Poly L, DL-Lactic Acid, and Composite Poly L, DL-Lactic Acid/β-Tricalcium Phosphate-Based Bioabsorbable Interference Screw Alex E. Santos, 1 Alex L. Braccialli, 1 Julio Vilela, 1 Cesar R. Foschini , 2 * Luiz E. A. Sanchez 2 1 Department of R&D of Sintegra Surgical Sciences Ltd., Medical Devices Company, Pompéia, SP, Brazil 2 Department of Mechanical Engineering, Sao Paulo State University – Unesp, Av. Eng. Luiz E. C. Coube 14-01, Bauru, SP, CEP 17033-360, Brazil There has been a growing interest in the use of bioab- sorbable polymers in interference screws for knee liga- ment reconstruction surgeries. This interest is driven by virtue of the relevant properties exhibited by these poly- mers. Among such essential properties include excel- lent biocompatibility and bioabsorption, good integration between graft/bone, in addition to the ease they offer when it comes to surgical revision. This article seeks to report the results obtained from the study aimed at the development of a bioabsorbable interfer- ence screw produced by the injection molding process with two distinct polymeric materials: PLDL poly(L,DL- Lactic acid) and a composite PLDL + 30 wt% TCP (β-tricalcium phosphate). Finite element analysis (FEA) was used for the development of the screw design. The mechanical strength of the screws was evaluated, where the maximum torque to break was found to sur- pass the insertion torque by 136% in PLDL material and by 190% in PLDL+TCP. The mean values of pullout force obtained for PLDL and PLDL+TCP were 1635 N and 809 N, respectively. An in vitro degradation test per- formed over a period of 180 days helped to assess the mechanical behavior during degradation and facilitated the comparison of the screws based on specific appli- cation requirements. The composite material (PLDL +TCP) exhibited a faster degradation process, with 88% loss of mechanical resistance following 180 days of degradation compared with 55% observed in the PLDL material. The results show that the addition of bioactive ceramic TCP contributed toward raising the initial mechanical resistance and acceleration during the pro- cess of degradation. POLYM. COMPOS., 2018. © 2018 Soci- ety of Plastics Engineers INTRODUCTION Currently, the most widely used fixation devices in ante- rior cruciate ligament (ACL) reconstructive surgery are the interference screws. This is because their usage in fixing provides an initial high strength and rapid bone integration, thus allowing a quicker rehabilitation [1–3]. As a result, the screws used in interference surgeries involving knee ligament reconstruction have evolved from metal to bioab- sorbable materials [4]. The reason for the use of bioabsorbable screws lies in the fact that they allow the growth of host tissue upon the screw degradation. Moreover, they do not present a major risk of graft laceration and are more advantageous with regard to MRI scans because they do not distort the image, thereby facilitating revision surgery [5]. Bioabsorbable screws are known to provide a secure initial fixation com- parable to that of metal screws. By virtue of these relevant factors, there has been a dramatic rise in the use of bioab- sorbable materials for ligament reconstruction surgery in recent times. Bioabsorbable polymers have been used in several applications, including biomechanical plates and screws for fixation and stabilization of fractures, cages and spacers used in spinal surgery [6]. The PLA has an additional methyl group in its monomer (lactic acid), which makes it more hydrophobic. Its isomers (L and DL – Lactic) possess different properties. The L- isomer (polylactic acid or PLLA) becomes highly hydro- phobic and crystalline over a prolonged degradation period (many years). The DL-isomer is highly amorphous and less stable—that is, it is characterized by a relatively more accelerated degradation period [7]. The copolymer poly(L-lactide-co-DL-lactide) or PLDL is less resistant to both hydrolysis and degradation. This can be explained by the addition of DL-isomers in the base polymerization of L-isomer, which renders the polymeric chains longer and less compacted, resulting in relatively lesser or no crystallinity, and consequently higher speed of degradation. The crystallinity property of the polymers also plays a role in defining the area in which they can be applied. The PLDL material, which contains L- and DL-isomers, is a Correspondence to: C. Foschini; e-mail: cfoschini@feb.unesp.br DOI 10.1002/pc.25025 Published online in Wiley Online Library (wileyonlinelibrary.com). © 2018 Society of Plastics Engineers POLYMER COMPOSITES—2018