Strong Hydrogels Research Articles

Thermoplastic Elastomer-Reinforced Hydrogels with Excellent Mechanical Properties, Swelling Resistance, and Biocompatibility.

Strong and tough hydrogels are promising candidates for artificial soft tissues, yet significant challenges remain in developing biocompatible, anti-swelling hydrogels that simultaneously exhibit high strength, fracture strain, toughness, and fatigue resistance. Herein, thermoplastic elastomer-reinforced polyvinyl alcohol (PVA) hydrogels are prepared through a synergistic combination of phase separation, wet-annealing, and quenching. This approach markedly enhances the crystallinity of the hydrogels and the interfacial interaction between PVA and thermoplastic polyurethane (TPU). This strategy results in the simultaneous improvement of the mechanical properties of the hydrogels, achieving a tensile strength of 11.19 ±0.80MPa, toughness of 62.67 ±10.66MJm-3, fracture strain of 1030 ±106%, and fatigue threshold of 1377.83 ±62.78 Jm-2. Furthermore, the composite hydrogels demonstrate excellent swelling resistance, biocompatibility, and cytocompatibility. This study presents a novel approach for fabricating strong, tough, stretchable, biocompatible, and fatigue- and swelling-resistant hydrogels with promising applications in soft tissues, flexible electronics, and load-bearing biomaterials.

A Water State Manipulation Strategy for Ultra‐Stiff Yet Highly Sensitive Hydrogels

AbstractHydrogels in water or aqueous solutions swell or shrink unidirectionally until reaching an equilibrium state, which has been extensively studied through both experimental analysis and theoretical prediction. In this work, an unexpected concurrent swelling and deswelling behavior of hydrogels is reported, which manipulates the water state in the polymer networks. The osmotic pressure‐driven rapid deswelling and the ionic electrostatic repulsion‐driven slow swelling of hydrogels occur simultaneously, affording double‐layered polyacrylamide (PAM) hydrogels, in which the rigid inner layer does not contains free water, while the soft outer layer comprises both bound and free water. The PAM hydrogels show uniaxial tensile fracture strengths and Young's moduli up to 104.2 MPa and 2.4 GPa, respectively, outperforming various polymeric and biological structural materials. This strategy is applicable to the general molding and three‐dimensional (3D) printing techniques, providing wide possibilities for engineering applications. Such strong and rigid hydrogels can simultaneously serve as structural materials for load‐bearing and act as functional materials for super‐stress (25 to 6000 N) and highly adaptable tactile sensing. These findings enrich the hydrogel swell/deswelling theory and broaden the engineering applications of hydrogels as structural materials.

Strong and tough polyvinyl alcohol hydrogels with high intrinsic thermal conductivity

Although polyvinyl alcohol (PVA) hydrogels display huge potential in tissue engineering, flexible and wearable electronic devices and soft robotics, their low intrinsic thermal conductivity and weak mechanical properties severely limit their wider applications in these areas. Herein, a Hofmeister effect-assisted “directional freezing-stretching” tactic is employed for simultaneously enhancing the intrinsic thermal conduction and mechanical properties of PVA hydrogels. The hydrogels are obtained through directional freezing followed by salting-out treatment and subsequent mechanical stretching and salting-out (DFS). The DFS PVA hydrogel with 15 wt% of PVA and a stretching ratio of 4 (DFS4) exhibits the highest thermal conductivity of 1.25 W/(m·K), which is 2.4 and 2.8 times that of PVA hydrogel prepared through frozen-thawed (FT) [0.52 W/(m·K)] and frozen-salted out (FS) [0.45 W/(m·K)] methods, respectively. The DFS4 PVA hydrogel also possesses greatly improved mechanical performances, exhibiting an elongation at break of 163.1%. In addition, the tensile strength, toughness, and elastic modulus of DFS4 PVA hydrogel significantly increase to 27.1 MPa, 25.3 MJ·m-3, and 21.5 MPa from 0.4 MPa, 0.32 MJ·m-3, and 0.07 MPa for FT PVA hydrogels, respectively. It is elucidated that the salting-out effect generates hydrophobic and crystalline regions, while directional freezing and stretching enhance the chain orientation in the DFS strategy. These effects synergistically contribute to the improvement of thermal conductivity and mechanical properties of PVA hydrogels.

Bamboo-inspired ultra-strong nanofiber-reinforced composite hydrogels

Biological materials, such as bamboo, are naturally optimized composites with exceptional mechanical properties. Inspired by such natural composites, traditional methods involve extracting nanofibers from natural sources and applying them in composite materials, which, however, often results in less ideal mechanical properties. To address this, this study develops a bottom-up nanofiber assembly strategy to create strong fiber-reinforced composite hydrogels inspired by the hierarchical assembly of bamboo. Self-assembled chitosan-sodium alginate nanofibers (CSNFs) are combined with tannic acid (TA) and poly(vinyl alcohol) (PVA) as the interfacial crosslinker and hydrogel matrix, respectively, to emulate the fundamental cellulose-lignin-hemicellulose composition unit of bamboo. Strong interfacial electrostatic interactions and hydrogen bonding form between the functional groups of these components. These molecular interactions can be further reinforced by constructing higher-order structure through stretch-induced orientation. The resulting composite hydrogel achieves good mechanical performance, including a high tensile strength of up to 60.2 MPa and a simultaneous high strength of 48.0 MPa and ultimate strain of 470%. This approach demonstrates a hierarchical bottom-up strategy to construct strong and robust composite hydrogels by effectively leveraging fundamental molecular interactions. By mimicking bamboo’s highly integrated structural composition, it offers a promising solution for creating advanced bioinspired materials with excellent mechanical properties.

Effectiveness of Voytik-Harbin Protocol in Fabrication of Ram's Testicular-Derived Hydrogel and Its Impact on Mouse In Vitro Spermatogenesis.

The utilization of decellularized extracellular matrix (dECM) derived from animal testis tissue has demonstrated potential as a component of tissue-specific scaffolds. Current research is mostly centered around dECM as a natural resource for culturing testicular cells. This study aimed to assess firstly the comparison of Voytik-Harbin (VH) and Frytes protocol in creating Ram's dECM testis hydrogel and secondly the evaluation of the best protocol effect on in vitro spermatogenesis. In this experimental study, the six testes of mature rams were decellularized and the hydrogel production was performed by i. The Frytes protocol utilized a concentration of 1 mg/mL of pepsin, dissolved in either 0.1 or 0.01 M HCl, and ii. The VH protocol was involved 10 mg of pepsin per 100 mg of ECM in 0.5 M of acetic acid. Subsequently, mouse testicular cells were cultivated on collagen hydrogel as the control and the more effective testicular-derived hydrogel (TDH) to evaluate the early stages of in vitro spermatogenesis. While the Freytes protocol produced a homogeneous pre-gel solution with both HCl concentrations; elevating the pH to 7.4 loosened the hydrogel and made gelation problematic. In contrast, the VH protocol solidified the hydrogel and produced a strong hydrogel due to its gelation consistency. Furthermore, the prepared hydrogel by VH with 25 mg of dECM had a significantly higher priority in terms of rheology and structure (P<0.05). Following mouse testicular cell culture, TDH and collagen hydrogel did not differ significantly in terms of cell survival rates and the mRNA expression of early spermatogenesis genes. Using the VH protocol for producing ram TDH resulted in a firm hydrogel with a high frequency of repeat, which may be suited for testicular cell growth.

Super Strong and Tough Hydrogels Constructed via Network Uniformization of Macromolecular Chains

Super Strong and Tough Hydrogels Constructed via Network Uniformization of Macromolecular Chains

Strong and conductive gelatin hydrogels enhanced by Hofmeister effect and genipin crosslinking for sensing applications

There is a growing interest in the development of conductive hydrogels based on natural polymers for sensing applications due to their flexibility, versatility and environmental friendliness. However, achieving strong hydrogels capable of withstanding mechanical stress while maintaining their desirable characteristics remains a challenge. This study proposed a strategy to tailor the mechanical and electrical conductivity of gelatin hydrogels by combining genipin crosslinking with the modulation of aggregation states of gelatin chains through Hofmeister effect. The obtained conductive gelatin hydrogels exhibit high tensile strength (5.48 MPa) and compressive stress at 80 % strain (5.66 MPa), excellent stretchability (>500 %), remarkable freezing-resistant performance, and good strain sensitivity. By virtue of these outstanding properties, the hydrogels were used as strain sensors for human motion detection, demonstrating a gauge factor of 0.6 at 110–200 % tensile strain. Additionally, the hydrogel sensors demonstrate a rapid response time (<0.32 s) and can withstand cyclic tensile/compressive loads at both room temperature and −20 °C, owing to their compact and stable network structure formed by the synergistic action of Hofmeister effect and chemical crosslinking. The strain sensors based on gelatin hydrogels can detect and track human movements, indicating promising applications in the field of wearable technology.

One-pot fabrication of sodium deoxycholate based supramolecular self-healing antibacterial double network hydrogels

Double network (DN) hydrogels have emerged as a significant technology for enhancement of mechanical strength of weak supramolecular gels. In the present study, we report the one-pot route for design of a low molecular weight gelator based DN hydrogel wherein sodium deoxycholate (NaDC) forms the primary network entangled with agar matrix. Various compositions of the reported agar-NaDC hydrogels were examined through FTIR, sol-gel transition temperature (Tsg), XRD, circular dichroism (CD), scanning electron microscopy (SEM), hydrophobicity probe studies, Zeta potential studies and rheology measurements. Analysis of all studies together reveal that 1 mg/ml agar-NaDC DN hydrogel is the optimum composition that exhibits dense networking with primarily β-sheet like structure, highest mechanical strength as well as self-healing characteristics with reversed optical activity and highest Tsg. Antibacterial activity studied using inhibition zone method suggests that 1 mg/ml agar-NaDC gel demonstrates significant bactericidal effect unlike the pure gel with an inhibition zone of ∼25 mm against E.coli after 24 h and ∼32 mm after 48 h incubation. The antibacterial activity was unique for this composition of the DN hydrogel which is attributed to its reversal in optical activity exhibiting positive cotton effect resulting in stronger interaction with the bacterial cell wall. Additionally, nearly 2 times reduced water absorption capacity of the 1 mg/ml agar-NaDC DN hydrogel compared to pure NaDC hydrogel ensures the retention of its mechanical strength as well as other properties in high moisture containing environment. Hence, the 1 mg/ml agar-NaDC DN hydrogel holds appreciable potential as a novel strong supramolecular self-healing antibacterial hydrogel with sustained release characteristics primarily important for biomedical applications.

Structural Changes of Water in Carboxymethyl Cellulose Nanofiber Hydrogels during Vapor Swelling and Drying.

Carboxymethyl cellulose nanofiber (CMCF) forms mechanically strong hydrogels via freeze cross-linking. We investigated the vapor swelling and drying processes of the freeze cross-linked CMCF hydrogels using infrared spectroscopy and X-ray diffraction. From the shifts of the O-H and C=O stretching modes, the structural changes of water and carboxymethyl celluloses (CMC) were analyzed. The results show that two types of bound water exist in CMCF hydrogels due to a difference in hydrophilicity between the amorphous and crystalline regions of CMCF. Bound water adsorbed on the amorphous region forms a strong hydrogen bond with dangling O-H or C=O bonds of CMC, whereas that adsorbed on the crystalline region has a weak hydrogen bond with the localized hydrophilic groups on the hydrophobic surface. Due to the difference in the hydrogen bonding strength of the two types of bound water, the vapor swelling process of water in CMCF hydrogels is classified into four stages. For the drying process, the residual water, which formed a strong hydrogen bond with the hydrophilic groups of the CMC, has effects on the CMCF structure. The present result suggests that the adsorption and desorption of water are important factors governing the physical and chemical properties of the CMCF hydrogels.

Poly(ionic liquid) functionalization: A general strategy for strong, tough, ionic conductive, and multifunctional polysaccharide hydrogels toward sensors

AbstractIonic conductive hydrogels (ICHs) prepared from natural bioresources are promising candidates for constructing flexible electronics for both commercialization and environmental sustainability due to their intrinsic characteristics. However, simultaneous realization of high stiffness, toughness, conductivity, and multifunctionality while ensuring processing simplicity is extremely challenging. Here, a poly(ionic liquid) (PIL)‐macromolecule functionalization strategy within a NaOH/urea system is proposed to construct high‐performance and versatile polysaccharide‐based ICHs (e.g., cellulosic ICHs). In this strategy, the elaborately designed “soft” (PIL chains) and “hard” (cellulose backbone) structures as well as the dynamic covalent and noncovalent bonds of the cross‐linked networks endow the hydrogel with high mechanical strength (9.46 ± 0.23 MPa compressive modulus), exceptional stretchability (214.3%), and toughness (3.64 ± 0.12 MJ m−3). Ingeniously, due to the inherent conductivity, design flexibility, and functional compatibility of the PILs, the hydrogels exhibit high conductivity (6.54 ± 0.17 mS cm−1), self‐healing ability (94.5% ± 2.0% efficiency), antibacterial properties, freezing resistance, water retention, and recyclability. Interestingly, this strategy is extended to fabricate diverse hydrogels from various polysaccharides, including agar, alginate, hyaluronic acid, and guar gum. In addition, multimodal sensing (strain, temperature, and humidity) is realized based on the stimulus‐responsive characteristics of the hydrogels. This strategy opens new perspectives for the design of biomass‐based hydrogels and beyond.

A high temperature-resistant, strong, and self-healing double-network hydrogel for profile control in oil recovery

Hydrogels are widely used in profile control to plug high-permeability zones in oil recovery. In this study, a novel double-network (DN) hydrogel is developed for profile control. The two networks of the prepared hydrogel are polyacrylamide (PAAm) crosslinked by N,N’-Methylenebisacrylamide (MBAA) and konjac glucomannan (KGM) crosslinked by borax (B), respectively. The two networks are interconnected by their interpenetrating structures and hydrogen bonds. Based on the results of a series of evaluation experiments, the AAm/KGM DN hydrogels developed in this study exhibit a strong mechanical strength with their fracture stresses exceeding 0.137 MPa. Meanwhile, the AAm/KGM DN hydrogels can remain thermally stable after being heated at 130 °C for 24 h, indicating the good high-temperature resistance of the new sample. Moreover, the prepared AAm/KGM DN hydrogels present excellent self-healing performance due to the abundant hydrogen bonds in their structures, which helps form stable and long-term plugging in porous media. In addition, the pure PAAm hydrogel and the AAm/KGM DN hydrogel are sheared into two dispersed particle gel (DPG) suspensions to investigate their plugging performances. The results demonstrate that the AAm/KGM DN DPG can effectively plug a high-permeability sandpack with a plugging efficiency of 93.2 %, while the pure AAm DPG can only provide a much lower plugging efficiency of 60.5 %. The AAm/KGM DN hydrogel developed in this study, with its high mechanical strength, high-temperature resistance, and self-healing capability, offers a promising new candidate for profile control in oil recovery.

Super Strong and Tough PVA Hydrogel Fibers Based on an Ordered‐to‐Disordered Structural Construction Strategy Targeting Artificial Ligaments

AbstractHydrogels with high strength, high modulus, and high toughness have great application potential in the field of artificial human load‐bearing tissues, but the preparation of materials with the above high performance is still a huge challenge. In this paper, a structural construction strategy of ordered‐to‐disordered (OTD) transition is proposed to obtain hydrogel fibers with high strength, high modulus, and high toughness. The structural construction strategy of OTD refers to the ordered‐to‐disordered transition of molecular segments in PVA polymer fibers through swelling and subsequent salting‐out treatment, while still maintaining the general order of the entire polymer chain. PVA molecular chain crystallites provide physical crosslinking to stabilize the structure. The results show that the elongation at break of the hydrogel fiber can reach 257%). The strength reaches 190.04 MPa, which is more than 4 times higher than that of human ligaments. The modulus reaches 137.31 MPa, which perfectly matches the human ligaments, and the toughness can reach 100.61 MJ m−3. In addition, it has stable mechanical properties in liquid environment and excellent biocompatibility, which has great application potential in the field of artificial ligaments. This OTD structural construction strategy provides a facile approach to achieving hydrogel fibers with desired mechanical properties.

Wood Cell Wall Nanoengineering toward Anisotropic, Strong, and Flexible Cellulosic Hydrogel Sensors.

Achieving highly ionic conductive hydrogels from natural wood remains challenging owing to their insufficient surface area and low number of active sites on the cell wall. This study proposes a viable strategy to design a strong and anisotropic wood-based hydrogel through cell wall nanoengineering. By manipulating the microstructure of the wood cell wall, a flexible cellulosic hydrogel is achieved through Schiff base bonding via the polyacrylamide and cellulose molecular chains. This results in excellent flexibility and mechanical properties of the wood hydrogel with tensile strengths of 22.3 and 6.1 MPa in the longitudinal and transverse directions, respectively. Moreover, confining aqueous salt electrolytes within the porous structure gives anisotropic ionic conductivities (19.5 and 6.02 S/m in the longitudinal and transverse directions, respectively). The wood-based hydrogel sensor has a favorable sensitivity and a stable working performance at a low temperature of -25 °C in monitoring human motions, thereby demonstrating great potential applications in wearable sensor devices.

Hydrogel Films with Impact Resistance by Sacrificial Micelle-Assisted-Alignment.

Various strategies are developed to engineer aligned hierarchical architectures in polymer hydrogels for enhanced mechanical performance. However, chain alignment remains impeded by the presence of hydrogen bonds between adjacent chains. Herein, a facile sacrificial micelle-assisted-alignment strategy is proposed, leading to well-aligned, strong and tough pure chitosan hydrogels. The sacrificial sodium dodecyl sulfate micelles electrostatically interact with the protonated chitosan chains, enabling chain sliding and alignment under uniaxial forces. Subsequently, sacrificial micelles can be easily removed via NaOH treatment, causing the reforming of H-bond in the chain networks. The strength of the pure chitosan hydrogels increases 140-fold, reaching 58.9±3.4MPa; the modulus increases 595-fold, reaching 226.4±42.8MPa. After drying-rehydration, the strength and modulus further rise to 70.3±2.4 and 403.5±76.3MPa, marking a significant advancement in high-strength pure chitosan hydrogel films. Furthermore, the designed multiscale architectures involving enhanced crystallinity, well-aligned fibers, strong interfaces, robust multilayer Bouligand assembly contribute to the exact replica of lobster underbelly with impact resistance up to 6.8±1.0kJ m-1. This work presents a promising strategy for strong, tough, stiff and impact-resistant polymer hydrogels via well-aligned hierarchical design.

Strong and tough anisotropic short-chain chitosan-based hydrogels with optimized sensing properties for flexible strain sensors

Conductive hydrogels are ideal candidates for developing flexible electronic devices, but they still cannot exhibit excellent strength, satisfactory toughness and high conductivity in sync, greatly limiting their further applications. Inspired by the structure-enhanced properties of natural tissues, we adopted a straightforward and efficient methodology for constructing strong and tough anisotropic short-chain chitosan-based hydrogels with salting-assisted tensile remodeling treatment. The anisotropic hydrogels present anisotropic mechanical and electrochemical performance due to the oriented arrangement of chitosan and P(AM-AA) macromolecular networks. The remarkable tensile strength, toughness, and conductivity of parallel-oriented hydrogels are up to 9.01 MPa, 32.77 MJ/m3, and 692.30 mS/m, respectively, which are much higher than that of isotropic and vertical-oriented hydrogels, verifying the structure-optimized mechanical and sensing performance. The anisotropic conductive polypolysaccharide hydrogels are assembled as strain sensors for real-time human movement monitoring, Morse code encryption and decryption transmission, and gesture prediction combined with a machine learning algorithm, providing new inspiration for blossoming strong, flexible electronic products.

Molecular Chain Rearrangement-Induced In Situ Formation of Nanofibers for Improving the Strength and Toughness of Hydrogels.

Although poly(vinyl alcohol) (PVA) hydrogel has high elasticity and is suitable for cartilage tissue engineering, it is difficult to have both high strength and toughness. In this study, a simple and universal strategy is proposed to prepare strong and tough PVA hydrogels by in situ forming nanofibers on the original network structure induced by a molecular chain rearrangement. Quenching-tempering alteratively in ethanol and water several times is carried out to strengthen PVA hydrogels (PVA-Etn hydrogels) due to the advantages of noncovalent bonds in adjustability and reversibility. The results show that, after three quenching-tempering cycles, PVA-Et3 hydrogel with water content up to 79 wt % shows comprehensive improved mechanical properties. The compression modulus, tensile modulus, fracture strength, tensile strain, and tear energy of the PVA-Et3 hydrogel are 270, 250, 260, 130, and 180% of the initial PVA hydrogel, respectively. The improved mechanical properties of the PVA-Et3 hydrogel are attributed to the strong cross-linked PVA chains and hydrogen bond-reinforced nanofibers. This study not only provides a simple and efficient solution for the preparation of strong and tough polymer scaffolds in tissue engineering but also provides new insights for understanding the mechanism of improving the mechanical properties of polymer hydrogels by adjusting the molecular structure.

Hydrotalcite-Enhanced Tough and Strong Hydrogel Endowed by Coordination and Electrostatic Interactions for Both Strain and Pressure Sensors.

Polymer hydrogels have a wide range of applications in the field of flexible wearable devices from the perspective of easy commercialization and environmental compatibility. However, traditional hydrogels often fail to achieve adequate mechanical strength and performance such as toughness, resilience, and ionic conductivity. Herein, a significant enhancement of tensile strength in 2 orders of magnitude (from 36 kPa to 1.5 MPa) is obtained by the introduction of hydrotalcite into polymer network via multiple, multilevel, and strong interactions of strengthened interface interactions, and the enhancement effect is superior to most of known records. Meanwhile, the enhanced conductivity may be rationally attributed to effective channels of hydrotalcite for ion transport. As a result, high toughness (9.5 MJ/m3), stretchability (1520%), excellent resilience (100% rebound of 400% strain), high conductivity (2.6 mS/cm), and low-temperature resistance are successfully achieved. The work shows an efficient approach to design desired ultratough and multifunctional hydrogels.

Strong and high-conductivity hydrogels with all-polymer nanofibrous networks for applications as high-capacitance flexible electrodes

Flexible devices, such as soft bioelectronics and stretchable supercapacitors, have their practical performance limited by electrodes which are desired to have high conductivity and capacitance, outstanding mechanical flexibility and strength, great electrochemical stability, and good biocompatibility. Here, we report a simple and efficient method to synthesize a nanostructured conductive hydrogel to meet such criteria. Specifically, templated by a hyperconnective nanofibrous network from aramid hydrogels, the conducting polymer, polypyrrole, assembles conformally onto nanofibers through in-situ polymerization, generating continuous nanostructured conductive pathways. The resulting conductive hydrogel shows superior conductivity (72 S cm−1) and fracture strength (27.2 MPa). Supercapacitor electrodes utilizing this hydrogel exhibit high specific capacitance (240 F g−1) and cyclic stability. Furthermore, bioelectrodes of patterned hydrogels provide favorable bioelectronic interfaces, allowing high-quality electrophysiological recording and stimulation in physiological environments. These high-performance electrodes are readily scalable to applications of energy and power systems, healthcare and medical technologies, smart textiles, and so forth.

Control nucleation for strong and tough crystalline hydrogels with high water content

Hydrogels, provided that they integrate strength and toughness at desired high content of water, promise in load-bearing tissues such as articular cartilage, ligaments, tendons. Many developed strategies impart hydrogels with some mechanical properties akin to natural tissues, but compromise water content. Herein, a strategy deprotonation-complexation-reprotonation is proposed to prepare polyvinyl alcohol hydrogels with water content as high as ~80% and favorable mechanical properties, including tensile strength of 7.4 MPa, elongation of around 1350%, and fracture toughness of 12.4 kJ m−2. The key to water holding yet improved mechanical properties lies in controllable nucleation for refinement of crystalline morphology. With nearly constant water content, mechanical properties of as-prepared hydrogels are successfully tailored by tuning crystal nuclei density via deprotonation degree and their distribution uniformity via complexation temperature. This work provides a nucleation concept to design robust hydrogels with desired water content, holding implications for practical application in tissue engineering.

Effective removal of aged protective coatings from natural heritage in yunyang using strong peelable hydrogels via enhanced interfacial interactions

Organic polymers such polyacrylates, silicones have been used to protect stone-based heritages. However, polymers degrade obviously with time which may lead to secondary damages to heritages. Removal of previously applied but now degraded polymers on stone surface becomes necessary for the long-term preservation of stone heritages. Current cleaning protocol is mainly based on dissolving or extraction of aged polymers by organic liquid, whose kinetics is dominated by the slow diffusion and dissolving processes at the interfaces. Such cleaning process is very time consuming and becomes almost not applicable in large area cleaning. In this work, peelable PVA-borate hydrogels are developed. Organic solvents are introduced to tune gel's mechanical strength and its interfacial adhesion strength. Aged polymer coating can be removed easily by mechanical peeling when appropriate adhesion forces between the gel and aged polymer coating are achieved. Such cleaning protocol has been successfully applied on a fossil wall around 1200 m2. Details, precautions and limitations of this protocol is discussed in this work.