Biomedical polymers thermal properties

Chemical structure of monomers and intermediates was confirmed by FT-IR and FT-NMR. Molecular weight distribution of polymers was assessed by GPC and intrinsic viscosity. The thermal property was examined by differential scanning calorimetry. The hydrolytic stability of the polymers was studied under in vitro conditions. With controlled drug delivery as one of the biomedical applications in mind, release studies of 5-fluorouracil and methotrexate from two of these polymers were also conducted. 

Mano JE, Koniarova D, Reis RL. Thermal properties of thermoplastic starch/synthetic polymer blends with potential biomedical apphcabihty. J. Mater. Sci. Mater. Med. 2003 14 127-135. 

Polyanhydrides are a class of bioerodible polymers that have shown excellent characteristics as drug delivery carriers. The properties of these biomaterials can be tailored to obtain desirable controlled release characteristics. Extensive research in this promising area of biomaterials is the focus of this entry. In the first part of the entry, the chemical structures and synthesis methods of various polyanhydrides are discussed. This is followed by a discussion of the physical, chemical, and thermal properties of polyanhydrides and their effect on the degradation mechanism of these materials. Finally, a description of drug release applications from polyanhydride systems is presented, highlighting their potential in biomedical applications. 

Sterihzabflity of biomedical polymers is an important aspect of the properties because polymers have lower thermal and chemical stability than other materials such as ceramics and metals, consequently, they are also more difficult to sterilize using conventional techniques. Commonly used sterilization techniques are dry heat, autoclaving, radiation, and ethylene oxide gas [ Block, 1977]. 

In general, polymers for biomedical and pharmaceutical applications are characterised in order to determine their molecular weight, composition and thermal properties. All of these characteristics may influence the properties of the final device or medicine. 

Degradable polymers such as polylactide (PLA), polyglycolide (PGA), poly(e-caprolactone) (PCL), poly(trimethylene carbonate) (PTMC) and poly (para-dioxanone) (PDO) have been widely investigated, and approved by FDA for use in the biomedical field (Middleton and Tipton, 2000). Table 4.1 presents the stmctures and thermal properties of these polymers. 

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. 

Besides the biomedical applications, terminal functionalization of hbPG can be used to change the thermal properties of the polymer. The attachment of mesogenic cyanohiphenyl end groups via spacers, results in liquid-crystalline hyperhranched polymers and increasey the glass transition to 40-50... 

DMA can also be used to investigate the effect of sterilisation on the structural and thermal properties of polymers and composites intended for biomedical use. Due to the sensitivity of some polymers to heat and solvent attack, one option to sterilise would be to y -irradiate. In a study investigating the properties of composite materials consisting of bioceramic fillers. 

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