Abstract
ABSTRACTPolymers are becoming more important in all economic sectors, and as environmental concerns grow, biopolymers are replacing metal- or oil-based polymers. Two of these polymers are polyhydroxybutyrate (PHB), which is known for good mechanical characteristics and the manufacturing from renewable resources, and polylactic acid (PLA), which is known for fast degradation rates and great benefits for packaging industry. They exhibit properties that make them competitive alternatives for the less eco-friendly polymers, but processing techniques are not as well-researched. In this study, we performed in vitro degradation and drug release studies with pure PHB and PLA and PHB/PLA blends (1:3). Therefore, polymers were stored at 65°C in a PBS-buffer under rather static conditions to simulate intraossal localization. The mass loss of all samples indicates a degradation of all polymers, and it was confirmed by decreasing molecular weight, decreasing pH, increasing crystallinity, and decreasing water contact angle. Following these measurements, a 60-day drug release study was performed, which revealed a four-phase drug release mechanism, including a diffusion-controlled initial burst release especially elevated for investigated blends due to eased medium interpenetration, and a secondary burst release after 20 days for both blends and the pure PLLA-Biomer with lower molecular weight. The intensity of the secondary burst release corresponded to observed degradation characteristics allowing the conclusion of a degradation controlled drug release here.
Highlights
The polymer market is expanding, and biopolymers are gaining importance as well
Studies differ a lot from each other due to the use of distinct media or further conditions, so that comparison of the behavior of different materials and correlation of drug release to polymer degradation is often hindered. Within this manuscript we provide an in vitro degradation and drug release study performed under identical rather static conditions, as for example observed in bone with low vascularization, allowing correlation of both mechanisms
Comparing again to mass loss measurements we find the same 10% for PLLA, indicating that drug release is mainly degradation controlled, while the diffusion coefficient of Fluorescein diacetate (FDAc) seems to be very low in the higher molecular weight PLLA
Summary
The polymer market is expanding, and biopolymers are gaining importance as well. In daily life, where climate change is one of the biggest issues for the decades, biopolymers are an important solution for a great number of challenges. Biopolymers are polymers that are produced from renewable raw materials, such as wheat or organisms (like bacteria), and/or they can be degraded naturally. Polyesters are an example of degradable, oil-based polymers, especially polyethylene terephthalate (PET), which is standardly produced from ethylene glycol and terephthalic acid Both materials are oil based, but there is a potential to make them more naturally. The second step is to produce terephthalic acid from renewable raw materials This is a great example for turning a biopolymer into a native biopolymer [2,3]. An advantage for biopolymers like PHB is that the required temperatures and pressures are lower for the different manufacturing methods, decreasing the relative costs of production [2,7]. A drug can be included in the polymer matrix quite since these films are made via solvent evaporation methods like dip coating or spray coating, so the drug can be mixed into the initial
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