Polymer degradation by hydrolysis

As mentioned above, PHB takes up minor quantities of water upon storage [152], that is, about 0.2 wt%. Despite this modest moisture content, the possibility of polymer degradation by hydrolysis must be taken into account since PHAs degrade in water at room temperature, albeit at a very low rate. This hydrolytic degradation is strongly accelerated at higher temperatures or in an alkaline medium [153]. 

It has been noticed for some time that there is a sudden release of acidic material due to autocatalysis effect on degradation of PLA or PLGA. LA- and GA-based polymers degrade by hydrolysis of the ester bonds, resulting in oligomers and monomers of... 

Polymer degradation by hydrolysis will be governed by the amount of water present in the formulation. The degradation rate is thus influenced by Ihe hydro-phobicity of the polymeric side chains and their ability to take on water. The hydrophobicity of the polymeric structure must strike a balance with the optimal hydrophobicity needed for protein adsorption and cellular attachment. In order for cells to adhere to a polymeric scaffold, the scaffold must be hydrophilic. However, many of the polymers utilized for scaffold fabrication are highly hydrophobic. Thus, surface modifications or pre-wetting the scaffold with a solvent is typically needed for successful cell adherence. 

Biodegradable polymers used in the field of controlled drug delivery are typically degraded by hydrolysis [38]. In addition, some biomedical polymers are enzymatically degradable [35,39]. Many factors are known to influence the bio-... 

The present paper reports on a study which was conducted to investigate the effect of NaOH on the in vitro release profiles of microspheres prepared with polylactides (2) Since these polyesters degrade by hydrolysis (4), it is possible that the molecular weight of the polymers can be decreased by the alkaline pH of the sodium oleate emulsifier solution (pH 10) during fabrication. This in turn could affect the release kinetics of the microspheres. 

These polylactides are known to degrade by hydrolysis (4.) Therefore, the most obvious explanation is that the molecular weight of the polymer is decreased by the NaOH. It has been reported (6) that drug release is increased when the polymer molecular weight is lowered. This would then account for the enhanced drug release observed. 

Both polymers degrade by a simple hydrolysis reaction, and no cellular or enzyme activity is necessary for suture absorption (16, 17) ... 

Polymers that have been synthesized by a stepwise condensation route (Section 1.2.1) that involves the evolution of water are susceptible to degradation by hydrolysis since this involves the reversal of the polymerization reaction. The conditions of high temperature and the presence of tmces of an acidic or basic catalyst are easily met in an extruder. The reaction is often auto-catalytic since the product of hydrolysis will be an acid end group. This shown in Scheme 1.73 for the acid-catalysed hydrolysis of poly(ethylene terephthalate) (PET). 

All aqueous microsphere dispersions must be dried after the capsules are completely hardened. Freeze-drying is a common method of gaining stable powders that can be stored and appHed. It is important to minimize the amount of resting water in the formulation, as not orJy the drug can be hydrolyzed but also the polymer. Polyesters and polyanhydrides both degrade by hydrolysis catalyzed by water consequently, the release mechanism usually depends on drug diffusion as well as on polymer degradation. 

Degradable polymers, particularly polymers that degrade by hydrolysis, are appealing materials for use in clinical medicine because they disappear after implantation. Degradation is often difficult to control families of related polymers provide the greatest versatility in design. 

The biological compatibility of materials used in the nontoxic category is vital and is the subject of continuing research. Since no material is completely inert, it is the level of interaction between an implant and the surrounding tissue that determines the acceptability of the material. Several other facts that are important in determining acceptability include mechanical properties of the polymer, e.g., wear resistance and fatigue, and bulk chemical properties such as resistance to degradation by hydrolysis, sensitivity to enzymes, and the way it reacts to the deposition of protein. 

Polydioxanone A synthetic polymer formed from dioxanone monomers which degrades by hydrolysis. 

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