Optofluidic rotation of living cells for single-cell tomography

Flow cytometry provides a high throughput, multi-dimensional analysis of cells flowing in suspension. In order to combine this feature with the ability to resolve detailed structures in 3D, we developed an optofluidic device that combines a microfluidic system with a dual beam trap. This allows for the rotation of single cells in a continuous flow, around an axis perpendicular to the imaging plane. The combination of both techniques enables the tomographic reconstruction of the 3D structure of the cell. In addition this method is capable to provide detailed 3D structural data for flow cytometry, as it improves the reconstructed z-resolution of a standard microscopy system to produce images with isotropic resolution in all three axes.

Separation of blood cells with differing deformability using deterministic lateral displacement(†)

Determining cell mechanical properties is increasingly recognized as a marker-free way to characterize and separate biological cells. This emerging realization has led to the development of a plethora of appropriate measurement techniques. Here, we use a fairly novel approach, deterministic lateral displacement (DLD), to separate blood cells based on their mechanical phenotype with high throughput. Human red blood cells were treated chemically to alter their membrane deformability and the effect of this alteration on the hydrodynamic behaviour of the cells in a DLD device was investigated. Cells of defined stiffness (glutaraldehyde cross-linked erythrocytes) were used to test the performance of the DLD device across a range of cell stiffness and applied shear rates. Optical stretching was used as an independent method for quantifying the variation in stiffness of the cells. Lateral displacement of cells flowing within the device, and their subsequent exit position from the device were shown to correlate with cell stiffness. Data showing how the isolation of leucocytes from whole blood varies with applied shear rate are also presented. The ability to sort leucocyte sub-populations (T-lymphocytes and neutrophils), based on a combination of cell size and deformability, demonstrates the potential for using DLD devices to perform continuous fractionation and/or enrichment of leucocyte sub-populations from whole blood.

Impact of heating on passive and active biomechanics of suspended cells

A cell is a complex material whose mechanical properties are essential for its normal functions. Heating can have a dramatic effect on these mechanical properties, similar to its impact on the dynamics of artificial polymer networks. We investigated such mechanical changes by the use of a microfluidic optical stretcher, which allowed us to probe cell mechanics when the cells were subjected to different heating conditions at different time scales. We find that HL60/S4 myeloid precursor cells become mechanically more compliant and fluid-like when subjected to either a sudden laser-induced temperature increase or prolonged exposure to higher ambient temperature. Above a critical temperature of 52 ± 1°C, we observed active cell contraction, which was strongly correlated with calcium influx through temperature-sensitive transient receptor potential vanilloid 2 (TRPV2) ion channels, followed by a subsequent expansion in cell volume. The change from passive to active cellular response can be effectively described by a mechanical model incorporating both active stress and viscoelastic components. Our work highlights the role of TRPV2 in regulating the thermomechanical response of cells. It also offers insights into how cortical tension and osmotic pressure govern cell mechanics and regulate cell-shape changes in response to heat and mechanical stress.

Dynamically reconfigurable fibre optical spanner

In this paper we describe a pneumatically actuated fibre-optic spanner integrated into a microfluidic Lab-on-a-Chip device for the controlled trapping and rotation of living cells. The dynamic nature of the system allows interactive control over the rotation speed with the same optical power. The use of a multi-layer device makes it possible to rotate a cell both in the imaging plane and also in a perpendicular plane allowing tomographic imaging of the trapped living cell. The integrated device allows easy operation and by combining it with high-resolution confocal microscopy we show for the first time that the pattern of rotation can give information regarding the sub-cellular composition of a rotated cell.

Prevalence of bronchoconstriction induced by eucapnic voluntary hyperpnoea in recreationally active individuals

OBJECTIVE

Exercise-induced bronchoconstriction (EIB) is more prevalent in elite athletes than in the general population. Many of these athletes provide a positive eucapnic voluntary hyperpnoea (EVH) challenge without previous diagnosis of EIB. It is unknown whether this is specific to elite athletes or whether the same risk applies to recreationally active individuals. The purpose of this study was to investigate the prevalence of a positive EVH challenge in a population of recreationally active individuals.

METHODS

136 recreationally active individuals (Age: 21.9 ± 3.7 years; Height: 175 ± 9 cm; Weight: 70.9 ± 10.0 kg) without previous history of asthma or EIB, volunteered to take part in the study. All participants completed an EVH challenge, which was deemed positive if FEV1 fell ≥10% from baseline at two consecutive time points, and was reversible following inhalation of a short acting β2-agonist.

RESULTS

18 of 136 (13.2%) participants had a positive EVH challenge. Of the 18 individuals, the fall in FEV1 from baseline ranged from -12% to -50%. At baseline, percentage predicted FEV1 (97.5 ± 12.5% versus 104.9 ± 10%; p < 0.01), FEV1/FVC ratio (79.5 ± 6.9% versus 87.8 ± 5.5%; p < 0.01), FEF25-75 (3.73 ± 1.00 versus 4.73 ± 1.00 l/s; p < 0.01) and predicted PEF (89.4 ± 8.8% versus 97.5 ± 13.6%; p < 0.05) values for EVH positive participants were significantly lower than EVH negative participants respectively.

CONCLUSIONS

Overall, 13.2% of recreationally active individuals with no previous history of asthma presented with a positive EVH challenge. Individuals who are recreationally active may benefit from an objective bronchial provocation challenge, given that self-reported symptoms alone only provide a supportive role towards a valid EIB diagnosis.

Significance of deep T-wave inversions in asymptomatic athletes with normal cardiovascular examinations: practical solutions for managing the diagnostic conundrum

Preparticipation screening programmes for underlying cardiac pathologies are now commonplace for many international sporting organisations. However, providing medical clearance for an asymptomatic athlete without a family history of sudden cardiac death (SCD) is especially challenging when the athlete demonstrates particularly abnormal repolarisation patterns, highly suggestive of an inherited cardiomyopathy or channelopathy. Deep T-wave inversions of ≥ 2 contiguous anterior or lateral leads (but not aVR, and III) are of major concern for sports cardiologists who advise referring team physicians, as these ECG alterations are a recognised manifestation of hypertrophic cardiomyopathy (HCM) and arrhythmogenic right ventricular cardiomyopathy (ARVC). Subsequently, inverted T-waves may represent the first and only sign of an inherited heart muscle disease, in the absence of any other features and before structural changes in the heart can be detected. However, to date, there remains little evidence that deep T-wave inversions are always pathognomonic of either a cardiomyopathy or an ion channel disorder in an asymptomatic athlete following long-term follow-up. This paper aims to provide a systematic review of the prevalence of T-wave inversion in athletes and examine T-wave inversion and its relationship to structural heart disease, notably HCM and ARVC with a view to identify young athletes at risk of SCD during sport. Finally, the review proposes clinical management pathways (including genetic testing) for asymptomatic athletes demonstrating significant T-wave inversion with structurally normal hearts.

Mechanical environment modulates biological properties of oligodendrocyte progenitor cells

Myelination and its regenerative counterpart remyelination represent one of the most complex cell-cell interactions in the central nervous system (CNS). The biochemical regulation of axon myelination via the proliferation, migration, and differentiation of oligodendrocyte progenitor cells (OPCs) has been characterized extensively. However, most biochemical analysis has been conducted in vitro on OPCs adhered to substrata of stiffness that is orders of magnitude greater than that of the in vivo CNS environment. Little is known of how variation in mechanical properties over the physiological range affects OPC biology. Here, we show that OPCs are mechanosensitive. Cell survival, proliferation, migration, and differentiation capacity in vitro depend on the mechanical stiffness of polymer hydrogel substrata. Most of these properties are optimal at the intermediate values of CNS tissue stiffness. Moreover, many of these properties measured for cells on gels of optimal stiffness differed significantly from those measured on glass or polystyrene. The dependence of OPC differentiation on the mechanical properties of the extracellular environment provides motivation to revisit results obtained on nonphysiological, rigid surfaces. We also find that OPCs stiffen upon differentiation, but that they do not change their compliance in response to substratum stiffness, which is similar to embryonic stem cells, but different from adult stem cells. These results form the basis for further investigations into the mechanobiology of cell function in the CNS and may specifically shed new light on the failure of remyelination in chronic demyelinating diseases such as multiple sclerosis.

Validation and perspectives of a femtosecond laser fabricated monolithic optical stretcher

The combination of high power laser beams with microfluidic delivery of cells is at the heart of high-throughput, single-cell analysis and disease diagnosis with an optical stretcher. So far, the challenges arising from this combination have been addressed by externally aligning optical fibres with microfluidic glass capillaries, which has a limited potential for integration into lab-on-a-chip environments. Here we demonstrate the successful production and use of a monolithic glass chip for optical stretching of white blood cells, featuring microfluidic channels and optical waveguides directly written into bulk glass by femtosecond laser pulses. The performance of this novel chip is compared to the standard capillary configuration. The robustness, durability and potential for intricate flow patterns provided by this monolithic optical stretcher chip suggest its use for future diagnostic and biotechnological applications.

Cardiac electromechanical delay is increased during recovery from 40 km cycling but is not mediated by exercise intensity

Cardiac electrical-mechanical delay (cEMD), left ventricular (LV) function, and cardiac troponin I (cTnI) were assessed after 40 km cycle time trials completed at high (HIGH) and moderate (MOD) intensities in 12 cyclists. Echocardiograms and blood samples were collected before, 10, and 60 min after cycling. cEMD as assessed by time from QRS onset to peak systolic (S') tissue velocity was lengthened after both bouts of cycling but was not mediated by cycling intensity (HIGH: 174 ± 52 vs 198 ± 26 ms; MOD: 151 ± 40 vs 178 ± 52 ms, P < 0.05). Global LV systolic function was unaltered by exercise. cEMD from QRS to peak early (E') diastolic tissue velocity was also increased post-exercise (HIGH: 524 ± 95 vs 664 ± 68 ms; MOD: 495 ± 62 vs 604 ± 91 ms, P < 0.05). Indices of LV diastolic function was reduced after cycling but were not mediated by exercise intensity. cTnI was elevated in two participants after HIGH trial (0.06 ug/L; 0.04 ug/L) and one participant after MOD trial (0.02 ug/L). While cEMD is lengthened and LV diastolic function was reduced post-cycling, altering time-trial intensity had little impact upon cEMD, LV function, and cTnI release.

Underlying cause discovered for a prior idiopathic AMI

The authors previously reported on an active, young male with normal coronaries who sustained an acute myocardial infarction (AMI). The acute cause was a coronary thrombus; however, the cause of this thrombus and a definitive diagnosis remained elusive for 18 months until a new series of events, including symptoms of breathlessness, dizziness and collapse led to acute hospital admission. CT scan revealed numerous deep venous thromboses in the right leg and bilateral pulmonary emboli (PE). Acute pharmacological thrombolysis eliminated breathlessness and significantly reduced the risk of mortality. Clinical consensus suggests a coagulopathy, requiring indefinite treatment with Warfarin. In young individuals presenting with AMI, lifestyle, personal, family and clinical history should be considered and coronary artery disease should not be assumed until further tests have eliminated coagulopathy. In those presenting with breathlessness and a history which includes AMI, a CT scan is indicated to eliminate concerns of venous thromboembolism generally and PE specifically where untreated survival times are short.

Diverse patterns of myocardial fibrosis in lifelong, veteran endurance athletes

This study examined the cardiac structure and function of a unique cohort of documented lifelong, competitive endurance veteran athletes (>50 yr). Twelve lifelong veteran male endurance athletes [mean ± SD (range) age: 56 ± 6 yr (50-67)], 20 age-matched veteran controls [60 ± 5 yr; (52-69)], and 17 younger male endurance athletes [31 ± 5 yr (26-40)] without significant comorbidities underwent cardiac magnetic resonance (CMR) imaging to assess cardiac morphology and function, as well as CMR imaging with late gadolinium enhancement (LGE) to assess myocardial fibrosis. Lifelong veteran athletes had smaller left (LV) and right ventricular (RV) end-diastolic and end-systolic volumes (P < 0.05), but maintained LV and RV systolic function compared with young athletes. However, veteran athletes had a significantly larger absolute and indexed LV and RV end-diastolic and systolic volumes, intraventricular septum thickness during diastole, posterior wall thickness during diastole, and LV and RV stroke volumes (P < 0.05), together with significantly reduced LV and RV ejection fractions (P < 0.05), compared with veteran controls. In six (50%) of the veteran athletes, LGE of CMR indicated the presence of myocardial fibrosis (4 veteran athletes with LGE of nonspecific cause, 1 probable previous myocarditis, and 1 probable previous silent myocardial infarction). There was no LGE in the age-matched veteran controls or young athletes. The prevalence of LGE in veteran athletes was not associated with age, height, weight, or body surface area (P > 0.05), but was significantly associated with the number of years spent training (P < 0.001), number of competitive marathons (P < 0.001), and ultraendurance (>50 miles) marathons (P < 0.007) completed. An unexpectedly high prevalence of myocardial fibrosis (50%) was observed in healthy, asymptomatic, lifelong veteran male athletes, compared with zero cases in age-matched veteran controls and young athletes. These data suggest a link between lifelong endurance exercise and myocardial fibrosis that requires further investigation.