Endophytic fungal extracts possess great potential as alternative antibacterial substances. Here, two extracts from the Australian endemic plant Eremophila longifolia were shown to reduce biomass and metabolic activity of the oral bacteria Streptococcus oralis and Porphyromonas gingivalis. As the effective concentration towards S. oralis was lower than the cytotoxic concentration towards oral epithelial cells, more detailed studies are warranted in the future.

Introduction

Electrical stimulation experiments with electrodes in direct contact with the sample are prone to electrochemical interface effects and non-linear electrochemical reactions such as corrosion. Moreover, the manufacturing uncertainties of the electrodes may cause changes in electrical properties. A consequence is not replicable or even repeatable experiments.

We present the results of investigating three different electrode setups used in recent research utilising impedance spectroscopy. These are the SNEX-100 from Microprobes Inc., Gaithersburg (USA), the ECIS culture plate 8W20idf from Applied BioPhysics Inc., Troy (USA) and custom-made electrodes for 6-well plates consisting of titanium rods.

Methods

We use electrochemical impedance spectroscopy to record the electrical impedance of the electrodes over a wide frequency range (roughly 1 Hz to 10 MHz) in a two-electrode setup, i.e. no reference electrode was utilised. To ensure replicability, the electrodes are immersed in solutions with known conductivity and a thermally stable environment. The validity of the recorded impedance spectra was checked using the LinKK test utilising the open-source software Im¬pe-dance¬Fitter. The spectra were evaluated to assess the system's electrochemical properties using the software's fitting capabilities. To identify changes in the system during stimulation, the current and voltage for each electrode should be tracked. Thus, the input current was monitored, and changes in impedance during stimulation were recognised by estimating the DC equivalent based on Ohm's law.

Based on the impedance measurements, numerical simulations were performed to gain insight into observables that cannot be measured directly and allow the prediction of the outcome of the experiments.

Results

From the different electrodes we investigated, the custom-made titanium electrodes serve as an example for corrosion. Energy Dispersive X-Ray Analysis revealed a build-up of a potassium layer on the electrode surface.

Unusual impedance spectra of the SNEX-100 electrodes indicate changed geometries due to manufacturing tolerances.

The ECIS culture plates show different total impedances in each well due to the non-negligible impedance of thin gold traces used in the culture plate. That makes the culture plates unsuitable for electrical stimulation experiments.

All impedance spectra show the expected double layer at low frequencies, characteristic of the electrode-electrolyte interface.

Conclusion

Using impedance spectroscopy for characterisation and monitoring gives access to the electrode state before, during and after stimulation. Knowing the specific shortcomings of each system allows improved experimental setups and thus increases replicability.

Acknowledgement

This work is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - SFB 1270/2 – 299150580.

Introduction

The development of an implantable biohybrid lung (BHL) is intended to provide an alternative to lung transplantation, which is currently the only treatment option for end-stage lung disease patients. The operating principle is based on the gas exchange hollow fiber membrane (HFM) technology used in clinically applied extracorporeal membrane oxygenation (ECMO), but to allow long-term use, the poly-4-methyl-1-pentene(PMP) HFM and all blood-contacting surfaces of the BHL are covered with an endothelial cells(EC) monolayer that prevents contact-activated thrombus formation and device occlusion. Therefore, ECs must endure the oxygen gradient between the oxygen-rich gas inside the HFMs and the hypercapnic/hypoxic patient blood. Thus, we investigated the influence of this clinically relevant oxygen tension on EC viability and function, under static and flow conditions.

Methods

PMP membranes (film and HFM) were coated with fibronectin and seeded with ECs. Upon reaching confluence, ECs were pre-cultivated under blood gas levels existing during respiratory insufficiency (50 mmHg pO2, 80 mmHg pCO2) for 24h followed by exposure to hyperoxia (>95% pO2) for 24h. Using a customized miniature oxygenator, endothelialized HFMs were additionally challenged with 15 ml/min medium flow. Remaining ECs were stained with calcein vital dye and immunostaining agents for Collagen-IV and VE-Cadherin detection via confocal microscopy. Expression level change of oxidative stress (HMOX1, GCLM)- or inflammation (ELAM, VCAM, ICAM) related genes were measured via qRT-PCR. Apoptosis (AnnexinV/PJ) and reactive oxygen species(ROS) accumulation (CellRox) were investigated using flow cytometry.

Results

Confocal microscopy imaging confirmed confluent and viable EC-monolayers with intercellular junctions and de novo synthesized Collagen-IV under pre-cultivation or hyperoxia. Also, no change in prothrombotic/proinflammatory gene regulation was detected. Under dynamic and hyperoxic conditions, oxidative- and flow stress-associated genes were appropriately upregulated to keep apoptosis and ROS levels at bay.

Conclusion

The results of this study underline the feasibility of biohybrid lung application under clinical conditions.

Introduction

It is one of the basic requirements for long-term implants like arterial stents to withstand cyclic dynamic loading without any loss of support function. The new revision of ASTM F2477:2023 describes a pressure controlled test principles ex-plicitly including dynamic loading by an outer hydraulic pressure. The technical realization of the test parameters to be controlled are demonstrated and discussed.

Methods

The stents are implanted in thin and flexible test tubes and placed in the test chamber which is pressurized by a static pressure and dynamic pressure load. Expected stent diameter change was estimated using mock vessels (ID=3.5 mm, diameter compliance of 5-7 %/100mmHg) and the outer diameter was measured at increasing steps of internal pressure (Δp = 0.05 bar = 37.5 mmHg) without stent and after implantation of a commercially available coronary stent.

The diameter change at accelerated test frequency has to be comparable to that at physiological pressure and frequency. This experimental prove is conducted using a setup with a high resolution line camera and the setup for pressure loading.

Results

Under simulated physiological conditions (pmean=100 mmHg, pdiast/psyst = 80/120 mmHg) the diameter compliance of the unstented vessel was 5.467 %/100 mmHg and that of the stented artery was about a magnitude smaller (0.489 %/100 mmHg). The amplitude of diameter change was comparable between 1 Hz and 50 Hz, but reduced at 100 Hz. Thus, the test frequency would have to be lower than 100 Hz.

Conclusion

The presented test method for pulsatile fatigue testing of stents is suitable to meets the requirement of the new standard for fatigue testing for arterial stents exposed to arterial pulse. The technical parameters can be adjusted and controlled with relevant precision. The method has several advantages (direct loading, high test frequency, no stent migration) which may help to increase acceptance.

Administering fluids and drugs intravenously is crucial in caring for vulnerable patient cohorts such as critically ill patients as well as neonatal and paediatrics patient populations. Studies have revealed severe contamination of infusion solution that could be avoided by utilizing in-line filters. The filtration performance consequently depends on the geometry of the filter housing. The purpose of our numerical study was to analyse the flow situation in filter housings depending on the geometry (diameter of the filter housing and distance between entrance and membrane). We compared the flow of two circular filter system with different housing width (D = 25 mm; L = 1.5 mm/3.0 mm) by means of computational fluid dynamics (CFD). The filter membrane was modelled by a porous jump condition. Both filter systems showed a highly reduced inflow on the membrane compared to the velocity in the Luer Lock ports. The wide filter housing facilitates a more homogenous inflow on the membrane (>92% of the membrane area is applied within a range of 5% of the mean velocity) compared to the narrow filter housing. Despite that difference both filter housings induced a well distributed flow through the filter membrane. However, for large filter systems (>50 mm diameter) the design of the filter housing could play a crucial role in optimising filter performance and therefore CFD should be considered.

After e-mail contact with Prof. Pott by Prof. Grabow, the article will be completed and submitted by April 24.

Due to direct contact with a living being for long periods of time, the biocompatibility of implant surfaces is particularly important. In this context, biointegration of implants highly depends on cell colonialization on and cell ingrowth in porous implant surfaces. In this study, the biocompatibility of medical device samples made of microwire and nanofiber substrates was compared according to ISO 10993-5. In particular, a metal tissue of microwire (stainless steel, 316L) and polymeric nanofiber nonwoven poly-L-lactic acid (PLLA) as well as titanium (Ti) sputtered variants thereof were tested in vitro (316L-Ti, PLLA-Ti). In order to evaluate their environmental compatibility and their effects on L929 cell line (murine fibroblasts) evaluation was performed via direct contact up to 96h. Briefly outlined, microwires were colonized immediately, whereas initially spherical cells settled on nanofiber substrates and later coalesced forming a common cell cluster. Independent of structure, ultrathin Ti coating improves cell viability. It can therefore be assumed that physical vapor deposition (PVD) sputtering of Ti on implant surfaces is a suitable approach to maintain or improve their biocompatibility, regardless of the surface structure of the implants.