Starting from the gauge invariant effective action in the quasi-multi-Regge kinematics (QMRK), we obtain the effective reggeized gluon (R) -particle (P) vertices of the following types: RP P , RRP , RRP P , RP P P , RRP P P , and RP P P P , where the on-mass-shell particles are gluons, or sets of gluons with small invariant masses. The explicit expressions satisfying the Bose-symmetry and gauge invariance conditions are obtained. As a comment to the Feynman rules for derivation of the amplitudes in terms of effective vertices we present a "vocabulary" for practitioners.

A new method of surface-selective laser sintering (SSLS) leads to the fabrication of threedimensional (3D) composite scaffolds (spatial resolution ∼200 μm) that are both bioactive and biodegradable. Moreover, the scaffolds can have very precise dimensions and intricate structure. Conventionally, in selective laser sintering (SLS), the polymer absorbs infrared (λ=10.6 μm) radiation and this leads to a volumetric absorption by the whole polymer particle. In other words, each particle of polymer is completely melted and fuses to the next in order to form the desired morphology. In our experiments we have used near-infrared (λ=0.97 μm) laser radiation, which polymer particles do not absorb at all. To initiate the sintering process a small quantity (< 0.1 wt.-%) of carbon microparticles were homogeneously distributed on the surfaces of the polymer particles. Thus, the melting process was limited to only the surfaces of each particle. The carbon microparticles are strong absorbers of laser radiation, and this opens up the technique to a range of polymers that up till now could not be processed by laser sintering. More importantly, since the laser melts only the surfaces of the particles, delicate bioactive species trapped within each particle retain their activity throughout the processing. We have demonstrated the application of this technique by the incorporation of the enzyme ribonuclease A into particles of poly(D,L-lactic) acid (PLA) and the assembly of 3D matrices at three different laser intensities, using a 0.97 μm wavelength continuous wave (CW) diode laser.Polymer composite structures, in which biologically active guest species are dispersed throughout a suitable porous polymer matrix to encourage formation of new tissue, have widespread biomedical applications as scaffolds for tissue engineering.[1,2] Conventional methods of preparing such composites normally use either organic liquid solvents (e.g., solvent casting, particulate leaching) or raised temperature (e.g., melt molding, thermally induced phase separation) to process the polymer. This often leads to solvent and thermally

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We have studied the effect of pulsed laser ablation conditions on the deposition of biocompatible apatite coatings on Ti and Ti–6Al–4V alloy at room temperature. We have made detailed analyses of the spatial distribution of the macroparticles (MP) and of the Ca/P ratio in the coatings. We find that (i) two types of MP are observed, differing in size, shape, and stoichiometry, and (ii) the size distribution of the MP has a maximum depending on the laser fluence and gas pressure in the deposition chamber. Manipulation of the laser deposition conditions allows fine control over both morphology and stoichiometry of coatings. Experimental results are explained on the basis of a theoretical model which includes the analysis of cluster-type ablation mechanisms due to the high pressures of gas evolved in thermal decomposition of the target material under laser irradiation.

The physical, chemical, and biological properties of pulsed laser deposited (PLD) and plasma sputtered (PS) hydroxyapatite (HA) coatings were compared. Human osteoblast-like cell responses to these coatings in vitro were assayed for proliferation and phenotypic expression. PS coatings formed smooth and continuous thin films that followed the contours of the substrate surface. PLD coatings consisted of numerous spheroidal micro- and macroparticles. The crystallinity of all coatings was quantified by comparison with the HA target used for both the PS and PLD processes. The XRD and FTIR results indicated that unannealed PLD coatings deposited at room temperature had X-ray spectra consistent with an amorphous structure and were found to dissolve after only a few hours in saline solution. Annealing at 400 degrees C increased the crystallinity (87-98%), which resulted in improved stability and cell activity. The PS coatings showed greater chemical stability than the unannealed PLD coatings and contained an approximate 15% crystalline phase, increasing to 65% postannealing. Cell proliferation and alkaline phosphatase production were significantly higher on unannealed PS specimens than the other coating treatments. There may be benefits in engineering the presence of a minor percentage of a microcrystalline phase in an amorphous or nanometer scale polycrystalline HA structure.