PacSurf2022 Session BI-MoM2: Biofunctional Surfaces and Coatings

Our understanding of the role of lipid membrane has evolved a long way from the Singer and Nicolson model of a fluid mosaic in which the bilayer served simply as a two-dimensional liquid providing a hydrophobic environment for membrane proteins. While inherently dynamic, membranes exhibit a wide polymorphism of co-existing structures that play important roles in cellular processes. Lipid films (monolayers and bilayers) are frequently used as models to understand and probe structural changes upon interaction with proteins, enzymes, drugs, drug delivery vehicles and foreign bodies such as pollutants and chemicals. Moreover, the understanding of such interactions and how they influence biomolecular conformation and structure, enables us to design lipid-based surface coatings that confer functionality (from simple biocompatibility to triggered drug delivery) to nanoparticles and other solid surfaces. Our work focuses on understanding the composition-structure-function relationships that govern such functionality suing a surface analysis approach that encompasses lateral and vertical structure on both the molecular and meso-/microscopic scales and employs a combination of surface x-ray scattering (GIXD, GIXOS, X-ray reflectivity), imaging (AFM, Brewster angle microscopy and imaging ellipsometry) and spectroscopic (IRRAS) techniques. The power of these methods for elucidating the inter-relationships between the structure and organization of biomembranes and their functional properties will be shown using examples of Langmuir films as model membranes. A focus of the talk will be on lipid-nanoparticle interactions. On one hand, nanoparticles can be considered pollutants or contaminants as their impacts on cellular components, including the cell membrane itself, are not well established. This will be exemplified by examining the impact of inhaled nanomaterials on the functional properties of pulmonary surfactant membranes, a lipid-protein film coating the air-alveolar surface. On the other hand, nanocarriers which are comparable in size to many cellular components and easily internalized, cause unique interactions with cells and therefore offer an intriguing route for the encapsulation and delivery of difficult to deliver drugs. In this case the nanoparticle-lipid membrane interactions have to be tuned to minimize deleterious effects and in fact using a lipid coating can not only provide the necessary biocompatibility but also to enhance the delivery of drugs using nanocarriers via a carefully selected coating composition.

One-dimensional (1-D) silicone micro- and/or nanostructures such as filaments, wires, fibers and tubes have attracted significant attention due to their remarkable application capabilities in a large range of material and surface science /1/. The chemical synthesis is surprisingly simple and based on the Droplet-Assited-Growth and Shaping process (DAGS)/2/. Here, we demonstrate a novel, extraordinarily simple and efficient dynamic DAGS synthesis strategy allowing for the one-step synthesis and in situ control of the shape of nanostructures. We demonstrate bamboo-shaped silicone nanorods (SNRs) obtained by the repetitive dynamic regulation of growth conditions, concomitant with the periodic purging and injection of precursors. The new resulting nanostructures endow these newly designed SNRs with a specific number of segments and a highly regular arrangement. This approach allows the silicone micro- and/or nanorods to be customized with different heights and different segment numbers tailor-made to the requirements for various properties. With this method, various properties can be controlled, for example mechanical stiffness and water repellence. The obtained SNR coatings exhibit for example stable water-resistance under both static and dynamic wetting conditions, robust chemical and mechanical durability, and excellent performance in buoyancy promotion, self-cleaning and water harvesting. Notably, the properties are obtained by fluorine-free compounds, are very environmentally friendly, and are based on a very simple, solvent-free one-step procedure accomplishable at room temperature and normal pressure. The well-structured ultra-long rods can also be fabricated with an ultrahigh aspect ratio (~ 176), still standing straight upwards and regular even the they consist of flexible and soft silicone material /3/. Finally, the presentation will give insight in new applications which are accessible due to the precise control of the nanstructures' shape.

/1/ G. Artus, S. Jung, J. Zimmermann, H. P. Gautschi, K. Marquardt, S. Seeger, EP1644450A2 [http://www.google.ch/patents/EP1644450A2?hl=de&cl=zh](2003), Adv. Mater. (2006),18, 2758, J. Zhang, S. Seeger, Angew. Chem.(2011) 50, 6652, Stojanovic, S. Olveira, M. Fischer, S. Seeger, Chem.Mat., 25, 2787(2013), X. Zhang, S. Seeger, Small, 15(34) 1901822 (2019)

/2/ G Artus, S Olveira, D Patra, S Seeger, Macromol.Rapid Comm. 2017, 38, 1600558

/3/ K Chen, S Liu, Y Lau, S Seeger, Small, in press (2022)

Silk fibroin (silk) materials have promise for use in the biomedical space owing to their incredible mechanical properties. Compared to other naturally-derived polymers, silk exhibits remarkable tensile strength because of a unique antiparallel β sheet secondary structure. Additionally, silk is favorable for use in biological settings because it is non-immunogenic and degrades via enzymatic hydrolysis into non-toxic byproducts in vivo. Silk can be fabricated into a range of architectures to mimic biological settings, including films, porous networks, and microparticles. These aspects illustrate silk’s utility in areas including biosensors, tissue engineering, and drug delivery. All biomedical applications, however, require silk to interact with biological species in specific ways. As with most polymers, silk lacks the necessary surface cues required to facilitate precise interactions with biological species. Thus, further modification is required to tailor silk materials’ surface properties and enhance their efficacy as biomaterials.

Low-temperature plasma (LTP) modification represents a relatively unexplored but highly promising area for silk construct modification. LTP processing negates the use of solvents and high temperature conditions associated with wet chemical modification. Moreover, LTP treatment can be conducted with a range of precursors, translating to a myriad of attainable surface chemistries. In this talk, I will highlight three LTP approaches our group recently investigated to modulate silk film surface properties. For example, we utilized LTP strategies to enhance silk film hydrophilicity using N₂ and H₂O(g) precursors. After N₂ and H₂O(g) LTP treatments, water contact angles (WCAs) decreased by ~35° and ~50°, respectively. Notably, all LTP-modified constructs exhibited minimal hydrophobic recovery after 6 weeks of aging. In addition, we have developed plasma-enhanced chemical vapor deposition approaches to modulate silk film surface properties. We utilized LTP copolymerization, where feedgas composition was tuned using two unique precursors: acrylic acid (to produce thin films with polar functional groups on the silk surface) and pentane (to produce thin films with non-polar functional groups on the silk surface). WCA goniometry and x-ray photoelectron spectroscopy were utilized to evaluate wettability and changes in surface chemistry following LTP treatment, respectively. We elucidated that surface properties depend on both feedgas composition and position of the film in the LTP reactor. In sum, LTP represents a promising avenue to customize silk surface properties for use in biomedical contexts.