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 ?????