The development of a micro-shunt made from poly(styrene-block-isobutylene-block-styrene) to treat glaucoma

Abstract

Glaucoma is the second leading cause of blindness with ∼70 million people worldwide who are blind from this disease. The currently practiced trabeculectomy surgery, the gold standard treatment used to stop the progression of vision loss, is rather draconian, traumatic to the patient and requires much surgical skill to perform. This article summarizes the more than 10-year development path of a novel device called the InnFocus MicroShunt®, which is a minimally invasive glaucoma drainage micro-tube used to shunt aqueous humor from the anterior chamber of the eye to a flap formed under the conjunctiva and Tenon's Capsule. The safety and clinical performance of this device approaches that of trabeculectomy. The impetus to develop this device stemmed from the invention of a new biomaterial called poly(styrene-block-isobutylene-block-styrene), or "SIBS." SIBS is ultra-stable with virtually no foreign body reaction in the body, which manifests in the eye as clinically insignificant inflammation and capsule formation. The quest for an easier, safer, and more effective method of treating glaucoma led to the marriage of SIBS with this glaucoma drainage micro-tube. This article summarizes the development of SIBS and the subsequent three iterations of design and four clinical trials that drove the one-year qualified success rate of the device from 43% to 100%. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 211-221, 2017.

Keywords: SIBS; biodegradation; entrepreneurship; glaucoma; trabeculectomy.

Figure 1

A simplified structure of poly(styrene‐block‐isobutylene‐block‐styrene) (SIBS) showing the central PIB block with polystyrene end segments (M ≫ N).

Figure 2

The synthesis of SIBS beginning with the di‐functional initiator—hindered dicumyl ether (HDCE), forming the di‐cation, then reacting with isobutylene (IB), then styrene to form the triblock polymer and finally quenching with methanol.

Figure 3

A section of the anterior segment of the eye where “a” points to a shunt across the trabecular meshwork to Schlemm's Canal, “b” points to a shunt from the anterior chamber to the suprachoroidal space and “c” points to a shunt from the anterior chamber to a space formed under the conjunctiva and Tenon's Capsule which, when filled with aqueous humor forms a bleb.

Figure 4

The three generations of glaucoma shunts: (A) the MIDI‐Tube used in the first Bordeaux study with the slotted inserter; (B) the MIDI‐Ray used in the first Dominican Republic study; and (C) the final design called the InnFocus MicroShunt® used thereafter.

Figure 5

Photograph of two glaucoma shunts in the same quadrant of the eye. The lower arrow points to a MIDI‐Tube (250 μm outer diameter). The upper arrow points to an InnFocus MicroShunt® (350 μm outer diameter) that was implanted 4 years later to further reduce intraocular pressure (courtesy Prof. Isabelle Riss).

Figure 6

Measured flow rate versus pressure of the InnFocus MicroShunt, which is 8.5 mm long with a lumen diameter of 70 μm. It requires approximately 5 mm Hg pressure to initiate flow through the MicroShunt.

Figure 7

Kaplan–Meier survival curves showing the qualified success rate of the four iterations of the glaucoma shunt and procedure. The final device using the InnFocus MicroShunt® with 0.4 mg/mL MMC provided near perfect results.

Figure 8

The final procedural iteration used to implant the InnFocus MicroShunt®.