Failure Determination in Embedded Biomaterials Rexxi Prasasya, Chou Mai, Hyungjin Kim Advisor: Prof. Willis Tompkins Client: Raj Ambay, MD, DDS, UWHC, Division of Plastic Surgery

Outline Background Problem Statement Competition Alternative Proposals Design Matrix Future Work References

Background Biomaterial Materials Applications Metal, polymer, biologically derived, ceramics Combination of materials Biocompatible Applications Repair Replacement Drug delivery system

Problem Statement Biomaterial failure determination Properties changes Physical, chemical, structural Quantification Non-invasive detection Hyungjin, in this slide you don’t need to mention anything about Host response. Just say that our goal is to determine failure within biomaterial by detecting changes in property (can be physical, chemical, or structural). We would like to quantify this change non-invasively. (Kao, 2008)

Competition MRI X-ray Structural changes Non-metal Expensive Detect density difference Low cost www.mritoday.net On MRI part don’t mention inflammation, say that it can detect structural changes, but only limited to non-metal biomaterial. http://www.almimar.com/catalog1.html

Design Requirements Determine change in property Detect failure in biomaterials Non-invasive Clinical utility Cost: less than $500 Note: Clinical utility means it can be easily integrated into hospital setting.

Alternative designs Impedance spectroscopy Elastography Microwave tomography

Design 1: Impedance Spectroscopy Contrasts materials’ abilities to resist the flow of electrical current Use high frequency AC source Example: impedance pneumography

Design 1: Pro’s and Con’s Hand-held device feasible Simple electronic circuit High impedance of biomaterials

Design 2: Elastography Exploit difference in stiffness Echoes from high frequency sound wave Combined ultrasound and compressive image (Itoh et al., 2006) www.howstuffworks.com

Design 2: Pro’s and Con’s High sensitivity Readily available Reduced cost ($100 - $200) per scanning Immediate diagnosis Con’s Complex system ($250,000) Requires multiple transducers Dependence on interpreter

Design 3: Microwave Tomography Detects differences in dielectric properties Captures reflected electromagnetic waves Example: ischemia detection Physiological condition: molecular constituent, ion concentration and mobility, concentration fo free water and bound water molecule, tissue temperature (Guerquin-Kern et al. 1985)

Design 3: Pro’s and Con’s Known dielectric properties Non-ionizing electromagnetic field High contrast ratio Limited access to microwave technology Variations in tissue dielectric properties At body temperature, dielectric constant of fat is about 5 and heart tissue is about 50 – so about 10 fold difference. Contrast range in X-ray region is less than 2% and less than 10% in ultrasound. Level of microwave field used in this procedure is comparable w/ that used in cell phones

Design Matrix Category Weight Impedance Spectroscopy Elastography Microwave Tomography Feasibility .30 1 9 8 Accuracy .20 7 Cost 5 Availability .10 2 Non-invasiveness .15 6 Accessibility .05 Total 4.4 7.8 6.9

Future Work Construction of phantom Qualitative testing Evaluation of transducers and frequencies Clinical applicability

Reference “A-Medic 500 Radiographic X-ray Unit.” http://www.almimar.com/catalog1.html. Accessed March 06, 2008. Guerquin-Kern. J.L, et al. “Active microwavetomographic imaging of isolated, perfused animal organs.” Bioelectromagnetic 1985, p. 145-146 “How elastography works.” www.howstuffworks.com. Accessed March 03, 2008. Itoh, K. et al. “Breast Disease: Clinical Application of US Elastography for Diagnosis.” Radiology 2006; p. 239:341. Kao, J. “BME 430 lecture notes”. 2008. www.mritoday.net. Accessed March 03, 2008.