**Abstract**

A material that presents both the appropriate set of bulk properties in conjunction with an optimal surface performance is hardly found. For this reason, there is the need of modifying its surface. This is a standard procedure in many application fields but particularly important in the medical and environmental research. In this chapter, we describe the use of sputtering, as the chosen technology for the deposition of thin films. The use of the modified surfaces in the medical and environmental fields will be highlighted by two case studies in each one. In biomedicine, the surface modification of medical invasive devices for orthopedic and neural applications will be presented. For the environmental aspect, the results of two bioremediation tools, for arsenic and uranium removal, based on the immobilization of bacterial cells will be discussed.

**Keywords:** thin films, sputtering, orthopedic implants, neural implants, bioremediation, biotools, arsenic, uranium

### **1. Introduction**

Although genetic engineering and tissue culture are very promising fields for the regeneration of tissues and organs of the human body, these areas are in the early stages of their development and far from a systematic and reliable application for the majority of the population. Therefore, it is still urgent to develop/modify nonbiological materials to be used as medical invasive devices.

The field of application of thin films in Biomedicine is very broad, but the main objective is always to modify the surface of a medical invasive device in order to confer to its surface a set of properties that the bulk material fails to present. These properties include antibacterial action [1], improving the adhesion and proliferation of specific eukaryotic cells [2, 3], inhibiting the immunological reaction of the organism [4], enhancing the compatibility of mechanical properties between invasive device and biological tissue [5], among others. Nowadays, due to the problem of bacterial resistance to antibiotics, there has been an enormous development in thin films that are able to reduce or even prevent bacterial adhesion/proliferation. However, for some applications, the development of thin films that allows the formation of bacterial biofilms is very important. One example is their use in bioremediation, which comprises the use of organisms, for example, bacteria, algae and plants, to alter or reduce the toxic impact of contaminants.

Arsenic (As) is a natural metalloid widely distributed in the air, water and soil and is considered as a major public health concern. Arsenic occurs in the environment as the structural analogue of phosphate, arsenate [As(V)] and as the most toxic form of arsenic oxyanions, arsenite [As(III)] [6, 7].

A large number of microorganisms have been described as arsenic resistant and different strategies have been connected to their ability to grow in environments contaminated with this metalloid. Based on this remarkable capacity, the use of microorganisms to remove arsenic from polluted environments has been seen as a promising solution for arsenic remediation. The arsenic bioaccumulation or biosequestration abilities exhibited by some strains have been used or enhanced in order to obtain efficient organisms to deal with arsenic-contaminated waters [8, 9].

On the other hand, former uranium mines are a source of environmental contamination, since the leaching of acid water resulting from mining activity can transfer heavy metals and radioisotopes to the surrounding environmental compartments. U in the environment occurs mainly as three different isotopes (238 U, 235 U and 234 U), all of them being radioactive; however, it is its chemical toxicity that is of greatest ecological risk. U at contaminated sites has two major oxidation states stable in aqueous media: U(VI), the most common oxidation state of the uranyl ions, (UO2) 2+, which is highly soluble and mobile; and U(IV), which is extremely insoluble and usually precipitates as uraninite, UO2. U(VI) is therefore considered to be more toxic since it is highly mobile in the environmental systems.

Microorganisms can use different mechanisms to immobilize U: (1) biosorption, by establishing nonspecific interactions between the U and the extracellular surfaces of microorganisms [10]; (2) bioaccumulation of U within the cells; (3) oxidation-reduction processes which transform soluble U forms, U(VI), into more stable forms, U(IV) [11] and (4) biomineralization by U precipitation as minerals [12]. Among the previous mechanisms, under aerobic conditions, biomineralization is the process that can be more feasible since it implies the immobilization of U(VI) soluble species with enzymatically-generated ligands like phosphate and sulfides.
