Research

Reversible Anti-Fouling Polymer Coatings

Fouling and fouling control are major challenges in a wide variety of applications, ranging from biomedical devices to membrane technology. Fouling of surfaces leads to an increase in energy consumption, together with an increase in operational and maintenance costs to keep these devices running. Currently used cleaning methods, which remove these fouling agents, are often incomplete and their harsh conditions may damage the system of interest. Coating the system with a dense layer of end-grafted polymer, a polymer brush, has proven to reduce the fouling behaviour, but their long-term stability is poor. Hence, irrespective of the cleaning or anti-fouling strategy employed, all surfaces will eventually become fouled.

We aim to develop reversible anti-fouling polymer coatings via a cheap and simple adsorption method. Moreover, if the polymer coating gets fouled or damaged, the coating can easily be removed and reapplied. This is expected to lead to a new generation of anti-fouling coatings that can easily be applied on large surfaces, and that can be easily regenerated when needed.

Sea creatures like mussels and sandcastle worms are able to anchor themselves underwater onto rocks (mussels) or glue sand grains together (sandcastle worms). One of the mechanisms that enables the strong underwater adhesion is the mixing of oppositely charged polyelectrolytes. The resulting dense liquid polymer phase is called a complex coacervate. Based on this principle, we aim to develop an adhesive that works in a wet environment. Due to the introduction of additional responsive motifs (thermo, pH, redox-sensitive) a large set of extra interactions are possible. These second interactions will be able to act synergistically to render the material more durable, firmer, stronger and adaptable depending on the targeted applications such as, for example, healing of deep tissue wounds.

Complex Coacervate-Based Adhesives

Well-defined hydrophobic/strong polyelectrolyte block copolymers for enhanced underwater adhesives

Strong polyelectrolytes are polymers that are formed through polymerization of charged monomers, with the presence of these charges being independent of the pH and temperature. In other words, and unlike weak polyelectrolytes, the charge density of these polymeric materials is insensitive to the environment. Block copolymers that combine such strong polyelectrolytes with hydrophobic features are therefore highly interesting for use in underwater adhesives (Adv. Mater., 2018, 30, 1704640). However, due to their amphiphilic nature, the synthesis, characterization and processing of such polymers remains a challenging task, and is likely even impossible.

To this end, in this research project new polymeric materials will be developed that are based on protected strong electrolytes and hydrophobic monomers, resulting in well-defined and fully hydrophobic block copolymers that can be synthesized, characterized and processed by the conventional methods. Subsequently, an external stimulus (either thermal or chemical) will transform the hydrophobic material into the desired ionic-hydrophobic block copolymer (See Figure). Before being applied in adhesives, a better understanding of the amphiphilic character is expected to be achieved by studying the self-assembly of these copolymers in bulk and solution, using techniques like light scattering, X-ray diffraction and electron microscopy.

In summary, the research project will involve the following aspects:

• Design and synthesis of new protected monomers;
• Preparation of block copolymers by living and/or controlled polymerization techniques;
• Studying the self-assembly of the deprotected materials in bulk and/or solution;
• Incorporation of the copolymers in polyelectrolyte-containing adhesives.

The synthesis and processing of strong fibrous materials in green conditions is extremely challenging: the most commonly used polymers are insoluble in water, which is therefore incompatible with the high concentrations and molecular weights required for fiber spinning. Natural materials, such as spider silk, circumvent this issue through a two step process: first undergoing liquid-liquid phase separation (LLPS) to form a concentrated phase, and secondly solidifying by the combination of chemical (pH changes, ion gradients) and physical (shear forces generated through extrusion) factors.

In our research, we use polyelectrolyte complexation to imitate this process. Polyelectrolyte complexes (PECs) are polymeric materials that can be easily processed in water, using only salt as a plasticizer. By decreasing the concentration of salt, these complexes transition from fully soluble in water, to a separate concentrated liquid phase, to an insoluble solid. Our aim is to use this processing approach to synthesize high performance fibers in green conditions, without the use of any toxic organic solvents.

By combining natural and synthetic polyelectrolytes, and taking advantage of the fiber alignment and conformational changes that can take place during extrusion, we aim to obtain materials with improved properties in terms of biocompatibility and mechanical behavior.

Melt electrowritten hierarchical scaffolds

Native tissues in the human body are characterized by unique architectures. The spatial micropatterned organization of cells and extracellular matrix dictates to the high extent mechanical performance of the tissue and cell behavior. Some of the tissues are characterized by specifically high complexity, with regional morphologies or gradual transition in structural features. Examples include hard-soft tissue interfaces, such as bone-tendon or bone-ligament junctions. The reconstruction of these zones is not trivial and there is currently a lack of material systems that can closely mimic their structure and function. 

We aim to reconstruct the architectures present in native tissues using Melt Electrowriting (MEW) approach. MEW is an additive manufacturing technique that uses a high voltage to deposit with unprecedented precision fibers with diameters in the micrometer range. High control over printed structures at very small scales and the flexibility in the printable designs makes MEW an excellent tool to recreate the complexity of native tissues. Using 2D and 3D patterned architectures we want to dictate the mechanical and biological performance of the scaffolds.

The small-scale hierarchical structures printed with high precision will serve as implantable systems or an in-vitro testing model.