by Keyword: Fluid

By year:[ 2021 | 2020 | 2019 | 2018 | 2017 | 2016 | 2015 | 2014 | 2013 | 2012 | 2011 | 2010 | 2009 | 2008 | 2007 | 2006 | 2005 ]

Williams, I., Lee, S., Apriceno, A., Sear, R. P., Battaglia, G., (2020). Diffusioosmotic and convective flows induced by a nonelectrolyte concentration gradient Proceedings of the National Academy of Sciences of the United States of America 117, (41), 25263-25271

Glucose is an important energy source in our bodies, and its consumption results in gradients over length scales ranging from the subcellular to entire organs. Concentration gradients can drive material transport through both diffusioosmosis and convection. Convection arises because concentration gradients are mass density gradients. Diffusioosmosis is fluid flow induced by the interaction between a solute and a solid surface. A concentration gradient parallel to a surface creates an osmotic pressure gradient near the surface, resulting in flow. Diffusioosmosis is well understood for electrolyte solutes, but is more poorly characterized for nonelectrolytes such as glucose. We measure fluid flow in glucose gradients formed in a millimeter-long thin channel and find that increasing the gradient causes a crossover from diffusioosmosis-dominated to convection-dominated flow. We cannot explain this with established theories of these phenomena which predict that both scale linearly. In our system, the convection speed is linear in the gradient, but the diffusioosmotic speed has a much weaker concentration dependence and is large even for dilute solutions. We develop existing models and show that a strong surface-solute interaction, a heterogeneous surface, and accounting for a concentration-dependent solution viscosity can explain our data. This demonstrates how sensitive nonelectrolyte diffusioosmosis is to surface and solution properties and to surface-solute interactions. A comprehensive understanding of this sensitivity is required to understand transport in biological systems on length scales from micrometers to millimeters where surfaces are invariably complex and heterogeneous.

Keywords: Convection, Diffusioosmosis, Microfluidics

Lidón, Laia, Urrea, Laura, Llorens, Franc, Gil, Vanessa, Alvarez, Ignacio, Diez-Fairen, Monica, Aguilar, Miguel, Pastor, Pau, Zerr, Inga, Alcolea, Daniel, Lleó, Alberto, Vidal, Enric, Gavín, Rosalina, Ferrer, Isidre, Del Rio, Jose Antonio, (2020). Disease-specific changes in Reelin protein and mRNA in Nnurodegenerative diseases Cells 9, (5), 1252

Reelin is an extracellular glycoprotein that modulates neuronal function and synaptic plasticity in the adult brain. Decreased levels of Reelin activity have been postulated as a key factor during neurodegeneration in Alzheimer’s disease (AD) and in aging. Thus, changes in levels of full-length Reelin and Reelin fragments have been revealed in cerebrospinal fluid (CSF) and in post-mortem brains samples of AD patients with respect to non-AD patients. However, conflicting studies have reported decreased or unchanged levels of full-length Reelin in AD patients compared to control (nND) cases in post-mortem brains and CSF samples. In addition, a compelling analysis of Reelin levels in neurodegenerative diseases other than AD is missing. In this study, we analyzed brain levels of RELN mRNA and Reelin protein in post-mortem frontal cortex samples from different sporadic AD stages, Parkinson’s disease with dementia (PDD), and Creutzfeldt-Jakob disease (sCJD), obtained from five different Biobanks. In addition, we measured Reelin protein levels in CSF samples of patients with mild cognitive impairment (MCI), dementia, or sCJD diagnosis and a group of neurologically healthy cases. The results indicate an increase in RELN mRNA in the frontal cortex of advanced stages of AD and in sCJD(I) compared to controls. This was not observed in PDD and early AD stages. However, Reelin protein levels in frontal cortex samples were unchanged between nND and advanced AD stages and PDD. Nevertheless, they decreased in the CSF of patients with dementia in comparison to those not suffering with dementia and patients with MCI. With respect to sCJD, there was a tendency to increase in brain samples in comparison to nND and to decrease in the CSF with respect to nND. In conclusion, Reelin levels in CSF cannot be considered as a diagnostic biomarker for AD or PDD. However, we feel that the CSF Reelin changes observed between MCI, patients with dementia, and sCJD might be helpful in generating a biomarker signature in prodromal studies of unidentified dementia and sCJD.

Keywords: Reelin, Creutzfeldt-Jakob disease, Alzheimer’s disease, Parkinson’s disease dementia, a-synucleopathies, Cerebrospinal fluid

Ruiz-Vega, G., Arias-Alpízar, K., de la Serna, E., Borgheti-Cardoso, L. N., Sulleiro, E., Molina, I., Fernàndez-Busquets, X., Sánchez-Montalvá, A., del Campo, F. J., Baldrich, E., (2020). Electrochemical POC device for fast malaria quantitative diagnosis in whole blood by using magnetic beads, Poly-HRP and microfluidic paper electrodes Biosensors and Bioelectronics 150, 111925

Malaria, a parasitic infection caused by Plasmodium parasites and transmitted through the bite of infected female Anopheles mosquitos, is one of the main causes of mortality in many developing countries. Over 200 million new infections and nearly half a million deaths are reported each year, and more than three billion people are at risk of acquiring malaria worldwide. Nevertheless, most malaria cases could be cured if detected early. Malaria eradication is a top priority of the World Health Organisation. However, achieving this goal will require mass population screening and treatment, which will be hard to accomplish with current diagnostic tools. We report an electrochemical point-of-care device for the fast, simple and quantitative detection of Plasmodium falciparum lactate dehydrogenase (PfLDH) in whole blood samples. Sample analysis includes 5-min lysis to release intracellular parasites, and stirring for 5 more min with immuno-modified magnetic beads (MB) along with an immuno-modified signal amplifier. The rest of the magneto-immunoassay, including sample filtration, MB washing and electrochemical detection, is performed at a disposable paper electrode microfluidic device. The sensor provides PfLDH quantitation down to 2.47 ng mL−1 in spiked samples and for 0.006–1.5% parasitemias in Plasmodium-infected cultured red blood cells, and discrimination between healthy individuals and malaria patients presenting parasitemias >0.3%. Quantitative malaria diagnosis is attained with little user intervention, which is not achieved by other diagnostic methods.

Keywords: Electrochemical magneto-immunosensor, Malaria quantitative diagnosis, Paper microfluidic electrode, Plasmodium LDH, Point-of-care (POC) testing

Sala-Jarque, Julia, Mesquida-Veny, Francina, Badiola-Mateos, Maider, Samitier, Josep, Hervera, Arnau, del Río, José Antonio, (2020). Neuromuscular activity induces paracrine signaling and triggers axonal regrowth after injury in microfluidic lab-on-chip devices Cells 9, (2), 302

Peripheral nerve injuries, including motor neuron axonal injury, often lead to functional impairments. Current therapies are mostly limited to surgical intervention after lesion, yet these interventions have limited success in restoring functionality. Current activity-based therapies after axonal injuries are based on trial-error approaches in which the details of the underlying cellular and molecular processes are largely unknown. Here we show the effects of the modulation of both neuronal and muscular activity with optogenetic approaches to assess the regenerative capacity of cultured motor neuron (MN) after lesion in a compartmentalized microfluidic-assisted axotomy device. With increased neuronal activity, we observed an increase in the ratio of regrowing axons after injury in our peripheral-injury model. Moreover, increasing muscular activity induces the liberation of leukemia inhibitory factor and glial cell line-derived neurotrophic factor in a paracrine fashion that in turn triggers axonal regrowth of lesioned MN in our 3D hydrogel cultures. The relevance of our findings as well as the novel approaches used in this study could be useful not only after axotomy events but also in diseases affecting MN survival.

Keywords: Neuromuscular junction, Microfluidics, Axotomy, Paracrine signaling

Diaz-Lucena, Daniela, Escaramis, G., Villar-Piqué, Anna, Hermann, Peter, Schmitz, Matthias, Varges, Daniela, Santana, Isabel, del Rio, José Antonio, Martí, E., Ferrer, Isidre, Baldeiras, I., Zerr, Inga, Llorens, Franc, (2020). A new tetra-plex fluorimetric assay for the quantification of cerebrospinal fluid β-amyloid42, total-tau, phospho-tau and α-synuclein in the differential diagnosis of neurodegenerative dementia Journal of Neurology 267, (9), 2567-2581

Background: Differential diagnosis of neurodegenerative dementia is currently supported by biomarkers including cerebrospinal fluid (CSF) tests. Among them, CSF total-tau (t-tau), phosphorylated tau (p-tau) and β-amyloid42 (Aβ42) are considered core biomarkers of neurodegeneration. In the present work, we hypothesize that simultaneous assessment of these biomarkers together with CSF α-synuclein (α-syn) will significantly improve the differential diagnostic of Alzheimer's disease and other dementias. To that aim, we characterized the analytical and clinical performance of a new tetra-plex immunoassay that simultaneously quantifies CSF Aβ42, t-tau, p-tau and α-syn in the differential diagnosis of neurodegenerative dementia. Methods: Biomarkers' concentrations were measured in neurological controls (n = 38), Alzheimer's disease (n = 35), Creutzfeldt-Jakob disease (n = 37), vascular dementia (n = 28), dementia with Lewy bodies/Parkinson's disease dementia (n = 27) and frontotemporal dementia (n = 34) using the new tetra-plex assay and established single-plex assays. Biomarker's performance was evaluated and diagnostic accuracy in the discrimination of diagnostic groups was determined using partial least squares discriminant analysis. Results: The tetra-plex assay presented accuracies similar to individual single-plex assays with acceptable analytical performance. Significant correlations were observed between tetra-plex and single-plex assays. Using partial least squares discriminant analysis, Alzheimer's disease and Creutzfeldt-Jakob disease were well differentiated, reaching high accuracies in the discrimination from the rest of diagnostic groups. Conclusions: The new tetra-plex assay coupled with multivariate analytical approaches becomes a valuable asset for the differential diagnosis of neurodegenerative dementia and related applications.

Keywords: Neurodegenerative dementia, Cerebrospinal fluid, Biomarker, Amyloid beta, Total-tau, Phospho-tau, α-Synuclein, Multiplexing

del Rio, Jose A., Ferrer, Isidre, (2020). Potential of microfluidics and lab-on-chip platforms to improve understanding of “prion-like” protein assembly and behavior Frontiers in Bioengineering and Biotechnology 8, 570692

Human aging is accompanied by a relevant increase in age-associated chronic pathologies, including neurodegenerative and metabolic diseases. The appearance and evolution of numerous neurodegenerative diseases is paralleled by the appearance of intracellular and extracellular accumulation of misfolded proteins in affected brains. In addition, recent evidence suggests that most of these amyloid proteins can behave and propagate among neural cells similarly to infective prions. In order to improve understanding of the seeding and spreading processes of these “prion-like” amyloids, microfluidics and 3D lab-on-chip approaches have been developed as highly valuable tools. These techniques allow us to monitor changes in cellular and molecular processes responsible for amyloid seeding and cell spreading and their parallel effects in neural physiology. Their compatibility with new optical and biochemical techniques and their relative availability have increased interest in them and in their use in numerous laboratories. In addition, recent advances in stem cell research in combination with microfluidic platforms have opened new humanized in vitro models for myriad neurodegenerative diseases affecting different cellular targets of the vascular, muscular, and nervous systems, and glial cells. These new platforms help reduce the use of animal experimentation. They are more reproducible and represent a potential alternative to classical approaches to understanding neurodegeneration. In this review, we summarize recent progress in neurobiological research in “prion-like” protein using microfluidic and 3D lab-on-chip approaches. These approaches are driven by various fields, including chemistry, biochemistry, and cell biology, and they serve to facilitate the development of more precise human brain models for basic mechanistic studies of cell-to-cell interactions and drug discovery.

Keywords: Lab-On-Chip, Amyloid propagation, Microfluidics, Fibril, Seeding, Spreading, Prion-like, Prionoid

Kaang, Byung Kwon, Mestre, Rafael, Kang, Dong-Chang, Sánchez, Samuel, Kim, Dong-Pyo, (2020). Scalable and integrated flow synthesis of triple-responsive nano-motors via microfluidic Pickering emulsification Applied Materials Today 21, 100854

Artificial micro-/nano-motors are tiny machines as newly emerging tools capable of achieving numerous tasks. In principle, the self-phoretic motions require asymmetric structures in geometry and chemistry. However, conventional production techniques suffered from complex and time consuming multi-step process in low uniformity, and difficult to endow multi-functions into motors. This work disclosed a continuous-flow synthesis of triple-responsive (thermophoretic, chemical and magnetic movement) nano-motors (m-SiO2/Fe3O4-Pdop/Pt) via microfluidic Pickering emulsification in a process of integrated and scalable manner. The droplet microfluidic process allows efficient self-assembly of the silica nanoparticles surrounding the spherical interface of resin droplet, rendering excellent Pickering efficiency and reproducibility, and followed by anisotropic decoration of polydopamine (Pdop) and Pt catalyst in a serial flow process. The obtained Janus nanoparticles reveal double- or triple-responsive self-propulsions with synergic mobility by combining thermophoresis powered by light, catalytic driven motion in H2O2 or magnetic movement by magnet. Further, a non-metallic polydopamine based thermophoretic motion as well as an automated nano-cleaner for rapid water purification by dye removal are convincingly functioned. Finally, this novel integrated flow strategy proves a scalable manufacturing production (> 0.7 g hr−1) of the nano-motors using inexpensive single microreactor, fulfilling quantitative and qualitative needs for versatile applications.

Keywords: Microfluidics Pickering emulsions, Triple-responsive motor, Adsorbent

Sierra, J., Marrugo-Ramírez, J., Rodriguez-Trujillo, R., Mir, M., Samitier, J., (2020). Sensor-integrated microfluidic approaches for liquid biopsies applications in early detection of cancer Sensors 20, (5), 1317

Cancer represents one of the conditions with the most causes of death worldwide. Common methods for its diagnosis are based on tissue biopsies—the extraction of tissue from the primary tumor, which is used for its histological analysis. However, this technique represents a risk for the patient, along with being expensive and time-consuming and so it cannot be frequently used to follow the progress of the disease. Liquid biopsy is a new cancer diagnostic alternative, which allows the analysis of the molecular information of the solid tumors via a body fluid draw. This fluid-based diagnostic method displays relevant advantages, including its minimal invasiveness, lower risk, use as often as required, it can be analyzed with the use of microfluidic-based platforms with low consumption of reagent, and it does not require specialized personnel and expensive equipment for the diagnosis. In recent years, the integration of sensors in microfluidics lab-on-a-chip devices was performed for liquid biopsies applications, granting significant advantages in the separation and detection of circulating tumor nucleic acids (ctNAs), circulating tumor cells (CTCs) and exosomes. The improvements in isolation and detection technologies offer increasingly sensitive and selective equipment’s, and the integration in microfluidic devices provides a better characterization and analysis of these biomarkers. These fully integrated systems will facilitate the generation of fully automatized platforms at low-cost for compact cancer diagnosis systems at an early stage and for the prediction and prognosis of cancer treatment through the biomarkers for personalized tumor analysis.

Keywords: Cancer, Circulant tumor cells (CTC), Circulant tumor DNA (ctDNA), Exosomes, Liquid biopsy, Microfluidic, Sensors

Lakey, A., Ali, Z., Scott, S. M., Chebil, S., Korri-Youssoufi, H., Hunor, S., Ohlander, A., Kuphal, M., Samitier, J., (2019). Impedimetric array in polymer microfluidic cartridge for low cost point-of-care diagnostics Biosensors and Bioelectronics 129, 147-154

Deep Vein Thrombosis and pulmonary embolism (DVT/PE) is one of the most common causes of unexpected death for hospital in-patients. D-dimer is used as a biomarker within blood for the diagnosis of DVT/PE. We report a low-cost microfluidic device with a conveniently biofunctionalised interdigitated electrode (IDE) array and a portable impedimetric reader as a point-of-care (POC) device for the detection of D-dimer to aid diagnosis of DVT/PE. The IDE array elements, fabricated on a polyethylenenaphtalate (PEN) substrate, are biofunctionalised in situ after assembly of the microfluidic device by electropolymerisation of a copolymer of polypyrrole to which is immobilised a histidine tag anti-D-Dimer antibody. The most consistent copolymer films were produced using chronopotentiometry with an applied current of 5μA for a period of 50 s using a two-electrode system. The quality of the biofunctionalisation was monitored using optical microscopy, chronopotentiometry curves and impedimetric analysis. Measurement of clinical plasma sample with a D-dimer at concentration of 437 ng/mL with 15 biofunctionalised IDE array electrodes gave a ratiometric percentage of sample reading against the blank with an average value of 124 ± 15 at 95% confidence. We have demonstrated the concept of a low cost disposable microfluidic device with a receptor functionalised on the IDE array for impedimetric detection towards POC diagnostics. Changing the receptor on the IDE array would allow this approach to be used for the direct detection of a wide range of analytes in a low cost manner.

Keywords: Electropolymerisation, Impedimetric sensing, Interdigitated electrodes, Microfluidics, Point-of-care diagnostics

Badiola-Mateos, M., Hervera, A., del Río, J. A., Samitier, J., (2018). Challenges and future prospects on 3D in-vitro modeling of the neuromuscular circuit Frontiers in Bioengineering and Biotechnology 6, Article 194

Movement of skeletal-muscle fibers is generated by the coordinated action of several cells taking part within the locomotion circuit (motoneurons, sensory-neurons, Schwann cells, astrocytes, microglia, and muscle-cells). Failures in any part of this circuit could impede or hinder coordinated muscle movement and cause a neuromuscular disease (NMD) or determine its severity. Studying fragments of the circuit cannot provide a comprehensive and complete view of the pathological process. We trace the historic developments of studies focused on in-vitro modeling of the spinal-locomotion circuit and how bioengineered innovative technologies show advantages for an accurate mimicking of physiological conditions of spinal-locomotion circuit. New developments on compartmentalized microfluidic culture systems (cμFCS), the use of human induced pluripotent stem cells (hiPSCs) and 3D cell-cultures are analyzed. We finally address limitations of current study models and three main challenges on neuromuscular studies: (i) mimic the whole spinal-locomotion circuit including all cell-types involved and the evaluation of independent and interdependent roles of each one; (ii) mimic the neurodegenerative response of mature neurons in-vitro as it occurs in-vivo; and (iii) develop, tune, implement, and combine cμFCS, hiPSC, and 3D-culture technologies to ultimately create patient-specific complete, translational, and reliable NMD in-vitro model. Overcoming these challenges would significantly facilitate understanding the events taking place in NMDs and accelerate the process of finding new therapies.

Keywords: 3D-culture, Compartmentalized microfluidic culture systems (cμFCS), HiPSC, In-vitro models, Neuromuscular circuit

Urrea, L., Segura, Miriam, Masuda-Suzukake, M., Hervera, A., Pedraz, L., Aznar, J. M. G., Vila, M., Samitier, J., Torrents, E., Ferrer, Isidro, Gavín, R., Hagesawa, M., Del Río, J. A., (2018). Involvement of cellular prion protein in α-synuclein transport in neurons Molecular Neurobiology 55, (3), 1847-1860

The cellular prion protein, encoded by the gene Prnp, has been reported to be a receptor of β-amyloid. Their interaction is mandatory for neurotoxic effects of β-amyloid oligomers. In this study, we aimed to explore whether the cellular prion protein participates in the spreading of α-synuclein. Results demonstrate that Prnp expression is not mandatory for α-synuclein spreading. However, although the pathological spreading of α-synuclein can take place in the absence of Prnp, α-synuclein expanded faster in PrPC-overexpressing mice.

Keywords: Amyloid spreading, Microfluidic devices, Prnp, Synuclein

Parra-Cabrera, C., Samitier, J., Homs-Corbera, A., (2016). Multiple biomarkers biosensor with just-in-time functionalization: Application to prostate cancer detection Biosensors and Bioelectronics 77, 1192-1200

We present a novel lab-on-a-chip (LOC) device for the simultaneous detection of multiple biomarkers using simple voltage measurements. The biosensor functionalization is performed in-situ, immediately before its use, facilitating reagents storage and massive devices fabrication. Sensitivity, limit of detection (LOD) and limit of quantification (LOQ) are tunable depending on the in-chip flown sample volumes. As a proof-of-concept, the system has been tested and adjusted to quantify two proteins found in blood that are susceptible to be used combined, as a screening tool, to diagnose prostate cancer (PCa): prostate-specific antigen (PSA) and spondin-2 (SPON2). This combination of biomarkers has been reported to be more specific for PCa diagnostics than the currently accepted but rather controversial PSA indicator. The range of detection for PSA and SPON2 could be adjusted to the clinically relevant range of 1 to 10. ng/ml. The system was tested for specificity to the evaluated biomarkers. This multiplex system can be modified and adapted to detect a larger quantity of biomarkers, or different ones, of relevance to other specific diseases.

Keywords: Adjustable sensing, Impedance measurements, In situ functionalization, Microfluidics, Prostate specific antigen, Self-assembled monolayers

Asadipour, N., Trepat, X., Muñoz, J. J., (2016). Porous-based rheological model for tissue fluidisation Journal of the Mechanics and Physics of Solids 96, 535-549

It has been experimentally observed that cells exhibit a fluidisation process when subjected to a transient stretch, with an eventual recovery of the mechanical properties upon removal of the applied deformation. This fluidisation process is characterised by a decrease of the storage modulus and an increase of the phase angle. We propose a rheological model which is able to reproduce this combined mechanical response. The model is described in the context of continua and adapted to a cell-centred particle system that simulates cell–cell interactions. Mechanical equilibrium is coupled with two evolution laws: (i) one for the reference configuration, and (ii) another for the porosity or polymer density. The first law depends on the actual strain of the tissue, while the second assumes different remodelling rates during porosity increase and decrease. The theory is implemented on a particle based model and tested on a stretching experiment. The numerical results agree with the experimental measurements for different stretching magnitudes.

Keywords: Cell remodelling, Cell rheology, Fluidisation, Softening, Viscoelasticity

Páez-Avilés, C., Juanola-Feliu, E., Punter-Villagrasa, J., Del Moral Zamora, B., Homs-Corbera, A., Colomer-Farrarons, J., Miribel-Català , P. L., Samitier, J., (2016). Combined dielectrophoresis and impedance systems for bacteria analysis in microfluidic on-chip platforms Sensors 16, (9), 1514

Bacteria concentration and detection is time-consuming in regular microbiology procedures aimed to facilitate the detection and analysis of these cells at very low concentrations. Traditional methods are effective but often require several days to complete. This scenario results in low bioanalytical and diagnostic methodologies with associated increased costs and complexity. In recent years, the exploitation of the intrinsic electrical properties of cells has emerged as an appealing alternative approach for concentrating and detecting bacteria. The combination of dielectrophoresis (DEP) and impedance analysis (IA) in microfluidic on-chip platforms could be key to develop rapid, accurate, portable, simple-to-use and cost-effective microfluidic devices with a promising impact in medicine, public health, agricultural, food control and environmental areas. The present document reviews recent DEP and IA combined approaches and the latest relevant improvements focusing on bacteria concentration and detection, including selectivity, sensitivity, detection time, and conductivity variation enhancements. Furthermore, this review analyses future trends and challenges which need to be addressed in order to successfully commercialize these platforms resulting in an adequate social return of public-funded investments.

Keywords: Bacteria, Dielectrophoresis, Impedance, Microfluidics, On-chip

Llorens, Franc, Zafar, Saima, Ansoleaga, Belén, Shafiq, Mohsin, Blanco, Rosi, Carmona, Marga, Grau-Rivera, Oriol, Nos, Carlos, Gelpí, Ellen, del Río, José Antonio, Zerr, Inga, Ferrer, Isidre, (2015). Subtype and regional regulation of prion biomarkers in sporadic Creutzfeldt-Jakob disease Neuropathology and Applied Neurobiology , 41, (5), 631-645

Aims Creutzfeldt-Jakob disease (CJD) is a rapid progressive neurological disease leading to dementia and death. Prion biomarkers are altered in the cerebrospinal fluid (CSF) of CJD patients, but the pathogenic mechanisms underlying these alterations are still unknown. The present study examined prion biomarker levels in the brain and CSF of sporadic CJD (sCJD) cases and their correlation with neuropathological lesion profiles. Methods The expression levels of 14-3-3, Tau, phospho-Tau and α-synuclein were measured in the CSF and brain of sCJD cases in a subtype- and region-specific manner. In addition, the activity of prion biomarker kinases, the expression levels of CJD hallmarks and the most frequent neuropathological sCJD findings were analysed. Results Prion biomarkers levels were increased in the CSF of sCJD patients; however, correlations between mRNA, total protein and their phosphorylated forms in brain were different. The observed downregulation of the main Tau kinase, GSK3, in sCJD brain samples may help to explain the differential phospho-Tau/Tau ratios between sCJD and other dementias in the CSF. Importantly, CSF biomarkers levels do not necessarily correlate with sCJD neuropathological findings. Interpretation Present findings indicate that prion biomarkers levels in sCJD tissues and their release into the CSF are differentially regulated following specific modulated responses, and suggest a functional role for these proteins in sCJD pathogenesis.

Keywords: Creutzfeldt-Jakob disease, Prion Protein, Cerebrospinal fluid, Prion Biomarkers, disease subtype, Glycogen synthase kinase 3

da Palma, R. K., Campillo, N., Uriarte, J. J., Oliveira, L. V. F., Navajas, D., Farré, R., (2015). Pressure- and flow-controlled media perfusion differently modify vascular mechanics in lung decellularization Journal of the Mechanical Behavior of Biomedical Materials , 49, 69-79

Organ biofabrication is a potential future alternative for obtaining viable organs for transplantation. Achieving intact scaffolds to be recellularized is a key step in lung bioengineering. Perfusion of decellularizing media through the pulmonary artery has shown to be effective. How vascular perfusion pressure and flow vary throughout lung decellularization, which is not well known, is important for optimizing the process (minimizing time) while ensuring scaffold integrity (no barotrauma). This work was aimed at characterizing the pressure/flow relationship at the pulmonary vasculature and at how effective vascular resistance depends on pressure- and flow-controlled variables when applying different methods of media perfusion for lung decellularization. Lungs from 43 healthy mice (C57BL/6; 7-8 weeks old) were investigated. After excision and tracheal cannulation, lungs were inflated at 10cmH2O airway pressure and subjected to conventional decellularization with a solution of 1% sodium dodecyl sulfate (SDS). Pressure (PPA) and flow (V'PA) at the pulmonary artery were continuously measured. Decellularization media was perfused through the pulmonary artery: (a) at constant PPA=20cmH2O or (b) at constant V'PA=0.5 and 0.2ml/min. Effective vascular resistance was computed as Rv=PPA/V'PA. Rv (in cmH2O/(ml/min)); mean±SE) considerably varied throughout lung decellularization, particularly for pressure-controlled perfusion (from 29.1±3.0 in baseline to a maximum of 664.1±164.3 (p<0.05), as compared with flow-controlled perfusion (from 49.9±3.3 and 79.5±5.1 in baseline to a maximum of 114.4±13.9 and 211.7±70.5 (p<0.05, both), for V'PA of 0.5 and 0.2ml/min respectively. Most of the media infused to the pulmonary artery throughout decellularization circulated to the airways compartment across the alveolar-capillary membrane. This study shows that monitoring perfusion mechanics throughout decellularization provides information relevant for optimizing the process time while ensuring that vascular pressure is kept within a safety range to preserve the organ scaffold integrity.

Keywords: Acellular lung, Fluid mechanics, Lung bioengineering, Lung scaffold, Organ biofabrication, Tissue engineering, Vascular resistance

Seo, K. D., Kwak, B. K., Sánchez, S., Kim, D. S., (2015). Microfluidic-assisted fabrication of flexible and location traceable organo-motor IEEE Transactions on Nanobioscience , 14, (3), 298-304

In this paper, we fabricate a flexible and location traceable micromotor, called organo-motor, assisted by microfluidic devices and with high throughput. The organo-motors are composed of organic hydrogel material, poly (ethylene glycol) diacrylate (PEGDA), which can provide the flexibility of their structure. For spatial and temporal traceability of the organo-motors under magnetic resonance imaging (MRI), superparamagnetic iron oxide nanoparticles (SPION; Fe3O4) were incorporated into the PEGDA microhydrogels. Furthermore, a thin layer of platinum (Pt) was deposited onto one side of the SPION-PEGDA microhydrogels providing geometrical asymmetry and catalytic propulsion in aqueous fluids containing hydrogen peroxide solution, H2O2. Furthermore, the motion of the organo-motor was controlled by a small external magnet enabled by the presence of SPION in the motor architecture.

Keywords: Flexible, Hydrogel, Magnetic resonance imaging, Microfluidics, Micromotor, Microparticle, Organo-motor, Poly (ethylene glycol) diacrylate, Self-propulsion, Superparamagnetic iron oxide nanoparticles

Rajzer, I., Menaszek, E., Kwiatkowski, R., Planell, J. A., Castaño, O., (2014). Electrospun gelatin/poly(ε-caprolactone) fibrous scaffold modified with calcium phosphate for bone tissue engineering Materials Science and Engineering: C 44, 183-190

In this study gelatin (Gel) modified with calcium phosphate nanoparticles (SG5) and polycaprolactone (PCL) were used to prepare a 3D bi-layer scaffold by collecting electrospun PCL and gelatin/SG5 fibers separately in the same collector. The objective of this study was to combine the desired properties of PCL and Gel/SG5 in the same scaffold in order to enhance mineralization, thus improving the ability of the scaffold to bond to the bone tissue. The scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and the wide angle X-ray diffraction (WAXD) measurements confirmed that SG5 nanoparticles were successfully incorporated into the fibrous gelatin matrix. The composite Gel/SG5/PCL scaffold exhibited more enhanced mechanical properties than individual Gel and Gel/SG5 scaffolds. The presence of SG5 nanoparticles accelerated the nucleation and growth of apatite crystals on the surface of the composite Gel/SG5/PCL scaffold in simulated body fluid (SBF). The osteoblast response in vitro to developed electrospun scaffolds (PCL and Gel/SG5/PCL) was investigated by using normal human primary NHOst cell lines. NHOst cell culture studies showed that higher alkaline phosphatase (ALP) activity and better mineralization were obtained in the case of composite materials than in pure PCL scaffolds. The mechanically strong PCL scaffold served as a skeleton, while the Gel/SG5 fibers facilitated cell spreading and mineralization of the scaffold.

Keywords: Bilayer fibrous scaffold, Ceramic nanoparticles, Electrospinning, Gelatin, Polycaprolactone, Biomechanics, Bone, Calcium phosphate, Cell culture, Electrospinning, Fourier transform infrared spectroscopy, Mechanical properties, Mineralogy, Nanoparticles, Phosphatases, Polycaprolactone, Scanning electron microscopy, X ray diffraction, Polycaprolactone, Alkaline phosphatase activity, Bone tissue engineering, Calcium phosphate nanoparticles, Ceramic nanoparticles, Fibrous scaffolds, Gelatin, Simulated body fluids, Wide-angle x-ray diffraction, Electrospuns, Scaffolds (biology), Electrospinning

Castillo-Fernandez, O., Rodriguez-Trujillo, R., Gomila, G., Samitier, J., (2014). High-speed counting and sizing of cells in an impedance flow microcytometer with compact electronic instrumentation Microfluidics and Nanofluidics , 16, (1-2), 91-99

Here we describe a high-throughput impedance flow cytometer on a chip. This device was built using compact and inexpensive electronic instrumentation. The system was used to count and size a mixed cell sample containing red blood cells and white blood cells. It demonstrated a counting capacity of up to ~500 counts/s and was validated through a synchronised high-speed optical detection system. In addition, the device showed excellent discrimination performance under high-throughput conditions.

Keywords: Electronics, Impedance, Microcytometry, Microfluidics, Red blood cells (RBCs), White blood cells (WBCs)

Rigat, L., Bernabeu, M., Elizalde, A., de Niz, M., Martin-Jaular, L., Fernandez-Becerra, C., Homs-Corbera, A., del Portillo, H. A., Samitier, J., (2014). Human splenon-on-a-chip: Design and validation of a microfluidic model resembling the interstitial slits and the close/fast and open/slow microcirculations IFMBE Proceedings XIII Mediterranean Conference on Medical and Biological Engineering and Computing 2013 (ed. Roa Romero, Laura M.), Springer (Seville, Spain) 41, 884-887

Splenomegaly, albeit variably, is a landmark of malaria infection. Due to technical and ethical constraints, however, the role of the spleen in malaria remains vastly unknown. The spleen is a complex three-dimensional branched vasculature exquisitely adapted to perform different functions containing closed/rapid and open/slow microcirculations, compartmentalized parenchyma (red pulp, white pulp and marginal zone), and sinusoidal structure forcing erythrocytes to squeeze through interstitial slits before reaching venous circulation. Taking into account these features, we have designed and developed a newfangled microfluidic device of a human splenon-on-a-chip (the minimal functional unit of the red pulp facilitating blood-filtering and destruction of malarial-infected red blood cells). Our starting point consisted in translating splenon physiology to the most similar microfluidic network, mimicking the hydrodynamic behavior of the organ, to evaluate and simulate its activities, mechanics and physiological responses and, therefore, enable us to study biological hypotheses. Different physiological features have been translated into engineering elements that can be combined to integrate a biomimetic microfluidic spleen model. The device is fabricated in polydimethylsiloxane (PDMS), a biocompatible polymer, irreversibly bonded to glass. Microfluidics analyses have confirmed that 90% of the blood circulates through a fast-flow compartment whereas the remaining 10% circulates through a slow compartment, equivalently to what has been observed in a real spleen. Moreover, erythrocytes and reticulocytes going through the slow-flow compartment squeeze at the end of it through 2μm physical constraints resembling interstitial slits to reach the closed/rapid circulation.

Keywords: Malaria, Microfluidics, Organ-on-a-chip, Spleen

Cabrera, I., Elizondo, E., Esteban, O., Corchero, J. L., Melgarejo, M., Pulido, D., Córdoba, A., Moreno, E., Unzueta, U., Vazquez, E., Abasolo, I., Schwartz, S., Villaverde, A., Albericio, F., Royo, M., García-Parajo, M. F., Ventosa, N., Veciana, J., (2013). Multifunctional nanovesicle-bioactive conjugates prepared by a one-step scalable method using CO2-expanded solvents Nano Letters 13, (8), 3766-3774

The integration of therapeutic biomolecules, such as proteins and peptides, in nanovesicles is a widely used strategy to improve their stability and efficacy. However, the translation of these promising nanotherapeutics to clinical tests is still challenged by the complexity involved in the preparation of functional nanovesicles and their reproducibility, scalability, and cost production. Here we introduce a simple one-step methodology based on the use of CO2-expanded solvents to prepare multifunctional nanovesicle- bioactive conjugates. We demonstrate high vesicle-to-vesicle homogeneity in terms of size and lamellarity, batch-to-batch consistency, and reproducibility upon scaling-up. Importantly, the procedure is readily amenable to the integration/encapsulation of multiple components into the nanovesicles in a single step and yields sufficient quantities for clinical research. The simplicity, reproducibility, and scalability render this one-step fabrication process ideal for the rapid and low-cost translation of nanomedicine candidates from the bench to the clinic.

Keywords: Bioconjugates, Compressed fluids, Liposomes, Manomedicine, Nanovesicles, Scale-up, Supercritical fluids

Salerno, A., Levato, R., Mateos-Timoneda, M. A., Engel, E., Netti, P. A., Planell, J. A., (2013). Modular polylactic acid microparticle-based scaffolds prepared via microfluidic emulsion/solvent displacement process: Fabrication, characterization, and in vitro mesenchymal stem cells interaction study Journal of Biomedical Materials Research - Part A , 101A, (3), 720-732

The present study reports a novel approach for the design and fabrication of polylactic acid (PLA) microparticle-based scaffolds with microstructural properties suitable for bone and cartilage regeneration. Macroporous PLA scaffolds with controlled shape were fabricated by means of a semicontinuous process involving (1) microfluidic emulsification of a PLA/ethyl lactate solution (5% w/v) in a span 80/paraffin oil solution (3% v/v) followed by (2) particles coagulation/assembly in an acetone/water solution for the development of a continuous matrix. Porous scaffolds prepared from particles with monomodal or bimodal size distribution, overall porosity ranges from 93 to 96%, interparticles porosity from 41 to 54%, and static compression moduli from 0.3 to 1.4 MPa were manufactured by means of flow rate modulation of of the continuous phase during emulsion. The biological response of the scaffolds was assessed in vitro by using bone marrow-derived rat mesenchymal stem cells (MSCs). The results demonstrated the ability of the scaffolds to support the extensive and uniform three-dimensional adhesion, colonization, and proliferation of MSCs within the entire construct.

Keywords: Green solvent, Microfluidic, Microstructure, Stem cells, Scaffold

Esquivel, Juan Pablo , Castellarnau, Marc , Senn, Tobias , Löchel, Bernd , Samitier, Josep , Sabaté, Neus , (2012). Fuel cell-powered microfluidic platform for lab-on-a-chip applications Lab on a Chip 12, (1), 74-79

The achievement of a higher degree of integration of components – especially micropumps and power sources – is a challenge currently being pursued to obtain portable and totally autonomous microfluidic devices. This paper presents the integration of a micro direct methanol fuel cell (mDMFC) in a microfluidic platform as a smart solution to provide both electrical and pumping power to a Lab-on-a-Chip system. In this system the electric power produced by the fuel cell is available to enable most of the functionalites required by the microfluidic chip, while the generated CO2 from the electrochemical reaction produces a pressure capable of pumping a liquid volume through a microchannel. The control of the fuel cell operating conditions allows regulation of the flow rate of a liquid sample through a microfluidic network. The relation between sample flow rate and the current generated by the fuel cell is practically linear, achieving values in the range of 4–18 mL min 1 while having an available power between 1–4 mW. This permits adjusting the desired flow rate for a given application by controlling the fuel cell output conditions and foresees a fully autonomous analytical Lab-on-a-Chip in which the same device would provide the electrical power to a detection module and at the same time use the CO2 pumping action to flow the required analytes through a particular microfluidic design.

Keywords: micro direct methanol fuel cell (mDMFC), Lab-on-a-chip (LOC), Microfluidic device

Comelles, J., Hortigüela, V., Samitier, J., Martinez, E., (2012). Versatile gradients of covalently bound proteins on microstructured substrates Langmuir 28, (38), 13688-13697

In this work, we propose an easy method to produce highly tunable gradients of covalently bound proteins on topographically modified poly(methyl methacrylate). We used a rnicrofluidic approach to obtain linear gradients with high slope (0.5, relevant at the single-cell level. These protein gradients were characterized using fluorescence microscopy and surface plasmon resonance. Both experimental results and theoretical modeling on the protein gradients generated have proved them to be highly reproducible, stable up to 7 days, and easily tunable. This method enables formation of versatile cell culture platforms combining both complex biochemical and physical cues in an attempt to approach in vitro cell culture methods to in vivo cellular microenvironments.

Keywords: Cell-migration, Microfluidic channel, Surface, Streptavidin, Molecules, Topography, Mechanisms, Generation, Responses, Guidance

Melchels, Ferry P. W., Tonnarelli, Beatrice, Olivares, Andy L., Martin, Ivan, Lacroix, Damien, Feijen, Jan, Wendt, David J., Grijpma, Dirk W., (2011). The influence of the scaffold design on the distribution of adhering cells after perfusion cell seeding Biomaterials 32, (11), 2878-2884

In natural tissues, the extracellular matrix composition, cell density and physiological properties are often non-homogeneous. Here we describe a model system, in which the distribution of cells throughout tissue engineering scaffolds after perfusion seeding can be influenced by the pore architecture of the scaffold. Two scaffold types, both with gyroid pore architectures, were designed and built by stereolithography: one with isotropic pore size (412 ± 13 [mu]m) and porosity (62 ± 1%), and another with a gradient in pore size (250-500 [mu]m) and porosity (35%-85%). Computational fluid flow modelling showed a uniform distribution of flow velocities and wall shear rates (15-24 s-1) for the isotropic architecture, and a gradient in the distribution of flow velocities and wall shear rates (12-38 s-1) for the other architecture. The distribution of cells throughout perfusion-seeded scaffolds was visualised by confocal microscopy. The highest densities of cells correlated with regions of the scaffolds where the pores were larger, and the fluid velocities and wall shear rates were the highest. Under the applied perfusion conditions, cell deposition is mainly determined by local wall shear stress, which, in turn, is strongly influenced by the architecture of the pore network of the scaffold.

Keywords: Scaffolds, Microstructure, Cell adhesion, Confocal microscopy, Image analysis, Computational fluid dynamics

Ivon Rodriguez-Villarreal, Angeles, Tarn, Mark D., Madden, Leigh A., Lutz, Julia B., Greenman, John, Samitier, Josep, Pamme, Nicole, (2011). Flow focussing of particles and cells based on their intrinsic properties using a simple diamagnetic repulsion setup Lab on a Chip 11, (7), 1240-1248

The continuous flow focussing and manipulation of particles and cells are important factors in microfluidic applications for performing accurate and reproducible procedures downstream. Many particle focussing methods require complex setups or channel designs that can limit the process and its applications. Here, we present diamagnetic repulsion as a simple means of focussing objects in continuous flow, based only on their intrinsic properties without the requirement of any label. Diamagnetic polystyrene particles were suspended in a paramagnetic medium and pumped through a capillary between a pair of permanent magnets, whereupon the particles were repelled by each magnet into the central axis of the capillary, thus achieving focussing. By investigating this effect, we found that the focussing was greatly enhanced with (i) increased magnetic susceptibility of the medium, (ii) reduced flow rate of the suspension, (iii) increased particle size, and (iv) increased residence time in the magnetic field. Furthermore, we applied diamagnetic repulsion to the flow focussing of living, label-free HaCaT cells.

Keywords: Feeble magnetic substances, On-chip, Blood-cells, Microfluidic device, Separation, Field, Levitation, Magnetophoresis, Fractionation, Nanoparticles

Malandrino, Andrea, Noailly, Jerome, Lacroix, Damien, (2011). The effect of sustained compression on oxygen metabolic transport in the intervertebral disc decreases with degenerative changes PLoS Computational Biology Plos Computational Biology , 7, (8), 1-12

Intervertebral disc metabolic transport is essential to the functional spine and provides the cells with the nutrients necessary to tissue maintenance. Disc degenerative changes alter the tissue mechanics, but interactions between mechanical loading and disc transport are still an open issue. A poromechanical finite element model of the human disc was coupled with oxygen and lactate transport models. Deformations and fluid flow were linked to transport predictions by including strain-dependent diffusion and advection. The two solute transport models were also coupled to account for cell metabolism. With this approach, the relevance of metabolic and mechano-transport couplings were assessed in the healthy disc under loading-recovery daily compression. Disc height, cell density and material degenerative changes were parametrically simulated to study their influence on the calculated solute concentrations. The effects of load frequency and amplitude were also studied in the healthy disc by considering short periods of cyclic compression. Results indicate that external loads influence the oxygen and lactate regional distributions within the disc when large volume changes modify diffusion distances and diffusivities, especially when healthy disc properties are simulated. Advection was negligible under both sustained and cyclic compression. Simulating degeneration, mechanical changes inhibited the mechanical effect on transport while disc height, fluid content, nucleus pressure and overall cell density reductions affected significantly transport predictions. For the healthy disc, nutrient concentration patterns depended mostly on the time of sustained compression and recovery. The relevant effect of cell density on the metabolic transport indicates the disturbance of cell number as a possible onset for disc degeneration via alteration of the metabolic balance. Results also suggest that healthy disc properties have a positive effect of loading on metabolic transport. Such relation, relevant to the maintenance of the tissue functional composition, would therefore link disc function with disc nutrition.

Keywords: Bovine nucleus pulposus, Human anulus fibrosus, Finite-element, Fluid-flow, Hydraulic permeability, Confined compression, Coupled diffusion, Solute transport, Water-content, Lumbar spine

Garcia-Manyes, S., Redondo-Morata, L., Oncins, G., Sanz, F., (2010). Nanomechanics of lipid bilayers: Heads or tails? Journal of the American Chemical Society American Chemical Society 132, (37), 12874-12886

Understanding the effect of mechanical stress on membranes is of primary importance in biophysics. Here we use force spectroscopy AFM to quantitatively characterize the nanomechanical stability of supported lipid bilayers as a function of their chemical composition. The onset of plastic deformation reveals itself as a repetitive jump in the approaching force curve, which represents a molecular fingerprint for the bilayer mechanical stability. By systematically probing a set of chemically distinct supported lipid bilayers (SLBs), we first show that both the headgroup and tail have a decisive effect on their mechanical properties. While the mechanical stability of the probed SLBs linearly increases by 3.3 nN upon the introduction of each additional -CH2- in the chain, it exhibits a significant dependence on the phospholipid headgroup, ranging from 3 nN for DPPA to 66 nN for DPPG. Furthermore, we also quantify the reduction of the membrane mechanical stability as a function of the number of unsaturations and molecular branching in the chemical structure of the apolar tails. Finally, we demonstrate that, upon introduction of cholesterol and ergosterol, contrary to previous belief the mechanical stability of membranes not only increases linearly in the liquid phase (DLPC) but also for phospholipids present in the gel phase (DPPC). Our results are discussed in the framework of the continuum nucleation model. This work highlights the compelling effect of subtle variations in the chemical structure of phospholipid molecules on the membrane response when exposed to mechanical forces, a mechanism of common occurrence in nature.

Keywords: Atomic-force microscopy, Molecular-dynamics simulation, Aqueous-electrolyte solutions, Supported planar membranes, Phospholipid-bilayers, Biological-membranes, Physical-properties, Fluid membranes, Model membranes, Chain-length

Santoro, R., Olivares, A. L., Brans, G., Wirz, D., Longinotti, C., Lacroix, D., Martin, I., Wendt, D., (2010). Bioreactor based engineering of large-scale human cartilage grafts for joint resurfacing Biomaterials 31, (34), 8946-8952

Apart from partial or total joint replacement, no surgical procedure is currently available to treat large and deep cartilage defects associated with advanced diseases such as osteoarthritis. In this work, we developed a perfusion bioreactor system to engineer human cartilage grafts in a size with clinical relevance for unicompartmental resurfacing of human knee joints (50 mm diameter x 3 mm thick). Computational fluid dynamics models were developed to optimize the flow profile when designing the perfusion chamber. Using the developed system, human chondrocytes could be seeded throughout large 50 mm diameter scaffolds with a uniform distribution. Following two weeks culture, tissues grown in the bioreactor were viable and homogeneously cartilaginous, with biomechanical properties approaching those of native cartilage. In contrast, tissues generated by conventional manual production procedures were highly inhomogeneous and contained large necrotic regions. The unprecedented engineering of human cartilage tissues in this large-scale opens the practical perspective of grafting functional biological substitutes for the clinical treatment for extensive cartilage defects, possibly in combination with surgical or pharmacological therapies to support durability of the implant. Ongoing efforts are aimed at integrating the up-scaled bioreactor based processes within a fully automated and closed manufacturing system for safe, standardized, and GMP compliant production of large-scale cartilage grafts.

Keywords: Bioreactor, Cartilage repair, Computational fluid dynamics, Scale-up, Regenerative medicine, Tissue engineering

Fumagalli, L., Ferrari, G., Sampietro, M., Gomila, G., (2009). Quantitative nanoscale dielectric microscopy of single-layer supported biomembranes Nano Letters 9, (4), 1604-1608

We present the experimental demonstration of low-frequency dielectric constant imaging of single-layer supported biomembranes at the nanoscale. The dielectric constant image has been quantitatively reconstructed by combining the thickness and local capacitance obtained using a scanning force microscope equipped with a sub-attofarad low-frequency capacitance detector. This work opens new possibilities for studying bioelectric phenomena and the dielectric properties of biological membranes at the nanoscale.

Keywords: Atomic-force microscopy, Nnear-field microscopy, Purple membrane, Scanning capacitance, Biological-systems, Fluid, Spectroscopy, Resolution, Proteins, Dynamics

Milan, J. L., Planell, J. A., Lacroix, D., (2009). Computational modelling of the mechanical environment of osteogenesis within a polylactic acid-calcium phosphate glass scaffold Biomaterials 30, (25), 4219-4226

A computational model based on finite element method (FEM) and computational fluid dynamics (CFD) is developed to analyse the mechanical stimuli in a composite scaffold made of polylactic acid (PLA) matrix with calcium phosphate glass (Glass) particles. Different bioreactor loading conditions were simulated within the scaffold. In vitro perfusion conditions were reproduced in the model. Dynamic compression was also reproduced in an uncoupled fluid-structure scheme: deformation level was studied analyzing the mechanical response of scaffold alone under static compression while strain rate was studied considering the fluid flow induced by compression through fixed scaffold. Results of the model show that during perfusion test an inlet velocity of 25mum/s generates on scaffold surface a fluid flow shear stress which may stimulate osteogenesis. Dynamic compression of 5% applied on the PLA-Glass scaffold with a strain rate of 0.005s(-1) has the benefit to generate mechanical stimuli based on both solid shear strain and fluid flow shear stress on large scaffold surface area. Values of perfusion inlet velocity or compression strain rate one order of magnitude lower may promote cell proliferation while values one order of magnitude higher may be detrimental for cells. FEM-CFD scaffold models may help to determine loading conditions promoting bone formation and to interpret experimental results from a mechanical point of view.

Keywords: Bone tissue engineering, Scaffold, Finite element analysis, Computational fluid dynamics, Mechanical stimuli

Olivares, A. L., Marshal, E., Planell, J. A., Lacroix, D., (2009). Finite element study of scaffold architecture design and culture conditions for tissue engineering Biomaterials 30, (30), 6142-6149

Tissue engineering scaffolds provide temporary mechanical support for tissue regeneration and transfer global mechanical load to mechanical stimuli to cells through its architecture. In this study the interactions between scaffold pore morphology, mechanical stimuli developed at the cell microscopic level, and culture conditions applied at the macroscopic scale are studied on two regular scaffold structures. Gyroid and hexagonal scaffolds of 55% and 70% porosity were modeled in a finite element analysis and were submitted to an inlet fluid flow or compressive strain. A mechanoregulation theory based on scaffold shear strain and fluid shear stress was applied for determining the influence of each structures on the mechanical stimuli on initial conditions. Results indicate that the distribution of shear stress induced by fluid perfusion is very dependent on pore distribution within the scaffold. Gyroid architectures provide a better accessibility of the fluid than hexagonal structures. Based on the mechanoregulation theory, the differentiation process in these structures was more sensitive to inlet fluid flow than axial strain of the scaffold. This study provides a computational approach to determine the mechanical stimuli at the cellular level when cells are cultured in a bioreactor and to relate mechanical stimuli with cell differentiation.

Keywords: Tissue engineering, Scaffold, Rapid prototyping, Computational fluid dynamics, Finite element

Mir, M., Homs, A., Samitier, J., (2009). Integrated electrochemical DNA biosensors for lab-on-a-chip devices Electrophoresis , 30, (19), 3386-3397

Analytical devices able to perform accurate and fast automatic DNA detection or sequencing procedures have many potential benefits in the biomedical and environmental fields. The conversion of biological or biochemical responses into quantifiable optical, mechanical or electronic signals is achieved by means of biosensors. Most of these transducing elements can be miniaturized and incorporated into lab-on-a-chip devices, also known as Micro Total Analysis Systems. The use of multiple DNA biosensors integrated in these miniaturized laboratories, which perform several analytical operations at the microscale, has many cost and efficiency advantages. Tiny amounts of reagents and samples are needed and highly sensitive, fast and parallel assays can be done at low cost. A particular type of DNA biosensors are the ones used based on electrochemical principles. These sensors offer several advantages over the popular fluorescence-based detection schemes. The resulting signal is electrical and can be processed by conventional electronics in a very cheap and fast manner. Furthermore, the integration and miniaturization of electrochemical transducers in a microsystem makes easier its fabrication in front of the most common currently used detection method. In this review, different electrochemical DNA biosensors integrated in analytical microfluidic devices are discussed and some early stage commercial products based on this strategy are presented.

Keywords: DNA, Electrochemical DNA biosensors, Electrochemistry, Lab-on-a-chip, Micro Total Analysis systems, Field-effect transistors, Sequence-specific detection, Chemical-analysis systems, Solid-state nanopores, Carbon nanotubes, Microfluidic device, Electrical detection, Hybridization, Molecules, Sensor

Rodriguez-Trujillo, R., Castillo-Fernandez, O., Garrido, M., Arundell, M., Valencia, A., Gomila, G., (2008). High-speed particle detection in a micro-Coulter counter with two-dimensional adjustable aperture Biosensors and Bioelectronics 24, (2), 290-296

This article presents the fabrication and characterisation of a high-speed detection micro-Coulter counter with two-dimensional (2D) adjustable aperture and differential impedance detection. The developed device has been fabricated from biocompatible and transparent materials (polymer and glass) and uses the principle of hydrodynamic focusing in two dimensions. The use of a conductive solution for the sample flux and non-conductive solutions for the focalising fluxes provides an adjustable sample flow where particles are aligned and the resistive response concentrated, consequently enhancing the sensitivity and versatility of the device. High-speed counting of 20 mu m polystyrene particles and 5 mu m yeast cells with a rate of up to 1000 particles/s has been demonstrated. Two-dimensional focusing conditions have been used in devices with physical cross-sectional areas of 180 mu m x 65 mu m and 100 mu m x 43 mu m, respectively, in which particles resulted undetectable in the absence of focusing. The 2D-focusing conditions have provided, in addition, increased detection sensitivity by a factor of 1.6 as compared to 1 D-focusing conditions.

Keywords: Impedance, Chip, Microfluidics

Rodriguez-Trujillo, R., Castillo-Fernandez, O., Arundell, M., Samitier, J., Gomila, G., (2008). Yeast cells detection in a very fast and highly versatile microfabricated cytometer MicroTAS 2008 12th International Conference on Miniaturized Systems for Chemistry and Life Sciences , Chemical and Biological Microsystems Society (San Diego, USA) , 1888-1890

A novel microfluidic chip able to detect a wide range of different cell sizes at very high rates is reported. The device uses two-dimensional hydrodynamic focusing [1] of the sample (conducting) flow by three non-conducting flows and high-speed differential impedance detection electronics. High-speed counting of 15μm polystyrene particles and 5μm yeast cells with a rate of up to 1000 particles/s has been demonstrated. Using of two-dimensional focusing effect turn out to be essential in a device with very large cross-sectional area (100x43 μm2) in which particles result undetectable in the absence of focusing.

Keywords: Coulter-counter, Impedance, Microfluidics, Polydimethylsiloxane