# Silk Protein-Based Membrane for Guided Bone Regeneration
## 4 Silk Mat as GBR Membrane
### In Vitro Properties of Silk Mat  
SF has been considered a cyto-compatible material [10]. Recently, sericin has been widely studied as a biomaterial, and most results seem to be promising [48; 54]. However, most papers studied sericin as a degumming by-product [45; 47]. Accordingly, they denatured sericin by boiling. Silk mat is mostly composed of silk fibroin and sericin [20]. As SF is hydrophobic and surrounded by bonding proteins, the fibroin effect on cellular culture is minimal in the silk mat. Natural sericin is fragmented in an aqueous solution and solubilized in water. The fragmented natural sericin is a biologically important component in the silk mat when it is used as a biomaterial [55]. The silk mat also has abundant protease inhibitors, which are released from the silk mat [103].  
When degumming products are given to RAW264.7 cells, TNF-\(\alpha\) (tumor necrosis factor-\(\alpha\)) is increased in a dose-dependent manner [55]. As TNF-\(\alpha\) is important in acute and chronic inflammation, degumming products should be used in a controlled manner. In the case of the silk mat, natural sericin will be released in a fragmented form. In addition, the content of sericin is different from the layers of the cocoon [101]. Considering dose-dependent TNF-\(\alpha\) induction by denatured sericin [55], the sericin content in the silk mat should be small. As the content of sericin is increased from the inner to the outer layers, the silk mat from the inner layer may be better than that from the outer layer. There are other bonding proteins to sericin, such as seroin and protease inhibitors [101]. Although few studies have been conducted on these proteins, they may induce TNF-\(\alpha\)-like sericin. In the case of seroin, it is abundant in the inner layer [101]. When TNF-\(\alpha\) induction experiments are done for the silk mat leaching solution, the least TNF-\(\alpha\)-induced silk mat comes from the middle layer of the silkworm cocoon [55].  
Silk sericin has been used as dressing materials and cosmetics [45; 47]. Implants coated with silk sericin show better bone formation than those without [54]. Accordingly, silk sericin may be beneficial for wound healing and bone regeneration [48; 54]. However, detailed characterization of silk sericin in previous studies has been largely unclear. Most studies categorize silk sericin as a whole silk industrial by-product from the degumming process; however, it may be different from silk sericin protein. In detail, silk sericin itself would also vary from species to species in silkworms. These differences may cause difficulty in reproducing the results of previous papers. The silk mat from the middle layer of  
Figure 9: Water drop experiment. As sericin content is increased from the inner to outer layers and sericin is a hydrophilic protein, water drops are adsorbed quickly in the middle and the outer layer groups.  
_B. mori_ has been used for a toxicological survey by the Korea Food and Drug Administration (KFDA), and permission to export was received. _B. mori_ cannot eat any contaminated mulberry leaves [104]. Chemically contaminated leaves are toxic for _B. mori_[104]. No micro-organism has been identified that can infect both human and _B. mori_[104]. In addition, infected larva cannot form cocoons [104]. Collectively, the silk mat from silkworm cocoons is a highly safe source of biomaterials compared with any materials from mammals.