The evaluation of seismocardiogram signal pre-processing using hybridized variational mode decomposition method.

This study aims to determine the performance of variational mode decomposition (VMD) combined with detrended fluctuation analysis (DFA) as a hybrid framework for extracting seismocardiogram and respiration signals from simulated single-channel accelerometry data and removing its contained noise. The method consists of two consecutive layers of VMD that each contribute to extracting respiration and SCG signal respectively. DFA is utilized to determine the number of modes produced by VMD and select the most appropriate modes to be the constituents of the reconstructed signal based on the Hurst exponent value thresholding. This hybridized VMD successfully extracted respiration and SCG signal with minimal mean absolute error value (0.516 and 0.849, respectively) and boosted the SNR to 2 dB and 4 dB, respectively in heavily noise-interfered conditions. This method also outperformed other empirical mode decomposition strategies and exhibits short computational time. Two main drawbacks exist in this framework, i.e. the determination of balancing parameter ( γ ) that is still conducted manually and the magnitude shifting phenomenon. In conclusion, the hybridized VMD shows an outstanding performance in denoising and extracting respiration and SCG signals from a single input that combines them and generally is impured by noise.

Correction to: The evaluation of seismocardiogram signal pre-processing using hybridized variational mode decomposition method.

[This corrects the article DOI: 10.1007/s13534-022-00235-x.].

Versatile and Low-Cost Fabrication of Modular Lock-and-Key Microfluidics for Integrated Connector Mixer Using a Stereolithography 3D Printing.

We present a low-cost and simple method to fabricate a novel lock-and-key mixer microfluidics using an economic stereolithography (SLA) three-dimensional (3D) printer, which costs less than USD 400 for the investment. The proposed study is promising for a high throughput fabrication module, typically limited by conventional microfluidics fabrications, such as photolithography and polymer-casting methods. We demonstrate the novel modular lock-and-key mixer for the connector and its chamber modules with optimized parameters, such as exposure condition and printing orientation. In addition, the optimization of post-processing was performed to investigate the reliability of the fabricated hollow structures, which are fundamental to creating a fluidic channel or chamber. We found out that by using an inexpensive 3D printer, the fabricated resolution can be pushed down to 850 µm and 550 µm size for squared- and circled-shapes, respectively, by the gradual hollow structure, applying vertical printing orientation. These strategies opened up the possibility of developing straightforward microfluidics platforms that could replace conventional microfluidics mold fabrication methods, such as photolithography and milling, which are costly and time consuming. Considerably cheap commercial resin and its tiny volume employed for a single printing procedure significantly cut down the estimated fabrication cost to less than 50 cents USD/module. The simulation study unravels the prominent properties of the fabricated devices for biological fluid mixers, such as PBS, urine and plasma blood. This study is eminently prospective toward microfluidics application in clinical biosensing, where disposable, low-cost, high-throughput, and reproducible chips are highly required.