Replica-producing techniques

Replica-producing techniques have been employed using various casting materials to produce an accurate, detailed reproduction of the evidence specimen. If the replica were of a high quality, comparisons could be made using the replica in place of the actual specimen. 

Figure 24. Electron micrograph showing the relatively featureless surface and the fractured interior of a water-in-oil emulsion. This image was prepared with a metal-coated frozen sample, a modification of direct observation in which the sample is coated sufficiently to prevent sample charging but not enough to produce a replica. This technique still requires an electron microscope with...

ME samples. A major advantage of cryo-TEM over FF-TEM, however, is the less invasive and time-consnming sample preparation as fracture and replica producing steps are not necessary. Cryo-TEM is a valuable technique not only for the investigation of MEs bnt colloidal structures in general, such as wormlike micelles [81], cubosomes [82], ISCOMS [83], etc. These samples are usually dilute and thin, hence one-layered samples can be prepared. Furthermore, investigations into improved sample preparation for FF-TEM and combinations of EE- and cryo-TEM can be fonnd in the literature [84], and it can be anticipated that cryo-TEM may be added to the various characterization techniques for MEs in the near future. 

Ragetly GR, Slavik GJ, Cunningham BT et al (2010) Cartilage tissue engineering on fibrous chitosan scaffolds produced by a replica molding technique. J Biomed Mater Res A... 

The printing process can be separated into two parts fabrication of the stamp and use of this stamp to pattern features defined by the relief on its surface. These two processes are typically quite different, although it is possible in some cases to use patterns generated by a stamp to produce a replica of that stamp. The structure from which the stamp is derived, which is known as the master , can be fabricated with any technique that is capable of producing well-defined patterns of surface relief. This master can then be used directly as the stamp, or it can be used to produce stamps via molding or printing procedures. 

Freeze-Fracture Method A sample preparation technique used in electron microscopy in which specimens are quickly frozen in a cryogen and then cleaved to expose interior surfaces. In some techniques, the sample is then observed directly in an electron microscope equipped with a cryogenic stage in other cases, the cleaved sample is coated with a metal coating to produce a replica, which is observed in the electron microscope. See also Electron Microscopy. 

Brittain et al. describe a series of soft lithographic methods that may be suited to the patterning of organic layers [82]. A pattern-transfer element is formed by pouring a liquid polymer, such as poly(dimethylsiloxane), onto a master made from silicon. The polymer is allowed to cure to form an elastomer, which can then be removed from the master. This replica can be used subsequently as a stamp to transfer chemical ink, such as a solution of an alkanethiol, to a surface. Features with dimensions of 40-100 nm can be produced with the technique of near-field, phase-shift photolithography [82]. 

Wax or plastic patterns (replicas) of the metal parts needed are produced by plastic injection molding techniques. 

In a typical treatment of polyethylene, 1-2 pm is removed from the surface, with the reagent attacking preferentially the non-crystalline material. The surface can then be studied either by two-stage replication or by high-resolution scanning electron microscopy (SEM). The latter gives somewhat lower resolution than TEM, but is much easier to use than the production of replicas. In this technique scattered or secondary electrons emitted from the surface are collected as an electron beam is scanned across it in a raster like that used to produce a television picture and the image is built up in a similar way from the intensity detected. 

Fig. 10.9 Formation of multiscale structures by combination of the breath figures approach and embossing techniques. The immiscibility between both homopolymers added (PS and PVP) due to the different hydrophilicity produces hierarchical ordered patterns where the PVP is located inside the pore and the PS at the pore wall. In addition, embossing produces an additional level of order at the micrometer length-scale as well as replicas. Reproduced with permission from ref. [205]...

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