The most conventional method of drug delivery is via the hypodermic needle. Yet risks and inefficiencies still exist which limit the spread of life saving medication and in some circumstances cause harm to people. The Nanopatch is a non-invasive drug delivery device, approximately 100 mm2 in size for humans, made up of a dense array of microprojections, ~21000 projections per cm2 and ~110 ìm in length. The drug or vaccine delivered by the Nanopatch is dry coated onto the projections, and the microprojections pierce the top layers of the skin to deliver the payload.
Work has been done on the mechanical properties of the skin and its effect on the Nanopatch (and related devices) however there has been limited development on the effect of adding deeper layers of human tissue to the system. This report endeavours to aid in the development of the Nanopatch by investigating the mechanical properties of Subcutaneous Adipose Tissue (fat, the first layer underneath the skin), the effect of thickness on the stiffness of the adipose tissue and finally the effect of this extra layer on the forces experienced by the Nanopatch.
The main findings of this research include the Young’s Modulus for Subcutaneous Adipose Tissue of 26.43 ±2.01 kPa, through indentation with a 13mm diameter flat cylinder indenter and a Neo-Hookean analytical method. Using this value a numerical model of full thickness skin was created with results from the works of Crichton et al 2013 (for the stiffness of skin), to determine the surface forces experienced by the indenter, to be applied to the Nanopatch. It was found that at the edge of the indenter (the exterior 3% specifically) experienced the highest force, in the range of 68-72% of the indentation force, whilst the remainder of the indenter experienced a force in the range of 1.3% of the indentation force.