References[1] Nasef MM, Guven O. Prog Polym Sci. 2012;37(12):1597-1656.[2] Quinn JF, Davis TP, Barner L, Barner-Kowollik C. Polymer. 2007;48(22):6467-6480.[3] Mosmann T. J Immunol Methods. 1983;65(1-2):55-63.

« Marie Skłodowska-Curie » scientific award in the field of 

materials science

Organisers:

Partners:

Marta Walo

Institute of Nuclear Chemistry and Technology

Dorodna 16 Street, Warsaw

Modification of polyurethane surface by RAFT mediated grafting initiated by gamma radiation

0

20

40

60

80

100

120

DG = 14%

Mn = 40400 Da

DG = 8%

Mn = 27650 Da

Me

tab

oli

c a

cti

vit

y /

%

24 h 72 h 7 days

PUR DG = 4%

Mn = 12960 Da

Surface modification is an attractive way of functionalization of wide range of polymers dedicated to different applications [1]. In the case of polyurethane (PUR) biomaterials contacting with blood, such as elements of artificial heart valves, vascular prostheses and catheters made of polyurethane, the hydrophobic character of the surface limiting their application. Therefore, the surface must be modified by various methods in order to obtain a material possessing the desired surface properties. One of the techniques used for this purpose is radiation grafting, but the recent research focuses on a novel method using a controlled radical polymerization of reversible addition - fragmentation chain transfer polymerization called RAFT polymerization. RAFT mediated grafting initiated by ionizing radiation in contrast to the traditional methods currently used, enable control the length of the grafted chains leading to a new material with a different topology and specific surface properties [2].

Conclusions

The results obtained by RAFT mediated grafting confirmed that this is a promising direction of the surface functionalization of polyurethanes. Even a small amount of grafted monomer improves the wettability of the PUR surface. Polyurethane matrix coated in poly(N-isopropylacrylamide), the polymer classified into group of thermosensitive polymers, exhibited hydrophilic properties in water at 25 oC, while at 35 oC the surface properties change into hydrophobic. Additionally narrow molecular weight distribution of grafted chains (PDI<1.3) was obtained. In vitro studies using osteoblast cells MG-63 confirmed that the modified matrices are not cytotoxic when degree of NIPAAm grafting is approximately 14% and an average molecular weight of the grafted chains (Mn) is about 40.000 Da.

40

60

80

100

DG = 14%Mn = 40400 Da

DG = 8% Mn = 27650 Da

DG = 4%, Mn = 12960 Da

Co

nta

ct a

ng

le /

deg

T = 25 oC

T = 35 oC

PUR

Fig.1. Representative SEM micrographs of (A) PUR and (B) PUR-g-PNIPAAm (DG = 14%, Mn = 40400 Da) modified by RAFT mediated grafting.

Cytotoxity test

Motivation RAFT mediated grafting initiated by gamma radiation

RAFT-mediated polymerization was used for grafting of N-isopropylacrylamide onto polyurethane surface to improve biocompability of the matrix surface. The degree of grafting (DG, wt. %) was calculated gravimetrically. The surface of pristine and grafted samples were investigated by scanning electron microscopy (SEM) and contact angle (CA) measurements. Grafting of PNIPAAm onto PUR surface in controlled manner was confirmed by gel permeation chromatography (GPC). In vitro cytotoxity experiments were carried out to study biocompability of pristine and modified samples using MTT assay [3]. Attachment and proliferation of MG-63 osteosarcoma cells on modified polyurethane films was investigated to assess the potential use of this material for biomedical applications.

Contact angle measurements

The purpose of the study

Thermosensitive changes of modified surface depending on molecular weight of grafted chains and grafting degree were studied. PUR samples modified by RAFT-mediated grafting (DG = 14%) showed that the PNIPAAm grafted surface is hydrophilic below the LCST (low critical solution temperature) whereas above 32 oC it shows hydrophobic character.

The growth of MG-63 cells was enhanced in comparison with pristine PUR only for modified PUR-g-PNIPAAm surface with the highest degree of grafting and the number-molecular weight of grafted chains of 40400 Da.

Fig. 2. Water contact angle depending on temperature for PUR and PUR-g-PNIPAAm modified by RAFT mediated grafting.

Fig. 3. Metabolic activity (MTT assay) of MG-63 cells seeded on 96-well microplates coated with PUR and PUR-g-PNIPAAm of different DG after 24 h, 72 h and 7 days.

Scanning electron microscopy (SEM)

A B