# New Resorbable Membrane Materials for Guided Bone Regeneration
## 3 Aliphatic Polyesters  
Aliphatic polyesters, such as poly(lactic acid) (PLA), poly(glycolic acid) (PGA), poly(\(\varepsilon\)-caprolactone) (PCL), poly(hydroxy valeric acid), poly(hydroxy butyric acid), and their copolymers, are another category of synthetic polymers and have been used as preparation materials for GBR membrane [4; 30; 31]. The advantages of aliphatic polyesters are that they are bioresorbable, and possess good processability and manageability, but their disadvantages include a lack of rigidity and stability [31]. Studies have been conducted to increase their advantages and reduce their disadvantages by modifying, mixing, and adding additives rather than using aliphatic polyesters alone (Table 2). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Experimental Model**} & \multicolumn{2}{c}{**Experimental Groups**} & \multirow{2}{*}{**Main Findings**} & \multirow{2}{*}{**Reference**} \\  & & **(Membrane with/without New Material)** & & \\ \hline \multirow{6}{*}{\(5\) mm Calvarial defect (rat)} & (i) & Bi-layer PLGA membrane (\(-30\)\({}^{\circ}\)C cooling) & \multirow{6}{*}{\(\bullet\)} & The solid layer of (ii) was thicker than (i); comparatively, (iii) had a solid surface and uniform layer \\  & (ii) & Bi-layer PLGA membrane (\(-70\)\({}^{\circ}\)C cooling) & \multirow{6}{*}{\(\bullet\)} & (i) and (ii) had significantly \\  & (iii) & PLGA membrane (GC membrane) & & formed bone compared to (iii) \\  & (iv) & Sham & & and (iv) \\  & & & & (i), (ii), and (iii) had similar \\  & & & biodegradation behaviors \\ \hline \multirow{6}{*}{\(5\) mm Calvarial defect (rat)} & (i) & PCL membrane & \multirow{6}{*}{\(\bullet\)} & \multirow{6}{*}{\(\bullet\)} \\  & (ii) & PCL/PLGA membrane & & \\ \cline{1-1}  & (iii) & PCL/gelatin membrane & & was significantly higher in (iv) \\ \cline{1-1}  & (iv) & PCL/DCP membrane & & \\ \hline \multirow{6}{*}{
\begin{tabular}{c} Osteoblast cell line \\ (MC3T3-E1)/\(4\times 2\) mm \\ Mandibular peri-implant defect (dog) \\ \end{tabular} } & \multirow{6}{*}{\(\bullet\)} & No difference was observed in \\  & & & osteogenic differentiation between \\  & & & (i) and (ii) on day 14. \\ \cline{1-1}  & & Collagen membrane & & (i) had similar levels of \\ \cline{1-1}  & & & biocompatibility and bone \\ \cline{1-1}  & & & regeneration to (ii) \\ \hline \multirow{6}{*}{\(7\times 5\times 5\) mm} & (i) & 3D-printed PCL membrane & \multirow{6}{*}{\(\bullet\)} & (ii) had significantly higher new \\  & & & (iii) & \\ \cline{1-1}  & & & bone plus bone substitute \\ \cline{1-1}  & & & (iii) & Collagen membrane \\ \hline \multirow{6}{*}{\(8\) mm Calvarial defect (rabbit)} & (i) & No membrane & \multirow{6}{*}{\(\bullet\)} & (iii) exhibited the greatest amount of \\  & & & (ii) & 3D-printed PCL/PLGA/\(\beta\)-TCP membrane & \\ \cline{1-1}  & & (iii) & 3D-printed & \\ \cline{1-1}  & & PCL/PLGA/\(\beta\)-TCP/rhBMP-2 membrane & & \\ \cline{1-1}  & & & \multicolumn{1}{c}{} & post-implantation, and these were \\ \cline{1-1}  & & & significantly different \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experimental studies evaluating the performance of modified aliphatic polyester membranes. Poly(lactic-co-glycolic acid) (PLGA) is a copolymer that can be prepared in different forms of copolymer depending on the ratio of PLA and PGA, with the advantages of biocompatibility, biodegradability, and processability [7; 36]. Bi-layer PLGA membrane is composed of a thin dense film that prevents the ingrowth of epithelial cells and a thick micro-fibrous layer that stabilizes blood clots and helps cell colonization and bone regeneration [37]. Its mechanical properties are sufficient for clinical use and it has a similar absorption rate to PLGA membrane and a higher rate of new bone formation than PLGA membrane [32]. The blended PCL/biphasic calcium phosphate (BCP) membrane produced significantly higher bone regeneration than PCL membrane, due to the osteoconductivity of BCP [33].