State Key Laboratory of Tribology Tsinghua University Beijing 100084 China;
State Key Laboratory of Tribology Tsinghua University Beijing 100084 China;
Department of Bioengineering Pennsylvania State University University Park Pennsylvania 16802 USA;
State Key Laboratory of Tribology Tsinghua University Beijing 100084 China;
State Key Laboratory of Tribology Tsinghua University Beijing 100084 China;
Department of Bioengineering Pennsylvania State University University Park Pennsylvania 16802 USA;