Bionic Self-Stimulated Cartilage

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Millions of American go through total knee replacement every year due to osteoarthritis. Surgical treatment of this disease is to implant replacement auto or allografts. Despite many advantages, these grafts poses several limitations including limit of supplies, donor site morbidity (for autografts) and immune response (in case of allografts). Consequently, engineered grafts - constructed in vitro by culturing autologous chondrocytes on synthetic biomaterial scaffolds – have received attentions. Yet, they also exhibit issues, one of which is the inefficiency of seeded-chondrocytes in these grafts to generate hyaline cartilages after implantation, preventing their widespread use. As such, we believe it is necessary to seek for a new approach to effectively stimulate and accelerate cartilage growth from commonly-used chondrocyte-seeded grafts, enhancing the grafts’ healing and regeneration capability. Electrical stimulation (ES) have been shown to exhibit profound effects on cartilage and bone repair/regeneration. However, current ES devices present many drawbacks including inefficiency of generated electrical field (for external ES devices), bulky size and toxic materials used in electrical stimulators, and non- degradability of implanted ES devices. Piezoelectric materials, which can generate electrical signals from deformation and vice versa, can be employed to create self-powered electrical stimulators. Interestingly, Poly-L-Lactid acid (PLLA), a biodegradable polymer which has been used in many medical implants, can exhibit piezoelectricity when being processed properly. Although not having a high piezoelectric constant, PLLA, owing to its low dielectric parameter, exhibits the same efficiency for energy conversion as the common Polyvinylidene fluoride (PVDF) polymer. In this project, we study the science and technology to create a biodegradable, highly efficient piezoelectric PLLA stimulator and integrate the stimulator with a biological chondrocyte-seeded cartilage graft, forming a bionic cartilage tissue. Hypothetically, this bionic cartilage will create a feedback loop in which more damaging joint-forces imparted on the cartilage would generate more useful electricity, which in turn enhances cartilage growth. Once less force is exerted on the implant, the graft will be subject to less electrical stimulation, avoiding harmful overdosing effect of electrical current on cartilage cells. The generated electrical outputs – in response to joint force - can be tailored and optimized by altering PLLA film’s properties (e.g. thickness, molecular weight, piezoelectric efficiency and number of PLLA layers etc.). As such, this “smart” bionic cartilage will offer an innovative approach, optimizing electric stimulation for cartilage repair and regeneration from autologous chondrocyte-seeded grafts.