An In Vitro Model for Uniaxial Stretching

Bryan J. Pfister, Timothy P. Weihs, Michael J. Betenbaugh, and Gang Bao
Johns Hopkins University
3400 North Charles Street
Baltimore, MD  21218
pfister@jhunix.hcf.jhu.edu
(410) 516-5336

Head injury is a significant health-care problem in our society. Severe mechanical impact loading as well as non-impact inertial loading to the head can manifest into numerous injuries and biological responses. Quick movements and impacts of the skull may result in large intracranial deformations of the brain tissue, vasculature, and connective tissues.  Automobile accidents, traumatic falls, and acts of violence are everyday occurrences that can easily provide the mechanical loading necessary to permanently damage our brain tissue. 

Traumatic brain injuries (TBI) quite often lead to permanent disability or death.  The Centers for Disease Control and Prevention (CDC) reports that about 1 million people are treated and released for mild brain injuries, while 230,000 are hospitalized and 50,000 die each year in the United States alone. Roughly, about 22% of those who sustain traumatic brain injuries eventually die.  The main causes of TBI are automobile accidents, falls, and violence.  The leading cause of TBI in people 5-64 years of age are auto accidents, while the elderly are prone to falls.  Of those who receive hospitalization, nearly 80,000 people a year are released with permanent disabilities.  Today, over 5.3 million Americans are living with some sort of brain injury related disability (Brain Injury Association 1999).
Bulk shearing of brain tissue during head injury often translates to a localized stretching of individual neurons and their processes.  It is therefore critical to perform uniaxial stretching of the neurons with strains and strain rates that mimic head injury conditions.  A unique in vitro injury device has been developed recently with the capability of stretching cultured neural cells at strains above 100% and strain rates above 100s^-1.  The device can be used to selectively stretch different sections of the neuron, e.g. the cell body or neurites individually.  

NT2-N cells are seeded upon an elastic substrate and clamped at both ends.  A voice coil actuator is used to apply predetermined strain and strain rates to the elastic well.  A cell adhesion essay is performed on the cell-membrane attachment to ensure adequate adhesion.  Injury of the cells upon stretch and the subsequent observations of the post injury process in the cell has led to a better understanding of the traumatic brain injury process.  This novel device will be used to address a wide range of biomechanical issues involved in DAI.