Microfluidic-Based Oxygen (O2) Sensors for On-Chip Monitoring of Cell, Tissue and Organ Metabolism

Oxygen (O2) quantification is essential for assessing cell metabolism, and its consumption in cell culture is an important indicator of cell viability. Recent advances in microfluidics have made O2 sensing a crucial feature for organ-on-chip (OOC) devices for various biomedical applications. OOC O2 sensors can be categorized, based on their transducer type, into two main groups, optical and electrochemical. In this review, we provide an overview of on-chip O2 sensors integrated with the OOC devices and evaluate their advantages and disadvantages. Recent innovations in optical O2 sensors integrated with OOCs are discussed in four main categories: (i) basic luminescence-based sensors; (ii) microparticle-based sensors; (iii) nano-enabled sensors; and (iv) commercial probes and portable devices. Furthermore, we discuss recent advancements in electrochemical sensors in five main categories: (i) novel configurations in Clark-type sensors; (ii) novel materials (e.g., polymers, O2 scavenging and passivation materials); (iii) nano-enabled electrochemical sensors; (iv) novel designs and fabrication techniques; and (v) commercial and portable electrochemical readouts. Together, this review provides a comprehensive overview of the current advances in the design, fabrication and application of optical and electrochemical O2 sensors.

Biomimetic Sensors to Detect Bioanalytes in Real-Life Samples Using Molecularly Imprinted Polymers: A Review

Molecularly imprinted polymers (MIPs) come with the promise to be highly versatile, useful artificial receptors for sensing a wide variety of analytes. Despite a very large body of literature on imprinting, the number of papers addressing real-life biological samples and analytes is somewhat limited. Furthermore, the topic of MIP-based sensor design is still, rather, in the research stage and lacks wide-spread commercialization. This review summarizes recent advances of MIP-based sensors targeting biological species. It covers systems that are potentially interesting in medical applications/diagnostics, in detecting illicit substances, environmental analysis, and in the quality control of food. The main emphasis is placed on work that demonstrates application in real-life matrices, including those that are diluted in a reasonable manner. Hence, it does not restrict itself to the transducer type, but focusses on both materials and analytical tasks.

Influence of bone conduction transducer type and placement on ocular and cervical vestibular evoked myogenic potentials

Evaluating the effectiveness of different bone conduction (BC) transducers with controlled coupling force to elicit cervical and ocular vestibular evoked myogenic potentials (cVEMPs, oVEMPs) in healthy subjects by comparing response rates, amplitudes, latencies, thresholds and asymmetry ratios. Prospective experimental study including healthy participants. VEMPs were measured to different stimulation modes; the BC transducer coupling force was controlled to 5.4 (± 0.5) Newton. cVEMPs: to bone conducted vibration (BCV) with the B81 transducer on the mastoid; oVEMPs: to BCV with the B81 on the mastoid, BCV with the B81 on the forehead, and BCV with the Mini-Shaker 4810 on the forehead. Air conducted sound (ACS) with insert earphones was used as reference. Data of 24 normal subjects (mean age 25.3 (± 3.0) years) were analyzed. ACS and BCV with the B81on the mastoid evoked cVEMPs in 100% of ears. The highest oVEMP response rates were obtained with the B81 on the mastoid (83–92%), the lowest with the B81 on the forehead (17–22%). The Mini-Shaker elicited lower response rates (65%) compared to results from the literature without coupling force control and compared to ACS (78–87%). Amplitudes were higher for BCV than ACS. ACS and BCV on the mastoid caused higher asymmetry compared to BCV forehead stimulation. The B81 was feasible to elicit VEMPs with mastoid placement and can be used as an approved medical device to measure BCV VEMPs in a clinical set-up. Normative asymmetry values have to be established due to higher variability for mastoid stimulation.

Influence of bone conduction transducer type and placement on ocular and cervical vestibular evoked myogenic potentials

Purpose: Evaluating the effectiveness of different bone conduction (BC) transducers with controlled coupling force to elicit cervical and ocular vestibular evoked myogenic potentials (cVEMPs, oVEMPs) in healthy subjects by comparing response rates, amplitudes, latencies, thresholds and asymmetry ratios.Methods: Prospective experimental study including healthy participants. VEMPs were measured to different stimulation modes; the BC transducer coupling force was controlled to 5.4 (±0.5) Newton. cVEMPs: to bone conducted vibration (BCV) with the B81 transducer on the mastoid; oVEMPs: to BCV with the B81 on the mastoid, BCV with the B81 on the forehead, and BCV with the Mini-Shaker 4810 on the forehead. Air conducted sound (ACS) with insert earphones was used as reference.Results: Data of 24 normal subjects (mean age 25.3 (± 3.0) years) were analyzed. ACS and BCV with the B81on the mastoid evoked cVEMPs in 100% of ears. The highest oVEMP response rates were obtained with the B81 on the mastoid (83 – 92%), the lowest with the B81 on the forehead (17 – 22%). The Mini-Shaker elicited lower response rates (65%) compared to results from the literature without coupling force control and compared to ACS (78 – 87%). Amplitudes were higher for BCV than ACS. ACS and BCV on the mastoid caused higher asymmetry compared to BCV forehead stimulation.Conclusion: The B81 was feasible to elicit VEMPs with mastoid placement and can be used as an approved medical device to measure BCV VEMPs in a clinical set-up. Normative asymmetry values have to be established due to higher variability for mastoid stimulation.

Effects of Self-Generated Noise on Quiet Threshold by Transducer Type in School-Age Children and Adults

Purpose Low-frequency detection thresholds in quiet vary across transducers. This experiment tested the hypothesis that transducer effects are larger in young children than adults, due to higher levels of self-generated noise in children. Method Listeners were normal-hearing 4.6- to 11.7-year-olds and adults. Warble-tone detection was measured at 125, 250, 500, and 1000 Hz with a sound-field speaker, insert earphones, and supra-aural headphones. Probe microphone recordings measured self-generated noise levels. Results Thresholds were similar across ages for speaker measurements. Transducer effects were larger for children than adults, with mean child–adult threshold differences at 125 Hz of 3.4 dB (insert earphones) and 6.6 dB (supra-aural headphones). Age effects on threshold were broadly consistent with noise levels measured in the ear canal. Conclusions Self-generated noise appears to elevate children's low-frequency thresholds measured with occluding transducers. These effects could be particularly relevant to the diagnosis of minimal and mild hearing loss in children.

Effects of Tinnitus Sound Therapy depending on Air- and Bone-Conduction Transducers

Purpose: The purpose of this study was to determine to compare the effects of sound therapy depending on air- and bone-conduction transducers (ACT and BCT). Methods: Participants were twenty adults who have diagnosed as subjective tinnitus in this study. All participants conducted a sound therapy using the level of mixing point for three months. Participants were randomly assigned to different groups, such as the ACT group, or BCT group. To identify the effects of sound therapy, Korean tinnitus primary function questionnaire (K-TPFQ) and visual analogue scale (VAS) were administered at pre- and post-treatment (3 months) sessions. Results: In a result of mixed model analysis of variance, all subcategories for VAS showed significant decrements of scores to the measurement session (pre- vs. post-session), but there was no different between groups. Also, the overall and all subcategories for K-TPFQ showed significant decrements of scores to the measurement session (prevs. post-session), but there was no different between groups. Conclusion: As a result of this study, the sound therapy using portable hearing devices with transducers is effective for subjective tinnitus sufferers. Because the transducer type does not significantly affect effectiveness of the sound therapy, therefore, audiologists or hearing professionals may recommend transducers, which the tinnitus sufferer prefers when they consider sound therapy.

Ultrasonographic honeycomb pattern of the spleen in cats: correlation with pathological diagnosis in 33 cases

Objectives The aim of this study was to evaluate the relationship between the ultrasonographic (US) diffuse honeycomb pattern (HCP) of the spleen and a pathological diagnosis in cats, and to assess the influence of transducer type on HCP visualisation. Methods Abdominal ultrasounds of cats with an HCP were reviewed and splenic size, shape, margination, other parenchymal alterations and splenic hilar lymphadenopathy were recorded. When applicable, images acquired with high-frequency linear and curvilinear transducers were compared to determine if an HCP was more frequently demonstrated on high-resolution images. A retrospective review of the corresponding splenic cytohistopathological samples was also performed. Results Thirty-three cats met the inclusion criteria. Five cases were diagnosed by histology and 28 by cytology, confirmed by PCR for antigen receptor rearrangements (PARR) in uncertain cases. There were 15 cases of lymphoid hyperplasia, eight cases of lymphoma (four B cell, three T cell and one large granular lymphocytes), six cats with splenitis, three with extramedullary haematopoiesis and one with histiocytic sarcoma. The prevalence of lymphoma in cats with an HCP of the spleen was 24%. Splenomegaly was the most frequent US feature associated with an HCP and was observed in all lymphoma cases. In the images obtained from both high-frequency linear and micro-convex transducers the visualisation of an HCP was enabled in all cases (24/24) and in 62.5% (15/24), respectively. Conclusions and relevance: Based on our findings, a US HCP of the spleen in cats can be associated with benign and malignant disorders and is infrequently associated with lymphoma in comparison with dogs. Cytological or histological examination, possibly supplemented by PARR, should always be performed for diagnostic support. Use of high-frequency linear transducers is recommended to properly recognise an HCP or subtle changes in splenic parenchyma.

Improved SH0 Guided Wave Transducers Based on Piezoelectric Fiber Patches

A piezoelectric fiber patch (PFP) is a transducer type that is suitable for guided-wave-based structural health monitoring (SHM) due to its light, thin, and flexible characteristics. In our previous work, a PFP-based transducer design for selective excitation of the zero-order shear horizontal wave mode (SH0) was introduced (shear horizontal PFP (SHPFP)). In this work, two modified SH0 wave PFP transducer designs are proposed: the rounded corner design and the dual design. The degree of improvement is determined by a numerical simulation and the dual design—the design with the most promise—is experimentally realized. Laser Vibrometry measured the generated wave field, confirming the results from the simulation. The new designs can generate an almost pure SH0 wave. The dual design has a very strong directivity that is useful for several guided-wave-based SHM applications. The conclusions on the design’s properties as a transmitter are also valid for its properties as a sensor due to the reciprocity of piezoelectric transducers.