Student projects

Interfacial fracture toughness between hydrogel and tissue

Project: Available

Type of project: Master project

Context: Due to their high water content and soft consistency, hydrogels are suitable biomaterials for a wide range of biomedical applications [1] such as drug delivery [2], tissue engineering [3] or tissue repair [4]. However, their field of applications is often limited by the lack of adhesion to biological tissue.

One way to evaluate adhesion is to force a crack to propagate at the hydrogel-tissue interface and calculate the interfacial fracture toughness. However, it is not straightforward to obtain this value. Indeed, it depends on many parameters, such as the geometry, crack length, critical stretch or stored energy of an un-notched sample, which are challenging to measure especially for samples composed of two or more different materials.

Since hydrogel and tissue show different properties, they deform differently in the XYZ directions under uniaxial loading. Therefore, in order to evaluate the interfacial fracture toughness, 3D digital image correlations (DIC) is used to measure the real critical stretches of the material and the tissue. Moreover, the interfacial fracture toughness should not depend on the geometry of the sample and is thus normalized with a geometrical factor. However, at this stage of the study, it is not clear if this empirical factor only depends on the geometry or also on the material.

Aim:

  • Determine the interfacial fracture toughness between two soft materials or between a hydrogel and a tissue via 3D Digital image correlations (DIC).
  • Estimate the geometrical factor and determine if it only depends on the geometry or also on the material.
  • Establish a model to evaluate the interfacial toughness of any soft materials.

Methods:

  • Sample preparation (hydrogel and tissue)
  • Mechanical testing: tensile and fracture tests
  • 3D digital image correlation
  • (FEM simulation)

References

[1] A. S. Hoffman, “Hydrogels for biomedical applications,” Adv. Drug Deliv. Rev., vol. 64, Supplement, pp. 18–23, décembre 2012.

[2] J. Li and D. J. Mooney, “Designing hydrogels for controlled drug delivery,” Nat. Rev. Mater., vol. 1, no. 12, p. 16071, Dec. 2016.

[3] K. Y. Lee and D. J. Mooney, “Hydrogels for Tissue Engineering,” Chem. Rev., vol. 101, no. 7, pp. 1869–1880, 2001.

[4] A. M. S. Costa and J. F. Mano, “Extremely strong and tough hydrogels as prospective candidates for tissue repair – A review,” Eur. Polym. J., vol. 72, pp. 344–364, Nov. 2015.

Contact the following person for details about the project (requirements, project workflow): celine.wyss@epfl.ch

The project will be between the Laboratory for processing of advanced composite (LPAC) and the Laboratory of Biomechanical Orthopedics (LBO), under the direction of Pierre-Etienne Bourban.

The details of the proposed work may be subjected to modifications.


How cell-matrix interaction is modulated by incorporated ECM-mimetic elements into pHEMA hydrogels?

Project: Available

Type of project: Master project

Requirement: Cell culture

Background: in microscopy and PCR analysis is a plus.

Description: Careful design of biomaterials properties, cell-scaffold interaction and mechanical stimulation are required to biophysically guide chondrocytes differentiation. One mechanism by which cells may sense the surrounding microenvironment is through their integrin interaction with anchored ligands within the extra cellular matrix (ECM). ECM-mimetic functionalization of synthetic hydrogels can therefore be adopted to enhance integrin mediated mechano-sensing. It is well known that Arginine, Glycine and Aspartate (RGD) sequence in ECM proteins such as fibronectin provides attachment sites for integrin receptors. However, the role of ECM-mimetic elements in chondrogenic differentiation of cells embedded in hydrogels could be debatable according to the current literature. The aim of this project is to evaluate chondro-progenitor cells behavior in response to incorporation of ECM-mimetic elements into pHEMA hydrogels in presence and absence of dynamic loading.

Contact the following person for details about the project: naser.nasrollahzadeh@epfl.ch


FE model for simulation of hydrogel injection into cerebral aneurysms

Project: Not Available

Type of project: Semester / Master project (open to be discussed)

Section(s): Mechanics 

Background: in Fluid-Structure Interaction with COMSOL or ANSYS is highly required for this project.

Description: Photopolymerizable hydrogels might be a promising solution to treat cerebral aneurysms. For this purpose, a microcatheter is placed at the aneurysm site and a balloon is inflated at the aneurysm neck to stop the blood flow. Hydrogel precursor is injected through a microcatheter in a liquid state and solidifies in situ by 405nm light illumination.

Aim: In this project, a FE model will be developped to simulate the injection of the hydrogel precursor into the aneurysm. Different parameters will be defined and optimized: injection speed of the hydrogel precursor, viscosity of the hydrogel precursor, position of the balloon to avoid overpressure…

Contact the following person for details about the project: oriane.poupart@epfl.ch


How does RGD peptide change mechanical properties and endothelial cell migration and adhesion to the hydrogel?

Project: Not Available

Type of project: Master project

Section: Materials Science / Bioengineering and Life Science

Background: Cell culture

Description: Photopolymerizable hydrogels might be a promising solution to treat cerebral aneurysms. For this purpose, the hydrogel needs to fulfill mechanical (similar properties to endothelium tissue) and biological requirements. One of the biological requirements is to induce endothelialization in order to completely occlude the aneurysm from the parent vessel. RGD peptide is well-known to increase cell adhesion.

Aim: Characterize the effect of the RGD peptide on cell migration and adhesion

Tasks:

  •  Characterize the mechanical properties of the hydrogel (photorheology, compression and fatigue)
  • Test the cell migration and adhesion in static conditions
  • Design a microfluidic system in order to test dynamically the cell migration and adhesion

Contact the following person for details about the project: oriane.poupart@epfl.ch


3D FE model for adhesion analysis of hydrogels on tissue

Project: Not Available

Type of project: Master / Semester (open to be discussed)

Section(s): Mechanics / Materials Science

Background: in simulation with commercial finite element software (Abaqus) is highly required for this project.

Description: The adhesive hydrogels has recently drawn a great attention in the biomedical field. The adhesion performance of hydrogel-tissue, however, is often very low. Therefore, the analysis of adhesion and the contributory parameters for the adhesive systems are highly beneficial. In this project, a FE model will be developed to simulate the adhesion of hydrogels and analyze the contributory parameters with ABAQUS/Explicit. Moreover, experimental measurements will be performed to define and assign the material properties, in order to analyze the experimental setup. 

Contact the following person for details about the project: peyman.karami@epfl.ch