Reconstruction of critical-sized mandibular defects in a sheep model using a PLLA-PGA-CC scaffold

Technical Summary: Reconstruction of Critical-Sized Mandibular Defects Using PLLA-PGA-CC Scaffolds

Problem Statement
Critical-sized bone defects are characterized by an inability to heal spontaneously, necessitating complex and often burdensome clinical interventions. While synthetic substitute materials have been investigated to address this challenge, there is a need to evaluate the efficacy of specific biodegradable combinations. Poly-L-lactic acid (PLLA) and polyglycolic acid (PGA) have emerged as promising scaffold materials, and the addition of inorganic components like calcium carbonate (CC) is hypothesized to offer further advantages. This study addresses the specific question of whether PLLA-PGA-CC scaffolds can effectively facilitate bone regeneration in critical-sized mandibular defects over an extended period.

Methodology
The study utilized a large animal model involving twelve female Merino sheep. Critical-sized defects were surgically created at the mandibular angle. The subjects were divided into two groups:

• Experimental Group (n=4): Defects were reconstructed using PLLA-PGA-CC scaffolds. These scaffolds were manufactured via computer-aided design and manufacturing (CAD/CAM) to feature an interconnected porous structure and were fixated using polyether ether ketone (PEEK) cages.
• Control Group (n=8): Defects were left empty to serve as a negative control.

Bone regeneration was monitored over a two-year observation period. Evaluation methods included:

1. Quantitative Imaging: Computed tomography (CT) scans were performed at 3, 12, and 24 months postoperatively to assess bone volume.
2. Histological Analysis: Tissue samples were examined to evaluate scaffold resorption, bone tissue formation, and tissue infiltration.

Key Results

• Surgical Outcome: All procedures were successful with no major complications reported.
• Quantitative Bone Volume: At 24 months, the scaffold group demonstrated a higher mean bone volume (7,472 mm³) compared to the control group (4,168 mm³). However, this difference did not reach statistical significance (p = 0.1).
• Histological Findings:
  • The scaffolds were confirmed to be biocompatible, showing resorption and the formation of compact lamellar bone tissue.
  • Limitations: The osteoconductive properties were found to be limited, evidenced by only minimal ingrowth of bone tissue into the scaffold's porous structure.
  • Adverse Tissue Response: Both the scaffold and control groups exhibited fibrous tissue infiltration and the formation of cyst-like cavities within the defect regions.

Significance and Claims
The paper concludes that while PLLA-PGA-CC scaffolds are biocompatible and demonstrate a trend toward enhanced bone regeneration compared to untreated defects, their clinical utility is constrained. The authors modestly assert that the material's suitability for reconstructing critical-sized bone defects is limited. This limitation is attributed primarily to the lack of effective osteoconductivity (minimal bone ingrowth) and the persistent presence of fibrous tissue infiltration and cyst-like cavities, which were observed in both the treated and control groups. Consequently, while the material shows potential, it does not fully overcome the challenges associated with critical-sized defect reconstruction in this specific model.