Polymer Interfaces: Synthetic Strategies Enabling Functionality, Adaptivity, and Spatial Control

Advancing Glucose Sensing Through Auto-Fluorescent Polymer Brushes: From Surface Design to Nano-Arrays

Designing smart (bio)interfaces with the capability to sense and react to changes in local environments offers intriguing possibilities for new surface-based sensing devices and technologies. Polymer brushes make ideal materials to design such adaptive and responsive interfaces given their large variety of functional and structural possibilities as well as their outstanding abilities to respond to physical, chemical, and biological stimuli. Herein, a practical sensory interface for glucose detection based on auto-fluorescent polymer brushes decorated with phenylboronic acid (PBA) receptors is presented. The glucose-responsive luminescent surfaces, which are capable of translating conformational transitions triggered by pH variations and binding events into fluorescent readouts without the need for fluorescent dyes, are grown from both nanopatterned and non-patterned substrates. Two-photon laser scanning confocal microscopy and atomic force microscopy (AFM) analyses reveal the relationship between the brush conformation and glucose concentration and confirm that the phenylboronic acid functionalized brushes can bind glucose over a range of physiologically relevant concentrations in a reversible manner. The combination of auto-fluorescent polymer brushes with synthetic receptors presents a promising avenue for designing innovative and robust sensing systems, which are essential for various biomedical applications, among other uses.

New Light in Polymer Science: Photoinduced Reversible Addition-Fragmentation Chain Transfer Polymerization (PET-RAFT) as Innovative Strategy for the Synthesis of Advanced Materials

Photochemistry has attracted great interest in the last decades in the field of polymer and material science for the synthesis of innovative materials. The merging of photochemistry and reversible-deactivation radical polymerizations (RDRP) provides good reaction control and can simplify elaborate reaction protocols. These advantages open the doors to multidisciplinary fields going from composite materials to bio-applications. Photoinduced Electron/Energy Transfer Reversible Addition-Fragmentation Chain-Transfer (PET-RAFT) polymerization, proposed for the first time in 2014, presents significant advantages compared to other photochemical techniques in terms of applicability, cost, and sustainability. This review has the aim of providing to the readers the basic knowledge of PET-RAFT polymerization and explores the new possibilities that this innovative technique offers in terms of industrial applications, new materials production, and green conditions.

Adaptable and Reprogrammable Surfaces

Establishing control over chemical reactions on interfaces is a key challenge in contemporary surface and materials science, in particular when introducing well-defined functionalities in a reversible fashion. Reprogrammable, adaptable and functional interfaces require sophisticated chemistries to precisely equip them with specific functionalities having tailored properties. In the last decade, reversible chemistries-both covalent and noncovalent-have paved the way to precision functionalize 2 or 3D structures that provide both spatial and temporal control. A critical literature assessment reveals that methodologies for writing and erasing substrates exist, yet are still far from reaching their full potential. It is thus critical to assess the current status and to identify avenues to overcome the existing limitations. Herein, the current state-of-the-art in the field of reversible chemistry on surfaces is surveyed, while concomitantly identifying the challenges-not only synthetic but also in current surface characterization methods. The potential within reversible chemistry on surfaces to function as true writeable memories devices is identified, and the latest developments in readout technologies are discussed. Finally, we explore how spatial and temporal control over reversible, light-induced chemistries has the potential to drive the future of functional interface design, especially when combined with powerful laser lithographic applications.

Seeing the Light: Advancing Materials Chemistry through Photopolymerization

The application of photochemistry to polymer and material science has led to the development of complex yet efficient systems for polymerization, polymer post-functionalization, and advanced materials production. Using light to activate chemical reaction pathways in these systems not only leads to exquisite control over reaction dynamics, but also allows complex synthetic protocols to be easily achieved. Compared to polymerization systems mediated by thermal, chemical, or electrochemical means, photoinduced polymerization systems can potentially offer more versatile methods for macromolecular synthesis. We highlight the utility of light as an energy source for mediating photopolymerization, and present some promising examples of systems which are advancing materials production through their exploitation of photochemistry.

Enabling the synthesis of homogeneous or Janus hairy nanoparticles through surface photoactivation

Nanoparticles (NPs) homogeneously covered with polymer chains or with chains of two different polymers segregated in distinct domains ("Janus" particles) possess remarkable features. Their unique colloidal properties can be finely tuned by the grafted polymers while the characteristics of the nano-core remain unaffected. Herein, a simple and robust photochemical approach is reported to synthesize, from 50 nm cores, homogeneous and Janus "hairy" nanoparticles with hydrophilic and amphiphilic properties, respectively. This is achieved by using a surface-anchored bis(acyl)phosphane oxide photoinitiator which allows a spatially controlled surface-initiated photopolymerization at room temperature. Homogeneous and Janus hairy nanoparticles dispersed in water have very different interaction behaviours which are directly visualized by in situ liquid cell transmission electron microscopy and confirmed by small angle X-ray scattering from a statistically relevant number of particles.

Stability of Diels–Alder photoadducts in macromolecules

The study investigates the thermal stability of ligation points resulting from photochemically induced Diels–Alder reactions within soft matter materials on the molecular level.

Precise syntheses of structurally possible all tetrablock quaterpolymers by a methodology combining living anionic polymerization with linking chemistry using 1 : 1 addition reaction

A methodology combining living anionic polymerization with linking chemistry using 1 : 1 addition reaction has been developed for the syntheses of tetrablock quaterpolymers composed of A, B, C, and D blocks.

Micellization of Photo-Responsive Block Copolymers

This review focuses on block copolymers featuring different photo-responsive building blocks and self-assembly of such materials in different selective solvents. We have subdivided the specific examples we selected: (1) according to the wavelength at which the irradiation has to be carried out to achieve photo-response; and (2) according to whether irradiation with light of a suitable wavelength leads to reversible or irreversible changes in material properties (e.g., solubility, charge, or polarity). Exemplarily, an irreversible change could be the photo-cleavage of a nitrobenzyl, pyrenyl or coumarinyl ester, whereas the photo-mediated transition between spiropyran and merocyanin form as well as the isomerization of azobenzenes would represent reversible response to light. The examples presented cover applications including drug delivery (controllable release rates), controlled aggregation/disaggregation, sensing, and the preparation of photochromic hybrid materials.

Self-Assembly of Double Hydrophilic Poly(2-ethyl-2-oxazoline)-b-poly(N-vinylpyrrolidone) Block Copolymers in Aqueous Solution

The self-assembly of a novel combination of hydrophilic blocks in water is presented, namely poly(2-ethyl-2-oxazoline)-b-poly(N-vinylpyrrolidone) (PEtOx-b-PVP). The completely water-soluble double hydrophilic block copolymer (DHBC) is formed via copper-catalyzed polymer conjugation, whereas the molecular weight of the PVP is varied in order to study the effect of block ratio on the self-assembly process. Studies via dynamic light scattering, static light scattering as well as microscopy techniques, e.g., cryo scanning electron microscopy or laser scanning confocal microscopy, show the formation of spherical particles in an aqueous solution with sizes between 300 and 400 nm. Particles of the DHBCs are formed without the influence of external stimuli. Moreover, the efficiency of self-assembly formation relies significantly on the molar ratio of the utilized blocks. The nature of the formed structures relies further on the concentration, and indications of particular and vesicular structures are found.

Photochemically Driven Polymeric Network Formation: Synthesis and Applications

Polymeric networks have been intensely investigated and a large number of applications have been found in areas ranging from biomedicine to materials science. Network fabrication via light-induced reactions is a particularly powerful tool, since light provides ready access to temporal and spatial control, opening an array of synthetic access routes for structuring the network geometry as well as functionality. Herein, the most recent light-induced modular reactions and their use in the formation of precision polymeric networks are collated. The synthetic strategies including photoinduced thiol-based reactions, Diels-Alder systems, and photogenerated reactive dipoles, as well as photodimerizations, are discussed in detail. Importantly, applications of the fabricated networks via the aforementioned reactions are highlighted with selected examples. Concomitantly, we provide future directions for the field, emphasizing the most critically required advances.

Controlled and tunable design of polymer interface for immobilization of enzymes: does curvature matter?

Control and tuning of surface properties is indispensable for the programmed and rational design of materials. Particularly, polymeric brush-modified colloids can be used as carrier materials for enzyme immobilization. Although it is of prime importance to control the brush architecture, there is still a lack of systematic investigations concerning the impact of grafting density on the properties of the designed interface, as well as on the immobilization of biomolecules. In this work, we investigate the surface properties of polymer brushes with different grafting densities prepared using a "grafting from" approach on flat and on colloidal particle substrates by varying the density of initiator groups. In this way, we control and tune interfacial properties of the carrier material such as swelling, charge, adhesion as well as adsorption of laccase from Trametes versicolor on the grafted polyelectrolyte layer. We show that there is no direct transferability of the results received from planar to curved substrates regarding the swelling behavior in dependence on the grafting density. The maximum of swelling degree of PDMAEMA layers is achieved at 0.34 nm^-2 and at 0.1 nm^-2 grafting density for planar and curved particle substrates, respectively. The adhesion properties of the polymeric layer on both substrates are also strongly influenced by the grafting density, i.e. a decrease of the grafting density causes a transition from the adhesive to non-adhesive state. As proven by the cryo-TEM and AFM force distance measurements, an immobilization of laccase from Trametes versicolor causes a decrease of the polymer swelling and therefore leads to the changes in the surface morphology, charge and adhesion performance of final polymer-enzyme layer. Moreover, the higher effectiveness and activity of laccase were observed for the intermediate grafting densities which seem to be preferable over the maximum brush densities.

RAFT polymerization to form stimuli-responsive polymers

Stimuli-responsive polymers respond to a variety of external stimuli, which include optical, electrical, thermal, mechanical, redox, pH, chemical, environmental and biological signals. This paper is concerned with the process of forming such polymers by RAFT polymerization.

Coding and decoding libraries of sequence-defined functional copolymers synthesized via photoligation

Designing artificial macromolecules with absolute sequence order represents a considerable challenge. Here we report an advanced light-induced avenue to monodisperse sequence-defined functional linear macromolecules up to decamers via a unique photochemical approach. The versatility of the synthetic strategy-combining sequential and modular concepts-enables the synthesis of perfect macromolecules varying in chemical constitution and topology. Specific functions are placed at arbitrary positions along the chain via the successive addition of monomer units and blocks, leading to a library of functional homopolymers, alternating copolymers and block copolymers. The in-depth characterization of each sequence-defined chain confirms the precision nature of the macromolecules. Decoding of the functional information contained in the molecular structure is achieved via tandem mass spectrometry without recourse to their synthetic history, showing that the sequence information can be read. We submit that the presented photochemical strategy is a viable and advanced concept for coding individual monomer units along a macromolecular chain.