Reactive polymer multilayers fabricated by covalent layer-by-layer assembly: 1,4-conjugate addition-based approaches to the design of functional biointerfaces

Reactive Multilayer Coating As Versatile Nanoarchitectonics for Customizing Various Bioinspired Liquid Wettabilities

In last few decades, multilayer coatings have achieved enormous attention owing to their unique ability to tune thickness, topography, and chemical composition for developing various functional materials. Such multilayer coatings were mostly and conventionally derived by following a simple layer-by-layer (LbL) deposition process through the strategic use of electrostatic interactions, hydrogen bonding, host-guest interactions, covalent bonding, etc. In the conventional design of multilayer coatings, the chemical composition and morphology of coatings are modulated during the process of multilayer constructions. In such an approach, the postmodulations of the porous multilayers with different and desired chemistries are challenging to achieve due to the lack of availability of readily and selectively reactive moieties. Recently, the design of readily and selectively reactive multilayer coatings (RMLCs) provided a facile basis for postmodulating the prepared coating with various desired chemistries. In fact, by taking advantage of the inherent ability of co-optimizing the topography and various chemistries in porous RMLCs, different durable bioinspired liquid wettabilities (i.e., superhydrophobicity, underwater superoleophobicity, underwater superoleophilicity, slippery property, etc.) were successfully derived. Such interfaces have enormous potential in various prospective applications. In this review, we intend to give an overview of the evolution of LbL multilayer coatings and their synthetic strategies and discuss the key advantages of porous RMLCs in terms of achieving and controlling wettability properties. Recent attempts toward various applications of such multilayer coatings that are strategically embedded with different desired liquid wettabilities will be emphasized.

Role of chemistry in bio-inspired liquid wettability

Chemistry and topography are the two distinct available tools for customizing different bio-inspired liquid wettability including superhydrophobicity, superamphiphobicity, underwater superoleophobicity, underwater superoleophilicity, and liquid infused slippery property. In nature, various living species possessing super and special liquid wettability inherently comprises of distinctly patterned surface topography decorated with low/high surface energy. Inspired from the topographically diverse natural species, the variation in surface topography has been the dominant approach for constructing bio-inspired antiwetting interfaces. However, recently, the modulation of chemistry has emerged as a facile route for the controlled tailoring of a wide range of bio-inspired liquid wettability. This review article aims to summarize the various reports published over the years that has elaborated the distinctive importance of both chemistry and topography in imparting and modulating various bio-inspired wettability. Moreover, this article outlines some obvious advantages of chemical modulation approach over topographical variation. For example, the strategic use of the chemical approach has allowed the facile, simultaneous, and independent tailoring of both liquid wettability and other relevant physical properties. We have also discussed the design of different antiwetting patterned and stimuli-responsive interfaces following the strategic and precise alteration of chemistry for various prospective applications.

Unconventional and Facile Fabrication of Chemically Reactive Silk Fibroin Sponges for Environmental Remediation

Silk fibroin and silk microfibers, both derived from silk cocoon, have been widely used for prospective biomedical, energy, and environmental applications. However, various complex and catalyst-based approaches have been adopted for chemical modification and integration of different functionalities in silk fibroin-based materials. Here, both tailored water wettability and mechanical property have been associated with silk microfiber reinforced silk fibroin sponges (SMFRSFSs) through the strategic introduction of β-sheets and a facile and catalyst-free chemical reaction at ambient conditions. While the controlled tailoring of β-sheets in the silk fibroin skeletal framework of the sponges allowed us to modulate the compressive modulus, the 1,4-conjugate addition reaction between amine residues of silk (fiber and fibroin) and acrylate groups of a multifunctional cross-linker provided residual chemical reactivity. Further, the chemically "reactive" sponge was postmodified with the selected alkylamines to introduce a wide range of water wettability (from 36 to 161°) without affecting the mechanical property. Thereafter, the silk cocoon-derived and extremely water-repellent sponge was used for environment-friendly cleaning of oil spillages through selective absorption-based and filtration-based oil/water separation at different and severe aqueous conditions. This silk cocoon-derived mechanically tailorable and chemically reactive sponge could also be useful for various biomedical and energy-related applications.

Customizing oil-wettability in air-without affecting extreme water repellency

Lotus leaf inspired superhydrophobic interfaces strongly repel the aqueous phase-but inherently display super-oil-affinity in air. However, superamphiphobic interfaces repel both the aqueous phase and the oil/oily phase strongly, due to their contact angles of above 150°. The fundamental criteria for optimizing such distinct super liquid wettabilities are different. Thus, in the past, distinct synthetic approaches were adopted to achieve these two different types of liquid-repellent interfaces for different prospective and relevant applications. Here, in this communication, a rapid and scalable spray deposition process is introduced for tailoring different oil-wettabilities in air, without perturbing the superhydrophobicity. An appropriate dilution of a reaction mixture of strategically selected two small molecules that readily reacted through the 1,4 conjugate addition reaction provided a facile basis for customizing oil wettability-starting from superoleophilicity to superoleophobicity, keeping intact the super water repellence. The synthesized superhydrophobic and superamphiphobic interfaces remained efficient for sustaining exposures of various practically relevant physical manipulations and abrasions and chemically complex aqueous phases. Furthermore, both the superhydrophobic and superamphiphobic interfaces were successfully extended for comparing the oil/water separation, anti-fouling and self-cleaning performances. Such a simple and common synthetic approach for preparing extremely water repellent interfaces that have differences in oil-wettability in air would be useful for practically relevant outdoor applications.

The synthesis of a chemically reactive and polymeric luminescent gel

In the past, chemically reactive polymeric interfaces have been considered to be of potential interest for developing functional materials for a wide range of practical applications. Furthermore, the rational incorporation of luminescence properties into such chemically reactive interfaces could provide a basis for extending the horizon of their prospective utility. In this report, a simple catalyst-free chemical approach is introduced to develop a chemically reactive and optically active polymeric gel. Branched-polyethyleneimine (BPEI)-derived, inherently luminescent carbon dots (BPEI-CDs) were covalently crosslinked with pentaacrylate (5Acl) through a 1,4-conjugate addition reaction under ambient conditions. The synthesized polymeric gel was milky white under visible light; however, it displayed fluorescence under UV light. Additionally, the residual acrylate groups in the synthesized fluorescent gel allowed its chemical functionality to be tailored through facile, robust 1,4-conjugate addition reactions with primary-amine-containing small molecules under ambient conditions. The chemical reactivity of the luminescent gel was further employed for a proof-of-concept demonstration of portable and parallel 'ON'/'OFF' toxic chemical sensing (namely, the sensing of nitrite ions as a model analyte). First, the chemically reactive luminescent gel derived from BPEI-CDs was covalently post-modified with aniline for the selective synthesis of a diazo compound in the presence of nitrite ions. During this process, the color of the gel under visible light changed from white to yellow and, thus, the colorimetric mode of the sensor was turned 'ON'. In parallel, the luminescence of the gel under UV light was quenched, which was denoted as the 'OFF' mode of the sensor. This parallel and unambiguous 'ON'/'OFF' sensing of a toxic chemical (nitrite ions, with a detection limit of 3 μM) was also achieved even in presence of other relevant interfering ions and at concentrations well below the permissible limit (65 μM) set by the World Health Organization (WHO). Furthermore, this chemically reactive luminescent gel could be of potential interest in a wide range of basic and applied contexts.

How Does Chemistry Influence Liquid Wettability on Liquid-Infused Porous Surface?

Design of Nepenthes pitcher-inspired slippery liquid-infused porous surface (SLIPS) appeared as an important avenue for various potential and practically relevant applications. In general, hydrophobic base layers were infused with selected liquid lubricants for developing chemically inert SLIPS. Here, in this current study, an inherently hydrophilic (soaked beaded water droplet with ∼20° within a couple of minutes), porous and thick (above 200 μm) polymeric coating, loaded with readily chemically reactive acrylate moieties yielded a chemically reactive SLIPS, where residual acrylate groups in the synthesized hydrophilic and porous interface rendered stability to the infused lubricants. The chemically reactive SLIPS is capable of reacting with the solution of primary amine-containing nucleophiles in organic solvent through 1,4-conjugate addition reaction, both in the presence (referred as "in situ" modification) and absence (denoted as pre-modification) of lubricated phase in the porous polymeric coating. Such amine reactive SLIPS was further extended to (1) examining the impact of different chemical modifications on the performance of SLIPS and (2) developing a spatially selective and "in situ" postmodification with primary amine-containing nucleophiles through 1,4-conjugate addition reaction. Moreover, the chemically reactive SLIPS was capable of sustaining various physical abrasions and prolonged (minimum 10 days) exposure to complex and harsh aqueous phases, where infused lubricants protect the residual acrylate groups from harsh aqueous exposures. Such, principle will be certainly useful for spatially selective covalent immobilization of water-insoluble functional molecules/polymers directly from organic solvents, which would be of potential interest for various applied and fundamental contexts.

Covalently Modulated and Transiently Visible Writing: Rational Association of Two Extremes of Water Wettabilities

Anticounterfeiting measures are of ever-increasing importance in society, e.g., for securing the authenticity of and the proof of origin for medical drugs. Here, an arms race of counterfeiters and valid manufacturers is taking place, resulting in the need of hard-to-forget, yet easy-to-read out marks. Anticounterfeiting measures based on micropatterns-while being attractive for their need in not widely available printing methods while still being easily read out with fairly common basic optical equipment-are often limited by being too easy to be destroyed by wear or handling. Here, nature-inspired wettability is rationally exploited for developing an unprecedented anticounterfeiting method, where hidden information can be only identified under direct exposures to an aqueous phase or mist and disappears again on air-drying the interface. A chemically reactive and hierarchically featured dip coating, capable of spatially selective covalent modification with primary amine containing small molecules, is developed for abrasion-tolerant patterning interfaces with two extremes of water wettabilities, i.e., superhydrophilicity and superhydrophobicity. Arbitrary handwriting with glucamine followed by chemical modification with octadecylamine, provided "invisible" text on the synthesized interface. The glucamine-treated region selectively becomes optically transparent and superhydrophilic due to rapid infiltration of the aqueous phase on exposure to liquid water or mist. The remaining interface remains opaque and superhydrophobic due to metastable entrapment of air. The hidden text became transiently and reversibly visible by the naked eye under exposure to liquid water/mist. Furthermore, microchannel-cantilever spotting (μCS) is adopted for demonstrating well-defined chemical patterning on the microscale. These patterns are at the same time highly resistant against wear and scratching because of the bulk functionalization, retaining the wetting properties (and thus pattern readout) even on serious abrasion. Such a simple synthesis of spatially controlled, direct, and covalently modulated wettability could be useful for various applied and fundamental contexts.

Catalyst-Free and Rapid Chemical Approach for in Situ Growth of "Chemically Reactive" and Porous Polymeric Coating

Design of "chemically reactive" coating with a tailored topography is a simple basis for optimizing various physical and chemical parameters, which is essential for achieving different biomimicked liquid wettability. In general, the essential topography and appropriate chemistry in the superhydrophobic coating is optimized following various top-down and bottom-up approaches, where various hydrophilic building blocks are associated using electrostatic interaction, hydrogen bonding, and other weak bonding (e.g., metal-thiol etc.), for both developing the desired hierarchical features and optimizing the appropriate chemistry on top of this featured interface. Such designs are inappropriate to sustain practically relentlessly harsh settings. So, further development for the synthesis of a durable and substrate-independent superhydrophobic coating is essential for various prospective applications in "real-world" scenarios. However, the design of highly abrasion-tolerant and "absolutely" substrate-independent artificial superhydrophobicity following a simple and scalable synthesis procedure is rare in literature. In this current work, a catalyst-free and facile chemical approach is adopted for an in situ and rapid deposition of a "chemically reactive" nanocomplex for decorating a wide range of substrates, including water-soluble, water-sensitive, highly flexible, rigid, and fibrous substrates with a highly tolerant biomimicked superhydrophobicity property. Branched poly(ethylenimine) (BPEI) and dipentaerythritol pentaacrylate (5Acl) mutually react through 1,4-conjugate addition reaction, and a hierarchically featured "chemically reactive" dip-coating is synthesized by the appropriate selection of the alcoholic solvent that is 1-heptanol. Furthermore, the choice of small alkylamines for post-covalent modifications of the "chemically reactive" dip-coating provided superhydrophobicity with a tailored water adhesion. A gradual increase in both roll-off angles, and the contact angle hysteresis (from 5° to 30°) was noted with a decrease in the hydrocarbon tail of selected alkylamines. The synthesized biomimicked interfaces are capable of performing under various practically relevant, severe physical and chemical challenges including bending, creasing, twisting, different physical abrasions (i.e., adhesive tape peeling test, abrasive sand paper test, etc.), high compressive strain, highly acidic and alkaline aqueous phases, artificial sea water, river water, etc. Moreover, this current approach was extended in developing various relevant functional materials, including superhydrophilic/superhydrophobic physical patterns on flexible papers and highly compressible super-oil-absorbent, etc.

Chemically reactive protein nanoparticles for synthesis of a durable and deformable superhydrophobic material

The past few decades have witnessed significant development in the field of artificially biomimicking extremely water repellent interfaces, developed mostly through tedious synthetic processes using synthetic/non-biodegradable polymers and fluorinated derivatives rendering health and environment related hazards. Only a few approaches furnish superhydrophobic materials that can withstand different harsh environments. Here, in this current design, naturally abundant and biodegradable bovine serum albumin (BSA) protein nanoparticles and cotton fibers are rationally selected for environment-friendly green synthesis of a highly sustainable and deformable artificial superhydrophobic material through strategic association of facile and rapid Michael addition reactions between amine and acrylate moieties under ambient conditions without the aid of any catalyst. This protein based nature-inspired interface can endure severe repetitive physical manipulations, abrasions and prolonged (30 days) chemical exposure i.e. extremes of pH, artificial sea water, river water and surfactant contaminated water. This highly durable and compressible superhydrophobic material was successfully exploited for efficient (above 2000 wt%), selective and repetitive removal of contaminating oils from aqueous phases under harsh chemical conditions. Such a durable biomimicking interface derived directly from serum protein following a facile synthetic approach would be useful for developing various other functional materials.

Poly(β-Amino Esters): Synthesis, Formulations, and Their Biomedical Applications

Poly(β-amino ester) (abbreviated as PBAE or PAE) refers to a polymer synthesized from an acrylate and an amine by Michael addition and has properties inherent to tertiary amines and esters, such as pH responsiveness and biodegradability. The versatility of building blocks provides a library of polymers with miscellaneous physicochemical and mechanical properties. When used alone or together with other materials, PBAEs can be fabricated into different formulations in order to fulfill various requirements in drug delivery (for instance, gene, anticancer drugs, and antimicrobials delivery) and natural complex mimicry (nanochaperones). This progress report discusses the recent developments in design, synthesis, formulations, and applications of PBAEs in biomedical fields and provides a perspective view for the future of the PBAEs.

Surface Functionalization of Silicon, HOPG, and Graphite Electrodes: Toward an Artificial Solid Electrolyte Interface

Electrografting of diazonium salts containing a protected alkyne moiety was used for the first functionalization of silicon and highly ordered pyrolytic graphite model surfaces. After deprotection with tetrabutylammonium fluoride, further layers were added by the thiol-yne click chemistry. The composition of each layer was characterized via X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. The same approach was then used to functionalize graphite powder electrodes, which are classically used as negative electrode in lithium-ion batteries. The effect of the coating on the formation of the solid electrolyte layer was investigated electrochemically by cyclovoltammetry and galvanostatic measurements. The modified graphite electrodes showed different reduction peaks in the first cycle, indicating reduced and altered decomposition processes of the components. Most importantly, the electrochemical investigations show a remarkable reduction of irreversible capacity loss of the battery.

Green and Rapid Synthesis of Durable and Super-Oil (under Water) and Water (in Air) Repellent Interfaces

In this letter, a single polymer is rapidly and covalently transformed into a chemically reactive and functional bulk polymeric coatings through a catalyst-free mutual chemical reaction between acrylates and amine groups at ambient condition-in the absence of any external reaction solvent, which is unprecedented in the literature. This facile and green chemical approach provided a common basis for achieving two distinct biomimicked wettabilities-that are superhydrophobicity (lotus-leaf mimicked) in air and superoleophobicity (fish-scale inspired) under water. The essential chemistry that conferred bioinspired wettability was optimized in the hierarchically featured polymeric material by postcovalent modulation of chemically reactive polymeric material with primary-amine-containing small moleculess, glucamine and octadecylamine. The inherently sticky and "chemically reactive" polymeric material having appropriate hierarchical topography is highly capable of providing substrate-independent (irrespective of chemical compositions and mechanical strength of the substrates) stable coatings with robust bioinspired (i.e., lotus leaf and fish scale) wettability.

Covalent layer-by-layer films: chemistry, design, and multidisciplinary applications

Covalent layer-by-layer (LbL) assembly is a powerful method used to construct functional ultrathin films that enables nanoscopic structural precision, componential diversity, and flexible design. Compared with conventional LbL films built using multiple noncovalent interactions, LbL films prepared using covalent crosslinking offer the following distinctive characteristics: (i) enhanced film endurance or rigidity; (ii) improved componential diversity when uncharged species or small molecules are stably built into the films by forming covalent bonds; and (iii) increased structural diversity when covalent crosslinking is employed in componential, spacial, or temporal (labile bonds) selective manners. In this review, we document the chemical methods used to build covalent LbL films as well as the film properties and applications achievable using various film design strategies. We expect to translate the achievement in the discipline of chemistry (film-building methods) into readily available techniques for materials engineers and thus provide diverse functional material design protocols to address the energy, biomedical, and environmental challenges faced by the entire scientific community.

Simultaneous and controlled release of two different bioactive small molecules from nature inspired single material

Simultaneous and extended (over 6 months) release of two different bioactive small molecules from single polymeric material was successfully achieved through strategic use of metastable trapped air for the first time.

Strategic Formulation of Graphene Oxide Sheets for Flexible Monoliths and Robust Polymeric Coatings Embedded with Durable Bioinspired Wettability †

Artificial bioinspired superhydrophobicity, which is generally developed through appropriate optimization of chemistry and hierarchical topography, is being recognized for its immense prospective applications related to environment and healthcare. Nevertheless, the weak interfacial interactions that are associated with the fabrication of such special interfaces often provide delicate biomimicked wettability, and the embedded antifouling property collapses on exposure to harsh and complex aqueous phases and also after regular physical deformations, including bending, creasing, etc. Eventually, such materials with potential antifouling property became less relevant for practical applications. Here, a facile, catalyst-free, and robust 1,4-conjugate addition reaction has been strategically exploited for appropriate covalent integration of modified graphene oxide to developing polymeric materials with (1) tunable mechanical properties and (2) durable antifouling property, which are capable of performing both in air and under oil. Furthermore, this approach provided a facile basis for (3) engineering a superhydrophobic monolith into arbitrary free-standing shapes and (4) decorating various flexible (metal, synthetic plastic, etc.) and rigid (glass, wood, etc.) substrates with thick and durable three-dimensional superhydrophobic coatings. The synthesized superhydrophobic monoliths and polymeric coatings with controlled mechanical properties are appropriate to withstand different physical insults, including twisting, creasing, and even physical erosion of the material, without compromising the embedded antiwetting property. The materials are also equally resistant to various harsh chemical environments, and the embedded antifouling property remained unperturbed even after continuous exposure to extremes of pH (pH 1 and pH 11), artificial sea water for a minimum of 30 days. These flexible and formable free-standing monoliths and stable polymeric coatings that are extremely water-repellent both in air and under oil, are of utmost importance owing to their suitability in practical circumstances and robust nature.

'Reactive' nano-complex coated medical cotton: a facile avenue for tailored release of small molecules

Controlled and sustained release of drug-like small molecules in an aqueous medium still remains a challenging problem due to rapid infiltration of liquid water in most reported drug release systems. However, internal-superhydrophobicity with an antifouling property extending beyond the surface of a material recently has been recognized as a potential avenue for sustained and extended release of drug-like small molecules. Sluggish removal of metastable trapped air in a superhyrophobic material provides a basis to achieve extended release of encapsulated small molecules. In this article, naturally abundant medical-cotton-extensively used in wound management including control of bleeding, absorbance of secretions and protecting wounds from contamination-is strategically exploited in tailoring (from rapid to extended) the release of small molecules by appropriate modulation of liquid water wettability. Modulation included bio-mimicked adhesive and non-adhesive superhydrophobicity of the medical cotton without erosion of any polymeric material. In this process, amine 'reactive' nano-complexes (RNC) were prepared by just mixing branched poly(ethylenimine) (BPEI) with dipentaerythritol pentaacrylate (5Acl) in ethanol with appropriate compositions. Then they were covalently immobilized on fibrous medical-cotton through a facile and robust 1,4-conjugated addition reaction. Residual acrylate moieties in the immobilized RNC provide an opportunity to tailor water wettability through strategic and appropriate post-chemical modification of RNC-coated medical cotton with a primary amine containing various small molecules. This medical-cotton with tunable wettability was exploited further to control the release rate of small molecules from rapid (<24 h) to sustained (>100 days) times. A volatile solvent induced transient and reversible switching of anti-fouling properties which allowed further varying the amount of post-loading small molecules into the medical cotton up to 2.36 wt% without compromising the embedded anti-wetting property. Thus, our current approach has immense potential to develop appropriate materials for a sustained and controlled release of small molecules from a clinically relevant substrate (i.e., medical-cotton) and may be useful in various bio-medical applications including improving wound management, preventing bacterial infections, better pain management, etc.

A general and facile chemical avenue for the controlled and extreme regulation of water wettability in air and oil wettability under water

The controlled modulation of both oil (under water) and water (in air) wettability is an emerging approach to develop several functional materials for various prospective applications including oil/water separation, anti-corrosive coatings, underwater robotics, protein crystallization, drug delivery, open microfluidics, water harvesting etc. Here, we report a 'reactive' and covalently cross-linked coating through a facile and robust Michael addition reaction, which is suitable for the controlled and extreme regulation of both water and oil wettability in air and under water respectively. Along with extremes (super-philicity and super-phobicity) of water (in air) and oil (under water) wettability, this single multilayer construction was also able to display special liquid wettability (i.e.; extremely liquid repellent-but with controlled adhesive properties) both in air and under water, after strategic post chemical modifications, again through 1,4-conjugate addition reaction. The super-wetting properties in the materials were able to withstand various physical and chemical insults including adhesive tape test, sand drop test, and exposure to extremes of pH, salt, and surfactant contaminated aqueous media. Moreover, this approach also allowed the decoration of various flexible and rigid substrates (i.e.; wood, Al-foil, synthetic fabric etc.) with various bio-inspired wettability properties including (1) non-adhesive superhydrophobicity (lotus leaf), (2) adhesive superhydrophobicity (rose petal), (3) underwater superoleophobicity (fish scale) etc. This single polymeric coating-which is capable of displaying several bio-inspired interfaces both in air and under water, even after harsh physical/chemical insults-would be useful in various prospective and relevant applications for practical scenarios.

Synthesis of 'reactive' and covalent polymeric multilayer coatings with durable superoleophobic and superoleophilic properties under water

Bioinspired underwater super-oil-wettability (superoleophilic/superoleophobic) properties are emerging as a potential avenue for developing smart materials for addressing issues related to healthcare, environment, energy, etc. However, the inherent poor durability of the materials that are mostly developed using polymeric hydrogel, metal oxide coatings and electrostatic multilayers often challenges the application of these wettability properties in practical scenarios. Here, 'amine-reactive' polymeric multilayers of nano-complex were developed to fabricate 'internal' underwater superoleophobic/superoleophilic coatings with impeccable physical/chemical durability. This allows the super-wetting properties to exist beyond the surface of the material and remain intact even after severe physical damage including erosion of the material and continuous exposure to an artificial-marine environment for more than 80 days. Moreover, this current design allowed for independent revalidation of some key hypotheses with direct experimental demonstrations, and provided a basis to develop highly durable super-oil-wettability properties under water. It is believed that this contemporary study will make a worthwhile contribution on developing multifunctional materials for widespread practical applications by exploiting these super-oil-wetting properties.

Layer-by-Layer Assembly of Amine-Reactive Multilayers Using an Azlactone-Functionalized Polymer and Small-Molecule Diamine Linkers

We report the reactive layer-by-layer assembly of amine-reactive polymer multilayers using an azlactone-functionalized polymer and small-molecule diamine linkers. This approach yields cross-linked polymer/linker-type films that can be further functionalized, after fabrication, by treatment with functional primary amines, and provides opportunities to incorporate other useful functionality that can be difficult to introduce using other polyamine building blocks. Films fabricated using poly(2-vinyl-4,4-dimethylazlactone) (PVDMA) and three model nondegradable aliphatic diamine linkers yielded reactive thin films that were stable upon incubation in physiologically relevant media. By contrast, films fabricated using PVDMA and varying amounts of the model disulfide-containing diamine linker cystamine were stable in normal physiological media, but were unstable and eroded rapidly upon exposure to chemical reducing agents. We demonstrate that this approach can be used to fabricate functionalized polymer microcapsules that degrade in reducing environments, and that rates of erosion, extents of capsule swelling, and capsule degradation can be tuned by control over the relative concentration of cystamine linker used during fabrication. The polymer/linker approach used here expands the range of properties and functions that can be designed into reactive PVDMA-based coatings, including functionality that can degrade, erode, and undergo triggered destruction in aqueous environments. We therefore anticipate that these approaches will be useful for the functionalization, patterning, and customization of coatings, membranes, capsules, and interfaces of potential utility in biotechnical or biomedical contexts and other areas where degradation and transience are desired. The proof of concept strategies reported here are likely to be general, and should prove useful for the design of amine-reactive coatings containing other functional structures by judicious control of the structures of the linkers used during assembly.

Intrinsic immunogenicity of rapidly-degradable polymers evolves during degradation

Recent studies reveal many biomaterial vaccine carriers are able to activate immunostimulatory pathways, even in the absence of other immune signals. How the changing properties of polymers during biodegradation impact this intrinsic immunogenicity is not well studied, yet this information could contribute to rational design of degradable vaccine carriers that help direct immune response. We use degradable poly(beta-amino esters) (PBAEs) to explore intrinsic immunogenicity as a function of the degree of polymer degradation and polymer form (e.g., soluble, particles). PBAE particles condensed by electrostatic interaction to mimic a common vaccine approach strongly activate dendritic cells, drive antigen presentation, and enhance T cell proliferation in the presence of antigen. Polymer molecular weight strongly influences these effects, with maximum stimulation at short degradation times--corresponding to high molecular weight--and waning levels as degradation continues. In contrast, free polymer is immunologically inert. In mice, PBAE particles increase the numbers and activation state of cells in lymph nodes. Mechanistic studies reveal that this evolving immunogenicity occurs as the physicochemical properties and concentration of particles change during polymer degradation. This work confirms the immunological profile of degradable, synthetic polymers can evolve over time and creates an opportunity to leverage this feature in new vaccines.

STATEMENT OF SIGNIFICANCE

Degradable polymers are increasingly important in vaccination, but how the inherent immunogenicity of polymers changes during degradation is poorly understood. Using common rapidly-degradable vaccine carriers, we show that the activation of immune cells--even in the absence of other adjuvants--depends on polymer form (e.g., free, particulate) and the extent of degradation. These changing characteristics alter the physicochemical properties (e.g., charge, size, molecular weight) of polymer particles, driving changes in immunogenicity. Our results are important as many common biomaterials (e.g., PLGA) are now known to exhibit immune activity that alters how vaccines are processed. Thus, the results of this study could contribute to more rational design of biomaterial carriers that also actively direct the properties of responses generated by vaccines.

Tunable hydrogel thin films from reactive synthetic polymers as potential two-dimensional cell scaffolds

This article describes the formation of cross-linked 10-200-nm-thick polymer hydrogel films by alternating the spin-coating of two mutually reactive polymers from organic solutions, followed by hydrolysis of the resulting multilayer film in aqueous buffer. Poly(methyl vinyl ether-alt-maleic anhydride) (PMM) was deposited from acetonitrile solution, and poly(N-3-aminopropylmethacrylamide-co-N-2-hydroxypropylmethacrylamide) (PAPMx, where x corresponds to the 3-aminopropylmethacrylamide content ranging from 10 to 100%) was deposited from methanol. Multilayer films were formed in up to 20 deposition cycles. The films cross-linked during formation by reaction between the amine groups of PAPMx and the anhydride groups of PMM. The resulting multilayer films were covalently postfunctionalized by exposure to fluoresceinamine, decylamine, d-glucamine, or fluorescently labeled PAPMx solutions prior to the hydrolysis of residual anhydride in aqueous PBS buffer. This allowed tuning the hydrophobicity of the film to give static water contact angles ranging from about 5 to 90°. Increasing the APM content in PAPMx from 10 to 100% led to apparent Young's moduli from 300 to 700 kPa while retaining sufficient anhydride groups to allow postfunctionalization of the films. This allowed the resulting (PMM/PAPMx) multilayer films to be turned into adhesion-promoting or antifouling surfaces for C2C12 mouse myoblasts and MCF 10A premalignant human mammary epithelial cells.

Covalently layer-by-layer assembled homogeneous nanolayers with switchable wettability

A layer-by-layer growth through alternating chemisorption of isocyanate functional star-shaped polyethers (NCO-sP(EO-stat-PO)) and a linear polymer ((PVFA-co-PVAm)) is described.

Sorption and release of drugs in/from cross-linked poly(ethyleneimine) multilayer films deposited onto silica microparticles

Multilayer thin films are useful materials in fabrication of controlled drug delivery systems and in controlling drug release processes. Herein, we report the fabrication of single polycation multilayers based on branched poly(ethylene imine) (PEI) mediated by dianhydrides (DA), as cross-linker and source of carboxylic groups, deposited onto Daisogel silica microparticles, and their sorption/release properties for some anionic drugs as a function of the cross-linker concentration. Pyromellitic dianhydride (PM) and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTCDA) were used as DA reagents. The monotonous increase of the (PEI-DA)n multilayers was demonstrated by Fourier transform infrared spectroscopy, point of zero charge (pzc), and X-ray photoelectron spectroscopy. The sorption properties of the PEI multilayer films for two drugs (diclofenac sodium, DS, and indomethacin, IDM) and a model dye (Ponceau SS, PSS) were influenced by the number of PEI layers and the weight ratio between cross-linker and silica microparticles during the cross-linking steps. It was found that the adsorbed amount of drugs increased with the number of PEI layers and with the decrease of DA concentration. The Langmuir, Sips, and Dubinin-Radushkevich model isotherms were applied to fit the sorption equilibrium data of IDM onto the Daisogel//(PEI-DA)n composites. The maximum equilibrium sorption capacity, qm, evaluated by the Langmuir model, at 25 °C, was 37.05 mg IDM/g of Daisogel//(PEI-BTCDA)8.5, and 39.99 mg IDM/g of Daisogel//(PEI-PM)8.5, for a weight percentage of DA/silica of 0.1% w/w. Cumulative release of DS was almost 100% within 180 min, while IDM was desorbed at a level of 35%, in 320 min, supporting a sustained release was gained with the cross-linked PEI films. The stability of the (PEI-DA)n multilayers during the successive sorption/desorption cycles of PSS was demonstrated.

Surface grafted chitosan gels. Part II. Gel formation and characterization

Responsive biomaterial hydrogels attract significant attention due to their biocompatibility and degradability. In order to make chitosan based gels, we first graft one layer of chitosan to silica, and then build a chitosan/poly(acrylic acid) multilayer using the layer-by-layer approach. After cross-linking the chitosan present in the polyelectrolyte multilayer, poly(acrylic acid) is partly removed by exposing the multilayer structure to a concentrated carbonate buffer solution at a high pH, leaving a surface-grafted cross-linked gel. Chemical cross-linking enhances the gel stability against detachment and decomposition. The chemical reaction between gluteraldehyde, the cross-linking agent, and chitosan was followed in situ using total internal reflection Raman (TIRR) spectroscopy, which provided a molecular insight into the complex reaction mechanism, as well as the means to quantify the cross-linking density. The amount of poly(acrylic acid) trapped inside the surface grafted films was found to decrease with decreasing cross-linking density, as confirmed in situ using TIRR, and ex situ by Fourier transform infrared (FTIR) measurements on dried films. The responsiveness of the chitosan-based gels with respect to pH changes was probed by quartz crystal microbalance with dissipation (QCM-D) and TIRR. Highly cross-linked gels show a small and fully reversible behavior when the solution pH is switched between pH 2.7 and 5.7. In contrast, low cross-linked gels are more responsive to pH changes, but the response is fully reversible only after the first exposure to the acidic solution, once an internal restructuring of the gel has taken place. Two distinct pKa's for both chitosan and poly(acrylic acid), were determined for the cross-linked structure using TIRR. They are associated with populations of chargeable groups displaying either a bulk like dissociation behavior or forming ionic complexes inside the hydrogel film.