Poly(3-hydroxybutyrate) (PHB) is a polyester which shows excellent biocompatibility and a PHB material is therefore considered suitable for many biomedical applications. A highly porous PHB material may be designed to facilitate the transport of small molecules and body fluids or serve as a biocompatible temporary barrier. In this study, PHB films with varying degree of porosity and pore interconnectivity were made by solvent casting using water-in-oil emulsion templates of varying composition. The morphology was characterized by SEM and the water permeability of the films was determined. The results show that an increased water content of the template emulsion resulted in a film with increased porosity. A fine tuning of the film morphology of the casted films was achieved by varying the salt content of the water phase of the template emulsion. The porosity of these films was roughly the same but the water permeability varied between and . It was concluded that the major determinant of the water permeability through these films is the pore interconnectivity. Furthermore, we report on the formation and water permeability of bilayer PHB films consisting of a porous layer combined with a dense backing layer. 1. Introduction Poly(3-hydroxybutyrate) (PHB) is considered to be a polymer that has high potential as a biodegradable implant material. The polymer is a well examined thermoplastic polyester of microbial origin which shows excellent biocompatibility in contact with tissue and blood [1–5]. The natural presence of low molecular weight PHB and the polymer degradation product, 3-hydroxybutyric acid, in the body is further evidence for the nontoxicity of PHB [6]. Besides the necessary biocompatibility of PHB, the use as an implant requires that the material is degraded during a period of time that is relevant for the application in question. PHB is one of the slowest degrading polyesters since the polymer is highly crystalline, preventing water penetration into the polymer matrix and subsequent scission of polymer chains [7]. An implant made out of PHB material can retain its integrity during an extended period of time in a wet environment and this feature may be attractive for certain applications. PHB has been investigated for many types of medical applications including gastrointestinal patches [8], nerve guides [9, 10], and scaffolds for tissue engineering [11]. The fabrication of highly porous materials with interconnected pores is of great interest in the field of tissue engineering since it enables the passage of fluid and transport of small
References
[1]
T. Saito, K. Tomita, K. Juni, and K. Ooba, “In vivo and in vitro degradation of poly(3-hydroxybutyrate) in rat,” Biomaterials, vol. 12, no. 3, pp. 309–312, 1991.
[2]
S. Gogolewski, M. Jovanovic, S. M. Perren, J. G. Dillon, and M. K. Hughes, “Tissue response and in vivo degradation of selected polyhydroxyacids: polylactides (PLA), poly(3-hydroxybutyrate) (PHB), and poly(3- hydroxybutyrate-co-3-hydroxyvalerate) (PHB/VA),” Journal of Biomedical Materials Research, vol. 27, no. 9, pp. 1135–1148, 1993.
[3]
T. Malm, S. Bowald, A. Bylock, and C. Busch, “Prevention of postoperative pericardial adhesions by closure of the pericardium with absorbable polymer patches: an experimental study,” The Journal of Thoracic and Cardiovascular Surgery, vol. 104, no. 3, pp. 600–607, 1992.
[4]
C. Doyle, E. T. Tanner, and W. Bonfield, “In vitro and in vivo evaluation of polyhydroxybutyrate and of polyhydroxybutyrate reinforced with hydroxyapatite,” Biomaterials, vol. 12, no. 9, pp. 841–847, 1991.
[5]
T. Malm, S. Bowald, A. Bylock, C. Busch, and T. Saldeen, “Enlargement of the right ventricular outflow tract and the pulmonary artery with a new biodegradable patch in transannular position,” European Surgical Research, vol. 26, no. 5, pp. 298–308, 1994.
[6]
S. Y. Lee, “Bacterial polyhydroxyalkanoates,” Biotechnology and Bioengineering, vol. 49, pp. 1–14, 1996.
[7]
Y. Doi, Y. Kanesawa, Y. Kawaguchi, and M. Kunioka, “Hydrolytic degradation of microbial poly(hydroxyalkanoates),” Die Makromolekulare Chemie, Rapid Communications, vol. 10, pp. 227–230, 1989.
[8]
T. Freier, C. Kunze, C. Nischan et al., “In vitro and in vivo degradation studies for development of a biodegradable patch based on poly(3-hydroxybutyrate),” Biomaterials, vol. 23, no. 13, pp. 2649–2657, 2002.
[9]
M. ？berg, C. Ljungberg, E. Edin et al., “Clinical evaluation of a resorbable wrap-around implant as an alternative to nerve repair: a prospective, assessor-blinded, randomised clinical study of sensory, motor and functional recovery after peripheral nerve repair,” Journal of Plastic, Reconstructive & Aesthetic Surgery, vol. 62, no. 11, pp. 1503–1509, 2009.
[10]
P.-N. Mohanna, R. C. Young, M. Wiberg, and G. Terenghi, “A composite pol-hydroxybutyrate-glial growth factor conduit for long nerve gap repairs,” Journal of Anatomy, vol. 203, no. 6, pp. 553–565, 2003.
[11]
C. Rentsch, B. Rentsch, A. Breier et al., “Evaluation of the osteogenic potential and vascularization of 3D poly(3)hydroxybutyrate scaffolds subcutaneously implanted in nude rats,” Journal of Biomedical Materials Research A, vol. 92, no. 1, pp. 185–195, 2010.
[12]
L. Lu, S. J. Peter, M. D. Lyman et al., “In vitro and in vivo degradation of porous poly(DL-lactic-co-glycolic acid) foams,” Biomaterials, vol. 21, no. 18, pp. 1837–1845, 2000.
[13]
A. G. Mikos, G. Sarakinos, S. M. Leite, J. P. Vacanti, and R. Langer, “Laminated three-dimensional biodegradable foams for use in tissue engineering,” Biomaterials, vol. 14, no. 5, pp. 323–330, 1993.
[14]
C. Vaquette, C. Frochot, R. Rahouadj, and X. Wang, “An innovative method to obtain porous PLLA scaffolds with highly spherical and interconnected pores,” Journal of Biomedical Materials Research B, vol. 86, no. 1, pp. 9–17, 2008.
[15]
H. Lo, M. S. Ponticiello, and K. W. Leong, “Fabrication of controlled release biodegradable foams by phase separation,” Tissue Engineering, vol. 1, pp. 15–28, 1995.
[16]
A. C. Richards Grayson, I. S. Choi, B. M. Tyler et al., “Multi-pulse drug delivery from a resorbable polymeric microchip device,” Nature Materials, vol. 2, no. 11, pp. 767–772, 2003.
[17]
W. H. Ryu, M. Vyakarnam, R. S. Greco, F. B. Prinz, and R. J. Fasching, “Fabrication of multi-layered biodegradable drug delivery device based on micro-structuring of PLGA polymers,” Biomedical Microdevices, vol. 9, no. 6, pp. 845–853, 2007.
[18]
A. Bergstrand, S. Uppstr？m, and A. Larsson, “Porous biodegradable coatings for drug delivery,” European Cells and Materials, vol. 21, supplement 1, p. 24, 2011.
[19]
A. Bergstrand, H. Andersson, J. Cramby, K. Sott, and A. Larsson, “Preparation of porous poly (3-hydroxybutyrate) films by water-droplet templating,” Journal of Biomaterials and Nanobiotechnology, vol. 3, pp. 431–439, 2012.
[20]
J. Hjartstam and T. Hjertberg, “Studies of the water permeability and mechanical properties of a film made of an ethyl cellulose-ethanol-water ternary mixture,” Journal of Applied Polymer Science, vol. 74, pp. 2056–2062, 1999.
[21]
H. Andersson, J. Hjartstam, M. Stading, C. von Corswant, and A. Larsson, “Effects of molecular weight on permeability and microstructure of mixed ethyl-hydroxypropyl-cellulose films,” European Journal of Pharmaceutical Sciences, vol. 48, pp. 240–248, 2013.
[22]
C. Pedros-Alio, J. Mas, and R. Guerrero, “The influence of poly-β-hydroxybutyrate accumulation on cell volume and buoyant density in Alcaligenes eutrophus,” Archives of Microbiology, vol. 143, no. 2, pp. 178–184, 1985.
