Empa, Dübendorf, Switzerland. INTRODUCTION: In nature many bacteria are able to accumulate polyhydroxyalkanoates (PHAs) as a carbon storage compound ...
EMPA20100741
European Cells and Materials Vol. 20. Suppl. 1, 2010 (page 12)
ISSN 1473-2262
Melt-Spun Fibers From Polyhydroxyalkanoate And Polylactate For Fiber Implant Applications M. Zinn1, S. Dilettoso1, S. Lischer1, K. Maniura1, S. Milz2,3, B. Weisse4, R. Hufenus1 1
Empa, St. Gallen Switzerland, Switzerland. 2 Anatomische Anstalt, LMU, Munich,
Munich, Germany. 3 AO Research Institute, Davos, Switzerland. 4Empa, Dübendorf, Switzerland. INTRODUCTION: In nature many bacteria are able to accumulate polyhydroxyalkanoates (PHAs) as a carbon storage compound. Depending on the cultivation conditions and the type of microorganism, these polyesters can be tailored and range from thermoplastic to elastomeric porperties [1]. Poly(3-hydroxybutyrate) (PHB) and the copolyester poly(3-hydroxybutyrate-co-3hydroxyvalerate) (PHB/HV) exhibit the cristallization rates required for an extrusion processes. The melt-spinning of fibers from PHAs has been reported but is a tedious process that can be applied only at small scale using special equipment [2]. Poly(L-lactate) (PLLA) is a polymer that is considered to be a renewable plastic since its raw material, lactic acid, is produced by bacterial fermentation from corn starch or sugar cane. The polymer is synthesized by a ring opening polymerization in a pure chemical process using stannous octoate. PLLA is certified by FDA as an implant material, whereas for PHA so far only academic studies have been reported. The goal of this project was to develop biodegradable fibers that are suitable for tendon repair. METHODS: PHB and PHB/HV up to a 3hydroxyvalerate content of 80 mol% have been produced in Cupriavidus necator in continuous cultivation [3]. The polymers were solvent extracted [1]. For melt-spinning larger quantities of PHA were required and therefore PHB was bought from Biomer (D) or Biocycle (Br), PHB/HV with 8 mol% HV content from Tianan (Enmat Y1000, CN). PLLA was bought from Nature Works (PLA 6200D, U.S.A.). All polymers were characterized using differential scanning calorimetry (DSC), thermogravimetry (TGA), and gel permeation chromatography (GPC). The meltspinning of PHAs and PLLA was carried out on Empa's custom-made pilot melt-spinning plant that allowed production of mono- and bicomponent fibers [4]. The fibers were tested using a tensile tester Zwick (CH) equipped with a 400 N load cell. Biocompatibility was assessed using human dermal fibroblasts (HDF).
RESULTS & DISCUSSION: PHB with a molecular weight of approx. 500 kDa could not be drawn to a fiber mainly because of the low crystallization rate of PHB. As a consequence large spherulitic structures formed which caused poor mechanical properties. The content of HV could be set during biosynthesis and resulted in a decrease of the cristallinity. Optimal performance was expected for PHB/HV with a HV content of 8 mol%. PHB/HV Enmat Y1000 with a molecular weight of 490 kDa, showed better melt stability due to a lower melting temperature (Tm = 170°C). Nevertheless, a pure PHB/HV fiber could not be produced due to winding problems (stickiness of the fiber). On the other hand, PLA 6200D by NatureWorks could be spun to fibers with reasonable mechanical properties. To overcome the difficulties with spinning PHB, bicomponent fibers with a PHB/HV core and a PLA sheath were successfully spun and were strong enough for the construction of a textile fabric. In vitro biocompatibility studies with HDF showed no toxicity of the bicomponent fibers. Fibroblasts emerging from cell reaggregates adhered to the textiles and grew along single fibers, covering them well after a cultivation period of 1 week. In vivo studies in rats are currently evaluated and first results showed no inflammation in the muscle around and only localized inflammatory reaction within the meshes of the textile implant structure. CONCLUSIONS: The processing of poly(3hydroxyalkanoates) to fibers can be done using the bicomponent spinning method with PLLA as the sheath material. We therefore propose that the degradation rate of the fiber/textile can be controlled by the content of the PHB/HV (slowly degrading) and PLLA (quick hydrolysis). Thus, the material has properties that are in particular interesting for tendon repair applications. REFERENCES: 1M. Zinn, B. et al., (2001) Adv. Drug Del. Rev. 53:5-21. 2R. Vogel et al., (2008) Macromol. Biosci.8: 426-43. 3M. Zinn, (2003) Eur. Cell. Mater. 5 Suppl. 1, 38. 4S. Houis, et al., (2007) Appl. Polym. Sci. 106, 1757-1767. http://www.ecmjournal.org
