Tribological process induced conformational transformation of protein may change the friction of cartilage Chih-Hung Chang a , Hsu-Wei Fang b,c, ⁎ , Huei-Ting Huang c , Hsuan-Liang Liu b,c , Wei-Ming Lee b , Man-Ching Hsieh c , Chiang-San Chen a a Division of Orthopaedics, Department of Surgery, Far Eastern Memorial Hospital, Pan-Chiao 220, Taipei, Taiwan b Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei 106, Taiwan c Institute of Biotechnology, National Taipei University of Technology, Taipei 106, Taiwan Received 5 October 2006; accepted 13 November 2006 Available online 5 December 2006 Abstract In-vitro testing procedures have been successfully developed to investigate the effects of tribological process induced transformation of protein-based lubricant on the friction change of articular cartilages. Serum and albumin solutions were the biological lubricants used in this study. The results indicated that the lubricating ability for cartilages deteriorates after the biological lubricants were articulated between polyethylene and stainless steel materials. In addition, the secondary structure change of the albumin molecule has been characterized after the molecules were articulated by the artificial joint materials. We have provided evidence that the conformational change of protein lubricants leads to the friction increase of articular cartilage. © 2006 Elsevier B.V. All rights reserved. Keywords: Partial joint arthroplasty; Cartilage; Friction; Albumin; Tribochemistry; UHMWPE 1. Introduction Partial joint arthroplasty surgeries have been widely applied to patients with unicondylar knee joint osteoarthritis or those who suffered from the femoral neck fracture. Unicompartmental knee arthroplasty (UKA) and bipolar hemiarthroplasty are two representative treatments. Coexistence of artificial joint materi- als and articular cartilages in the joint area constitutes the unique feature and it may play a critical role of the subsequent progression of the cartilage degeneration. The most common failure mechanism of UKA is component loosening, polyethylene wear and progression of disease in the un-resurfaced compartment [1]. Degeneration in the opposite compartment is a common cause of failure after unicompart- mental arthroplasty [2–7]. Some authors have suggested that overcorrection of joint deformity results in the transfer of increased forces to the uninvolved compartment and accelerating degeneration [4,8]. However, the complete explanation of the progression of patello-femoral arthritis is still not provided. In addition, Elsaid et al. [9] further suggested that the decreased synovial fluid lubrication might be related to cartilage damage. Unipolar hemiarthroplasty can be a successful treatment for displaced femoral neck fractures in selected low demand elderly patients. However, bipolar hemiarthroplasty also is associated with groin pain, acetabular cartilage deterioration related to time and activity as well as polyethylene wear at the bearing surface of the femoral head and the mobile acetabular implant, which can lead to osteolysis, implant loosening, and early revision surgery [10,11]. The influence of bipolar hemiarthroplasty on acetabular cartilage had been discussed in the researches comparing bipolar hemiarthroplasty to total hip arthroplasty in patient with femoral head osteonecrosis [11]. Evaluations of the acetabular cartilages during the hemiarthroplasty revision surgeries have indicated that degenerative changes of the cartilages were present [12,13]. They concluded that even healthy cartilage could not tolerate the Materials Letters 61 (2007) 3381 – 3384 www.elsevier.com/locate/matlet ⁎ Corresponding author. Department of Chemical Engineering, Mail stop 2521, National Taipei University of Technology, 1, Sec. 3, Chung-Hsiao E. Road, Taipei 106, Taiwan. Tel.: +886 930380200; fax: +886 227418575. E-mail address: hwfang@ntut.edu.tw (H.-W. Fang). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.11.077