Mechanical Testing Mechanical Testing System Coupled with an System Coupled with an Environmental Chamber Environmental Chamber

for Hydrogelsfor HydrogelsTeam: Charlie Haggart, Gabriel J. Martínez-Díaz, Team: Charlie Haggart, Gabriel J. Martínez-Díaz,

DarcéeDarcée Nelson, and Michael PichéNelson, and Michael Piché

Client: Weiyuan John Kao, Ph.D.Client: Weiyuan John Kao, Ph.D.Advisor: Paul ThompsonAdvisor: Paul Thompson

BME 400 Midsemester PresentationBME 400 Midsemester Presentation10/18/0210/18/02

OverviewOverview

Problem StatementProblem Statement Project BackgroundProject Background Design Specifications & ConstraintsDesign Specifications & Constraints

Environmental ChamberEnvironmental Chamber• Prototype TestingPrototype Testing

Creep Testing SystemCreep Testing System• Design AlternativesDesign Alternatives

Future WorkFuture Work AcknowledgementsAcknowledgements

Problem StatementProblem Statement

Test compatibility of environmental chamber Test compatibility of environmental chamber built during BME 301 with Instron 1000built during BME 301 with Instron 1000

Test hydrogel samples using Instron 1000Test hydrogel samples using Instron 1000 Compare results with Instron 5548 dataCompare results with Instron 5548 data

Design and build creep testing system Design and build creep testing system Study viscoelastic properties of hydrogelsStudy viscoelastic properties of hydrogels

Background - HydrogelsBackground - Hydrogels

Cross-linked polymeric structuresCross-linked polymeric structures Ability to absorb water and/or biological Ability to absorb water and/or biological

fluidsfluids Experience physical changes Experience physical changes

Dependent onDependent on pH and temperature pH and temperature Applications:Applications:

Drug delivery vessels, bandages, and skin Drug delivery vessels, bandages, and skin adhesives for wound/burn care adhesives for wound/burn care

Background - BME 301Background - BME 301

Drafted procedure to fabricate tensionDrafted procedure to fabricate tension stencils (used in making hydrogel stencils (used in making hydrogel samples)samples) In accordance with ASTM standardsIn accordance with ASTM standards

Designed and built environmental Designed and built environmental chamberchamber Used in tensile testing of hydrogel samplesUsed in tensile testing of hydrogel samples For use with Instron 1000 in 1313 Eng. HallFor use with Instron 1000 in 1313 Eng. Hall

Environmental Chamber Environmental Chamber Design Design

Specifications/ConstraintsSpecifications/Constraints Withstand temperature (25 – 40˚C) and pH Withstand temperature (25 – 40˚C) and pH

(4 – 8) of solution (4 – 8) of solution

Cause no interference with tensile testing Cause no interference with tensile testing of hydrogel samplesof hydrogel samples

Solution must not contact Instron 1000 Solution must not contact Instron 1000

Environmental Chamber TestingEnvironmental Chamber Testing

Temperature TestTemperature Test 4 L deionized H4 L deionized H22OO Physiological 37 °CPhysiological 37 °C ASTM tensile test ASTM tensile test

duration - 0.5 to 5.0 duration - 0.5 to 5.0 minutes minutes

Results:Results: 2.5 °C drop 2.5 °C drop over 30 minutes over 30 minutes durationduration

34

34.5

35

35.5

36

36.5

37

37.5

0 5 10 15 20 25 30 35

Time (s)

Tem

per

atu

re (

C)

Trial 1 Trial 2

Environmental Chamber TestingEnvironmental Chamber Testing

Grip SensitivityGrip Sensitivity Instron 2711 Series - lever action gripsInstron 2711 Series - lever action grips Will grips be sensitive enough for tensile Will grips be sensitive enough for tensile

testing of hydrogels?testing of hydrogels?• YESYES• 80% of hydrogel samples fractured at gauge length80% of hydrogel samples fractured at gauge length• 20% fractured at point of contact with lower grip20% fractured at point of contact with lower grip

Environmental Chamber TestingEnvironmental Chamber Testing

Compatibility with Instron 1000Compatibility with Instron 1000

Issue: Top plate (obstruction) Issue: Top plate (obstruction) • Solution: Removal of plateSolution: Removal of plate

Issue: Protective seal (moisture) Issue: Protective seal (moisture) • Solution: Machine new adaptorSolution: Machine new adaptor

Background - Creep TestingBackground - Creep Testing

Tests effects of prolonged Tests effects of prolonged loading of a materialloading of a material

Monitors strain of a Monitors strain of a material under a constant material under a constant stress for a long period of stress for a long period of time.time.

AF

σstress

LΔL

εstraini

Components of Creep Testing Components of Creep Testing ApparatusApparatus

• Specimen GripsSpecimen Grips To hold specimen during testingTo hold specimen during testing

• ExtensometerExtensometer To measure the change in length of the To measure the change in length of the

specimenspecimen• Loading device (Weights)Loading device (Weights)• ChamberChamber

To keep specimen in conditions for which the To keep specimen in conditions for which the creep properties are of interestcreep properties are of interest

Product Design SpecificationsProduct Design Specifications ChamberChamber

Material: Material: transparent, durable, easy to manufacture, insulating, and transparent, durable, easy to manufacture, insulating, and resistant to corrosionresistant to corrosion

Must maintain constant temperatureMust maintain constant temperature ExtensometerExtensometer

Accurate to 1 mm and preciseAccurate to 1 mm and precise Capable of logging data for up to 1 dayCapable of logging data for up to 1 day

GripsGrips Must allow for fracture at gauge lengthMust allow for fracture at gauge length Must not slipMust not slip

Loading System (Weights)Loading System (Weights) Must be variable between 0 and 50 g.Must be variable between 0 and 50 g.

Design Alternatives:Design Alternatives:Digital CameraDigital Camera

Take pictures of sample at periodic Take pictures of sample at periodic intervalsintervals

Measurement scale on sample or on Measurement scale on sample or on chamberchamber

Sample elongation calculated from each Sample elongation calculated from each imageimage

Design Alternatives:Design Alternatives:Ultrasonic TransducersUltrasonic Transducers

Ultrasonic waves are Ultrasonic waves are emitted from position emitted from position on the sample and on the sample and received from a fixed received from a fixed locationlocation

Time difference is Time difference is proportional to proportional to displacementdisplacement

Picture from http://www.piezotechnologies.com/

Design Alternatives: Design Alternatives: Linear Displacement TransducerLinear Displacement Transducer

Output voltage varies Output voltage varies with changes in with changes in displacementdisplacement

ExamplesExamples Linear Potentiometers Linear Potentiometers

(resistance)(resistance) LVDTs (inductance) LVDTs (inductance)

Picture taken from http://www.novotechnik.com/linear.html

Final DesignFinal Design

TestingTesting PEG-diacrylate hydrogels with ASTM dog-PEG-diacrylate hydrogels with ASTM dog-

bone shapebone shape In airIn air In distilled waterIn distilled water

10 samples tested10 samples tested

Experimental Set-upExperimental Set-up

Preliminary ResultsPreliminary Results Room TemperatureRoom Temperature

25 g weight applied to sample25 g weight applied to sample Immediately stretched ~13 mmImmediately stretched ~13 mm No further creep up to 1 hourNo further creep up to 1 hour

Other samples withstood maximum loads of 85 to Other samples withstood maximum loads of 85 to >195 g, however, samples were dry and brittle at >195 g, however, samples were dry and brittle at this timethis time

Preliminary ResultsPreliminary Results Distilled Water @ 40 Distilled Water @ 40 ºCºC

Samples with 5-10 g broke after 5 sec.Samples with 5-10 g broke after 5 sec. Samples with 1g broke after 5 sec – 2 minSamples with 1g broke after 5 sec – 2 min 6/7 samples broke at the gauge length6/7 samples broke at the gauge length

Preliminary ConclusionsPreliminary Conclusions All samples should be placed in aqueous All samples should be placed in aqueous

solution prior to testingsolution prior to testing Samples should be tested within 24 hours of Samples should be tested within 24 hours of

cross-linking to minimize degradationcross-linking to minimize degradation Samples should be more homogenousSamples should be more homogenous

Future WorkFuture Work Tensile TestingTensile Testing

Prototype TestingPrototype Testing Tensile testingTensile testing

Creep TestingCreep Testing Additional design considerations:Additional design considerations:

• Data acquisition and loggingData acquisition and logging

• Temperature controlTemperature control PrototypePrototype

AcknowledgementsAcknowledgements

Professor KaoProfessor Kao Paul ThompsonPaul Thompson BME DepartmentBME Department Professor WebsterProfessor Webster Bill Hagquist, ME ShopBill Hagquist, ME Shop John Dreger, 1313 Eng. HallJohn Dreger, 1313 Eng. Hall Ralph Wiggam, Springfield ElementaryRalph Wiggam, Springfield Elementary