Multi-layer PDMS films having antifouling property for biomedical applications.

Poly(dimethylsiloxane) (PDMS) elastomer is now a well-known material for packaging implantable biomedical micro-devices owing to unique bulk properties such as biocompatibility, low toxicity, excellent rheological properties, good flexibility, and mechanical stability. Despite the desirable bulk characteristics, PDMS is generally regarded as a high-flux material for oxygen and water vapor to penetrate compared with other polymeric barrier materials, which is related to the defect-induced penetration through the packaging coating prepared by the traditional deposition techniques. Besides, its hydrophobic nature causes serious fouling problems and limits the practical application of PDMS-based devices. In this work, the performance of silicone thin films as a packaging layer was improved by the fabrication of the roller-casted multiple thin layers to minimize a defect-induced failure. To confer hydrophilicity and cell fouling resistance, high-density and well-defined poly(oligo(ethylene glycol) methacrylate) (POEGMA) brushes were tethered via the surface-initiated atom transfer radical polymerization (SI-ATRP) technique on the roller-casted multiple thin PDMS layers. The characteristics of fabricated substrates were determined by static water contact angle measurement, X-ray photoelectron spectroscopy, and attenuated total reflection-Fourier transform infrared spectroscopy. In vitro cell behavior of POEGMA-grafted PDMS substrates was evaluated to examine cell-fouling resistance.

In situ probing of switchable nanomechanical properties of responsive high-density polymer brushes on poly(dimethylsiloxane): An AFM nanoindentation approach.

Nanomechanical characteristics of end grafted polymer brushes were studied by AFM based, colloidal probe nanoindentation measurements. A high-density polymer brush of poly(2-hydroxyethyl methacrylate) (PHEMA) was precisely prepared on the surface of a flexible poly(dimethylsiloxane) (PDMS) substrate oxidized in ultraviolet/ozone (UVO). Exposure times less than 10min resulted in laterally homogeneous oxidized surfaces, characterized by a SiOx thickness ∼35nm and an increased modulus up to 9MPa, as shown by AFM nanoindentation measurements. We have demonstrated that a high surface density of up to ∼0.63chains/nm2 of the well-defined PHEMA brushes can be grown from the surface of oxidized PDMS by surface-initiated atom transfer radical polymerization (SI-ATRP) from trimethoxysilane derivatives mixed-SAM. The reversible nanomechanical changes of PHEMA layer between extended (hydrated state) and collapsed (dehydrated state) chain upon immersing in selective and non-selective solvents were investigated by in situ AFM nanoindentation analysis in liquid environments. The elastic modulus derived from force-indentation curves obtained for swollen PHEMA grafted chains in water was estimated to be equal 2.7±0.2MPa, which is almost two orders of magnitude smaller than the modulus of dry PHEMA brush. Additionally, under cyclohexane immersion, the modulus of the PHEMA layer decreased by one order of magnitude, indicating a more compact chain packing at the PDMS surface.

Relationships between the morphology, swelling and mechanical properties of poly(dimethyl siloxane)/poly(acrylic acid) interpenetrating networks.

A limitation in the use of hydrophilic polymers as implantable devices is their inherently poor mechanical strength. Using interpenetrating polymer networks (IPNs) consisting of both hydrophilic and hydrophobic networks is an effective method of strengthening these polymers. In this work, a series of poly(dimethyl siloxane) (PDMS)/poly(acrylic acid) (PAAc) sequential IPNs were synthesized and their properties, including swelling, morphology, and mechanical strength, were investigated. A reinforcing effect of the addition of PAAc to PDMS was observed at a concentration of 20 wt%, where this component had a bimodal size distribution. All of the IPNs exhibited rubbery behavior in the swollen state. Phase inversion in the IPNs occurred at about 60 wt% of PAAc. However, the swelling data showed that the phase inversion in the swollen state occurred at PAAc contents lower than those for dry IPNs. The improved cell behavior, reported in previous works for PDMS/PAAc IPNs with about 20 wt% PAAc, can, in addition to the increased surface wettability, be attributed to the bimodality of PAAc particles size distribution in the IPN.