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Femtosecond laser-enabled intrastromal keratoplasty: a new surgical model for evaluating implantable ocular biomaterials

Poster Details

First Author: N.Lagali SWEDEN

Co Author(s):    M. Rafat   M. Koulikovska   M. Xeroudaki   P. Fagerholm     

Abstract Details



Purpose:

To use femtosecond laser-enabled intra-stromal keratoplasty (FLISK) as a surgical model to test various biomaterials in vivo for biocompatibility, degradation, and regenerative capacity in an ocular environment.

Setting:

Ophthalmology Department, Institute for Clinical and Experimental Medicine, Linköping University, Sweden.

Methods:

Biomaterials were synthesized from purified, medical-grade porcine type I collagen extracted from porcine skin. Different chemical cross-linking agents were used to form transparent hydrated implants from the porcine collagen. Additionally, implants were designed with a central transparent optic and semi-transparent to non-transparent peripheral skirt to facilitate in vivo tracking. The implants were tested in vivo by ocular implantation in 25 male New Zealand white rabbits. Using a newly-developed model of femtosecond laser-enabled intra-stromal keratoplasty (FLISK), a disc of 150µm thickness and 3mm diameter of native corneal stromal tissue was excised, and replaced with either the same disc of native rabbit tissue (autograft), or with 150µm thick versions of four different biomaterials. Each experimental group consisted of 5 rabbits, which were examined during a 3-month postoperative period. Postoperative in vivo examinations included photography, anterior segment optical coherence tomography (ASOCT), and in vivo confocal microscopy of the cornea (IVCM). Excised tissue was fixed in formalin or glutaraldehyde for immunohistochemical or transmission electron microscopic analysis, respectively.

Results:

All femtosecond laser surgeries were completed successfully using a custom-designed double lamellar keratoplasty procedure using the IntraLase iFs 150kHz femtosecond laser system (Abbott Medical Optics, Santa Ana, CA, USA). Corneal disc extractions and disc insertions were completed without complications. Immediate postoperative examination revealed variable swelling of implants, while the semi-transparent skirt could be visualized by photography. No sutures were used to retain implants. One month after implantation, all but one implant was retained, and all initially swelled implants thinned, based on ASOCT examination. Scar tissue developed at interfaces, while implant materials remained transparent to varying degrees. By IVCM, it was observed that the semi-transparent skirt began to degrade to a variable extent, and macrophages were present where biodegradation was observed. No inflammation or vascularization of implants was observed, despite the absence of postoperative steroid treatment. Three months after implantation, all implants including the autografts thinned further, macrophages were observed more frequently in association with degrading biomaterial, and both semi-transparent skirt and transparent biomaterial regions were visible. Implants were invaded by stromal cells, and a limited stromal nerve invasion of implants was also observed. At three months, almost all implanted materials remained transparent in vivo.

Conclusions:

The FLISK procedure facilitates stromal excision and replacement, without disrupting epithelium or the most anterior or posterior layers of the cornea. The surgery did not require sutures or postoperative steroid use, and did not stimulate inflammation or neovascularization on clinical observation. Various biomaterial formulations were retained for 3 months in vivo in the rabbit cornea, and slowly degraded over time while stromal cells, macrophages, and corneal nerves were recruited to restore the morphologic and physiologic corneal milieu. The model of FLISK is amenable for in vivo testing of implantable ocular biomaterials, for pre-validation of future ocular therapeutic approaches. FINANCIAL INTEREST: One of more of the authors... has significant investment interest in a company producing, developing or supplying product or procedure presented, One of more of the authors... travel has been funded, fully or partially, by a company producing, developing or supplying the product or procedure presented, One of more of the authors... research is funded, fully or partially, by a company producing, developing or supplying the product or procedure presented

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