An Introduction to Continuum Phenomena in Biomedical

Engineering Eric A. Nauman, Ph.D.,

Director, HIRRT Laboratory

School of Mechanical Engineering, Weldon School of Biomedical Engineering, Department of Basic Medical Sciences

A Brief History 1972 Moorhead, MN

A Brief History 1972 Moorhead, MN 1995 B.M.E. University of Delaware

A Brief History 1972 Moorhead, MN 1995 B.M.E. University of Delaware 1998 M.S. University of California,

Berkeley 2000 Ph.D. University of California,

Berkeley

A Brief History 1972 Moorhead, MN 1995 B.M.E. University of Delaware 1998 M.S. University of California,

Berkeley 2000 Ph.D. University of California,

Berkeley 2000 - 2004 Assistant Professor of

Biomedical Engineering Tulane University

A Brief History 1972 Moorhead, MN 1995 B.M.E. University of Delaware 1998 M.S. University of California,

Berkeley 2000 Ph.D. University of California,

Berkeley 2000 - 2004 Assistant Professor of

Biomedical Engineering Tulane University

2004 – Present Assistant/Associate/Full Professor of Mechanical Engineering, Biomedical Engineering and BMS

Other things I do

The Eye is Even More Amazing Than You Think

•  The eye focuses light on the retina which then uses biochemistry to transmit signals through the optic nerve head and on to the brain

•  Visual processing requires about 30% of your cortext (compared to 8% for touch and 3% for hearing)

•  There is a weak spot

The Lamina Cribrosa Holds the Back of the Eye Together

•  Idealized models allow us to calculate the mechanical properties and mass transport characteristics of the tissue.

The Mechanics of the LC are Directly Related to Glaucoma

Bone Fractures and Ruptures of Tendons and Ligaments

•  Not all bone fractures are traumatic – but most of them are.

•  There are lots of ways to

hurt yourself.

Bone Fractures and Ruptures of Tendons and Ligaments

•  Not all bone fractures are traumatic – but most of them are

•  There are lots of ways to hurt yourself

Basketball Injuries are Related to Head Injuries in Football?

•  Kevin Ware •  Kevin Ware -

High Definition

Tendon and Ligament Injuries!

Tendon and Ligament Injuries!

Tendon and Ligament Injuries!

Tendon and Ligament Injuries!

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The Knee – in Detail

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Multi-scale Models of Vascular Transport for Drug Delivery

Intravascular Space

Extravascular Space

Vessel Wall

Cell

Plasma Skimming

Layer

Interstitial Space

Red Blood Cell Extravascular

Flux

Let’s Talk about Brain Injury

–  Why is it important? –  Military –  Sports –  Motor Vehicle Collisions

–  What can we do? –  Develop methods to detect,

prevent, and treat TBI based on quantitative data and continuum level modeling

So Why Do We Study Football Players?

The Original Question… “Why do some players, who have similar magnitude and number of blows to the head, sustain concussions and others do not?”

What we learned …

Our current definitions of TBI need to be re-examined in light of advances in medical imaging.

Traumatic Brain Injury •  TBI Case Definition (CDC, 1995):

–  Injury to the head with one or more of -  Skull fracture, -  Observed or self-reported decrease/loss of

consciousness -  Amnesia -  Neurological or neuropsychological abnormality -  Diagnosed intracranial lesion (hemorrhage, contusion,

penetrating wound) -  Death resulting from head trauma

“Concussion”

Redefining Brain Injury On November 1, 2010, the world’s perception of what constitutes “traumatic brain injury” began to change.

Traditional Concussion Mechanics

Concussion Biomechanics •  Not a contact phenomenon

–  Brain does not hit cranial vault

•  Rotational shear and pressure gradients –  Whiplash induces concussions (Ommaya 1968) –  Concussions without head motion (Gurdjian 1976) –  Frontal lobe (anterior fossa) a critical injury ROI in

biomechanics and in CTE (Ommaya 1974; McKee 2009)

Adapted from P.V. Bayly, et al. J Neurotrauma. 2005 Aug; 22(8):845-56. Time

Concussion Biomechanics •  Focal Injury

–  Coup/contrecoup phenomenon –  Primary axotomy & hematoma

•  Diffuse injury –  Possibly a result of whole-brain

shearing •  Rotational acceleration

–  Tied to focal & diffuse injury –  Rotational strains may induce motor/

consciousness deficits –  Not reflected in any head injury criteria

P.V. Bayly, et al. J Neurotrauma. 2005 Aug; 22(8):845-56.

Imaging  Quanti+ies  Injury...  

P121 (Season 2)

P213 (Season 4)

Pre-Season

Pre-Season

Concussion! (24 hrs)

“Healthy”

Symptoms  Do  Not  

Normal Control

Football Helmet Telemetry •  Football: Helmet Impact Telemetry

(HIT™) System (Simbex; Lebanon, NH) –  Measures six linear accelerations

•  Approximates linear acceleration at head center of mass

•  Approximates impact location •  Soccer: Prototype sensor (X2Impact,

LLC; Seattle, WA) –  Concept similar to HIT System

Image from Chicago Tribune, 6 October 2010

Concussed Players Exhibit Deficits in Multiple Locations

Scatter plot for COI+/FOI+ group

Scatter plot for COI-/FOI- group

Scatter plot for COI-/FOI+ group

Microstructural Models Must Account for Multiple Cell Types

What Do All These Problems Have in Common?

–  Large Deformations –  Hierarchical Structure –  Fluids and Solids

Interact (sometimes gases too)

–  Multiaxial –  Nonlinear Constitutive

Laws –  Need to Connect to

Medical Imaging