Development of a porous poly(DL-lactic acid-co-glycolic acid)-based scaffold for mastoid air-cell regeneration

Abstract

Objectives/hypothesis: To develop a porous, biodegradable scaffold for mastoid air-cell regeneration.

Study design: In vitro development of a temperature-sensitive poly(DL-lactic acid-co-glycolic acid)/poly(ethylene glycol) (PLGA/PEG) scaffold tailored for this application.

Methods: Human mastoid bone microstructure and porosity were investigated using micro-computed tomography. PLGA/PEG-alginate scaffolds were developed, and scaffold porosity was assessed. Human bone marrow mesenchymal stem cells (hBM-MSCs) were cultured on the scaffolds in vitro. Scaffolds were loaded with ciprofloxacin, and release of ciprofloxacin over time in vitro was assessed.

Results: Porosity of human mastoid bone was measured at 83% with an average pore size of 1.3 mm. PLGA/PEG-alginate scaffold porosity ranged from 43% to 78% depending on the alginate bead content. The hBM-MSCs proliferate on the scaffolds in vitro, and release of ciprofloxacin from the scaffolds was demonstrated over 7 to 10 weeks.

Conclusions: The PLGA/PEG-alginate scaffolds developed in this study demonstrate similar structural features to human mastoid bone, support cell growth, and display sustained antibiotic release. These scaffolds may be of potential clinical use in mastoid air-cell regeneration. Further in vivo studies to assess the suitability of PLGA/PEG-alginate scaffolds for this application are required.

Keywords: Scaffold; alginate; ciprofloxacin; mastoid; poly(DL-lactic acid-co-glycolic acid).

Figure 1. Microstructure of human mastoid bone

(A) Micro-CT x-ray slice image of human mastoid bone. (B) Micro-CT 3D reconstruction of human mastoid bone.

Figure 2. Microstructure of PLGA/PEG-alginate scaffolds

(A) Porosity of PLGA/PEG-alginate scaffolds calculated by density measurements. (B) Light microscope images of 40% PLGA/PEG-60% alginate scaffolds before freeze-drying (top image) and after freeze-drying for 24 hours (bottom image). (C) Micro-CT x-ray slice and 3D reconstruction of 40% PLGA/PEG-60% alginate scaffold after freeze-drying for 24 hours.

Figure 3. Image comparison of human mastoid bone and PLGA/PEG scaffold

Light microscope image of human mastoid bone section (left) and 40% PLGA/PEG-60% alginate scaffold (right). Scaffold was submerged in saline at 37°C for 2 weeks prior to imaging.

Figure 4. PLGA/PEG particle sintering within PLGA/PEG-alginate scaffolds at 37C

(A) Compressive strength of 40% PLGA/PEG-60% alginate scaffolds sintered for 3, 4 and 5 hours at 37°C. Error bars represent standard deviation. (B) Representative scanning electron microscopy image of a 40% PLGA/PEG-60% alginate scaffold sintered for 4 hours at 37°C and freeze-dried for 24 hours.

Figure 5. Proliferation of human bone marrow-derived mesenchymal stem cells on PLGA/PEG-alginate scaffolds

(A) Number of viable human bone marrow mesenchymal stem cells (hBM-MSCs) on 40% PLGA/PEG-60% alginate as measured by the Prestoblue metabolic activity assay over 7 days in culture. Error bars represent standard deviation. (B) Representative images of hBM-MSC-seeded 40% PLGA/PEG-60% alginate scaffold 3 days post-seeding following Live/Dead staining. PLGA/PEG particles rendered in blue using Leica LCS confocal macroscope software in order to visualise the particles (blue) and pore spaces between particles (black) Size bar = 200μm.

Figure 6. Ciprofloxain release from PLGA/PEG-alginate scaffolds

Cumulative release profiles for ciprofloxacin from 40% PLGA/PEG-60% alginate scaffolds represented as percentage of total loaded drug released. Two different drug loading methods were used, method A (‘PLGA/PEG-alginate cipro’) and method B (PLGA/PEG-alginate cipro melt-blend’).