Medical implants are commonly used in modern medicine but still harbor the risk of microbial infections caused by bacterial biofilms. As their retrospective treatment is difficult, there is a need for biomedical materials that inhibit bacterial colonization from the start without using antibacterial agents, as these can promote resistance development. The promising concept of slippery liquid-infused porous surfaces (SLIPS) possesses enormous potential for this purpose. In the present study, this principle was applied to titanium, a common material in implantology, and its biofilm-repellent properties were demonstrated. To simplify prospective approval of the medical device and to avoid chemical contamination, surface structuring was performed by ultrashort pulsed laser ablation. Four different structures (hierarchical micro- and nanosized spikes, microsized grooves, nanosized ripples, and unstructured surfaces) and five infusing perfluoropolyethers of different viscosities were screened; the best results were obtained with the biomimetic, hierarchical spike structure combined with lubricants of medium viscosities (20-60 cSt at 37 °C, 143 AZ, and GPL 104). The surfaces exhibited extremely low contact angle hysteresis, as is typical for liquid-infused materials and a reliable 100-fold reduction of human oral pathogen Streptococcus oralis biofilms. This characteristic was maintained after exposure to shear forces and gravity. The titanium SLIPS also inhibited adherence of human fibroblasts and osteoblasts. Toxicity tests supported the explanation that solely the surface's repellent properties are responsible for the vigorous prevention of the adhesion of bacteria and cells. This use of physically structured and liquid-infused titanium to avoid bioadhesion should support the prevention of bacterial implant-associated infections without the use of antibacterial agents.

Stromal riboflavin gradients are similar when applied in dextran for 30 minutes and HPMC for 10 minutes. When using HPMC solutions, a shallower cross-linked volume is expected due to a higher corneal hydration. [J Refract Surg. 2016;32(12):798-802.].

Citation: Seiler TG, Ehmke T, Fischinger I, et al. Two-photon fluorescence microscopy for determination of the riboflavin concentration in the anterior corneal stroma when using the Dresden protocol. Invest Ophthalmol Vis Sci. 2015;56:6740-6746. DOI:10.1167/iovs.15-17656 PURPOSE. To determine the riboflavin concentration gradient in the anterior corneal stroma when using the Dresden protocol with different dextran solutions. METHODS.Three different groups of porcine corneas, five each, were compared regarding the riboflavin concentration in the anterior stroma. Before all experiments, stable hydration conditions were established for the corresponding solution. All groups were treated with 0.1% riboflavin in different dextran solutions (15%, 16%, 20%). After imbibition, two-photon microscopy was used to determine fluorescence intensity. For signal attenuation and concentration determination corneas were saturated and measured a second time by twophoton microscopy. Additionally, the distribution was calculated mathematically and compared to the empiric results.RESULTS. Riboflavin concentration is decreasing with depth for all dextran solutions. A nearly constant concentration could be determined over the first 75 lm. Analysis of the fit functions leads to diffusion coefficients of D ¼ 2.97 3 10 À7 cm 2 /s for the 15% dextran solution, D ¼ 2.34 3 10 À7 cm 2 /s for the 16% dextran solution, and D ¼ 1.28 3 10 À7 cm 2 /s for the 20% dextran solution.The riboflavin gradients of the 20% dextran group were statistically significantly different from 15% dextran starting at a depth of 220 lm and deeper (P ¼ 0.047). The 16% dextran group differed statistically at a depth of 250 lm and deeper (P ¼ 0.047). These results show a significant difference to those published previously. CONCLUSIONS.With correct settings two-photon microscopy is a precise way to determine the concentration of riboflavin in cornea. The measured gradient is excellently fit by a Gaussian distribution, which comes out as a solution of Fick's second law.

Multimodal nonlinear microscopy allows imaging of highly ordered biological tissue due to spectral separation of nonlinear signals. This requires certain knowledge about the spectral distribution of the different nonlinear signals. In contrast to several publications we demonstrate a factor of 122 relating the full width at half maximum of a gaussian laser pulse spectrum to the corresponding second harmonic pulse spectrum in the spatial domain by using a simple theoretical model. Experiments on monopotassium phosphate crystals (KDP-crystals) and on porcine corneal tissue support our theoretical predictions. Furthermore, no differences in spectral width were found for epi- and trans-detection of the second harmonic signal. Overall, these results may help to build an optimized multiphoton setup for spectral separation of nonlinear signals.

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