Analysis of red blood cell mechanical properties

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged PDF version of thesis.Includes bibliographical references (p. 118-126).Decreased deformability of human red blood cells (RBCs) is both a cause of disease and biomarker for disease (1). To traverse blood capillaries, the biconcave disk-shaped RBC must deform dramatically, since the diameter of the unconstrained RBC is larger than that of the capillaries. If the RBC becomes immobilized in a capillary, hypoxia and tissue injury may result, potentially leading to death. Changes in RBC deformability may be attributable to genetics (e.g. sickle cell anemia (2) and spherocytosis (3)), drug exposure (e.g. pentoxifylline (4)), and disease (e.g. diabetes (5) and malaria (6)). Within the past 15 years, microfabrication techniques have enabled the creation of pores comparable in size and shape to the smallest human capillaries (7) and slits in the spleen (8). We use this microfabrication ability to create devices that analyze and separate RBCs of different deformability. The first device we create is an automated 'deformability cytometer' that measures dynamic mechanical responses of 103~104 individual cells in a cell population. Fluorescence measurements of each cell are simultaneously acquired, resulting in a population-based correlation between biochemical properties (e.g. cell surface markers) and dynamic mechanical deformability. This device is especially applicable to heterogeneous cell populations, and we demonstrate its ability to mechanically characterize a small number of ring-stage malaria-infected RBCs in a large population of healthy RBCs. Next we present a device whose design is based on the architecture of the human spleen. This device is able to continuously separate more deformable from less deformable RBCs. We demonstrate the ability of this device to separate schizont-stage malaria-infected RBCs from healthy RBCs. Together, these devices enable the analysis and separation of single-RBCs based on deformability.by Hansen Chang Bow.Ph.D

Characterization of nanofilter arrays for small molecule separation

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 59-60).Experimental studies were performed to evaluate methods of improving separation resolution and speed in microfabricated nanofilter arrays. Experiment parameters investigated include electric field strength, nanofilter geometry, and buffer concentration. DNA polymers of size 25-1000 base pairs were the subject of our study. We concluded that increasing electric field strength resulted in inferior separation for larger DNA polymers (400-1000 bp). Additionally, we quantified the improvement in resolution of smaller nanofilter pores and lower buffer concentration. A theoretical model based on Macrotransport Theory was developed to estimate average species velocity and peak dispersion.by Hansen Chang Bow.S.M

Dynamic deformability of Plasmodium falciparum-infected erythrocytes exposed to artesunate in vitro

Artesunate (ART) is widely used for the treatment of malaria, but the mechanisms of its effects on parasitized red blood cells (RBCs) are not fully understood. We investigated ART's influence on the dynamic deformability of ring-stage Plasmodium falciparum infected red blood cells (iRBCs) in order to elucidate its role in cellular mechanobiology. The dynamic deformability of RBCs was measured by passing them through a microfluidic device with repeated bottleneck structures. The quasi-static deformability measurement was performed using micropipette aspiration. After ART treatment, microfluidic experiments showed 50% decrease in iRBC transit velocity whereas only small (~10%) velocity reduction was observed among uninfected RBCs (uRBCs). Micropipette aspiration also revealed ART-induced stiffening in RBC membranes. These results demonstrate, for the first time, that ART reduces the dynamic and quasi-static RBC deformability, which may subsequently influence blood circulation through the microvasculature and spleen cordal meshwork, thus adding a new aspect to artesunate's mechanism of action.Singapore-MIT Alliance for Research and Technology CenterNational Institutes of Health (U.S.) (Grant R01 HL094270-01A1

A microfabricated deformability-based flow cytometer with application to malaria

Malaria resulting from Plasmodium falciparum infection is a major cause of human suffering and mortality. Red blood cell (RBC) deformability plays a major role in the pathogenesis of malaria. Here we introduce an automated microfabricated “deformability cytometer” that measures dynamic mechanical responses of 10[superscript 3] to 10[superscript 4] individual RBCs in a cell population. Fluorescence measurements of each RBC are simultaneously acquired, resulting in a population-based correlation between biochemical properties, such as cell surface markers, and dynamic mechanical deformability. This device is especially applicable to heterogeneous cell populations. We demonstrate its ability to mechanically characterize a small number of P. falciparum-infected (ring stage) RBCs in a large population of uninfected RBCs. Furthermore, we are able to infer quantitative mechanical properties of individual RBCs from the observed dynamic behavior through a dissipative particle dynamics (DPD) model. These methods collectively provide a systematic approach to characterize the biomechanical properties of cells in a high-throughput manner.National Institutes of Health (U.S.) (Grant R01 HL094270-01A1)National Institutes of Health (U.S.) (Grant 1-R01-GM076689-01)Singapore-MIT Alliance for Research and Technology Cente

The impact of stratified hypoalbuminemia and dialysis on morbidity/mortality after posterior spinal fusion surgery: An ACS-NSQIP study.

BackgroundPreoperative optimization in patients undergoing posterior spinal fusion is essential to limit the number and severity of postoperative complications. Here, we, additionally, evaluated the impact of hypoalbuminemia on morbidity and mortality after posterior spinal fusion surgery.MethodsThis retrospective analysis was performed using data from a prospective multicentric database (ACSNSQIP:2015-2020) regarding patients undergoing posterior spinal fusions. Factors studied included; baseline demographics and 30-day postoperative complications (i.e., reoperations, readmissions, and mortality rates).ResultsThere were 6805 patients who met the inclusion criteria. They averaged 62 years of age and had an average BMI of 30.2. Within the 30-day postoperative period, 634 (9.3%) sustained complications; 467 (6.9%) were readmitted, 263 (3.9%) required reoperations, and 37 (0.5%) expired. Although multiple preoperative risk factors were analyzed, hypoalbuminemia, severe hypoalbuminemia, and dialysis were the strongest independent risk factors associated with complications (i.e., reoperations, readmissions, and mortality).ConclusionHypoalbuminemia, severe hypoalbuminemia, and dialysis were significant predictors for morbidity and mortality after posterior spinal fusion surgery

Clinical and Cost-Effectiveness of Lumbar Interbody Fusion Using Tritanium Posterolateral Cage (vs. Propensity-Matched Cohort of PEEK Cage)

Introduction: Surgical management of degenerative lumbar spine disorders is effective at improving patient pain, disability, and quality of life; however, obtaining a durable posterolateral fusion after decompression remains a challenge. Interbody fusion technologies are viable means of improving fusion rates in the lumbar spine, specifically various graft materials including autograft, structural allograft, titanium, and polyether ether ketone. This study assesses the effectiveness of Tritanium posterolateral cage in the treatment of degenerative disk disease. Methods: Nearest-neighbor 1:1 matched control transforaminal lumbar interbody fusion with PEEK vs. Tritanium posterior lumbar (PL) cage interbody fusion patients were identified using propensity scoring from patients that underwent elective surgery for degenerative disk diseases. Line graphs were generated to compare the trajectories of improvement in patient-reported outcomes (PROs) from baseline to 3 and 12 months postoperatively. The nominal data were compared via the χ2 test, while the continuous data were compared via Student's t-test. Results: The two groups had no difference regarding either the 3- or 12-month Euro-Qol-5D (EQ-5D), numeric rating scale (NRS) leg pain, and NRS back pain; however, the Tritanium interbody cage group had better Oswestry Disability Index (ODI) scores compared to the control group of the PEEK interbody cage at both 3 and 12 months (p=0.013 and 0.048). Conclusions: Our results indicate the Tritanium cage is an effective alternative to the previously used PEEK cage in terms of PROs, surgical safety, and radiological parameters of surgical success. The Tritanium cohort showed better ODI scores, higher fusion rates, lower subsidence, and lower indirect costs associated with surgical management, when compared to the propensity-matched PEEK cohort

Pf155/RESA protein influences the dynamic microcirculatory behavior of ring-stage Plasmodium falciparum infected red blood cells.

International audienceProteins exported by Plasmodium falciparum to the red blood cell (RBC) membrane modify the structural properties of the parasitized RBC (Pf-RBC). Although quasi-static single cell assays show reduced ring-stage Pf-RBCs deformability, the parameters influencing their microcirculatory behavior remain unexplored. Here, we study the dynamic properties of ring-stage Pf-RBCs and the role of the parasite protein Pf155/Ring-Infected Erythrocyte Surface Antigen (RESA). Diffraction phase microscopy revealed RESA-driven decreased Pf-RBCs membrane fluctuations. Microfluidic experiments showed a RESA-dependent reduction in the Pf-RBCs transit velocity, which was potentiated at febrile temperature. In a microspheres filtration system, incubation at febrile temperature impaired traversal of RESA-expressing Pf-RBCs. These results show that RESA influences ring-stage Pf-RBCs microcirculation, an effect that is fever-enhanced. This is the first identification of a parasite factor influencing the dynamic circulation of young asexual Pf-RBCs in physiologically relevant conditions, offering novel possibilities for interventions to reduce parasite survival and pathogenesis in its human host