Mechanical Testing System Coupled with an Environmental Chamber for Hydrogels Team Charlie Haggart Gabriel J Mart nez D az Darc e Nelson and Michael Pich Client Weiyuan John Kao Ph D Advisor Paul Thompson BME 400 Midsemester Presentation 10 18 02 Overview Problem Statement Project Background Design Specifications Constraints Environmental Chamber Prototype Testing Creep Testing System Design Alternatives Future Work Acknowledgements 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 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 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 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 Environmental Chamber Testing Temperature Test 4 L deionized H2O Physiological 37 C ASTM tensile test duration 0 5 to 5 0 minutes Results 2 5 C drop over 30 minutes duration 37 5 37 Temperature C 36 5 36 35 5 35 34 5 34 0 5 10 15 20 Time s Trial 1 Trial 2 25 30 35 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 Environmental Chamber Testing Compatibility with Instron 1000 Issue Top plate obstruction Solution Removal of plate Issue Protective seal moisture Solution Machine new adaptor 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 L strain Li F stress A 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 Product Design Specifications Chamber Extensometer Accurate to 1 mm and precise Capable of logging data for up to 1 day Grips Material transparent durable easy to manufacture insulating and resistant to corrosion Must maintain constant temperature Must allow for fracture at gauge length Must not slip Loading System Weights Must be variable between 0 and 50 g Design Alternatives Digital Camera Take pictures of sample at periodic intervals Measurement scale on sample or on chamber Sample elongation calculated from each image 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 http www piezotechnologies com Design Alternatives Linear Displacement Transducer Output voltage varies with changes in displacement Examples Linear Potentiometers resistance LVDTs inductance Picture taken from http www novotechnik com linear html Final Design Testing PEG diacrylate hydrogels with ASTM dog bone shape In air In distilled water 10 samples tested Experimental Set up 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 Preliminary Results Distilled Water 40 C 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 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 Future Work Tensile Testing Prototype Testing Tensile testing Creep Testing Additional design considerations Data acquisition and logging Temperature control Prototype Acknowledgements Professor Kao Paul Thompson BME Department Professor Webster Bill Hagquist ME Shop John Dreger 1313 Eng Hall Ralph Wiggam Springfield Elementary