Manufacturing solid free-form

First, a 3D stmcture is designed using CAD software. Data obtained from computerized tomography (CT) or magnetic resonance imaging (MRI) medical scans can be used to create a customized CAD model. This CAD model is then expressed in a series of cross-sectional layers. The complex scaffold architecture must be built using layer-by-layer (LBL) manufacturing processes known collectively as solid free-form fabrication (SFF). 

Physical Form. For compounders, physical form is an important characteristic. They prefer solid, free-flowing, nondusty materials whereas polymer manufacturers prefer materials that are liquid and easily emulsified. Undesirable are semicrystalline materials which may stratify during storage. 

Leaching equipment such as agitators or grinding mills may discharge their effluent into a cascade of thickeners for continuous countercurrent washing of the finely divided solids free of adhering solute. The same type of cascade can also be used to wash the solids formed during chemical reactions, as in the manufacture of phosphoric acid, by treatment of phosphate rock with sulfuric acid, or of blanc fixe, by reaction of sulfuric acid and barium sulfide, or of lithopone. 

The water reaction evolves carbon dioxide and is to be avoided with solid elastomers but is important in the manufacture of foams. These reactions cause chain extension and by the formation of urea and urethane linkages they provide sites for cross-linking, since these groups can react with free isocyanate or terminal isocyanate groups to form biuret or allophanate linkages respectively (Figure 27.5). 

Oral Administration. Oral administration is the preferred route of administration. There is a general consensus among pediatricians and parents that children younger that 5 years of age have great difficulty with, or are unable to swallow, a solid oral dosage form. Manufacturers, therefore, have developed liquid formulations for many of the commonly used pediatric products. The liquid dosage form, however, is not free of problems. Liquid products are often unstable and have short expiration dates accurate measurement and administration of the prescribed dose is also a problem, especially in infants. 

Seaweeds. The earliest successful manufacture of iodine started in 1817 using certain varieties of seaweeds. The seaweed was dried, burned, and the ash lixiviated to obtain iodine and potassium and sodium salts. The first process used was known as the kelp, or native, process. The name kelp, initially applied to the ash of the seaweed, has been extended to include the seaweed itself. About 20 t of fresh seaweed was used to produce 5 t of air-dried product containing a mean of 0.38 wt % iodine in the form of iodides of alkali metals. The ash obtained after burning the dried seaweed contains about 1.5 wt % iodine. Chemical separation of the iodine was performed by lixiviation of the burned kelp, followed by solid—liquid separation and water evaporation. After separating sodium and potassium chloride, and sodium carbonate, the mother liquor containing iodine as iodide was treated with sulfuric acid and manganese dioxide to oxidize the iodide to free iodine, which was sublimed and condensed in earthenware pipes (57). 

Both of the solid forms are supplied by the manufacturer either as a slab or as a uniform, free-flowing crumb and may contain a suitable food-grade antioxidant. The crumb form, in addition, may contain a suitable food-grade partitioning agent. 

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