Development of an oxirane/acrylate interpenetrating polymer network (IPN) resin system.

OBJECTIVE: Develop a hydrophobic, degradation-resistant dental restorative based on an Oxirane-Acrylate IPN System (OASys) with low shrinkage-stress to substantially extend clinical lifetime. METHODS: Unfilled OASys blends were prepared using dipenta-erythritol-hexaacrylate (DPHA) and p-cycloaliphatic-diepoxide (EP5000). Varying proportions of camphorquinone/iodonium photoinitiator, with a co-reactant oligomeric-diol, served as the experimental curing system. The effects of oxirane-acrylate ratio on the degree-of-cure (Durometer-D hardness), hydrophobicity (contact angle), mechanical properties (3-point bending), near-infrared FTIR degree-of-conversion (DoC), polymerization shrinkage, and shrinkage stress were determined. 70:30 BisGMA:TEGDMA resin served as control. RESULTS: Oxirane tended to decrease hardness and increase hydrophobicity. 0:100, 25:75, 50:50 EP5000:DPHA are harder after 24h than control. 75:25 and 100:0 EP5000:DPHA increased in hardness over 24h, but were softer than control. All groups increased in contact angle over 24h. After 24h, 50:50, 75:25 and 0:100 EP5000:DPHA were more hydrophobic (∼75-84°) than the control (∼65°). Acrylate DoC was ∼60% across all experimental groups. Initial oxirane conversion varied from ∼42% in 100:0 EP5000:DPHA to ∼82% 75:25 EP5000:DPHA. However, oxirane DoC increased for 100:0 EP5000:DPHA to ∼73° over 24h, demonstrating dark cure. Moduli and ultimate transverse strengths of OASys groups were higher than for 0:100 EP5000:DPHA, with 50:50 EP5000:DPHA having higher modulus than other experimental groups. However, the control had higher modulus and UTS than all experimental groups. Volumetric shrinkage averaged 7% for experimental groups, but stress decreased dramatically with increasing oxirane content. SIGNIFICANCE: Hydrophobic, low shrinkage-stress OASys resins are promising for development of composites that improve longevity and reduce the cost of dental care.

Identification of a signaling cascade that maintains constitutive δ-opioid receptor incompetence in peripheral sensory neurons.

µ-Opioid receptor (MOR) agonists are often used to treat severe pain but can result in adverse side effects. To circumvent systemic side effects, targeting peripheral opioid receptors is an attractive alternative treatment for severe pain. Activation of the δ-opioid receptor (DOR) produces similar analgesia with reduced side effects. However, until primed by inflammation, peripheral DOR is analgesically incompetent, raising interest in the mechanism. We recently identified a novel role for G-protein-coupled receptor kinase 2 (GRK2) that renders DOR analgesically incompetent at the plasma membrane. However, the mechanism that maintains constitutive GRK2 association with DOR is unknown. Protein kinase A (PKA) phosphorylation of GRK2 at Ser-685 targets it to the plasma membrane. Protein kinase A-anchoring protein 79/150 (AKAP), residing at the plasma membrane in neurons, scaffolds PKA to target proteins to mediate downstream signal. Therefore, we sought to determine whether GRK2-mediated DOR desensitization is directed by PKA via AKAP scaffolding. Membrane fractions from cultured rat sensory neurons following AKAP siRNA transfection and from AKAP-knock-out mice had less PKA activity, GRK2 Ser-685 phosphorylation, and GRK2 plasma membrane targeting than controls. Site-directed mutagenesis revealed that GRK2 Ser-685 phosphorylation drives the association of GRK2 with plasma membrane-associated DOR. Moreover, overexpression studies with AKAP mutants indicated that impaired AKAP-mediated PKA scaffolding significantly reduces DOR-GRK2 association at the plasma membrane and consequently increases DOR activity in sensory neurons without a priming event. These findings suggest that AKAP scaffolds PKA to increase plasma membrane targeting and phosphorylation of GRK2 to maintain DOR analgesic incompetence in peripheral sensory neurons.