(I-345) The Development of a Mechanical Stimulation System for the in Vitro Knee Joint Model

Knee joint deterioration, primarily manifested as osteoarthritis, poses a significant

challenge as a common age-related condition affecting millions worldwide. Slowing down the degenerative process holds immense value in improving patient outcomes. Chondrocytes, responsible for

cartilage formation, play a vital role in endochondral ossification and must endure prolonged mechanical

stress without degradation. Understanding the relationship between chondrocyte degradation and various

mechanical stress loads is crucial, as it could inform recommendations for low-impact activities that

minimize the impact on knee joint chondrocytes. To investigate this relationship, we aim to develop a

physiological mechanical stimulation system for an in vitro bone/cartilage model. Existing cartilage systems do not provide accurate in vitro stimulation, which can lead to functional and morphological deterioration of the cells. Our goal is to create a knee joint model that accurately assesses the strength, durability, and degradation of knee joint cells under stressful conditions. This model will simulate shear and compressive loading, closely resembling the in vivo environment within the knee, by mechanically loading bone/cartilage cells through a PDMS model. By cultivating Osteoblasts or chondrocytes in a microenvironment replicating the in vivo knee system, we will assess the impact of various stimulation processes on the metabolism, morphology, and behavior of Osteoblasts or chondrocytes. This research has the potential to shed light on effective strategies for preserving chondrocyte function and mitigating knee joint deterioration.

To test our hypothesis, we initiated the development of knee stimulation. The process began with simple SolidWorks drawings, followed by the creation of a prototype. The prototype

underwent multiple iterations, incorporating more durable materials and establishing a system capable of

applying two distinct types of motion to the knee. Specifically, it applies a rotational force from above

while the base of the system moves linearly. Throughout this procedure, we explored the differences

between 2D and 3D cell cultures. Osteoblast cell line MG-63 (CRL-1427, Human bone cell of a patient with Osteosarcoma) was used for our experiment because it is easy to handle. Once we prove our concept using Osteoblasts, then we will use Chondrocytes to develop a cartilage model. In a 2D cell culture, cells grow on the surface of a PDMS cell culture chamber, forming a flat shape that facilitates easy observation of cell confluency (Figure A). Conversely, 3D cell culture involves growing cells suspended within a hydrogel, enabling them to experience varying degrees of loading and force within the device without harm (Figure C).

The knee stimulation device was designed, printed, assembled for testing. The mechanical strain of the device was operated through the programmed Arduino code. Once we verified the function of the device, the PDMS device, where bone cells grow, was inserted between the Femur part and the Tibia part within the Knee stimulator (Figure E). Bone cells along with the PDMS device were subjected to linear moving stimulation. Presented below are two photos illustrating the 2D culture before and after exposure to the stimulation through a linear-stretching stimulator that was previously developed. These preliminary data exemplify the type of results we aim to demonstrate once the cells are placed in the device. Our specific objectives include observing changes in cell morphology post-implantation and comparing the growth disparities between the 2D cultures and the cells grown in alginate media while suspended.

In conclusion, our study focused on investigating the effects of mechanical stimulation on

MG-63 bone cells as part of understanding knee joint deterioration and potential strategies for its

mitigation. We developed a knee stimulation device capable of applying rotational and linear motion to

the knee, allowing for controlled mechanical loading. By comparing 2D and 3D cell cultures, we explored

the advantages of the latter, which involved growing cells suspended in a hydrogel to mimic the in vivo

environment more accurately. Preliminary data analysis indicated notable changes in cell morphology and

growth patterns following stimulation, highlighting the potential of our device in promoting chondrocyte

preservation. These findings contribute to the ongoing research aiming to develop alternate stress-loading

activities that could minimize the impact on chondrocyte cells in knee joints, offering new insights into

therapeutic approaches for knee joint deterioration.

This project was supported in part by the George Fox University Grant GFU2023G10 and Richter’s Scholars Program. 

Grace Tully1 and Young Bok(Abraham) Kang1

1 Biomedical Engineering, George Fox University, Newberg, OR, USA