1National Institute for Laser, Plasma and Radiation Physics - INFLPR, Bucharest-Magurele, Romania 2 University of Bucharest, Faculty of Chemisty, 4-12 Regina Elisabeta Street, Bucharest, Romania

3 University of Bucharest, Faculty of Physics, Atomistilor Street, no. 405, Magurele, Romania

*Correspondent author: maria.dumitrascu@inflpr.ro

Radiation synthesis and characterization of the

network structure of PVP- collagen

superabsorbent hydrogels

A. Scarisoreanu1, M. Demeter1,2*, I. Calina1,3, C. Vancea1,3, E. Stancu1,3, E. Badita1

Fourth International Conference on Radiation and Applications in Various Fields of Research

May 23 – 27, 2016, Nĭs, Serbia

Outline

1. Introduction

2. Experimental section

2.1. Synthesis of PVP-collagen superabsorbent hydrogels

2.2. Experimental setup

2.2. Characterization

3. Results and discussions: 3.1. Gel fraction

3.2. Swelling degree

3.3. Hydrogel compositions

3.4. Rheological analysis (G’ and G’’ determination)

3.5. Network parameters

4. Conclusions

1. Introduction – Superabsorbent polymers

Definiton: moderately crosslinked, 3-D, hydrophilic network polymers that

can absorb and conserve considerable amounts of aqueous fluids even under

certain heat or pressure [1].

Applications:

• diaper industry

• agriculture

• medicine, pharmacy

• tissue engineering

• wound dressings

Fig. 1. Example of PVPCOL hydrogels:

A - swollen COLPVP (70 :30)

B - dried COLPVP hydrogels;

C - swollen COLPVP hydrogel (50 :50)

SD =10 000 %

The purpose of study

• to develop new PVPCOL superabsorbent hydrogel

with better swelling, network parameters and

mechanical properties through electron beam

radiation synthesis in the presence of sodium

salts of acrylic acid and a water soluble crosslinking

agent, N’N methylene-bis-acrylamide to be use in

medical field as wound dressings.

Collagen Type I (1%, w/w) Mw = 300 000 g/mol

Polyvinylpirrolidone (10%, w/w) Mw = 360 000 g/mol

2.1. Synthesis of PVP-collagen superabsorbent hydrogels

Mixtures of PVP-collagen

30:70, 50:50 and 70:30

0.075; 0.05; 0.02 moles of Acrylic Acid (99%, anhydrous)

0.07; 0.04; 0.013 moles of NaOH

2 %, 1%; 0.5 % of N’N-Methylenebis(acrylamide) 99%

Fig. 2. Plastic syringes

with PVP-collagen

blends before EB

irradiation

2.2. Experimental setup – electron beam (EB) irradiation

• Linear electron accelerator ALIN 10

(6. 23 MeV, INFLPR, Magurele -

Romania)

• Absorbed doses:

• 5; 7.5; 10; 12.5; 25; and 40 kGy

• Average dose rate: 1.88 kGy/min.

• Dosimetry:

- graphite calorimeter (built by our

group according to ISO/ASTM 51631

[5] and calibrated at the Institute of

Nuclear Chemistry and Technology,

Poland). Fig. 3. PVP-collagen hydrogels after

EB irradiation

3.1. Gel fraction

The sol fraction was removed by

immersing the cylindrical hydrogel

samples with the thickness of 4-5

mm in deionised water for 48 h at

constant room temperature (25ºC),

in accordance with the method

described by Nagasawa et al. [6].

After 48 h, the swollen gels were

dried again in a vacuum oven at a

constant temperature to constant

weight.

The gel fraction (G) was calculated

from the initial dry gel weight (Wi)

and the dried insoluble part of the

sample after water extraction

(Wd):

Fig. 3. Gel fraction of PVPCOL hydrogels with

0.02 moles AAc and 0.5 % NMBAm

% *1  00   d

i

WG

W

3.2. Swelling degree (1)

Hydrogel dried samples with a 0.1-0.2

g mass were placed in silk bags,

weighed and then immersed in

deionised water. At the established

reading time, the silk bags were moved

out, carefully blotted with filter paper

and then weighed again.

After swelling, based on dry (Wd) and

swollen (Ws) gel weights, the swelling

degree (SD) was calculated as:

Fig. 4 . Swelling degree of PVPCOL hydrogels

A - with 0.075 moli AAc and 2% NMBAm

B - with 0.05 moli AAc and 1% NMBAm

A

B

     

  100

s d

d

W WSD x

W

3.2. Swelling degree (2)

Fig. 5. Swelling degree of PVPCOL hydrogels

- with 0.02 moles AAc and 0.5 % NMBAm

3.3. Hydrogel compositions – FTIR investigations

Fig. 6. FTIR spectra of PVPCOL dried hydrogels

with 0.075 moli AAc and 2% NMBAm

The ATR-FTIR spectra are

presented only in the 4000 - 2500

cm-1 range, this area is the most

specific for hydrogels structure.

Hydrogels present a large band

between 3550 and 3000 cm−1

linked to the stretching O–H from

the intermolecular and intra-

molecular hydrogen bonds.

The vibrational band observed

between 2800 and 3000 cm−1

refers to the stretching C–H from

alkyl groups [7].

The shifting of the FTIR band

position towards the lower

wavenumbers or increase of

intensity can be related to the

crosslinking reactions.

0.02 moles AAc

0.5 % NMBAm

0.05 moles Aac

1% NMBAm

In the FTIR spectra of PVP-collagen

hydrogels, the large band specific to

stretching vibration of νO–H was found

at 3330, 3367 and 3390 cm-1.

This band shifted toward the higher

wavenumbers function of hydrogel

composition.

The stretching vibrations of alkyl groups

were found at 2920 cm-1 and 2855 cm-1.

In the case of PVP-collagen 50:50 and

70:30, the increase of band intensity of

O–H function of radiation dose was

observed

At higher absorbed dose the position of

absorption band is shifted to lower wave

numbers.

3.4. Rheological analysis - (G’ and G’’ determination)

• In order to determine the elastic moduli of the gels (G’-elastic

modulus and G”-viscous modulus), oscillatory rheological

measurements were performed.

• All measurements were performed at 25oC in the linear viscous

elastic region, at the rate of deformation γ = 0.1-1% and the

frequency range of ω0 = 0.01-1 Hz, using a Thermo MARS II

Rheometer equipped with a 20 mm diameter plate (plate geometry).

The gap size was settled at 0.139 mm.

• This measurements were performed to determine the strengthen of

PVPCOL hydrogels and for calculation of molecular weight between

crosslinks (Mc)

3.5. Network parameters

n2,x polymer volume fraction in the swollen state and

after irradiation

Mc molecular weight of the polymer chain between two

crosslinks

x mesh size

1

21/ (1 / ( 1)x w wn

1/ 32 / 3' 

2 2MG A RT

c r m

1/ 22

1/ 3 2

McC

s nl

Mr

x n

Tabel 1. Network parameters of PVP-collagen hydrogel

Dose

(kGy)

G’

(Pa)

(g/mol)

(mol/cm3)

ξ

(nm)

5 6344 7174 1.39E-04 56

7.5 4950 9293 1.08E-04 60

10 4595 9891 1.01E-04 63

12.5 3923 11745 8.51E-05 69

25 3574 15517 6.44E-05 72

40 3601 13498 7.41E-05 77

The elastic modulus (G’) decreased with radiation dose

According to rheological tests, the stronger gel was obtained at 5 kGy for

PVPCOL hydrogel with 70:30 in composition

The Mc increase as function of absorbed dose up to 25 kGy

The crosslinking density decreased with the absorbed dose, as a direct

consequence of the increase of the mesh size

4. Conclusions

• PVP-COL superabsorbent hydrogels with a

swelling degree over 10 000% were obtained

• Gels with excellent mechanical properties (6 kPa)

can be obtained from a COLPVP 70:30 blend

• The addition of 0.02 moles of AAc and

0.5 % NMBAm and irradiating at 5 kGy, has given

the best results for the PVP-collagen hydrogel

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Thank you!

Acknowledgement: This work was supported by the National Authority for Scientific Research and Innovation, Romania (Nucleus Program PN0939/0402) and INFLPR.