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Biodegradable thin films are environmentally friendly materials that have been successfully applied in a wide range of applications within the medical field including tissue engineering, surgical sutures, gene therapies and controlled drug delivery tools, as well as within the field of agriculture, packaging and fiber production.
As stated in its name, the biodegradability of thin films, along with its chemical structure, allows is a significant parameter in its ability to be utilized in these applications. Recently, there has been a remarkable increase in the use of biodegradable polymers for these applications due to its strong properties of durability, versatility, lightness, performance, ease of processing, high productivity, low cost and resistance to corrosion1.
The Role of Crystallization in Biodegradable Polymers
The useful properties of biodegradable polymer thin films are primarily associated with their crystalline structure. For example, poly(butylene adipate) (PBA) is a commonly used biodegradable polyester that is separated into both a-PBA and b-PBA that is determined by their respective a- or b-crystals1.
The specific crystalline structures of both a-PBA and b-PBA are determining factors of the biodegradability behavior of these polymers, as a-PBA exhibits a faster rate of degradation as compared to its b-PBA counterpart, which is due to the larger size of the a-crystals. It is therefore particularly useful for industries that are interested in utilizing biodegradable polymer thin films to investigate how crystallinity of these materials affects their properties, as well as methods in which these crystal structures can be modified.
Controlling the Crystallization of Biodegradable Polymers in Thin Films
Unfortunately, the crystallization behavior of biodegradable polymers on a large industrial scale has not bee widely studied, as this specific property does not typically affect the film’s properties of adhesion or biocompatibility. Current methods of controlling the crystalline structure of biodegradable polymer thin films involve manipulation of the surface properties or confinement effects of the material.
Epitaxial crystallization is one type of procedure that occurs under the effect of other materials and can ultimately affect the topology and nucleation behavior of a polymer thin film by causing lattice mismatching on the polymer substrates2. Additional contributing factors on crystallization kinetics of these materials include the interface and thickness of the thin film in affecting the glass transition temperature, as well as molecular chain mobility and nucleation types. To study these properties, researchers have utilized a combination of atomic force microscopy (AFM) and broadband dielectric spectroscopy to trace any changes of these properties within the thin film.
Without a unique interaction between the polymer and the substrate material, crystallization kinetics are often slowed to a point that will eventually decrease the crystallinity of the final product as a result of the limited mobility of the molecular changes at this interface between the two materials. Materials that exhibit good lattice matching will often also achieve more rapid crystallization and an overall improvement of the biodegradable properties of the thin film as a result of the improved chain alignment at fixed angles that range from 0° to 90°. Although these aspects of the crystallization of biodegradable thin films have been determined, further research regarding methods that can be utilized for inducing specific crystalline structures for these materials must still be conducted.
Sources and Further Reading
- Schaschke, C. J. (2015). Polyester-Based (Bio)degradable Polymers as Environmentally Friendly Materials for Sustainable Development. International Journal of Molecular Sciences. 16(1), 564-596. DOI: 10.3390/ijms16010564.
- Li, S., Sun, X., Li, H., & Yan, S. (2018). The crystallization behavior of biodegradable polymer in thin film. European Polymer Journal. 102, 238-253. DOI: 10.1016/j.eurpolymj.2018.03.029.
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