ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

CALCULATION OF THE HEAT POWER REQUIRED FOR A
THERMO-SENSITIVE DRUG DELIVERY SYSTEM IN KNEE
CARTILAGE
1. ABSTRACT
M. Nassajian Moghadam 1 and D.P. Pioletti 2
We want to use a self-heating (dissipative) material implanted in a cartilage defect to
deliver a drug under a delayed mechanical loading. The goal of this study is to estimate
the value of the dissipative power needed from the self-heating material to increase its
temperature up to 2°C when cyclic deformations are applied. To estimate this value, we
model heat transfer between an implanted material -a cylindrical hydrogel in our case-,
and the cartilage when cartilage and hydrogel deform periodically during slow running.
The motion of the synovial fluid within the intra-articular gap and inside the porous
cartilage during its deformation plays an important role in the regulation of heat. We
consider this effect in our model. The calculation is performed in Comsol multi-physics
environment. Model parameters such as heat capacity, conductivity of human cartilage
and synovial fluid are experimentally obtained. Our results showed that the self-heating
material should provide a dissipative power of about 0.27 mW/mm 3 to induce a
temperature increase of 2°C in the hydrogel.
2. INTRODUCTION
The different structures composing a synovial joint present viscoelastic behavior.
Viscoelasticity is associated with dissipation processes, which in turn may locally
generate heat in tissues such as cartilage. It has been shown during an ex vivo study on
human hips, that cyclic loading could induce a 2°C temperature increase in the cartilage
[1]. Factors possibly influencing the amount of heat produced in synovial joint are the
performed and duration activity, the body weight, the coefficient of friction in the joint
and the lubricating property of the synovial fluid [2].
Heat transfer in human cartilage involves complicated processes such as heat
conduction in tissues, heat transfer due to perfusion of the synovial fluid through the
pores of the tissue, metabolic heat generation and viscous heat dissipation from the
cartilage when it is deformed. Several groups have studied the effect of these factors on
heat regulation in knee either mathematically or experimentally [3-5]. The goal of the
present study is to simulate heat regulation in knee cartilage when the cartilage is
deformed sinusoidally, considering synovial fluid flow in a 3D finite element
poroelastic model. In particular, the objective is to optimize the amount of dissipation
which would be required to increase by 2°C the temperature of a material used to treat
cartilage defect, considering the heat transfer mechanism in the knee joint.
1 PhD Student, Laboratory of Biomechanical Orthopedics, EPFL, Lausanne, Switzerland
2 Assistant Professor, Laboratory of Biomechanical Orthopedics, EPFL, Lausanne, Switzerland