Development of a Novel Valve-Controlled Drug-Elutable Microstent for Microinvasive Glaucoma Surgery: In Vitro and Preclinical In Vivo Studies

Purpose: Microinvasive glaucoma surgery (MIGS) has become an important treatment approach for primary open-angle glaucoma, although the safe and long-term effective lowering of intraocular pressure with currently available implants for MIGS is not yet achieved to a satisfactory extent. The study focusses on the development and in vitro and in vivo testing of a novel microstent for MIGS. Methods: A silicone elastomer-based microstent was developed. Implants were manufactured using dip coating, fs-laser cutting, and spray coating. Within the current study no antifibrotic drug was loaded into the device. Sterilized microstents were analyzed in vitro regarding pressure–flow characteristics and biocompatibility. Six New Zealand white rabbits were implanted with a microstent draining the aqueous humor from the anterior chamber into the subconjunctival space. Drainage efficacy was evaluated using oculopressure tonometry as a transient glaucoma model. Noninvasive imaging was performed. Results: Microstents were manufactured successfully and characterized in vitro. Implantation in vivo was successful for four animals with additional device fixation. Without additional fixation, dislocation of microstents was found in two animals. Safe and effective intraocular pressure reduction was observed for the four eyes with correctly implanted microstent during the 6-month trial period. Conclusions: The described microstent represents an innovative treatment approach for MIGS. The incorporation of a selectively antifibrotic drug into the microstent drugelutable coating will be addressed in future investigations. Translational Relevance: The current preclinical study successfully provided proof of concept for our microstent for MIGS which is suitable for safe and effective intraocular pressure reduction and offers promising perspectives for the clinical management of glaucoma

Monitoring of oxidative and metabolic stress during cardiac surgery by means of breath biomarkers: an observational study

Research articl

Application of 3R principles in small animal GLP testing of biomaterials

On the protection of animals used for scientific purposes, the EU Parliament adopted Directive 2010/63/EU. The essential factor is the 3R principle: Replacement, Reduction and Refinement. In 2013, the third amendment to the German Animal Welfare Act was revised and adapted to the European Directive. The majority of animals in science are used in basic research, as well as in translational and applied research. In medical research, animal experimentation is conducted to clarify previously unknown life processes and basic biological relationships, in order to improve diagnostics and treatment of human diseases. Before an animal experiment can be performed, it must be reported to and approved by the responsible authorities. The planned research project must be justified scientifically, and it must be demonstrated that the personnel and spatial/ technical prerequisites are in place to successfully complete the project. If all conditions are met, the approval can be granted, but may be subject to conditions. The guiding principle of essentiality also affects the procedure of the experiments: The number of animals used and the pain, suffering and damage caused to these animals must be limited to what is absolutely necessary. In this context, the 3R principle has to be applied. To obtain reliable results, it is essential that the laboratory animals are in normal physiological conditions and free of pain and fear. Scientific interest and animal welfare are therefore not in opposition, but rather mutually dependent. In our GLP (Good Laboratory Practice) laboratory we test new drug release systems for different biomedical applications in rabbits after careful selection of the animal model. Stress during animal experiments must be avoided as far as possible. Providing pain-killers and ensuring the best possible husbandry and care conditions are crucial for the animal’s wellbeing and absence of pain and anxiety. In the present work we report our different experience in a GLPcertified biomaterial test laboratory

Vascular response towards biodegradable sirolimus-eluting polymeric scaffolds in the porcine model

In this study, PLLA-based sirolimus-eluting polymer scaffolds and permanent bare-metal stents (316L) were implanted interventionally into both common carotid arteries (CCA) of 6 female pigs via the left common iliac artery (8F-sheath). The pigs were administered dual antiplatelet drugs peroral starting 3 days before the procedure until the end of the study. Stented CCA segments were explanted after 12 weeks, and processed for quantitative histomorphometry, and estimation of vascular inflammation and injury scores. SIR/polymer scaffolds showed a decreased residual lumen area and higher restenosis after 12 weeks (4.45 ± 2.23 mm² and 61.68 ± 22.39%) as compared to the 316L reference stent (16.53 ± 1.23 mm² and 6.65 ± 1.30%). After 12 weeks, inflammation score and vascular injury score were higher in the SIR/polymer group (1.90 ± 1.15 and 1.26 ± 0.87) compared to the 316L group (0.57 ± 0.37 and 0.83 ± 0.34)

Quantification method for timolol from in vivo samples for the development of a new glaucoma drug depot

Glaucoma is the second most common cause of blindness. An increased intraocular pressure is the only treatable symptom of glaucoma. Because patients often exhibit a poor therapy adherence, a drug depot consisting of ELA-NCO and hyaluronic acid with timolol was developed to ensure sustained drug release. This drug depot is formed by in situ polymerisation after injection into the subconjunctival space. To test the in vivo drug release of timolol in serum and aqueous humour, a liquid chromatography mass spectrometry (LCMS) method was developed and tested using spike- and recovery experiments, and on in vivo samples after topical application. Samples of serum and aqueous humour were taken from New Zealand White rabbits. For topical application, a commercially available formulation of timolol was used. This study presents results concerning the recovery of timolol from spiked samples. Serum and aqueous humour samples were spiked with timolol maleate to a final concentration of 50 ng/mL. Subsequently, the samples were extracted and analysed by LCMS. External calibration of the developed method showed high linearity. Recovery experiments showed no loss of timolol. Hence, the extraction method is robust and able to recover the whole amount of timolol from aqueous humour and serum

Development of a limbal fixation mechanism for a minimally invasive implantable glaucoma microstent

Glaucoma represents a chronic eye disease that becomes increasingly prevalent worldwide. Therapies are commonly based on the reduction of intraocular pressure (IOP). Implant devices for micro-invasive glaucoma surgery (MIGS) represent a promising therapy option in refractory cases but suffer from limitations in long term efficacy or from dislocation associated complications. Our approach of an innovative drug-eluting glaucoma microstent for MIGS was presented previously. Within the current work we developed concepts and prototypes of a mechanism for the fixation of our glaucoma microstent in the region of the corneal limbus. A tripod and a haptics design of the fixation mechanism were developed and manufactured. Semifinished products were tested with regard to dimensional stability and mechanical properties according to the standard ANSI Z80.27-2014. Considering the mechanical properties of ocular target tissues, a gelatin based in vitro model for the measurement of microstent retention force was developed. Retention force testing of microstent prototypes in vitro resulted in a proof of concept for the fixation mechanism. Future studies will focus on the use of smaller fixation fibers, for example commercially available suture material, and on an overall miniaturization of the fixation mechanism enabling the use of our applicator device with a 22G x 1½” cannula