Brenda S. Cho

Fabrication of microfluidic mixers and artificial vasculatures using a high-brightness diode-pumped Nd:YAG laser direct write method

This paper describes a direct write laser technology, which is fast and flexible, for fabricating multiple-level microfluidic channels. A high brightness diode-pumped Nd-YAG laser with slab geometry was used for its excellent beam quality. Channels with flat walls and staggered herringbone ridges on the floor have been successfully fabricated and their ability to perform passive mixing of liquid is discussed. Also, a multi-width multi-depth microchannel has been fabricated to generate biomimetic vasculatures whose channel diameters change according to Murrays law, which states that the cube of the radius of a parent vessel equals the sum of the cubes of the radii of the daughters. The multi-depth architecture allows for flow patterns to resemble physiological vascular systems with lower overall resistance and more uniform flow velocities throughout the network compared to planar patterning techniques which generate uniformly thin channels. The ability to directly fabricate multiple level structures using relatively straightforward laser technology enhances our ability to rapidly prototype complex lab-on-a-chip systems and to develop physiological microfluidic structures for tissue engineering and investigations in biomedical fluidics problems.

Isolation of motile spermatozoa from semen samples using microfluidics

A microfluidic device was designed with two parallel laminar flow channels where non-motile spermatozoa and debris would flow along their initial streamlines and exit one outlet, whereas motile spermatozoa had an opportunity to swim into a parallel stream and exit a separate outlet. Motile sperm samples were prepared with density gradient separation (n = 5). Sperm motility was assessed the following day after exposing aliquots to polydimethylsiloxane (PDMS) used to construct the device. There was no difference in sperm motility when compared with unexposed aliquots (P > 0.05). Unprocessed semen samples (n = 10) were placed in wider channels and sperm motility and strict morphology were assessed from sorted outlets. Sperm motility increased from 44 +/- 4.5% to 98 +/- 0.4% (P < 0.05) and morphology increased from 10 +/- 1.05% to 22 +/- 3.3% (P < 0.05) following processing. Finally, density gradient prepared samples (n = 6) containing 5 x 10(6) motile spermatozoa/ml and 50 x 10(6) round immature germ cells/ml were sorted and assessed in a similar fashion. The ratio of motile spermatozoa to round immature germ cells in the wide inlet (1:10) was significantly improved in the thin outlet (33:1) (P < 0.05). This microfluidic device provides a novel method for isolating motile, morphologically normal spermatozoa from semen samples without centrifugation. This technology may prove useful in isolating motile spermatozoa from oligozoospermic samples, even with high amounts of non-motile gamete and/or non-gamete cell contamination. A movie sequence showing streaming and sorting of spermatozoa may be purchased for viewing on the internet at www.rbmonline.com/Article/847 (free to web subscribers).

Female Gender Attenuates Cytokine and Chemokine Expression and Leukocyte Recruitment in Experimental Rodent Abdominal Aortic Aneurysms

Abstract:  Female gender appears to be protective in the development of abdominal aortic aneurysms (AAAs). This study sought to identify gender differences in cytokine and chemokine expression in an experimental rodent AAA model. Male and female rodent aortas were perfused with either saline (control) or elastase to induce AAA formation. Aortic diameter was determined and aortic tissue was harvested on postperfusion days 4 and 7. Cytokine and chemokine gene expression was examined using focused gene arrays. Immunohistochemistry was used to quantify aortic leukocyte infiltration. Data were analyzed by Students t‐tests and ANOVA. Elastase‐perfused female rodents developed significantly smaller aneurysms compared to males by day 7 (93 ± 10% vs. 201 ± 25%, P= 0.003). Elastase‐perfused female aortas exhibited a fivefold decrease in expression of the BMP family and ligands of the TNF superfamily compared to males. In addition, the expression of members of the TGF β and VEGF families were three to fourfold lower in female elastase‐perfused aortas compared to males. Multiple members of the interleukin, CC chemokine receptor, and CC ligand families were detectable in only the male elastase‐perfused aortas. Female elastase‐perfused aortas demonstrated a corollary twofold lower neutrophil count (females: 17.5 ± 1.1 PMN/HPF; males: 41 ± 5.2 neutrophils/HPF, P= 0.01) and a 1.5‐fold lower macrophage count (females: 12 ± 1.1 macrophages/HPF; males: 17.5 ± 1.1 macrophages/HPF, P= 0.003) compared to male elastase‐perfused aortas. This study documents decreased expression of multiple cytokines and chemokines and diminished leukocyte trafficking in female rat aortas compared to male aortas following elastase perfusion. These genes may contribute to the gender disparity seen in AAA formation.

Decreased Collagen and Increased Matrix Metalloproteinase-13 in Experimental Abdominal Aortic Aneurysms in Males Compared with Females

BACKGROUND This study examined differences in sex in collagen regulation during rodent experimental abdominal aortic aneurysm formation. METHODS Infrarenal aortas of male and female rats were perfused with elastase or saline (control). Aortic diameters were measured at baseline (day 0) and on postoperative days 7 and 14. Transforming growth factor-beta 1, collagen subtypes I and III, and matrix metalloproteinase-13 (MMP-13; collagenase-3) expression and/or protein levels from aortic tissue were determined by real-time reverse transcription polymerase chain reaction and Western blotting. Aortic tissue was stained for total collagen, neutrophils, and macrophages using immunohistochemistry on days 4 and 7. RESULTS At 7 and 14 days after perfusion, aortic diameter increased in elastase-perfused males compared with females (P < .001 for each). At 4 and 7 days postperfusion, significantly more neutrophils and macrophages were present in elastase-perfused males compared with females. By 7 days postperfusion, protein levels of transforming growth factor-beta 1 were less in males compared with females (P = .04). Type I collagen levels also decreased on days 7 (P < .001) and 14 (P = .002), and type III collagen levels decreased on days 7 (P < .001) and 14 (P < .001) in males compared with females. With Massons trichrome stain, less adventitial collagen was observed in the elastase-perfused males compared with females. MMP-13 expression (P < .001) and protein levels (P = .006) in elastase-perfused males were greater than females on day 14. CONCLUSION This study documents a decrease in types I and III collagen with a concurrent increase in MMP-13 after elastase perfusion in males compared with females. These data suggest that alterations in extracellular matrix collagen turnover may be responsible for altered abdominal aortic aneurysm formation between sexes.

Differential Regulation of Aortic Growth in Male and Female Rodents Is Associated With AAA Development

BACKGROUND The objective was to examine effects of gonadal hormone manipulation on aortic diameter and macrophage infiltration in rodents during abdominal aortic aneurysm (AAA) formation. METHODS Experiment 1: 17-beta estradiol and testosterone pellets were implanted in male (ME) and female (FT) rats. No pellet was implanted in shams (MES, FTS). Experiment 2: Testes and ovaries were removed from males (MO) and females (FO), respectively. No organs were removed from shams (MOS, FOS). Experiment 3: Male and female rats were orchiectomized and oophorectomized, respectively. Four weeks post-castration, testosterone (MOT) and 17-beta estradiol (FOE) pellets were implanted. Shams underwent castration, but no pellet was implanted (MOTS, FOES). All rats underwent infrarenal aortic infusion with elastase postimplantation/postcastration. Diameters were measured on postoperative d 14. Tissue was stained for macrophages by immunohistochemistry. RESULTS Diameter (P = 0.046) and macrophage counts (P = 0.014) decreased in ME compared with shams, but not in females treated with testosterone (FT). Diameter (P = 0.019) and macrophage infiltration (P = 0.024) decreased in MO compared with shams, but not in FO. Diameter increased in MOT compared with MOTS (P = 0.033), but decreased in FOE compared with FOES (P = 0.002). Macrophages decreased in FOE compared with FOES (P = 0.002). CONCLUSION This study documents a decrease in AAA diameter in males treated with estrogen or undergoing orchiectomy, but no changes in females treated with testosterone or undergoing oophorectomy; and an increase in diameter in MOT and a decrease in FOE. These data suggest that gonadal hormones differentially regulate AAA growth in association with changes in macrophages.

Attenuation of Experimental Aortic Aneurysm Formation in P-Selectin Knockout Mice

Abstract:  The aim of this study was to determine the role of P‐selectin, an adhesion molecule found on the surface of activated platelets and endothelial cells during experimental aortic aneurysm formation. Infrarenal abdominal aortas of C57 black wild‐type (WT) mice and P‐selectin knockout (PKO) mice were measured in situ and then perfused with porcine pancreatic elastase (0.332 U/mL). Whole blood was drawn from the tail artery on day 2 pre‐perfusion to determine total and differential white blood cell (WBC) counts. On day 14 postperfusion, aortic diameters (AD) of WT mice (N= 19) and PKO mice (N= 9) were measured. An aortic aneurysm was defined as a 100% or greater increase in AD from pre‐perfusion measurement. Immunohistochemistry, including H&E, trichrome and von Gieson staining, was performed on harvested aortic tissue. Statistical analysis was performed by t‐test and Fishers exact test. There were no significant differences in peripheral leukocyte counts at baseline between the two groups. WT mice had significantly larger AD compared to PKO mice at day 14 postperfusion (116 % vs. 38 %, P < 0.001). Aortic aneurysm penetrance was 52% in WT mice, while 0% (P= 0.01) of PKO mice formed aneurysms. On histologic examination, WT mouse aortas were associated with a significant inflammatory response and degradation of elastin and collagen fibers, while PKO mouse aortas lacked signs of inflammation or vessel wall injury. P‐selectin deficiency attenuates aneurysm formation in the elastase aortic perfusion model. This was associated with a blunting of the inflammatory response and preserved vessel wall intergrity following elastase perfusion in the P‐selectin knockout mice. Further investigation to elucidate the independent contributions of endothelial cell and platelet P‐selectin in experimental aortic aneurysm formation is required.

Differential Effect of 17-ß-Estradiol on Smooth Muscle Cell and Aortic Explant MMP21

OBJECTIVE The present investigation tested the hypothesis that intrinsic gender-related differences exist in rat aortic smooth muscle cell matrix metalloproteinase 2 (MMP2). METHODS This investigation comprised 3 sets of experiments. Experiment I: Adult male and female rat aortic smooth muscle cells (RASMCs) at passages 4-8 were stimulated in serum-free media for 48 h with interleukin(IL)1beta at doses encountered in human abdominal aortic aneurysms (2 ng/mL). Messenger RNA was extracted from the RASMCs, and gene expression of MMP2 and tissue inhibitor of metalloproteinase 2 (TIMP2), a major MMP2 inhibitor, was measured by real-time polymerase chain reaction. MMP2 protein levels in conditioned media were measured by Western blotting, and MMP2 and TIMP2 activity quantified by standard and reverse gelatin zymography. Experiment II: Male and female RASMCs were incubated for 48 h in Dulbeccos modified Eaglers medium containing IL-1beta and 17-beta-estradiol at doses from 1x10(-10) to 1x10(-6) molar. MMP2 activity in the conditioned media was then determined. Experiment III: Male rats underwent sustained 17-beta-estradiol exposure for 21 d using extended-release, subcutaneously implanted pellets prior to sacrifice and aortic explantation. Aortas from males, females, and estradiol-treated males were stimulated with IL-1beta for 48-h, and MMP2 activity in the conditioned media was determined. RESULTS Experiment I: MMP2 gene expression was 3-fold higher in male compared with female IL-1beta stimulated RASMCs (P<0.0001). MMP2:TIMP2 gene expression ratio was 7.5-fold greater in male versus female RASMCs. MMP2 protein levels were 3-fold higher (2.68 versus 0.96 o.d./mg total protein, P=0.003) in male versus female RASMCs. Gelatinolytic activity was more than 6-fold higher (15,010 versus 2,472 o.d./mg total protein, P=0.002) in male versus female RASMCs. Experiment II: MMP2 activity in male and female RASMCs was not altered by a wide range of 17-beta-estradiol concentrations. Experiment III: When pretreated with 17-beta-estradiol, MMP2 activity in the media of male rat whole-aortic explants decreased 2-fold (P=0.002). This post-17-beta-estradiol treatment male level was not different than baseline female aortic explant MMP2 levels. CONCLUSIONS MMP2 is higher in male RASMCs compared to female RASMCs. Exogenous 17-beta-estradiol did not alter MMP2 activity in vitro, but in vivo 17-beta-estradiol exposure greatly decreased male aortic MMP2 production to levels seen in the female aorta. Gender differences in MMP2 are speculated to be associated with phenotypic differences in human abdominal aortic aneurysm formation.

Gravity-Driven Micropump with a Steady Flow Rate

This paper describes a MIcrofluidic Gravity pump (MIG-pump). Unlike conventional microscale gravity-driven systems where flow rates change with decrease in fluid volume at the supply reservoir, the MIG-pump can deliver fluid at a steady flow rate over extended periods of time. The flow rate is maintained by the use of horizontally oriented reservoirs, which allow a constant hydraulic pressure to be maintained between the inlet and outlet. The MIG-pump is useful for a variety of applications including multiple laminar flow generation and cell sorting.

Diffusion of Alexa Fluor 488-Conjugated Dendrimers in Rat Aortic Tissue

Abstract:  In this study, the distribution of labeled dendrimers in native and aneurysmal rat aortic tissue was examined. Adult male rats underwent infrarenal aorta perfusion with generation 5 (G5) acetylated Alexa Fluor 488‐conjugated dendrimers for varying lengths of time. In a second set of experiments, rats underwent aortic elastase perfusion followed by aortic dendrimer perfusion 7 days later. Aortic diameters were measured prior to and postelastase perfusion, and again on the day of harvest. Aortas were harvested 0, 12, or 24 h postperfusion, fixed, and mounted. Native aortas were harvested and viewed as negative controls. Aortic cross‐sections were viewed and imaged using confocal microscopy. Dendrimers were quantified (counts/high‐powered field). Results were evaluated by repeated measures ANOVA and Students t‐test. We found that in native aortas, dendrimers penetrated the aortic wall in all groups. For all perfusion times, fewer dendrimers were present as time between dendrimer perfusion and aortic harvest increased. Longer perfusion times resulted in increased diffusion of dendrimers throughout the aortic wall. By 24 h, the majority of the dendrimers were through the wall. Dendrimers in aneurysmal aortas, on day 0 postdendrimer perfusion, diffused farther into the aortic wall than controls. In conclusion, this study documents labeled dendrimers delivered intra‐arterially to native rat aortas in vivo, and the temporal diffusion of these molecules within the aortic wall. Increasing perfusion time and length of time prior to harvest resulted in continued dendrimer diffusion into the aortic wall. These preliminary data provide a novel mechanism whereby local inhibitory therapy may be delivered locally to aortic tissue.

Micromachining of microfluidic devices using a high-brightness diode-pumped Nd: YAG laser

Microchannels for microfluidic applications are usually structured by lithography-based etching techniques. These techniques require a mask, which is expensive and time consuming to fabricate. Fabrication of structures with multiple levels also require multiple exposures with registration between different level structures, further complicating the process. Oftentimes, redesigns of these micro components are inevitable adding to the cost and time required for fabrication. This paper describes a direct write laser technology, that is fast and flexible, for fabricating microfluidic channels. Channels with flat walls, with straight obliquely oriented ridges and with staggered herringbone rides on the floor have been successfully fabricated and their ability to perform passive mixing of liquid is discussed.Microchannels for microfluidic applications are usually structured by lithography-based etching techniques. These techniques require a mask, which is expensive and time consuming to fabricate. Fabrication of structures with multiple levels also require multiple exposures with registration between different level structures, further complicating the process. Oftentimes, redesigns of these micro components are inevitable adding to the cost and time required for fabrication. This paper describes a direct write laser technology, that is fast and flexible, for fabricating microfluidic channels. Channels with flat walls, with straight obliquely oriented ridges and with staggered herringbone rides on the floor have been successfully fabricated and their ability to perform passive mixing of liquid is discussed.