Spatially controlled photochemical peptide and polymer conjugation on biosurfaces

Photo-cross-linked and pH-Switchable Soft Polymer Nanocapsules from Polyglycidyl Ethers

Soft polymer nanocapsules and microgels, which can adapt their shape and, at the same time, sequester and release molecular payloads in response to an external trigger, are a challenging complement to vesicular structures like polymersomes. In this work, we report the synthesis of such capsules by photo-cross-linking of coumarin-substituted polyglycidyl ethers, which we prepared by Williamson etherification of epichlorohydrin (ECH) repeating units with 7-hydroxycoumarin in copolymers with tert-butyl glycidyl ether (tBGE). To control capsule size, we employed the prepolymers in an o/w miniemulsion, where they formed a gel layer at the interface upon irradiation at 365 nm by [2π + 2π] photodimerization of the coumarin groups. Upon irradiation at 254 nm, the reaction could be reversed and the gel wall could be repeatedly disintegrated and rebuilt. We further demonstrated (i) reversible hydrophilization of the gels by hydrolysis of the lactone rings in coumarin dimers as a mechanism to manipulate the permeability of the capsules and (ii) binding functional molecules as amides. Thus, the presented nanogels are remarkably versatile and can be further used as a carrier system.

Mussel-Inspired and Bioclickable Peptide Engineered Surface to Combat Thrombosis and Infection

Thrombosis and infections are the two major complications associated with extracorporeal circuits and indwelling medical devices, leading to significant mortality in clinic. To address this issue, here, we report a biomimetic surface engineering strategy by the integration of mussel-inspired adhesive peptide, with bio-orthogonal click chemistry, to tailor the surface functionalities of tubing and catheters. Inspired by mussel adhesive foot protein, a bioclickable peptide mimic (DOPA)4-azide-based structure is designed and grafted on an aminated tubing robustly based on catechol-amine chemistry. Then, the dibenzylcyclooctyne (DBCO) modified nitric oxide generating species of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelated copper ions and the DBCO-modified antimicrobial peptide (DBCO-AMP) are clicked onto the grafted surfaces via bio-orthogonal reaction. The combination of the robustly grafted AMP and Cu-DOTA endows the modified tubing with durable antimicrobial properties and ability in long-term catalytically generating NO from endogenous s-nitrosothiols to resist adhesion/activation of platelets, thus preventing the formation of thrombosis. Overall, this biomimetic surface engineering technology provides a promising solution for multicomponent surface functionalization and the surface bioengineering of biomedical devices with enhanced clinical performance.

Shining Light on Cyclopentadienone-Norbornadiene Diels-Alder Adducts to Enable Photoinduced Click Chemistry with Cyclopentadiene

A new Diels-Alder (DA)-based photopatterning platform is presented, which exploits the irreversible, light-induced decarbonylation and subsequent cleavage of cyclopentadienone-norbornadiene (CPD-NBD) adducts. A series of CPD-NBD adducts have been prepared and systematically studied toward the use in a polymeric material photopatterning platform. By incorporating an optimized CPD-NBD adduct into polymer networks, it is demonstrated that cyclopentadiene may be unveiled upon 365 nm irradiation and subsequently clicked to a variety of maleimides with spatial control under mild reaction conditions and with fast kinetics. Unlike currently available photoinduced Diels-Alder reactions that rely on trapping transient, photocaged dienes, this platform introduces a persistent, yet highly reactive diene after irradiation, enabling the use of photosensitive species such as cyanine dyes to be patterned. To highlight the potential use of this platform in a variety of material applications, we demonstrate two proof-of-concepts: patterned conjugation of multiple dyes into a polyacrylate network and preprogrammed ligation of streptavidin into poly(ethylene glycol) hydrogels.

Light-Triggered Click Chemistry

The merging of click chemistry with discrete photochemical processes has led to the creation of a new class of click reactions, collectively known as photoclick chemistry. These light-triggered click reactions allow the synthesis of diverse organic structures in a rapid and precise manner under mild conditions. Because light offers unparalleled spatiotemporal control over the generation of the reactive intermediates, photoclick chemistry has become an indispensable tool for a wide range of spatially addressable applications including surface functionalization, polymer conjugation and cross-linking, and biomolecular labeling in the native cellular environment. Over the past decade, a growing number of photoclick reactions have been developed, especially those based on the 1,3-dipolar cycloadditions and Diels-Alder reactions owing to their excellent reaction kinetics, selectivity, and biocompatibility. This review summarizes the recent advances in the development of photoclick reactions and their applications in chemical biology and materials science. A particular emphasis is placed on the historical contexts and mechanistic insights into each of the selected reactions. The in-depth discussion presented here should stimulate further development of the field, including the design of new photoactivation modalities, the continuous expansion of λ-orthogonal tandem photoclick chemistry, and the innovative use of these unique tools in bioconjugation and nanomaterial synthesis.

Nitric oxide-generating compound and bio-clickable peptide mimic for synergistically tailoring surface anti-thrombogenic and anti-microbial dual-functions

Application of extracorporeal circuits and indwelling medical devices has saved many lives. However, it is accompanied with two major complications: thrombosis and infection. To address this issue, we apply therapeutic nitric oxide gas (NO) and antibacterial peptide for synergistically tailoring such devices for surface anti-thrombogenic and antifouling dual functions. Such functional surface is realized by stepwise conjugation of NO-generating compound of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelated copper ions (Cu-DOTA) and dibenzylcyclooctyne- (DBCO-) modified antimicrobial peptide based on carbodiimide and click chemistry respectively. The integration of peptide and Cu-DOTA grants the modified surface the ability to not only efficiently inhibit bacterial growth, but also catalytically generate NO from endogenous s-nitrosothiols (RSNO) to reduce adhesion and activation of platelets, preventing the formation of thrombus. We envision that the stepwise synergistic modification strategy by using anticoagulant NO and antibacterial peptide would facilitate the surface multifunctional engineering of extracorporeal circuits and indwelling medical devices, with reduced clinical complications associated with thrombosis and infection.

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We report a bionic surface strategy for blood-contacting devices by integrating anti-thrombogenic and anti-microbial dual functions. Here, we engineer an endothelium-mimicking surface by combination of the nitric oxide (NO)-generating property and anti-microbial functions of a healthy endothelium, in which the generated gas signal molecule NO and the anti-microbial peptide (AMP) jointly provide synergistic effects against thrombogenicity and biofouling.

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An endothelium-bionic surface strategy is proposed for tailoring surface multi-functionalities.

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Carbodiimide and click chemistries were used for realizing synergistic tethering of NO-generating species and bio-clickable antimicrobial peptide.

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The integration of NO and antimicrobial peptide imparts the tubing surface with anti-thrombogenic and anti-fouling dual functions. The integration of NO releasing and AMP tethering endows the tubing surface with significant anti-thrombogenic and anti-fouling properties. We envision that this bio-inspired surface engineering strategy will provide a promising solution to address the clinical issues.

Covalent Attachment of P15 Peptide to Ti Alloy Surface Modified with Polymer to Enhance Osseointegration of Implants

Titanium (Ti) and its alloys are used in orthopedic and dental implants due to their excellent physical properties and biocompatibility. Although Ti exhibits superior osteoconductive properties compared to those of polymer-based implants, improved bone-on growth properties are required for enhanced surgical outcomes and improved recovery surgical interventions. Herein, we demonstrate a novel surface modification strategy to enhance the osteoconductivity of Ti surfaces through the grafting-from procedure of a reactive copolymer via surface-initiated atom transfer radical polymerization (SI-ATRP). Then, postpolymerization conjugation of the P15 peptide, an osteoblast binding motif, was successfully carried out. Subsequent in vitro studies revealed that the surface modification promoted osteoblast attachment on the Ti discs at 6 and 24 h. Moreover, mineral matrix deposition by osteoblasts was greater for the surface-modified Ti than for plain Ti and P15 randomly absorbed onto the Ti surface. These results suggest that the strategy for postpolymerization incorporation of P15 onto a Ti surface with a polymer interface may provide improved osseointegration outcomes, leading to enhanced quality of life for patients.

Dynamic Nitroxide Functional Materials

A substrate-independent and versatile coating platform for (spatially resolved) surface functionalization, based on nitroxide radical coupling (NRC) reactions and the formation of thermo-labile alkoxyamine functional groups, was introduced. Nitroxide-decorated poly(glycidyl methacrylate) (PGMA) microspheres, obtained through bioinspired copolymer surface deposition using dopamine and a nitroxide functional dopamine derivative as monomers, were conjugated with small functional groups in a rewritable process. Reversible coding of the nitroxide functional microspheres by NRC and decoding through thermal alkoxyamine fission were monitored and characterized by electron paramagnetic resonance (EPR) spectroscopy and X-ray photoelectron spectroscopy (XPS). In addition, this nitroxide coating system was exploited in "grafting-to" polymer surface ligations of poly(methyl methacrylate) (PMMA) and poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) in spatially confined areas. Polymer strands terminated with an Irgacure 2959 (2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone) photoinitiator were obtained through chain-transfer polymerization, and subsequently coupled to nitroxide-immobilized poly(dopamine) (PDA)-coated silicon substrates by using rapid photoclick NRC reactions. Light-driven polymer surface coding was visualized by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and XPS imaging.

Spatially-Resolved Multiple Metallopolymer Surfaces by Photolithography

A tetrazole-based photoligation protocol for the spatially-resolved encoding of various defined metallopolymers onto solid surfaces is introduced. By using this approach, fabrication of bi- and trifunctional metallopolymer surfaces with different metal combinations were achieved. Specifically, α-ω-functional copolymers containing bipyridine as well as triphenylphosphine ligands were synthesized through reversible addition-fragmentation chain transfer (RAFT) polymerization, and subsequently metal loaded to afford metallopolymers of the widely-used metals gold, palladium, and platinum. Spatially-resolved surface attachment was achieved by means of a nitrile imine-mediated tetrazole-ene cycloaddition (NITEC) based photoligation protocol, exploiting tethered tetrazoles and metallopolymers equipped with a maleimide chain terminus. Metallopolymer coated surfaces with three different metals were prepared and characterized by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and spatially-resolved X-ray photoelectron spectroscopy (XPS) mapping, supporting the preserved chemical composition of the surface-bound metallopolymers. The established photochemical technology platform for arbitrary spatially-resolved metallopolymer surface designs enables the patterning of multiple metallopolymers onto solid substrates. This allows for the assembly of designer metallopolymer substrates.

Light-Induced Step-Growth Polymerization of AB-Type Photo-Monomers at Ambient Temperature

We introduce two AB-type monomers able to undergo a facile catalyst-free photoinduced polycycloaddition of photocaged dienes, enabling rapid Diels-Alder ligations under UV-irradiation (λ_max = 350 nm) at ambient temperature, closely adhering to Carother's equation established by a careful kinetic study (17800 g mol^-1 < M_w < 24700 g mol^-1). The resulting macromolecules were in-depth analyzed via size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy. Additionally, SEC hyphenated to high resolution-electrospray ionization-mass spectrometry (HR-ESI-MS) enabled the careful mapping of the end group structure of the generated polymers. Furthermore, we demonstrate that both monomer systems can be readily copolymerized. The study thus demonstrates that Diels-Alder ligation resting upon photocaged dienes is a powerful tool for accessing step-growth polymers.

Photo-induced chemistry for the design of oligonucleotide conjugates and surfaces

A photocaged diene is introduced at the 5′-end of oligonucleotides using the H-phosphonate approach and subsequently employed for the light-induced conjugation to a protein and the spatially controlled immobilization onto surfaces.

Writing and erasing hidden optical information on covalently modified cellulose paper

A strategy for preparing photoresponsive cellulose paper enabling the storage of short-lived optical data by covalent means is disclosed.

Thiol-ene and photo-cleavage chemistry for controlled presentation of biomolecules in hydrogels

Hydrogels have emerged as promising scaffolds in regenerative medicine for the delivery of biomolecules to promote healing. However, increasing evidence suggests that the context that biomolecules are presented to cells (e.g., as soluble verses tethered signals) can influence their bioactivity. A common approach to deliver biomolecules in hydrogels involves physically entrapping them within the network, such that they diffuse out over time to the surrounding tissues. While simple and versatile, the release profiles in such system are highly dependent on the molecular weight of the entrapped molecule relative to the network structure, and it can be difficult to control the release of two different signals at independent rates. In some cases, supraphysiologically high loadings are used to achieve therapeutic local concentrations, but uncontrolled release can then cause deleterious off-target side effects. In vivo, many growth factors and cytokines are stored in the extracellular matrix (ECM) and released on demand as needed during development, growth, and wound healing. Thus, emerging strategies in biomaterial chemistry have focused on ways to tether or sequester biological signals and engineer these bioactive scaffolds to signal to delivered cells or endogenous cells. While many strategies exist to achieve tethering of peptides, protein, and small molecules, this review focuses on photochemical methods, and their usefulness as a mild reaction that proceeds with fast kinetics in aqueous solutions and at physiological conditions. Photo-click and photo-caging methods are particularly useful because one can direct light to specific regions of the hydrogel to achieve spatial patterning. Recent methods have even demonstrated reversible introduction of biomolecules to mimic the dynamic changes of native ECM, enabling researchers to explore how the spatial and dynamic context of biomolecular signals influences important cell functions. This review will highlight how two photochemical methods have led to important advances in the tissue regeneration community, namely the thiol-ene photo-click reaction for bioconjugation and photocleavage reactions that allow for the removal of protecting groups. Specific examples will be highlighted where these methodologies have been used to engineer hydrogels that control and direct cell function with the aim of inspiring their use in regenerative medicine.

Phototriggered functionalization of hierarchically structured polymer brushes

The precise design of bioactive surfaces, essential for the advancement of many biomedical applications, depends on achieving control of the surface architecture as well as on the ability to attach bioreceptors to antifouling surfaces. Herein, we report a facile avenue toward hierarchically structured antifouling polymer brushes of oligo(ethylene glycol) methacrylates via surface-initiated atom transfer radical polymerization (SI-ATRP) presenting photoactive tetrazole moieties, which permitted their functionalization via nitrile imine-mediated tetrazole-ene cyclocloaddition (NITEC). A maleimide-functional ATRP initiator was photoclicked to the side chains of a brush enabling a subsequent polymerization of carboxybetaine acrylamide to generate a micropatterned graft-on-graft polymer architecture as evidenced by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Furthermore, the spatially resolved biofunctionalization of the tetrazole-presenting brushes was accessed by the photoligation of biotin-maleimide and subsequent binding of streptavidin. The functionalized brushes bearing streptavidin were able to resist the fouling from blood plasma (90% reduction with respect to bare gold). Moreover, they were employed to demonstrate a model biosensor by immobilization of a biotinylated antibody and subsequent capture of an antigen as monitored in real time by surface plasmon resonance.

Renewable, fluorescent, and thermoresponsive: cellulose copolymers via light-induced ligation in solution

We introduce a mild photochemically driven strategy for the synthesis of fluorescent cellulose copolymers in solution using filter paper as the starting material.

Surface modification of intraocular lenses with hyaluronic acid and lysozyme for the prevention of endophthalmitis and posterior capsule opacification

Posterior capsule opacification is one of the complications of cataract surgery caused by the adhesion and reproduction of residual human lens epithelial cells (HLECs) on the posterior capsule.

Interface-controlled calcium phosphate mineralization: effect of oligo(aspartic acid)-rich interfaces

The phase behavior of an amphiphilic block copolymer based on a poly(aspartic acid) hydrophilic block and a poly(n-butyl acrylate) hydrophobic block was investigated at the air–water and air–buffer interface.

A supramolecular two-photon-active hydrogel platform for direct bioconjugation under near-infrared radiation

A novel hydrogel self-assembled from partially methacrylated polyethyleneimine shows photo-activity at near-infrared wavelengths and offers a selective platform for the rapid and direct conjugation of biomolecules by two-photon laser irradiation without additional initiators.

Surface plasmon resonance: advances of label-free approaches in the analysis of biological samples

Surface plasmon resonance sensors have made vast advancements in the sensing technology and the number of applications achievable. New developments in surface plasmon resonance sensors have gained considerable momentum promoted by the urgent needs of fast, reliable and label-free methods for detection and quantification of analytes in molecular biology, medicine and other life sciences. However, even if enormous improvements in the limits of detections have been achieved, this technology still faces important challenges to be translated to clinical practice or in-field measurements. This paper reviews the important recent advances of this technology for the label-free detection in real biological samples and we discussed the key challenges to be overcome to transit from prototypes to commercial biosensors.

Spatial and Temporal Control of Thiol-Michael Addition via Photocaged Superbase in Photopatterning and Two-Stage Polymer Networks Formation

Photochemical processes enable spatial and temporal control of reactions, which can be implemented as an accurate external control approach in both polymer synthesis and materials applications. "Click" reactions have also been employed as efficient tools in the same field. Herein, we combined photochemical processes and thiol-Michael "click" reactions to achieve a "photo-click" reaction that can be used in surface patterning and controlled polymer network formation, owing to the ease of spatial and temporal control through use of photolabile amines as appropriate catalysts.

Grafting hyaluronic acid onto gold surface to achieve low protein fouling in surface plasmon resonance biosensors

Antifouling surfaces capable of reducing nonspecific protein adsorption from natural complex media are highly desirable in surface plasmon resonance (SPR) biosensors. A new protein-resistant surface made through the chemical grafting of easily available hyaluronic acid (HA) onto gold (Au) substrate demonstrates excellent antifouling performance against protein adsorption. AFM images showed the uniform HA layer with a thickness of ∼10.5 nm on the Au surface. The water contact angles of Au surfaces decreased from 103° to 12° with the covalent attachment of a carboxylated HA matrix, indicating its high hydrophilicity mainly resulted from carboxyl and amide groups in the HA chains. Using SPR spectroscopy to investigate nonspecific adsorption from single protein solutions (bovine serum albumin (BSA), lysozyme) and complex media (soybean milk, cow milk, orange juice) to an HA matrix, it was found that ultralow or low protein adsorptions of 0.6-16.1 ng/cm(2) (e.g., soybean milk: 0.6 ng/cm(2)) were achieved on HA-Au surfaces. Moreover, anti-BSA was chosen as a model recognition molecule to characterize the immobilization capacity and the antifouling performance of anti-BSA/HA surfaces. The results showed that anti-BSA/HA sensor surfaces have a high anti-BSA loading of 780 ng/cm(2), together with achieving the ultralow (<3 ng/cm(2) for lysozyme and soybean milk) or low (<17 ng/cm(2) for cow milk and 10% blood serum) protein adsorptions. Additionally, the sensor chips also exhibited a high sensitivity to BSA over a wide range of concentrations from 15 to 700 nM. Our results demonstrate a promising antifouling surface using extremely hydrophilic HA as matrix to resist nonspecific adsorption from complex media in SPR biosensors.

Photo-patterning of non-fouling polymers and biomolecules on paper

Functional cellulose substrates with tetrazole moieties are generated to serve as universal platforms for the spatio-temporal immobilization of synthetic ultra-low fouling polymer brushes and protein species via a nitrile imine-mediated tetrazole-ene cycloaddition (NITEC)-based protocol. Poly(carboxybetaine acrylamide) brushes are grafted from initiators photo-patterned by NITEC utilizing single electron transfer living radical polymerization. Streptavidin is photo-immobilized with remarkable efficiency, opening the possibility to generate new materials for biomedical and biosensing applications.

Exploiting end group functionalization for the design of antifouling bioactive brushes

The Diels–Alder reaction between cyclopentadiene and maleimide is exploited to immobilize proteins on the chain-end of polymer brushes.