A Study of Tensile Degradation of Bioresorbable Materials Used for ...

Degradation of Bioresorbable Tensile Bars
Titanium fixation also presents the inconvenience of limited mobility. As noted above,
titanium can be used in spinal fixation. The spine needs to be an extremely mobile part of the
human body both rotating and bending forward and backwards. Although titanium is flexible
enough to allow bones to grow, it cannot bend in the way a human back bends. This causes
limited mobility when titanium is used in the spinal cord fixation. Mobility is a crucial issue
when used in the neck. For example, if disks of vertebrae in the neck are replaced with titanium
because of a rupture, the neck will have a severely diminished range of motion. The patient will
not be able to rotate with the same mobility as prior to the rupture. Titanium is the most
biocompatible material with the body in terms of medical applications; however, it has numerous
downfalls and inconveniences that make the medical world wonder if there is a better device for
internal fixation.
Chemical Makeup of Bioresorbable Polymers
There are numerous compounds of bioresorbable polymers used in medical applications.
Each polymer has a base. Most commonly, the polymers are either poly lactic acid (PLA) based
or milk based. The resorbable materials are compounded with other materials. The poly
lactic/poly glycolic acid (PLA/PGA) compound is the one most commonly used in implants or
fixation. This PLA/PGA combination can be used when the implant is needed in vitro short term.
Because it is necessary that the bioresorbable polymers are stable enough to maintain their form,
a low concentration of glycolic acid must be present. Glycolic acid is a liquefying chemical that
when present in a high concentration could cause the tensile bar to be unable to maintain its
shape. Even though there are multiple variations of the lactide to glycolide ratio, the most
widespread is the 90% lactide and 10% glycolide adaptation. The polymer is easiest to handle in
this combination because it does not illustrate the soft, gooey attribute of a high concentration of
glycolide (Bibber, 2009, p. 1).
With the characteristic of degrading in the presence of heat and moisture, it is difficult to
store biomaterials in an environment where they will not suffer premature degradation. Even the
slightest change in moisture intake or temperature can cause a bioresorbable pellet to begin to
break down as if it were in the body doing its job. Because of this complexity, bioresorbables are
stored in nitrogen sealed packets to prevent disbanding of the polymers (Bibber, 2009, p. 1). As
shown below in Table1, each compound of biodegradable polymers has different physical
characteristics.
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