Recycled Porcine Bone Powder as Filler in Thermoplastic Composite Materials Enriched with Chitosan for a Bone Scaffold Application

Abstract

This work aims to synthesize biocompatible composite materials loaded with recycled porcine bone powder (BP) to fabricate scaffolds for in-situ reconstruction of bone structures. Polylactic acid (PLA) and poly(ε-caprolactone) (PCL) were tested as matrices in percentages from 40 wt% to 80 wt%. Chitosan (CS) was selected for its antibacterial properties, in the amount from 5 wt% to 15 wt%, and BP from 20 wt% to 50 wt% as active filler to promote osseointegration. In this preliminary investigation, samples have been produced by solvent casting to introduce the highest possible percentage of fillers. PCL has been chosen as a matrix due to its greater ability to incorporate fillers, ensuring their adequate dispersion and lower working temperatures compared to PLA. Tensile tests demonstrated strength properties (6-10 MPa) suitable for hard tissue engineering applications. Based on the different findings (integration of PLA in the composite system, improvements in CS adhesion and mechanical properties), the authors supposed an optimization of the synthesis process, focused on the possible implementation of the electrospinning technique to develop PCL-BP composites reinforced with PLA-CS microfibers. Finally, biological tests were conducted to evaluate the antibacterial activity of CS, demonstrating the applicability of the materials for the biomedical field.

Keywords: PCL; PLA; antibacterial activity; bone scaffold; chitosan; mechanical properties; recycled bone powder; thermoplastic composites.

Figure 1

Origin of the BP (provided by Tecnoss™) used in this work.

Figure 2

SEM images of BP at low (a) and high (b) magnifications.

Figure 3

Dimensional distribution of the BP used in this work. Each color represents a particle size pair of BP (μm)–Volume (%) obtained from the MasterSizer analyzer.

Figure 4

Thickness measurement on solvent-casted polymer-BP films.

Figure 5

Dog-bone specimen preparation for tensile test: Die-cutting method.

Figure 6

Comparison between a well-made disk (a) and a solvent-casted specimen with unsuitable features (b).

Figure 7

(a) Cross-section of PLA sample filled with 40 wt% of BP. (b) SEM micrograph PLA surface in the composite with 30 wt% of BP, highlighting air bubbles resulted from solvent casting; (c) SEM micrograph of PLA-BP sample (50 wt% of BP), where the inorganic particles are not detectable; (d) SEM image of sample constituted by 50 wt%BP and 50wt%PLA. In this case, the micrograph shows the poor cohesion between matrix and filler.

Figure 8

(a) Cross-section image of PCL50-BP50. (b) Interfacial adhesion between PCL and BP in PCL50-BP50 sample. (c) Distribution of CS filler in PCL45-BP50-CS5 specimen. (d) Detail on the interfacial adhesion of CS in PCL matrix.

Figure 9

Tensile strength results.

Figure 10

Young’s modulus and elongation-at-break results.

Figure 11

Stress vs. strain curves from tensile test.

Figure 12

Implementation of the production technology of thermoplastic composites: Future upgrade.

Figure 13

S. aureus and E. coli bacterial adhesion on PLA-CS-BP matrices. The inhibition of bacterial adhesion was significant with * p < 0.05 (t-Test).

Figure 14

Relative growth of S. aureus and E. coli strains on CS loaded PLA-BP scaffolds after 24 h of culture. * p < 0.05 vs. control (t-Test).