Controlled
release of drugs from medical implants is an effective
approach to reducing foreign body reactions and infections. We report
here on a one-step 3D printing strategy to create drug-eluting polymer
devices with a drug-loaded bulk and a drug-free coating. The spontaneously
formed drug-free coating dramatically reduces the surface roughness
of the implantable devices and serves as a protective layer to suppress
the burst release of drugs. A high viscosity liquid silicone that
can be extruded based on its shear-thinning property and quickly vulcanize
upon exposure to ambient moisture is used as the ink for 3D printing. S-Nitrosothiol type nitric oxide (NO) donors in their crystalline
forms are selected as model drugs because of the potent antimicrobial,
antithrombotic, and anti-inflammatory properties of NO. Direct ink
writing of the homogenized polymer-drug mixtures generates rough and
ill-defined device surfaces because of the exposed S-nitrosothiol microparticles. When a low-viscosity silicone (polydimethylsiloxane)
is added into the ink, this silicone diffuses outward upon deposition
to form a drug-free outermost layer without compromising the integrity
of the printed structures. S-Nitrosoglutathione (GSNO)
or S-nitroso-N-acetylpenicillamine
(SNAP) embedded in the printed silicone matrix releases NO under physiological
conditions from days to about one month. The microsized drug crystals
are well-preserved in the ink preparation and printing processes,
which is one reason for the sustained NO release. Biofilm and cytotoxicity
experiments confirmed the antibacterial property and safety of the
printed NO-releasing devices. This additive manufacturing platform
does not require dissolution of drugs and involves no thermal or UV
processes and, therefore, offers unique opportunities to produce drug-eluting
silicone devices in a customized manner.
SynopsisMany UV-cured acrylates, epoxides, and thiol-enes suffer a dramatic, reversible loss of tensile strength during exposure to moisture and/or elevated temperatures. Certain formulations are especially sensitive and lose up to 95% of their dry tensile strength in a humid environment. Glass transition temperatures of these materials are also much lower in high humidity than they are in low humidity. It is proposed that these losses of physical properties in high humidity are due to reduced intersegmental attractions of polymer chains caused by preferential hydrogen bonding to water.
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