Small punch test on the retina: strain-rate influence and material calibration

Inherited retinal diseases are one of the leading causes of blindness among working age adults. The best option for the treatment is represented by gene therapy, delivered by subretinal injections. The main limitation of this approach is the risk of retinal damage or detachment during the procedure. For this reason, a material model of the retina is being developed to simulate the drug injection. This model should be able to describe the behaviour of the retina when subjected to different loading configuration and strain rates, to determine the best combination of injection site, volume and rate to guide the drug injection procedure. To obtain the data for the development of the model, mechanical tests at different scales are being performed. Here we present an investigation of the influence of the strain rate on the behaviour of the retina, carried out by small punch test. This setup was employed to test the retina under a biaxial loading configuration, rather than a more common uniaxial tensile test. The experimental curves were then compared with a finite element model to determine the best-fitting constitutive parameters through a surface response approach. The results obtained showed that the retina can be modelled as an hyperelastic material for large deformations, while at small deformations the model is unable to capture the behaviour of the tissue. Future considerations regarding possible improvements of the model include variations in the boundary conditions as well as other constitutive models for the retina.