Microdomain-structured materials

As stated in Chapter 1, microdomain-structured surfaces are believed to play an important role in their interactions with cells, proteins, and other biological elements. In this Chapter, the author will discuss biomedical behavior of three types of microdomain-structured materials segmented polyurethanes, A-B-A block copolymers, and polyamine-graft copolymers. 

The random-network concept discussed above may be applicable, in principle, to the surfaces of some microdomain-structured materials. As stated in Sect. 4.2, the HEMA-STY copolymer showed the best blood compatibility after... 

As aforementioned, diblock copolymer films have a wide variety of nanosized microphase separation structures such as spheres, cylinders, and lamellae. As described in the above subsection, photofunctional chromophores were able to be doped site-selectively into the nanoscale microdomain structures of the diblock copolymer films, resulting in nanoscale surface morphological change of the doped films. The further modification of the nanostructures is useful for obtaining new functional materials. Hence, in order to create further surface morphological change of the nanoscale microdomain structures, dopant-induced laser ablation is applied to the site-selectively doped diblock polymer films. 

Drug Release from PHEMA-l-PIB Networks. Amphiphilic networks due to their distinct microphase separated hydrophobic-hydrophilic domain structure posses potential for biomedical applications. Similar microphase separated materials such as poly(HEMA- -styrene-6-HEMA), poly(HEMA-6-dimethylsiloxane- -HEMA), and poly(HEMA-6-butadiene- -HEMA) triblock copolymers have demonstrated better antithromogenic properties to any of the respective homopolymers (5-S). Amphiphilic networks are speculated to demonstrate better biocompatibility than either PIB or PHEMA because of their hydrophilic-hydrophobic microdomain structure. These unique structures may also be useful as swellable drug delivery matrices for both hydrophilic and lipophilic drugs due to their amphiphilic nature. Preliminary experiments with theophylline as a model for a water soluble drug were conducted to determine the release characteristics of the system. Experiments with lipophilic drugs are the subject of ongoing research. 

A series of polyamine-graft copolymers (See Sect. 4.3) were found to form microdomain structure and to exhibit unique biomedical behavior at the interface with living cells, e.g. blood platelets or lymphocytes. Although a number of postulates were proposed to explain the unique behavior of microdomain-structured surface, mechanisms for the mode of interaction of living cells with any of the domain-structured materials have not been adequately explained. In Sect. 4, the author will review results on the biomedical behavior of SPUs, HEMA-STY, and polyamine-graft copolymers, and discuss their interfacial properties in terms of the random network concept of water molecules on the material s surface. 

In order to study the detailed behavior of LC block copolymers, it would be ideal to create monodispersed LC-BCP samples with well defined architecture for each block over a wide range of molecular weights. LC-BCP systems with narrow polydisper-sity should form well-ordered microdomain structures while LC-BCPs with broad molecular weight distributions would probably not. Synthesis of such materials still remains a challenge. 

Theoretical approximations and morphology predictions were recently carried out for miktoarm star terpolymers of the ABC type. The literature concerning theoretical predictions for this complex architeaure is rather limited, as the synthesis of such materials leading to morphologically three-phase stmaures has been developed rather recently. The behavior of miktoarm star terpolymers was simulated using the Monte Carlo calculation method. This approach was already used for the microdomain structural behavior of diblock copolymers of the AB type, and the consideration that needed to be taken into account for the calculations was the addition of the C chain at the common junction point of the A... 

Previous publications [136, 137] reviewed models proposed for HS achieved with the diisocyanate MDI and extended with BDO. A detailed morphological analysis [137] of a series of such materials showed that the hard microdomain structure was in qualitative agreement with the model proposed by Koberstein and Stein [136], This model was based on the partial solubilization of short HS into the soft microphase. HS shorter than the critical length for microphase separation were presumed to remain within the soft microphase while longer segments aggregated into lamellar hard microdomains of thickness proportional to the critical sequence... 

The development of fundamentally new structural materials requires achieving functional parameters that are conditioned by the properties of microdomains and developing processes at the atomic and molecular level, in monolayers and nanovolumes. 

Yui N, Kataoka K, Sakurai Y, Akutsu T (eds) (1986) Microdomain-structured polymers as antithrombogenic materials in artificial heart. Springer, Berlin Heidelberg New York... 

We assumed polypeptide microdomains would be formed in the matrix from vinyl polymer chains on the electrode (Figure 1), since multiphase materials including block and graft copolymers have been known in general to form microdomain structures in the solid state (72). In fact, some of those containing polypeptide segments were found to have microdomains composed of polypeptide (72-/<. In the present case, the segments from polypeptide was considered to form hydrophilic microdomains after hydrolysis. 

Figure 25.2 Representation of the equilibrium microdomain structure as/a is increased for fixed xN. (Reproduced with permission from F.S. Bates and G.H. Fredrickson, Block copolymers - Designer soft materials, Physics Today, 52, 32, 1999. 1999 American Institute of Physics.)...

The crystallization of homopolymers yields a hierarchical structure in polymer materials, which substantially controls their physical properties. Therefore, the crystalline morphology of homopolymers has been one of the important research subjects in polymer science. In addition, the crystallization of homopolymers spatially confined in various nanodomains, such as micelles, AAO, or microdomain structures, may bring new information on crystallization mechanisms of homopolymers, because it will be possible to highlight a specific crystallization mechanism (e.g., nucleation or crystal growth) in the overall crystallization process consisting of several combined mechanisms. Furthermore, the crystallization in nanodomains has the possibility of providing new polymer materials, and their physical properties should be unique as compared with usual polymer materials. This is because the substantial control of nano-ordered structures formed in polymer materials will be possible by this crystallization, which is never achieved by the crystallization of neat homopolymers. 

The basic research on the crystallization in more complicated systems started recently to find ouf unique morphologies formed in polymer systems. The crystallization of block copolymers is a striking example of such crystallization, which is intimately dependent on the molecular characteristics of crystalline block copolymers. For example, the crystallization of crystalline-amorphous diblock copolymers yields the lamellar morphology or crystalline microdomain structure depending on xN of block copolymers, Tg of amorphous blocks, crystallization conditions, and so on. These kinds of crystallization have the possibility of developing new crystalline polymer materials. Therefore, we strongly anticipate future advances in this research field. 

In an experiment carried out with 100 mg/1 methylene blue concentration the behaviour was the same as described before, but, there was a time in which SC-155 reached the saturation and the material stopped the adsorption the AC-ref instead continued the adsorption at longer times due to its higher carbon contents. Then, the great difference in adsorption kinetics observed between SC-155 and AC-ref is justified by the more expanded structure of carbon microdomains of SC-155 than the reference, and by the higher radius of meso-macropores observed for the SC-155 the last point provides an easy access of molecules to be adsorbed into the grains of the material, minimizing diffusional problems. 

---