Surface spectroscopic imaging of PEG-PLA tissue engineering constructs with ToF-SIMS

Poly(lactic acid) (PLA) has been studied extensively in the field of tissue engineering due to its well-established biodegradability and biocompatibility. To improve its non-fouling properties we entrapped poly(ethyl glycol) (PEG), into the surface, which was characterised by a combination of ToF-SIMS and XPS. Cell attachment was subsequently investigated as a function of the amount of entrapped PEG. XPS was instrumental in quantifying the amount of PEG entrapped at higher concentrations, whereas the significantly higher sensitivity and superior imaging capabilities of ToF-SIMS enabled a full characterisation of the PEG distribution at the low concentrations required for the desired non-fouling properties, which were well below the XPS quantification limit. It was found that pronounced segregation effects leading to the formation of PEG-enriched domains ranging between ca. 5 and several tens of microns across were present at all PEG concentrations investigated.     

Rate equations for multi-photon excitation in strong fields

The excitation of an N-level quantum oscillator by a strong oscillating electric field in the presence of external perturbations can in general be described by a Boltzmann equation for the density matrix. In this paper it is shown that under certain circumstances this may be reduced to a set of rate equations for the level populations. In contrast to the weak field situation, these rate equations explicitly contain multi-photon transition rates.     

Measurement of total protein in urine: Comparison of two dye-binding procedures with a gel filtration/modified biuret method

Two dye-binding methods for the determination of urinary total protein concentration have been compared to a biuret-based procedure requiring a preliminary gel filtration step. The biuret-based procedure is claimed to be both specific and sensitive for the measurement of protein in urine. With those urines having relatively low protein concentrations, the dye-binding methods provide values about one-half of those given by the modified biuret procedure. This difference disappears when urines containing high levels of protein are measured. The lower results obtained at normal protein levels are most likely caused by the inability of dye-binding methods to measure proteins of high carbohydrate content (such as uromucoid) accurately. In spite of this limitation, both dye-binding methods appear suitable for routine use. In contrast to the biuret-based procedure, we found the dye-binding methods to be free from interferences by compounds known to appear in urine in high concentrations.     

The elastic microstructure of various tissues

Previous work has indicated that a modified Quate-Lemons scanning acoustic microscope (SAM) is capable of measuring the acoustic propagation properties of sections of biological tissue. The lens is excited by an impulse, rather than a tone burst, and the undemodulated returning signal from the tissue is recorded. The variations in received signal with time are used to deduce the sound speed, attenuation, impedance, and section thickness. In this article, the technique is applied to various types of tissue, and the variations in acoustic propagation properties are computed. Conventional tone burst SAM images at 425 MHz are compared with the time resolved data in order to elucidate the contrast mechanisms. The effects of varying the frequency and position of the focal plane on the tone burst images are interpreted in the light of the broadband results.     

Spectrophotometric determination of osmium with quinisatin oxime

A spectrophotometric determination of osmium has been developed, based on the purple color (absorption maximum at 515 mμ) formed by reaction of osmium with quinisatin oxime in buffered solution of dimethyl formamide and methanol. The absorbances are reproducible, and the system conforms to Beer's law. The method compares favorably in sensitivity with existing methods for osmium. The optimum concentration range (for 1 cm optical path) is about 2 to 10 p.p.m. of osmium. Although the maximum color develops slowly, it is stable for 7 days or longer. Several elements, notably iron, cobalt, and ruthenium, interfere, so that separation, is necessary. A reaction ratio of 1:2 for osmium and quinisatin oxime was clearly indicated; some evidence was also obtained for the presence of higher complexes.