hydrogels as actuaters
TRANSCRIPT
Hydrogels for Artificial Muscles
Major Project Presentation
Supervised by,Dr. Sureyya SaricilarProf. Geoffrey Spinks
Submitted by,Karthika Prasad3372194
AIM
Attempt to make double network hydrogels fit enough to work as actuators for artificial muscles.
Introduction
Hydrogels - water swollen three dimensional networks of polymer chains.
Quite similar to biological systems.
Interesting stimuli response
Wide applications in biological system
Why double network hydrogel ?
Compression of Single Network hydrogel
Compression of Double Network Hydrogel
EXPERIMENTAL
Materials used• 2-acrylamido-2-methyl propanesulfonic acid (PAMPS)• Potassium persulphate(KPS), • N,N methylene bis acryl amide, (NMBA)• Acrylic acid, (AAc)• 2-hyroxy-2-methylpipus phenone• Triethylene glycol dimethacrylate
• Swelling and Mechanical properties of 1.5mm thick
PAMPS-AAc DN hydrogel studied
• The pH response of various thickness of hydrogels studied
DN hydrogel• 1st network was immersed in the 2nd network
solution• Kept under UV for 6 hours to let polymerization
take place.
Preparation of HydrogelsDN hydrogel was synthesized by polyemerization technique
1st Network• Desired concentrations of PAMS, KPS and
NMBA mixed• Was kept oven at 60 C for 24 hours.
2nd Network • AAc, 2-hyroxy-2-methylpipus phenone and
Triethylene glycol dimethacrylate were mixed at desired concentrations
Experimental
1.5mm 0.5mm 0.16mm
Materials of various thickness were used to prepare gels
Swelling experiment
PAMPS/AAc hydrogels samples were cut into circles and were socked in buffer solutions with pH values varying from 2.14 to 7.96.
Increase in the weight of hydrogel were noted in each case.
Mechanical Tests
CompressionCompression tests were carried out using a mechanical
tester ( Instron ). Circular shaped gel samples swollen in buffer solution
of varying pH (2.14, 2.91.3.72.4.72,5.72.6.91.7.96) were used.
Mechanical tests
Tensile testThe samples were cut into dumbbell shape.Procedure similar as compression test using the
INSTRON testing machine.Samples were then placed into different buffer
solutions of pH varying from pH 2.2 to pH 7.96.
Actuation test
The pH sensitivity of the DN hydrogels was tested by performing actuation test
Gels were cut into rectangular pieces and were soaked in pH 2.14 and pH 7.96 to reach equilibrium
Gels of 3 different thicknesses that’s 1.5mm, 0.5mm and 0.16mm were used to do the actuation test.
Results and Discussion
General comments
Transparent Tough Contains more than 90% water Sample gels soaked in pH 4.72 and pH 5.72 were opaque
Swelling experimentsThe samples were dried after equilibrium swelling have
been attainedEquilibrium water content = [(Ws – Wd)/Wd]* 100Ws and Wd are the weights of swollen and the dry hydrogel
respectively
Fig:1 Swelling behavior of DN hydrogel at different pH
Swelling experiment
Samples showed a tremendous increase in their weights for the first 4 hours
Gels from pH 2.14 to pH 3.72 and from pH 5.72 to pH 7.96 are in swollen state
Gel at pH 4.72 was in shrunken state and was opaque due to the salt effect between the COO- ion in the 2nd network and K+ ion present in the electrolyte
Mechanical tests
Compression Graphical representation of Compressive behavior of
hydrogels at different pH
Fig 2:Compressive stress-strain behavior at pH 2.14 to 7.96
0 0.2 0.4 0.6 0.8 1 1.20
0.5
1
1.5
2
2.5
3
3.5
pH 2.14pH 2.91pH 3.72pH 4.72pH 5.72pH 6.91pH 7.96
Strain (mm/mm)
Str
ess (
Mpa)
Compression contd…
Compressive stress varied from 0.3MPa to 3.3Mpa with 99% strain at all the cases
The modules varied from 30KPa to 340KPaModules was calculated by dividing stress
with strainGels were strong at pH less than 4 due to
hydrogen bonding
Tensile test
Fig :3 Tensile stress-strain behavior at pH2.14 to pH 7.96
0 200 400 600 800 1000 1200 14000
0.1
0.2
0.3
0.4
0.5
0.6
Tensile strenth- 1.5mm thick wire
pH 2.14
pH 2.91
pH 3.72
pH 4.72
pH 5.72
pH 6.91
Tensile Strain %
Te
ns
ile
Str
es
s (
MP
a)
Tensile test cond..Fracture strain of 1120% at lower pH (pH
2.14) and around 120% at higher pH (pH 6.91)
Fracture strength varied from 0.09MPa (pH 6. 91) to 0.5Mpa (pH 2.14).
First linear part of the tensile curve gave the Young’s Modulus of each sample
Modulus varied from 165KPa (pH 6.91) to 346 KPa(pH 2.14)
Actuation test Gels of varying thickness were used Cyclic transaction between pH 4.72 and pH 7.96
Fig 4 Cyclic transaction between pH 4.72 and pH 7.96 of 1.5mm thick gel
Maroon color – pH 4.72 to pH 7.96
Blue color – pH 7.96 to pH 4.72
Actuation test
Fig: 5 Cyclic actuation of 0.5mm thick gel
Actuation test
Fig: 6 Cyclic actuation of 0.16mm thick gel
Actuation test
The 1.5 mm thick wire took more time for expansion and contraction when compared to the other two.
The transactions took place due to the effect of pH on the gel and due to the applied stress.
Diffusion took place along the axis where force was applied.
ConclusionActuation behavior of the gel was studied
with the help of testing swellability and mechanical properties of gel.
The strength of the hydrogel was not as high as anticipated.
As the thickness of the gel decreases, the quicker response towards pH will be showed by the gel.
AcknowledgementDr. Sureyya Saricilar,-whose
encouragement, guidance and support from the initial to the final level enabled me to develop an understanding of the subject.
Prof. Geoff Spinks, who made available his support in a number of ways.
I am indebted to Dr. Philip Whitten and Gina Gilbert who trained me to use the mechanical tester at IPRI.
Any Questions ?????