What Has Been Trending in the Research of Polyhydroxyalkanoates? A Systematic Review

Abstract

Over the past decades, enormous progress has been achieved with regard to research on environmentally friendly polymers. One of the most prominent families of such biopolymers are bacterially synthesized polyhydroxyalkanoates (PHAs) that have been known since the 1920s. However, only as recent as the 1990s have extensive studies sprung out exponentially in this matter. Since then, different areas of exploration of these intriguing materials have been uncovered. However, no systematic review of undertaken efforts has been conducted so far. Therefore, we have performed an unbiased search of up-to-date literature to reveal trending topics in the research of PHAs over the past three decades by data mining of 2,227 publications. This allowed us to identify eight past and current trends in this area. Our study provides a comprehensive review of these trends and speculates where PHA research is heading.

Keywords: biotechnology; composites; data mining; medicine; polyhydroxyalkanoate; polyhydroxyalkanoate (PHA) synthesis; renewable production; trends.

Figure 1

Diagram of the method and steps of systematic literature review (SLR). HDBSCAN, Hierarchical Density-Based Spatial Clustering of Applications with Noise; TF-IDF, term frequency–inverted document frequency.

Figure 2

The network of authors of the most frequently quoted in analyzed journals. From each publication, analyzed pairs were identified consisting of: (1) author of the paper and (2) author of referenced paper, represented by the lines in the graphic. All identical pairs in whole corpus were summed up. The greater the sum, the stronger the relation is, which is visualized by the increased font size in the iconographic. The network of relations allows to discover groups of cooperating scientists. These relations are probably based on common university, field of study, etc.

Figure 3

Number of publications in polyhydroxyalkanoate research identified in Web of Science Core Collection for years 1988–2019.

Figure 4

Trends discovered in research on polyhydroxyalkanoates in years 1988–2019 based on the most important terms found during the term frequency–inverted document frequency (TF-IDF) analysis of publications. A trend occurs when the average number of articles exceeds a certain expert-determined level per given time.

Figure 5

Modification of a polyhydroxyalkanoate (PHA) structure through selected chemical reactions. Carboxylation by addition of carboxylic functional group to the polymeric macromer which can serve as functional binding sites for bioactive moieties. Hydroxylation resulting in shortened hydroxy-terminated PHA chains important in block copolymerization reactions. Epoxidation is useful in diverse reactions such as cross-linking, copolymerization, and bioactive moieties attachment thanks to the high reactivity of the epoxide group. Halogenation which relies on the addition of halogen atoms such as chlorine, bromine, or fluorine to the olefinic bonds of unsaturated PHA, being an excellent method in diversifying functions and applications of the polymer. Graft copolymerization results in the formation of a modified segmented copolymer. Chemical-, radiation-, or plasma discharge-induced reaction evokes improvement of selected polymer properties, i.e., increased wettability or mechanical strength.