (HW) and royal jelly (RJ) for cosmetic applications as a facial peel-off mask. HW, which is industrial waste from the water-reduction process of honey, was sterilized by autoclaving and filtration through a 0.22 µm membrane. The film-forming gels were developed using various types of film-forming polymers, including polyvinyl alcohol (PVA 117), carboxymethyl cellulose (CMC), and hydroxyethyl cellulose (HEC). The gel formulations were characterized in terms of their external appearance, viscosity, pH, and drying time, whereas the films generated were characterized by a texture analyzer, microscopic investigation, Fourier transform infrared, and an X-ray diffractometer. The findings highlighted that HW has short storage shelf life due to microbial contamination. Sterilizations were required before further product development. The film-forming gel was created by using the combination of PVA 117, CMC, and HEC. HW and RJ were successfully incorporated into the film-forming gel. However, HW resulted in a decrease in the gel viscosity and mechanical properties of its film. Interestingly, the drying time was dramatically decreased, which would be more desirable for its use as a peel-off mask. Furthermore, incorporation of royal jelly enhanced the viscosity of the gels as well as improved the mechanical properties of the film. No effect on the chemical and crystal structure of the films was detected after the incorporation. Therefore, the film-forming gels containing HW and RJ, possessing aesthetic attributes that extended to both the gels themselves and the resultant films, were suitable for use as a peel-off mask.

Developing a Prolamin-Based Gel for Food Packaging: In-Vitro Assessment of Cytocompatibility.

Growing environmental concerns drive efforts to reduce packaging waste by adopting biodegradable polymers, coatings, and films. However, biodegradable materials used in packaging face challenges related to barrier properties, mechanical strength, and processing compatibility. A composite gel was developed using biodegradable compounds (prolamin, d-mannose, citric acid), as a coating to increase the oxygen barrier of food packaging materials. To improve gel stability and mechanical properties, the gels were physically cross-linked with particles synthesized from tetraethyl orthosilicate and tetramethyl orthosilicate precursors. Additionally, biocompatibility assessments were performed on human keratinocytes and fibroblasts, demonstrating the safety of the gels for consumer contact. The gel properties were characterized, including molecular structure, morphology, and topography. Biocompatibility of the gels was assessed using bioluminescent ATP assay to detect cell viability, lactate dehydrogenase assay to determine cell cytotoxicity, and a leukocyte stimulation test to detect inflammatory potential. A composite gel with strong oxygen barrier properties in low-humidity environments was prepared. Increasing the silane precursor to 50 wt% during gel preparation slowed degradation in water. The addition of citric acid decreased gel solubility. However, higher precursor amounts increased surface roughness, making the gel more brittle yet mechanically resistant. The increase of precursor in the gel also increased gel viscosity. Importantly, the gels showed no cytotoxicity on human keratinocytes or fibroblasts and had no inflammatory effects on leukocytes. This composite gel holds promise for oxygen barrier food packaging and is safe for consumer contact. Further research should focus on optimizing the stability of the oxygen barrier in humid environments and investigate the potential sensitizing effects of biodegradable materials on consumers.

Konjac glucomannan and xanthan synergistic interaction gel: Underlying mechanism for improvement of gel mechanical properties induced by freeze-thaw treatment

Synergistic interaction gels (SIGs) formed by mixing konjac glucomannan (KGM) and xanthan at an appropriate ratio have gained increased interest due to its inherent versatility. However, their mechanical properties were not high enough to meet the needs of practical applications. This work demonstrated that freeze-thaw treatment (FT) significantly improved their mechanical properties, and the underlying mechanisms were proposed. Relative lower frozen temperature (−40 °C or −80 °C) and more freeze-thaw cycles reduced the pore size, decreased the average size of orderings (crystalline structure) and increased the ordering content (at −40 °C or under third cycle at −80 °C, except for KGM/xanthan SIGs with a ratio of KGM to xanthan at 2:8) for KGM/xanthan SIGs. Those undoubtedly increased the crosslinking density and improved the gel structure, which was responsible for the increment of G' (at 25–30 °C) and gel hardness, and reduction of water holding capacity. Freeze-thaw treatment with −15 °C did not increase the ordering contents and gel hardness, but enhanced the G' (at 25–30 °C). It is possible that freezing at −15 °C enhanced gel structure rigidity by increasing the molecular entanglement via squeezing of ice crystals and rearrangement of molecular chains. Those results are helpful to rational design and production of KGM/xanthan SIGs with physical methods.

Constructing ROS-Responsive Supramolecular Gel with Innate Antibacterial Properties.

Bacterial infections, especially antibiotic-resistant bacterial infections, pose a significant threat to human health. Supramolecular gel with innate antibacterial properties is an advanced material for the treatment of bacterial infections, which have attracted great attention. Herein, a reactive oxygen species (ROS)-responsive innate antibacterial supramolecular gel is developed by a bottom-up approach based on phenylalanine and hydrazide with innate antibacterial properties. The structure of gelators and intermediate products was characterized by proton nuclear magnetic resonance (1H NMR) and a high-resolution mass spectrum (HRMS). The results of 1H NMR and the Fourier transform infrared spectrum (FT-IR) experiment disclosed that hydrogen bonding and the π-π stacking force are the important self-assembly driving forces of gelators. The microstructure and mechanical properties of gel were studied by Scanning electron microscope (SEM) and Rheometer, respectively. An in vitro degradation experiment proved that the gelator has ROS-responsive degradation properties. The in vitro drug release experiment further manifested that antibiotic-loaded gel has ROS-responsive drug-release performances. An in vitro cytotoxicity experiment showed that the supramolecular gel has good biocompatibility and could promote cell proliferation. The in vitro antibacterial experiment proved that the supramolecular gel has excellent inherent antibacterial properties, and the antibacterial rate against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) was 98.6% and 99.1%, respectively. The ROS-responsive supramolecular gel as a novel antibacterial agent has great application prospects in treating antibiotic-resistant bacterial-infected wounds and preventing the development of bacterial resistance.

Gelatine based gel polymer electrolyte towards more sustainable Lithium-Oxygen batteries

The lithium-oxygen battery has attracted wide interest thanks to its very high theoretical energy density, and as such it is considered by many as a valid battery of the future candidate. However, the challenges in its practical application are many, such as liquid electrolyte evaporation in semi-open systems, as well as solvents instability in a highly oxidizing environment. In this work, we propose to use gelatin, from cold water fish skin, a waste from the fishing industry, to prepare an efficient gel electrolyte for future Li-O2 battery applications. After a single step methacrylation in water, methacrylated gelatine is directly cross-linked in presence of liquid electrolyte through UV- initiated radical polymerization. The obtained gel polymer electrolytes present good thermal and mechanical properties, good electrochemical stability against Li metal and ionic conductivities as high as 2.51 mS cm−1 at room temperature. the Li-O2 cells assembled with this bio-renewable gel polymer electrolytes were able to perform more than 100 cycles at 0.1 mA cm−2, under constant O2 flow, at room temperature and at a fixed capacity of 0.2 mAh cm−2. Cathodes post- mortem analysis confirmed that the cross-linked gelatin matrix was able to slow down solvent degradation and therefore enhance the cell reversibility.

Vanillin crosslinked 3D porous chitosan hydrogel for biomedicine applications: Preparation and characterization

Crosslinked chitosan (CS) is one of the most useable hydrogels in biomedicine and tissue engineering. Unlike most chitosan crosslinkers that are toxic, such as glutaraldehyde, vanillin is a natural, biocompatible, and antimicrobial alternative. The crosslinking of chitosan and vanillin consists of Schiff base bonds between the amines of chitosan and the aldehydes of vanillin, in addition to hydrogen bonds formed across the network. In most studies, the combination of chitosan and vanillin has been investigated in small sizes (micro/nanoscale and biofilms). In this study, a chitosan-vanillin (CV) hydrogel was studied on a macroscale with a three-dimensional porous structure, and it was compared with chitosan crosslinked with glutaraldehyde (CG) on the same scale. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (FE-SEM) used to identify the bonds formed and examine the morphology of the hydrogels. The gel content, swelling, porosity, mechanical properties, cell viability (on L929 and mesenchymal cells), and antibacterial activity (against Escherichia coli and Staphylococcus aureus) of the samples were investigated. The results showed that the CV had both gel content and high porosity (>90%), with an interconnected porous network of uniform pore size. The CV hydrogel exhibited good antibacterial activity and cell viability. In terms of mechanical properties, CV has weaker mechanical properties compared to CG in the dry state, while the mechanical properties of CV have more improved in the swollen state compared to CG.

Development of Natural Active Agent-Containing Porous Hydrogel Sheets with High Water Content for Wound Dressings

This work was concerned with the fabrication of a porous hydrogel system suitable for medium to heavy-exudating wounds where traditional hydrogels cannot be used. The hydrogels were based on 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPs). In order to produce the porous structure, additional components were added (acid, blowing agent, foam stabilizer). Manuka honey (MH) was also incorporated at concentrations of 1 and 10% w/w. The hydrogel samples were characterized for morphology via scanning electron microscopy, mechanical rheology, swelling using a gravimetric method, surface absorption, and cell cytotoxicity. The results confirmed the formation of porous hydrogels (PH) with pore sizes ranging from ~50–110 µm. The swelling performance showed that the non-porous hydrogel (NPH) swelled to ~2000%, while PH weight increased ~5000%. Additionally, the use of a surface absorption technique showed that the PH absorbed 10 μL in <3000 ms, and NPH absorbed <1 μL over the same time. Incorporating MH the enhanced gel appearance and mechanical properties, including smaller pores and linear swelling. In summary, the PH produced in this study had excellent swelling performance with rapid absorption of surface liquid. Therefore, these materials have the potential to expand the applicability of hydrogels to a range of wound types, as they can both donate and absorb fluid.

Radiation Synthesis of Edible Coating Films of Nanocurcumin Based on Carboxymethyl Chitosan/Polyvinyl Alcohol to Extend the Shelf Life of Sweet Orange "Valencia"

AbstractEdible coating CMCS/PVA/Cur and films were prepared using γ-irradiation to extend the shelf-life of sweet orange "Valencia" fruits. Water-soluble CMCS was synthesized by carboxymethylation of chitosan. Extraction of curcumin from turmeric powder and conversion to Cur-NPs of 76–108 nm average size was achieved. CMCS/PVA/Cur membranes were prepared via the casting method and gamma-irradiation technique. The chemical properties were studied by FTIR and XRD as well as studying the effect of irradiation dose on gel content, water swelling, and mechanical properties. FTIR and XRD results confirm the interaction between functional groups of Cur-NPs with CMCS/PVA polymer chains. Results indicated that the membrane possessed good tensile strength and gel content of 97.4% and the swelling was significantly decreased with increasing the irradiation dose. Fruits were dipped in CMCS/PVA/Cur coatings at different concentrations of Cur-NPs (0, 2.5, 5, and 10%) and stored at room temperature of 65–70% RH for about 70 days. The efficiency of coatings was assessed by decay (%), weight loss (%), pH, vitamin C content, total soluble solids (TSS), titratable acidity (TA), and TSS/TA ratio. Quality characteristics of coated fruits were better than uncoated fruits especially the coating solution of 2.5% Cur-NPs provides accepted freshness and quality. No decay was noticed for the coated fruits till 56 days, whereas the control exhibited decay of 36%. The prepared coating solutions possessed good antimicrobial activity and cytocompatibility characteristics and showed normal viability even at all concentrations. Results demonstrated a promising packaging material to extend the shelf life and freshness of orange fruits.

Ionogel Electrolytes Supported by Zwitterionic Copolymers Featuring Lithium Ion-Mediated, Noncovalent Cross-Links

A series of ionogel electrolytes, composed of an ionic liquid/lithium salt solution supported by a linear zwitterionic (ZI) copolymer scaffold containing solely noncovalent cross-links, were created in order to study the effects of varying the ZI fraction within the copolymer as well as the lithium ion concentration on gel mechanical properties and ion transport. The copolymer scaffold was synthesized via in situ UV photopolymerization of the ZI monomer 2-methacryloyloxyethyl phosphorylcholine (MPC) together with the non-ZI comonomer 2,2,2-trifluoroethyl methacrylate (TFEMA) in varying ratios, using a fixed fraction of 25 mol % total monomers. Ionic liquid electrolyte (ILE) solutions of 0.1, 0.3, 0.5, or 1 M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) dissolved in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP TFSI) were employed. For ionogels created using the 1 M LiTFSI ILE, varying the MPC content from 6.3 mol % to 17 mol % in the precursor solution resulted in a substantial increase in gel elastic modulus, from 20 kPa to 11 MPa. In contrast, room temperature ionic conductivity values for the same samples remained nearly constant, varying from 0.57–0.70 mS cm–1. While the in situ photopolymerization approach remains highly versatile for ionogel formation, an alternative method is introduced here for the first time that can produce ionogels “on-demand” using a pre-made ZI copolymer/ionic liquid solution to which a Li+ ILE is subsequently added.

Mechanical properties of silica aerogels controlled by synthesis parameters

Development of silica aerogels for real applications requires control of their mechanical properties. Based on the sol-gel procedure and using the alkoxide precursor of silica (TMOS), native silica aerogels were synthesized. This work explores the influence of three synthesis parameters, namely, TMOS concentration, catalyst concentration, and solvents (MeOH, EtOH, IPA), on the gel point, shrinkage and mechanical properties of aerogels. Structural studies were conducted to determine how the analysed synthesis parameters influenced the spatial network of aerogels and their elasticity. The analysis of the relationship between Young's modulus (E) and bulk density (ρ), E∝ρα, showed that the catalyst concentration appeared the most interesting parameter because, while the ρ did not change with an increase in the catalyst concentration, there was a significant increase in the E. We associate this observation with an increase in specific surface area, reflecting an increase in bond diameter between secondary particles formed in the aerogel.

Injectable cell-laden hybrid bioactive scaffold containing bioactive glass microspheres.

The rising incidence of bone disorders has resulted in the need for minimally invasive therapies to meet this demand. Injectable bioactive filler, alone or with cells, could be applied in a minimally invasive manner to fulfill irregular cavities in non-load bearing sites, which do not require high mechanical properties. Thermosensitive chitosan hydrogels that transition from a liquid to a mechanically stable solid at body temperature provide interesting features as in-situ injectable cytocompatible biomaterials, but they are not osteoconductive. Osteoconductivity can be applied in combination with bioactive ceramics e.g., 45S5-Bioglass® (BG). However, BG addition in chitosan hydrogels results in pH elevation, due to rapid ions release, which adversely affects gel formation, mechanical properties, and cytocompatibility. To address this, we created hybrid hydrogels, where BG is concentrated in chitosan-based microbeads, incorporated in in-situ gelling chitosan hydrogels. We then compared the hybrid hydrogels' properties to chitosan hydrogels with homogenously distributed BG. By varying the stirred emulsification process, BG percentage, and CH formulation, we could tune the microbeads' properties. Incorporation of BG microbeads drastically improved the hydrogel's compressive modulus in comparison to homogeneously distributed BG. It also strongly increased the survival and metabolic activities of encapsulated cells. Calcium/phosphate increase on BG microbeads suggests hydroxyapatite formation. The small diameter of microbeads allows minimally invasive injection through small needles. The feasibility of freezing and thawing microbeads provides the possibility of long-term storage for potential clinical applications. These data indicate that this hybrid hydrogel forms a promising injectable cell-laden bioactive biomaterial for the treatment of unloaded bone defects.

Insight into the self-assembly and gel formation of a bioactive peptide derived from bovine casein

The self-assembling and gelation properties of a bioactive peptide derived from bovine casein (FFVAPFPEVFGK) were studied in the peptide's natural form (uncapped, uncapFFV) and capped with protecting groups added to both termini (capped, capFFV). Although the natural peptide (uncapFFV) did not demonstrate self-assembly, the capped peptide (capFFV) spontaneously self-assembled and formed a self-supporting gel. Variations in peptide concentration and incubation time influenced the gel's mechanical properties, suggesting the peptide's properties could be tuned and exploited for different applications. These results suggest that food-derived bioactive peptides have good potential for self-assembly and therefore utilisation as gels in functional foods and nutraceuticals. Self-assembly is a natural phenomenon that occurs in many fundamental biological processes. Some peptides can self-assemble and form gels with tunable properties under given conditions. These properties, along with peptide bioactivity, can be combined to make unique biomaterials. Instead of synthesising the self-assembling bioactive peptides, we aim to extract them from natural sources. In order to use these peptides for different applications, it is essential to understand how we can trigger self-assembly and optimise the assembly conditions of these peptide gels. The self-assembling and gelation properties of a bioactive peptide derived from bovine casein (FFVAPFPEVFGK) were studied in the peptide's natural form (uncapped, uncapFFV) and capped with protecting groups added to both termini (capped, capFFV). Although the natural peptide (uncapFFV) did not demonstrate self-assembly, the capped peptide (capFFV) spontaneously self-assembled and formed a self-supporting gel. Variations in peptide concentration and incubation time influenced the gel's mechanical properties, suggesting the peptide's properties could be tuned and exploited for different applications. These results suggest that food-derived bioactive peptides have good potential for self-assembly and therefore utilisation as gels in functional foods and nutraceuticals.