Minimally invasive photopolymerization in intervertebral disc tissue cavities

Abstract

Photopolymerized hydrogels are commonly used for a broad range of biomedical applications. As long as the polymer volume is accessible, gels can easily be hardened using light illumination. However, in clinics, especially for minimally invasive surgery, it becomes highly challenging to control photopolymerization. The ratios between polymerizationvolume and radiating-surface-area are several orders of magnitude higher than for ex-vivo settings. Also tissue scattering occurs and influences the reaction.We developed a Monte Carlo model for photopolymerization, which takes into account the solid/liquid phase changes, moving solid/liquid-boundaries and refraction on these boundaries as well as tissue scattering in arbitrarily designable tissue cavities. The model provides a tool to tailor both the light probe and the scattering/absorption properties of the photopolymer for applications such as medical implants or tissue replacements. Based on the simulations, we have previously shown that by adding scattering additives to the liquid monomer, the photopolymerized volume was considerably increased.In this study, we have used bovine intervertebral disc cavities, as a model for spinal degeneration, to study photopolymerization in-vitro. The cavity is created by enzyme digestion. Using a custom designed probe, hydrogels were injected and photopolymerized. Magnetic resonance imaging (MRI) and visual inspection tools were employed to investigate the successful photopolymerization outcomes.The results provide insights for the development of novel endoscopic light-scattering polymerization probes paving the way for a new generation of implantable hydrogels.

Photo-polymerization, swelling and mechanical properties of cellulose fibre reinforced poly(ethylene glycol) hydrogels

“…Specifically in biomedical or dental applications, for which a lower UV exposure time of cells or tissue and shorter surgery time are desirable. As we previously discussed [20], addition of light scattering particles, such as intralipids, is an effective method to decrease the required hydrogel curing time and achieve a photopolymerization of the volume. However, this curing acceleration is associated with decreasing the mechanical properties of the final material.…”

A photopolymerized composite hydrogel and surgical implanting tool for a nucleus pulposus replacement

“…However, we demonstrated previously that volumes of more than 2 ml (i.e. enough for a human NP) can be photopolymerized in less than 10 min using the same optical device [68]. It is also possible to choose different photoinitiators such as Eosin Y with higher photopolymerization rates in the range between 10 s and 3 min [69].…”