Soft poly(n -butyl acrylate) networks with tailored mechanical properties designed as substrates for in vitro models

Elastic and Self-Healing Copolymer Coatings with Antimicrobial Function

The revolutionary self-healing function for long-term and safe service processes has inspired researchers to implement them in various fields, including in the application of antimicrobial protective coatings. Despite the great advances that have been made in the field of fabricating self-healing and antimicrobial polymers, their poor transparency and the trade-off between the mechanical and self-healing properties limit the utility of the materials as transparent antimicrobial protective coatings for wearable optical and display devices. Considering the compatibility in the blending process, our group proposed a self-healing, self-cross-linkable poly{(n-butyl acrylate)-co-[N-(hydroxymethyl)acrylamide]} copolymer (AP)-based protective coating combined with two types of commercial cationic antimicrobial agents (i.e., dimethyl octadecyl (3-trimethoxysilylpropyl) ammonium chloride (DTSACL) and chlorhexidine gluconate (CHG)), leading to the fabrication of a multifunctional modified compound film of (AP/b%CHG)-grafted-a%DTSACL. The first highlight of this research is that the reactivity of the hydroxyl group in the N-(hydroxymethyl)acrylamide of the copolymer side chains under thermal conditions facilitates the "grafting to" process with the trimethoxysilane groups of DTSACL to form AP-grafted-DTSACL, yielding favorable thermal stability, improvement in hydrophobicity, and enhancement of mechanical strength. Second, we highlight that the addition of CHG can generate covalent and noncovalent interactions in a complex manner between the two biguanide groups of CHG with the AP and DTSACL via a thermal-triggered cross-linking reaction. The noncovalent interactions synergistically serve as diverse dynamic hydrogen bonds, leading to complete healing upon scratches and even showing over 80% self-healing efficiency on full-cut, while covalent bonding can effectively improve elasticity and mechanical strength. The soft nature of CHG also takes part in improving the self-healing of the copolymer. Moreover, it was discovered that the addition of CHG can enhance antimicrobial effectiveness, as demonstrated by the long-term superior antibacterial activity (100%) against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria and the antifouling function on a glass substrate and/or a silica wafer coated by the modified polymer.

A reversible water-based electrostatic adhesive

Commercial adhesives typically fall into two categories: structural or pressure sensitive. Structural glues rely on covalent bonds formed during curing and provide high tensile strength whilst pressure-sensitive adhesives use physical bonding to provide weaker adhesion, but with considerable convenience for the user. Here, a new class of adhesive is presented that is also reversible, with a bond strength intermediate between those of pressure-sensitive and structural adhesives. Complementary water-based formulations incorporating oppositely charged polyelectrolytes form electrostatic bonds that may be reversed through immersion in a low or high pH aqueous environment. This electrostatic adhesive has the advantageous property that it exhibits good adhesion to low-energy surfaces such as polypropylene. Furthermore, it is produced by the emulsion copolymerization of commodity materials, styrene and butyl acrylate, which makes it inexpensive and opens the possibility of industrial production. Bio-based materials have been also integrated into the formulations to further increase sustainability. Moreover, unlike other water-based glues, adhesion does not significantly degrade in humid environments. Because such electrostatic adhesives do not require mechanical detachment, they are appropriate for the large-scale recycling of, e.g., bottle labels or food packaging. The adhesive is also suitable for dismantling components in areas as varied as automotive parts and electronics.

Synthesis of Poly(methacrylic acid-co-butyl acrylate) Grafted onto Functionalized Carbon Nanotube Nanocomposites for Drug Delivery

Design of a smart drug delivery system is a topic of current interest. Under this perspective, polymer nanocomposites (PNs) of butyl acrylate (BA), methacrylic acid (MAA), and functionalized carbon nanotubes (CNTs_f) were synthesized by in situ emulsion polymerization (IEP). Carbon nanotubes were synthesized by chemical vapor deposition (CVD) and purified with steam. Purified CNTs were analyzed by FE-SEM and HR-TEM. CNTs_f contain acyl chloride groups attached to their surface. Purified and functionalized CNTs were studied by FT-IR and Raman spectroscopies. The synthesized nanocomposites were studied by XPS, ¹³C-NMR, and DSC. Anhydride groups link CNTs_f to MAA-BA polymeric chains. The potentiality of the prepared nanocomposites, and of their pure polymer matrices to deliver hydrocortisone, was evaluated in vitro by UV-VIS spectroscopy. The relationship between the chemical structure of the synthesized nanocomposites, or their pure polymeric matrices, and their ability to release hydrocortisone was studied by FT-IR spectroscopy. The hydrocortisone release profile of some of the studied nanocomposites is driven by a change in the inter-associated to self-associated hydrogen bonds balance. The CNTs_f used to prepare the studied nanocomposites act as hydrocortisone reservoirs.

Fabrication of bicontinuous double networks as thermal and pH stimuli responsive drug carriers for on-demand release

The fabrication, via a two steps approach, of a novel bicontinuous Double Network (BCDN) material is reported. We first use a bicontinuous emulsion as template to obtain a poly(butyl acrylate) (PBA) and poly(acrylic acid) (PAA) bicontinuous amphiphilic material. The material is then swollen with the precursor of a second hydrophilic polymer (PNIPAM, poly(N-isopropylacrylamide)). After polymerization of these precursors, the two responsive polymers, PNIPAM and PAA, form a double-network within a bicontinuous templated material, i.e. a bicontinuous double network (BCDN) material. The advantages of using such unique and complex double network architecture are manifold. PBA increases the mechanical properties of the hydrogel all together with the hydrophilic double network that also decouples the pH and temperature responsiveness. Among different possible applications, we tested this responsive hydrogels for its biomedical application. It can be used as pH and temperature sensitive devices for on-demand drug delivery. In addition, the release of a drug confined in the amphiphilic bicontinuous structure follows different kinetics profiles, depending on pH and temperature. This last result indicates that it is possible to control and regulate the release of an encapsulated drug according to the fluctuations of physiological conditions.

Modulating human mesenchymal stem cells using poly(n-butyl acrylate) networks in vitro with elasticity matching human arteries

Non-swelling hydrophobic poly(n-butyl acrylate) network (cPnBA) is a candidate material for synthetic vascular grafts owing to its low toxicity and tailorable mechanical properties. Mesenchymal stem cells (MSCs) are an attractive cell type for accelerating endothelialization because of their superior anti-thrombosis and immune modulatory function. Further, they can differentiate into smooth muscle cells or endothelial-like cells and secret pro-angiogenic factors such as vascular endothelial growth factor (VEGF). MSCs are sensitive to the substrate mechanical properties, with the alteration of their major cellular behavior and functions as a response to substrate elasticity. Here, we cultured human adipose-derived mesenchymal stem cells (hADSCs) on cPnBAs with different mechanical properties (cPnBA250, Young's modulus (E) = 250 kPa; cPnBA1100, E = 1100 kPa) matching the elasticity of native arteries, and investigated their cellular response to the materials including cell attachment, proliferation, viability, apoptosis, senescence and secretion. The cPnBA allowed high cell attachment and showed negligible cytotoxicity. F-actin assembly of hADSCs decreased on cPnBA films compared to classical tissue culture plate. The difference of cPnBA elasticity did not show dramatic effects on cell attachment, morphology, cytoskeleton assembly, apoptosis and senescence. Cells on cPnBA250, with lower proliferation rate, had significantly higher VEGF secretion activity. These results demonstrated that tuning polymer elasticity to regulate human stem cells might be a potential strategy for constructing stem cell-based artificial blood vessels.

Temperature-Controlled Orientation of Proteins on Temperature-Responsive Grafted Polymer Brushes: Poly(butyl methacrylate) vs Poly(butyl acrylate): Morphology, Wetting, and Protein Adsorption

Poly( n-butyl methacrylate) (PBMA) or poly( n-butyl acrylate) (PBA)-grafted brush coatings attached to glass were successfully prepared using atom-transfer radical polymerization "from the surface". The thicknesses and composition of the PBMA and PBA coatings were examined using ellipsometry and time-of-flight secondary ion mass spectrometry (ToF-SIMS), respectively. For PBMA, the glass-transition temperature constitutes a range close to the physiological limit, which is in contrast to PBA, where the glass-transition temperature is around -55 °C. Atomic force microscopy studies at different temperatures suggest a strong morphological transformation for PBMA coatings, in contrast to PBA, where such essential changes in the surface morphology are absent. Besides, for PBMA coatings, protein adsorption depicts a strong temperature dependence. The combination of bovine serum albumin and anti-IgG structure analysis with the principal component analysis of ToF-SIMS spectra revealed a different orientation of proteins adsorbed to PBMA coatings at different temperatures. In addition, the biological activity of anti-IgG molecules adsorbed at different temperatures was evaluated through tracing the specific binding with goat IgG.

Influence of different surface treatments of poly(n-butyl acrylate) networks on fibroblasts adhesion, morphology and viability

BACKGROUND

Physical and chemical characteristics of implant materials determine the fate of long-term cardiovascular devices. However, there is still a lack of fundamental understanding of the molecular mechanisms occurring in the material-tissue interphase. In a previous study, soft covalently crosslinked poly(n-butyl acrylate) networks (cPnBA) were introduced as sterilizable, non-toxic and immuno-compatible biomaterials with mechanical properties adjustable to blood vessels. Here we study the influence of different surface treatments in particular oxygen plasma modification and fibrinogen deposition as well as a combinatorial approach on the adhesion and viability of fibroblasts.

MATERIAL AND METHODS

Two types of cPnBA networks with Young's moduli of 0.19±0.01 MPa (cPnBA04) and 1.02±0.01 MPa (cPnBA73) were synthesized and post-modified using oxygen plasma treatment (OPT) or fibrinogen coating (FIB) or a combination of both (OPT+FIB). The water contact angles of the differently post-treated cPnBAs were studied to monitor changes in the wettability of the polymer surfaces. Because of the key role of vascular fibroblasts in regeneration processes around implant materials, here we selected L929 fibroblasts as model cell type to explore morphology, viability, metabolic activity, cell membrane integrity as well as characteristics of the focal adhesions and cell cytoskeleton on the cPnBA surfaces.

RESULTS

Compared to non-treated cPnBAs the advancing water-contact angles were found to be reduced after all surface modifications (p < 0.05, each), while lowest values were observed after the combined surface treatment (OPT+FIB). The latter differed significantly from the single OPT and FIB. The number of adherent fibroblasts and their adherence behavior differed on both pristine cPnBA networks. The fibroblast density on cPnBA04 was 743±434 cells·mm-2, was about 6.5 times higher than on cPnBA73 with 115±73 cells·mm-2. On cPnBA04 about 20% of the cells were visible as very small, round and buckled cells while all other cells were in a migrating status. On cPnBA73, nearly 50% of fibroblasts were visible as very small, round and buckled cells. The surface functionalization either using oxygen plasma treatment or fibrinogen coating led to a significant increase of adherent fibroblasts, particularly the combination of both techniques, for both cPnBA networks. It is noteworthy to mention that the fibrinogen coating overruled the characteristics of the pristine surfaces; here, the fibroblast densities after seeding were identical for both cPnBA networks. Thus, the binding rather depended on the fibrinogen coating than on the substrate characteristics anymore. While the integrity of the fibroblasts membrane was comparable for both polymers, the MTS tests showed a decreased metabolic activity of the fibroblasts on cPnBA.

CONCLUSION

The applied surface treatments of cPnBA successfully improved the adhesion of viable fibroblasts. Under resting conditions as well as after shearing the highest fibroblast densities were found on surfaces with combined post-treatment.

Nanostructured Thermal Responsive Materials Synthesized by Soft Templating

We capitalized herein the inherent tortuosity of bicontinuous microemulsion to conceive nanostructured drug-delivery devices. First, we show that it is possible to synthesize bicontinuous materials with continuous hydrophilic domains of the poly(N-isopropylacrylamide) (PNIPAM) network entangled with continuous hydrophobic polymer domains, with dual-phase continuity being imposed by the bicontinuous microemulsions used as a soft template. Particular attention is paid to the microemulsion formulations using a surfmer to preserve the one-to-one replication of the bicontinuous nanostructure after polymerization. These materials keep a volume phase transition with temperature that allows considering them as drug carriers for controlled release. PNIPAM, which plays the role of the active ingredient reservoir, is confined in the bicontinuous structure. As expected, the PNIPAM enclosure limits the surface area in contact with the releasing aqueous solution and thus slows down the desorption of aspirin, which is used as a model drug. The hydrophobic polymers play the role of in situ-created transport barriers without hindering it as all the loaded aspirin in this bicontinuous structure still remains available.

Body temperature-responsive two-way and moisture-responsive one-way shape memory behaviors of poly(ethylene glycol)-based networks

In this work, crosslinked shape-memory polymer networks were prepared by thermally induced free-radical polymerizations of methacrylate-terminated poly(ethylene glycol) (PEG) and n-butyl acrylate (BA), which integrate thermal-responsive two-way and moisture-responsive one-way shape memory effects (SME).

Viability, morphology and function of primary endothelial cells on poly(n-butyl acrylate) networks having elastic moduli comparable to arteries

Soft hydrophobic poly(n-butyl acrylate) networks (cPnBA) were developed as entropy elastic substrates for passive mechanical stimulation of cells, where the elastic modulus of the cPnBAs could be systematically adjusted by variation of the cross-link density. The networks were synthesized by thermally-induced radical polymerization from n-butyl acrylate, with poly(propylene glycol) dimethacrylate (PPGDMA) acting as cross-linker, whereby the purity of the cPnBAs was confirmed by(1) H-NMR spectroscopy and gas chromatography. In this work two cPnBA polymer networks with an elastic modulus around 200 kPa and 1 MPa were investigated having an elastic modulus similar to that of arteries. Both cPnBAs exhibited an almost smooth surface with a surface roughness (R q) in the wet state ranging from 17 to 37 nm and a similar zetapotential, indicating an almost identical chemical composition within the topmost surface layer in terms of functional groups. In contrast, wettability of the samples was found to be different with an advancing angle ( advancing) of 123 ± 3.8° for cPnBA0250, while for cPnBA1100 significantly lower values for advancing (111 ± 3.8°) were obtained. First in vitro tests were performed with primary endothelial cells (HUVEC) to study its effects on vascular cell functions. Within the time period of cultivation (72 h), the cells on the cPnBA samples reached subconfluence and showed a viability rate of almost 100%. Although cell density differed after 72 h with more cells on cPnBA0250 than on cPnBA1100, both materials showed no significant effect on the cell morphology, the cellular LDH-release, which was used as marker for the integrity of the cell membrane, and the organisation of the VE-cadherin. However, lower cell density and less actin stress fibre formation on cPnBA1100 might indicate that cell-material interaction was weaker on cPnBA1100 than on cPnBA0250. The secretion of the vasoactive cytokines prostacyclin (PGI2) and thromboxane A2 (TXA2) was low compared to previously reported values. However, the anti-thrombogenic ratio of PGI2/TXA2 - which is balanced under physiological conditions - with much higher PGI2 compared to TXA2 (up to 17.6-fold after 72 h for cPnBA1100) suggests that this material might be effective to preventing thrombosis.

Cellular modulation by the elasticity of biomaterials

The elasticity of the extracellular matrix has been increasingly recognized as a dominating factor of cell fate and activities. This review provides an overview of the general principles and recent advances in the field of matrix elasticity-dependent regulation of a variety of cellular activities and functions, the underlying biomechanical and molecular mechanisms, as well as the pathophysiological implications.

Pro-angiogenic CD14(++) CD16(+) CD163(+) monocytes accelerate the in vitro endothelialization of soft hydrophobic poly (n-butyl acrylate) networks

As the majority of the polymers used as cardiovascular grafts so far do not match the elasticity of human arteries (100-1000kPa) and the required endothelialization, a multifunctional material approach is needed to allow the adjustment of the mechanical properties while at the same time exhibiting a haemocompatible surface. Recently soft poly(n-butyl acrylate) networks (cPnBA) with adjustable mechanical properties were introduced as candidate materials with a surface that can be endothelialized. In this study, angiogenically stimulated intermediate CD163(+) monocytes/macrophages (aMO2) were utilized as a cellular cytokine release system to realize the functional endothelialization of the hydrophobic cPnBA surface. We investigated the influence of co-cultured aMO2 on the morphology, density and cytokine secretion of human umbilical venous endothelial cells (HUVEC) seeded on cPnBA with an elastic modulus of around 250kPa (cPnBA0250). A functional confluent HUVEC monolayer could be developed in the co-culture within 3days. In contrast, the HUVEC in the monoculture exhibited stress fibres, broadened marginal filament bands and significantly more and larger cell-free areas in the monolayer, indicating incomplete cell-substrate binding. Remarkably, a functional confluent monolayer formation could only be achieved in co-cultures; it did not develop with the sole supplementation of recombinant VEGF-A(165) to the HUVEC monocultures (unpublished data). The study demonstrated the multifunctional potential of cPnBA in combination with aMO2 as a cellular cytokine release system, adapting their secretion to the demand of HUVEC. In this way, a functional confluent monolayer could be generated within 3days.

Thermal Properties and Crystallinity of Grafted Copolymer Networks containing a Crystallizable Poly(ε-caprolactone) Crosslinker in an aqueous environment

Here we introduce a multifunctional copolymer network system with adjustable thermomechanical properties, which is also capable to show a substantial water uptake and in this way should allow the additional alteration of the overall elastic properties besides the variation of the crosslinking density. The swelling capacity in water, the thermal properties as well as the crystallinity of a series of grafted copolymer networks named CLEG composed of water swellable poly(ethylene glycol) (PEG) side chains and crystallizable poly(ε-caprolactone) (PCL) segments acting as covalent crosslinker were explored in an aqueous environment.

The water swelling capability of the CLEG polymer networks was found to increase from 120% to 240% with increasing weight content of PEG. In contrast to the dry state, where two well separated melting temperatures could be observed for all CLEG samples, in aqueous environment only one melting temperature slightly above 40 °C, was obtained, whereby the overall crystallinity after swelling with water was strongly related to the PCL content in the CLEG polymer networks.