Periodic polymer surfaces, morphology

Fig. 4 and Fig. 5 show the surface morphologies aftm photo-ablation of PMMA/pyrene, and CMS, CMS/pyrene respectively. In these figures a copper-mesh mask was used in contact with the polymer films for the gena-atkm of sharp etch patterns. For PMMA/pyrene films, in the low pyrene concentration range, the etched surface is quite rough with dendritic and needle-like structures as well as solidified droplets on the bottom of the irradiated areas present although the edges of the etched features are reasonably sharp (Fig. 4a). When the laser fiuence is increased, the etched surface becomes cleaner and more smooth. At a high pyrene concentration, clean and sharp etch patterns can be obtained at a relatively low fiuence, e.g., at a = 1.04 x 10 cm and F = 0.3 J/cm as shown in Fig. 4b. In most cases, periodic structures are observed near the edges of the wire mask, which most likely result from the optical diffraction effect of the wires.

Statically seeded disks were cultured for periods between 7 and 35 days on PHP and subsequently prepared for analysis. SEM was used to examine cell morphology on the polymer surface and inside of the polymers. SEM analysis (Eigure 7.13) shows surface and transverse sections seeded with primary rat osteoblasts and demonstrates that the cells reached confluence on the surface after 14 days (Eigure 7.13 (a)) and formed a continuous, thick layer that at later time points became multilayered sheets, with fibrous matrix present (Figure 7.13 (b)). Osteoblasts were also observed within the polymers (Figure 7.13 (c)), but these were fewer in number and were present as either individual cells or in isolated colonies. 

AFM is widely used in the analysis of polymer surfaces, such as morphology and molecidar structure of crystalline and oriented polymers, block copolymers, and polymer blends. The example shown in Figure 10.13(b) is the AFM three-dimensional smface image of the fracture surface of a composite. A lamellar structure is clearly observed, with periodicity of about 200 nm, comparable to values obtained from the SEM micrographs [Figure 10.13(a)]. 

The majority of the aforementioned capsules were either not sufficiently mechanically stable or suffered from other surface or matrix related deficiencies. These deficiencies include poor morphology, such as capsule sphericity and surface smoothness, which result from an osmolar imbalance. Membranes are also often leaky (an internal polymer slowly diffuses out through the capsule wall) or shrink in either PBS or in culture media over a period of a few hours. Exceptionally, some capsules are observed to swell excessively and burst. Furthermore, some complex membranes, although stable in water, dissolve over several days upon a contact with culture media. This is true for pectin based capsules (pectin/calcium salt) and for alginate-chitosan membranes and maybe a consequence of the polycation substitution by electrolytes present in the media [10]. In order to improve the existing binary capsules several approaches, both traditional and novel, have been considered and tested herein. These are discussed in the following sections. 

In the case of a semicrystalline polymer such as PP, the microstructural features are likely to appear at the scale of the spherulites (typically 5-100 pm in diameter) or even closer at the scale of the long period of the lamellar stacks (10-100 nm). In order to accede to the latter details, it was shown previously (48) that etching of the polished surface with oxidizing acids engraves the amorphous interstices and let the crystalline morphology appear lamellae, or at least stacks of lamellae, become visible. 

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