Morphological changes of veins and perivenous tissues during endovenous laser coagulation using 2-µm laser radiation and various types of optical fibers.

OBJECTIVE: To determine the morphological changes in veins and perivenous tissues after endovenous laser coagulation (EVLC) using laser radiation with a wavelength of 1910 nm and different types of fibers (bare tip and radial). METHODS: The EVLC procedure was carried out on 22 surface veins of six sheep. The radiation source was a diode-pumped solid-state laser, which was based on a LiYF4:Tm crystal and had an emission wavelength of 1910 nm and a maximum output power of 10 W. Two types of optical fibers were used: (1) bare tip and (2) radial or radial with two rings. Histological and morphometric methods were used, and the statistical digital data were analyzed. RESULTS: The use of a linear endovenous energy density of 20 J/cm and optical bare fibers for veins with diameters of 3-4 mm resulted in a slit-shaped or wide venous wall perforation. A thermal effect was observed on the perivenous connective tissue (PVCT), which caused damage to its structures. Wide perforations were accompanied by complete destruction of the PVCT in the projection of the formed defect. The distance between the remaining vein wall fragment, located opposite to the perforation, and injured small vessels was 257.7 ± 23.6 µm. The radius of thermal damage increased to 2073.5 ± 8.0 µm near the vessel perforation. Using optical radial fibers for veins with diameters of 3.9 ± 0.5 mm did not lead to perforations. The destructive effect of the laser on small vessels of the PVCT extended to a distance of 425.7 ± 22.0 µm. CONCLUSIONS: Analysis of thermal vessel damage in perivenous tissue after EVLC with bare-tip fiber shows that in the projection of a wide perforation, the damaged vessels of the PVCT are located at a large distance from the coagulated vein wall. On the opposite side of the perforation, the distance from the coagulated vein wall to the damaged vessels of the PVCT is significantly reduced because of the minimal output of laser radiation energy through the poorly damaged part of the wall. Using an optical radial fiber facilitates the application of a uniform distribution of thermal energy to the vein wall and damage to all its layers; at the same time, it minimizes the thermal energy that extends beyond the vein wall and damages the surrounding tissue. CLINICAL RELEVANCE: The use of radiation with a wavelength of 1910 nm will make it possible to carry out endovenous laser coagulation of varicose veins at lower power values compared with radiation in the micron and one and a half micron regions of the spectrum. Understanding of morphological changes of veins and perivenous tissues after endovenous laser coagulation with 1910-nm laser radiation and different types of optical fibers (bare-tip, radial, radial 2ring) help predict possible complications and reduce their rate.

Hydrophobic up-conversion carboxylated nanocellulose/fluoride phosphor composite films modified with alkyl ketene dimer.

Hydrophobic up-conversion nanocomposite films have been developed based on TEMPO-oxidized cellulose nanofibrils (TOCNF) modified with alkyl ketene dimer (AKD) as a matrix and MF2:Ho (M = Ca, Sr) as a phosphor. Fabrication of homogeneous, strong and translucent TOCNF/MF2:Ho-AKD films with water contact angle of 123 ±â€¯2° was accomplished with mild drying at 110 °C. These hydrophobic nanocomposite films demonstrated stable up-conversion luminescence in the visible spectral range upon excitation of the 5I7 level of Ho3+ ions by laser irradiation at 1912 nm both under ambient conditions and in a humid atmosphere (92 ±â€¯2% humidity). The absence of luminescence quenching in a high humidity atmosphere for TOCNF/MF2:Ho-AKD composite films was considered to be due to the reliable shielding effect of the hydrophobic TOCNF-AKD matrix. The films show promise for visualizing 2 µm laser radiation in medicine and monitoring of the atmosphere.

Optimization of endovenous laser coagulation: in vivo experiments.

Finding optimal parameters of endovenous laser coagulation using the radiation with a wavelength of 1910 nm. In vivo experiments have been carried out on the small saphenous veins of three sheep of Edilbay breed and the dependence of venous wall and surrounding tissue damage on the radiation power was analyzed on the basis of morphological study results, as well as ultrasound examination and clinical observation of animals in the postoperative period. As radiation source, we used the diode-pumped solid-state laser, based on the LiYF4:Tm crystal, with emission wavelength of 1910 nm. For morphological study, veins were harvested immediately and 40 days after operation. Histological analysis of the vein after treatment with 1.5-W radiation revealed asymmetric wall injury and a thrombus formation in the lumen. The blood thrombus formation and pronounced vein wall damage was observed after treatment with 3-W radiation. Perivenous tissue injury is insignificant and does not lead to postoperative complications as in the case of using 1.5-W radiation. Increasing the radiation power to 4 W results in the total vein wall destruction and the thrombus formation, which persists for 40 days after the procedure. Based on the results of clinical observations of animals with registration of skin wound healing, as well as the results of histological examination of veins harvested immediately after the EVLC and 40 days after, it was concluded that the laser power value of 3-4 W can be recommended for use in the clinic.

Investigation of endovenous laser ablation of varicose veins in vitro using 1.885-µm laser radiation.

This paper presents the results of endovenous laser ablation (EVLA) of varicose veins in vitro using radiation of a solid-state laser based on the crystal LiYF4:Tm, with a wavelength of 1.885 µm and power output of around 3 W. An experimental series with saline solution and red blood cell (RBC) suspension in the venous lumen was performed to identify the impact of a heated carbonized layer precipitated on the fiber end face versus the efficiency of EVLA. Results of these experiments confirmed that the presence of a heated carbonized layer on the fiber end face increases the efficiency of EVLA.

Synthesis of well-ordered COF monolayers: surface growth of nanocrystalline precursors versus direct on-surface polycondensation.

Two different straightforward synthetic approaches are presented to fabricate long-range-ordered monolayers of a covalent organic framework (COF) on an inert, catalytically inactive graphite surface. Boronic acid condensation (dehydration) is employed as the polymerization reaction. In the first approach, the monomer is prepolymerized by a mere thermal treatment into nanocrystalline precursor COFs. The precursors are then deposited by drop-casting onto a graphite substrate and characterized by scanning tunneling microscopy (STM). While in the precursors monomers are already covalently interlinked into the final COF structure, the resulting domain size is still rather small. We show that a thermal treatment under reversible reaction conditions facilitates on-surface ripening associated with a striking increase of the domain size. Although this first approach allows studying different stages of the polymerization, the direct polymerization, that is, without the necessity of preceding reaction steps, is desirable. We demonstrate that even for a comparatively small diboronic acid monomer a direct thermally activated polymerization into extended COF monolayers is achievable.

Design of chemically activated polymer microwells by one-step UV-lithography for stem cell adhesion.

A novel method to produce sub-microwalled chemically activated polymer microwells by one-step UV-lithography under ambient conditions which are selectively coated with gelatin is introduced. The dimensions as well as the shape of the resulting polystyrene structures are both tunable merely by the irradiation time through one and the same mask. It is shown that the UV-irradiation initiates three effects at those surface areas which are not covered by the mask: (i) oxidation, (ii) cross-linking, and (iii) degradation of polystyrene. The superposition of those effects results in the formation of microscaled, oxidized polymer wells separated by polymer walls, whereas the polymer walls are formed below the mask structures. Topographical changes induced by the UV-irradiation are investigated by atomic force microscopy after different irradiation times. It is shown by X-ray photoelectron spectroscopy and ellipsometric investigations that the chemical composition of the irradiated areas and the degradation of polystyrene reach an equilibrium state after an irradiation time of 10 min. The lateral distribution of the cross-linked and oxidized and of the nonmodified polystyrene after irradiation was determined by fluorescence microscopy and time-of-flight secondary ion mass spectrometry. After the irradiated samples were treated with gelatin solution, it was found that stem cells selectively attach to the irradiated areas. This is due to the selective immobilization of the gelatin on the irradiated polymer areas, which was proved by X-ray photoelectron spectroscopy experiments.

TOF-SIMS analysis of structured surfaces biofunctionalized by a one-step coupling of a spacer-linked GRGDS peptide.

Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) was applied to validate GRGDS peptide patterned surfaces. The structuring of the surfaces included several steps: micro contact printing (microCP), chemical etching and aminofunctionalization followed by chemical coupling of spacer-linked GRGDS peptides via an isothiocyanate anchor. TOF-SIMS analysis of characteristic ions and molecular fragments with a lateral resolution of 100 nm allowed proving the change in chemical properties of the surface with each step during the structuring process. We found that the application of polydimethylsiloxane as stamp material resulted in the contamination of the surface with this polymer. TOF-SIMS investigations, however, also showed that during the preparation process the contaminations were removed and do not influence the bio functionality of the surface patterns. The results of the surface analysis carried out with TOF-SIMS were confirmed by complementary cell adhesion experiments with murine fibroblasts. As a result, specific cell adhesion restricted to GRGDS peptide functionalized areas was obvious by the formation of focal adhesion contacts in the fibroblasts. Thus, TOF-SIMS is the method of choice in chemical characterization of surfaces in structuring and functionalization processes, because it offers the opportunity to follow surface contamination during the preparation process and to assess the influence of the contamination on the applicability of the final substrate.