INTRODUCTION
General introduction of hydrogels
Gels are solid substances that retain their shape without flowing, and hydrogels, a specific type of gel, consist of hydrophilic polymer chains that absorb water while remaining insoluble The structural integrity of hydrogels is maintained through cross-linking, which can be physical (like chain entanglements or ionic bonds) or chemical (such as covalent bonds) These materials are characterized by their high water content, often exceeding 99.9%, and their ability to respond to stimuli like pH, temperature, or light Hydrogels are biocompatible and biodegradable, making them suitable for biological and environmental applications, including implants and pollutant removal Additionally, some hydrogels exhibit electrical conductivity, facilitating their use in supercapacitor development, which is essential for advancing electronics.
Brown seaweed is a natural source of alginate, a versatile copolymer made up of α-l-guluronic acid (G) and β-d-mannuronic acid (M) units arranged in a linear structure The unique composition and arrangement of these copolymers lead to significant variations, with G blocks being essential for ion binding and gel formation These G blocks can easily form Ca-alginate hydrogels through interactions with multivalent cations like Ca2+ Due to its environmental sustainability, biocompatibility, biodegradability, and favorable rheological properties, alginate is an ideal choice for hydrogel formulation.
Conductive hydrogels are a novel class of hybrid materials that merge the water-retaining properties of traditional hydrogels with electrical conductivity Recent advancements have successfully incorporated metal nanoparticles into the hydrogel matrix, resulting in enhanced properties and stimuli-responsive behavior These innovative materials are being utilized across various applications, such as artificial muscles, switches, memory devices, catalysts, and photographic materials By harnessing the combined benefits of conductivity and hydrogel characteristics, conductive hydrogels present exciting opportunities for creating advanced functional materials.
In 2020, Zhao and colleagues created a conductive hydrogel network through in situ polymerization using quaternate chitosan and oxidized dextran as a dynamic Schiff crosslinker This innovative hydrogel demonstrated antibacterial properties and achieved a conductivity of 0.43 mS/cm Notably, it preserved cell viability and enhanced cell proliferation, highlighting its potential for biomedical applications.
Topic importance
Conductive hydrogels have garnered significant interest due to their unique mechanical and electrical properties A recent survey highlighted the fabrication methods and applications of these materials In this study, an alginate-based conductive hydrogel was synthesized, and a reconstruction process was developed to improve its properties This process enabled the production and evaluation of various conductive hydrogels in terms of mechanical performance and conductivity Additionally, self-welding conductive hydrogels were created, with their shear stress measured These findings offer valuable insights into the synthesis and characteristics of conductive alginate-based hydrogels for diverse applications.
Aim of this capstone project
In this project, we aim to create conductive alginate-based hydrogels that exhibit superior mechanical properties and electrical conductivity through a reconstruction process The mechanical characteristics of these hydrogels will be assessed using tensile testing methods.
By incorporating conductive materials into the alginate matrix and subjecting it to a reconstruction process, the resulting hydrogel exhibits superior tensile strength and conductivity compared to traditional hydrogels.
Research limitations
In this study, we developed initial conductive hydrogels using 5 wt% alginate combined with varying concentrations of activated carbon (0 wt%, 2 wt%, 4 wt%, and 8 wt%) To obtain the hydrogels in a dry form, we employed two drying methods: natural drying at room temperature and drying in a laboratory furnace at 75°C.
Approaching methods
- Surveyed the recent developments and applications of conductive hydrogels
- Synthesized an initial set of conductive alginate-based hydrogels and developed a reconstruction process for them
- Used the developed reconstruction process to fabricate a series of conductive hydrogels
- Evaluated the mechanical properties and conductivity of the fabricated conductive hydrogels
- Prepared applications of the conductive hydrogels
- Describing the molecular structure of sodium alginate;
- Outlining a process for creating conductive hydrogels based on alginate using a diffusion method;
- Testing the mechanical properties of the hydrogels by conducting a tensile test;
- Explaining the method used for measuring the conductivity of the hydrogels.
Structure of the report
The thesis is structured into six chapters, beginning with Chapter 2, which explores key concepts, definitions, and essential background information while summarizing prior research, identifying gaps, and highlighting the unique contributions of the proposed work Chapter 3 details the materials and equipment necessary for the project and outlines strategies to tackle its challenges, supported by theoretical explanations In Chapter 4, the discussion will focus on experimental results, comparing outcomes and drawing conclusions Chapter 5 emphasizes the self-welding method and the application of conductive hydrogels through this technique Finally, Chapter 6 synthesizes the findings, lessons learned, and future directions for development.
FABRICATING ALGINATE HYDROGELS
Fundamental of hydrogels fabrication
A commonly used method for creating hydrogels involves linking together multiple types of monomers using a multifunctional co-monomer as a cross-linking agent [9]
To produce hydrogels, it is essential to choose water-soluble monomers and their linear polymers Various polymerization techniques, including bulk, solution, and suspension methods, can be employed, with initiation possible through chemical, photo, thermal, redox, gamma ray, or microwave processes.
The formation of hydrogels can be achieved through the cross-linking of pre-formed linear polymers using irradiation or chemical compounds For instance, the reaction between α,ω-hydroxyl poly(ethylene glycol) and a diisocyanate, with a triol as a cross-linker, leads to the creation of hydrophilic cross-linked polyurethanes Ionic polymer networks are formed using monomers with ionizable groups or those capable of undergoing substitution reactions post-polymerization, resulting in hydrogels that may contain weakly acidic groups like carboxylic acids or strong acidic and basic groups such as sulfonic acids Common cross-linking agents, including divinyl benzene and EGDMA, are frequently used alongside monomers like acrylic acid and acrylamide, allowing for the synthesis of hydrogels with tailored properties such as biodegradability and mechanical strength Another strategy involves converting the hydroxyl terminal groups of poly(ethylene glycol) into methacrylate for cross-linking via radical polymerization Additionally, synthesizing biodegradable hydrogels often requires incorporating biodegradable organic components, either by modifying existing biodegradable polymers or integrating them into the hydrogel's structure, emphasizing the importance of selecting suitable monomers and synthetic methods.
Tanaka, Gong, and Osada explored innovative techniques to enhance the mechanical properties of hydrogels Their review highlights the effectiveness of sliding cross-linking agents, double networks, and nano clay-filling in the preparation of hydrogels with superior performance.
The mechanical properties of polyrotaxane gels are highlighted in a comparison of their states: as-prepared, dried, and fully swollen (equilibrium) Defined in the research by Tanaka, Gong, and Osada, a 'topological (TP) gel' exhibits remarkable swelling capabilities, expanding to approximately 500 times its original weight and demonstrating significant stretchability.
Figure 2.1 A comparison of a polyrotaxane gel in as-prepared (a), dried (b), and fully swollen
(equilibrium) states (c) of TP gel
To successfully regenerate hydrogels, it is essential to understand the principles of selecting appropriate monomers and designing effective cross-linkers This knowledge enables researchers to fine-tune mechanical and chemical properties to align with their specific research objectives.
For the scope of this study, the type of hydrogel to be regenerated is alginate hydrogels Alginate hydrogels are typically prepared using divalent ions such as Ca 2+ and
Mg 2+ serves as an effective ionic crosslinking agent, interacting with G-block branches to create an egg-box structure in hydrogels In contrast, CaCl2, the most widely used cross-linker, can lead to an excessively rapid gelation rate, adversely affecting the hydrogel's homogeneity and mechanical properties To manage gelation rates, alternative soluble crosslinkers such as CaSO4 or CaCO3 can be employed Additionally, factors like alginate concentration, crosslinked ion concentration, experimental methods, and temperature can be adjusted to fine-tune the mechanical properties of hydrogels Increasing alginate or crosslinked ion concentrations results in denser, stiffer hydrogels, while lower concentrations yield softer, more porous structures By modifying these parameters, researchers can effectively tailor the mechanical properties of alginate hydrogels for their specific applications.
A thermoresponsive hydrogel can be created using sodium alginate in combination with PNIPAAm, making it an excellent choice for producing such hydrogels.
Alginate, a water-soluble polysaccharide derived from brown seaweed, is recognized for its biocompatibility, biodegradability, non-toxicity, and potential for chemical modification This copolymer consists of α-L-guluronic acid (G) and β-D-mannuronic acid (M) linked by 1-4 bonds The alignment of G-blocks can form diamond-shaped cavities that facilitate the cooperative binding of divalent cations, such as calcium ions, leading to the formation of physically crosslinked hydrogels.
Covalent crosslinking is an effective method for creating alginate hydrogels, involving the use of crosslinking agents to connect polymer chains Functional groups such as -OH, -COOH, and -NH2 in both natural and synthetic polymers react with crosslinkers like glutaraldehyde and poly(ethylene glycol)-diamine to form these hydrogels The formation of alginate gels occurs through the reaction of carboxylic groups in alginate with crosslinking molecules that contain primary diamines The mechanical properties and swelling behavior of alginate hydrogels are influenced by the type of crosslinking agents and the density of crosslinking Higher crosslinking density improves mechanical strength, while the choice of crosslinking molecules affects swelling properties Utilizing hydrophilic crosslinkers, such as PEG, helps maintain the hydrophilic nature of the hydrogel, making it advantageous for biomedical applications This method enables precise control over hydrogel characteristics by varying crosslinking density and the types of crosslinking agents used.
Figure 2.2 Schematic showing of covalent crosslinking of alginate using adipic acid dihydrazide as cross-linker [38]
There are various physical and chemical methods to create alginate gels; however, it is important to acknowledge the potential for cells to participate in the gel formation process
Polymer chains with specific ligands can bind to cell surface receptors, enabling cells to crosslink with the polymers and form gels While alginate chains typically lack bioactive ligands for cell anchoring, their modification with cell adhesion peptides such as Arg-Gly-Asp (RGD) allows for effective cell binding This modification facilitates the formation of a polymer network through receptor-ligand interactions, resulting in a uniform cell dispersion within RGD-modified alginate solutions Consequently, these gels demonstrate high biocompatibility and mechanical strength, even without the use of chemical crosslinking agents.
Figure 2.3 Schematic showing of construction of cell crosslinked hydrogel of ligand- modified alginate [15].
Alginate- based hydrogels
Alginates are natural polymers located in the cell walls and intercellular matrix of brown seaweeds, contributing to their mechanical strength and flexibility essential for survival in ocean environments These compounds readily interact with various salts found in seawater, such as calcium, sodium, magnesium, strontium, and barium ions.
[16] Chemically, alginate consists of unbranched binary copolymers composed of monomers of (1-4)-linked β-dmannuronic acid (M) and α-l-guluronic acid (G) residues, which can form M-, G-, and MG- sequential block structures [16] (Figure 2.4)
Figure 2.4 Schematic showing of chemical perspective of Alginate [16]
After harvesting seaweed biomass, it undergoes a washing process with tap water, followed by drying in the shade and cutting into smaller pieces The extraction of dry, powdered sodium alginate from brown seaweeds can be achieved through various methods, which are categorized based on the intermediates produced during the extraction The first category yields calcium alginate and alginic acid as intermediates, while the second category exclusively produces alginic acid without the formation of calcium alginate.
Figure 2.5 Schematic showing a typical process for the extraction of sodium alginate from brown algae [17]
Alginate is a water-soluble linear polysaccharide made up of M and G blocks, which can form either homogeneous (poly-G, poly-M) or heterogeneous (MG) structures The unique configurations of monomers in these blocks result in varying geometries, with G-blocks appearing warped and M-blocks resembling ribbons Increasing the G-block content and molecular weight enhances the strength and porosity of alginate hydrogels, while a higher concentration of M-blocks yields softer, more elastic hydrogels Additionally, alginates can form acid gels at pH levels below the pKa of uronic acid residues, with precipitation occurring at pH values lower than 3.38 – 3.65 Ion density also plays a crucial role in influencing the water solubility of alginate salts.
Figure 2.6 (A) alginate monomers (M versus G); (B) the macromolecular conformation of the alginate polymer; (C) chain sequences [39]
Alginate exhibits diverse physical properties influenced by the size and arrangement of its M and G blocks, including thickness, hydrogel strength, and water absorption capacity Its molecular weight ranges from 33,000 to 400,000 g/mol, with higher molecular weights significantly affecting hydrogel characteristics Although alginate is insoluble in water and organic solvents, its salts and esters are soluble This versatile biopolymer is widely used in pharmaceuticals and biomedical applications, acting as a suspension and viscosity enhancer, aiding in artificial organ implants, and demonstrating gel-forming capabilities Alginate is prized for its non-toxicity, eco-friendliness, biodegradability, and biocompatibility.
Alginate gelation occurs when non-toxic substances are introduced, replacing sodium ions with calcium (Ca²⁺) or magnesium (Mg²⁺) ions, leading to the crosslinking of polymer chains The hydrogel's properties, such as water absorption, toughness, porosity, biocompatibility, and degradability, are affected by the composition, molecular weight, and type of ions utilized The gelation rate can be adjusted, with slower rates enhancing stability and control over the 3D structure formation Calcium chloride is frequently used to provide calcium ions, though it may lead to rapid and uncontrolled gel formation Additionally, the ratio of M and G blocks in alginate significantly influences these properties.
The ratio of G-blocks to M-blocks in alginate hydrogels is crucial for determining their properties, as it varies with the type of algae used During hydrogel formation, G-blocks interact with calcium ions to create a stable structure that can accommodate Ca²⁺ ions The bonding process occurs when sodium in the G-blocks is replaced by calcium, leading to different mechanical properties Hydrogels with a higher G-block content are more stable and less prone to shrinkage but are also more likely to break In contrast, a greater proportion of M-blocks results in softer, more elastic hydrogels that are less prone to breakage Thus, the balance of M-blocks and G-blocks significantly affects the stretchability and flexibility of alginate hydrogels.
Figure 2.7 Alginate gelation occurs due to the interaction between alginate and divalent cations (Ca 2+ ), which results in an egg-box structure [20].
Conductive hydrogels and their applications
Conductive hydrogels are formed by integrating crosslinked hydrogel networks with conductive materials, including conductive polymers, carbon-based substances, metal nanoparticles, and ionic salts This fusion results in a polymeric blend or co-network The pioneering development of conductive hydrogels occurred in 2013, when Panhuis et al successfully combined gellan gum with the conductive polymer PEDOT:PSS.
As the volume fraction of PEDOT:PSS in hydrogels increased from 0.35% to 1.05%, their electrical conductivity rose significantly from 0.138 ± 0.007 to 0.315 ± 0.014 S m−1 However, this enhancement in conductivity resulted in a notable decrease in tensile strength, dropping from around 10 kPa to approximately 2 kPa In 2014, Devaki et al reported the development of conductive nanocomposite hydrogels utilizing silver nanoparticles and a polyacrylic acid network, with methylol urea (MU) incorporated into the formulation.
The fabrication process utilized a reducing agent and crosslinker for gelation, resulting in hydrogels with an impressive electrical conductivity of 0.57 S cm−1 when compared to 7.85 g of AgNO3, 62.5 g of acrylic acid monomer, and 31.25 g of MU However, these hydrogels exhibited very poor mechanical properties.
In 2014, Park and colleagues successfully developed a self-healing and conductive co-network hydrogel by polymerizing conductive pyrrole monomer in an agarose solution As the concentration of pyrrole increased from 15 to 450 mM, the tensile strength of the hydrogels decreased from 9 to 4 kPa, and the strain reduced from 35% to 10% Conversely, the conductivity of the hydrogels improved significantly, rising from 0.2 to 0.7 S cm−1, showcasing the remarkable electrical properties of the resulting hydrogel.
S cm−1), its mechanical properties were still limited within the kPa range of moduli and strength, which significantly hindered its applicability in various fields [28]
Figure 2.8 Conductive hydrogels (a) The poly(acrylic acid) (PAAc) network was used to fabricate conductive nanocomposite hydrogels with the incorporation of silver nanoparticles
The production of self-healing and conductive hydrogels utilizes polypyrrole and agarose, highlighting innovative synthesis methods Additionally, polyampholyte hydrogels are characterized through a detailed schematic illustration of their structure and synthesis process Furthermore, the ionic interactions between poly(acrylic acid) (PAAc) and Fe³⁺ ions within the KCl-Fe³⁺/PAAc hydrogel network are depicted, along with the tensile test specimen, showcasing the material's mechanical properties.
Polyampholyte hydrogels, made from charged polymers that promote ion movement, present a promising solution for enhancing mechanical properties and conductivity Research by Sun et al in 2018 introduced salt-mediated polyampholyte hydrogels, achieving notable metrics of tensile strength at approximately 1.3 MPa, work of extension around 6.7 MJ m−3, and conductivity of 0.03 S cm−1 However, despite their conductivity, these hydrogels demonstrated limited self-recovery, managing to recover only within 2 hours under a force of about 0.7 MPa.
Recent advancements in conductive hydrogels have demonstrated promising mechanical properties through innovative methods such as physically crosslinking with multivalent ions like Fe3+ via coordinate-covalent interactions with -COOH groups Saha et al introduced conductive supramolecular hydrogels that achieved an electrical conductivity of 0.09 S cm−1, despite a tensile strength of only 430 kPa In 2018, Li et al developed dual physically crosslinked hydrogels using P(AAm-co-AAc) chains and Fe3+ ions, resulting in a higher tensile strength of 4.34 MPa, albeit with lower conductivity at 0.002 S cm−1 Fu et al also created hydrogels combining hydroxyethyl cellulose with Fe3+ and -COOH groups, achieving impressive mechanical properties and conductivity values Despite these advancements, further enhancements in self-recovery rates are essential for the application of conductive hydrogels in electronic devices like force and strain sensors, highlighting the need for ongoing development in this field.
Conductive hydrogels have emerged as innovative materials with significant potential in biomedicine, electronics, and energy storage These hydrogels consist of a water-swollen polymer matrix embedded with conductive elements like metallic particles or carbon nanotubes, enabling electrical conductivity Their remarkable mechanical properties, including high stretchability and flexibility, make them suitable for biocompatible applications in soft tissues Furthermore, their strong adhesion to biological tissues positions them as excellent candidates for flexible electrodes in various biomedical applications.
Conductive hydrogels are emerging as a valuable resource in bioelectronics, serving as flexible and biocompatible electrodes for diverse biomedical applications, including sensing and stimulation These innovative materials have enabled the creation of flexible, skin-like sensors capable of monitoring various physiological parameters effectively.
Conductive hydrogels are versatile materials capable of measuring 13 parameters, including temperature, pressure, and sweat composition, with significant applications in healthcare, sports, and military sectors Furthermore, these hydrogels have been utilized to create implantable devices aimed at treating neurological disorders like epilepsy and Parkinson's disease By delivering targeted electrical stimulation to specific brain regions, these devices can alleviate symptoms and enhance the quality of life for patients.
Figure 2.9 ColHA hydrogel was prepared via HRP-catalyzed crosslinking of collagen and
Hyaluronic acid (HA) modified with phenol groups can be utilized to create a hydrogel that supports 3D cell culture and is effective for wound healing This innovative hydrogel serves as a biomimetic dressing, promoting spontaneous wound healing.
Conductive hydrogels are increasingly utilized in biomedical applications, particularly in the development of neural interfaces that enhance brain-computer interfaces and neural prostheses Recent research highlights the effectiveness of conductive hydrogels in extending the longevity and stability of brain implants Additionally, studies have showcased the creation of flexible and stretchable neural electrode arrays using conductive hydrogels, enabling them to adapt to the brain's curvature.
In a study involving a pig heart, a 6-mm needle was used to puncture the ventriculus sinister, resulting in immediate high-pressure bleeding Following this, a hydrogel was injected to seal the punctured cavity, rapidly curing upon UV irradiation Remarkably, the bleeding ceased within 30 seconds due to the effective application of the hydrogel, which also provided coverage for the punctured area This innovative approach demonstrates the potential of hydrogel in managing cardiac punctures effectively.
The use of synthetic hydrogels in ophthalmology, specifically for contact lenses
Contact lenses have evolved significantly since their inception in the 1500s, particularly with the introduction of poly(2-hydroxyethyl methacrylate) lenses in the 1960s For optimal performance, contact lenses must prioritize maximum oxygen permeability and minimize mechanical stress on the cornea The hydrogels utilized in contact lens production need specific characteristics, including adequate water content, mechanical strength, oxygen permeability, surface wettability, optical clarity, stability, and biological compatibility Various monomers can enhance the water content of these hydrogels, with silicone hydrogels being notable for their excellent swelling properties and high oxygen permeability Additionally, the incorporation of hydrophilic chains can help mitigate drying effects, while the siloxymethacrylate monomer, known as "TRIS," is frequently employed to achieve superior oxygen permeability.
In the experiment, a hydrogel solution was introduced into a petri dish containing a pre-polymerized hydrogel layer, with steel balls serving as molds for rat eyeballs A magnified view of one eyeball mold is shown, emphasizing the intricate details Following the polymerization of the hydrogel, both the petri dish and steel balls were removed, and the indented sections of the hydrogel were punch cut to create round-shaped, plano-concave hydrogel contact lenses.
MATERIALS AND METHODS
Materials and types of equipment
Sodium chloride, anhydrous calcium chloride, and copper (II) chloride dihydrate were sourced from Xilong Scientific Co., Ltd in the Republic of China, while steam-activated charcoal was obtained from Duchefa Biochemie in the Netherlands Sodium alginate (viscosity 80cP – 120cP) was acquired from FUJIFILM Wako Pure Chemical Corporation in Japan, and glycerol (99%) was purchased from Fisher All compounds were utilized in their original form without additional purification Distilled water was used for hydrogel preparation, and an electronic scale was employed for precise chemical measurements.
Figure 3.1 Sodium chloride (NaCl) Figure 3.2 Calcium chloride (CaCl2)
Figure 3.3 Copper (II) chloride Figure 3.4 Charcoal (steam activated) dihydrate (CuCl2 + 2H20)
Figure 3.5 Alginate 80 ~ 120 (Na-alginate, Figure 3.6 Glycerol 99% viscosity 80cP – 120cP)
Figure 3.7 Distilled water Figure 3.8 Electronic scale
The initial parameters of the gel sample, which will be used for testing, will be measured using an Atorn electronic caliper (Figure 3.9) The measurements will include the
18 length, width, and thickness of the test specimen These measured parameters will then be utilized to calculate other process parameters
Figure 3.9 Atorn electronic calliper 3.1.3 Conductivity measurement
Electrical conductivity, also known as specific conductance, measures a material's ability to conduct electric current, reflecting its capacity to facilitate the flow of electrical charge This intrinsic property varies based on the material's composition and structure, allowing for the assessment of its efficiency in transmitting electrical currents.
Electrical conductivity (σ) is the reciprocal of the electrical resistivity (ρ):
(1) With resistivity for a material with a uniform cross-section is:
R is the electrical resistance (be measured by (Figure 3.10))
A is the cross-sectional area
Figure 3.10 Dedicated resistance tester CD800A 3.1.4 Mechanical properties measurement
The mechanical properties of Ca-alginate conductive hydrogels were evaluated through tensile testing using a PT-1699vdo tensile strength tester equipped with a 50-kg load cell Tests were conducted at ambient conditions of 26 °C and 65% humidity, with rectangular samples measuring 50 mm in length, 5 mm in width, and 2 mm in thickness The samples were secured in the tester with a 10 mm gap between clamps, and a constant deformation speed of 500% per minute was applied until fracture occurred Each gel sample underwent three measurements, and tensile stress-strain curves were analyzed to determine Young's modulus values by fitting a linear regression within a strain range of 1-3%.
Figure 3.11 Tensile strength tester (PT-1699vdo, PRO TEST, Taiwan) with a 50-kg load cell
The water content of each hydrogel was determined by measuring their weights in a water-equilibrated state (W wet) and after drying them at 120°C for 24 hours (W dry).
Hydrogels making processes
Our research aimed to identify the most effective hydrogels by developing three distinct types through varying processes Each method involved different execution orders and chemical concentrations, resulting in hydrogels with unique properties Specifically, we focused on creating conductive calcium alginate hydrogels, denoted as [Ca-alginate@C/0.5/5/y], where 'y' indicates the initial sodium alginate and activated carbon concentration (wt%) We tested four weight percentages for 'y': 0, 2, 4, and 8 wt% Additionally, the hydrogels were immersed in NaCl, CaCl2, and CuCl2 aqueous solutions, with the immersion sequence altered across the three processes This strategic variation allowed us to observe significant differences in the final properties of the hydrogels produced.
The process of creating initial Ca-alginate with 4 wt% of C involves several key steps: (a) inserting the solution into the reaction mold, (b) allowing complete gelation to occur, (c) immersing the gel in a CaCl2 aqueous solution, and (d) resulting in a conductive Ca-alginate hydrogel.
In the preparation of our hydrogel, we utilized a composite formulation of sodium alginate and carbon, labeled as [Ca-alginate@C/0.5/5/y], where 'y' indicates the initial carbon concentration The formulation consisted of 5% wt sodium alginate and activated carbon at varying concentrations of 0, 2, 4, or 8 wt%, with distilled water making up the remainder to total 100 wt%.
After reconstitution, the compound was allowed to sit undisturbed for one day, securely sealed with parafilm and foil The seal was then carefully opened on the following day to stir the mixture for gradual dissolution, after which it was resealed This process was repeated over approximately seven days until complete dissolution was achieved Once the solution was prepared, it was poured into a mold with specific dimensions, measuring 150 mm in length and width.
A silicone rubber sheet, measuring 3 mm in thickness, is applied to both sides of the mold to ensure proper molding and prevent leakage, while the mold itself has dimensions of 120 mm and a thickness of 5 mm.
The mold serves as a barrier and provides support for the hydrogel during the solidification process The introduction of CaCl2 aqueous solution is crucial for enhancing gel formation and strengthening the structural integrity of the hydrogel.
Initially, the Na-alginate fibers were disordered and irregular The infiltration of Ca²⁺ ions from a CaCl₂ aqueous solution into the C-alginate matrix led to a progressive interlinking of the alginate fibers and the aggregation of carbonaceous entities This transformation resulted in a rigid, non-flowing hydrogel matrix To maintain a continuous supply of Ca²⁺ ions for ongoing gel formation, fresh CaCl₂ aqueous solution was regularly added to the mold.
After the gel formation, the mold was gently removed, releasing the gel, which was then soaked in a CaCl2 aqueous solution for about 24 hours This immersion facilitated the absorption of Ca2+ ions, improving the gel's structural integrity and strength Following this, a careful rinsing process with distilled water was performed to eliminate any remaining impurities on the gel's surface.
The culmination of this meticulously orchestrated process yielded hydrogels distinguished by their unique attributes, starkly diverging from the characteristics of the original compound (Figure 3.13d)
To provide a clearer demonstration of the superior properties of the hydrogels, we expanded our research beyond the steps of demolding and immersion in CaCl2 aq solution
After extensive testing of various processes and compounds, we identified and refined two highly effective gel fabrication methods This careful evaluation led to the development of hydrogels with exceptional conductivity and water content, showcasing significant advancements in hydrogel synthesis.
The schematic in Figure 3.14 illustrates the process of obtaining freeze-dried hydrogels through Procedure A It showcases various samples: (a) the sample after immersion in NaCl, (b) following immersion in H2O, (c) after immersion in CaCl2 and subsequent washing in H2O, (d) the sample post freeze-drying at room temperature, (e) another sample immersed in CaCl2 and washed in H2O, and (f) the sample immersed in CuCl2 and washed in H2O.
The Ca-alginate gel was immersed in a NaCl aqueous solution for about 5 hours, triggering a chemical reaction where Na+ ions interacted with the molecular structure of Ca-alginate This interaction caused the rupture of Ca-alginate bonds as Na+ ions replaced Ca2+ ions, filling the spaces between the alginate fibers.
The expulsion of Ca²⁺ ions from the gel's surface led to a significant reduction in its structural integrity, resulting in a softer and more fragile gel After 5 hours in a NaCl solution, the gel was removed and soaked in distilled water for 30 minutes, causing the previously bonded carbon molecules to expand and visibly increase the gel's size.
When alginate fibers are immersed in distilled water, both the sodium ions within the bonds and those on the gel's surface are effectively removed This process aims to disrupt the calcium-alginate bond and eliminate all Ca²⁺ ions, restoring the gel to its original composition Notably, despite these changes, the gel retains its structural integrity and shape without dissolving.
The hydrogel was immersed in a CaCl2 solution, allowing the Ca2+ ions to penetrate deeply and integrate into its molecular structure This process involved reconnecting the dispersed alginate fibers and drawing them closer together, enhancing the hydrogel's overall stability and integrity.
Calcium ions (Ca 2+) attracted free carbon molecules, causing them to arrange more closely within the hydrogel matrix This resulted in the creation of a hydrogel with the same composition as the original, but with significantly enhanced strength due to the formation of strong Ca-alginate bonds and the close alignment of Ca-alginate and free carbon bonds This interaction between Ca 2+ ions and hydrogel components produced a structurally reinforced hydrogel with improved mechanical properties and integrity.
EXPERIMENT AND RESULTS
Experiment, comparison, and evaluation
To fully understand the analysis results, it is crucial to grasp key concepts such as tensile strain, which denotes the deformation of a material under tensile stress, and tensile strength, the maximum stress a material can endure before failure Additionally, Young's modulus will be calculated to evaluate the stiffness and elastic behavior of various Ca-alginate samples The work of extension, representing the energy absorbed during deformation, will also be assessed to determine the resilience of the hydrogels Furthermore, measuring conductivity and water content will yield important insights into the electrical and hydration properties of the samples.
Once the initial gel selection is complete, the subsequent step involves the preparation of samples for testing The gel is cut into individual samples with dimensions of
50 (mm) × 5 (mm) × 2 (mm) (length × width × thickness) (refer to Figure 4.1) This cutting process yields multiple samples from each gel, providing a sufficient number of replicates for subsequent analyses and comparisons
Figure 4.1 (a) Testing sample of Ca-alginate with 0 wt% (b) Testing sample of Ca-alginate with 2 wt% (c) Testing sample of Ca-alginate with 4 wt% (d) Testing sample of Ca-alginate with 8 wt% a b c d
4.1.1 The comparison of the results from the initial gel fabrication
The initial stage of the process focuses on establishing the concentration and ratio of alginate and carbon to produce gel pieces that exhibit optimal mechanical properties and electrical conductivity This foundational step is essential for the successful progression of the project in later phases.
The research team will examine the mechanical properties and electrical conductivity of four alginate hydrogels, all containing a consistent alginate concentration of 5 wt% The study will focus on hydrogels with varying carbon contents of 0 wt%, 2 wt%, 4 wt%, and 8 wt%.
Figure 4.2 Stress-strain curves of initial (Ca-alginate@C/0.5/5/y), with varying y values (0,
2, 4, and 8 wt%) (a) Intial gels with 5 wt% Alg, 0 wt% C; (b) Intial gels with 5 wt% Alg, 2 wt% C; (c) Intial gels with 5 wt% Alg, 4 wt% C and (d) Intial gels with 5 wt% Alg, 8 wt% C
Figure 4.3 Properties of initial (Ca-alginate@C/0.5/5/y), with varying y values (0, 2, 4, and
8 wt%) (a) Young modulus, (b) Tensile strength, (c) Tensile strain, (d) Work of extension, (e) Conductivity and (f) Water content
The Ca-alginate sample with 0 wt% carbon demonstrates superior quality, exhibiting the highest nominal stress and tensile strain among the tested samples In particular, the alginate hydrogel with 5 wt% alginate and 0 wt% carbon stands out in performance.
The 32 carbon content exhibits a tensile strain exceeding 150%, outperforming other types with strains below this threshold The hydrogel containing 5 wt% alginate and 0 wt% carbon shows a favorable nominal stress range of 0.6 MPa to 0.8 MPa, while other types peak at 0.6 MPa For a more detailed analysis, additional calculations will be performed to ascertain Young's modulus, work of extension, and tensile strength, with the results presented in bar charts for enhanced visualization and comparison.
The alginate hydrogel containing 5 wt% alginate and 0 wt% carbon exhibits exceptional mechanical properties, with a Young's modulus of approximately 1.4 MPa, significantly higher than other gel types, which remain below 1 MPa This gel also demonstrates superior tensile strength, reaching close to 0.8 MPa, while other formulations do not exceed 0.6 MPa Additionally, in terms of work of extension, the alginate hydrogel achieves over 0.7 MJ.m -3, far surpassing the maximum of 0.3 MJ.m -3 observed in other gels Overall, the 5 wt% alginate and 0 wt% carbon hydrogel stands out as the most effective gel type in terms of mechanical performance.
The electrical conductivity of alginate hydrogels varies with carbon content, as shown in Figure 4.3e The highest conductivity is observed in the hydrogel containing 5 wt% alginate and 8 wt% carbon, measuring approximately 0.06 S/m In comparison, hydrogels with 5 wt% alginate and 4 wt% carbon demonstrate a conductivity near 0.05 S/m, while those with 5 wt% alginate and 2 wt% carbon exhibit slightly over 0.02 S/m.
The gel composed of 5 wt% alginate and 8 wt% carbon exhibits the highest electrical conductivity performance, significantly surpassing the 0.02 S/m threshold observed in gels with 5 wt% alginate and 0 wt% carbon.
The water content of various alginate hydrogels is ranked in ascending order: the gel containing 5 wt% alginate and 8 wt% carbon has a water content of approximately 90%, followed closely by the gel with 5 wt% alginate and 4 wt% carbon, also near 90% The gel with 5 wt% alginate and 2 wt% carbon shows a water content of about 92%, while the gel with 5 wt% alginate and 0 wt% carbon has the highest water content at 95%.
33 with a 5 wt% alginate and 0 wt% carbon composition has the highest water content among the gel types
The analysis of the bar charts reveals that the Ca-alginate sample with 0 wt% C demonstrates superior Young's modulus, tensile strength, tensile stress, and work of extension Nonetheless, when making selections, it is crucial to emphasize the importance of conductivity and water content.
The Ca-alginate sample containing 4 wt% C exhibits slightly reduced Young's modulus, tensile strength, and tensile stress compared to the 0 wt% C sample Nonetheless, it outperforms the other samples in conductivity, a crucial factor for its intended application.
For optimal experimentation, it is recommended to use the Ca-alginate sample with 4 wt% carbon, as it strikes a favorable balance between mechanical properties and electrical conductivity This specific composition will allow for further exploration and optimization of the Ca-alginate hydrogel's properties for the intended application However, the mechanical properties and electrical conductivity of hydrogels with 5 wt% alginate and 4 wt% carbon did not meet the research team's specifications Therefore, further investigation into different concentrations will be conducted to identify the ideal formulation for these hydrogels.
4.1.2 Discussion of the results of process A
The stress-strain curves for procedure A (Ca-alginate@C/0.5/5/y) illustrate the effects of varying y values (0, 2, 4, and 8 wt%) on the gels Specifically, the analysis includes gels formulated with 5 wt% alginate and different carbon concentrations: (a) 0 wt% C, (b) 2 wt% C, (c) 4 wt% C, and (d) 8 wt% C These variations in carbon content significantly influence the mechanical properties of the gels.
Figure 4.5 Properties of procedure A (Ca-alginate@C/0.5/5/y), with varying y values (0, 2,
4, and 8 wt%) (a) Young modulus, (b) Tensile strength, (c) Tensile strain, (d) Work of extension, (e) Conductivity and (f) Water content
During tensile testing, stress-strain curves are carefully documented for each gel sample, offering crucial insights into the correlation between applied stress and the resulting strain These curves are essential for accurately assessing the stiffness and elastic properties of the gel, particularly through the determination of Young's modulus values.
36 determined using a linear regression analysis within a strain range of 1-3% This analysis ensures an accurate assessment of the gel's mechanical properties (Figure 4.4)
Three representative stress-strain curves have been selected from the compiled data for comparison across various procedures These curves effectively highlight the key characteristics and variations in the gel samples, facilitating a thorough analysis of how different procedures influence the mechanical behavior of the gel.
Summary
To achieve our project objectives, we conducted experiments to select an alginate hydrogel with 5 wt% alginate and 4 wt% carbon, which demonstrated suitable mechanical and electrical conductivity We then explored various gel preparation processes, ultimately identifying two methods that provided stable and reliable results, with process B yielding the highest quality conductive alginate hydrogel Finally, we modified the Cu 2+ concentration in process B, resulting in a gel with 0.01M Cu 2+ that exhibited enhanced mechanical and electrical properties.
After extensive preparation, experimentation, comparison, and evaluation, our team has selected a final alginate hydrogel formulation consisting of 5 wt% alginate and 4 wt% carbon, produced using process B with a Cu 2+ concentration of 0.01M This gel type will serve as the foundation for further development in the project's application phase.
SELF-WELDING AND APPLICATIONS
Self- welding
This chapter focuses on the self-welding capability of the selected electrically conductive hydrogel, which consists of 5 wt% alginate and 4 wt% carbon, developed using process B with a Cu²⁺ concentration of 0.01M Additionally, it explores the application of self-welding joints in the fabrication of flexible circuits.
The electrically conductive hydrogel exhibits a remarkable self-welding ability, enabling it to autonomously rejoin separated sections without external assistance This unique capability facilitates the reconnection of hydrogel parts through physical or electrochemical interactions Various mechanisms, including the establishment of chemical interactions between polymer chains, contribute to this self-welding process, enhancing the functionality and resilience of the hydrogel.
5.1.1 The process of manufacturing a self-welding joint
The manufacturing process of a self-welding joint is illustrated in Figure 5.1, which includes several stages: (a) the initial sample, (b) the sample after immersion in NaCl, (c) the sample washed with H2O, (d) the sample coated with Glycerol-Alginate, (e) two samples that are attached, (f) the joint after immersion in CaCl2, and (g) the joint after immersion in CuCl2.
To initiate the fabrication process, the research team developed gels, specifically a Cu-Alginate and C matrix structure identified in Chapter 4, known for its superior mechanical and electrical conductivity (Figure 5.1a).
Next, the samples were immersed in NaCl for a period of 5 hours During this stage, Na molecules penetrated the gel surface and attacked the Cu-Alginate bonds, displacing
The replacement of Cu²⁺ ions with Na in the gel structure led to weaker interactions between Na molecules and Alg fibers As a result, the stability of the gel diminished, making it more susceptible to sliding, ultimately transforming the structure into Na-Alg.
The gel was rinsed with water for 45 minutes to eliminate any residual free Cu molecules and weakly bonded Na molecules, ensuring that only Alg remained within the gel structure.
Next, glycerol was applied to the gel It is important to note that this process took
The process involved two hours of continuous scraping of the gel surface, with a fresh layer of glycerol applied every 10 minutes This procedure caused the Alg fibers to completely detach, resulting in the loss of their interconnections.
The research team combined two glycerol-treated gel pieces, revealing that the zigzag structure of the Alg fibers on the surface resulted in weak bonding between them (Figure 5.1e).
The gel pieces were immersed in a CaCl2 solution for one day, allowing calcium molecules to penetrate the gel surface and interact with Alg bonds to form Ca-Alg bonds This process enhanced the gel's self-healing capabilities.
After rinsing with water, free calcium ions are removed, leaving only tightly bound calcium within the Ca-Alginate network The joint is then immersed in a CuCl2 solution, allowing Cu molecules to penetrate the Ca-Alginate hydrogel's surface These Cu molecules displace calcium ions, forming new bonds with the Alginate fibers While most calcium ions become free, some remain bonded alongside the Cu molecules, enhancing the joint's strength compared to the previous step due to the incorporation of copper.
After successfully synthesizing the bond between two individual gel pieces through the self-welding capability of alginate hydrogel, the research team will investigate
54 more in the gel properties which is self-welding In this stage, we will keep the same test as we have done in every previous test
To maintain accurate documentation and protect data integrity during testing operations, precise recording procedures will be implemented, especially given the delicate nature of the sample post-self-welding Shear stress and load force measurements will be electronically logged to ensure real-time and accurate data collection, minimizing the risk of errors or data loss Conducting multiple trials will help account for variability in results, enabling the identification of trends and patterns.
Figure 5.2 The quality testing process for the self-welded joint (a) Sample Placement, (b)
Lowering the Machine, (c) Measurement of Initial Length, (d) Observation of Crack Formation
This stage of the study concentrates on the shear stress and load force of the 4 wt% Ca-alginate sample during the self-welding process, with other previously mentioned tests excluded Following the tests, the data will be analyzed using a double-line chart, which provides a visual representation for comparing the collected data points and enables a comprehensive analysis (Figure 5.3).
Figure 5.3 Mechanical Properties of the self-welding of sample Ca-alginate with 4 wt%
The double-line chart illustrates the shear stress and load force measurements from the self-welding process In this chart, the x-axis represents the relevant displacement, while the y-axis displays the corresponding values of shear stress and load force.
The self-welding process demonstrates a maximum force of approximately 8N and a shear stress of around 0.3 MPa These findings suggest that the Ca-alginate sample containing 4 wt% C is capable of enduring substantial force and shear stress during self-welding.
The shear stress measurement of around 0.3 MPa highlights the efficiency of the self-welding process, demonstrating its ability to create strong cohesive bonds within the Ca-alginate gel Shear stress, defined as the force exerted parallel to the sample's surface, facilitates sliding or deformation, confirming the success of the self-welding mechanism.
Applications
After successfully applying the self-welding capability of alginate hydrogels, the research team will proceed to fabricate electrical circuits from the flexible connections created in the previous step
The research team aims to utilize the self-welding capability of alginate hydrogel to develop a flexible and straightforward circuit system This innovative circuit will incorporate essential electronic components, including three resistors, one NPN transistor, a 2V LED bulb, and a power source set to 55V Unlike traditional circuits that rely on wires for conductivity, this design employs self-welding joints, showcasing alginate hydrogel as a viable alternative to conventional conductive materials.
Figure 5.4.Wiring diagram of flexible circuit
The research team has designed a simple circuit with a width of 5 (mm) for the connections, and the length of the connections is depicted in Figure 5.4
After obtaining the assembly diagram, the research team proceeds with the steps to create a flexible electrical circuit
The base plate, measuring 90 mm × 70 mm × 2 mm, is depicted before the self-welding process After the self-welding is completed, the base plate and its joints are shown, successfully forming an electrical circuit.
The research team will begin by attaching connections to a base sheet made of a gel composed of 5 wt% alginate and 0 wt% carbon, as illustrated in the circuit diagram (Figure 5.5a) Utilizing the self-welding properties of alginate hydrogel, these connections will securely bond to the base sheet without requiring extra adhesive Upon finishing the self-welding process, a simple and flexible circuit board will be produced (Figure 5.5b).
Figure 5.6 The circuit after immersing it in the solution containing Ca 2+ ions a b
The research team submerged the entire circuit in a Ca 2+ ion solution, enabling it to reform based on the principles outlined in section 5.1 This process resulted in a highly flexible circuit, as demonstrated in Figure 5.6.
Figure 5.7 The circuit after being immersed CuCl2 solution
Next, the research team will immerse the circuit in a CuCl2 solution with a concentration of 0.1 M in order to increase the hardness and durability of the entire circuit (Figure 5.7)
Figure 5.8 The circuit after the electronic components have been installed
The final step is to test whether this circuit board functions smoothly under real- life conditions To evaluate the sample's electrical conductivity, a simple circuit will be
59 constructed, consisting of components such as one transistor, three resistors, one LED light, and a power source adjusted to 55V (Figure 5.8)
This electrical circuit is designed to measure the conductivity of self-welded samples when exposed to electrical current By integrating the sample into the circuit, researchers can analyze its electrical conductivity and assess any enhancements resulting from the self-welding process.
During testing, the electrical current in the circuit will be monitored, while the LED light's behavior is observed The LED light acts as an indicator to determine if the self-welded Ca-alginate sample can effectively transmit electrical current and generate visible light.
Upon powering the completed circuit, the research team observed that the LED light illuminated brightly and maintained stability, indicating that the electric circuit utilizing conductive alginate hydrogel as a material operates effectively and reliably.
Figure 5.9 The circuit after being powered up
The experimental testing yielded successful results, but the research team noted several areas for discussion Firstly, while the LED light provided illumination, its low power output suggests limited practical applications Secondly, the circuit received a supply voltage of approximately 55V.
The research team concludes that alginate hydrogel is a promising alternative to traditional conductive materials in fields like medicine and electronics, despite the inconvenience of requiring voltage regulators To enhance its potential, further research is necessary to improve the electrical conductivity of alginate hydrogel and assess its compatibility with household power sources.
CONCLUSIONS
Summary
This thesis aims to explore and enhance alginate-based hydrogels, which are polymers sourced from seaweed The focus is on improving their electrical conductivity and mechanical properties through a restructuring process.
The research team has successfully identified the ideal composition for an alginate-based hydrogel that exhibits enhanced mechanical properties and electrical conductivity, consisting of a mixture of 5 wt% alginate.
4 wt% carbon The hydrogel was produced using the DriedRT/Na/Ca/Cu method with a Cu 2+ concentration of 0.01 M
Furthermore, the research team has successfully applied these results along with the self-welding ability of alginate hydrogel to create flexible electrical circuits with excellent conductivity and flexibility.
Dicussions
Strengths: The research team has successfully accomplished the assigned tasks
We have developed a suitable methodology through a process of research, experimentation, comparison, analysis, and iterative refinement This has led to the identification of an optimal approach and its practical application
Weaknesses: The research team faced limitations in implementing more effective processes, methods, and applications due to constraints in terms of time, knowledge, and budget.
Recommendations
Future research should prioritize the optimization of hydrogel manufacturing processes, enhancing their properties and expanding their applications across various industries and medical fields Key areas of investigation include the composition, cross-linking methods, and post-processing techniques, which are essential for improving the mechanical, electrical, and biological characteristics of hydrogels This approach will enable the full utilization of hydrogels in critical applications such as tissue engineering, drug delivery systems, wound healing, and wearable electronics.
[1] C Mauli Agrawal, Joo L Ong, and Mark R Appleford, Synthesis and applications of hydrogels, Introduction to Biomaterials: Basic Theory with Engineering Applications, pp.159-161, 2014
[2] Sutapa Biswas Majee and Susheel Kalia, An Introduction to Hydrogels and Some Recent Applications, Emerging Concepts in Analysis and Applications of Hydrogels, 2016
[3] Mohamed Fertah, Isolation and Characterization of Alginate from Seaweed, Seaweed Polysaccharides, pp.11-26, 2017
[4] Kurt I Draget and Catherine Taylor, Chemical, physical and biological properties of alginates and their biomedical implications, Food Hydrocolloids, Volume 25, Issue 2, pp 251-256, 2011
[5] Sharma Ashwini K., Kumar Vinod, Kaith Balbir Singh, Kalia, S., & Swart, H C., Conducting polymer hydrogels and their applications Polymer-Plastics Technology and Engineering, 54(3), pp 265-292, 2015
[6] Xu Junpeng, Tsai Yu-Liang, & Hsu Shan-Hui, Design strategies of conductive hydrogel for biomedical applications Journal of Materials Chemistry B, pp 1923-1936, 2021
[7] Yong Xu, Michelle Patino Gaillez, Rebecca Rothe, Sandra Hauser, Dagmar Voigt, Jens Pietzsch, Yixin Zhang, Conductive Hydrogels with Dynamic Reversible Networks for Biomedical Applications, Advance Healthcare Material, pp 1-4, 2021
Researchers Tran Van Tron, Md Tariful Islam Mredha, Pathak Surajit, Yoon Hyung-Kwon, Cui Jiwei, and Jeon Ikchan have developed conductive tough hydrogels featuring a staggered ion-coordinating structure that significantly enhances the self-recovery rate Their findings, published in ACS Applied Materials & Interfaces, demonstrate the potential of these innovative materials for various applications in soft robotics and wearable electronics.
[9] Cek Subramanian, Hydrogels: Classification, Synthesis, Characterization, and Application, Encyclopedia of Biomedical Polymers and Polymeric Biomaterials, pp 3879-
[10] Nikolaos A Peppas, Fundamentals, Hydrogels in Medicine and Pharmacy, pp 2-10,
[11] Jindrich Kope ˇ cek ˇ and Jiyuan Yang, Hydrogels as smart biomaterials, Polymer International, pp 1078-1098, 2007
[12] Guo Tao Chao, Synthesis, characterization, and hydrolytic degradation behaviour of a novel biodegradable pH-sensitive hydrogel based on polycaprolactone, methacrylic acid, and poly(ethylene glycol), pp 37-45, 2007
[13] Yoshimi Tanaka, Novel hydrogels with excellent mechanical performance, Trends in Polymer Science, pp 2-5, 2004
[14] Min Liu, Injectable Thermoresponsive Hydrogel Formed by Alginateg-Poly(N- isopropyl acrylamide) Releasing Doxorubicin Encapsulated Micelles as Smart Drug Delivery System, pp 2-5, 2017
[15] Farhad Abasalizadeh, Alginate-based hydrogels as drug delivery vehicles in cancer treatment and their applications in wound dressing and 3D bioprinting, Journal of Biological Engineering, pp 2-7, 2020
[16] Mohamed Fertah, Isolation and Characterization of Alginate from Seaweed, Seaweed Polysaccharides, pp 12-16, 2017
[17] Kuen Yong Lee, David J Mooney, Alginate: Properties and biomedical applications, Progress in Polymer Science 37, pp 106–126, 2012
[18] Kurt Ingar Draget *, Gudmund Skja˚k-Brổk, Olav Smidsrứd, Alginate based new materials, pp 621-630, 1997
[19] Kurt I Draget*, Catherine Taylor, Chemical, physical and biological properties of alginates and their biomedical implications, Food Hydrocolloids, pp 251–256, 2011
Alginate-based hydrogels have emerged as effective drug delivery vehicles in cancer treatment, showcasing significant potential in applications such as wound dressing and 3D bioprinting Researchers including Farhad Abasalizadeh, Sevil Vaghefi Moghaddam, Effat Alizadeh, Elahe Akbari, Elmira Kashani, Seyyed Mohammad Bagher Fazljou, Mohammadali Torbati, and Abolfazl Akbarzadeh have contributed to this field, highlighting the versatility and efficacy of alginate hydrogels in enhancing therapeutic outcomes.
[21] S Giridhar Reddy, Alginates - A Seaweed Product: Its Properties and Applications, London, United Kingdom: IntechOpen, 2021
[22] I Fernández Farrés*, I.T Norton, Formation kinetics and rheology of alginate fluid gels produced by in-situ calcium release, Food Hydrocolloids, pp 76-84, 2014
[23] Rohini Kuttiplavil Narayanan, Sivakala Sarojam, Sudha Janardhanan Devaki, Electrically conducting silver nanoparticle–polyacrylic acid hydrogel by in situ reduction and polymerization approach, Materials Letters, vol 116, pp 135-138, 2014
[24] Kyuhyun Im, Sang Won Kim, Jineun Kim, Dae-Young Chung, Tae-Ho Kim, Kyoung
Ho Jo, Jong Hoon Hahn, Zhenan Bao, Sungwoo Hwang and Nokyoung Park, Jaehyun Hur, Polypyrrole/Agarose-Based Electronically Conductive and Reversibly Restorable Hydroge, American Chemical Society, vol 8, no 10, pp 10066–10076, 2014
[25] Naziha Chirani, L’Hocine L.H’ Yahia, Lukas Gritsch, Federico Leonardo Motta and Soumia Chirani and Silvia Faré, History and Applications of Hydrogels, Journal of Biomedical Sciences, vol 4 No 2, pp 1-23, 2015
[26] Marc in het Panhuis and Holly Warren, Electrically conducting PEDOT:PSS - gellan gum hydrogels, UNIVERSITY OF WOLLONGONG, AUSTRALIA, 2013
[27] Stevens Leo, Calvert Paul, Wallace, Gordon G., & in het Panhuis, M., Ionic-covalent entanglement hydrogels from gellan gum, carrageenan and an epoxy-amine, Soft Matter, pp 2168-2176, 2013
[28] Lee, J Y., & Kim, M J., Conductive polymer hydrogels for biomedical applications: past, present, and future Advanced healthcare materials, 1700624, 2018
[29] Yixuan Li, Xu Fang, Junqi Sun, Tangjie Long, Salt-Mediated Polyampholyte Hydrogels with High Mechanical Strength, Excellent Self-Healing Property, and Satisfactory Electrical Conductivity, ADVANCED FUNCTIONAL MATERIALS, vol 28, pp 1-9, 2018
[30] Yunzhou Guo, Xiao Zhou, Qiangqiu Tang, Hua Bao, Gengchao Wang and Petr Saha,
A self-healable and easily recyclable supramolecular hydrogel electrolyte for flexible supercapacitors, Journal of Materials Chemistry A, vol 4, no 22, pp 8769–8776, 2016
Rongzhe Li and colleagues (2018) explored the development of integrated functional high-strength hydrogels that utilize metal-coordination complexes and hydrogen-bonding dual physically cross-linked networks Their research, published in Macromolecular Rapid Communications, highlights innovative approaches to enhance the mechanical properties and functional capabilities of hydrogels This study contributes significantly to the field of materials science by presenting new methods for creating robust hydrogel structures.
In their 2018 study published in the European Polymer Journal, Sayed Mir Sayed and colleagues explored the enhancement of mechanical properties and self-healing efficiency in hydroxyethyl cellulose-based conductive hydrogels The research focuses on leveraging supramolecular interactions to improve these hydrogels, contributing to advancements in material science and potential applications in flexible electronics and biomedical devices.
Hussain Imtiaz and colleagues have developed hydroxyethyl cellulose-based self-healing hydrogels that exhibit improved mechanical properties through metal-ligand bond interactions This innovative research, published in ACS Applied Polymer Materials, highlights the potential of these hydrogels for various applications due to their enhanced durability and self-repair capabilities.
[34] Guo Qipeng, Liu Qian, Chen, S., Yang, S., Zhang, X., & Wang, J., Conductive hydrogels for biomedical applications Journal of Materials Chemistry B, pp 1333-1353,
[35] Akhtar, A et al., Hydrogel-based delivery of brain-derived neurotrophic factor for the treatment of Parkinson's disease Journal of Controlled Release, 349-361, 2019
[36] Jin, Y., Hu, M., Sun, J., Zhang, Y., Yang, J., Zhao, C., & Wang, X., A conductive hydrogel platform for long-term stability and functionality of neural implants Science Advances, 2021
Researchers Canan Dagdeviren and colleagues have developed conformable amplified lead zirconate titanate sensors that exhibit an enhanced piezoelectric response, specifically designed for monitoring cutaneous pressure This innovative technology, detailed in their article published in Nature Communications, demonstrates significant advancements in sensor performance, offering promising applications in medical and wearable technology.
[38] Michalek, Radka Hobzova, Martin Pradny, Miroslava Duskova, Hydrogels Contact Lenses in: Bio-medical Applications of Hydrogels Handbook, Springer, pp 303-315, 2010
[39] Brian J Tighe, Silicone hydrogel materials-how do they work? In: Michael D Sweeney (ed) Silicone Hydrogels: The Rebirth of Continuous Wear Contact Lenses Butterworth-Heinemann, Oxford, pp 1-21, 2000
In situ formed collagen-hyaluronic acid hydrogel serves as a biomimetic dressing that enhances spontaneous wound healing, as detailed in the research by Huiyan Ying, Juan Zhou, Mingyu Wang, Dandan Su, Qiaoqiao Ma, Guozhong Lv, and Jinghua Chen published in Materials Science and Engineering: C This innovative hydrogel, discussed in the article, demonstrates significant potential in promoting tissue repair and regeneration, making it a valuable advancement in wound care technology.
[41] Andre Childs, Hao Li, Daniella M Lewittes, Biqin Dong, Wenzhong Liu, Xiao Shu, Cheng Sun & Hao F Zhang, Fabricating customized hydrogel contact lens, 2016.