Biomedical polymers effect

Fig. 3.2 Typical molecular weight distribution and viscosity dependence for biomedical polymers. Effect of entanglement molecular weight and viscosity on the morphology of electrospin-ning/spraying products...

Sn(II) 2-ethylhexanoate, which has been approved for surgical and pharmacological applications by the FDA, is generally employed as the catalyst for the synthesis of biomedical polymers. However, it has been reported that Sn(II) 2-ethylhexanoate cannot be removed by a purification process such as the dissolution/precipitation method, thus the residual Sn may be concentrated within matrix remnants after hydrolytic degradation (2). To avoid the potential harmful effects of metallic residues in biomedical polymer materials, enzymatic polymerization is one of the powerful candidates for polymer synthesis (3). Enzymes, natural kinds of protein without toxicity, have remarkable properties... 

Biomedical polymer is directly applied to human body and is closely related to human health. Therefore, the materials used for clinic should be strictly controlled, otherwise, it may cause adverse effect instead of life saving. Below are requirements on properties and performances of the biomedical polymer ... 

Chu CC, Zhang L, Coyne LD. Effect of gamma irradiation and irradiation temperature on hydrolytic degradation of synthetic absorbable sutures. In Proceedings, Clemson University Conference on Medical Textiles and Biomedical Polymers and Materials 1996. 

The effect of molecular structure on the properties of biomedical polymers... 

Shalaby W, Park H (1994) Chemical modification of proteins and polysaccharides and its effect on enzyme-catalyzed degradation. In Shalaby S (ed) Biomedical polymers. Hansra-Publishers, Munich, pp 213—258... 

Williams, D.E (1994) Molecular biointeractions of biomedical polymers with extracellular exudate and inflammatory cells and their effect on biocompatibility, in-vivo. Biomaterials. 15, 779-785. 

Tyrosine-derived polycarbonates provided a convenient model system to study the effect of pendent chain length on the thermal properties and the enthalpy relaxation (physical aging). It is noteworthy that enthalpy relaxation kinetics are not usually reported in the biomedical literature and that a recent study by Tangpasuthadol (Tangpasuthadol, 1995) represents one of the first attempts to evaluate physical aging in a degradable biomedical polymer. 

In connection with biomedical polymers, the chemistry of the polymeric drugs is under continuous advancement. The most effective anticarcinogenic reagents are now targeted by the design of specifically functionalized polymers. The functional polymeric composites are also particularly attractive as implant materials. 

Among other uses, these polymers have been employed in a variety of biomedical applications. Poly(phosphazenes) containing organic side chains, derived from the anaesthetics procaine and benzocaine, have been used to prolong the anaesthetic effect of their precursor drugs. They have also been used as the bioerodable matrix for the controlled delivery of drugs. 

Nanoparticles such as those of the heavy metals, like cadmium selenide, cadmium sulfide, lead sulfide, and cadmium telluride are potentially toxic [14,15]. The possible mechanisms by which nanoparticles cause toxicity inside cells are schematically shown in Fig. 2. They need to be coated or capped with low toxicity or nontoxic organic molecules or polymers (e.g., PEG) or with inorganic layers (e.g., ZnS and silica) for most of the biomedical applications. In fact, many biomedical imaging and detection applications of QDs encapsulated by complex molecules do not exhibit noticeable toxic effects [16]. One report shows that the tumor cells labeled with QDs survived in circulation and extravasated into tissues... 

Some polymer materials, particularly biomedical materials and step-growth polymers, comprise crosslinked networks. The effect of irradiation on networks, compared with linear polymers, will depend on whether scission or crosslinking predominates. Crosslinking will cause embrittlement at lower doses, whereas scission will lead progressively to breakdown of the network and formation of small, linear molecules. The rigidity of the network, i.e. whether in the glassy or rubbery state (networks are not normally crystalline), will affect the ease of crosslinking and scission.. ... 

Methoxy poly(ethyleneglycol) (mPEG) was the most frequently used semitelechelic polymer for over 2 decades. It has been successfully used for the modification of various proteins, biomedical surfaces and hydrophobic anticancer drugs (for reviews see References [3,9,10]. Recently, a number of new semitelechelic (ST) polymers, such as ST-poly(A -isopropylacry-lamide) (ST-PNIPAAM) [11-15], ST-poly(4-acryloylmorpholine) (ST-PAcM) [16], ST-poly(A-vinylpyrrolidone) (ST-PVP) [17], and ST-poly[A-(2-hydroxypropyl)methacrylamide] (ST-PHPMA) [18-21] have been prepared and shown to be effective in the modification of proteins or biomedical surfaces. 

Anderson et al. [59, 75,76] have been pursuing their extensive researches on the biomedical behavior of PEUUs having various formulations modified with hydrophobic acrylate (or methacrylate) polymer or copolymer additives. The most distinguished additive was Methacrol 2138F, which is a copolymer between diisopropylaminoethyl methacrylate and decyl methacrylate [co(DIPAM/DM)] (in a 3-to-l ratio). The protein adsorption assay showed that PEUU (Biomer-type) films loaded or coated with Methacrol or poIy(DIPAM) adsorbed significantly lower amounts of human blood proteins (Fb, IgG, factor VIII, Hageman factor and Alb) than the base PEUU or PEUUs modified by other additives. It was revealed from their experiments that poly(DIPAM) as well as Methacrol exhibited a prominent suppressing effect on the protein adsorption process. 

---