Shear-Thinning and Temperature-Dependent Viscosity Relationships of Contemporary Ocular Lubricants

PURPOSE

To evaluate the shear viscosity of contemporary, commercially available ocular lubricants at various shear rates and temperatures and to derive relevant mathematical viscosity models that are impactful for prescribing and developing eye drops to treat dry eye disease.

METHODS

The shear viscosity of 12 ocular lubricants was measured using a rheometer and a temperature-controlled bath at clinically relevant temperatures at which users may experience exposure to the drops (out of the refrigerator [4.3°C]; room temperature [24.6°C]; ocular surface temperature [34.5°C]). Three replicates for each sample at each temperature were obtained using a standard volume (0.5 mL) of each sample. The viscosity of each ocular lubricant was measured over the full range of shear rates allowed by the rheometer.

RESULTS

The shear viscosity of the same ocular lubricant varied significantly among the three temperatures. In general, a higher temperature resulted in smaller viscosities than a lower temperature (an average of -48% relative change from 4.3°C to 24.6°C and -21% from 24.6°C to 34.5°C). At a constant temperature, the viscosity of an ocular lubricant over the studied shear rates can be well approximated by a power-law model.

CONCLUSIONS

Rheological analysis revealed that the ocular lubricants exhibited shear-thinning behavior at the measured temperatures. Differences in the ocular lubricants' formulations and measured temperatures resulted in different viscosities.

TRANSLATIONAL RELEVANCE

When prescribing eye drops, eye care professionals can select the optimal one for their patients by considering a variety of factors, including its rheological property at physiologically relevant shear rates and temperatures, which can improve residence time on the ocular surface, while ensuring appropriate comfort and vision. However, care must be taken when using the derived mathematical models in this study because the in vivo shear behavior of the ocular lubricants has not been examined and might show deviations from those reported when placed on the ocular surface.

In situ monitoring of the morphology evolution of interfacially-formed conductive nanocomposite films and their use as strain sensors

HYPOTHESIS

Understanding and monitoring the film formation of interfacially formed layered films allows for the design of conductive nanocomposite films suitable for strain sensing.

EXPERIMENTS

To understand the mechanism of interfacial film formation, the hexane/water interface was monitored during the evaporation process via confocal laser scanning microscopy. Scanning electron microscopy and atomic force microscopy were utilized to investigate final film morphology. Tensile testing was used to determine their mechanical properties under uniaxial strain.

FINDINGS

Conductive nanocomposite films were formed at the hexane/water interface. Due to their low colloidal stability in hexane, the Vulcan carbon (VC) nanoparticles settled to the hexane/water interface prior to the onset of paraffin wax precipitation. Consequently, after the evaporation of hexane a two-layer structured film was formed. The bottom (water-facing, VC-rich) layer was conductive due to the existence of a percolated network of nanoparticle aggregates, while the top (hexane facing, paraffin-rich) layer was not conductive. The films showed high sensitivity for strains between 1% and 10%. We propose that the mechanism of strain sensing is similar to that of layer-structured sensors fabricated through embedding conductive nanofillers onto flexible polymeric substrates. The advantage of the films derived by the method proposed here is their ease of fabrication as well as their low cost.

Comparison of Arthrodesis and Non-fusion to Treat Lisfranc Injuries

OBJECTIVE

"Lisfranc joint injury" is comprised of a tarsometatarsal joint-complex injury. The Lisfranc complex injury is always a challenge for orthopedists, and the optimum treatment is still up for debate. Anatomic reduction and stable internal fixation prove to have no satisfactory outcomes. This research aims to compare the clinical curative effects, complications and radiographic features of arthrodesis and non-fusion of the Lisfranc joint in the follow-up of the patients who suffered Lisfranc injuries.

METHODS

A comparative retrospective study of 25 patients with acute or subacute Lisfranc complex injuries was conducted between September 2013 and March 2015 in the First Affiliated Hospital of Soochow University. All patients were classified by Myerson classification. Eight patients were treated with arthrodesis, while 17 patients received non-fusion operations. The clinical curative effects, complications and image differences were compared between the two groups. American Orthopaedic Foot and Ankle Society (AOFAS) hindfoot score, Short Form-36 (SF-36) and Visual Analogue Scale (VAS) score were evaluated for each patient during the follow-up. All statistics were analyzed using the SPSS software system.

RESULTS

All fractures healed for both the arthrodesis group and the non-fusion group. Patients in the arthrodesis group had a higher AOFAS score compared with patients in the non-fusion group (94.00 vs. 88.58, P = 0.034). Complications occurred in eight patients (8/17, 47%) in the non-arthrodesis group, including the second and third phalanx abduction (1), talipes cavus (2), eversion deformity of front foot (3), eversion deformity of calcaneus (1), as well as postoperative infection (1). Only two patients (2/8, 25%) in the arthrodesis group suffered complications. One was a limitation of motion of the front foot and pain during walking; the other was an eversion deformity of front foot.

CONCLUSION

Primary arthrodesis has advantages compared to primary open reduction and internal fixation (ORIF): reduced foot deformity rates, sustained biomechanical morphology of the feet, reduced complications, higher level of function recovery, shorter time of surgical procedures, fewer complications, higher AOFAS score and fewer frequency of complications. According to our research, primary arthrodesis may be a better choice for treating Lisfranc injury.

In vitro and in vivo combined antibacterial effect of levofloxacin/silver co-loaded electrospun fibrous membranes

The Lev@MSN@Ag–PLLA fibers provided an advanced synergistic antibacterial nanoplatform of low dosage for the treatment of drug-resistant bacterial infections.

Synthesis, characterization, and air stability study of pyrimido[4,5-g]quinazoline-4,9-dione-based polymers for organic thin film transistors

This study reports the synthesis of two novel π-conjugated pyrimido[4,5-g]quinazoline-4,9-dione (PQ) based polymers and reveals that the air stability of PQ based polymers is critically affected by the donor comonomer.