Molecular weight consolidation

Kerns and co-workers demonstrated the application of LC/MS and LC/MS/MS standard method approaches in preclinical development for the metabolite identification of buspirone, a widely used anxiolytic drug (Kerns et al., 1997). The success of this method relies on the performance of the LC/MS interface and the ability to generate abundant ions that correspond to the molecular weight of the drug and drug metabolites. The production of abundant molecular ions is an ideal situation for molecular weight confirmation because virtually all the ion current is consolidated into an adduct of the molecular ion (i.e., [M+H]+, [M+NH3]+). 

These pure dextran phosphates exhibit immunostimulatory effects independent of the molecular weight. It was shown that the mitogenic response of murine splenocytes can be enhanced [101]. Moreover, dextran phosphate (Mw 40 000 g mol-1) increases the survival rate of mice infected with influenza A2 virus (H2N2). Intraperitoneal administration of dextran phosphate, an interferon inducer, shows a 1-day delay in the virus growth in lung, and production of HAI antibody, when compared to the non-treated or dextran-treated mice as controls. More significant was the 2-day delay in the development of lung consolidation, which led to 40% survival of the treated mice [102]. 

Monomers with low molecular weights will diffuse into the wood more rapidly than polymers such as PEG. In a second phase, their in situ radiation curing will form wood consolidants that are much stronger than PEG. However, this method requires very heavy irradiation equipment, which is usually available only in nuclear research centers. The irradiation cell dimensions and the 7-source geometry limit the size of the artifacts. For mainly these reasons, the radiation process was applied in very few institutions and in most cases only at the experimental level. The Nucleart Laboratory, which routinely conserves waterlogged wood by this technique, is located in the Grenoble Nuclear Research Center of the French Atomic Energy Commission. 

At a conceptual level, polyethylene consists only of carbon and hydrogen, as was described in the previous chapter. However, if the discussion of polyethylene is to proceed from ideal abstractions to actual physical implants, three "real world" steps need to occur. First, the ultra-high molecular weight polyethylene (UHMWPE) must be polymerized from ethylene gas. Second, the polymerized UHMWPE, in the form of resin powder, needs to be consolidated into a sheet, rod, or near-net shaped implant (Figure 2.1). Finally, in most instances, tire UHMWPE implant needs to be machined into its final shape (Figure 2.1). A small subset of implants are consolidated into their final form directly, in a process known as direct compression molding (DCM), witiiout need of additional machining. 

UHMWPE is produced as powder and must be consolidated under elevated temperatures and pressures because of its high melt viscosity. As already discussed in Chapter 1, UHMWPE does not flow like lower molecular weight polyethylenes when raised above its melt temperature. For this reason, many thermoplastic processing techniques, such as injection molding, screw extrusion, or blow molding, are not practical for UHMWPE. Insfead, semifinished UHMWPE is typically produced by compression molding and ram extrusion. 

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