In this paper we describe a new process for fabricating ultra-thick microfluidic devices utilizing SU-8 50 negative photoresist (PR) by standard UV lithography. Instead of using a conventional spin coater, a simple 'constant-volume-injection' method is used to create a thick SU-8 PR film up to 1.5 mm with a single coating. The SU-8 PR is self-planarized during the modified soft-baking process and forms a highly-uniform surface without any edge bead effect, which commonly occurs while using a spin coater. Photomasks can be in close contact with the PR and a better lithographic image can be generated. Experimental data show that the average thickness is 494.32 ± 17.13 µm for a 500 µm thick film (n = 7) and the uniformity is less than 3.1% over a 10 × 10 cm 2 area. In this study, the temperatures for the soft-baking process and post-exposure baking are 120 • C and 60 • C, respectively. These proved to be capable of reducing the processing time and of obtaining a better pattern definition of the SU-8 structures. We also report on an innovative photomask design for fabricating ultra-deep trenches, which prevents the structures from cracking and distorting during developing and hard-baking processes. In this paper, two microfluidic structures have been demonstrated using the developed novel methods, including a micronozzle for thruster applications and a microfluidic device with micropost arrays for bioanalytical applications.

This paper describes a fast, low-cost but reliable process for the fabrication of microfluidic systems on soda-lime glass substrates. Instead of using an expensive metal or polisilicon/nitride layer as an etch mask, a thin layer of AZ 4620 positive photoresist (PR) is used for buffered oxide etching (BOE) of soda-lime glass. A novel two-step baking process prolongs the survival time of the PR mask in the etchant, which avoids serious peeling problems of the PR. A new process to remove precipitated particles generated during the etching process is also reported in which the glass substrate is dipped into a 1 M hydrochloride solution. A microfluidic channel with a depth of 35.95 ± 0.39 µm is formed after 40 min BOE in an ultrasonic bath. The resulting channel has a smooth profile with a surface roughness of less than 45.95 ± 7.96 Å. Glass chips with microfluidic channels are then bonded at 580 • C for 20 min to seal the channel while a slight pressure is applied. A new bonding process has been developed such that the whole process can be finished within 10 h. To our knowledge, this is the shortest processing time that has ever been reported. In the present study, an innovative microfluidic device, a 'micro flow-through sampling chip', has been demonstrated using the fabrication method. Successful sampling and separation of Cy5-labelled bovine serum albumin (BSA) and anti-BSA has been achieved. This simple fabrication process is suitable for fast prototyping and mass production of microfluidic systems.

We have previously shown that melatonin reduces infarct volumes and enhances neurobehavioral and electrophysiological recoveries following transient middle cerebral artery (MCA) occlusion in rats. In the study, we examined whether melatonin would display neuroprotection against neuronal, axonal and oligodendrocyte pathology after 24 hr of reperfusion following 1 hr of MCA occlusion in mice. Melatonin (5 mg/kg) or vehicle was given intraperitoneally at the commencement of reperfusion. Neurological deficits were assessed 24 hr after ischemia. Gray matter damage was evaluated by quantitative histopathology. Axonal damage was determined with amyloid precursor protein and microtubule-associated protein tau-1 immunohistochemistry to identify postischemic disrupted axonal flow and oligodendrocyte pathology, respectively. Oxidative damage was assessed by 8-hydroxy-2'-deoxyguanosine (8-OHdG) and 4-hydroxynonenal (4-HNE) immunohistochemistry. Relative to controls, melatonin-treated animals not only had a significantly reduced volume of gray matter infarction by 42% (P<0.001), but also exhibited a decreased score of axonal damage by 42% (P<0.001) and a reduction in the volume of oligodendrocyte pathology by 58% (P<0.005). Melatonin-treated animals also had significantly reduced immunopositive reactions for 8-OHdG and 4-HNE by 53% (P<0.001) and 49% (P<0.001), respectively. In addition, melatonin improved sensory and motor neurobehavioral outcomes by 47 and 30%, respectively (P<0.01). Thus, delayed (1 hr) treatment with melatonin reduced both gray and white matter damage and improved neurobehavioral outcomes following transient focal cerebral ischemia in mice. The finding of reduced oxidative damage observed with melatonin suggests that its major mechanisms of action are mediated through its antioxidant and radical scavenging activity.

:  Melatonin has been reported to reduce infarct volumes induced by transient middle cerebral artery (MCA) occlusion. We examined whether melatonin could improve electrophysiological and neurobehavioral recoveries in rats after 72 hr of reperfusion following 1.5 hr of MCA occlusion. Melatonin (5 mg/kg) or vehicle was given intravenously at the commencement of reperfusion. Neurobehavioral outcome was serially examined, and somatosensory evoked potentials (SSEP) were recorded prior to ischemia and at 72 hr after the onset of reperfusion. Brain infarction was assessed upon killing. Before ischemia‐reperfusion, stable SSEP waveforms were consistently recorded after individual fore‐ or hindpaw stimulation. The amplitude between the first positive (P1) and the first negative (N1) peaks and the P1 latency did not differ significantly between controls and melatonin‐treated animals. At 72 hr of reperfusion, controls had severely depressant SSEPs recorded from ischemic fore‐ and hindpaw cortical fields, and the amplitudes decreased to 36 and 35% of baselines, respectively (P < 0.001). These animals also had transcallosal electrophysiological diaschisis in the SSEPs recorded at the contralateral hindpaw cortical field (P < 0.01). Relative to controls, melatonin‐treated animals not only had significantly improved amplitudes of the SSEPs recorded from both ischemic fore‐ and hindpaw cortical fields, by 33 and 37% of baselines, respectively (P < 0.001), but also exhibited diminished transcallosal electrophysiological diaschisis following ischemia‐reperfusion. In addition, melatonin improved sensory and motor neurobehavioral outcomes by 40 and 28%, respectively (P < 0.001), and reduced cortical and striatal infarct sizes by 32 and 40%, respectively (P < 0.05). Thus, delayed intravenous administration with melatonin both enhances electrophysiological and neurobehavioral recoveries and reduces cortical and striatal infarct sizes after cerebral ischemia and reperfusion injury.

We have recently shown that melatonin decreases the late (24 hr) increase in blood–brain barrier (BBB) permeability and the risk of tissue plasminogen activator‐induced hemorrhagic transformation following ischemic stroke in mice. In the study, we further explored whether melatonin would reduce postischemic neurovascular oxidative/nitrosative damage and, therefore, improve preservation of the early increase in the BBB permeability at 4 hr after transient focal cerebral ischemia for 60 min in mice. Melatonin (5 mg/kg) or vehicle was given intraperitoneally at the beginning of reperfusion. Hydroethidine (HEt) in situ detection and immunohistochemistry for nitrotyrosine were used to evaluate postischemic accumulation in reactive oxygen and nitrogen species, respectively, in the ischemic neurovascular unit. BBB permeability was evaluated by spectrophotometric and microscopic quantitation of Evans Blue leakage. Relative to controls, melatonin‐treated animals not only had a significantly reduced superoxide accumulation in neurovascular units in boundary zones of infarction, by reducing 35% and 54% cytosolic oxidized HEt in intensity and cell‐expressing percentage, respectively (P < 0.001), but also exhibited a reduction in nitrotyrosine by 52% (P < 0.01). Additionally, melatonin‐treated animals had significantly reduced early postischemic disruption in the BBB permeability by 53% (P < 0.001). Thus, melatonin reduced postischemic oxidative/nitrosative damage to the ischemic neurovascular units and improved the preservation of BBB permeability at an early phase following transient focal cerebral ischemia in mice. The findings further highlight the ability of melatonin in anatomical and functional preservation for the ischemic neurovascular units and its relevant potential in the treatment of ischemic stroke.

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