The surfaces of standard untreated polystyrene cell culture dishes have been oxidatively modified for up to 8 min exposure time using an ultraviolet ozone treater in order to promote cell adhesion. Surface oxygen chemisorption and topographical modification has been characterized using monochromatic X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. The oxidation process is shown to proceed at low exposure times (<60 s) via the formation of CsOR groups, although some R2CdO and RO-CdO groups are also formed. At longer treatments, RO-CdO groups become the dominant species, although the other groups are also present. The maximum level of oxygen reached is 36 atomic %. Some of the oxygen present at surfaces treated at times of >60 s is in the form of loosely bound low molecular weight oxidized material (LMWOM) which is produced by oxidative scission of the PS backbone. Water washing leads to a reduction in surface oxygen content mainly by the removal of ROsCdO and R2CdO functional groups. The residual stable oxygen levels, which can be introduced, are approximately 20-25 atomic %. Surface chemistry changes are accompanied by the formation of surface spikes which are about 30 nm high and 300-400 nm wide. A correlation between treatment time/oxygen level and overall roughness is observed. The effect of washing upon the topography is to slightly increase the surface roughness, although not to a significant degree. The attachment kinetics of adhesion for Chinese hamster ovary cells show that adhesion occurs much more rapidly for oxidized surfaces than for untreated control materials. A direct correlation between the levels of oxidation and the rate of cell adhesion is demonstrated.

Ultra-high-molecular-weight polyethylene (UHMWPE) has a long history of use in medical devices, primarily for articulating surfaces due to its inherent low surface energy which limits tissue integration. To widen the applications of UHMWPE, the surface energy can be increased. The increase in surface energy would improve the adsorption of proteins and attachment of cells to allow tissue integration, thereby allowing UHMWPE to potentially be used for a wider range of implants. The attachment and function of human primary osteoblast-like (HOB) cells to surfaces of UHMWPE with various levels of incorporated surface oxygen have been investigated. The surface modification of the UHMWPE was produced by exposure to a UV/ozone treatment. The resulting surface chemistry was studied using X-ray photoelectron spectroscopy (XPS), and the topography and surface structure were probed by atomic force microscopy (AFM) and scanning electron microscopy (SEM), which showed an increase in surface oxygen from 11 to 26 atom % with no significant change to the surface topography. The absolute root mean square roughness of both untreated and UV/ozone-treated surfaces was within 350-450 nm, and the water contact angles decreased with increasing oxygen incorporation, i.e., showing an increase in surface hydrophilicity. Cell attachment and functionality were assessed over a 21 day period for each cell-surface combination studied; these were performed using SEM and the alamarBlue assay to study cell attachment and proliferation and energy-dispersive X-ray (EDX) analysis to confirm extracellular mineral deposits, and total protein assay to examine the intra- and extracellular protein expressed by the cells. HOB cells cultured for 21 days on the modified UHMWPE surfaces with 19 and 26 atom % oxygen incorporated showed significantly higher cell densities compared to cells cultured on tissue culture polystyrene (TCPS) from day 3 onward. This indicated that the cells attached and proliferated more readily on the UV/ozone-treated UHMWPE surfaces than on untreated UHMWPE and TCPS surfaces. Contact guidance of the cells was observed on the UHMWPE surfaces by both SEM and AFM. Scanning electron micrographs showed that the cells were confluent on the modified UHMWPE surfaces by day 10, which led to visible layering of the cells by day 21, an indicator of nodule formation. In vitro mineralization of the extracellular matrix expressed by the HOB cells on the modified UHMWPE surfaces was confirmed by SEM and EDX analysis; spherulite structures were observed near cell protrusions by day 21. EDX analysis confirmed the spherulites to contain calcium and phosphorus, the major constituents in calcium phosphate apatite, the mineral phase of bone. Overall cell attachment, functionality, and mineralization were found to be enhanced on the UV/ozone-modified UHMWPE surfaces, demonstrating the importance of optimizing the surface chemistry for primary HOB cells.

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The levels of the cytosolic serine/threonine protein phosphatases (PP) in rat adipocyte extracts have been determined, by using both reference substrates and hormone-sensitive lipase (HSL) as substrates. Adipocytes contain significant levels of both PP1 and 2A (1.6 and 2.0 m-units/ml of packed cells respectively), with lower levels of PP2C and virtually no PP2B activity. PP2A and 2C exhibit similar degrees of activity against HSL phosphorylated at site 1, together accounting for 92% of the total. In contrast, site 2 is dephosphorylated predominantly by PP2A (over 50% of total activity), whereas PP1 and PP2C contribute approx. 20% and 30% respectively to the total phosphatase activity against that site. Total phosphatase activity in the adipocyte extracts was 2-3-fold higher against site 2 than against site 1. The possible significance of these findings to the regulation of HSL activity in adipose tissue in vivo is discussed.

Triacylglycerol hydrolase activities were characterised in homogenates, cytosol, and microvillous membranes (MVM) of human placenta. Homogenates of placenta exhibited three distinct triacylyglycerol hydrolase activities with pH optima 4.5, 6.0 and 8. 0. On further fractionation, placental cytosol exhibited both acid cholesterol ester hydrolase (pH 4.5) and hormone sensitive lipase (pH 6.0) activities, whereas purified placental MVM exhibited two distinct triacylyglycerol hydrolase activities; a minor activity at pH 8.0 and a second major activity at pH 6.0. Triacylglycerol hydrolase activity at pH 8.0 of MVM appeared to be lipoprotein lipase (consistent with criteria such as serum stimulation and salt inhibition), whereas at pH 6.0 the activity was unique in that it was almost abolished by serum, but was not affected by high NaCl concentrations. Our data, for the first time, demonstrate that human placental MVM, in addition to lipoprotein lipase, contain a newly identified triacylglycerol hydrolase activity at pH 6.0.