1. Mechanical Testing System Coupled with an Environmental Chamber for Hydrogels
Team: Charlie Haggart, Gabriel J. Martínez-Díaz,
Darcée Nelson, and Michael Piché
Client: Weiyuan John Kao, Ph.D.
Advisor: Paul Thompson
BME 400 Midsemester Presentation
10/18/02

2. Overview Problem Statement Project Background
Design Specifications & Constraints
Environmental Chamber
Prototype Testing
Creep Testing System
Design Alternatives
Future Work
Acknowledgements

3. Problem Statement
Test compatibility of environmental chamber built during BME 301 with Instron 1000
Test hydrogel samples using Instron 1000
Compare results with Instron 5548 data
Design and build creep testing system
Study viscoelastic properties of hydrogels

4. Background - Hydrogels
Cross-linked polymeric structures
Ability to absorb water and/or biological fluids
Experience physical changes
Dependent on pH and temperature
Applications:
Drug delivery vessels, bandages, and skin adhesives for wound/burn care

5. Background - BME 301
Drafted procedure to fabricate tension stencils (used in making hydrogel samples)
In accordance with ASTM standards
Designed and built environmental chamber
Used in tensile testing of hydrogel samples
For use with Instron 1000 in 1313 Eng. Hall

6. Environmental Chamber Design Specifications/Constraints
Withstand temperature (25 – 40˚C) and pH (4 – 8) of solution
Cause no interference with tensile testing of hydrogel samples
Solution must not contact Instron 1000

7. Environmental Chamber Testing
Temperature Test
4 L deionized H2O
Physiological 37 °C
ASTM tensile test duration to 5.0 minutes
Results: 2.5 °C drop over 30 minutes duration

8. Environmental Chamber Testing
Grip Sensitivity
Instron 2711 Series - lever action grips
Will grips be sensitive enough for tensile testing of hydrogels?
YES
80% of hydrogel samples fractured at gauge length
20% fractured at point of contact with lower grip

9. Environmental Chamber Testing
Compatibility with Instron 1000
Issue: Top plate (obstruction)
Solution: Removal of plate
Issue: Protective seal (moisture)
Solution: Machine new adaptor

11. Background - Creep Testing
Tests effects of prolonged loading of a material
Monitors strain of a material under a constant stress for a long period of time.

12. Components of Creep Testing Apparatus
Specimen Grips
To hold specimen during testing
Extensometer
To measure the change in length of the specimen
Loading device (Weights)
Chamber
To keep specimen in conditions for which the creep properties are of interest

13. Product Design Specifications
Chamber
Material: transparent, durable, easy to manufacture, insulating, and resistant to corrosion
Must maintain constant temperature
Extensometer
Accurate to 1 mm and precise
Capable of logging data for up to 1 day
Grips
Must allow for fracture at gauge length
Must not slip
Loading System (Weights)
Must be variable between 0 and 50 g.

14. Design Alternatives: Digital Camera
Take pictures of sample at periodic intervals
Measurement scale on sample or on chamber
Sample elongation calculated from each image
What do we do? Wouldn’t you like to know….

15. Design Alternatives: Ultrasonic Transducers
Ultrasonic waves are emitted from position on the sample and received from a fixed location
Time difference is proportional to displacement
Picture from

16. Design Alternatives: Linear Displacement Transducer
Output voltage varies with changes in displacement
Examples
Linear Potentiometers (resistance)
LVDTs (inductance)
Picture taken from

17. Final Design

18. Testing PEG-diacrylate hydrogels with ASTM dog-bone shape
In air
In distilled water
10 samples tested

19. Experimental Set-up
Nerds will be photo of our set-up

20. Preliminary Results Room Temperature 25 g weight applied to sample
Immediately stretched ~13 mm
No further creep up to 1 hour
Other samples withstood maximum loads of 85 to >195 g, however, samples were dry and brittle at this time

21. Preliminary Results Distilled Water @ 40 ºC
Samples with 5-10 g broke after 5 sec.
Samples with 1g broke after 5 sec – 2 min
6/7 samples broke at the gauge length
Should this data be more organized, in chart form, perhaps?

22. Preliminary Conclusions
All samples should be placed in aqueous solution prior to testing
Samples should be tested within 24 hours of cross-linking to minimize degradation
Samples should be more homogenous
Placing samples in aqueous solution will prevent them from drying out and becoming brittle, which changes the mechanical properties
Samples should be tested immediately after being made to reduce degradation
Heterogeneous samples account for the differences in time to failure. A suggestion is add the same amount of hydrogel solution to every stencil with a 1000 micron pipette.

23. Future Work Tensile Testing Creep Testing Prototype Testing
Additional design considerations:
Data acquisition and logging
Temperature control
Prototype

24. Acknowledgements Professor Kao Paul Thompson BME Department
Professor Webster
Bill Hagquist, ME Shop
John Dreger, 1313 Eng. Hall
Ralph Wiggam, Springfield Elementary