Biomedical subjects

Xun Ma

Publications and source records attributed to Xun Ma.

4 recordsLinked to original sources

PubMed2004

[A biomechanical study on cervical spinal posture and prior loading history affecting spinal compressive strength].

OBJECTIVE: The purpose of this study is to investigate the effect of cervical spinal posture and prior loading history on spinal compressive strength. METHODS: Twelve human cadaver cervical spines were harvested and dissected into 24 motion segments containing 2 vertebrae and the intervertebral discs (C3,4 and C5,6). Compressive loads were applied on so that the effects of 2 loading conditions (dehydrated, superhydrated) and 2 postures (neutral trunk, flexed) could be examined. Dissection techniques and X-rays were used to determine the tissue injuries. RESULTS: Specimens had a lower ultimate compressive strength (P <0.001) in flexed posture than in neutral trunk posture. Under the injury loading in neutral trunk posture, superhydrated specimens had a lower strength (29%, P <0.01) than dehydrated specimens did. CONCLUSION: The spine may be more prone to injury early in the morning when the discs are at highest level of hydration and the cervical spine is in fully flexed posture.

Biomechanical Phenomena↗

PubMed2004

Crust effect on multiscale pattern formations in drying micelle solution drops on solid substrates.

Spherical micelles of a polystyrene-b-poly(dimethylsiloxane) (PS-b-PDMS) diblock copolymer with the number-average molecular weight of 193 000 g/mol for PS and 39 000 g/mol for PDMS were obtained by using n-dodecane or n-octane as the selective solvent for the PDMS block. The drying process of micelle solution drops with relatively high polymer concentration on solid substrates and the resultant drying patterns were studied using optical microscopy and atomic force microscopy. The drying drops exhibited an inner solution "cap" connecting with an outer gelled "foot" through a transition zone. A crust was first formed on the surface of the transition zone and remained on the top of the foot region. An inhomogeneous stress perpendicular to the radial direction within the crust, which was due to the solvent evaporation accompanied by the receding of the solution cap, induced regular 45 degrees -tilted stripes (pleats) in the transition zone and main radial cracks in the foot region. The stripes and cracks have periods of a few and tens of microns, respectively. Concave micelle "bricks" were also observed between cracks. In addition to micelle close packing, these patterns demonstrate that drying micelle solution drops may provide a potential means to manipulate fine and multiscale structures for technological applications.

Journal Article↗

PubMed2003

Manipulating supramolecular self-assembly via tailoring pendant group size of linear vinyl polymers.

In a series of poly[di(alkyl) vinylterephthalates] (PDAVTs) synthesized via radical polymerization, fine-tuning the size and shape of the side groups manipulated the supramolecular self-assembly and led to control over the formations between amorphous and 2D ordered hexagonal phases. To introduce the 2D long-range ordered structure, the size of the ester side groups at the 2- and 5-positions of the phenyl rings laterally attached to the backbones had to be in the range of propyl/isopropyl to hexyl. The relatively extended backbones observed in these polymers were attributed to steric effects from the side groups. When the n-alkyl groups were larger than hexyl, the ability to form the liquid crystalline phase gradually decreased. A completely disordered phase could be observed by substituting dodecyl groups as side groups.

Journal Article↗

PubMed2003

Identification of oligoclonal CD4 T cells in diffuse large B cell lymphomas.

Human B cell lymphomas often contain CD4 T cells. Here we show that, in diffuse large B cell lymphomas (DLCL), such T cells are oligoclonal. The CDR3 lengths and nucleotide sequences of oligoclonal TCRBV of CD4 T cells in an original and relapsed lymphoma from one patient were compared. Three BV23 sequences were identical (12/17 and 16/16 clones in primary and relapsed lymphomas, respectively), but were absent in CD4 T cells from another patient's DLCL. Two of the repetitive BV23 sequences were found in peripheral blood CD4 T cells (5/17 clones); gamma-irradiated DLCL from this patient stimulated syngeneic BV23 response in CD4 cells (92% of BV23 had the same CDR3 length). Skew in TCRBV representation was observed in CD4 T cells from all the DLCL. One DLCL, with overrepresentation of BV13S1 in CD4 cells, stimulated the same TCR in CD4 cells from three unrelated individuals. These findings support the conclusion that there is clonal selection of CD4 T cells in DLCL.

Adult↗