Angioplasty over the years has proven to be an excellent substitute for open heart surgery where an artery/vien, blocked by atherosclerosis, is expanded using a stent. Metallic and coated metallic stents have been used for angioplasty. Metal stents might induce blood clotting, release cytotoxic heavy metal ions which are potential inducers of allergies, clotting, immune reactions and hyperproliferation of smooth muscle cells and also lead to protein absorption which activates clotting factors. Biodegradable polymers have also been tried as stent materials, but the loss of radial strength over time is a big problem associated with them. The use of a hybrid stent, consisting of biodegradable polymer and biocompatible stainless steel, is proposed. The use of such a system would require excellent adhesion between the stent metal and the biodegradable polymer. This study presents the electrochemically induced micromechanical interlocking to enhance adhesion between 304 stainless steel and high density polyethylene. High density polyethylene was used instead of biodegradable polymer for initial investigation. Electrochemical etching on the stainless steel wire was accomplished by immersing a stainless steel wire in a sodium carbonate electrolyte while applying a known voltage through the wire. The electrochemical etching of the stainless steel wire resulted in pitting under suitable conditions. The etching time, voltage and electrolyte concentration were varied to achieve different pit sizes and pit distributions on the stainless steel wire. An image analysis was conducted using an image analysis software to find the exact pit size and pit distribution on the stainless steel wire from electrochemical etching. A statistical model based on design of engineering experiments was derived. Etched and the unetched wires were molded with high density polyethylene and a mechanical test was conducted to measure the force required to pull the wire out of the polymer and verified using calculations based on the pit size and pit distribution of the pits on the surface of the wire. Electrochemical etching produced burr free surface features. It was observed that the pH level in the electrolyte contributes to the pit size and pit distribution. The results of the statistical model were consistent with the experimental values and it was possible to optimize the electrochemical etching parameters for maximum pit size and pit distribution. It was also observed that while voltage and etching time contribute to pit size and pit distribution, the electrolyte concentration does not have significant effect on the pit size and pit distribution. The calculated pull out force and measured values were off by 22.7%. The lower value of calculated force could result from neglecting some of the smaller pits while performing the image analysis. The average adhesive strength of the etched samples was 276% higher than that of the unetched samples.

The major impact of this research lies in the aspect of improved design and long term biocompatibility of materials used for implants. There are two goals in this research. The first goal is to develop a methodology to quantitatively measure cell-material adhesion. The second goal is to obtain fundamental understanding of cell-material adhesion mechanisms. A rotating parallel disk is used to measure cell adhesion. The rotational system applies a controlled shear stress to the cultured cells. The shear stress experienced by the cells varies with radial location, being highest at the edge and zero at the disk?s center. There is a critical point along the radius where the shear stress experienced by the cells equals their adhesion strength. The cells outside it are removed and the cells inside it remain attached to the surface. NIH 3T3 Swiss mouse fibroblasts and chick retina neuron cells from 6-day embryos are used in this study. The fibroblasts were cultured on poly(methyl methacrylate) (PMMA), polycarbonate (PC), and on gold coated poly(vinylidene fluoride) (Au/PVDF). The critical shear stress for fibroblasts was the lowest for PC with 5.09 dynes/cm2 and highest for PMMA with 21.0 dynes/cm2. This four-fold difference is mainly due to the chemical structure of PMMA which promotes higher cell adhesion when compared to PC. Neurons were cultured on poly-D-lysine coated glass to promote cell adhesion. The critical shear stress of neuron cells varied from 3.94 to 27.8 dynes/cm2 these values are directly proportional to the applied shear stress. The neuron adhesion plateau at ~27 dynes/cm2 which indicates the maximum adhesion strength of the neuron/poly-D-lysine coated glass pair. This thesis contains six chapters. Chapter I describes the importance of cell adhesion for biocompatibility. Chapter II describes in more detail the goals of this research and the expected results. Chapter III lists all the materials, equipment, and methods used in this study. The most significant results are summarized in Chapter IV. The observations and results obtained are explained in detail in Chapter V and Chapter VI describes the key outcomes as well as proposes questions for the advancement of this research.

The adhesive effects between abrasive particle and work on tool wear of the polishing process were considered in the study. Adhesive strength of the interfaces may affect wear rates of tool on the different adhesive way. Several sets of experiments were designed to reveal some phenomena about the wear rates of tool and work. There are variations in the adhesive of the interface causing different degree of tool wear for distinct kind of abrasive particle¡Bwork and tool¡¦s material. The experimental study demonstrated that the wear rate of tool was related to the adhesive strength between abrasive particle and work. Any change of the adhesive strength may significantly alter the wear rate of tool. An analytical study was done to examine the role played by the adhesive strength at the interfaces of abrasive particle on the wear rates of tool and work. It was derived from the law of force equilibrium and the principle of minimum potential energy. Tool wear was affected for polishing process by altering adhesive strength. The computer simulations indicated that an enhancement of adhesion between abrasive particle and work would always increase the wear rate at tool while the wear rate of work could be increased or decreased. To prove analytical study was reasonable by experimental study. Finally,the possible causes of observed phenomena and the limitations of the study were discussed.

Abstract¡G This study imitated the IC package with different solder mask thickness in different environment of the temperature and moisture to see if the adhesion strength changed after IR-Reflow process. The temperature and moisture of the environment were decided base on the possible conditions that the IC package might encounter in the real situation. After the temperature and moisture in the environment worked interactively and reciprocally, we found that the thickness of solder mask indeed cause the change of adhesion strength. The thickness of solder mask affected by the raising of the temperature and moisture caused the apparent reduction of the interface adhesion strength due to the softening of the material and the penetrating of the moisture. Besides, the specimen fracture surface occurred between solder mask and FR-4 substrate under any experimental conditions and progress confirmed that the measured strength is the adhesion strength between solder mask and FR-4.

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references.

Thesis (M.S.)--Rutgers University, 2009. / "Graduate Program in Biomedical Engineering." Includes bibliographical references (p. 79-81).

Thesis (Ph. D.)--Lehigh University, 2003. / Includes bibliographical references and vita.

Thesis (Ph. D.)--Lehigh University, 2003. / Includes vita. Includes bibliographical references (leaves 156-166).

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / Microbiology / Master / Master of Philosophy