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Biomedical subjects

Min-Hui Li

Publications and source records attributed to Min-Hui Li.

9 recordsLinked to original sources
PubMed2006

Artificial muscles based on liquid crystal elastomers.

This paper presents our results on liquid crystal (LC) elastomers as artificial muscle, based on the ideas proposed by de Gennes. In the theoretical model, the material consists of a repeated series of main-chain nematic LC polymer blocks, N, and conventional rubber blocks, R, based on the lamellar phase of a triblock copolymer RNR. The motor for the contraction is the reversible macromolecular shape change of the chain, from stretched to spherical, that occurs at the nematic-to-isotropic phase transition in the main-chain nematic LC polymers. We first developed a new kind of muscle-like material based on a network of side-on nematic LC homopolymers. Side-on LC polymers were used instead of main-chain LC polymers for synthetic reasons. The first example of these materials was thermo-responsive, with a typical contraction of around 35-45% and a generated force of around 210 kPa. Subsequently, a photo-responsive material was developed, with a fast photochemically induced contraction of around 20%, triggered by UV light. We then succeeded in preparing a thermo-responsive artificial muscle, RNR, with lamellar structure, using a side-on nematic LC polymer as N block.Micrometre-sized artificial muscles were also prepared. This paper illustrates the bottom-up design of stimuli-responsive materials, in which the overall material response reflects the individual macromolecular response, using LC polymer as building block.

Artificial Organs↗
PubMed2006

Influence of hyperbaric oxygen on tumor necrosis factor-alpha and nitric oxide production in endotoxin-induced acute lung injury in rats.

We previously demonstrated that hyperbaric oxygen (HBO) treatment alleviated lipopolysaccharide (LPS)-induced acute lung injury in rats. However, the mechanisms responsible for the protective effect are still not fully understood. To obtain further information on the protective effect of HBO, in this study we investigated the role of tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) in intratracheal spraying LPS-induced acute lung injury in rats after HBO or hyperoxia treatment. The results showed that HBO but not hyperoxia attenuated the TNF-alpha level in plasma and bronchoalveolar lavage (BAL) fluid, NO concentration in BAL and plasma, and inducible NO synthase protein expression in lung tissue based on the Western blotting and immunohistochemical staining.

Acute Disease↗
PubMed2006

Formation of polymer vesicles by liquid crystal amphiphilic block copolymers.

We report the formation of polymer vesicles (or polymersomes) by a new class of amphiphilic block copolymers in which the hydrophobic block is a side-on nematic liquid crystal polymer. Two series of these block copolymers, named PEG-b-PA444 and PEG-b-PMAazo444, with different hydrophilic/hydrophobic ratios were synthesized and characterized in detail. Polymersomes and nanotubes were formed by adding water into a solution of copolymers in dioxane. Polymersomes in water were finally obtained by dialyzing the resulting mixture against water. These self-assemblies have been studied by classical TEM and cryo-TEM. For the PEG-b-PA444 series, polymersomes were observed for hydrophilic/hydrophobic ratios ranging from 40/60 to 19/81. For PEG-b-PMAazo444 series, polymersomes were observed for hydrophilic/hydrophobic ratios ranging from 26/74 to 18/82. For a PEG-b-PA444 sample with hydrophilic/hydrophobic ratio equal to 25/75, a tubular morphology with tube diameter of typically 100 nm and tube length of up to 10 mum was also observed together with polymersomes during addition of water into the polymer solution in dioxane.

Journal Article↗
PubMed2006

Hemorrhage from an enlarged emphysematous bulla during commercial air travel.

Pulmonary bullae are a common late complication in patients with emphysema. Non-communicating emphysematous bullae may expand during air travel when the ambient pressure is reduced, resulting in various forms of barotrauma including pneumothorax and air embolism. We report a 62-yr-old man with emphysema who developed hemoptysis during international commercial air travel. CT scan of the chest obtained after the travel showed air-fluid level in an enlarged bulla. He underwent resection of the bulla and had a full recovery. This is a unique presentation of stretch injury of a bulla as a form of pulmonary barotrauma occurring during commercial air travel. With the most recent ruling by the Federal Aviation Administration to allow patients with advanced chronic obstructive lung disease to travel by air with their own supplemental oxygen devices, physicians need to be aware of this type of pulmonary barotrauma and properly advise such patients who are planning to travel by air.

Aerospace Medicine↗
PubMed2005

Isokinetic muscle strength of the trunk and bilateral knees in young subjects with lumbar disc herniation.

STUDY DESIGN: Cross-sectional study comparing normal subjects and patients with lumbar disc herniation. OBJECTIVE: To evaluate trunk and knee muscle strength in patients with L4-L5 and/or L5-S1 disc herniation. SUMMARY OF BACKGROUND DATA: Numerous studies have shown that patients with low back pain have weaker trunk muscles. The strength of trunk and knee muscles has not been investigated simultaneously in patients with lumbar disc herniation. METHODS: Forty-one controls and 2 patients were included. Isokinetic strength of the trunk and bilateral knees was tested on a calibrated isokinetic testing machine (Biodex System 3 Pro) regardless of the laterality of the radiculopathy. The testing was carrying out at two different velocities: 60 degrees and 120 degrees per second. RESULTS: Total trunk strength and knee strength were significantly lower in these patients (4.34 +/- 1.06 and 4.06 +/- 1.16 vs. 6.21 +/- 1.05 and 5.83 +/- 1.09 Nm/kg at 60 degrees and 120 degrees per second, respectively, P < 0.001). In patients with unilateral sciatica, there was no significant difference (P > 0.05) in unilateral knee strength between sciatica-involved and -uninvolved limbs (1.89 +/- 0.5, 1.08 +/- 0.45, 1.48 +/- 0.58, 0.93 +/- 0.41 vs. 1.68 +/- 0.45, 0.91 +/- 0.38, 1.41 +/- 0.48, 0.79 +/- 0.39 Nm/kg in sciatica-uninvolved vs. sciatica-involved limbs during extension and flexion at 60 degrees and 120 degrees per second, respectively). Total trunk strength was significantly correlated with total knee strength in both groups. CONCLUSIONS: In the patients with lumbar disc herniation, muscle strength of the trunk and knees was decreased to a similar extent. Weaker knee strength was found on either side of the lower extremity in the patients with unilateral sciatica, regardless of its location.

Adult↗
PubMed2005

L-Arginine prevents air embolism-induced acute lung injury in rats.

OBJECTIVE: Pulmonary air embolism, causing vessel obstruction and primary or secondary reactions of blood, can lead to acute lung injury. In addition, nitric oxide has been known to play a key role in various causes of lung injury. In this study we employed the isolated rat lung model to investigate the effects of l-arginine on air embolism-induced lung injury. DESIGN: Randomized, controlled study. SETTING: Animal-care facility procedure room. SUBJECTS: Forty-two adult male Sprague-Dawley rats each weighing 250-350 g. INTERVENTIONS: Infusion of air at the rate of 0.25 mL/min for 1 min into the pulmonary artery in isolated and perfused rat lung resulted in pulmonary hypertension and lung edema. Air embolism elicited a significant increase in microvascular permeability as measured by the capillary filtration coefficient, lung weight gain, lung weight-to-body weight ratio, pulmonary arterial pressure, and protein concentration of bronchoalveolar lavage fluid. MEASUREMENTS AND MAIN RESULTS: Pretreatment with L-arginine (4 mmol/L) significantly attenuated the acute lung injury induced by air embolism as shown by a significant decrease in all of the assessed variables but did not alter the pulmonary arterial pressure (p < .05). The protective effect of l-arginine was blocked when N(G)-nitro-L-arginine methyl ester (5 mmol/L) was added. Pretreatment with N(G)-nitro-L-arginine methyl ester exacerbated air embolism-induced lung injury. CONCLUSIONS: Our findings suggest that L-arginine can prevent air embolism-induced lung injury.

Acute Disease↗
PubMed2002

Faceted monodomains of liquid crystal smectic blue phases.

Smectic blue phases (BP(Sm)) are mesophases of thermotropic liquid crystals, which exhibit both three-dimensional orientational order, such as classical blue phases, and smectic positional order. The BP(Sm) phases appear as the three-dimensional counterpart of the twist grain boundary phases. By growing large faceted monocrystals of BP(Sm) phase, we provide, for the first time at the length scale of the lattice parameter, information on the symmetry of the orientational unit cell. This study leads us to suggest an orthorhombic structure, contrary to the previous results obtained by x-ray scattering at the length scale of the smectic order.

Journal Article↗