Biomedical and Biological Materials
Organised by ESIS TC14 “Integrity of Biomedical and Biological Materials”
Monday, 6 July 2020
10.30 – 11.00: Break
12.30 – 14.00: Lunch break
14.45 – 15.30: Mechanistic prediction of in-stent restenosis based on computer modelling of stent deployment, tissue damage and growth
Liguo Zhao (Loughborough University, UK), voice over: V.V. Silberschmidt (Presentation)
15.30 – 16.00: Break
16.00 – 17.00: Final test
Bone is a natural hierarchical composite tissue incorporating hard mineral nano-crystals of hydroxyapatite (HAp) and organic binding material containing elastic collagen fibers. We investigated the structure and deformation of ovine bone using synchrotron X-Ray tomographic imaging and scattering. X-Ray experiments were performed in three-point bending with an in situ rig. Tomography was used to visualise the sample position and structure within the rig with respect to the laboratory coordinate system and the beam. Wide Angle X-Ray Scattering (WAXS) and Small Angle X-Ray Scattering (SAXS) 2D patterns were collected. Data interpretation reveals that sample shape has a strong effect on the observed scattering patterns, and needs to be accounted for in order to extract deformation (strain) data. Internal residual strains revealed in this way are likely to be linked to bone structure and function. Novel combined tomographic and diffraction analysis paves the way for advanced characterization of complex shaped samples using the Dual Imaging And Diffraction (DIAD) paradigm.
Hip joint replacement is one of the most frequently used surgical procedures worldwide. More than 200,000 surgeries are performed only in Europe each year. Replacing degenerated or fractured hip has been made possible by insertion of metallic femoral support into a channel made inside the femoral bone, whereas ultra-high molecular weight polyethylene (UHMWPE) has been used for acetabular bone cup inlay, to bond femoral support and acetabular cup. A more advanced design of this implant included cementless bonding.
Fracture of femoral component is well-documented complication after the implementation of hip prosthesis. Most stem fractures occurred at a region of the modular femoral neck, mainly at the junction of the neck to the femoral stem, where corrosion is a significant problem. Analyses of femoral component fractures identified several factors that contribute to failure, including material and design, implant positioning, cementing technique, and patient characteristics. Static failure can be analysed by using linear elastic or elastic plastic fracture parameters, applied to a given hip implant case. Another important aspect of hip integrity is impact loading, i.e. it toughness, since brittle fracture due to stambling represents common mode of failure. Anyhow, the most important aspect of this problem is fatigue, i.e. crack growth caused by amplitude loading, such as walking.
The material fatigue crack growth resistance ca be determined by using the standard procedure prescribing measurement of the fatigue crack growth rate da/dN, which develops from the existing crack. Experimental testing to determine the fatigue crack growth rate da/dN and fatigue threshold values deltaKth is typically performed by using a three point bending specimens on a resonant high frequency testing machine. Using experimental data for material constants in Paris law, C and m, fatigue crack growth in hip implant can be simulated by applying the extended finite element method. In this way one can get crack length in dependence of number of cycles for a given implant geometry, including crack, and amplitude loading.
Synthetic polymers have transformed the manufacture of medical devices, implants and soft-tissue prostheses since their conception at the turn of the 20th century. 3D printing introduced a variety of orthopaedic implants and medical devices via the processing of polymeric biomaterials. The manufacture, material characterisation, mechanical testing, biological testing and additive manufacture of novel polymeric blends for biomedical applications are presented and compared to state-of-the-art biomaterials.
This lecture will introduce bioprinting, particularly for tissue engineering scaffolds, and discuss the materials, manufacturing process, design methods and mechanical characterisation.
Prof. José Manuel García-Aznar, Prof. Maria Jose Gómez-Benito (University of Zaragoza, Spain, email@example.com) “Different numerical strategies to simulate the structural integrity of endothelial monolayers”
The endothelial barrier is a dynamic structure, in which, cell-cell junctions are binding and unbinding all the time. The unbinding junctions form gaps in the endothelial monolayer, which favours several physiological and pathological processes in the cell body, such as, the immune system cell migration; but also pathological processes as cancer cell migration to different sites in the body to form secondary tumours, thus metastasizing.
To understand how endothelial cell junctions are formed and broken we adopt two different approaches: a) a three-dimensional continuum approach b) and a discrete two-dimensional one. Both approaches allow us to evaluate the structural integrity of endothelial monolayers, improving the understanding of different key events during opening and closures of gap junctions.
In-stent restenosis (ISR), defined as a reduction of lumen diameter by more than 50% after stent implantation, is one of the major issues for percutaneous coronary intervention. In this paper, finite element simulations were carried out to model the stenting procedure, quantify the tissue damage caused by stenting and predict the subsequent evolution of ISR over a defined time. In particular, a tissue-growth model, associated with vessel damage, was introduced to predict the growth of the arterial layer, a major contributor to ISR. The evolution of ISR showed a strong dependency on stent designs and materials, in a direct correlation with the peak lumen diameter achieved during stent implantation. Such correlation can be used directly to predict ISR for a given peak lumen diameter and time point.