Session: ASME Undergraduate Student Design Expo

Paper Number: 175205

Cell Adhesion on Ti-Al6-V4 Using Laser Spallation Technique 

The integration and long-term performance of orthopedic implants, particularly cementless hip replacements, rely on the ability of the implant to achieve strong osseointegration while resisting bacterial colonization. Surface roughness plays a key role in both processes, influencing how cells and bacteria interact with implant surfaces. While prior studies have focused on cell proliferation across different surface finishes and only compare adhesion qualitatively, few have directly measured how roughness affects cell adhesion strength quantitatively. This research addresses this gap using the laser spallation technique to evaluate the adhesion strength of MG-63 osteoblast-like cells on both wrought and sandblasted Ti6Al4V (Ti64) substrates.

Surface roughness is modified by sandblasting Ti64 with 18-50 grit aluminum oxide particles to simulate the texture of cementless orthopedic implants. The smooth, untreated Ti64 has an average roughness of 0.7 ± 0.07 µm, while the roughened surface achieves a roughness of 2.83 ± 0.2 µm. MG-63 cells are seeded onto both types of substrates at a seeding density of 175k and cultured for 42 hours at 37ºC and 5% CO₂ to allow for adhesion. The laser spallation technique is used to generate tensile stress waves via an Nd:YAG laser pulse. When the tensile stress exceeds the adhesive strength of the cell monolayer, ejection of cells occurs in a process called spallation. Spallation events are recorded at each loading magnitude, which is controlled by laser fluence in terms of energy per area. Each sample is loaded 12 times at varying fluence values, and failure percentages (i.e., spallation events) are recorded. A Weibull cumulative distribution function is used to model failure verses laser fluence for each surface.

Results show that MG-63 cells adhere more strongly to the wrought Ti64, with a 50% failure fluence of 16.58 mJ/mm². In comparison, the sandblasted Ti64 exhibits failure at a lower value, with a 50% failure fluence at 11.60 mJ/mm². These preliminary findings indicate that although increased surface area can promote cellular interaction, excessive roughness may disrupt the formation of uniform focal adhesions, potentially interfering with cell adhesion and cell spreading. There may be an optimal range of surface roughness, beyond which cell adhesion is reduced for either too smooth or too rough surfaces.

This study demonstrates that the laser spallation technique is a valuable, non-contact method for quantifying cell adhesion on roughened implant surfaces. The data also supports the concept of an optimal surface roughness range for maximizing osteoblast adhesion. In future work, this technique will be used to compare cell adhesion data with bacterial adhesion data on the same surfaces, enabling calculation of an adhesion index. This metric could help guide the development of implant surfaces that support osseointegration while reducing the risk of biofilm formation, improving patient outcomes in orthopedic applications.

Presenting Author: Karl Kain Youngstown State University

Presenting Author Biography: My name is Karl Kain and I am a Mechanical Engineering student at Youngstown State University. I compete in track and field as a decathlete while also pursuing research in biomedical applications. I am an Ohio Space Grant Consortium scholar working with Dr. Park on biohybrid microrobots and gastrointestinal in vitro models.

In summer 2025 I completed a National Science Foundation REU at the University of Kentucky in the Grady Lab, where I studied bioactive interfaces and devices. I presented this research at the program symposium and placed second in the poster competition.

Balancing Division I athletics with engineering has taught me discipline, time management, and resilience. I plan to continue into a master’s degree in biomedical engineering with interests in biomechanics, biointerfaces, and human performance. My goal is to contribute to new biomedical technologies that improve health and performance while growing as both a researcher and engineer.

Authors:

Karl Kain Youngstown State University
Sahar Afshari University of Kentucky
Martha Grady University of Kentucky