Avi PatelFollow

Date of Completion

Spring 5-5-2019

Thesis Advisor(s)

Thanh Duc Nguyen; David Goldhamer; Maryann Morris; Kathryn Ratcliff; Pamela Erickson

Honors Major

Molecular and Cell Biology

Second Honors Major

Individualized Major


Bioelectrical and Neuroengineering | Biology and Biomimetic Materials | Biomaterials | Biomechanical Engineering | Biomedical | Cell Biology | Cellular and Molecular Physiology | Medical Biophysics | Medical Biotechnology | Medical Cell Biology | Medical Molecular Biology | Molecular Biology | Molecular, Cellular, and Tissue Engineering | Musculoskeletal Diseases | Orthopedics | Other Biomedical Engineering and Bioengineering | Other Materials Science and Engineering | Polymer and Organic Materials | Structural Biology | Structural Materials


Background: Reconstruction of bone fractures and defects remains a big challenge in orthopedic surgery. While regenerative engineering has advanced the field greatly using a combination of biomaterial scaffolds and stem cells, one matter of difficulty is inducing osteogenesis in these cells. Recent works have shown electricity’s ability to promote osteogenesis in stem cell lines when seeded in bone scaffolds; however, typical electrical stimulators are either (a) externally housed and require overcomplex percutaneous wires be connected to the implanted scaffold or (b) implanted non-degradable devices which contain toxic batteries and require invasive removal surgeries.

Objective: Here, we establish a biodegradable, piezoelectric Poly-L-Lactic Acid (PLLA) scaffold that uses external, non-invasive ultrasound to generate an electric charge that promotes stem cell osteogenesis.

Methods: Demonstration of this system included (1) development of a piezoelectric PLLA mesh, (2) verification of its piezoelectric efficacy and degradation, (3) manufacturing of a PLLA scaffold, (4) in vitro testing of the system’s ability to enhance bone regeneration compared to a control, and (5) using assessments of cell proliferation and differentiation through protein, mineral, and gene assays.

Results: Ultimately a 3000rpm electrospun PLLA nanofiber film that could output 40mV when stimulated with 40kHz 0.4W/cm2 ultrasound was assembled into a bone scaffold and seeded with adipose-derived stem cells (ADSCs). In vitro testing showed that relative to a control, in cells subjected to the experimental conditions alkaline phosphatase production increased 5-fold, mineral production increased 18-fold, osteocalcin gene 40-fold, and osterix gene 100-fold.

Conclusion: The production of surface-level charge from ultrasonic stimulation of PLLA and the use of that charge to promote osteogenic differentiation in ADSCs was successfully demonstrated. The fact that PLLA was successfully used in combination with externally applied ultrasound to produce electrical charge opens up new frontiers for the field of tissue regeneration. This advancement helps make tissue engineering a tool that can tackle problems of even greater magnitude.