# Surface-Modified Ceramic Boron Carbide as a Platform for Specific Targeting in Tumour Environments
## 1 Introduction  
Boron carbide is one of the two known types of diamond-like carbides, and it is characterised by its high hardness. Its properties make it useful for applications such as abrasives for polishing, ballistic armour, and neutron radiation absorption [1]. One of the most interesting applications of boron carbide in medicine is its use as a potential boron carrier for boron neutron capture therapy (BNCT) [2, 3]. BNCT is a treatment modality aimed at improving the therapeutic ratio for traditionally difficult to treat tumours. It is based on nuclear capture and fission following the irradiation of nonradioactive boron-10 with low thermal neutrons. The most challenging aspect of successful treatment with BNCT is the precise delivery of boronated compounds to the tumour [4]. The primary advantage of boron carbide (B4C) is its high boron content (80-91 at.%) [5]. These results show that synthesised boron carbide has got a significant concentration of the desirable \({}^{10}\)B isotope. In addition, this covalent compound is chemically inert and degrades slowly in the body. Previous boron carriers for BNCT therapy, such as BPA (o-boronophenylalanine) and BSH (sodium salt of thioborate anion), have low concentrations of the desired element. The surface of the obtained boron carbide was modified with compounds containing functional groups to enhance the selectivity and efficiency of the carrier. Functional groups enable the attachment of various Hope molecules to the surfaces of nanoparticles, which will selectively deliver boron to the tumour environment. Dextrin and dextran T70 contain a carboxyl group (COOH) in their structure, whereas lysine and arginine amino acids possess both a carboxyl group (COOH) and an amine group (NH2). In contrast, sorbitol is characterised by numerous hydroxyl (OH) groups. These functional groups provide a means of attaching specific proteins that can interact with the targeted cancer cells. In large-scale production, boron carbide is typically derived from boric acid or boron oxide via carbothermic reduction [6]. This process entails heating the acid or oxide with carbon to 2000 \({}^{\circ}\)C, utilising various forms of carbon such as graphite, carbon nanotubes, and carbon black. However, this technique has drawbacks, as it results in a coarse-grained product with a high concentration of impurities, as well as the loss of boron due to the oxidation of boron oxide, leading to a heterogeneous end product [7; 8]. An alternative method is magnetothermal reduction, which involves the reduction of boron anhydride in the presence of carbon, magnesium, or its alloys. This process must be carried out under protective gases, such as argon or hydrogen, owing to the high vapour pressure of magnesium. The resulting powder is fine, as the magnesium oxide present in the system inhibits the growth of boron carbide grains. However, this method also has disadvantages, because stable magnesium borides are present in the final product [9; 10; 11]. A method for obtaining boron carbide for special applications, such as the production of B4C with a high boron content, is the elemental synthesis method, which utilises high-purity elements to guarantee a product that is free of impurities [8]. The process of obtaining boron carbide using this method involves two steps. First, a stoichiometric mixture of amorphous boron and carbon is granulated and then placed in an inert atmosphere or vacuum at 1500 \({}^{\circ}\)C.  
In the realm of boron neutron capture therapy (BNCT), the use of traditional boron compounds is limited by therapeutic efficacy, primarily because of the short duration of their concentration in tumour cells. To enhance the efficacy of this treatment, researchers have sought to optimise the delivery of boron compounds to the tumour tissues, thereby increasing the boron concentration and the contrast in boron content between tumour and normal tissues.