The investigation of marine derived diatom biosilica used in 3D printed biopolymer scaffold for bone repair strategies

  • Ri Han

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

The first successful silica-based biomaterial was Bioglass 45S5 developed by Larry Hench in 1970s. It is currently used clinically mainly for dental applications and has been used in over a million patients worldwide. Although, Bioglass has performed well as a bone filler material, when incorporated into a polymer, to create biomaterials for load bearing applications, it performed poorly with significant polymer degradation and reduction in thermo-mechanical properties. As silica is known to be of benefit in bone regeneration, this study has investigated the potential of adding natural silica isolated from diatoms into medical grade polymers, as an alternative to Bioglass. Diatoms are unicellular microalgae with unique porous cell walls made of silica. This study investigated the potential use of diatoms as an alternative to bioactive in bioresorbable polymer scaffolds that were manufactured using 3D printing. It was hypothesised that the addition of diatom silica would improve the mechanical properties of these scaffolds.

This PhD project focuses on 3D printed medical biopolymer scaffolds fabricated using an FDM 3D printer for bone repair strategy. Poly (DL-lactide-co-glycolide) (PDLGA) bioresorbable thermoplastic polymer was the main material applied in this research. Diatom biosilica (purified from C. meneghiniana diatom) and 45S5 Bioglass were incorporated with PDLGA polymer to create the new biomedical materials for bone regeneration. Prior to the incorporation of diatoms in PDLGA, their dissolution behaviour was studied in different pH conditions. MCM-41 type mesoporous silica was also studied as a control sample under the same conditions. To manufacture the porous scaffolds, the Bioglass/diatom was blended in the polymer and then fabricated into filament which was then printed with FDM 3D printer. Both the filaments and the polymer scaffolds were studied by mechanical analysis, including tensile and compression test. Nuclear magnetic resonance (NMR) was also applied to analyse the degraded polymer in PBS buffer. In addition, inductively coupled plasma (ICP), Thermogravimetric analysis (TGA), Scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) were performed as chemical analysis in this project.

Diatoms were successfully purified to diatom biosilica using a washed treatment followed by heat treatment at 550 °C for one hour in a furnace. Diatom-PDLGA filaments (1 and 5wt%) were successfully fabricated with a suitable diameter and surface for 3D printing. Porous 3D scaffolds were printed at 220 °C (lwt% diatom- PDLGA scaffold) and 225 °C (5wt% diatom-PDLGA scaffold) using FDM 3D printer. Bioglass-PDLGA scaffold and pure PDLGA scaffold were also printed. Compression tests on diatom-PDLGA scaffolds confirmed they had comparable strength to cancellous bone (2 to 12 MPa). A 26-week degradation study was performed on the scaffolds. The diatom-PDLGA scaffolds kept their compressive strength for 4 weeks longer than pure PDLGA scaffold and bioglass-PDLGA scaffold. The release rate of Si4+ ions from scaffolds was also profiled. The diatom- PDLGA scaffolds demonstrated a typical exponential increase in Si4+ ions release with respect to time (up to 272 ppm), in a steady and slower release manner. Bioglass-PDLGA scaffolds, however, had a burst release of Si4+ ions.
Date of AwardDec 2019
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsMarine Institute
SupervisorPamela Walsh (Supervisor) & Fraser Buchanan (Supervisor)

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