FACILITIES AND CAPABILITIES
The Center for Applied Biomechanics (CAB) is collaborative research facility supported by the School of Engineering and Applied Science and the School of Medicine at the University of Virginia. The facility is dedicated to a broad array of experimental and computational biomechanics research. Research at the CAB involves tissue characterization ranging from the nano- to macro- length scales with numerous customized apparati and techniques. Time scales involved in the studies range from microsecond to hours with loading environments encompassing blast to quasi-static conditions. The 13,000 ft2 facility includes numerous dedicated experimental test spaces, a computational work group, a centralized data acquisition facility, a machine shop, an electronics shop, several freezer refrigeration storage facilities for biological tissue, and a biological specimen preparation room. The facility also houses over 30 professional research staff and nearly 30 graduate and undergraduate students.
Dynamic and Quasi-Static Test Equipment
The CAB possesses a number of universal test machines ranging from table top to freestanding biaxial machines. Fixture hardware includes three- and four-point bending, tensile grips (hydraulic and manual), capstan grips, and custom-built devices. An environmental chamber is capable of controlling temperature and humidity during testing.
Instron Model 8874
This machine is typically utilized for component and small sample testing and the characterization of the viscoelastic properties of tissues. It is a compact biaxial servohydraulic testing system capable of applying axial loads of +/- 10 kN and torsional loads of +/- 100 Nm at rates approaching 2 m/s. The system may be accessed via both manual and software control interfaces allows adaptive feedback control in both position and force modes. Integrated data acquisition capability allows it to record 16 channels of test data at sampling rates of up to 5 kHz. The system allows the performance of quasi-static, step/relaxation, and rapid failure tests as well as cyclic, fatigue-type sequences. The system is also fully compatible with LabVIEW.
Tinius Olsen LoCap Test Machine (T.O.)
The computer controlled T.O. is a device capable of conducting mechanical property tests for biomaterials, metals, and composites. It has a load range of 0.002 to 140,000 N with a cross head speed of 0.05 to 50 cm per minute. The T.O. is used mainly for compression tests, tension tests, and bending tests. An expanded work area of 75 cm between machine columns permits full component testing of larger biological specimens.
Instron Model 8500
The CAB possesses three Interlaken test frames outfitted with Instron 8500 servo-hyrdraulic conrole systems. Each frame is capable of tensile and compression loads in excess of 50 kN and displacement rates exceeding 1.0 m/s. The 8500 Series of servohydraulic testing systems are used for higher capacity fatigue and static testing of biomedical components, where more working space, higher maximum actuator movement and more customization may be needed.
Instron Model 1000
The Instron 1000 is a screw-driven test machine that can be used in either tension or compression. For the tabletop device, crosshead speeds range from 0.125 to 50.0 cm/min with a total crosshead travel of 110 cm and a horizontal clearance of 25 cm. The system is used for smaller specimens tested at relatively low displacement rates.
Customized Test Apparatus
Customized devices have been developed for micro- and macro-scale indentation testing using linear servoelectric motors with displacement control feedback loops. This system has been used for indentation testing of abdominal organs, brain tissue, and cartilage. A specialized harmonic excitation system has been developed for defining material properties of anisotropic soft tissues. The system employs electrodynamic shakers oriented at adjustable positions to create biaxial loading conditions. Frequencies in excess of 1000 Hz are possible. The system has been used to characterize human skin and aorta tissues.
Instrumentation
The CAB maintains an extensive inventory of over 500 calibrated sensors dedicated to biomechanical research. The most commonly used sensors are piezo-electric accelerometers, strain gauge load cells, magneto hydrodynamic (MHD) angular rate sensors, pressure transducers, acoustic crack detection sensors, and potentiometers measuring displacements or angles. Load cells can be a simple type for measuring a single force or complex multi-axis units, measuring several forces and/or moments. Customized instrumentation packages are also configured by CAB personnel.
DATA ACQUISITION
144-channel DSP Technology TRAQ-P System
This computer-controlled system is modular and all the channels are identical. Moveable breakout boxes allow sensors to be connected to the system at any of the various test sites within the lab facility. The system itself is centrally located and is situated in a climate-controlled room.
Each data channel consists of a programmable signal conditioning module, a digitizer and solid-state memory. The signal conditioners are capable of supplying a programmable sensor supply voltage, amplifying the sensor signal and applying a programmable-frequency anti-aliasing low-pass filter to the incoming signal. Digitizers are 12 bits and can sample at rates up to 100,000 samples per second. All digitizers in the system sample simultaneously. The system contains enough memory to allow 14,000 samples per channel to be recorded. Several triggering options allow flexibility in capturing the data from complex test events. Recorded data is transferred through a GPIB 488 link to non-volatile storage in the control computer.
Control of the data-collection process is accomplished with DSP Technology IMPAX software, running on a Pentium computer. Numerous options are provided for flexibility in configuring various types of tests, testing sensors and processing data. Most post-test data processing is done with custom in-house software.
Dewetron Dewe-5000
The portable Dewe-5000 data acquisition system includes 64 dynamic channels and up to 256 static channels controlled by a Pentium 4-based PC. .
TDAS G5 Data Acquisition System
The CAB has two TDAS G5 data acquisition systems providing a total of 64 channels. The unique design of the TDAS G5 DAS includes 16-bit A/D converters, programmable signal conditioning, 100 KHz per channel simultaneous sampling and non-volatile memory. The ultra-small design (25 x 54 x 85 mm) and modular configuration make the system versatile and transportable. The system has fully programmable signal conditioning with gains from 1 to 4,000, Sensor ID capabilities, and comprehensive fault detection and self diagnostics. For impact and dynamic testing conditions, the devices are factory tested to 500+ Gs.
Ancillary Products Include:
PC-based National Instruments System
Additional data acquisition capability is provided by a PC-based system utilizing a 733 MHz. Pentium III computer and five PCI-6110E multi-function boards supplied by National Instruments. This system consists of 20 data channels with 200 kHz. hardware anti-aliasing filters and is capable of sampling rates up to one megahertz. The system is controlled by software written in National Instruments LabVIEW.
IMAGING SYSTEMS
ATOS Digitizer
The ATOS II (GOM mbH) uses advanced camera technology and software to collect and process surface data from biological specimens. This surface data provides detailed geometric information on biological specimens for stress/strain calculations as well as FE model implementation. With a variable reference frame, the system is capable of collecting up to 1,300,000 surface points in under seven seconds. A minimum point spacing of 0.03-0.1 5mm allows detailed specimen geometry to be assessed. Previous applications have been used for cartilage depth estimations and ligament cross-sectional areas. Significant improvements in cross-sectional and volumetric accuracy relative to laser devices have been achieved due to the ability to measure concave surface geometry.
ARAMIS Non-Contact Strain Measurement
ARAMIS is a non-contact measuring system, which is well suited for measuring three-dimensional deformation and strain distributions of biological specimens under static or dynamic load. The deformation measuring system ARAMIS records an object under load using CCD cameras. For each stage of load, the 3D coordinates of the object surface are calculated on the basis of digital image processing delivering also the 3D displacement and the surface strain.
The dimensioning of specimens, the exact determination of material properties and the improvement of FE calculation models are possible using the ARAMIS system. Previous applications of the system at the CAB include strain field measurement in both hard and soft tissues.
VICON MX System
For measuring of kinematics in large field of view three-dimensional events, the CAB uses a VICON MX system. The system is an advanced optical motion capture system capable of tracking phototargets at speeds up to 2,000 frames per second. The major components include 12 cameras, controlling hardware modules, and Bodybuilder software to analyze and present the data. Supplemental light sources dedicated to each camera enable target visualization under very bright ambient conditions and permit concurrent digital video photography.
HIGH SPEED CAMERAS AND MOTION ANALYSIS EQUIPMENT
In addition to standard CCD video cameras, the CAB possesses a number of customized digital camera systems for viewing biomechanical tests.
Phantom v5.0 Camera
The Phantom v5.0 high speed digital imaging system is the first commercially available Complementary Metal-Oxide Semiconductor (CMOS) camera to offer rates of 1,000 pictures per second at 1024x1024 pixels. The advanced SR-CMOS sensor developed by Vision Research, Inc. has been designed exclusively for high speed use, balancing sensitivity and resolution. For example, the v5.0 can record at 3,800pps for 1 second using the central 512x512 pixels of the sensor, using a camera equipped with the standard 1 gigabyte of image memory.
Kodak HG and RO Imagers
The CAB maintains 4 Kodak HG and RO digital color imagers. Test events can be recorded with the capability of capturing up to 2000 full video frames per second at a resolution of 512 X 384 pixels. Because they are constructed to withstand shock at levels of up to100 g’s, these imagers are capable of being mounted directly on the impact devices.
Kodak Ektapro EM Motion Analyzer, Model 1012
The EktaproÓ EM system is utilized to record test events in black and white digital format at rates of up to 1000 full video frames per second. Up to 4800 full-frame images may be recorded and subsequently downloaded to VHF videotape or directly to a PC through a GPIB interface for analysis and storage. The system also has an immediate playback capability, allowing instantaneous review and evaluation of test results.
Photo-Sonics 16 mm 1-B High-speed Motion Picture Cameras
Four Photo-Sonics 16 mm 1-B movie cameras are available for use in situations requiring photographic-quality records of high-speed test events. As is the case with the RO imagers described above, these cameras are designed and constructed to withstand the high-g environment associated with impact testing. Servo-controlled motors provide accurate frame rates of up to 1000 frames per second. Camera synchronization and actual film speeds at any point on the film record can be determined by referencing commonly generated timing marks which are simultaneously recorded on the film in each camera at precise, known frequencies.
Redlake Hycam 16mm High Speed Motion Picture Camera
The Hycam camera can film events at rates of up to 11,000 frames per second; it is utilized to produce photographic quality records of test events involving extremely high velocities and short durations. As is the case with the Photo-SonicsÒ cameras, synchronization information, as well as the actual frame rate associated with any part of the film record, may be determined by referencing the commonly generated timing marks recorded on the film.
NAC Film Motion Analyzer Model 160F
Test kinematics recorded on 16 mm film are analyzed using a NAC film analyzer which, in conjunction with a PC, allows user-identified points to be digitized, tracked, and plotted throughout the duration of the test event. The system includes a display/digitization screen, MAPÓ film analysis software, and accessories to capture 35 mm still photographs from the movie film.
SOFTWARE
The CAB is extensively involved in developing finite element and multi-body models of biomechanical tissues and structures. A host of implicit and explicit codes are used to develop these models. Applications of the models include assessment of complex loading to the tissues, understanding failure mechanisms, and identifying parameters of tissue constitutive models through iterative solution techniques. To facilitate development of geometric models, customized and commercial visualization software, such as the Voxar 3D program, are used.
MADYMO
MADYMO (version 6.0, TNO Netherlands) is an integrated multi-body dynamics and finite element program for simulation of human motion. It has been designed especially for the study of the complex dynamic response of the human body and its environment under dynamic and impact loading conditions. Contact algorithms have been developed to evaluated loading of body structures from either external or internal forces. Anthropometric scaling of models is facilitated by using a geometric database of human and adult dimensions. The predictions of the models have been compared with laboratory test data and the models have been refined to improve the agreement between simulation and experiment.
LS-DYNA
LS-DYNA (LSTC, Inc) is a general purpose nonlinear finite element program capable of simulating complex real world problems. Implicit and explicit methods as well as single and multi-processor capabilities are imbedded in the code. The CAB maintains an extensive database of whole-body, tissue (structural), and material models for tissue characterization under complex loading. For parameter identification studies using nonlinear constitutive models, LS-Dyna is used in conjunction with LS-Opt. LS-OPT is a design optimization and probabilistic analysis package with an interface to LS-DYNA.
Voxar 3D
Voxar 3D is an advanced 3D visualization and analysis software package. It can perform visualizations of CT, MR, and PET studies. Voxar 3D allows 2D views, multiplanar (MPR) views, as well as 3D views. In the MPR views, the images can be reformatted into any linear or curved plane needed. In this view, distance and angle measurements can be made. In the 3D view, volumetric measurements can be made. Voxar 3D can also perform 3D segmentation, so you only see and analyze the bones and tissues desired. This software has the ability to read the scans in several formats. It can also export them in different formats such as bitmap, jpg, or dicom.
COMPUTERS
The CAB maintains a network of more than 65 personal computers. Each researcher has a PC computer with standard software and the specialized programs needed for their projects. The computers are networked so that they can use programs accessible on the University of Virginia mainframe computers. In addition to the custom biomechanics and simulation software described herein, the University of Virginia has site licenses for a large number of technical and commonly used software programs.
FACILITITES FOR BIOLOGICAL TESTING AND STORAGE
The laboratory has storage facilities for cadaveric material that will be used for testing. This material is prepared in a special room that is in the building so that surgical and/or other necessary procedures to inplant instrumentation can be completed on-site before testing. Two walk-in and twelve chest freezers can be used to store biological specimens for longer periods while upright and walk-in coolers are available for shorter term storage. Customized fast-freeze cryotanks are used to rapidly freeze smaller biological specimens and to minimize the size of ice crystals generated during the process.