Heat impact during laser ablation extraction of mineralised tissue micropillars

Abstract

The underlying constraint of ultrashort pulsed laser ablation in both the clinical and micromachining setting is the uncertainty regarding the impact on the composition of material surrounding the ablated region. A heat model representing the laser-tissue interaction was implemented into a finite element suite to assess the cumulative temperature response of bone during ultrashort pulsed laser ablation. As an example, we focus on the extraction of mineralised collagen fibre micropillars. Laser induced heating can cause denaturation of the collagen, resulting in ultrastructural loss which could affect mechanical testing results. Laser parameters were taken from a used micropillar extraction protocol. The laser scanning pattern consisted of 4085 pulses, with a final radial pass being 22 $$\upmu {\text {m}}$$ μ m away from the micropillar. The micropillar temperature was elevated to 70.58 $$^{\circ }{\text {C}}$$ ∘ C , remaining 79.42 $$^{\circ }{\text {C}}$$ ∘ C lower than that of which we interpret as an onset for denaturation. We verified the results by means of Raman microscopy and Energy Dispersive X-ray Microanalysis and found the laser-material interaction had no effect on the collagen molecules or mineral nanocrystals that constitute the micropillars. We, thus, show that ultrashort pulsed laser ablation is a safe and viable tool to fabricate bone specimens for mechanical testing at the micro- and nanoscale and we provide a computational model to efficiently assess this.

An experimentally informed statistical elasto-plastic mineralised collagen fibre model at the micrometre and nanometre lengthscale

“…Three consecutive FIB milling steps (dual FIB-SEM Quanta 3D FEG, FEI, USA) at gallium ion currents of 7.0 nA (coarse), 0.5 nA (intermediate) and 0.3 nA (polishing) were then used to cut the pre-pillars down to their final dimensions of in diameter at an aspect ratio of 2.1. The reader is referred to 39 for further details on the preparation steps, and 39 and 110 to show that the sample preparation procedure did not have a significant influence on the tissue properties.…”

The elasto-plastic nano- and microscale compressive behaviour of rehydrated mineralised collagen fibres

“…The plasma mediated ablation process minimised the thermal impact during manufacturing. Raman measurements and finite element analyses were used to confirm that the physio-chemical properties were not changed by the laser ablation, and that the ablation process did not exceed the denaturation temperature for dry collagen [56,70]. Focused ion beam milling (Quanta 3D FEG, FEI, USA) was then used to cut the final micropillars.…”