Med-Tech Innovation Surface modification


Enhancing Polymer Surface DEGRADATION


Electron-beam irradiation can be used to achieve controlled degradation of bioresorbable polymers. Here, a group of academic and industry researchers shows its effects on the surface properties of poly-l-lactide.


The investigation


The mechanism of degradation of bioresorbable polymers can be classified as either surface erosion or bulk erosion. For applications such as tissue fixation, drug delivery and regenerative medicine, surface erosion would be the more desirable mode of degradation, whereby the rate of degradation of polymer bonds is faster than the rate at which water can diffuse into the matrix. Thus, the device will degrade from surface to core. An important attribute of bioresorbable polymers is the ability to tailor both their mechanical properties and their degradation kinetics, which has led to their use in the above applications.1


Bioresorbable


polymers have generated significant expectation as materials for achieving improved osteosynthesis. A central challenge for these materials remains the assurance of consistent and predictable in vivo degradation. Moreover, the associated “acid burst


22 ¦ November/December 2011


effect,” which can occur during implantation, also needs to be addressed.2


A way in which to refine the


control of polymer degradation is to use electron-beam (e-beam) radiation. Previous work illustrated the potential of using e-beam radiation at energies of <1.5 MeV to influence polymer properties in a depth-dependent manner that leads to the initiation of pseudo surface erosion in vitro.3


Moreover,


the precise manipulation of e-beam process conditions allowed for the treatment of bioresorbable polymers on a scale relevant to medical devices such as anterior cruciate ligament interference screws. By using lower energies and higher doses, it is envisaged that the critical need for an early initiation of surface degradation/erosion in a controlled manner will be addressed. The potential of e-beam radiation to simultaneously


affect the surface properties of bioresorbable polymers such as poly-l-lactide (PLLA) is an area of investigation.


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