# Modification of PLA Scaffold Surface for Medical Applications
## 1 Introduction  
The use of a biomaterial which allows cells to grow on it creates the possibility of preparation of adequate tissue in laboratory conditions in the future. The tissue grown on biomaterial will be able to replace damaged parts of the human body. Cellular scaffolds should be the mechanical support for cells and tissues. Scaffold ought to merge multiplying cells, regulate their progression and diversification, and affect their size and shape. Polymeric membrane surfaces are characterized by a small number of poorly connected pores, so it is hard for tissues to penetrate them. Moreover, it makes the transport of nutrients and metabolites difficult [1]. For this reason, a method which allows the increase of the number of pores, wettability of the surface, and improvement of the conditions of nutrient transportation into the membrane is being studied. The main direction of this research is to develop methods for the surface modification of polymeric materials that will enable the increase of their surface roughness, adhesive strength, wettability, and number of built-in functional groups. Chemical and physical methods are used to modify the surface of polymeric materials. The chemical methods mainly consist of immersion of the modified material in highly oxidizing liquids [2]. The main disadvantages of such techniques are the corrosive impact of the used liquids, high consumption of water used during flushing of the modified material, significant environmental contamination with aggressive chemicals, low productivity of the modification processes, and high process costs. There are many physical methods [3, 4]. One of them is modification with low-temperature plasma. The advantages of plasma processes are the relatively low operating costs and simple construction of the reactors used for modification. Polymer materials used in tissue engineering can be divided into natural and synthetic types [5]. The most commonly used polymer materials are easily processed and bioresorb to nontoxic substances, such as carbon dioxide and water. Among the large group of biomaterials used to produce three-dimensional scaffold biodegradable polymers, polylactide (PLA), polyglycoloide (PGA), polylactide-glycoloide (PLGA) copolymer, and polycaprolactone (PCL) deserve special attention [6; 7; 8]. Polylactide is a frequently used biodegradable polymer. It is thermoplastic, has good mechanical properties, and is completely biodegradable and biocompatible. PLA is obtained from lactic acid by two methods: ring-opening polymerization and direct polycondensation [9]. In recent years, one of the methods of plastic modification used in material engineering and medicine has been plasma electric discharge [10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. The main purpose of modifying the surface layer of polymeric materials is to improve the wettability and adhesive properties. The use of plasma modification is an effective and economical surface treatment technique for many polymer materials. The advantage of this method is the ability to induce a selective change of the surface properties. The use of various gases such as argon, oxygen, nitrogen, fluorine, carbon dioxide, or water vapor allows the creation of unique surface properties, depending on the type of polymer used. The use of oxygen plasma can increase the surface energy of polymers, while the action of plasma generated in fluorine can reduce the surface energy and improve the chemical resistance. By using plasma generated in an inert gas, the polymer surface can be crosslinked [21]. The use of plasma jet discharge has also reduced the hydrophobicity of polymeric materials. Polypropylene (PP-H), acrylonitrile butadiene styrene (ABS), and high impact polystyrene (HIPS) polymers were treated in a plasma jet reactor in helium and air. There was no effect by an increase of the gas flow rate and the concentration of air in the gas on the change of the contact angle. The plasma exposure time on the sample's surface was 30 s [12].