Safety and efficacy of Mg-Dy membrane with poly-L-lactic acid coating for guided bone regeneration

Abstract

The aim of this study was to evaluate safety and efficacy of a poly-L-lactic acid (PLLA)-coated magnesium (Mg)-Dysprosium (Dy) membrane in guided bone regeneration (GBR) using a rabbit calvarium model. The microstructure of the Mg-Dy membrane surface and thickness of the PLLA coating were examined. In vitro degradation and cytotoxicity test was conducted. The in vivo study used 24 white male rabbits with two 8 mm-diameter defects created on the calvaria; 12 defects were randomly assigned per group: (1) Negative control, (2) positive control, (3) uncoated Mg, and (4) PLLA-coated Mg group. Specimens were harvested at 4, 8, and 12 weeks postoperatively for radiological, histological, and histomorphometric analyses. The PLLA-coated Mg-Dy membrane showed a low degree of degradation, indicating that the coating exerted a protective effect. In the cytotoxicity test, no deformed or degenerated cells were observed. In the in vivo study, radiographic and histomorphometric analyses indicated favorable new bone formation and maintenance of the graft material for PLLA-coated Mg group. PLLA-coated Mg group, compared to the uncoated counterpart, restored the bony contour more completely, without inducing significant inflammatory response. Our results support the safety and efficacy of PLLA-coated Mg-Dy membranes for GBR both in vitro and in vivo.

Keywords: Biocompatible coated material; Biodegradable membrane; Dental implant; Guided tissue regeneration; Magnesium; New Zealand white rabbit.

Fig. 1

Preparation of PLLA-coated Mg-Dy membrane. (A) Design. (B) Three-dimensional representation. (C) Schematic diagram of the folding process of Mg-Dy membranes. (D) Frontal view before folding. (E) Top view before folding. (F) Frontal view after folding. (G) Top view after folding. All measurements in Fig. 1 are in mm.

Fig. 2

Clinical images demonstrating the group assignment. Two defects per rabbit were randomly assigned to either the NC or PC group on the right side and the uncoated Mg group or the PLLA-coated Mg group on the left side, respectively.

Fig. 3

SEM images of the uncoated and PLLA-coated Mg-Dy membrane and PLLA coating. Original magnification of 10× (A), 50× (B), 100× (C), 300× (D), and 500× (E) of uncoated Mg-Dy membrane. Original magnification of 10× (F), 50× (G), 100× (H), 300× (I), and 500× (J) of PLLA-coated Mg-Dy membrane. Original magnification of 100× (K), 300× (L), and 500× (M) of PLLA coating. (N) Measurement of PLLA coating thickness.

Fig. 4

In vitro degradation and cytotoxicity tests. (A) Weight changes in Mg-Dy membrane with or without PLLA coating. (B) Photographic images showing changes in the shapes of Mg-Dy membranes with or without coating. Microscopic observation of the growth inhibition and lysis state of L-929 cells in various treatments for MC (C), PC (D), uncoated Mg-Dy membrane (E), and PLLA-coated Mg-Dy membrane (F). (G) L-929 cell viability by MTT assay.

Fig. 5

In vivo micro-CT analysis. Comparison of NBV (A), RMV (B), and TBV (C) among groups at 4, 8, and 12 weeks. Comparison of the residual volume (D) and surface area (E) of the Mg-Dy membrane between the uncoated and PLLA-coated Mg group. (F) 3D-reconstructed images showing the shape of residual Mg-Dy membranes with or without PLLA coating. (G) Coronally sectioned micro-CT images showing the shape of residual Mg-Dy membranes with or without PLLA coating. ^*P < 0.05.

Fig. 6

Representative histological images for each group at each time point. (A) H&E-stained histological images. (B) MT-stained histological images.

Fig. 7

In vivo histomorphometric analysis. Comparison of the percentages of NBA (A), RMA (B), and TBA (C) by histomorphometric analysis among the groups. Comparison of inflammatory response score (D) and number of MNGCs (E) among the groups. ^*P < 0.05, ^**P < 0.01.