## 1 Introduction
One of the earliest in vivo studies was reported in 2013, in which pure Zn wires were implanted in the walls of the abdominal aortas of adult rats and left in for up to 6 months with no toxicity or negative tissue effects [3]. In a second study from the same lab, using the same experimental paradigm, Zn wires were left in for up to 20 months with no toxicity and the authors demonstrated a uniform corrosion rate of 0.25 mm/yr [21; 22]. More recently, pure Zn stents, created by laser cutting, were inserted into the abdominal aortas of adult rabbits [9]. After 12 months, the arteries remained open, only mild inflammation was seen, and no pathology was seen in any other bodily organ. The corrosion pattern was well characterized, and some features were a loss of \(\sim\)20% of the stents by 6 months and \(\sim\)42% of the stents by 12 months. In addition, the corrosion products had not accumulated, showing good cellular clearance of these materials [9]. Alloys of Zn-Mg alloys are also of interest but have previously been considered primarily for orthopedic applications [23; 24]. Zn-1 Mg, Zn-1 Ca, and Zn-1 Sr alloys have corrosion rates between 0.08-0.12 mm year\({}^{-1}\) in [PERSON]'s solution [25], which are lower than most Mg alloys. For biodegradable implants, this moderate corrosion rate is critical, especially for cardiovascular stent applications. However, going forward, it will be important to control the corrosion rate of Zn alloys for use in different stent applications, for example, veins versus arteries, different sizes of blood vessels, or vessels with different blood flow rates. The corrosion rate of metal can be altered either by alloying the pure metal or by modifying the surface of the metal via coating with biocompatible polymers. The work described here first examines the suitability of using photo-chemical etching to create Zn cardiovascular stent structures,using pure Zn, and then examines initial in vivo tissue compatibility studies of this Zn material. This investigation also compares the in vitro corrosion rate of uncoated Zn stents with that of stents coated with Parylene C. Among the many potential polymeric coatings [16; 19], a chlorinated Parylene, known as Parylene C, was selected as a good candidate for improving metallic implant interactions with blood [26] and we further hypothesized that it would slow the corrosion rate of Zn, which is desired in some applications, as discussed above. It was reported by [PERSON] et al. [27], that Parylene C coated stents showed very low platelet attachment when compared to uncoated tantalum stents, thus hindering thrombogenicity. Parylene C is a U.S. Food and Drug Administration (FDA)-approved biocompatible polymer. It is also a transparent, crystalline and thermoplastic substance with good elastic properties, which is an important quality that is needed when the stent expands. Parylene C is used in many technical applications because it increases the surface hydrophobicity of the coated objects. In addition, at higher blood flows, Parylene C-coated surfaces demonstrated lower rates of protein adsorption, thus suppressing clotting [26]. In addition, the relatively low permeability of Parylene C [28] suggests that a conformal coating of the polymer would slow down the corrosion of biodegradable implants by preventing contact with physiological solutions. All these potential benefits of a conformal Parylene C coating on blood-exposed medical implants led us to apply this polymer on the surface of Zn stents and to study its effect on the corrosion rate of the materials.