High strength bioresorbable bone plates: preparation, mechanical properties and in vitro analysis

Article type: Research Article

Authors: Hasirci, V. | Lewandrowski, K.U. | Bondre, S.P. | Gresser, J.D. | Trantolo, D.J. | Wise, D.L.^;

Affiliations: Middle East Technical University, Department of Biological Sciences, Biotechnology Research Unit, Ankara 06531, Turkey | Orthopaedic Research Laboratories, Massachusetts General Hospital, 55 Fruit St., Boston, MA 02114, USA | Cambridge Scientific, Inc., 180 Fawcett St., Cambridge, MA 02138, USA

Note: [] Corresponding author. Tel.: 617 576 2663; Fax: 617 547 2663; E‐mail: dtrantolo@aol.com.

Abstract: Biodegradable bone plates were prepared as semi‐interpenetrating networks (SIPN) of crosslinked polypropylene fumarate (PPF) within a host matrix of either poly(lactide‐co‐glycolide) – 85 : 15 (PLGA) or poly(l‐lactide‐co‐d,l‐lactide) – 70 : 30 (PLA) using N‐vinylpyrrolidone (NVP), ethylene glycol dimethacrylate (EGDMA), 2‐hydroxyethyl methacrylate (HEMA), and methyl methacrylate (MMA) as crosslinking agents. Hydroxyapatite (HAP), an inorganic filler material, was used to further augment mechanical strength. The control crosslinking agent (NVP) was replaced partially and totally with other crosslinking agents. The amount of crosslinking agent lost, the characterization change in the mechanical properties and the dimensional stability of the bone plates after in vitro treatment was calculated. The optimum crosslinking agent was selected on the basis of low in vitro release of NVP from SIPN matrix. Bone plates were then prepared using this crosslinking agent at 5 MPa pressure and at temperatures between 100–140°C to determine if there was any augmentation of mechanical properties in the presence of the crosslinked network. In vitro analysis showed that 90% of the crosslinking agent was lost on plates using NVP as a crosslinking agent. This loss was reduced to 50% when NVP was partially replaced with EGDMA or MMA. EGDMA was determined to be superior because (1) its low release as a crosslinking agent, (2) flexural plate strength of 50–67 MPa, (3) flexural modulus of 7–13 GPa, and (4) manufacturability stiffness of 300–600 N/m. HAP‐loading resulted in an additional increase in values of mechanical parameters. Substituting PLGA with PLA in the PPF‐SIPN did not show any additional improvement of mechanical properties.

Keywords: Semi‐interpenetrating network, bioresorbable, bone plates, poly(lactide‐co‐glycolide), polypropylene fumarate

Journal: Bio-Medical Materials and Engineering, vol. 10, no. 1, pp. 19-29, 2000