"For achieving early intervention treatment to help patients to delay or avoid joint replacement surgery, a personalized scaffold should be designed coupling the effects of mechanical, fluid mechanical, chemical and biological factors on tissue regeneration, which results in time-consuming and cost-consuming trial-and-error analyses to investigate in vivo test and related experimental tests.
To optimize the fluid mechanical and material property to predict osteogenesis and cartilage regeneration for the in vivo and clinical trial, a simulation approach is developed for scaffold design, which is composed of a volume of fluid (VOF) model as well as a discrete phase model (DPM) and a cell impinging model (CIM).
Blood is considered as continuity fluid, which could carry bone mesenchymal stem cells (BMSCs) to attach on the scaffold, VOF model is used to control the movements of these two immiscible fluids. Considering BMSCs as discrete particles, cell attachment is governed by DPM with Stanton-Rutland Model through Eularian-Lagrangian approach. The interaction of cell with scaffold is simulated by the CIM, which governed not only by cell physical properties (viscosity, surface tension, and density) but also by the impingement conditions (cells velocity and diameter).
In DPM Model, discrete particles representing the BMSCs were carried by the fluid phase and trajectories of cells were predicted by integrating the force balance on cell written in a Lagrangian reference frame. All particles (BMSCs) are set as non-rotating. Particles impingement causes energy loss because of the inelastic collision.
In CIM model, cell imping model for simulating cell adhesion on scaffold are defined as three regimes, including stick, rebound, spread when cells impinge the scaffold wall.
In VOF model, blood is seen as non-Newtonian fluid which was chosen to simulate the fluid of blood. Air and blood are governed by the continuity equation and Navier-Stokes equations. Non-Newtonian fluids will be calculated by the power law for non-Newtonian viscosity.
Five young female sheep with a mean weight of 81.6 ± 6.4 kg were operated in the Royal Veterianary College (RVC). All sheep were treated according to Animals (Scientific Procedures) Act (ASPA). According to the results from the micro-CT and CT images analysis, in horizontal, the side edge of the scaffold column group has more bone ingrowth than in the middle. In the middle, above 30% of void space were occupied by the new regenerative bone tissue, around 40% on the subside of the scaffold and upper 50% of regenerative bone tissue occupied the space.
The simulation results showed that cell attached mass showed a decreasing trend from external to the middle of the scaffold. The results matched the in sheep vivo test with high accuracy. This approach not only predict the final bio-performance of the scaffold, it could also enable to optimize the scaffold structure and materials by their biochemical, biological and biomechanical properties."