Tissue-polymer interactions

Hydrogels Hydrogels consist of a cross-linked polymer system or a meshlike structure that is flexible and can swell in the presence of water, producing a hydrophilic surface and masking the components below. The most widely used hydrogels consist of poly(hydroxyethyl methacrylate) (PHEMA), poly(ethylene glycol) (PEG), or poly(vinyl alcohol) (PVA) and tend to have reduced interaction with tissue.22 31 44 53 55... 

Polymer/tissue interfacial properties the implant interface is a unique site where different chemicals coexist and interact. If the surface of an implant has an affinity towards specific chemicals, an abnormal boundary layer will develop. The subsequent intra-layer rearrangement or reactions with other species then trigger tissue reactions. The defence reactions of the host tissue often lead to encapsulation of an... 

Surface characterization is very important in the development of blood-compatible biomaterials, since the surface characteristics of the polymer have been linked to polymer-tissue and polymer-blood interactions. Further information on surface characterization of biomaterials can be found elsewhere (20, 21). 

Gosiewska, A., Rezania, A., Dhanaraj, S., Vyakamam, M., Zhou, J Burtis, D., Brown, L., Kong, W., Zimmerman, M., and Geesin, J. C. (2001), Development of a three-dimensional transmigration assay for testing cell-polymer interactions for tissue engineering sqtplications. Tissue Eng. 7(3) 267-m. 

As mentioned, the overall degradation rate is affected by numerous phenomena. Today, it is still not possible to bmld a mathematical model that predicts the final degradation rate and accounts for aU possible variables, starting from polymer processing and manufacturing to device hydrolysis. The description is even more compUcated in vivo, where polymer—tissue interactions also can play a significant role in the final behavior of bioresorbable polymers. 

Interactions of Tissue- and Blood-Cells with the Polymer Surface Material... 

Smart biomaterials will likely be resorbable polymers tailored at the molecular level and able to respond to changes in the miCToenvironment and interactions with tissue cells. A great challenge for the future development of biomaterials is the controlled differentiation of target cells in the presence of biomaterials. Typically, differentiation is controlled by soluble growth factors and cytokines. 

Despite the universal use of sutures for wound closure, there is a need to utilize adhesives instead, because of their ease of use and the reduced risk of infection. Alkyl cyanoacrylate adhesives have been studied extensively for this use, and a significant amount of research has been performed to evaluate their interaction with living tissue [40,41 J. They have been approved for external use only, because of concerns with the fact that the polymers do not readily biodegrade and can cause inflammation around the area to which it was applied. However, these concerns are reduced for -butyl cyanoacrylate, as compared to the ethyl cyanoacrylate. There is even some evidence that their use as liquid sutures actually reduces the rate of infection around the healing wound or surgical incision [42J. 

A different pH-triggered deshielding concept with hydrophilic polymers is based on reversing noncovalent electrostatic bonds [78, 195, 197]. For example, a pH-responsive sulfonamide/PEl system was developed for tumor-specific pDNA delivery [195]. At pH 7.4, the pH-sensitive diblock copolymer, poly(methacryloyl sulfadimethoxine) (PSD)-hZocA -PEG (PSD-b-PEG), binds to DNA/PEI polyplexes and shields against cell interaction. At pH 6.6 (such as in a hypoxic extracellular tumor environment or in endosomes), PSD-b-PEG becomes uncharged due to sulfonamide protonation and detaches from the nanoparticles, permitting PEI to interact with cells. In this fashion PSD-b-PEG is able to discern the small difference in pH between normal and tumor tissues. 

Fabrication approaches have been previously used in two-dimensional (2D) micropattemed model systems and have led to insights on the effect of cell-cell and cell-polymer scaffold interactions on hepatocyte and endothelial cell fate. Extending these studies, the application of 3D fabrication techniques may also prove useful for studying structure-function relationships in model tissues. 

Saltzman, W. M., Cell Interactions with polymers, in Principles of Tissue Engineering (R. Lanza Ed.), pp. 228-246. RG Landes Company, Austin, TX (1997). 

The suitable materials for the above mentioned domains are polymers, metals and ceramics. Among these, polymers play an important role. Even the polymers have a lot of remarkable properties that could be used in biomaterials design, the interaction between these artificial materials and tissues and blood could create serious medical problems such as clot formation, activating of platelets, and occlusion of tubes for dialysis or vascular grafts. In the last few years, novel techniques of synthesis have been used to correlate desirable chemical, physical and biological properties of biomaterials. 

The polymer/SWCNT composites can be used as Scaffolds in tissue engineering. The donor-acceptor interactions can be used to assemble thin polymer/SWCNT films stepwise. This method also can be expended to more thermally and oxidatively stable polymer systems. For example, the P4VP/SWCNT films can be used as scaffolds for the synthesis of novel hybrid structures (Correa-Duaite et al., 2004). The polyethyl-enimine (PEI)-SWCNTs composites were used as a substrate for cultured neurons, and promoted neurite outgrowth and branching (Rouse et al., 2004). Correa-Duarte et al. (2004 Landi et al., 2005) reported that 3D-MWCNT-based networks are ideal candidates for scaffolds/matrices in tissue engineering. 

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