Synthesis, mechanical properties and biocompatibility of novel biodegradable Poly(amide-imide)s for spinal implant

Varieties of novel Poly(amide-imide)s (PAIs) were synthesized from N,N′-(4,4′-diphthaloyl)-bis-l-amino acids via the direct polycondensation with 4,4′-diaminodiphenyl ether (ODA) in a green medium of molten tetrabutylammonium bromide (TBAB). The pure PAI containing no l-amino acid was also synthesized by a three-step method. We examined and made comparisons of both the novel PAIs and the pure PAI on their thermostability, mechanical properties, degradability, hydrophilicity and the in vitro biocompatibility. Mechanical tests demonstrated that the novel PAIs had tensile strengths in the range of 3.11-10.79 MPa and tensile modulus in the range of 241-517 MPa. Compared to those of the pure PAI, the novel PAIs were two to six times bigger in the strength and two to four times larger in the modulus. Due to the additions of flexible l-amino acids in the novel PAIs, the average degradation rates were 1.2-2.4 times faster than those of the pure PAI. The preliminary biocompatibility studies of bone marrow mesenchymal stem cells (BMSCs) revealed that the novel PAIs are cell compatible. While one of the novel PAIs incorporated with l-phenylalanine exhibited higher cell adhesion, proliferation and differentiation than those of the pure PAI and the other novel PAIs, suggesting that the different l-amino acids incorporation in the novel PAIs change the cell growth environment somehow.