# Bone Incorporation of a Poly (L-Lactide-Co-D, L-Lactide) Internal Fixation Device in a Rat’s Tibia: Microtomographic, Confocal LASER, and Histomorphometric Analysis

## TL;DR

This study shows that a biodegradable screw made of PLDLLA promotes new bone growth in rats without needing removal surgery.

## Contribution

The study demonstrates the biocompatibility and bone integration of a PLDLLA internal fixation device in a rat tibia model.

## Key findings

- MicroCT showed increased bone volume and trabecular separation at 28 and 42 days.
- Cortical new bone formation was significantly higher at 42 days compared to earlier time points.
- Confocal microscopy showed no significant differences in mineral apposition rate at later time points.

## Abstract

Poly (L-lactide-co-D, L-lactide) and PLDLLA have mechanical properties such as biodegradability, biocompatibility, thermoplastic capacity, and physical properties. In addition, their use eliminates the need for removal in subsequent surgeries and reduces the discomfort and risks associated with additional procedures. Given these advantages, a national company is currently developing an internal fixation device manufactured for PLDLLA, and it is essential to evaluate its bone incorporation process. The PLDLLA fixation device tested in this animal study was biocompatible and facilitated the formation of new bone around the device. Therefore, to avoid a second surgical procedure, this device is a highly effective option for those seeking a reliable and safe solution for bone fixation procedures.

This study evaluated the bone incorporation process of a screw-shaped internal fixation device made of poly (L-lactide-co-D, L-lactide) (PLDLLA). Thirty-two male Wistar rats received 32 fixation devices (2 mm × 6 mm) randomly assigned to either the right or left tibia and one implant in each animal. After 7, 14, 28, and 42 days, the rats were euthanized and the specimens were subjected to microtomographic computed tomography (microCT) and histomorphometric analyses to evaluate bone interface contact (BIC%) and new bone formation (NBF%) in cortical and cancellous bone areas. The animals euthanized on days 28 and 42 were treated with calcein and alizarin red, and confocal LASER microscopy was performed to determine the mineral apposition rate (MAR). Micro-CT revealed a higher percentage of bone volume (p < 0.006), trabecular separation (p < 0.001), and BIC in the cortical (p < 0.001) and cancellous (p = 0.003) areas at 28 and 42 days than at 7 and 14 days. The cortical NBF at 42 days was greater than that at 7 and 14 days (p = 0.022). No statistically significant differences were observed in cancellous NBF or MAR at 28 and 42 days. Based on these results, it can be seen that the PLDLLA internal fixation device is biocompatible and allows new bone formation around the screw thread.