# Crosslinked Bifunctional Particles for the Removal of Bilirubin in Hyperbilirubin Cases
## 1 Introduction  
Hyperbilirubin is indeed a serious medical condition that can have life-threatening consequences for patients with liver dysfunction. The accumulation of excess bilirubin in the blood can lead to a range of symptoms, including jaundice, fatigue, and abdominal pain. In severe cases, the buildup of bilirubin can lead to brain damage and death [1, 2]. Bilirubin exists in three different states in the human body. Direct or conjugated bilirubin is formed in the liver when bilirubin is conjugated, or attached, to glucuronic acid. This form of bilirubin is water soluble and can be excreted in the bile and ultimately eliminated from the body. Non-conjugated bilirubin, also known as unconjugated bilirubin, is the form of bilirubin that is not attached to glucuronic acid. Instead, it binds to albumin in their primary binding sites with high affinity (with a constant of 1.4\(\cdot\)10\({}^{7}\) L/mol [3]) and even in secondary sites with lower affinity [4], being finally transported to the liver for processing. Free bilirubin is not bound to either glucuronic acid or albumin and is therefore not water soluble. As a result, it can accumulate in tissues, causing damage and leading to hyperbilirubin. Free bilirubin is the most dangerous due to its insolubility in plasma [5]. It is therefore crucial to develop new materials for the removal of bilirubin from the blood, especially for patients with liver dysfunction. Liver transplantation is currently the most effective treatment for hyperbilirubinemia in cases where other treatments have failed. However, the availability of donors is limited, and the procedure itself can be risky and expensive. Hemodialysis [6] is a treatment option that can help remove bilirubin from the blood, but it is not selective and can also remove other important substances from the blood. Another treatment option also based in hemodialysis is the Molecular Adsorbent Recirculating System (MARS(r)), which is a form of extracorporeal liver support that can selectively remove bilirubin and other toxins from the blood. However, MARS(r) treatment is expensive, complex [7], and can cause coagulopathies in some patients [8]. Most of the alternatives being explored for the treatment of hyperbilirubinemia involve the use of particulate materials for the hemodialysis process. Some of the commonly used materials include poly(styrene-methyl methacrylate) [7; 8], polystyrene-divinylbenzene [9; 10] polyvinyl alcohol gels [11], or polyethersulphone particles [12]. However, their current selectivity for bilirubin removal is limited. Previous work has also explored the use of particles based on styrene (St) and methyl methacrylate (MMA) for bilirubin removal [13]. However, these particles experience a large swelling effect when they come into contact with blood, which can lead to blood coagulation and make them unsuitable for use in patient treatment. One solution to the swelling problem is to incorporate crosslinkers during the synthesis of the particles. This creates a three-dimensional network that promotes stiffer polymers and improves their mechanical stability. The best way to avoid or at least reduce the problem of swelling is the use of chemical compounds able to link the polymer chains to form a stable tridimensional network that avoids the swelling or shrinking of the materials. These crosslinkers have been widely described previously in the literature for the synthesis of polymeric particles [14; 15; 16]. Some of the crosslinkers previously described in the literature are ethylene glycol dimethacrylate (EGDMA) [17; 18; 19], \(N\),\(N\)-methylenebisacrylamide (NNMBA) [20], or cyclodextrin [21]. However, the most common crosslinker for styrene-based particles is divinylbenzene (DVB) [22; 23; 24; 25]. For that reason, DVB was selected in this work. Thus, this research proposes the synthesis of new crosslinked particles of poly(styrene-co-divinylbenzene) functionalized with PEGMA and/or GMA brushes by means of suspension polymerization.