The impact of antifouling layers in fabricating bioactive surfaces

Dual-filler mixed matrix membrane with covalent-organic framework and nano TiO2/polyether sulfone for efficient antibody purification

With the rapid expansion of antibody drug market, most biopharmaceutical industries urgently need to optimize their downstream purification processes to reduce production costs and improve market competitiveness. In this study, a dual-filler polyether sulfone (PES) mixed matrix membrane (MMM) that combines covalent-organic framework (COF) with nano TiO2 was developed to overcome the drawbacks of conventional protein A based purification methods. Firstly, COF@TiO2 dual-filler was prepared by Schiff base reaction. The proposed dual-filler MMM was fabricated via nonsolvent-induced phase separation (NIPS), followed by functionalization with a Fab-specific affinity peptide (m-EDPW) of trastuzumab through atom-transfer radical-polymerization method. The resulting m-EDPW@COF@TiO2/PES affinity membrane effectively integrates the merits of COF and TiO2 and show synergistic effects, demonstrating satisfactory hydrophilicity, anti-fouling ability (BSA rejection rate: 97.7 %), enrichment recovery (90.8 %), binding capacity for trastuzumab (386.6 mg/g), and long-term stability (∼ 21 days). Particularly, this affinity membrane showed good selectivity and specificity, enabling the successful purification of trastuzumab from spiked HCC1937 cancer cell culture medium with satisfactory purity (~ 97.4 %) and preservation of the antibody secondary structure. This study not only developed a novel affinity membrane with satisfactory antibody separation performance but also opened a new route for developing dual-filler or multi-filler MMM for highly efficient downstream protein purification.

A bioactive Cu-grafted gel coating with micro-nano structures for simultaneous enhancement of bone regeneration and infection resistance

Prosthetic joint infection (PJI) remains a significant challenge in clinical applications. It not only impedes the recovery of bone tissue at the site of bone defect but also leads to multiple debridements, long-lasting antibiotic treatment and even secondary replacement. Titanium alloy Ti6Al4V (TC4) is widely used in orthopedic implants due to its excellent mechanical properties and biocompatibility; however, it lacks inherent antibacterial and osteoinductive functions. In this study, a composite coating based on polyvinyl alcohol (PVA) with tissue repair and antibacterial properties was applied on the surface of TC4. A PVA gel coating functionalized with terpyridine and catechol groups (PVA-TP-CA) was synthesized and subsequently complexed with copper (Cu) ions. The differential binding affinities of TP and CA groups to Cu enabled a sustained and controlled release of metal ions. Furthermore, a micro-nano surface structure was fabricated on TC4 using femtosecond laser technology to achieve a micro-nano structure interface and enhanced bonding strength. Biological evaluations demonstrated that the modified surface significantly improved the antibacterial, angiogenic, and osteogenic properties of TC4. These findings indicate that this multifunctional composite coating holds great promise for surface modification of orthopedic implants, offering an effective strategy for preventing PJI while promoting bone regeneration.

Trimethylamine N-oxide-derived zwitterion coating for polyurethane ureteral stents prevents encrustation formation

A ureteral stent with strong resistance to proteins, bacteria, and multivalent ions is crucial for the safe treatment of urologic diseases. Generally, the proteins, bacteria, and multivalent ions present in urine tend to bind to the stent surface, leading to aggregation, nucleation, and subsequent stent encrustation. Stent encrustation can induce or exacerbate urinary tract infections and obstructions, thereby seriously harming kidney function. Although hydrophilic coatings on ureteral stents can reduce the binding of proteins, bacteria, and multivalent ions, encrustation still occurs. To date, preventing stent encrustation formation remains a significant challenge. Here, we grafted dense trimethylamine oxide (TMAO)-derived zwitterionic polymers onto the stent surface via a branched amplification strategy. These zwitterions can strongly bind water molecules, forming a stable hydration layer that repels proteins, bacteria, and multivalent ions from adhering to the surface of the polyurethane ureteral stent, thus rendering the stent anti-encrustation. The results showed that the TMAO-derived zwitterion-coated stents exhibited a significantly reduced encrustation weight (13.8% of the original polyurethane stent) and demonstrated good safety. This approach offers a promising method for enhancing stent encrustation resistance. STATEMENT OF SIGNIFICANCE: This study successfully developed a TMAO-derived zwitterionic coating on the surface of a polyurethane stent, creating a superhydrophilic surface with a minimal contact angle of 5.2o. This surface effectively shields the stent from interactions with proteins, bacteria, and multivalent ions in urine, demonstrating favorable anti-protein adsorption and antibacterial adhesion properties. The superhydrophilic surface formed by the TMAO-derived zwitterionic coating on the stents (PTMAO-s) provides strong anti-fouling resistance and enhanced anti-encrustation properties. Under identical conditions, the encrustation resistance of PTMAO-s is approximately 7.2-fold greater than that of original polyurethane stents (PU), 3.6-fold greater than Bard commercial stents, and 2.1-fold greater than betaine-coated stents (PSBG-s).

Antifouling Polymer Coatings for Bioactive Surfaces

Bioactive surfaces play a pivotal role in biomedical applications by enabling precise biological interactions through immobilized functional molecules. However, their performance is often hindered by nonspecific protein adsorption and cell adhesion. Antifouling polymer coatings have emerged as an effective solution, creating hydration barriers to preserve functionality and reduce biofouling. This review provides an overview of the recent advances in the development of antifouling polymer coatings for bioactive surfaces, with particular focus on nonionic polymers, such as polyethylene glycol (PEG), and zwitterionic polymers like poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC). Among them, zwitterionic polymers, with their unique charge-balanced structures, exhibit exceptional hydration, protein resistance, and stability, making them particularly promising for biomedical applications. In addition, key applications of these bioactive surfaces, including their use in anticoagulant materials, antibacterial coatings, and biosensor interfaces, are also discussed. The discussion concludes with an address of the field's challenges and future directions, highlighting the need for innovative materials that balance antifouling properties, biocompatibility, and long-term stability for both clinical and industrial use. This review aims to review the latest advancements in antifouling polymer coatings for bioactive surfaces and provide insights into optimizing multifunctional bioactive surfaces to meet the evolving and dynamic demands of the biomedical field.

Synergistic coating of Laponite swollen-layer and heparin composite for enhanced antifouling and antithrombotic performance

When implantable medical devices come into contact with blood, acute thrombosis and inflammation often occur due to the adhesion and denaturation of plasma proteins, ultimately degrading device performance. To address this issue, we developed a gel-like coating with superhydrophilic properties, incorporating a heparin based outer layer designed to minimize foreign body reactions and enhance hemocompatibility. The coating was engineered using a layer-by-layer (LbL) assembly of poly-l-lysine (PLL), laponite (Lap), and heparin (Hep), utilizing electrostatic interactions. The successful formation of stable layers was confirmed by QCM-D analysis. The inner layer, composed of PLL/Lap multilayers, formed a gel-like structure that maintained superhydrophilicity and effectively prevented cell adhesion. The outermost PLL/Hep multilayers significantly suppressed thrombus formation by inhibiting plasma protein and red blood cell adsorption as well as platelet activation. The coating exhibited excellent stability, retaining its superhydrophilic properties and heparin functionality even after 7 days of immersion in DPBS. Additionally, in vitro hemocompatibility and cytocompatibility tests confirmed its non-toxicity and overall biocompatibility. These results highlight the potential application of this coating to various implantable medical devices, providing a robust solution for improving device performance and safety.

A percolation-type criticality threshold controls immune protein coating of surfaces

When a material enters the body, it is immediately attacked by hundreds of proteins, organized into complex networks of binding interactions and reactions. How do such complex systems interact with a material, "deciding" whether to attack? We focus on the "complement" system of ∼40 blood proteins that bind microbes, nanoparticles, and medical devices, initiating inflammation. We show a sharp threshold for complement activation upon varying a fundamental material parameter, the surface density of potential complement attachment points. This sharp threshold manifests at scales spanning single nanoparticles to macroscale pathologies, shown here for diverse engineered and living materials. Computational models show these behaviors arise from a minimal subnetwork of complement, manifesting percolation-type critical transitions in the complement response. This criticality switch explains the "decision" of a complex signaling network to interact with a material, and elucidates the evolution and engineering of materials interacting with the body.

Interpenetrated Polymer Network Systems (PEG/PNIPAAm) Using Gamma Irradiation: Biological Evaluation for Potential Biomedical Applications

The potential antimicrobial and antibiofouling properties of previously synthesized PEG/NiPAAm interpenetrated polymer networks (IPNs) were investigated against three of the most common bacteria (E. coli, S. aureus, and S. epidermidis). The main goal was to evaluate the material's biocompatibility and determine its potential use as an antifouling component in medical devices. This was intended to provide an alternative option that avoids drug usage as the primary treatment, thus contributing to the fight against antimicrobial resistance (AMR). Additionally, characterization and mechanical testing of the IPN were carried out to determine its resistance to manipulation processes in medical/surgical procedures. IPNs with different NiPAAm ratios exhibited excellent cytocompatibility with BALB/3T3 murine fibroblast cells, with cell viability values of between 90 and 98%. In addition, the results regarding the adsorption of albumin as a model protein showed a nearly constant adsorption percentage of almost zero. Furthermore, the bacterial inhibition tests yielded promising results, demonstrating effective pathogen growth inhibition after 48 h. These findings suggest the material's suitability for use in biomedical applications.

Recent Progress in antibacterial hydrogel coatings for targeting biofilm to prevent orthopedic implant-associated infections

The application of orthopedic implants for bone tissue reconstruction and functional restoration is crucial for patients with severe bone fractures and defects. However, the abiotic nature of orthopedic implants allows bacterial adhesion and colonization, leading to the formation of bacterial biofilms on the implant surface. This can result in implant failure and severe complications such as osteomyelitis and septic arthritis. The emergence of antibiotic-resistant bacteria and the limited efficacy of drugs against biofilms have increased the risk of orthopedic implant-associated infections (OIAI), necessitating the development of alternative therapeutics. In this regard, antibacterial hydrogels based on bacteria repelling, contact killing, drug delivery, or external assistance strategies have been extensively investigated for coating orthopedic implants through surface modification, offering a promising approach to target biofilm formation and prevent OIAI. This review provides an overview of recent advancements in the application of antibacterial hydrogel coatings for preventing OIAI by targeting biofilm formation. The topics covered include: (1) the mechanisms underlying OIAI occurrence and the role of biofilms in exacerbating OIAI development; (2) current strategies to impart anti-biofilm properties to hydrogel coatings and the mechanisms involved in treating OIAI. This article aims to summarize the progress in antibacterial hydrogel coatings for OIAI prevention, providing valuable insights and facilitating the development of prognostic markers for the design of effective antibacterial orthopedic implants.

Universal and One-Step Modification to Render Diverse Materials Bioactivation

Bioactive materials that can support cell adhesion and tissue regeneration are greatly in demand in clinical applications. Surface modification with bioactive molecules is an efficient strategy to convert conventional bioinert materials into bioactive materials. However, there is an urgent need to find a universal and one-step modification strategy to realize the above transformation for bioactivation. In this work, we report a universal and one-step modification strategy to easily modify and render diverse materials bioactivation by dipping materials into the solution of dibutylamine-DOPA-lysine-DOPA (DbaYKY) tripeptide-terminated cell-adhesive molecules, β-peptide polymer, or RGD peptide for only 5 min. This strategy provides materials with a stable surface modification layer and does not cause an undesired surface color change like the widely used polydopamine coating. This one-step strategy can endow material surfaces with cell adhesion properties without concerns on nonspecific conjugation of proteins and macromolecules. This universal and one-step surface bioactivation strategy implies a wide range of applications in implantable biomaterials.

Brush Polymer Coatings with Hydrophilic Main-Chains for Improving Surface Antibacterial Properties

Polymer coatings with improved surface antibacterial properties are of great importance for the application and development of implantable medical devices. Herein, we report the design, preparation, and antibacterial properties of a series of brush polymers (Dex-KEs) with hydrophilic dextran main-chains and mixed-charge polypeptide (KE) side-chains. Dex-KEs showed higher bactericidal activity and antifouling and antibiofilm properties than maleic acid modified dextran (Dex-Ma), KE, Dex-Ma/KE blend coatings, and brush polymer coatings with hydrophobic main-chains (AcDex-KEs). They also showed negligible in vitro cytotoxicity toward different mammalian cells and good in vivo biocompatibility. Dex-KE-coated implants exhibited potent in vivo resistance to bacterial infection before or after implantation.

Multifunctional antibacterial chitosan-based hydrogel coatings on Ti6Al4V biomaterial for biomedical implant applications

Among biomedical community, great efforts have been realized to develop antibacterial coatings that avoid implant-associated infections. To date, conventional mono-functional antibacterial strategies have not been effective enough for successful long-term implantations. Consequently, researchers have recently focused their attention on novel bifunctional or multifunctional antibacterial coatings, in which two or more antibacterial mechanisms interact synergistically. Thus, in this work different chitosan-based (CHI) hydrogel coatings were created on Ti6Al4V surface using genipin (Ti-CHIGP) and polyethylene glycol (Ti-CHIPEG) crosslinking agents. Hydrogel coatings demonstrated an exceptional in vivo biocompatibility plus a remarkable ability to promote cell proliferation and differentiation. Lastly, hydrogel coatings demonstrated an outstanding bacteria-repelling (17-28 % of S. aureus and 33-43 % of E. coli repelled) and contact killing (186-222 % of S. aureus and 72-83 % of E. coli damaged) ability. Such bifunctional antibacterial activity could be further improved by the controlled release of drugs resulting in powerful multifunctional antibacterial coatings.

Selective Grafting of Protease-Resistant Adhesive Peptides on Titanium Surfaces

In orthopedic, dental, and maxillofacial fields, joint prostheses, plates, and screws are widely used in the treatment of problems related to bone tissue. However, the use of these prosthetic systems is not free from complications: the fibrotic encapsulation of endosseous implants often prevents optimal integration of the prostheses with the surrounding bone. To overcome these issues, biomimetic titanium implants have been developed where synthetic peptides have been selectively grafted on titanium surfaces via Schiff base formation. We used the retro-inverted sequence (DHVPX) from [351-359] human Vitronectin and its dimer (D2HVP). Both protease-resistant peptides showed increased human osteoblast adhesion and proliferation, an augmented number of focal adhesions, and cellular spreading with respect to the control. D2HVP-grafted samples significantly enhance Secreted Phosphoprotein 1, Integrin Binding Sialoprotein, and Vitronectin gene expression vs. control. An estimation of peptide surface density was determined by Two-photon microscopy analysis on a silanized glass model surface labeled with a fluorescent analog.

Selective Polyetheretherketone Implants Combined with Graphene Cause Definitive Cell Adhesion and Osteogenic Differentiation

INTRODUCTION

Polyetheretherketone (PEEK) has good biosafety and chemical stability for bone repair. However, PEEK is biologically inert and cannot promote bone apposition. This study investigated whether graphene-modified PEEK (G-PEEK) could improve cell adhesion and osteogenic differentiation.

METHODS

G-PEEK was prepared by melted blending and was characterized. In vitro, the biocompatibility of G-PPEK and the ability to promote cell adhesion and osteogenic differentiation in rabbit bone marrow mesenchymal stem cells (rBMSCs) were examined using live and dead cell double staining, the cell counting kit-8 (CCK-8) assay, immunofluorescence and quantitative real-time PCR (qRT‒PCR). An in vivo rabbit extra-articular graft-to-bone healing model was established. At 4 and 12 weeks after surgery, CT analysis and histological evaluation were performed.

RESULTS

In vitro, G-PEEK significantly improved the adhesion and proliferation of rBMSCs, with good biocompatibility. In vivo, G-PEEK promoted new bone formation at the site of the bone defect.

CONCLUSION

G-PEEK showed excellent osteogenesis performance, which promises new applications in implant materials.

Antifouling poly(PEGMA) grafting modified titanium surface reduces osseointegration through resisting adhesion of bone marrow mesenchymal stem cells

As an alternative strategy to achieve the desired bone augmentation, tenting screw technology (TST) has considerably broadened the indications for implant treatment. Titanium tenting screws are typically used in TST to maintain the space for bone regeneration. However, a high degree of osteogenic integration complicate titanium tenting screw removal and impact the bone healing micro-environment. Previous efforts have been focused on modifying titanium surfaces to enhance osseointegration while ignoring the opposite process. Due to the vital role of bone marrow mesenchymal stem cells (BMSCs) in bone regeneration, it might be feasible to reduce osseointegration around titanium tenting screws by resisting the adhesion of BMSCs. Herein, poly(ethylene glycol)methyl ether methacrylate (poly(PEGMA)) with an optimal length of PEG chain was incorporated with a Ti surface in terms of surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET ATRP). The cell apoptosis analysis showed that the new surface would not induce the apoptosis of BMSCs. Then, the adhesive and proliferative behaviors of BMSCs on the surface were analyzed which indicated that the poly(PEGMA) surface could inhibit the proliferation of BMSCs through resisting the adhesion process. Furthermore, in vivo experiments revealed the presence of the poly(PEGMA) on the surface resulted in a lower bone formation and osseointegration compared with the Ti group. Collectively, this dense poly(PEGMA) surface of Ti may serve as a promising material for clinical applications in the future. STATEMENT OF SIGNIFICANCE: The significance of this research includes: The poly(ethylene glycol)methyl ether methacrylate (poly(PEGMA)) with an optimal length of PEG chain was grafted onto a Ti surface by surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET ATRP). The PEGMA surface could reduce the osteogenic integration by preventing the adhesion of cells, resulting in a lower pullout force of the modified implant and thereby desirable and feasible applications in dental surgery.

Recycling protein selective adsorption on fluorine-modified surface through fluorine-fluorine interaction

Low surface energy materials with micro-nano structures have been widely developed to prevent non-specific adhesion of biomolecules. Herein we put forward a new approach based on the antifouling and self-assembly properties of fluorine components, to construct a non-specific protein resistance surface with selective protein adsorption property. Briefly, the antifouling surface (SN-F) was obtained by a simple one-step modification on silicon nanowire arrays (SiNWAs) with fluorine coupling agent 1 H,1 H,2 H,2 H-perfluorodecyltrimethoxysilane (FAS). And protein was fluorinated by conjugation with an amphiphilic fluoro-copolymer, produced from 2-methacrylamido glucopyranose (MAG) and trifluoroethyl methacrylate (TFEMA) via RAFT polymerization. The properties of the materials were characterized by ¹H nuclear magnetic resonance (¹H NMR), infrared spectroscopy (FTIR), water contact angle, and X-ray photoelectron spectroscopy (XPS) etc., and protein adsorption was investigated by protein content measurement, fluorescence detection, and electrophoresis. It was observed that the adsorption for native proteins on SN-F was at an extremely low level, while the adsorption for the fluoro-copolymer conjugated protein (PFG-BSA) was significantly increased. When the percentage of TFEMA in the fluoro-copolymer was as high as 52.0%, the fluorinated protein adsorbed on SN-F was more than 35 times of native proteins on the surface. Moreover, the platform could resist IgG adhesion in serum after the adsorption of fluorinated protein, and it could be recycled three times after 75% ethanol treatment. In conclusion, SN-F showed non-specific protein resistance through low surface energy and specific protein adsorption by fluorine-fluorine self-assembly. The fluorinated nanostructured platform has a great potential in controlling protein adsorption and release.

Antifouling Gold-Inlaid BSA Coating for the Highly Efficient Capture of Circulating Tumor Cells

Large amounts of coexisting contamination in complex biofluid samples impede the quantified veracity of biomarkers, which is the key problem for disease confirmation. Herein, amyloid-like transformed bovine serum albumin inlaid with gold nanoparticles was used as a coating (BGC) on a substrate composed of silicon nanowires (SW; BGC-SW) under ambient conditions. After modification with the recognition group, BGC-SW could serve as an outstanding platform for the selective separation and sensitive detection of biomarkers in complicated biosamples. First, the BGC on SW with a large surface area exhibits excellent adhesion resistance. The attached amounts of contaminations in biofluids were decreased by over 78% compared with native bovine serum albumin (BSA) as the blocking agent. This is because the phase-transformed BSA coating provides stronger interactions with the SW than bare BSA, which results in a tighter attachment and more uniform coverage of the BGC. Furthermore, the gold matrix laid inside the antiadhesive coating ensures simple cross-linking with the recognition groups to selectively capture various biomarkers in complex biofluids and create a gentle release method. Circulating tumor cells (CTCs) were chosen as template biomarkers to verify the application of A-BGC-SW (BGC-SW modified with sgc8-aptamer) in various separation processes of untreated biofluids. The results showed that approximately six cells could be captured from a 1 mL fresh blood sample containing only 10 CTCs. The easy fabrication and excellent antiadhesion property endow A-BGC-SW with great potential in the field of biological separation.

Photo-switchable supramolecular comb-like polymer brush based on host-guest recognition for use as antimicrobial smart surface

Bacterial infections from biomedical devices pose a great threat to the health of humans and thus place a heavy burden on society. Therefore, developing efficient antibacterial surfaces has attracted much attention. However, it is a challenge to identify or develop a combination that efficiently integrates multiple functions via topological tailoring and on-demand function-switch via non-contact and noninvasive stimuli. To resolve this issue, a highly hydrophilic comb polymer brush was constructed here based on supramolecular host-guest recognition. Azobenzene (azo)-modified antifouling and antibacterial polymers were incorporated into cyclodextrin (CD)-modified antifouling polymer brushes grafted on the surface. The surface thus obtained possessed excellent antifouling performance with a low bacterial density of ∼6.25 × 10⁵ cells per cm² after 48 h and exhibited a high efficiency of ∼88.2% for killing bacteria. Besides, irradiation with UV light resulted in the desorption of the azo-polymers and a release of ∼85.1% attached bacteria. Irradiating visible light led to the re-adsorption of azo-polymers, which regenerated the fresh surface; the process could be repeated for at least three cycles, and the surface still maintained low bacterial attachments with a cell density of ∼7.10 × 10⁵ cells per cm², high sterilization efficiency of ∼93.8%, and a bacteria release rate of ∼83.1% in the 3rd cycle. The photo-switchable antibacterial surface presented in this research will provide new insights into the development of smart biomedical surfaces.

Medical gloves modified by a one-minute spraying process with blood-repellent, antibacterial and wound-healing abilities

During clinical surgery, bleeding that occurs in the operative region is inevitable. Due to the blood adhesion on ordinary medical gloves, it reduces surgery quality to a certain extent and even prolongs operation time. Herein, we show that medical blood-repellent gloves (MBRG) can be obtained by spraying the blood-repellent mist spray (MS) on the surface of ordinary medical gloves, which are available for immediate use in around one minute. After the modification, MBRG not only have a significantly higher blood repellent rate than that of ordinary medical gloves, but also can effectively inhibit the growth of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), and even promote the healing of infected wounds. MS is easy to prepare, low-toxic, and can be widely used on the surface of various medical gloves, such as rubber gloves, polyethylene film gloves, and nitrile gloves, which may have an impact on the development of future medical gloves.

Functional nanomaterials, synergisms, and biomimicry for environmentally benign marine antifouling technology

Marine biofouling remains one of the key challenges for maritime industries, both for seafaring and stationary structures. Currently used biocide-based approaches suffer from significant drawbacks, coming at a significant cost to the environment into which the biocides are released, whereas novel environmentally friendly approaches are often difficult to translate from lab bench to commercial scale. In this article, current biocide-based strategies and their adverse environmental effects are briefly outlined, showing significant gaps that could be addressed through advanced materials engineering. Current research towards the use of natural antifouling products and strategies based on physio-chemical properties is then reviewed, focusing on the recent progress and promising novel developments in the field of environmentally benign marine antifouling technologies based on advanced nanocomposites, synergistic effects and biomimetic approaches are discussed and their benefits and potential drawbacks are compared to existing techniques.

A sandcastle worm-inspired strategy to functionalize wet hydrogels

Hydrogels have been extensively used in many fields. Current synthesis of functional hydrogels requires incorporation of functional molecules either before or during gelation via the pre-organized reactive site along the polymer chains within hydrogels, which is tedious for polymer synthesis and not flexible for different types of hydrogels. Inspired by sandcastle worm, we develop a simple one-step strategy to functionalize wet hydrogels using molecules bearing an adhesive dibutylamine-DOPA-lysine-DOPA tripeptide. This tripeptide can be easily modified with various functional groups to initiate diverse types of polymerizations and provide functional polymers with a terminal adhesive tripeptide. Such functional molecules enable direct modification of wet hydrogels to acquire biological functions such as antimicrobial, cell adhesion and wound repair. The strategy has a tunable functionalization degree and a stable attachment of functional molecules, which provides a tool for direct and convenient modification of wet hydrogels to provide them with diverse functions and applications.