Melt-spun polyhydroxyalkanoate monofilaments were successfully processed into woven and knitted textiles using industrial machinery, demonstrating their feasibility for textile applications. The filaments, composed of P(3HB)/P(3HB-co-4HB), exhibited an average tensile strength of ∼138 MPa and an elongation at break of ∼55%, with crystallinity of ∼30%. Cyclic loading of the filaments revealed pronounced hysteresis during the first cycle, which diminished in subsequent cycles. However, a relaxation time of 120 s was sufficient to reset the molecular conformational changes that occurred during the previous cycles. Furthermore, the incorporation of beta tricalcium phosphate (β-TCP) particles during melt spinning reduced tensile strength but improved thermal stability, enhancing processability. These findings highlight the potential of P(3HB)/P(3HB-co-4HB) monofilaments for sustainable textile applications requiring mechanical resilience and thermal robustness.

The textile industry faces an urgent need for sustainable alternatives to petroleum-derived fibers, with bio-based and biodegradable polymers emerging as promising candidates. In this work, we demonstrate the successful melt-spinning of polyhydroxyalkanoate (PHA) monofilaments, specifically P(3HB)/P(3HB-co-4HB), into woven and knitted textiles using standard industrial machinery. This is relevant, as PHA processing into textile-grade fibers has remained a major challenge due to its thermal sensitivity and mechanical limitations.

The resulting monofilaments exhibited tensile strengths of ~138 MPa and elongation at break of ~55%, with crystallinity around 30%. Mechanical testing under cyclic loading revealed pronounced hysteresis during the first cycle, which diminished in subsequent cycles; importantly, a short relaxation period of 120 s was sufficient to reset conformational changes, demonstrating recoverability under repeated stress. Beta tricalcium phosphate (ß-TCP) particles were incorporated during melt-spinning. While this reduced tensile strength, it significantly improved thermal stability, thereby expanding the processability window for melt spinning.

The influence of beta-tricalcium phosphate (ß-TCP) particles on the early cell attachment of MC3T3-E1 osteoblast precursor cells is investigated on a poly(3-hydroxybutyrate)/poly(3-hydroxybutyrate-co-4-hydroxybutyrate) polymer blend. MC3T3-E1 cells adhere to both polymer blends, with and without ß-TCP. In both cases, the cells show a typical cell morphology and focal adhesions on the polymer surface. The ß-TCP does not significantly improve the cell adhesion and hydrophilicity of the polymer films. Further, ß-TCP does not alter the degradation behavior of the poly(3-hydroxybutyrate)/poly(3-hydroxybutyrate-co-4-hydroxybutyrate) blend when exposed to phosphate buffered saline solution for up to 70 days. However, the results confirm that the polyhydroxyalkanoate blends used in this study are non-cytotoxic and maintain structural integrity over time. These findings highlight the blend's promise for usage in long-term biomedical applications, particularly in bone tissue engineering, because of their stability in isotonic medium. 

Medical textiles are among the fastest growing sectors in the textile industry, with rapid progression especially in wound healing and implantable devices. Considerable attention is paid to the development of new fibre-based absorbable polymer implants because they reduce or eliminate the need for additional surgery to remove implanted structures. For bioabsorbable implants, the rate, mechanism and products of degradation must be carefully controlled to ensure the material functions as intended. Specifically, the degradation rates of the product should ideally be in alignment with the formation of new tissue, and the degradation products must be non-toxic and have minimal interference with the surrounding tissue and the body. 

Polyhydroxyalkanoates (PHAs) are a group of thermoplastic, biobased and biodegradable polyesters, showing promising potential for the use in medical textiles. This is because of their favourable degradation properties, which are considered superior to those of currently used biomaterials. However, PHAs like poly(3-hydroxybutyrate) entail challenges regarding their melt processability, due to the closeness of their thermal degradation temperature to the melting temperature and secondary crystallisation, which results in material embrittlement. 

This thesis investigates the melt spinnability of different PHAs, in particular a semi- crystalline and amorphous blend of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate), using different processing methods. There was also an aim to improve the bioactivity of the filaments by adding bioceramics during filament production. 

It was possible to melt spin rather amorphous fibres from the semi-crystalline and amorphous polymer blend that showed similar mechanical properties to bone and could be processed into knitted and woven textile structures, which demonstrates the PHA filament’s potential to be used for medical textiles.

We investigated the melt-spinning potential of a poly(3-hydroxybutyrate)/poly(3-hydroxybutyrate-co-4-hydroxybutyrate) blend using a piston spinning machine with two different spinneret diameters (0.2 and 0.5 mm). Results from the differential scanning calorimetry, dynamic mechanical thermal analysis, and tensile testing showed distinct filament properties depending on the monofilaments’ cross-sectional area. Finer filaments possessed different melting behaviors compared to the coarser filaments and the neat polymer, indicating the formation of a different type of polymer crystal. Additionally, the mechanical properties of the finer filament (tensile strength: 21.5 MPa and elongation at break: 341%) differed markedly from the coarser filament (tensile strength: 11.7 MPa, elongation at break: 12.3%). The hydrolytic stability of the filaments was evaluated for 7 weeks in a phosphate-buffered saline solution and showed a considerably reduced elongation at break of the thinner filaments. Overall, the results indicate considerable potential for further filament improvements to facilitate textile processing.

Hydroxyapatite (HA) has shown very promising results in hard tissue engineering because of its similarity to bone and hence the capability to promote osteogenic differentiation. While the bioactivity of HA is uncontested, there are still uncertainties about the most suitable hydroxyapatite particle shapes and sizes for textile scaffolds. This study investigates the influence of the shape and size of HA particles on as spun fibers of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and HA, their mechanical and thermal properties as well as their influence on the fiber degradation in simulated blood matrix and their capability to mineralize in simulated body fluid. The key findings were that the different HA particles’ size does not affect the melting temperature and still maintains a thermal stability suitable for fiber production. Tensile testing revealed decreased mechanical properties for PHBV/HA as spun fibers, independently of the particle morphology. However, HA particles with 30 nm in width and 100 nm in length at 1 wt% HA loading achieved the highest tenacity and elongation at break amongst all composite fibers with HA. Besides, the Ca/P ratio of their mineralization in simulated body fluid is the closest to the one of mineralized human bone, indicating the most promising bioactivity results of all HA particles studied.

The superior biocompatibility and biodegradability of polyhydroxyalkanoates (PHAs) compared to man-made biopolymers such as polylactic acid promise huge potential in biomedical applications, especially tissue engineering (TE). Textile fiber-based TE scaffolds offer unique opportunities to imitate the anisotropic, hierarchical, or strain-stiffening properties of native tissues. A combination of PHAs' enhanced biocompatibility and fiber-based TE scaffolds could improve the performance of TE scaffolds. However, the PHAs' complex crystallization behavior and the resulting intricate spinning procedures remain a challenge. This review focuses on discussing the developments in PHA melt and wet spinning, their challenges, process parameters, and fiber characteristics while revealing the lack of an in-depth fiber characterization of wet-spun fibers compared to melt-spun filaments, leading to squandered potential in scaffold development. Additionally, the biomedical application of PHAs other than poly-4-hydroxybutyrate is hampered by a failure of polymer purity to meet the requirements for biomedical applications.