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Mobility-Enhancing Coatings for Vitreoretinal Surgical Devices: Hydrophilic and Enzymatic Coatings Investigated by Microrheology
journal contribution
posted on 2015-10-07, 00:00 authored by Juho Pokki, Jemish Parmar, Olgaç Ergeneman, Hamdi Torun, Miguel Guerrero, Eva Pellicer, Jordi Sort, Salvador Pané, Bradley J. NelsonOphthalmic wireless microrobots are
proposed for minimally invasive vitreoretinal surgery. Devices in
the vitreous experience nonlinear mobility as a result of the complex
mechanical properties of the vitreous and its interaction with the
devices. A microdevice that will minimize its interaction with the
macromolecules of the vitreous (i.e., mainly hyaluronan (HA) and collagen)
can be utilized for ophthalmic surgeries. Although a few studies on
the interactions between the vitreous and microdevices exist, there
is no literature on the influence of coatings on these interactions.
This paper presents how coatings on devices affect mobility in the
vitreous. Surgical catheters in the vasculature use hydrophilic polymer
coatings that reduce biomolecular absorption and enhance mobility.
In this work such polymers, polyvinylpyrrolidone (PVP), polyethylene
glycol (PEG), and HA coatings were utilized, and their effects on
mobility in the vitreous were characterized. Hydrophilic titanium
dioxide (TiO2) coating was also developed and characterized.
Collagenase and hyaluronidase enzymes were coated on probes’
surfaces with a view to enhancing their mobility by enzymatic digestion
of the collagen and HA of the vitreous, respectively. To model the
human vitreous, ex vivo porcine vitreous and collagen were used. For
studying the effects of hyaluronidase, the vitreous and HA were used.
The hydrophilic and enzymatic coatings were characterized by oscillatory
magnetic microrheology. The statistical significance of the mean relative
displacements (i.e., mobility) of the coated probes with respect to
control probes was assessed. All studied hydrophilic coatings improve
mobility, except for HA which decreases mobility potentially due to
bonding with vitreal macromolecules. TiO2 coating improves
mobility in collagen by 28.3% and in the vitreous by 15.4%. PEG and
PVP coatings improve mobility in collagen by 19.4 and by 39.6%, respectively,
but their improvement in the vitreous is insignificant at a 95% confidence
level (CL). HA coating affects mobility by reducing it in collagen
by 35.6% (statistically significant) and in the vitreous by 16.8%
(insignificant change at 95% CL). The coatings cause similar effects
in collagen and in the vitreous. However, the effects are lower in
the vitreous, which can be due to a lower concentration of collagen
in the vitreous than in the prepared collagen samples. The coatings
based on enzymatic activity increase mobility (i.e., >40% after
15 min experiments in the vitreous models) more than the hydrophilic
coatings based on physicochemical interactions. However, the enzymes
have time-dependent effects, and they dissolve from the probe surface
with time. The presented results are useful for researchers and companies
developing ophthalmic devices. They also pave the way to understanding
how to adjust mobility of a microdevice in a complex fluid by choice
of an appropriate coating.
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biomolecular absorptionphysicochemical interactionscoatings causeVitreoretinal Surgical Devicesvitreous experience nonlinear mobilitycontrol probesvitreoretinal surgeryvivo porcine vitreousvitreal macromoleculesvasculature useHydrophilic titanium dioxideSurgical cathetershyaluronidase enzymesHA coatingsPEGEnzymatic Coatings InvestigatedCLTiO 2 coatingactivity increase mobilityprobe surface15 min experimentspolymer coatingsdecreases mobilityvitreous modelscollagen samplesPVP coatingsHA coating
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