Silicon Nitride 3D Printed Implants with Improved Material Properties for Bone Defect Repair
Authors: Alakija Femi K. , Mills David K. 
Published: May 2022

Introduction

Perioperative or latent infections are the typical causes of revision surgeries, requiring the removal and replacement of infected implants. Therefore, biomaterials which promote osseointegration while minimizing the risk of infection are necessary for improved spinal fusion outcomes. Many biomaterials such as PEEK or Titanium are used as an implant. However, most have poor osteoconductive and bacteriostatic properties. Conversely, SN has demonstrated both enhanced osteogenic, hardness, and antimicrobial properties. SN has extremely high strength even up to >1200°C, excellent wear and chipping resistance, high hardness, high fracture toughness. Halloysite nanotubes (HNTs) and metal nanoparticles have been shown to enhance polylactic acid (PLA) and possess antibacterial properties. This research aims to fabricate 3D implants by combining antimicrobial and base polymer powders.

Methods

We used a patented electrodeposition process to coat magnesium (Mg) on the HNT outer surfaces to add additional antimicrobial properties and favorable mechanical properties due to the addition of HNTs. The experiment was set up with SN and metalized halloysite in three concentrations (1%, 5%, and 10%) to achieve the best concentration for the experiment. SEM, EDS, and FTIR were used to confirm Mg presence on the HNT outer surface. Flexural strength test, Hardness test, compression test, contact angle, and porosity test were all used for mechanical testing of the 3D printed composite implant. Gentamicin sulfate, a naturally producing antibiotic by gram‐negative bacteria that can inhibit the growth of both gram‐negative and gram‐positive bacteria, was loaded into the HNT in the fabricated 3D printed implant. Its antimicrobial activity was tested against gram‐positive and gram‐negative bacteria. Samples were conditioned, and then the evaluation of invitro preosteoblast response was evaluated by performing a cytotoxicity test and proliferation assay. Stimulated body fluid was used for in‐vitro assessment to measure the biodegradability of the 3D printed composite.

Results

Antimicrobial testing showed a pronounced bacterial growth inhibition. The effect of SN and metalized HNT on preosteoblasts showed no toxicity and enhanced cell proliferation. In addition, 5% and 10% of SN/MgHNT‐PLA showed greater flexural strength and hardness while also showing a low contact angle after surface coating with protein. SN/MgHNT‐PLA implants also degraded slowly over time.

Discussion

The favorite antimicrobial activity results were obtained by loading the HNT before coating with Mg and then blending with SN. Due to the beneficial physicochemical and biological properties, SN particles have shown great potential as multifunctional building blocks for composites and orthopedic coatings in hard tissue repair/regeneration applications. The introduction of SN on implants enhances cellular surface structure, surface roughness, hydrophilicity, and protein adsorption capability of SN/MgHNT‐PLA 3D printed implants.

Significance/clinical relevance

Fabricated SN/HNT composite implants showed outstanding mechanical, excellent bacteriostatic property, and osteogenic activity, and offers promise in orthopedic applications.