Low Fouling Electrospun Scaffolds with Clicked Bioactive Peptides for Specific Cell Attachment

Peptide grafting strategies before and after electrospinning of nanofibers

Nanofiber films produced by electrospinning currently provide a promising platform for different applications. Although nonfunctionalized nanofiber films from natural or synthetic polymers are extensively used, electrospun materials combined with peptides are gaining more interest. In fact, the selection of specific peptides improves the performance of the material for biological applications and mainly for tissue engineering, mostly by maintaining similar mechanical properties with respect to the simple polymer. The main drawback in using peptides blended with a polymer is the quick release of the peptides. To avoid this problem, covalent linking of the peptide is more beneficial. Here, we reviewed synthetic protocols that enable covalent grafting of peptides to polymers before or after the electrospinning procedures to obtain more robust electrospun materials. Applications and the performance of the new material compared to that of the starting polymer are discussed.

Functionalizable Antifouling Coatings as Tunable Platforms for the Stress-Driven Manipulation of Living Cell Machinery

Cells are continuously sensing their microenvironment and subsequently respond to different physicochemical cues by the activation or inhibition of different signaling pathways. To study a very complex cellular response, it is necessary to diminish background environmental influences and highlight the particular event. However, surface-driven nonspecific interactions of the abundant biomolecules from the environment influence the targeted cell response significantly. Yes-associated protein (YAP) translocation may serve as a marker of human hepatocellular carcinoma (Huh7) cell responses to the extracellular matrix and surface-mediated stresses. Here, we propose a platform of tunable functionable antifouling poly(carboxybetain) (pCB)-based brushes to achieve a molecularly clean background for studying arginine, glycine, and aspartic acid (RGD)-induced YAP-connected mechanotransduction. Using two different sets of RGD-functionalized zwitterionic antifouling coatings with varying compositions of the antifouling layer, a clear correlation of YAP distribution with RGD functionalization concentrations was observed. On the other hand, commonly used surface passivation by the oligo(ethylene glycol)-based self-assembled monolayer (SAM) shows no potential to induce dependency of the YAP distribution on RGD concentrations. The results indicate that the antifouling background is a crucial component of surface-based cellular response studies, and pCB-based zwitterionic antifouling brush architectures may serve as a potential next-generation easily functionable surface platform for the monitoring and quantification of cellular processes.

Modulation of Living Cell Behavior with Ultra-Low Fouling Polymer Brush Interfaces

Ultra-low fouling and functionalizable coatings represent emerging surface platforms for various analytical and biomedical applications such as those involving examination of cellular interactions in their native environments. Ultra-low fouling surface platforms as advanced interfaces enabling modulation of behavior of living cells via tuning surface physicochemical properties are presented and studied. The state-of-art ultra-low fouling surface-grafted polymer brushes of zwitterionic poly(carboxybetaine acrylamide), nonionic poly(N-(2-hydroxypropyl)methacrylamide), and random copolymers of carboxybetaine methacrylamide (CBMAA) and HPMAA [p(CBMAA-co-HPMAA)] with tunable molar contents of CBMAA and HPMAA are employed. Using a model Huh7 cell line, a systematic study of surface wettability, swelling, and charge effects on the cell growth, shape, and cytoskeleton distribution is performed. This study reveals that ultra-low fouling interfaces with a high content of zwitterionic moieties (>65 mol%) modulate cell behavior in a distinctly different way compared to coatings with a high content of nonionic HPMAA. These differences are attributed mostly to the surface hydration capabilities. The results demonstrate a high potential of carboxybetaine-rich ultra-low fouling surfaces with high hydration capabilities and minimum background signal interferences to create next-generation bioresponsive interfaces for advanced studies of living objects.

Combinatorial functionalization with bisurea-peptides and antifouling bisurea additives of a supramolecular elastomeric biomaterial

The bioactive additive toolbox to functionalize supramolecular elastomeric materials expands rapidly. Here we have set an explorative step toward screening of complex combinatorial functionalization with antifouling and three peptide-containing additives in a bisurea-based supramolecular system. Thorough investigation of surface properties of thin films with contact angle measurements, X-ray photoelectron spectroscopy and atomic force microscopy, was correlated to cell-adhesion of endothelial and smooth muscle cells to apprehend their respective predictive values for functional biomaterial development. Peptides were presented at the surface alone, and in combinatorial functionalization with the oligo(ethylene glycol)-based non-cell adhesive additive. The bisurea-RGD additive was cell-adhesive in all conditions, whereas the endothelial cell-specific bisurea-REDV showed limited bioactive properties in all chemical nano-environments. Also, aspecific functionality was observed for a bisurea-SDF1α peptide. These results emphasize that special care should be taken in changing the chemical nano-environment with peptide functionalization. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1725-1735.

Guided protein/cell patterning on superhydrophilic polymer brushes functionalized with mussel-inspired polydopamine coatings

A simple approach for preparing bicomponent polymer patterns was developed by coating polydopamine (PDA) on superhydrophilic poly(2-acryl-amido-2-methylpropane sulfonic acid) (PAMPS) brushes. Well-defined and versatile arrays of proteins and cells were achieved without harm to proteins and cells.

Introduction of Nature's Complexity in Engineered Blood-compatible Biomaterials

Biomaterials with excellent blood-compatibility are needed for applications in vascular replacement therapies, such as vascular grafts, heart valves and stents, and in extracorporeal devices such as hemodialysis machines and blood-storage bags. The modification of materials that are being used for blood-contacting devices has advanced from passive surface modifications to the design of more complex, smart biomaterials that respond to relevant stimuli from blood to counteract coagulation. Logically, the main source of inspiration for the design of new biomaterials has been the endogenous endothelium. Endothelial regulation of hemostasis is complex and involves a delicate interplay of structural components and feedback mechanisms. Thus, challenges to develop new strategies for blood-compatible biomaterials now lie in incorporating true feedback controlled mechanisms that can regulate blood compatibility in a dynamic way. Here, supramolecular material systems are highlighted as they provide a promising platform to introduce dynamic reciprocity, due to their inherent dynamic nature.

Optimisation of grafting of low fouling polymers from three-dimensional scaffolds via surface-initiated Cu(0) mediated polymerisation

Well-controlled low fouling polymers brushes were grafted from the surface of biodegradable electrospun fibres for advanced tissue engineering applications.

Facile modification of electrospun fibrous structures with antifouling zwitterionic hydrogels

Electrospinning technology can easily produce different shaped fibrous structures, making them highly valuable to various biomedical applications. However, surface contamination of biomolecules, cells, or blood has emerged as a significant challenge to the success of electrospun devices, especially artificial blood vessels, catheters and wound dressings etc. Many efforts have been made to resist the surface non-specific biomolecules or cells adsorption, but most of them require complex pre-treatment processes, hard-to-remove metal catalysts or rigorous reaction conditions. In addition, the stability of antifouling coatings, especially in complex conditions, is still a major concern. In this work, inspired by the interpenetrating polymer network and reinforced concrete structure, an efficient and facile strategy for modifying hydrophobic electrospun meshes and tubes with antifouling zwitterionic hydrogels has been introduced. The resulting products could efficiently resist the adhesion of proteins, cells, or even fresh whole blood. Meanwhile, they could maintain the shapes and mechanical strength of the original electrospun structures. Furthermore, the hydrogel structures could retain stable in a physiological condition for at least 3 months. This paper provided a general antifouling and hydrophilicity surface modification strategy for various fibrous structures, and could be of great value for many biomedical applications where antifouling properties are critical.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

Controlling integrin-based adhesion to a degradable electrospun fibre scaffold via SI-ATRP

While polycaprolactone (PCL) and similar polyesters are commonly used as degradable scaffold materials in tissue engineering and related applications, non-specific adsorption of environmental proteins typically precludes any control over the signalling pathways that are activated during cell adhesion to these materials. Here we describe the preparation of PCL-based fibres that facilitate cell adhesion through well-defined pathways while preventing adhesion via adsorbed proteins. Surface-initiated atom transfer radical polymerisation (SI-ATRP) was used to graft a protein-resistant polymer brush coating from the surface of fibres, which had been electrospun from a brominated PCL macroinitiator. This coating also provided alkyne functional groups for the attachment of specific signalling molecules via the copper-mediated azide-alkyne click reaction; in this case, a cyclic RGD peptide with high affinity for α_vβ₃ integrins. Mesenchymal stem cells were shown to attach to the fibres via the peptide, but did not attach in its absence, nor when blocked with soluble peptide, demonstrating the effective control of cell adhesion pathways.

Polycaprolactone Microfibrous Scaffolds to Navigate Neural Stem Cells

Fibrous scaffolds have shown promise in tissue engineering due to their ability to improve cell alignment and migration. In this paper, poly(ε-caprolactone) (PCL) fibers are fabricated in different sizes using a microfluidic platform. By using this approach, we demonstrated considerable flexibility in ability to control the size of the fibers. It was shown that the average diameter of the fibers was obtained in the range of 2.6-36.5 μm by selecting the PCL solution flow rate from 1 to 5 μL min^-1 and the sheath flow rate from 20 to 400 μL min^-1 in the microfluidic channel. The microfibers were used to create 3D microenvironments in order to investigate growth and differentiation of adult hippocampal stem/progenitor cells (AHPCs) in vitro. The results indicated that the 3D topography of the PCL substrates, along with chemical (extracellular matrix) guidance cues supported the adhesion, survival, and differentiation of the AHPCs. Additionally, it was found that the cell deviation angle for 44-66% of cells on different types of fibers was less than 10°. This reveals the functionality of PCL fibrous scaffolds for cell alignment important in applications such as reconnecting serious nerve injuries and guiding the direction of axon growth as well as regenerating blood vessels, tendons, and muscle tissue.