Temperature-responsive and biocompatible nanocarriers based on clay nanotubes for controlled anti-cancer drug release

Administration of temperature-responsive drug carriers that release anticancer drugs at high temperatures can benefit hyperthermia therapies because of the synergistic effect of anticancer drug molecules and high temperature on killing the cancer cells. In this study, we design and characterize a new temperature-responsive nanocarrier based on a naturally occurring and biocompatible clay mineral, halloysite nanotubes. Poly(N-isopropylacrylamide) brushes were grown on the surface of halloysite nanotubes using a combination of mussel-inspired dopamine polymerization and surface-initiated atom transfer radical polymerization. The chemical structure of the hybrid materials was investigated using X-ray photoelectron spectroscopy, thermogravimetric analysis and energy-dispersive X-ray spectroscopy. The hybrid material was shown to have a phase transition temperature of about 32 °C, corresponding to a 40 nm thick polymer layer surrounding the nanotubes. Cell studies suggested that grafting of poly(N-isopropylacrylamide) brushes on the polydopamine-modified halloysite nanotubes suppresses the cytotoxicity caused by the polydopamine interlayer and drug release studies on nanotubes loaded with doxorubicin showed that thanks to the poly(N-isopropylacrylamide) brushes a temperature-dependent drug release is observed. Finally, a fluorescent dye molecule was covalently attached to the polymer-grafted nanotubes and stimulated emission depletion nanoscopy was used to confirm the internalization of the nanotubes in HeLa cells.

Wireless Rehabilitation Training Sensor Arrays Made with Hot Screen-Imprinted Conductive Hydrogels with a Low Percolation Threshold

Herein, we propose a highly sensitive wireless rehabilitation training ball with a piezoresistive sensor array for patients with Parkinson's disease (PD). The piezoresistive material is a low percolation threshold conductive hydrogel which is formed with polypyrrole (PPy) nanofibers (NFs) as a conductive filler derived from a polydopamine (PDA) template. The proton acid doping effect and molecular template of PDA are essential for endowing PPy NFs with a high aspect ratio, leading to a low percolation threshold (∼0.78 vol %) and a low Young's 004Dodulus of 37.69 kPa and hence easy deformation. The piezoresistive sensor exhibited a static and dynamic stability of 10,000 s and 15,000 cycle times, respectively. This stability could be attributed to the increased hydrophilicity of conductive fillers, enhancing the interfacial strength between the conductive filler and the matrix. The interaction between the PDA-PPy NFs and the hydrogel matrix endows the hydrogel with toughness and ensures the stability of the device. Additionally, the microdome structure of the conductive hydrogel, produced by hot screen-imprinting, dramatically improves the sensitivity of the piezoresistive sensor (∼856.14 kPa^-1). The microdome conductive hydrogel can distinguish a subtle pressure of 15.40 Pa compared to the control hydrogel without a microstructure. The highly sensitive piezoresistive sensor has the potential to monitor the hand-grip force, which is not well controlled by patients with PD. The rehabilitation training ball assembled with a sensor array on the surface and a wireless chip for communication inside is built and used to monitor the pressure in real time through the WeChat applet. Thus, this work has significantly broadened the application of hydrogel-based flexible piezoresistive sensors for human activity monitoring, which provides a promising strategy to realize next-generation electronics.

Engineering Hydrogel Adhesion for Biomedical Applications via Chemical Design of the Junction

Hydrogel adhesion inherently relies on engineering the contact surface at soft and hydrated interfaces. Upon contact, adhesion normally occurs through the formation of chemical or physical interactions between the disparate surfaces. The ability to form these adhesion junctions is challenging for hydrogels as the interfaces are wet and deformable and often contain low densities of functional groups. In this Review, we link the design of the binding chemistries or adhesion junctions, whether covalent, dynamic covalent, supramolecular, or physical, to the emergent adhesive properties of soft and hydrated interfaces. Wet adhesion is useful for bonding to or between tissues and implants for a range of biomedical applications. We highlight several recent and emerging adhesive hydrogels for use in biomedicine in the context of efficient junction design. The main focus is on engineering hydrogel adhesion through molecular design of the junctions to tailor the adhesion strength, reversibility, stability, and response to environmental stimuli.

Stable Fabrication of Zwitterionic Coating Based on Copper-Phenolic Networks on Contact Lens with Improved Surface Wettability and Broad-Spectrum Antimicrobial Activity

Ocular dryness and contact lens(CL)-related microbial keratitis (MK) are two major risks of wearing CLs. The development of multifunctional surface coating for CLs with excellent hydrating and antimicrobial properties is a practical strategy to improve the comfort of CL wearers and to prevent corneal infection. Here, we develop zwitterionic and antimicrobial metal-phenolic networks (MPNs) based on the coordination of copper ions (Cu^II) and the poly(carboxylbetaine-co-dopamine methacrylamide) copolymer (PCBDA), which can be easily one-step prepared onto CLs due to the near-universal adherent properties of catechol groups. The zwitterionic and antifouling carboxybetaine (CB) groups of the Cu^II-PCBDA coating can significantly increase the wettability of CLs and reduce their protein adsorptions, resulting in a lens surface that is more water retentive and with lower protein binding to prevent tear film evaporation and eye dryness. In addition, since the immobilized copper ions in the MPNs impart them with ion-mediated antimicrobial activity, the Cu^II-PCBDA coating exhibits a strong and broad-spectrum antimicrobial activity against MK related pathogenic microbes, including bacteria, such as Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, and fungi, such as Candida albicans. Compared with a pristine CL, the Cu^II-PCBDA-coated CL effectively inhibited biofilm formation even after daily exposure to the above microbial environment for 14 days. Notably, the Cu^II-PCBDA coating developed in this study is not only biocompatible with 100% cell viability following direct contact with human corneal epithelial cells (HCECs) for 48 h but also maintains the optical clarity of the native CLs. Thus, the Cu^II-PCBDA coating has a great application potential for the development of a multifunctional surface coating for CLs for increased CL comfort and prevention of MK.

Antimicrobial Titanium Surface via Click-Immobilization of Peptide and Its in Vitro/Vivo Activity

The use of antimicrobial peptides (AMPs)-functionalized titanium implants is an efficient method for preventing bacterial infection. However, the attachment of AMPs to the surface of titanium implants remains a challenge. In this study, a "clickable" titanium surface was developed by using a silane coupling agent with an alkynyl group. The antimicrobial titanium implant was then constructed through the reaction between the "clickable" surface and azido-AMPs (PEG-HHC36:N₃-PEG₁₂-KRWWKWWRR) via click chemistry of Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). Such an antimicrobial titanium implant, with an AMP density of 897.4 ± 67.3 ng/cm² (2.5 ± 0.2 molecules per nm²) on the surface, exhibited good and stable antimicrobial activity, inhibited 90.2% of Staphylococcus aureus and 88.1% of Escherichia coli after 2.5 h of incubation, and even inhibited 69.5% of Staphylococcus aureus after 4 days of degradation. The CCK-8 assay indicated that the antimicrobial titanium implant exhibited negligible cytotoxicity to mouse bone mesenchymal stem cells. In vivo assay illustrated that this implant could kill 78.8% of Staphylococcus aureus after 7 days. This method has great potential for the preparation of antimicrobial titanium implants and the prevention of infections in the clinic.

Phototriggered Growth and Detachment of Polymer Brushes with Wavelength Selectivity

Both phototriggered growth and removal of polymer chains from surfaces are efficient ways to finely tune interface properties. Combining these two capabilities in one system with independent control can significantly increase the feasibility of photoregulation on surface modification but has not been reported yet. Herein we describe a novel approach to control both the growth and the detachment of polymer brushes independently by light with different wavelengths. The approach is based on a nitrodopamine-based initiator (NO₂-BDAM) which contains a catechol structure for surface modification, alkyl bromide group for radical polymerization, and o-nitrophenyl ethyl moiety for photolysis. When dimanganese decacarbonyl (Mn₂(CO)₁₀) was applied together with NO₂-BDAM as an initiating system, visible light (460 nm) can be used to trigger the site-specific growth of polymer brushes. Resulting polymer brushes can be selectively removed by UV light (360 nm). This method is suitable for different monomers on various substrates, suggesting a facile and robust method to regulate surface properties.

Simple and Green Strategy for the Synthesis of "Pathogen-Mimetic" Glycoadjuvant@AuNPs by Combination of Photoinduced RAFT and Bioinspired Dopamine Chemistry

Innate immune responses recognizing pathogen associated molecular patterns (PAMPs) play a crucial role in adaptive immunity. Toll-like receptors (TLRs) and C-type lectin receptors (CLRs) contribute to antigen capture, uptake, presentation and activation of immune responses. In this contribution, metal-free reversible addition-fragmentation chain transfer (RAFT) polymerization of N-3,4-dihydroxybenzenethyl methacrylamide (DMA) and 2-(methacrylamido) glucopyranose (MAG) under sunlight irradiation using 2-cyanoprop-2-yl-α-dithionaphthalate (CPDN) as iniferter agent, can be employed to fabricate the multivalent glycopolymer containing bioresponsive sugar group and multifunctional catechol functionalities. The polymerization behavior is investigated and it presents controlled features. Moreover, bioinspired dopamine chemistry can be successfully utilized to form in situ glycopolymer-coated gold nanoparticles (AuNPs) without the need of additional reducing reagent, design "pathogen-mimetic" glycoadjuvant recognized by both CLRs and TLRs. The synthetic glycoadjuvant is found to enhance the adjuvant activity as "infected signals" in vitro.

Reversible Tethering of Polymers onto Catechol-Based Titanium Platforms

In this article, we report on the reversible tethering of end-functionalized polymers onto catechol-based titanium platforms by exploiting the reversible Diels-Alder (DA) cycloaddition reaction. For this purpose, furan and maleimide end-functionalized polymers, prepared via reversible addition-fragmentation chain transfer polymerization, were covalently grafted through a DA reaction onto reactive titanium platforms elaborated from catechol-based anchors incorporating either the furan or the maleimide moiety. As a proof of concept, a hydrophilic poly(oligo(ethylene glycol)acrylate) (POEGA) and a hydrophobic poly(2,2,2-trifluoroethyl acrylate) (PTFEA) were grafted onto titanium surfaces and subsequently detached by exploiting the thermoreversible nature of the DA reaction [i.e., retro Diels-Alder (rDA)]. These polymers were interchanged by performing a second DA reaction, thereby allowing the titanium surface wettability to be switched from hydrophobic to hydrophilic on demand. The grafting of furan/maleimide end-functionalized polymers onto functionalized (maleimide/furan, respectively) catechol-based titanium platforms and the subsequent rDA/DA sequence used for switching the titanium surface were evidenced by attenuated total reflectance-Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, and contact angle measurements.

Vancomycin-conjugated polythiophene for the detection and imaging of Gram-positive bacteria

Vancomycin-conjugated polythiophene was synthesized for the discrimination and elimination of Gram-positive bacteria.

Conjugation of Lectin to Poly(ε-caprolactone)-block-glycopolymer Micelles for In Vitro Intravesical Drug Delivery

Amphiphilic poly(ε-caprolactone)-block-poly[2-(α-d-mannopyranosyloxy) ethyl acrylamide] (PCL-b-PManEA) block copolymers were synthesized via a combination of ring-opening polymerization (ROP), reversible addition-fragmentation chain transfer (RAFT) polymerization and reactive ester-amine reaction. The PCL-b-PManEA block copolymers can self-assemble into micelles and encapsulate anticancer drug doxorubicin (DOX). To enhance mucoadhesive property of the resulting DOX-loaded PCL-b-PManEA micelles, Concanavalin A (ConA) lectin was further conjugated with the micelles. Turbidimetric assay using mucin shows that the DOX-loaded PCL-b-PManEA@ConA micelles are mucoadhesive. DOX release from the DOX-loaded PCL-b-PManEA@ConA micelles in artificial urine at 37 °C exhibits an initial burst release, followed by a sustained and slow release over three days. Confocal laser scanning microscope (CLSM) images indicate that the DOX-loaded PCL-b-PManEA@ConA micelles can be effectively internalized by UMUC3 human urothelial carcinoma cells. The DOX-loaded PCL-b-PManEA@ConA micelles exhibit significant cytotoxicity to these cells.

Surface patterned pH-sensitive fluorescence using β-cyclodextrin functionalized poly(ethylene glycol)

This paper reports the development of a pH-responsive molecular pattern that shows specific and selective affinity for particular host-guest interactions, and its use as a pH fluorescent sensor. The pH-responsive boronate ester is formed via interactions between the diol group of β-cyclodextrin (CD) and phenylboronic acid of poly(ethylene glycol), and is strategically designed to allow reversible formation of a molecular lining pattern. Printing on a versatile substrate provides a method to monitor the positioning of different molecules by using a pH-responsive boronate ester, allowing specific host-guest interactions on any surface. Confocal laser scanning microscopy, fluorescence spectroscopy, and (1)H NMR results indicate that the assembled CD monolayer can be removed by washing with an acidic pH buffer, demonstrating the presence of a boronate ester connective bridge, which is acid labile. Therefore, visualization of the pH-responsive fluorescence sensor using a rhodamine-CD complex allows straightforward discrimination between different molecules on any substrate, thus facilitating application of this sensor in clinical diagnostics and environmental monitoring.

Substrate-Independent Robust and Heparin-Mimetic Hydrogel Thin Film Coating via Combined LbL Self-Assembly and Mussel-Inspired Post-Cross-linking

In this work, we designed a robust and heparin-mimetic hydrogel thin film coating via combined layer-by-layer (LbL) self-assembly and mussel-inspired post-cross-linking. Dopamine-grafted heparin-like/-mimetic polymers (DA-g-HepLP) with abundant carboxylic and sulfonic groups were synthesized by the conjugation of adhesive molecule, DA, which exhibited substrate-independent adhesive affinity to various solid surfaces because of the formation of irreversible covalent bonds. The hydrogel thin film coated substrates were prepared by a three-step reaction: First, the substrates were coated with DA-g-HepLP to generate negatively charged surfaces. Then, multilayers were obtained via LbL coating of chitosan and the DA-g-HepLP. Finally, the noncovalent multilayers were oxidatively cross-linked by NaIO4. Surface ATR-FTIR and XPS spectra confirmed the successful fabrication of the hydrogel thin film coatings onto membrane substrates; SEM images revealed that the substrate-independent coatings owned 3D porous morphology. The soaking tests in highly alkaline, acid, and concentrated salt solutions indicated that the cross-linked hydrogel thin film coatings owned high chemical resistance. In comparison, the soaking tests in physiological solution indicated that the cross-linked hydrogel coatings owned excellent long-term stability. The live/dead cell staining and morphology observations of the adhered cells revealed that the heparin-mimetic hydrogel thin film coated substrates had low cell toxicity and high promotion ability for cell proliferation. Furthermore, systematic in vitro investigations of protein adsorption, platelet adhesion, blood clotting, and blood-related complement activation confirmed that the hydrogel film coated substrates showed excellent hemocompatibility. Both the results of inhibition zone and bactericidal activity indicated that the gentamycin sulfate loaded hydrogel thin films had significant inhibition capability toward both Escherichia coli and Staphylococcus aureus bacteria. Combined the above advantages, it is believed that the designed heparin-mimetic hydrogel thin films may show high potential for applications in various biological and clinical fields, such as long-term hemocompatible and drug-loading materials for implants.

Catechol-based layer-by-layer assembly of composite coatings: a versatile platform to hierarchical nano-materials

Inspired by the marine mussel's ability to adhere to surfaces underwater, an aqueous catechol-based dip coating platform was developed. Using a catechol-functionalized polyacrylamide binder in combination with inorganic nanoparticles enables the facile fabrication of robust composite coatings via a layer-by-layer process. This modular assembly of well-defined building blocks provides a versatile alternative to electrostatic driven approaches with layer thickness and refractive indices being readily tunable. The platform nature of this approach enables the fabrication of hierarchically ordered nano-materials such as Bragg stacks.

Bioinspired Titanium Drug Eluting Platforms Based on a Poly-β-cyclodextrin-Chitosan Layer-by-Layer Self-Assembly Targeting Infections

In the field of implantable titanium-based biomaterials, infections and inflammations are the most common forms of postoperative complications. The controlled local delivery of therapeutics from implants through polyelectrolyte multilayers (PEMs) has recently emerged as a versatile technique that has shown great promise in the transformation of a classical medical implant into a drug delivery system. Herein, we report the design and the elaboration of new biodegradable multidrug-eluting titanium platforms based on a polyelectrolyte multilayer bioactive coating that target infections. These systems were built up in mild conditions according to the layer-by-layer (L-b-L) assembly and incorporate two biocompatible polysaccharides held together through electrostatic interactions. A synthetic, negatively charged β-cyclodextrin-based polymer (PCD), well-known for forming stable and reversible complexes with hydrophobic therapeutic agents, was exploited as a multidrug reservoir, and chitosan (CHT), a naturally occurring, positively charged polyelectrolyte, was used as a barrier for controlling the drug delivery rate. These polyelectrolyte multilayer films were strongly attached to the titanium surface through a bioinspired polydopamine (PDA) film acting as an adhesive first layer and promoting the robust anchorage of PEMs onto the biomaterials. Prior to the multilayer film deposition, the interactions between both oppositely charged polyelectrolytes, as well the multilayer growth, were monitored by employing surface plasmon resonance (SPR). Several PEMs integrating 5, 10, and 15 bilayers were engineered using the dip coating strategy, and the polyelectrolyte surface densities were estimated by colorimetric titrations and gravimetric analyses. The morphologies of these multilayer systems, as well as their naturally occurring degradation in a physiological medium, were investigated by scanning electron microscopy (SEM), and their thicknesses were measured by means of profilometry and ellipsometry studies. Finally, the ability of the coated titanium multilayer devices to act as a drug-eluting system and to treat infections was validated with gentamicin, a relevant water-soluble antibiotic commonly used in medicine due to its broad bactericidal spectrum.

Poly(L-lysine) Interfaces via Dual Click Reactions on Surface-Bound Custom-Designed Dithiol Adsorbates

Surfaces modified with poly(L-lysine) can be used to immobilize selected biomolecules electrostatically. This report describes the preparation of a set of self-assembled monolayers (SAMs) from three different azide-terminated adsorbates as platforms for performing controlled surface attachments and as a means of determining the parameters that afford stable poly(L-lysine)-modified SAM surfaces having controlled packing densities. A maleimide-terminated alkyne linker was "clicked" to the azide-terminated surfaces via a copper-catalyzed cycloaddition reaction to produce the attachment sites for the polypeptides. A thiol-Michael addition was then used to immobilize cysteine-terminated poly(L-lysine) moieties on the gold surface, avoiding adsorbate self-reactions with this two-step procedure. Each step in this process was analyzed by ellipsometry, X-ray photoelectron spectroscopy, polarization modulation infrared reflection-absorption spectroscopy, and contact angle goniometry to determine which adsorbate structure most effectively produced the targeted polypeptide interface. Additionally, a series of mixed SAMs using an azidoalkanethiol in combination with a normal alkanethiol having an equivalent alkyl chain were prepared to provide data to determine how dilution of the azide reactive site on the SAM surface influences the initial click reaction. Overall, the collected data demonstrate the advantages of an appropriately designed bidentate absorbate and its potential to form effective platforms for biomolecule surface attachment via click reactions.

Bioinspired adhesive polymer coatings for efficient and versatile corrosion resistance

Bioinspired organic polymer is demonstrated for efficient and versatile corrosion resistance. Present method affords a thin, transparent and highly adhesive protective coatings for wide range of structural metals/alloys.

Fabrication of a photocontrolled surface with switchable wettability based on host-guest inclusion complexation and protein resistance

A novel surface-modification strategy has been developed for the construction of a photocontrolled silicon wafer surface with switchable wettability based on host-guest inclusion complexation. The silicon wafer was first modified by guest molecule azobenzene (Azo) via a silanization reaction. Subsequently, a series of polymers with different polarities were attached to host molecule β-cyclodextrin (β-CD) to prepare β-CD-containing hemitelechelic polymers via click chemistry. Finally, a photocontrolled silicon wafer surface modified with polymers was fabricated by inclusion complexation between β-CD and Azo, and the surface properties of the substrate are dependent on the polymers we used. The elemental composition, surface morphology, and hydrophilic/hydrophobic property of the modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscope, and contact angle measurements, respectively. The antifouling property of the PEG-functionalized surface was evaluated by a protein adsorption assay using bovine serum albumin, which was also characterized by XPS. The results demonstrate that the surface modified with PEG possesses good protein-resistant properties.