A series of random aromatic-aliphatic thermotropic copolyesters comprising p-hydroxybenzoic acid (NBA), vanillic acid (VA), 4,4'-sulfonyl bis(2-methylphenol) (dBPS) and three aliphatic diacids (Spacer), developed for potential applications in orthopaedic medicine, have been characterized in the context of their structure and mechanical properties. Each of the three polymers comprised the following molar percentages of monomer units 50/25/12.5/12.5 (HBA/VA/dBPS/Spacer). Oriented fibres prepared from the materials via melt-spinning have been analyzed using X-ray diffraction to evaluate order parameters describing the degree of molecular orientation and mechanical measurements to determine their tensile properties. In addition, measurements of the bulk isotropic and shear moduli of one polymer composition have also been performed. To obtain an understanding of the material properties the aggregate model due to Ward has been applied to the orientation dependence of the measured elastic moduli and the development of mechanical anisotropy. (C) 2010 Elsevier Ltd. All rights reserved.