Improving the Performance of a Series-Parallel System Based on Lindley Distribution

In this article, the performance of a series-parallel system is improved. The system components are assumed to follows independently and identically Lindley distributed with three parameters. The system reliability for the given system will be improved by using reduction method, hot, cold and imperfect duplication method. Some reliability measures are derived. Two types of reliability equivalence factors and gamma fractiles are calculated. A numerical example is introduced to explain the theoretical results

A renewably sourced, circular photopolymer resin for additive manufacturing

The additive manufacturing of photopolymer resins by means of vat photopolymerization enables the rapid fabrication of bespoke 3D-printed parts. Advances in methodology have continually improved resolution and manufacturing speed, yet both the process design and resin technology have remained largely consistent since its inception in the 1980s1. Liquid resin formulations, which are composed of reactive monomers and/or oligomers containing (meth)acrylates and epoxides, rapidly photopolymerize to create crosslinked polymer networks on exposure to a light stimulus in the presence of a photoinitiator2. These resin components are mostly obtained from petroleum feedstocks, although recent progress has been made through the derivatization of renewable biomass3,4,5,6 and the introduction of hydrolytically degradable bonds7,8,9. However, the resulting materials are still akin to conventional crosslinked rubbers and thermosets, thus limiting the recyclability of printed parts. At present, no existing photopolymer resin can be depolymerized and directly re-used in a circular, closed-loop pathway. Here we describe a photopolymer resin platform derived entirely from renewable lipoates that can be 3D-printed into high-resolution parts, efficiently deconstructed and subsequently reprinted in a circular manner. Previous inefficiencies with methods using internal dynamic covalent bonds10,11,12,13,14,15,16,17 to recycle and reprint 3D-printed photopolymers are resolved by exchanging conventional (meth)acrylates for dynamic cyclic disulfide species in lipoates. The lipoate resin platform is highly modular, whereby the composition and network architecture can be tuned to access printed materials with varied thermal and mechanical properties that are comparable to several commercial acrylic resins

Hybrid polymer networks of carbene and thiol ene

Thiol/ene-based resorbable elastomers display tough elongation but lack adhesion to soft tissues. Carbene-based bioadhesives (e.g. CaproGlu) allow soft tissue adhesion, but the covalent crosslinks limit extensibility after photoactivation. Herein thiol/ene resorbable elastomers are combined with a carbene bioadhesive into a 3-component hybrid network by exploiting tunable photoactivation of each macromolecule independently or simultaneously. Dual crosslinking was monitored by photorheometry, where 405 nm initiates formation of a thiol/ene elastomeric network, followed by 365 nm activation of diazirine-grafted polycaprolactone tetrol (CaproGlu). Dynamic shear moduli, gelation point, elongation at break, and lap shear stress of the hybrid polymer network are evaluated with respect to absorbed light energy dose. Surface-exposed unreacted CaproGlu enables adhesion of the hybrid network to various substrates, as well as intermolecular crosslinking within the transparent matrix. The network morphology and functional group conversion is evaluated through scanning electron microscopy and infrared spectroscopy, respectively. For the first time, we demonstrate hybrid thiol/ene/diazirine double sided bioadhesives with tunable dynamic moduli in the range of 10–800 kPa and 160 kPa lap-shear adhesion strength.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)Nanyang Technological UniversitySubmitted/Accepted versionThis work is funded by Institute of Advanced Studies Birmingham Visiting Fellowship, ‘Strong Elastomeric Bioadhesives Towards Tendon Repair’; Ministry of Education Tier 1 Grant RT07/20: Fiber-optic orthopaedic implants for bone-implant adhesion, Ministry of Education Tier 2 Grant (MOE2018-T2-2-114): CaproGlu, Double sided wet-tissue adhesives, NTUitive POC (Gap) Fund NGF/2018/05: Aesthetic Applications of CaproGlu Bioadhesives, and A*STAR IAF PP Grant (H19/01/ a0/0II9): CathoGlu Bioadhesives-preventing catheter extravasation and skin infections