Technical noteIntraluminal magnetisation of bowel by ferromagnetic particles for retraction and manipulation by magnetic probes
Introduction
Retraction of bowel during minimal access surgery (MAS) remains problematic as the moist low friction serosal surface is difficult to grasp with laparoscopic graspers. One study documented the low percentage (62%) of successful grasping actions and indicated the need for improvement in laparoscopic grasper design [1].
We have been investigating tissue magnetisation by magnetic nano- and micro-particles for MAS applications and have previously reported two tissue ferromagnetisation approaches for tissue retraction: (i) surface magnetisation by applying a small volume of glue-based magnetic media to the mucosal/serosal surface [2], and (ii) by interstitial injection of phosphate-buffered saline (PBS) ferrofluids [3]. In these experiments injected ferromagnetisation was shown to be superior to surface magnetisation by surface magnetic pellets, as the latter tended to peel off the tissue during retraction by magnetic probes. However, the restricted sub-mucosal space limited our injected media volume thus retraction force in previous interstitial injection method.
In the present study, we report a novel method of magnetisation of a bowel segment by intra-luminal injection of magnetic ferrofluids using a custom-designed intra-abdominal suction–injection probe. We compare the behaviour of stainless steel microparticles (SS-μPs) and iron oxide nanoparticles (IO-nPs). The latter family of nPs was chosen due to their well-established clinical use for applications including MRI contrast agents [4], [5], [6], [7], [8]. Detailed characterisation of magnetic particles used for making the magnetic ferrofluids for intraluminal bowel magnetisation and the retraction forces obtained in ex vivo experiments using porcine bowel segments are reported and the comparison of four micro- and nano-particles allowed the identification of the rules to engineer the next generation of particles.
Section snippets
Magnetic particles
Stainless steel microparticles and iron oxide nanoparticles were used as model magnetic particles. Two types of stainless steel microparticles (SS-μPs) were investigated: stainless steel type 410 microparticles (SS410-μPs, from Goodfellow) and stainless steel type 430 microparticles (SS430-μPs, from Alfa). Iron oxide nanoparticles were made in-house by forced hydrolysis (IOiH-nPs) and compared with commercial iron oxide powder (IOAlfa-nPs, from Alfa). These types of materials were previously
Characterisation of magnetic particles
Four types of magnetic particles were investigated, Table 1 lists the physical properties as obtained by SEM and XRD, SQUID at 300 K, and ICP-OES.
Fig. 1a presents the morphology as observed by electron microscopy for iron oxide nanoparticles. XRD patterns, Fig. 1b, are characteristic of Fe3O4 and were used to extract the crystalline grain size. Magnetic properties were quantified at room temperature in terms of magnetisation as function of applied magnetic field and the resulting curves are
Discussion
The suction–injection probe first tented the target bowel segment and generated large lumen space in order to facilitate intraluminal injection of ferrofluid into lumen. This avoids fluid to be injected into sub-mucosa or through the bowel into abdominal space. The injected fluid was temporarily maintained in the intended lumen section of the intestine due to its high viscosity (i.e., glycerol suspension), and the magnet probe was then located at the injection section immediately after
Conclusion
The physical properties of magnetic particles were investigated and the relative performances were compared. Injectable high viscosity magnetic ferrofluids were developed for magnetic bowel retraction and were characterised in an ex vivo porcine bowel model. The present approach utilises the magnetic interactions to retract internally magnetised bowels towards an external (intra-abdominal) magnetic probe for safe and effective bowel manipulations. The results of the current experiments indicate
Funding
This work has been financially supported by the Engineering and Physical Sciences Research Council (EPSRC), UK, under Grant EP/HO 10033/1.
Ethical approval
Ethical approval has not been required for this work.
Conflict of interest
The authors report no conflict of interest.
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