Semester and Master Projects

Semester and Master Projects Fall 2020

Bio-inspired hydrogel nanocomposites

The good biocompatibility renders hydrogels well-suited biomaterials that are often used in biomedicine. Currently, hydrogels are commercialized as superabsorbent materials, wound dressings, and drug delivery systems. However, state-of-the-art applications of hydrogels are severely limited due to their poor mechanical properties and limited bioactivity. Novel strategies, such as infiltrating nanoparticles inside the polymeric network, promise to increase the versatility of hydrogels for load-bearing applications by combining a soft organic scaffold with a hard inorganic filler. Stemming from this idea, the project aims at developing a bioinspired polysaccharide-based hydrogel nanocomposite, with superior mechanical properties and enhanced bioactivity, which could be of great interest in the field of tissue engineering as replacement for damaged tissues or as scaffold for cell growth.

In this project you will learn the basics of hydrogel fabrication, as well as of nanoparticles synthesis. In parallel, you will gain experience in different characterization techniques. In a more advanced stage of the project, you will investigate the effect of directed alignment on the resulting mechanical properties. If you are interested in the project, do not hesitate to contact me at [email protected].

Prototyping and assessing a new mechanical test (bulge testing) for thin hydrogel sheets

Commercially available synthetic hydrogels are not commonly used for load bearing applications, because they are too soft and elastic. Instead, they are used to keep materials hydrated, for example, as contact lenses, plasters, or in the food industry. To enable the use of hydrogels for load bearing applications, they must be made stiffer without compromising their toughness too much. However, the poor understanding of the influence of the structure of hydrogels on their mechanical properties is partially due to the lack of standardized mechanical test of such soft materials. Thin hydrogel sheets are particularly difficult to handle when removed from their mould, to be mounted on a rheometer / tensile tester. Using the bulge testing method, we aim at achieving highly reproducible mechanical characterisation of hydrogel sheets.

In this project, you will further develop our current prototype blister tester to characterize the mechanical properties of hydrogel sheets. You will test different geometries to find an ideal combination of hydrogel sheets. You will then proceed to test hydrogels of various compositions and microstructures using the bulge test you developed. If you are interested, contact me at [email protected]

Assembly of bio-Inspired, structured hydrogels using microfluidic devices

Many natural materials have well-defined structures, imparting them unique mechanical properties. A prominent example is the mussel byssus, an acellular, soft material that attaches the animal to the rocky seashore and withstands high stresses, even during storms and heavy conditions. Inspired by nature, we produce micro-granulated hydrogels with locally varying compositions to increase their mechanical properties. To achieve this goal, we produce aqueous drops using microfluidics. These drops are assembled into superstructures and converted into microstructured hydrogels. Such hydrogels can potentially be used for load-bearing applications, such as artificial tendons or other soft implants.

In this project you will learn how to fabricate and use microfluidic devices to control the assembly of drops on a microfluidic chip. You will learn how nanoliter-sized drops are produced, stabilized, and immobilized using capillary forces. You will then use this knowledge to produce soft, bio-inspired composite materials with highly controlled structures. In addition, you will learn how to characterize their mechanical properties with tensile tests. If you are interested in this project and you would like to know more, please contact [email protected] .

Keywords: microfluidics, bio-inspired assembly, capillary forces, structured hydrogels, mechanical characterization

Structured nanocomposites via biomineralization

Nature produces materials from only a very limited number of elements without the use of advanced processing tools. Yet, many of these materials display fascinating mechanical properties. Natural composites that display excellent mechanical properties, such as nacre, inspired a lot of research to fabricate stiff and tough composites possessing hierarchal structures. However, despite the very nice work that has been done in this field, the structures of synthetic materials often differ from those of natural counterparts. The goal of this project is to develop processing methods that more closely resemble natural ones to fabricate strong and tough composites.

In this project, you will study different strategies to mineralize hydrogels and characterize the structure, composition, and mechanical properties of them. You will learn how to fabricate hydrogel scaffolds and how to mineralize them. You will characterize their mechanical properties using nanoindentation and 3-points bending test. If you are interested, please contact Ran Zhao: [email protected].

Microcapsules with switchable permeability

Microcapsules are widely used for encapsulating active ingredients in drug delivery, cosmetics and food additives. Most of the microcapsules are single-use delivery carriers because the release is diffusion-controlled or cargo is released when the shell becomes defective. A possibility to design sustainable capsules whose permeability can be dynamically tuned is the use of ionically crosslinked polymers as shell materials. Inspired by the adhesive chemistry of mussel threads, we are developing ionically cross-linkable capsules.

In this project, you will learn how to fabricate monodisperse-single-emulsion drops via microfluidic devices and how to convert them into viscoelastic capsules. You will study the influence of the composition and the surrounding environment on the permeability of the shell. If you are interested in this topic, please, contact [email protected] for further information.

Surface functionalization of emulsion drops

Surfactants are typically used to stabilize emulsion drops. We recently introduced a surfactant that in addition also imparts surface functionality to she emulsion drops. This opens up new possibilities to use surfactants not only to stabilize emulsion drops but also to convert them into capsules.

In this project, you will measure how the surfactant composition and concentration influences the interfacial tension and how that relates to the stability of emulsion drops. You will learn how to quantify the interfacial tension using a pendent drop set-up and how to quantify the stability of emulsion drops. If you are interested or you have any questions, please don’t hesitate to contact me via email: [email protected]

Master Project Fall 2020

The influence of humidity and trace gases on the crystallization of minerals

The control over the crystallization of solid matter is key to many applications, such as bio mineralization, drug production, catalysis, or carbon capture and storage. The kinetics of the crystallization of dry amorphous phases depends on many different parameters including the interaction of these metastable phases with surfaces, and the composition of the gas phase they are exposed to. The goal of this project is to investigate the influence of additives present in the amorphous phase and the composition of the gas phase on the crystallization of amorphous minerals. You will create amorphous particles composed of calcium carbonate, calcium phosphate, or similar inorganic materials within small millimeter droplets and in airborne aerosols and deposit them on a sample holder. By use of laboratory based infrared and Raman spectroscopy, you will study the influence of the different gases dry amorphous particles are exposed to, such as CO2, NH4, or H2O on the stability of the samples and follow their structure in situ. In addition, you will characterize the structure of the samples with XRD and synchrotron-based X-ray spectroscopy.

The Thesis Project will be mainly performed at the Paul Scherrer Institut, Villigen PSI (www.psi.ch), in close cooperation with the SMAL laboratory at EPFL.

If you are interested, please contact Thomas Huthwelker ([email protected]) or Esther Amstad ([email protected]).