Biofunctionalization of polydimethylsiloxane (PDMS) for tissue engineering applications

Abstract

PDMS was used as the screening platform of stem cell differentiation as a result of matrix stiffness. PDMS was chosen because it is easy to fabricate and the modulus could be easily tuned using the different curing agent ratio. As PDMS is hydrophobic and has low surface reactivity, surface modification of PDMS needs to be carried out first. To ensure effective biofunctionalization of PDMS, an optimum material stiffness, wettability and activated surface of PDMS must be obtained. To achieve the aforementioned condition, oxygen plasma treatment is conducted on three kind of substrate with three kinds of PDMS substrate fabricated with different elastomer base to curing agent ration, 1:10, 1:50, and 1:70. The Young’s moduli of the three kinds of PDMS substrates are 399 kPa, 45.6 kPa and 5.49 kPa respectively, as assessed by rheometer.

There are three variables of plasma treatment condition that can be manipulated to achieve an activated PDMS surface, namely the plasma power (50 W, 100 W, and 150 W), exposure time (30 s, 60 s, 90s, and 120 s) and oxygen flow rate (10 sccm, 15 sccm, and 20 sccm). The activity of plasma treated PDMS surface was evaluated by the free radical amount generated, which was measured by DPPH assay. Moreover, the wettability of the plasma treated PDMS surface was measured using goniometer.

The maximum amount of free radical concentration was achieved under the duration of 60 s, plasma power of 50 W and oxygen flow rate of 15 sccm for 1:10 ratio sample; duration of 90 s, plasma power of 100 W and oxygen flow rate of 20 sccm for 1:50 ratio sample, and duration of 120 s, plasma power of 150 W and oxygen flow rate of 10 sccm for 1:70 ratio sample.

Because of its hydrophobicity, PDMS has a water contact angle at around 108o before surface modification. After oxygen plasma treatment, the water contact angle drop to below 35o, which shows a hydrophilic properties of the treated surface and hence a better wettability.