CN107670107B

CN107670107B - biosynthetic cornea

Info

Publication number: CN107670107B
Application number: CN201710620903.3A
Authority: CN
Inventors: 罗伯特·C·常; 詹姆斯·W·波拉里克
Original assignee: Fibrogen China Medical Technology Development Co Ltd
Current assignee: Dianjing Biomedical Technology Suzhou Co ltd
Priority date: 2016-07-27
Filing date: 2017-07-26
Publication date: 2021-08-06
Anticipated expiration: 2037-07-26
Also published as: CN113456889B; CN107670107A; CN113456889A; HK1250668A1

Abstract

The present invention provides for the manufacture of biosynthetic corneas for providing optically clear corneal implants for use as scaffolds for regenerative repair of damaged, diseased or defective corneas.

Description

Biosynthetic cornea

Technical Field

The present invention relates to synthetic cornea replacement and provides a method of manufacturing a biosynthetic cornea for providing an optically clear corneal implant for use as a scaffold for regenerative repair of damaged, diseased or defective corneas.

Background

The cornea serves as a protective barrier for the eye and also refracts and focuses light onto the retina. Loss or distortion of optical clarity of the corneal surface due to disease or trauma is a major cause of blindness. Estimated 800 to 1000 million people worldwide are prepared to benefit from corneal transplants, but the lack of donor corneas and the associated costs limit the availability of surgery. For example, approximately 200 million people in china suffer from corneal blindness. While corneal transplantation is the standard of care for corneal blindness in the united states and some european countries, donor corneas are severely lacking in china for this procedure. According to the estimates of the World Health Organization (WHO) and the ORBIS international organization, only 5000-6000 corneal transplantation operations are performed in China every year. In other words, over 99.5% of patients are not treated. Ophthalmologists and patients are urgently awaiting alternative methods for corneal transplantation.

In expanding attempts to transplant corneas, recent efforts have focused on the development of synthetic replacement corneas. Among the various materials proposed for the manufacture of such synthetic replacement corneas, certain collagens have been used in the manufacture of synthetic corneal inlays and implants, either alone or in combination with other polymeric materials. See, e.g., international publication nos. WO 88/02622, WO 90/05755, WO 2006/015490, WO 2006/020859, and WO 2007/028258; see also, e.g., Li et al (2003) Proc Natl Acad Sci USA 100 (26): 15346-15351, Liu et al (2006) Biomacromolecules 7: 1819-1828, Liu et al (2008) Biomaterials 29: 1147 1158, Merrett et al (2008) Invest Ophthalmol Vis Sci 49 (9): 3887-3894. Recombinant Human Collagen (RHC) is considered a promising material for the manufacture of corneal implants because it is non-toxic, non-immunogenic and non-inflammatory. To date, good results have been obtained in human patients using corneal implants made of cross-linked recombinant human collagen. (see Fagerholm et al (2009) Clin Transl Sci 2 (2): 162- > 164, Fagerholm et al (2010) Sci Transl Med.2 (46): 1-8, Fagerholm et al (2014) Biomaterials 35: 2420- > 2427). However, these prior art implants have various drawbacks, including insufficient tensile strength, which prevents the use of conventional sutures. (Fagerholm et al, supra). Previous efforts to increase the tensile strength of corneal implants made of collagen have resulted in implants with reduced optical clarity.

Thus, there remains a pressing need for synthetic corneal substitutes that retain the advantages of collagen, but still achieve improved suturability, and even provide optically high clarity. The present invention meets this need by providing a biosynthetic cornea with increased optical clarity.

Disclosure of Invention

The present invention provides a biosynthetic cornea designed to produce an optically clear corneal implant. The biosynthetic corneas of the present invention are also useful as scaffolds for the regenerative repair of damaged, diseased or defective corneas. The biosynthetic corneas of the invention are made from highly purified recombinant human collagen arranged in highly dense ordered arrays of small diameter microfibers. The composition results in a biosynthetic cornea with improved suturability. Because the biosynthetic cornea of the present invention has greater optical clarity, it is an improvement over synthetic replacement corneas provided in the prior art, including synthetic replacement corneas previously made of collagen. Surprisingly, the biosynthetic cornea of the present invention provides this excellent optical clarity while allowing for higher collagen content and improved suturability as compared to prior art synthetic replacement corneas.

In a preferred embodiment, the biosynthetic cornea comprises highly purified recombinant human type III collagen. In a particular embodiment, the biosynthetic cornea consists essentially of highly purified recombinant human type III collagen. The biosynthetic corneal membranes of the invention are fabricated to produce a highly dense ordered array of small diameter direct amide crosslinked collagen microfibers. In one embodiment, the collagen microfibers of the present invention have a more consistent and narrower fiber diameter than synthetic replacement corneas provided in the prior art, including synthetic replacement corneas previously made from collagen. The diameter of the microfibers of the present invention is less than 25nm, while the diameter of the natural corneal fibers is about 25 nm. The final collagen concentration in the biosynthetic cornea is about 8-18% (w/w), specifically about 8-15%, more specifically about 8-11%. In a particularly preferred embodiment, the collagen content is about 8-9% (w/w), in particular about 8.36%. In another particularly preferred embodiment, the collagen content is about 11-15% (w/w), particularly about 11%, about 12%, about 13%, about 14% or about 15%.

In a first aspect, the invention provides a biosynthetic cornea consisting essentially of amide cross-linked recombinant human type III collagen, having a collagen content of 8-18% (w/w) and an optical density of about 0.09 or less at 300nm light wavelength. In particular embodiments, the biosynthetic cornea has a collagen content of about 8% to about 15%. In various embodiments, the collagen in the biosynthetic cornea is substantially arranged in a dense ordered array of small diameter microfibers. In various embodiments, the biosynthetic cornea has an optical density of ≦ 0.05, specifically ≦ 0.04, even more specifically ≦ 0.03 at a light wavelength of 380-750 nm.

In a second aspect, the present invention provides a biosynthetic cornea of the first aspect prepared by a process comprising the steps of: (a) mixing the recombinant human type III collagen gel with a carbodiimide crosslinker in a solution buffered to a pH of 5.2-5.3 at about 0-3 ℃ to a final collagen concentration of 8-18% (w/w), specifically 8-15%, more specifically 8-11%, and a molar ratio of collagen amine groups to carbodiimide crosslinker of about 1:0.3, about 1:0.4, about 1:0.5, or about 1: 0.6; (b) extruding the mixture into a mold having a cavity with a size, thickness and curvature suitable for a host cornea; and (c) incubation at room temperature (18-24 ℃, more preferably about 21 ℃) at about 100% humidity overnight to allow completion of the crosslinking process within the mold. In a particularly preferred embodiment, the solution is buffered to a pH of 5.2 to 5.3 using 2- (N-morpholino) ethanesulfonic acid (MES) at a crosslinking final concentration of 0.150 to 0.340M, more particularly about 0.157 to 0.277M, even more particularly about 0.165M. In a specific embodiment, the molar ratio of collagen amine groups to carbodiimide crosslinking agent is about 1: 0.4. In a specific embodiment, the mixing is performed at about 0 ℃.

In a specific embodiment of the second aspect, the biosynthetic cornea is prepared by a process comprising the steps of: (a) mixing a recombinant human type III collagen gel with N-hydroxysuccinimide (NHS) in a solution buffered to a pH of 5.2-5.3 at about 0-3 ℃ to a final collagen concentration of 8-18% (w/w), particularly 8-15%, more particularly 8-11%, with a molar ratio of collagen amine groups to NHS selected from about 1:0.3, about 1:0.4, about 1:0.5 or about 1: 0.6; (b) adding 1-ethyl-3- (3-dimethylaminopropyl) -carbodiimide (EDC) to the mixture at about 0-3 ℃ such that the molar ratio of EDC to NHS is about 1v 1; (c) mixing at about 0-3 ℃ and extruding the mixture into a mold having a cavity with a size, thickness and curvature suitable for a host cornea; and (d) incubation at about 100% humidity at room temperature overnight to allow completion of the crosslinking process within the mold. In a particularly preferred embodiment, the solution is buffered to a pH of 5.2-5.3 using MES at a final crosslinking concentration of about 0.150-0.350M, more particularly about 0.157-0.277M, and even more particularly about 0.165M. In a specific embodiment, steps (a) through (c) are performed at about 0 ℃. In a preferred aspect, the molar ratio of collagen amine groups to NHS to EDC is about 1: 0.4.

In an alternative embodiment, the collagen content of the biosynthetic cornea is 7-9% and is prepared by the process of the following steps: (a) mixing the recombinant human type III collagen gel with N-hydroxysuccinimide (NHS) in a solution buffered to pH5.1-5.3 at 0-3 ℃ to obtain a final collagen concentration of 7-9% and a collagen amino group to NHS ratio of 1: 0.4; (b) adding 1-ethyl-3- (3-dimethylaminopropyl) -carbodiimide (EDC) to the mixture at 0-3 ℃ such that the molar ratio of EDC to NHS is 1: 1; (c) mixing at 0-3 ℃ and extruding the mixture into a die having a cavity with a size, thickness and curvature suitable for a host cornea; and (d) incubating overnight at room temperature at about 100% humidity to allow completion of the crosslinking process within the mold. In a particularly preferred embodiment, the solution is buffered to a pH of 5.1-5.3 using MES having a final crosslinking concentration of about 0.150-0.350M, more particularly about 0.157-0.277M, even more particularly about 0.165M. In a specific embodiment, steps (a) through (c) are performed at about 0 ℃.

The biosynthetic corneas of the present invention provide scaffolds and templates to promote host tissue ingrowth and corneal regeneration. The biosynthetic cornea is intended to be fixed in the recipient's corneal bed after surgical removal of the anterior layer of the damaged, diseased or defective cornea. Epithelial cells will migrate along the surface of the corneal implant to form an intact re-epithelialized layer and restore the ocular tear film. At the same time, stromal cells and nerve fibers migrate into the corneal implant. The corneal implant is remodeled by ingrown cells and eventually replaced by natural corneal tissue.

In one embodiment, the biosynthetic corneas of the present invention have the shape of a contact lens and are designed to have the same curvature as a natural human cornea.

Drawings

Figure 1 shows a visual comparison of the optical clarity of a biosynthetic cornea of the invention (sample a2) compared to a representative synthetic surrogate cornea produced using methods disclosed in the art (sample B2).

FIG. 2. FIG. 2A shows the optical density (absorbance) of light through a wavelength spectrum of 300-800nm for a biosynthetic cornea of the present invention (sample A1), and for a representative alternative synthetic cornea produced using methods disclosed in the art (sample B1).

Figure 2B shows the optical density (absorbance) of light through a wavelength spectrum of 300-800nm for a biosynthetic cornea of the present invention (sample a2), and for a representative alternative synthetic cornea produced using methods disclosed in the art (sample B2).

FIG. 3 shows a side-by-side comparison of (A) a transmission electron micrograph of a biosynthetic cornea of the present invention (sample A) with (B) a transmission electron micrograph of a representative alternative synthetic cornea produced using methods disclosed in the art (sample B); bar 0.5 μm.

Figure 4 shows the optical density (absorbance) of light through a wavelength spectrum of 300-800nm for a biosynthetic cornea of the present invention (sample a1), and for representative alternative synthetic corneas produced using methods disclosed in the art (samples B3, B4, and B5), while maintaining the pH at 5.2 during manufacture.

Fig. 5 shows an exemplary configuration of a biosynthetic cornea of the present invention.

Figure 6 shows a three-dimensional representation of a biosynthetic cornea of the present invention.

Detailed Description

Before the present compositions and methods are described, it is to be understood that this invention is not limited to the particular compounds, compositions, methods, protocols, cell lines, assays, and reagents described, as these may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention, and is in no way intended to limit the scope of the present invention as set forth in the appended claims.

It must be noted that, as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods, devices, and materials are now described. All publications cited herein are incorporated by reference in their entirety for the purpose of describing and disclosing the methodologies, reagents, and tools reported in the publications that might be used in connection with the invention.

The practice of the present invention will employ, unless otherwise indicated, conventional methods of chemistry, biochemistry, molecular biology, cell biology, genetics, immunology and pharmacology, within the skill of the art. Such techniques are explained fully in the literature. (see, e.g., Troy, DB and Beringer, P., eds. (2006) Remington: pharmaceutical science and practice, 21 st edition, Lippincott Williams & Wilkins; Colwick, S., and Kaplan, N.O., EDS., methods of enzymology, Academic Press, Inc.; DMWeir and C.C.Blackwell, eds. (1986) Handbook of Experimental Immunology, Vols.I-IV, Blackwell Scientific Publications, Green, MR and Sambrook, J., eds. (2012) Molecular Cloning: A Laboratory Manual, fourth edition, Vols.I-III, Cold Spring Harbor Press; Shortrain, K., Mshy., K., Mhz., 5. biological science & S.I-II., John II, Molecular Cloning, Vol.I-IV, and so on

The present invention provides a biosynthetic cornea designed to produce an optically clear corneal implant. The present implants also serve as scaffolds for the regenerative repair of damaged, diseased or defective corneas. Biosynthetic corneas are made from high purity human collagen arranged in highly dense ordered arrays of small diameter microfibers. In particular, collagen microfibrils are arranged in a highly dense parallel array. Because the biosynthetic cornea of the present invention has greater optical clarity, it is an improvement over synthetic replacement corneas provided in the prior art, including synthetic replacement corneas previously made of collagen. Surprisingly, the biosynthetic cornea of the present invention provides such excellent optical clarity while allowing for higher collagen content and improved suturability as compared to prior art devices.

Biosynthetic corneal delineation

The biosynthetic cornea of the present invention is an optically clear corneal implant made of high purity type I or type III collagen, preferably recombinant human collagen type I or type III. In particular embodiments, the biosynthetic cornea comprises or consists essentially of high purity recombinant human type III collagen. In a preferred embodiment, the collagen used in the biosynthetic cornea of the present invention is highly purified recombinant human type III collagen produced by engineered yeast, as described in U.S. patent 5,593,859. The use of recombinant collagen produced in yeast eliminates safety concerns for contaminants derived from tissue components of human or animal origin, including, for example, transmissible spongiform encephalopathies. The final collagen concentration in the biosynthetic cornea is about 8-18% (w/w), specifically about 8-15%, more specifically about 8-11%. In a particularly preferred embodiment, the collagen content is about 8.0-9.0%, in particular about 8.36%. In another particularly preferred embodiment, the collagen content is about 11-15%, particularly about 11%, about 12%, about 13%, about 14% or about 15%. In an alternative embodiment, the final collagen concentration in the biosynthetic cornea is 7-9%.

The biosynthetic corneas of the present invention are colorless and optically clear by visual inspection. See, e.g., fig. 1, sample a 2. Typically, the biosynthetic corneas of the invention have an absorbance (optical density) of ≦ 0.09 for light wavelengths of 300 nm. In particular, for the biosynthetic cornea of the present invention, the absorbance (optical density) over the visible spectrum (380-750nm) is ≦ 0.05, specifically ≦ 0.04, even more specifically ≦ 0.03. In a preferred embodiment, the absorbance across the visible spectrum averages about 0.020 to about 0.013 (equivalent to about 95 to 97% transmission). See, e.g., fig. 2A, sample a1, and fig. 2B, sample a 2. In all examples, the white light transmission was > 87% and the backscattering was ≦ 3%.

The collagen in the biosynthetic cornea of the present invention contains direct amide cross-links between collagen molecules. Direct amide crosslinking enhances the initial structural integrity of the implant while still allowing the implanted biosynthetic cornea to be replaced over time by natural regenerative processes. The direct amide cross-linked collagen is arranged in a highly dense ordered array of small diameter collagen microfibrils. In particular, collagen microfibrils are arranged in a highly dense parallel array. See, for example, fig. 3A. This dense and ordered arrangement of collagen in a parallel array of small diameter microfibers provides optical high definition to the biosynthetic cornea of the present invention, even while increasing collagen content and thus improving structural integrity. The biosynthetic corneas of the present invention are an improvement over synthetic corneas available in the prior art by providing higher optical clarity, particularly by providing higher collagen content while maintaining optical high clarity.

In various embodiments, the biosynthetic cornea is molded into the shape of a contact lens, wherein its diameter, thickness and radius of curvature are determined based on parameters appropriate for the particular host subject. In particular embodiments, the biosynthetic cornea is designed such that its diameter, thickness, and radius of curvature conform to the natural shape of a human cornea. See, for example, fig. 5 and 6. For human subjects, the diameter of the biosynthetic cornea is made typically ≧ 10mm, particularly 10-12mm, and the thickness is about 350-550 μm, particularly about 500 μm. See, for example, fig. 5. The radius of curvature (R) of the biosynthetic cornea is about 6.5-7.8mm, in particular about 7.7 mm.

The biosynthetic cornea is designed to be fixed in the recipient's corneal bed after surgical removal of the damaged, diseased, or defective anterior corneal layer. The biosynthetic cornea may be temporarily held in place using sutures. The biosynthetic corneas of the present invention provide excellent optical clarity while allowing higher collagen content and improved suturability as compared to prior art synthetic replacement corneas. The biosynthetic cornea of the present invention supports epithelial cell migration across the outer surface of the corneal implant, allowing the reformation of an intact epithelial layer and restoring the tear film. The biosynthetic corneas of the invention also support migration of stromal cells and nerve fibers into the corneal implant. As these cells migrate, new corneal tissue will gradually form, and the biosynthetic cornea will gradually be degraded and replaced over time.

Biosynthetic corneal manufacturing

The biosynthetic corneas of the present invention can be made with collagen type I or type III collagen obtained from any source using the methods described herein, which have improved clarity over synthetic replacement corneas provided in the prior art, including synthetic replacement corneas previously made from collagen. The starting material should be of high purity and consist essentially of a single species of type I or type III collagen. Preferably, the biosynthetic cornea of the invention is made of human type I collagen or type III collagen, in particular of type recombinant human collagen type I or III. A particularly preferred starting material for biosynthetic corneal manufacture is recombinant human type III collagen produced by yeast fermentation, for example, as described in U.S. patent 5,593,859. In a particularly preferred embodiment, the biosynthetic cornea is made from recombinant human type III collagen prepared using a Pichia pastoris (Pichia pastoris) strain of human genes into which type III collagen and prolyl 4-hydroxylase have been inserted. This starting material is preferred to avoid the use of components of animal and human origin (to ensure safety) and includes numerous downstream purification steps that produce a highly pure collagen product. The purified collagen is sterile lyophilized prior to production of the biosynthetic cornea.

Biosynthetic corneal manufacturing is performed in an environment with strict sterility and particle control (ISO class 5). The lyophilized collagen was tested for collagen content, sterility and endotoxin prior to reconstitution with sufficient water for injection (WFI) to form a collagen solution. Any air bubbles are removed from the collagen solution, for example by centrifugation. Collagen crosslinking is carried out at a temperature of about 0-3 ℃, particularly at about 0 ℃, and under conditions such that no gas bubbles are introduced into the reaction. Suitable apparatus for mixing reagents to avoid the introduction of gas bubbles is provided, for example, in international publication number WO 2006/015490 (see, e.g., page 26, line 24 to page 27, line 2, and fig. 1-3).

The collagen solution is first brought to the final starting concentration in a buffer solution at a pH of 5.1-5.3, more particularly 5.2-5.3. Preferred buffer solutions contain 2- (N-morpholino) ethanesulfonic acid (MES) at a final crosslinking concentration of about 0.150 to about 0.340M, specifically about 0.157 to about 0.277M, more specifically about 0.165M. The buffer solution may also comprise N-hydroxysuccinimide (NHS) or NHS may be added to the buffered collagen solution at a later time, in either case at a molar ratio of NHS to collagen amine groups of about 0.3: 1 to about 0.6: 1, for example about 0.3: 1, about 0.4:1, about 0.5: 1 or about 0.6: 1. In particular, the molar ratio of NHS to collagen amine groups is about 0.4: 1. In an alternative embodiment where the collagen concentration of the biosynthetic cornea is 7-9%, the pH is 5.1-5.3 and the molar ratio of NHS to collagen amine groups is about 0.4: 1.

The carbodiimide crosslinking agent was then added to the collagen/NHS buffered mixture such that the molar ratio of carbodiimide crosslinking agent to NHS was about 1: 1. Water-soluble carbodiimide crosslinking reagents are preferred because unreacted reagents and by-products from the crosslinking reaction can be more easily and thoroughly removed after the formation of the biosynthetic horn. In a specific embodiment, the carbodiimide crosslinking reagent is selected from the group comprising 1-ethyl-3- (3-dimethylaminopropyl) -carbodiimide (EDC) and N-cyclohexyl-N' - (2-morpholinoethyl) -carbodiimide methyl p-toluenesulfonate (CMC). In a preferred embodiment, the carbodiimide crosslinking agent is EDC. The collagen/NHS/carbodiimide crosslinker solution is thoroughly mixed at about 0-3 c, particularly about 0 c, for no more than about 0.25-2 minutes, preferably no more than about 1 minute.

The well-mixed collagen solution is then immediately extruded into a mold having a cavity with a size, thickness and curvature suitable for the particular host cornea, and incubated overnight at room temperature (18-24 ℃, more preferably about 21 ℃) at about 100% humidity to allow the crosslinking process within the mold to complete. In-mold crosslinking enhances the structural integrity of the implant while still maintaining clarity.

The implant is then removed from the cast and washed thoroughly with Phosphate Buffered Saline (PBS) to remove all by-products of the crosslinking reaction. The biosynthetic corneas of the invention can then be tested for sterility, endotoxin, size, collagen content, melting temperature, and light transmittance. The biosynthetic corneas produced by the described methods meet at least the criteria set forth in table 1.

TABLE 1

Testing	Acceptance criteria
		Appearance of the product	Clear, colorless implants. Has no major defect
Determination of collagen concentration by refractive index	8% to 18% (w/w)
		Differential Scanning Calorimetry (DSC)	62.9 ℃ to 50.6 DEG C
Diameter of	≥10mm
		Transmittance of white light	＞87％
Back scattering	≤3％
		Endotoxin test by Limulus Amebocyte Lysate (LAL)	Less than or equal to 2.0 EU/implant
Sterility of	Is sterile

The biosynthetic corneas are stored in sterile solution, such as sterile PBS.

In an alternative embodiment where the collagen concentration of the biosynthetic cornea is 7-9%, the biosynthetic cornea is prepared by the in-mold crosslinking process described above, comprising the specific steps of: (a) mixing the recombinant human type III collagen gel and NHS in a solution buffered to pH5.1-5.3 at 0-3 ℃ to obtain a final collagen concentration of 7-9% with a ratio of collagen amino groups to NHS of 1: 0.4; (b) EDC is added to the mixture at 0-3 ℃ so that the molar ratio of EDC to NHS is 1:1, so that crosslinking occurs; (c) mixing at 0-3 ℃ and extruding the mixture into a die having a cavity with a size, thickness and curvature suitable for a host cornea; and (d) incubating overnight at room temperature at about 100% humidity to allow completion of the crosslinking process within the mold.

Biosynthetic corneal uses

The biosynthetic corneas of the invention are useful for partial thickness corneal implants for the treatment of vision impairment due to corneal dysfunction. The biosynthetic cornea provides an optically clear implant and serves as a scaffold for the regenerative repair of damaged, diseased or defective corneas. In a particular embodiment, the biosynthetic cornea is used for anterior lamellar keratoplasty. After surgical removal of the damaged, diseased or defective anterior corneal layer, a sterile implant is secured in the recipient's corneal bed, for example by suturing. The key surgical steps are as follows: (1) removing pathological corneal tissue using an Anterior Lamellar Keratoplasty (ALK) or Deep Anterior Lamellar Keratoplasty (DALK) technique; (2) cutting the biosynthetic cornea into a layered implant having a diameter 0.25mm greater than the recipient's corneal bed; (3) placing the implant on the corneal bed and the anchors with sutures; (4) an inert bandage contact lens is placed on the eye and topical steroid/antibiotic drops are applied until the contact lens and suture are removed.

Device performance

The semipermanent nature of the biosynthetic cornea of the present invention promotes tissue regeneration by migrating host corneal cells within the implant matrix, wherein the host corneal cells proliferate, slowly degrade the implant, and synthesize new corneal tissue rich in type I collagen. In addition, nerve regeneration and restoration of tear film function were observed after implantation of the biosynthetic cornea of the present invention. The biosynthetic cornea of the present invention is also an advantageous substrate that allows host epithelial cells to migrate over the outer surface of the implant, regenerating a new epithelial cell layer similar to that found in naturally occurring corneas.

Examples of the invention

The invention will be further understood by reference to the following examples, which are merely illustrative of the invention. The scope of the invention is not limited to the exemplary embodiments, which are intended as illustrations of only a single aspect of the invention.

Example 1. production of biosynthetic cornea and ophthalmic devices.

The biosynthetic cornea of the present invention is comprised of small diameter collagen microfibers arranged in a highly dense ordered array, particularly in a highly dense parallel array. The biosynthetic cornea of the present invention is an improvement in providing a higher degree of optical clarity compared to the synthetic replacement corneas of the prior art. Surprisingly, the biosynthetic corneas of the present invention provide this superior optical clarity while providing a higher collagen content and improved suturability as compared to prior art synthetic replacement corneas. A comparison of the biosynthetic corneas of the present invention with synthetic replacement corneal inlays or implants (so-called "ophthalmic devices") disclosed in the art is provided to demonstrate these improved properties.

The biosynthetic corneas of the present invention are prepared using the methods described herein, and an "ophthalmic device" is prepared using the method disclosed in international publication No. WO 2006/015490. The same recombinant human type III collagen (rhc-III) gel was used as a starting material for the biosynthesis of corneal and ophthalmic devices. While the methods described herein can be used to prepare improved biosynthetic corneas from any highly purified collagen type I or type III starting material, rhc-III is the preferred starting material for producing the optimal biosynthetic corneas of the present invention.

High purity rhc-III (FibroGen, San Francisco CA) was produced by yeast fermentation of Pichia pastoris transfected with human type III collagen gene and human prolyl 4-hydroxylase gene. See, for example, U.S. patent 5,593,859. For the purpose of ensuring safety, animal or human components are not used in the production process of the recombinant human collagen. To prepare a 20% (w/w) rhc-III gel, 700mg of freeze-dried rhc-III was dissolved and homogenized in 2.8mL water for injection (WFI). The final gel is centrifuged to remove any air bubbles if necessary. Also, 18% and 15% gels were prepared.

A. Biosynthetic cornea

A first biosynthetic cornea of the invention was made by mixing 400 μ l of 15% (w/w) rhc-III gel with 285 μ l of 2- (N-morpholino) -ethanesulfonic acid (MES) buffer, pH5.2, 0.625M at about 0 ℃. A solution of 7.5% (w/w) NHS was prepared in MES buffer pH5.2, 0.625M and a solution of 10% (w/w) EDC was prepared in MES buffer pH5.2, 0.625M, respectively. An aliquot of 14.5 μ l of NHS solution was mixed with the collagen solution at about 0 ℃ and then 18.2 μ l of EDC solution was added. The collagen/NHS/EDC solution was then mixed vigorously at about 0 ℃ for about 25 seconds. EDC: NHS: collagen-NH of the final mixture₂The molar ratio is 0.4: 1. The mixture was then poured into a plastic mold and incubated overnight at room temperature (about 21 ℃) at 100% humidity. The biosynthetic cornea was then removed from the mold and washed with PBS to remove residual crosslinking agent. The resulting biosynthetic cornea contained about 8.36% (w/w) rhc-III, and was labeled herein as sample A1.

A second biosynthetic cornea of the invention was made by mixing 520. mu.l of 20% (w/w) rhc-III gel with 150. mu.l MES buffer, pH5.2, 0.625M at about 0 ℃. A20% (w/w) solution of NHS was prepared in 0.625M MES buffer (pH5.2) and a 20% (w/w) solution of EDC was prepared in 0.625M MES buffer (pH 5.2). An aliquot of 9.5 μ l of NHS solution was mixed with the collagen solution at about 0 ℃ and then 16.0 μ l of EDC solution was added. The collagen/NHS/EDC solution was then mixed vigorously at about 0 ℃ for 25 seconds. EDC: NHS: collagen-NH of the final mixture₂The molar ratio is 0.4: 1. The mixture was then poured into a plastic mold and incubated overnight at room temperature (about 21 ℃) at 100% humidity. The biosynthetic cornea was then removed from the mold and washed with PBS to remove residual crosslinking agent. The resulting biosynthetic cornea contained about 15% (w/w) rhc-III and was designated herein as sample A2.

B. Ophthalmic apparatus of the prior art

International publication No. WO 2006/015490 ('490 publication) and international publication No. WO 2006/020859 (' 859 publication) disclose and claim ophthalmic devices comprising collagen. Both applications have the same filing date and claim the benefit of the same priority document. The disclosures of both publications are essentially identical. Thus, the methods disclosed in the ' 490 publication referred to herein may also be found in the ' 859 publication, and reference to the ' 490 publication is made merely for convenience and is not meant to convey any other meaning.

Although the' 490 publication provides several examples of ophthalmic devices with collagen from various sources including pigs and cattle, only examples 18 and 21 use recombinant human collagen, and only example 21 uses rhc-III. In example 21, 0.625M 2- (N-morpholino) -ethanesulfonic acid (MES) was used without pH adjustment with NaOH. Without adjustment, the pH of the 0.625M MES solution was

And the EDC/NHS solution is very unstable (continuous bubbling) and a stable EDC/NHS solution for crosslinking cannot be prepared. Therefore, WFI (pH) was used in this example

) Instead of 0.625M MES, a stable EDC/NHS solution for crosslinking was prepared. This adjustment is consistent with scientific publications written by some authors of '490 and' 859, in which collagen is crosslinked in an "aqueous solution" using EDC/NHS. (see, e.g., Merrett et al (2008) Invest Ophthalmol Vis Sci 49: 3887-. Example 21 three different molar ratios of EDC/NHS to collagen-NH were also used₂1:1, 2: 1 and 3: 1, but no differences were reported.

An 8.36% (w/w) collagen ophthalmic device was manufactured by mixing 300. mu.l of 18% (w/w) rhc-III gel with 300. mu.l of 0.625M MES at 0-5 ℃. The crosslinking solution was prepared by dissolving 33.5mg EDC and 20.1mg NHS in 125. mu.l WFI at 0-5 deg.C, then vigorously mixing 57. mu.l EDC/NHS solution with the collagen solution at 0-5 deg.C for 25 seconds. Final mixtureEDC, NHS, collagen-NH₂The ratio was 3.6: 1. The mixture was then cast into a plastic mold and incubated at 100% humidity at room temperature for 16 hours followed by incubation at 37 ℃ for another 5 hours. The ophthalmic device was then removed from the mold and washed with PBS to remove residual crosslinker. The resulting ophthalmic device contained about 8.36% (w/w) rhc-III, and is designated herein as sample B1.

A 14% collagen content device was attempted using the method of example 21 in the' 490 publication. Ophthalmic devices were made by mixing 490. mu.l of 20% (w/w) rhc-III gel with 150. mu.l WFI at 0-5 ℃. The crosslinking solution was prepared by dissolving 98.6mg EDC and 59.2mg NHS in 375. mu.l WFI at 0-5 deg.C, then 57. mu.l EDC/NHS solution was mixed vigorously with the collagen solution at 0-5 deg.C for 25 seconds. EDC: NHS: collagen-NH of the final mixture₂The ratio is 2: 1. The mixture was then cast into a plastic mold and incubated at 100% humidity at room temperature for 16 hours, followed by incubation at 37 ℃ for another 5 hours. The ophthalmic device was then removed from the mold and washed with PBS to remove residual crosslinker. The resulting ophthalmic device contained about 14% (w/w) rhc-III, and is designated herein as sample B2.

For direct comparison with the biosynthetic corneas of the present invention, ophthalmic devices having a final collagen content of 8.36% (w/w) were also prepared using the above method, the solution being maintained at pH5.2, NHS/EDC/collagen-NH₂The molar ratio is based on example 21 in the' 490 publication. Although the '490 publication reports ratios of 3: 1, 2: 1, and 1:1, the ratios found based on actual calculations of the' 490 publication are 3.6: 1, 2.4: 1, and 1.2: 1, respectively. Samples B3, B4, and B5 were ophthalmic devices fabricated at pH5.2 using ratios of 3.6: 1, 2.4: 1, and 1.2: 1, respectively.

Example 2 comparison between biosynthetic cornea and ophthalmic device.

The transparency and clarity of the biosynthetic cornea and ophthalmic device were examined by visual inspection and absorbance of light across the visible spectrum. As shown in fig. 1, sample a2 was more transparent and exhibited higher clarity than sample B2 by visual inspection.

For the absorbance test, samples a1, a2, B1 and B2 were equilibrated with PBS buffer at room temperature. The equilibrated samples were then placed in 1.5ml semimicroscale disposable cuvettes (Brand GMBH & Co. KG, Germany) and scanned from 300nm to 800nm at a rate of 10nm/sec using a Beckman DU530 spectrometer (Beckman Coulter, Inc., Brea CA). The absorbance (optical density) is plotted against wavelength and used as an indicator of sample clarity. Generally, the lower the absorbance of the sample, the greater the optical clarity. As shown in fig. 2A, sample a1 has a lower absorbance profile than sample B1, indicating that the biosynthetic cornea of the present invention has improved optical clarity over ophthalmic devices made according to prior art methods. Specifically, the absorbance range of sample A1 in the visible spectrum (380-750nm) was 0.024 to 0.009 (average 0.013. + -. 0.004), while the absorbance range of sample B1 was 0.057 to 0.018 (average 0.031. + -. 0.011). As shown in fig. 2B, sample a2 has a lower absorbance profile than sample B2, indicating that the biosynthetic cornea of the present invention has improved optical clarity over ophthalmic devices made according to prior art methods. Specifically, the absorbance range of sample a2 over the visible spectrum was 0.029 to 0.006 (average 0.013 ± 0.006), while the absorbance range of sample B2 was 0.423 to 0.127 (average 0.225 ± 0.085). The absorbance of samples a1 and a2 was equal to about 97% white light transmission. In addition, the biosynthetic corneas of the invention maintain a high level of clarity over a final collagen concentration range of 8.36-15% (w/w). The ability to prepare high-definition, biosynthetic corneas with reduced sample-to-sample variation is important to the development of commercial manufacturing protocols.

To further understand the physical properties that provide improved clarity in the biosynthetic corneas of the present invention, sample a2 and sample B2 were further analyzed by transmission electron microscopy. As shown in fig. 3A, sample a2 shows a highly dense ordered array of small diameter collagen microfibers, particularly a highly dense parallel array of small diameter microfibers. In contrast, as shown in fig. 3B, sample B2 shows a more random arrangement of collagen microfibers with greater variability in orientation and diameter. Because normal corneal stroma is characterized by a uniform distribution of small diameter microfibers regularly packed within the sheet (see, e.g., Hassell and Birk (2010) Exp Eye Res 91 (3): 326-335), sample A2 more closely reflects the structural properties of normal cornea.

Example 3. crosslinking parameters for production of biosynthetic corneas.

In developing the biosynthetic corneas of the present invention, experiments were conducted to identify the parameters required to reproducibly produce a biosynthetic cornea with optically high definition, including a high collagen content biosynthetic cornea with optically high definition. One specific parameter investigated is the pH sensitivity of the procedure used to make the biosynthetic cornea. The '490 publication generally states that "the pH used in making such devices is generally less than about 6.0, e.g., the pH may be between about 5.0 and about 5.5" (see, e.g., page 19, lines 3 through 5 of the' 490 publication). Most of the examples provided in the' 490 publication are performed at pH5.5, while some examples simply indicate that the pH is adjusted to about 5. No preference is disclosed.

To investigate the effect of the pH of the crosslinking reaction on the optical clarity of the biosynthetic cornea, a series of crosslinking reactions were performed using the general procedure disclosed in example 1A above, with the pH of the crosslinking reaction being controlled at pH5.5, pH5.4, pH 5.3 or pH 5.2. Experiments were performed using an initial concentration of 0.625M MES (final concentration of about 0.165M MES in the crosslinking reaction), but final concentrations in the range of 0.157-0.277M produced similar results. As shown in table I, significant effects were observed at different pH levels, both clarity (measured by mean absorbance) and reproducibility (measured by standard deviation between samples, N ═ 4) improved when crosslinking was performed at lower pH. Both pH5.2 and pH 5.3 produced significantly higher definition biosynthetic corneas, and higher reproducibility between experiments than reactions performed at pH5.4 or pH 5.5.

Table 1. absorbance of crosslinked biosynthetic corneas at the indicated pH.

Wavelength (nm)	pH 5.2	pH 5.3	pH 5.4	pH 5.5
					800	0.011±0.0015	0.014±0.0017	0.023±0.0085	0.047±0.0235
700	0.014±0.0020	0.018±0.0014	0.028±0.0072	0.052±0.0218
					600	0.018±0.0014	0.025±0.0017	0.036±0.0079	0.062±0.0201
500	0.025±0.0017	0.035±0.0017	0.049±0.0061	0.080±0.0192
					400	0.042±0.0019	0.056±0.0021	0.075±0.0057	0.115±0.0197
300	0.116±0.0061	0.141±0.0046	0.176±0.0109	0.245±0.0210

The ability to produce high-definition, biosynthetic corneas with reduced sample-to-sample variability is important to the development of commercial manufacturing protocols. The biosynthetic corneas of the invention are manufactured in a process that includes crosslinking collagen at a pH of 5.2-5.3.

The biosynthetic corneas of the present invention were compared to the ophthalmic devices manufactured as above, based on the improved clarity observed with pH5.2, except that the pH was maintained at 5.2. A clarity comparison of sample a1 with samples B3, B4 and B5 is shown in fig. 4. As can be seen from the figure, sample a1 has a lower absorbance profile than samples B3, B4 and B5, demonstrating improved optical clarity of the biosynthetic cornea of the present invention compared to ophthalmic devices made according to prior art methods (except for controlling the pH at 5.2 during manufacture). Specifically, as in example 2, the absorbance range of sample A1 in the visible spectrum (380-; the absorbance range of sample B4 was 0.061 to 0.015 (mean 0.026 ± 0.009); the absorbance of sample B5 was 0.049 to 0.013 (average 0.096 ± 0.007). Thus, while pH is a factor in improving the biosynthetic cornea of the present invention, additional factors in the process result in improved clarity of the biosynthetic cornea relative to prior art ophthalmic devices.

General parameters that distinguish the process for making the biosynthetic cornea of the present invention from ophthalmic devices as disclosed in the' 490 publication are shown in table 2.

TABLE 2 comparison of biosynthetic corneal and ophthalmic device procedures

EXAMPLE 4 biosynthetic corneal features

The biosynthetic cornea of the invention has the following characteristics:

sources of materials: the high purity collagen may be obtained from any suitable source, and is preferably a single collagen type, particularly type I or type III, most particularly type I or type III recombinant human collagen. In a preferred embodiment, the collagen is recombinant human type III collagen. In the most preferred embodiment, recombinant human type III collagen for use in the biosynthesis of the cornea is produced by yeast fermentation, in particular using a pichia pastoris strain transfected with a gene encoding human type III collagen and a gene encoding human prolyl 4-hydroxylase. For the purpose of safety assurance, it is preferable that animal or human components are not used in the production process of the recombinant human collagen.

Composition comprising a metal oxide and a metal oxide: the biosynthetic cornea comprises or consists essentially of 8-18% (w/w) amide cross-linked type I or type III collagen, in particular recombinant human collagen type I or type III, preferably recombinant human collagen type III, wherein the cross-linking reaction is carried out at a fixed ph of 5.2-5.3 and a temperature of 0-3 ℃. The biosynthetic corneas are stored in a solution that is kept sterile, for example, in sterile phosphate buffered solution (pH 7.4, 0.144g/l potassium dihydrogen phosphate, 9.0g/l sodium chloride, and 0.795g/l disodium hydrogen phosphate).

Appearance of the product: colorless and transparent, without obvious defects.

Diameter of：≥10mm

Thickness of: 350-550 μm: alternatively 468-609 μm.

Thermal stability: the melting temperature Tm is 62.9-50.6 ℃ as measured using differential scanning calorimetry.

White light conductivity：＞87％

Rate of backscattering：≤3％

Collagen content: 8-18% (w/w), more particularly 8-15%; and 7-9% is selected as the other.

Biological Properties: biosynthetic corneas are sterile and non-pyrogenic. The endotoxin content in the product is not more than 2.0 EU/unit. There is no delayed hypersensitivity, acute systemic toxicity or subchronic toxicity.

Implant: the extent of inflammatory cell response at 12 weeks post-implantation did not exceed grade 1, after 1, 4 and 12 weeks of subcutaneous implantation of the product, and corresponding observations of the product.

Example 5 biosynthesis of cornea

The biosynthetic cornea of the present invention is produced by the following steps. An aliquot of rhc-III gel (10.5% -13.5% collagen) was mixed with 0.625M MES buffer (pH5.2) to a target collagen concentration of 8.0%. 1 part of the NHS solution was mixed with 9 parts of 0.625M MES buffer (pH5.2) by weight to prepare a 10% NHS solution. An aliquot of the 10% NHS solution was mixed with the collagen solution in a ratio of 0.4: 1(0.4 moles NHS to 1 mole collagen amine groups). The NHS-rhc-III mixture was cooled to 0.0 ℃ for at least 45 minutes. By weight, 1 part of the EDC solution was mixed with 9 parts of 0.625M MES buffer (pH5.2) to prepare a 10% EDC solution. Fresh 10% EDC solutions were prepared for each aliquot of rhc-III gel and used within 10 minutes from preparation. An aliquot of a 10% solution of EDC was added to the cooled NHS-rhc-III mixture in a ratio of 0.4: 1(0.4 moles of EDC to 1 mole of collagen amine groups). EDC: NHS: collagen-NH of the final mixture₂The ratio is 0.4: 1. The collagen/NHS/EDC solution was then mixed vigorously at 0.0 ℃ for 30 seconds, then immediately poured into a plastic mold and transferred to a sterile environment humidified to saturation with water for injection (WFI) and incubated overnight at ambient temperature. Then, the user can use the device to perform the operation,the biosynthetic cornea was removed from the mold and washed three times with 7.5mL of PBS to remove any residual crosslinking agent. The biosynthetic corneas were stored in PBS. The target collagen concentration of the biosynthetic cornea was 8.0%.

The resulting biosynthetic cornea had the following characteristics:

TABLE 3 biosynthetic corneal characteristics

Parameter(s)	First batch	Second batch
			Appearance of the product	Clear, colorless and free of defects	Clear, colorless and free of defects
Concentration of collagen¹	8.7％	8.6％
			Thermal stability²	54℃	54.4℃
Diameter of	12mm	12mm
			Transmittance of white light	97％	97％
Back scattering	0％
			Thickness of	0.581-0.582mm	0.510mm

¹By refractive index measurement

²By differential scanning calorimetry

Claims

1. A biosynthetic cornea comprised of amide-crosslinked recombinant human type III collagen, having a collagen content of 8% to 18% (w/w) and having an optical density at a light wavelength of 300nm ≦ 0.09, prepared by a process comprising the steps of:

(a) mixing the recombinant human type III collagen gel with NHS in a solution buffered to pH5.2-5.3 at 0-3 ℃ to obtain a final collagen concentration of 8-18% (w/w) with a molar ratio of collagen amine groups to NHS selected from 1:0.3, 1:0.4, 1:0.5 or 1: 0.6;

(b) adding EDC to the mixture at 0-3 ℃ such that the molar ratio of EDC to NHS is 1:1, such that crosslinking occurs;

(c) mixing at 0-3 ℃ and extruding the mixture into a die having a cavity with a size, thickness and curvature suitable for a host cornea; and

(d) incubate at 100% humidity at room temperature overnight to allow completion of the crosslinking process within the mold.

2. The biosynthetic cornea of claim 1, wherein the collagen content is 8% to 15% (w/w).

3. The biosynthetic cornea of claim 1, wherein said recombinant human type III collagen is arranged in a dense ordered array of small diameter microfibers.

4. The biosynthetic cornea of claim 1, wherein said optical density is less than or equal to 0.05 at a light wavelength of 380-750 nm.

5. The biosynthetic cornea of claim 1, wherein the solution is buffered to pH5.2-5.3 with MES at a cross-linking final concentration of 0.150-0.350M.

6. The biosynthetic cornea of claim 5, wherein said cross-linking final concentration of MES is 0.157-0.277M.

7. The biosynthetic cornea of claim 1, wherein the final collagen concentration is 8-15% (w/w).

8. The biosynthetic cornea of claim 1, wherein the collagen amine group to NHS to EDC molar ratio is 1:0.4: 0.4.

9. The biosynthetic cornea of claim 1, wherein steps (a) through (c) occur at 0 ℃.

10. The biosynthetic cornea of claim 1, prepared by a process comprising:

(i) by mixing recombinant human type III collagen gel with MES buffer solution (pH5.2, 0.625M) at 0 deg.C;

(ii) preparing 7.5% (w/w) NHS solution in MES buffer of pH5.2, 0.625M, and 10% (w/w) EDC solution in MES buffer of pH5.2, 0.625M, respectively;

(iii) mixing the aliquots of NHS solution with collagen solution at 0 ℃;

(iv) adding an EDC solution; and

(v) vigorously mixing the collagen/NHS/EDC solution at 0 deg.C;

wherein the EDC of the final mixture is NHS collagen-NH₂The molar ratio was 0.4:0.4: 1.

11. A biosynthetic cornea, prepared by a process comprising:

(a) mixing the recombinant human type III collagen gel with NHS in a solution buffered to pH5.1-5.3 at 0-3 ℃ to obtain a final collagen concentration of 7-9% (w/w) with a collagen amine group to NHS molar ratio of 1: 0.4;