Characterization and analysis of extended-wear silicone hydrogel contact lenses utilizing novel silicone macromers.

Contact lenses are one of the most successful biomaterials in history with a global market estimated to be worth over $17 billion in 2025. Silicone hydrogel contact lenses dominate the market and are complex biphasic biomaterials with several critical material properties needed for clinical use. Careful consideration of composition and chemistry is needed to identify formulations of lenses meeting all commercial standards with the potential for improved manufacturability, cost, and/or next generation use. Four silicone macromers were investigated in this work with varying symmetry of siloxane units and macromer structure, number of siloxane groups, branching, length, and concentration. Novel silicone hydrogel lenses were produced and evaluated for optical transmittance, elastic modulus, oxygen transmissibility, water content, and surface wettability. Several lenses met commercial standards and demonstrated an increase in oxygen permeability (Dk) and inverse relationship with elastic modulus and siloxane concentration, respectively. A hydrophobic/hydrophilic ratio below 1.4 was needed for a co-continuous water phase. Substitution of methoxypropyl groups for butyl groups increased hydrophobic microdomains leading to decreased optical quality and mechanical properties. Generally, fluorine-containing silicone macromers allowed for a wider range of successful compositions, and above a certain hydrophilic composition, the presence of trifluoropropyl groups resulted in improved solubility and optically clear lenses. Data also showed asymmetric siloxane macromers have potential to meet critical lens properties at lower overall siloxane content. New lens materials with wider composition ranges meeting all clinical lens properties is a significant challenge and may significantly expand the field.

Applications of Hybrid Polymers Generated from Living Anionic Ring Opening Polymerization.

Increasingly precise control of polymer architectures generated by "Living" Anionic Ring-Opening Polymerization (Living AROP) is leading to a broad range of commercial advanced material applications, particularly in the area of siloxane macromers. While academic reports on such materials remain sparse, a significant portion of the global population interacts with them on a daily basis-in applications including medical devices, microelectronics, food packaging, synthetic leather, release coatings, and pigment dispersions. The primary driver of this increased utilization of siloxane macromers is their ability to incorporate the properties of silicones into organic structures in a balanced manner. Compared to organic polymers, the differentiating properties of silicones-low Tg, hydrophobicity, low surface energy, and high free molal space-logically lend themselves to applications in which low modulus, release, permeability to oxygen and moisture, and tactile interaction are desired. However, their mechanical, structural and processing properties have until recently precluded practical applications. This review presents applications of "Living" AROP derived polymers from the perspective of historical technology development. Applications in which products are produced on a commercial scale-defined as not only offered for sale, but sold on a recurrent basis-are emphasized. Hybrid polymers with intriguing nanoscale morphology and potential applications in photoresist, microcontact printing, biomimetic soft materials, and liquid crystals are also discussed. Previously unreported work by the authors is provided in the context of this review.

Single-Molecule Orthogonal Double-Click Chemistry-Inorganic to Organic Nanostructure Transition.

Thiasilacyclopentane (TSCP) and azasilacyclopentane (ASCP) heteroatom cyclics have proven capable of rapidly converting hydroxylated surfaces to functionalized surfaces in inorganic click reactions. In this work, we demonstrate that the use of these reagents can be extended to "simultaneous double-clicking" when both inorganic and organic substrates are present at the onset of the reaction. The simultaneous double-click depends on a first ring-opening click with an inorganic substrate that is complete in ∼1 s at 30 °C and results in the reveal of a cryptic mercaptan or secondary amine group, which can then participate in a second click with an organic substrate. TSCPs and ASCPs can take part in tandem double-click reactions in which the organic substrate is added to the reaction mixture after the initial inorganic click reaction is completed. Additionally, ASCPs with exocyclic functionality, specifically N-alkenyl-, N-aminoalkyl, and N-alkynyl-ASCPs, are shown to be options for tandem double-clicking in which functionalization proceeds in two independent steps and the sequence of the double-click reaction can be reversed.

Synthesis and Exploratory Deposition Studies of Isotetrasilane and Reactive Intermediates for Epitaxial Silicon.

A synthetic method is presented for the production of isotetrasilane, a higher order perhydridosilane, with the purity and volume necessary for use in extensive studies of the chemical vapor deposition (CVD) of epitaxial silicon (e-Si) thin films. The chemical characteristics, thermodynamic properties, and epitaxial film growth of isotetrasilane are compared with those of other perhydridosilanes. A film-growth mechanism distinct from linear perhydridosilanes H(SiH2) nH, where n ≤ 4, is reported. Preliminary findings are summarized for CVD of both unstrained e-Si and strained e-Si doped with germanium (Ge) and carbon (C) employing isotetrasilane as the source precursor at temperatures of 500-550 °C. The results suggest that bis(trihydridosilyl)silylene is the likely deposition intermediate under processing conditions in which gas-phase depletion reactions are not observed.

Surface-Triggered Tandem Coupling Reactions of Cyclic Azasilanes.

Cyclic azasilanes have been synthesized for the purpose of developing coupling agents appropriate for a variety of nanotechnologies including surface modification of nanoparticles, nanocrystals, mesoporous materials and substrates. N-Methyl-aza-2,2,4-trimethylsilacyclopentane is representative of this class of compounds. Preliminary data for the treatment of inorganic surfaces, including nanoparticles and oxidized silicon wafers, with cyclic azasilanes suggest high-density monolayer deposition by a ring-opening reaction. Cyclic azasilanes contain a cryptic amine functionality that can perform a subsequent tandem coupling reaction with functional molecules after the surface-triggered ring-opening reaction, allowing for a one-pot self-assembly route on nanostructures. Tandem coupling reactions are demonstrated via addition reactions of the cryptic amine with epoxy and acrylate systems.

Soft Materials with Recoverable Shape Factors from Extreme Distortion States.

Elastomeric polysiloxane nanocomposites with elongations of >5000% (more than 3× greater than any previously reported material) with excellent shape recovery are presented. Highly deformable materials are desirable for the fabrication of stretchable implants and microfluidic devices. No crosslinking or domain formation is observed by a variety of analytical techniques, suggesting that their elastomeric behavior is caused by polymer chain entanglements.

In vitro assessments of reverse glenoid stability using displacement gages are misleading - recommendations for accurate measurements of interface micromotion.

BACKGROUND: Baseplate micromotion of the reverse shoulder glenoid component can lead to implant loosening. We hypothesized that a remotely positioned displacement gage measures elastic deformation of the system rather than actual micromotion at the implant/bone interface. METHODS: Reverse glenoid components were implanted into polyurethane blocks of 3 different densities. A 700 N compressive load was maintained and a vertical 700 N shear load was applied for 1000 cycles. In addition to the typical gage measurement, a digital image analysis of micromotion at the implant/block interface using high resolution cameras was performed. The measurements were validated on human specimens. A finite element model was implemented to study the isolated effect of block deformation on baseplate displacements. FINDINGS: With the gage, typically reported micromotions were measured. Two orders of magnitude lower micromotions were detected using interface image-based analysis. The finite element simulation showed that elastic deformation alone can cause micromotion magnitudes as measured with displacement gages. Polyurethane blocks of 20 and 15 lbs per cubic foot density best reproduced micromotions as measured on human specimens. INTERPRETATION: We found considerably less relative micromotion at the implant/bone interface than previously assumed. Gage measurements quantify elastic deformation and not true interface micromotion. High resolution digital imaging at the implant/bone interface is strongly recommended for an accurate assessment of reverse glenoid component micromotion. Tests should further adopt 20 or 15 pcf bone test surrogates. Further studies are required to identify the failure modes encountered in vivo, and a corresponding in vitro testing methodology can then be developed.

Design of stable polyether-magnetite complexes in aqueous media: effects of the anchor group, molecular weight, and chain density.

The colloidal stability of polymer-stabilized nanoparticles is critical for therapeutic use. However, phosphates in physiological media can induce polymer desorption and consequently flocculation. Colloidal characteristics of PEO-magnetite nanoparticles with different anchors for attaching PEO to magnetite were examined in PBS. The effects of the number of anchors, PEO molecular weight, and chain density were examined. It was observed that ammonium phosphonates anchored PEO to magnetite effectively in phosphate-containing solutions because of interactions between the phosphonates and magnetite. Additionally, a method to estimate the magnetite surface coverage was developed and was found to be critical to the prediction of colloidal stability. This is key to understanding how functionalized surfaces interact with their environment.

Synthesis and colloidal properties of polyether-magnetite complexes in water and phosphate-buffered saline.

Biocompatible magnetic nanoparticles show great promise for many biotechnological applications. This paper addresses the synthesis and characterization of magnetite nanoparticles coated with poly(ethylene oxide) (PEO) homopolymers and amphiphilic poly(propylene oxide-b-ethylene oxide) (PPO-b-PEO) copolymers that were anchored through ammonium ions. Predictions and experimental measurements of the colloidal properties of these nanoparticles in water and phosphate-buffered saline (PBS) as functions of the polymer block lengths and polymer loading are reported. The complexes were found to exist as primary particles at high polymer compositions, and most formed small clusters with equilibrium sizes as the polymer loading was reduced. Through implementation of a polymer brush model, the size distributions from dynamic light scattering (DLS) were compared to those from the model. For complexes that did not cluster, the experimental sizes matched the model well. For complexes that clustered, equilibrium diameters were predicted accurately through an empirical fit derived from DLS data and the half-life for doublet formation calculated using the modified Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Deviation from this empirical fit provided insight into possible additional interparticle hydrophobic interactions for select complexes for which the DLVO theory could not account. While the polymers remained bound to the nanoparticles in water, most of them desorbed slowly in PBS. Desorption was slowed significantly at high polymer chain densities and with hydrophobic PPO anchor blocks. By tailoring the PPO block length and the number of polymer chains on the surface, flocculation of the magnetite complexes in PBS was avoided. This allows for in vitro experiments where appreciable flocculation or sedimentation will not take place within the specified time scale requirements of an experiment.

Stability of polydimethylsiloxane-magnetite nanoparticle dispersions against flocculation: interparticle interactions of polydisperse materials.

The colloidal stability of dispersions comprised of magnetite nanoparticles coated with polydimethylsiloxane (PDMS) oligomers was investigated theoretically and experimentally. Particle-particle interaction potentials in a theta solvent and in a good solvent for the PDMS were predicted by calculating van der Waals, electrostatic, steric, and magnetic forces as functions of interparticle separation distances. A variety of nanoparticle sizes and size distributions were considered. Calculations of the interparticle potential in dilute suspensions indicated that flocculation was likely for the largest 1% of the population of particles. Finally, the rheology of these complexes over time in the absence of a solvent was measured to probe their stabilities against flocculation as neat fluids. An increase in viscosity was observed upon aging, suggesting that some agglomeration occurs with time. However, the effects of aging could be removed by exposing the sample to high shear, indicating that the magnetic fluids were not irreversibly flocculated.