# New Resorbable Membrane Materials for Guided Bone Regeneration
## 5 Silk-Based Materials  
Silk, a natural macromolecule produced by _Bombyx mori_, has been used as a suturing material [55]. Silk membrane has excellent biocompatibility and mechanical strength, and a competitive price without the risk of disease transmission of mammalian origin [1; 56; 57]. Since silk degrades very slowly, it can generally be considered to be non-degradable [58]. However, alterations in silk processing can accelerate degradation to meet the clinical requirements by changing the conformation of the protein structure [58; 59]. Thus, silk has been developed as a novel degradable membrane. Silk fibers are composed of sericin, a glue-like protein that encases and binds fibroin fibers together, and fibroin, which is the core filament responsible for the elasticity of silk [58; 60]. Sericin has been reported to cause adverse effects in those with biocompatibility and hypersensitivity to silk [58]. Therefore, silk fibroin membranes from which sericin was removed via degumming have been studied [55; 57; 59; 61; 62; 63; 64; 65]. Silk fibroin has the advantages of low inflammation, and excellent biocompatibility and mechanical properties [1; 62]. Silk fibroin membrane, combined with other biomaterials, has also been reported to improve bone regeneration (Table 3). Chitosan/fibroin/HA membrane, with osteoconductivity of HA, has been reported to produce similar bone regeneration to collagen membrane. Chitosan, derived from the natural polymer \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Experimental** & \multicolumn{2}{c}{**Experimental Groups**} & \multicolumn{2}{c}{**Main Findings**} & **Reference** \\ \cline{3-5}
**Model** & **(Membrane with/without new Material)** & & **(i)** & **(i)** \\ \hline
8 mm Calvariat & (i) & Chitosan/fibroin-HA membrane & & \\ defect (rat) & (ii) & Collagen membrane & (Bio-Gide) & \\  & (iii) & No membrane & & \\ \hline
8 mm Calvariat & (i) & Chitin/fibroin-HA membrane & & \\ defect (rat) & (ii) & Collagen membrane & (Bio-Gide) & \\  & (iii) & No membrane & & \\  & (iii) & No membrane & & \\ \hline  & & & & \\  & (i) & 4-HR-incorporated silk & & \\  & & fabric membrane & & \\ defect (rabbit) & (ii) & Silk fabric membrane & & \\  & (iii) & No membrane & & \\  & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Experimental studies evaluating the performance of modified silk membranes. chitin, is a polyheterosaccharide with flexibility, antibacterial activity, and a hydrophilic surface that promotes cell adhesion, proliferation, and differentiation [62]. Fibroin/HA membrane containing chitin, an acetylated chitosan with antibacterial and anti-inflammatory activity, instead of chitosan, also has significant effects on new bone formation [63]. Silk fibroin membrane with 4-hexylIncorcion1 (4-HR) produced significantly more new bone formation than an unfilled control group [61, 66]. 4-HR is an antimicrobial agent that inhibits the inflammatory response and accelerates the partial degradation of the silk membrane [65, 66, 67]. Silk membrane is manufactured using various methods such as electrospinning [1, 64, 68], casting [55, 66, 57, 63, 56], and simple separation [68, 69]. Scanning electron microscope images of silk membranes manufactured by each technique are shown in Figure 2. Regardless of the production method, silk membranes produce effective bone regeneration without inflammation. Electrospinning produces nanofibers using high voltage [70]. Silk fibroin nanofibrous membrane thus exhibited significantly higher tensile strength than collagen membrane and improved new bone regeneration without any adverse inflammatory reactions by promoting early osteogenesis [1, 64]. The casting technique produces a transparent silk fibroin membrane, and this film type membrane showed higher new bone formation than the unfilled control group [55]. Compared to collagen membrane, the film type of membrane produced similar bone regeneration without any adverse inflammatory reactions [57].