When designing a new osteosynthesis device, the biomechanical competence must be evaluated with respect to the acting loads. In a previous study, the loads on the proximal phalanx during rehabilitation exercises were calculated. This study aimed to assess the safety of a novel customizable osteosynthesis device compared to those loads to determine when failure would occur. Forty proximal phalanges were dissected from skeletally mature female sheep and divided into four testing groups. A custom 3D printed cutting and drilling guide was used to create a reduced osteotomy and pilot holes to insert four 1.5 mm cortical screws. A novel light-curable polymer composite was used to fixate the bones with an in situ fixation patch. The constructs were tested in cyclic four-point bending in a bioreactor with ringer solution at 37°C with a valley load of 2 N. Four groups (N = 10) had increasing peak loads based on varying safety factors relative to the physiological loading (G1:100x, G2:150x, G3:175x, G4:250x). Each specimen was tested for 12,600 cycles (6 weeks of rehabilitation) or until failure occurred. After the test the thickness of the patch was measured with digital calipers and data analysis was performed in Python and R.Introduction
Method
Several synthetic polymers have been widely investigated for their use in bone tissue engineering applications, but the ideal material is yet to be engineered. Triazine-trione (TATO) based materials and their derivatives are novel in the field of biomedical engineering but have started to draw interest. Different designs of the TATO monomers and introduction of different chemical linkages and end-groups widens the scope of the materials due to a range of mechanical properties. The aim of our work is to investigate novel TATO based materials, with or without hydroxyapatite filler, for their potential in bone tissue engineering constructs. Initially the biocompatibility of the materials was tested, indirectly and directly, according to ISO standards. Following this the osteoconductive properties were investigated with primary osteoblasts and an osteoblastic cell line. Bone marrow derived mesenchymal stem cells were used to evaluate the osteogenic differentiation and consequently the materials potential in bone tissue engineering applications.
The objective of this study was to investigate how a new customizable light-curable osteosynthesis method (AdFix) compared to traditional metal hardware when loaded in torsion in an ovine phalanx model. Twenty-one ovine proximal phalanges were given a 3mm transverse osteotomy and four 1.5mm cortex screws were inserted bicortically on either side of the gap. The light-curable polymer composite was then applied using the method developed by Hutchinson [1] to create osteosyntheses in two groups, having either a narrow (6mm, N=9) or a wide (10mm, N=9) fixation patch. A final group (N=3) was fixated with conventional metal plates. The constructs were loaded in torsion at a rate of 6°/second until failure or 45° of rotation was reached. Torque and angular displacement were measured, torsional stiffness was calculated as the slope of the Torque-Displacement curve, and maximum torque was queried for each specimen. The torsional stiffnesses of the narrow, wide, and metal plate constructs were 39.1 ± 6.2, 54.4 ± 6.3, and 16.2 ± 3.0 Nmm/° respectively. All groups were statistically different from each other (p<0.001). The maximum torques of the narrow, wide, and metal plate constructs were 424 ± 72, 600 ± 120, and 579 ± 20 Nmm respectively. The narrow constructs were statistically different from the other two (p<0.05), while the wide and metal constructs were not statistically different from each other (p=0.76). This work demonstrated that the torsional performance of the novel solution is comparable to metal fixators. As a measure of the functional range, the torsional stiffness in the AdhFix exceeded that of the metal plate. Furthermore, the wide patches were able to sustain a similar maximum toque as the metal plates. These results suggest AdhFix to be a viable, customizable alternative to metal implants for fracture fixation in the hand.
