Self-structuring of lamellar bridged silsesquioxanes with long side spacers

Diurea cross-linked bridged silsesquioxanes (BSs) C(10)C(11)C(10) derived from organosilane precursors, including decylene chains as side spacers and alkylene chains with variable length as central spacers (EtO)(3)Si- (CH(2))(10)-Y(CH(2))(n)-Y-(CH(2))(10)-Si(OEt)(3) (n = 7, 9-12; Y = urea group and Et = ethyl), have been synthesized through the combination of self-directed assembly and an acid-catalyzed sol gel route involving the addition of dimethylsulfoxide (DMSO) and a large excess of water. This new family of hybrids has enabled us to conclude that the length of the side spacers plays a unique role in the structuring of alkylene-based BSs, although their morphology remains unaffected. All the samples adopt a lamellar structure. While the alkylene chains are totally disordered in the case of the C(10)C(7)C(10) sample, a variable proportion of all-trans and gauche conformers exists in the materials with longer central spacers. The highest degree of structuring occurs for n = 9. The inclusion of decylene instead of propylene chains as side spacers leads to the formation of a stronger hydrogen-bonded urea-urea array as evidenced by two dimensional correlation Fourier transform infrared spectroscopic analysis. The emission spectra and emission quantum yields of the C(10)C(n)C(10) Cm materials are similar to those reported for diurea cross-linked alkylene-based BSs incorporating propylene chains as side spacers and prepared under different experimental conditions. The emission of the C(10)C(n)C(10) hybrids is ascribed to the overlap of two distinct components that occur within the urea cross-linkages and within the siliceous nanodomains. Time-resolved photoluminescence spectroscopy has provided evidence that the average distance between the siliceous domains and the urea cross-links is similar in the C(10)C(n)C(10) BSs and in oxyethylene-based hybrid analogues incorporating propylene chains as side spacers (diureasils), an indication that the longer side chains in the former materials adopt gauche conformations. It has also allowed us to demonstrate for the first time that the emission features of the urea-related component of the emission of alkylene-based BSs depend critically on the length of the side spacers

Redesigned Silk: A New Macroporous Biomaterial Platform for Antimicrobial Dermal Patches with Unique Exudate Wicking Ability

Silk is one of the most important materials in the history of medical practice. Owing to its excellent strength, biocompatibility and degradability, silk from Bombyx mori – which is structured as a concentric assembly of silk fibroin (SF) coated by a sheath of sericin (SS) – has long been used for wound treatment. Here, we recapitulate for the first time the topology of native silk fibers using a radically new materials design-oriented approach to achieve unprecedented porous dermal patches suitable for controlled drug delivery. The method implies four steps: (1) removing SS; (2) creating anisotropic macroporosity in SF via ice templating; (3) stabilizing the SF foam with a methanolic solution of Rifamycin (Rif) antibiotic; and (4) coating Rif-loaded redesigned SF foams with a SS sheath. The core-shell SS@SF foams exhibit water wicking properties accommodate up to ~20% lateral deformation. Moreover, monitoring of antibacterial activity against Staphylococcus aureus revealed that the SS@SF foams’ Rif release extended up to 9 days. We anticipate that reverse-engineering of silk foams opens exciting new avenues towards the fabrication of advanced drug eluting silk-based biomaterial platforms with improved performance. The present approach can be generalizable to re-build multicomponent biological materials with tunable porosity.<br /

Lamellar Salt-Doped Hybrids with Two Reversible Order/Disorder Phase Transitions

A lamellar bilayer hierarchically structured amide cross-linked alkyl/siloxane hybrid matrix (mono-amidosil, m-A(14)) was doped with a wide concentration range of potassium triflate (KCF₃SO₃), magnesium triflate (Mg­(CF₃SO₃)₂), and europium triflate (Eu­(CF₃SO₃)₃). In the K⁺-, Mg²⁺-, and Eu³⁺-based samples with <i>n</i> ≥ 5, 20, and 60 (where <i>n</i> is the molar ratio of amide CO groups per cation), respectively, the original lamellar structure of m-A(14) coexists with a new lamellar phase with lower interlamellar distance. The texture of the mono-amidosils doped with K⁺, Mg²⁺, and Eu³⁺ ions mimics cabbage leaves, foliated schist, and sea sponges, respectively. In the three series of materials, the cations bond to the oxygen atoms of the amide carbonyl groups. The amide–amide hydrogen-bonded array of m-A(14) is less perturbed by the inclusion of KCF₃SO₃ and Mg­(CF₃SO₃)₂ than by the incorporation of Eu­(CF₃SO₃)₃. The degree of ionic association is low for <i>n</i> ≥ 20. The cations coordinate to the oxygen atoms of the triflate ions, forming contact ion pairs at higher salt content. In the Mg­(CF₃SO₃)₂- and Eu­(CF₃SO₃)₃-containing materials with <i>n</i> = 5 and 10, respectively, crystalline salt is formed. The structural changes undergone by the alkyl chains of selected mono-amidosils in a heating/cooling cycle are reversible, are time-independent, and exhibit two distinct hysteresis domains, one associated with the order/disorder phase transition of the original lamellar bilayer structure of m-A(14) and the second one associated with the order/disorder phase transition of the new lamellar bilayer structure formed in the presence of the salts