Design of a Cranial Vascular Mechanics Model Sean S. Kohles, PhD Director, Kohles Bioengineering, Portland, OR; Adjunct Associate Professor, Mechanical Engineering, PSU & OSU, and Surgery, OHSU

Purpose of this Seminar Introduce myself as potential project advisor Describe design objectives and motivation for the proposed project: –Medical issues –Biologic and biomimetic materials –End users –Performance specifications

Kohles Training University of Wisconsin –Engineering Mechanics (BS, MS) –Bioengineering (PhD) –Orthopedic Surgery (Postdoc) University of Oregon –Exercise Science (Visiting Assistant Professor)

Previous Position: Worcester Polytechnic Institute, Massachusetts Tenure-track faculty in –Biomedical Engineering Biomechanics, biomaterials, biotransport, and design courses –Mechanical Engineering –Biology & Biotechnology Adjunct appointments –Clinical Science (Tufts Univ School of Vet Med) –Physiology & Orthopedics (Univ of Mass Med School)

Kohles Research Foci Biomechanics and biotransport –Tissue and implant mechanics Biomaterials and tissue engineering Surgical device design –Orthopedic, dental, minimally invasive Biostatistics and mathematical modeling

Current Vascular Mechanics Project Collaboration with Biomedical Signal Processing (PSU) and Complex Systems (OHSU) Laboratories: –James McNames, PhD; ECE-PSU –Brahm Goldstein, MD; Pediatrics-OHSU –Wayne W. Wakeland, PhD; Systems Science-PSU –Mark Weislogel, PhD; ME-PSU

Design Objectives Create a proof-of-concept mechanical model of cranial vascular mechanics: 1.Flow system with variable control of… Fluid pressure and volume Fluid pathways (vessel tubes vs porous media) 2.Head analog which simulates key tissues (biomimetics) Hard and soft tissues, fluids Synthetic composite arrangement

Brain and Cardiovascular Biomechanics The head or cranium is a natural thick-walled pressure vessel Cranial tissues contained within the bony calvarium: –Brain and connective tissues (1200 mL), static –Cerebral spinal fluid, CSF (150 mL), dynamic –Blood (150 mL), dynamic Hydrostatic (buoyancy forces in CSF) and hydrodynamic (blood flow) states

Brain and Cardiovascular Biomechanics Pulsatile flow driven by the heart –Volumetric flow to the brain 750 ml/min –Vessel pathway controls mass transport Arteries to arterioles to capillaries to venules to veins –Normal arterial pressure range 60 to 160 mmHg or 8 to 21.3 kPa fainting to edema –Autoregulatory system Heart rate, vessel dilation/constriction, etc.

Medical Significance Traumatic brain injury (TBI) due to an external physical force such as acquired during an auto accident. –Leading cause of death and disability in children and adolescents in the United States The brain swells as a consequence of the injury, the pressure within the calvarium increases causing regional or global ischemia –Decreased blood supply due to constriction or obstruction of the blood vessels. This secondary injury, in turn, causes cell death and potentially permanent impairment or brain death.

Medical Device ‘State of the Art’ Few technologies other than medical images exist to monitor brain, post injury Current devices ‘tap’ into cranium and vessels to measure static/dynamic pressures New devices measure volume change (  V) associated with pressure change (  P) –Compliance, S =  V/  P –Combined measure of flow resistance in vessels and compressibility or distensibility of cranial tissues P V

Medical Needs No physical models exist to… –Judge accuracy of current devices –Complement mathematical models which attempt to predict autoregulatory system –Educate physicians and researchers on the unique mechanical dependence of brain function

Proposed Project Team 2 or 3 ME students with interests in biomechanics and biomaterials –Advised by Dr. Kohles and ME Design Faculty 2 ECE students with interests in biosensors and controls –Advised by Dr. McNames and BSP Lab Faculty Resources: Bench space in the Microgravity and Surface Tension Lab, 449-SB2, thanks to Dr. Weislogel

Design Loop: Creativity with a Purpose Practical Problem (Need) Motivates Design Question Design Solution Finds Design Problem/ Goal Defines Helps to Solve Contributions/Constraints: Clients & Users Design & Performance Specifications

Nuclear Magnetic Resonance and Computed Tomographic Images