Ultrasonic Vitrectomy Performance Assessment Using Micro-Extensional Rheology

Abstract

Purpose The purpose of this study was to assess the performance of ultrasonic (US) vitrectomy devices by quantifying and comparing its impact on extracted vitreous properties to conventional pneumatic blade (PB) cutters using micro-extensional rheology. US vitrectomy is a new technology that offers an alternative to PB cutters used in vitreo-retinal surgeries. Methods Thirty-six porcine vitreous samples were extracted using US and PB cutters. Each sample was kept at 4°C and tested within 24 hours postmortem and 4 hours post-vitrectomy. A recently developed micro-extensional rheology technique is used to infer the relative protein fragment size of extracted vitreous by quantifying the extensional relaxation time. Results US-extracted vitreous exhibited extensional relaxation times orders of magnitude lower than PB-extracted vitreous (0.37 ms and 27.25 ms, respectively). Relaxation time is directly correlated to the fragment size of the collagen fibers in the vitreous. The formation of beads-on-a-string droplets within the PB samples indicates the presence of larger collagen fragments. These droplets were not seen on US samples. Conclusions This new micro-extensional rheology technique can identify significant differences in physical properties of extracted vitreous. Long relaxation times and beads-on-a-string droplets within the PB vitreous samples indicate larger protein fragments compared to the US samples. Translational Relevance Higher fragmentation of vitreous and lower extensional relaxation times may improve retina safety due to a reduction in vitreo-retinal traction resulting from the continuous shear action and aspiration applied by ultrasonic vitrectomy technology.

An Inverse Method to Determine Mechanical Parameters of Porcine Vitreous Bodies Based on the Indentation Test

“…Finally, the indentation load was kept positive, suggesting that the force applied by the mechanical testing machine was higher than the surface tension. Therefore, the surface tension of the vitreous body could not be ignored, which was approved by previous studies [ 8 , 11 , 23 , 37 , 38 ]. The adhesive force of the vitreous body was measured by stretching the vitreous body between the cleated parallel plate and stage of the rheometer [ 8 ].…”

“…The adhesive force of the vitreous body was measured by stretching the vitreous body between the cleated parallel plate and stage of the rheometer [ 8 ]. Due to surface tension, an elasto-capillary liquid bridge formed between the probe and the vitreous body droplet as the sample dripped from the probe to the rest of the droplet [ 37 ]. The pressure acting on the indenter below zero during relaxation was probably affected by surface tension of the vitreous body [ 11 ].…”

“…Recently, Chen [ 11 ] proposed a simple indentation method to identify vitreous liquefaction by comparing of relative differences of some typical mechanical parameters during relaxation; however, the pressure acting on the indenter was only recorded, which was probably affected by surface tension of the vitreous body. In fact, an elasto-capillary liquid bridge formed between the probe and the vitreous body droplet as the sample dripped from the probe to the rest of the droplet [ 37 ]. Forces due to surface tension were proved to affect elastic deformation, leading to the elasto-capillary phenomena [ 38 ].…”

Trocars, Probes and Duty Cycles in Vitrectomy Devices

“…Görev döngüsü, probun boşta veya aspire ederek (kapalı) geçirdiği süreye kıyasla keserek (açık) geçirdiği sürenin oranını temsil eder. 25,26 Görev döngüsü, vitrektomi ameliyatının verimliliğini ve etkinliğini etkileyen kritik bir parametredir. Kesme ve aspirasyon arasındaki dengeyi belirleyerek doku çıkarma oranını, uygulanan emme miktarını ve genel cerrahi sonuçları etkiler.…”

Shear thinning behavior of cerebrospinal fluid with elevated protein or cellular concentration

“…To analyze the extensional rheological properties of the CSF, we adapted a simple rheometric method to apply a large strain rate to the samples (Figure 1) [21]. A droplet, typically between 50 and 100 μL, was dispensed onto a hydrophobically treated substrate to create a domed droplet.…”