| 1. |
- Ahn, Jae-Il, et al.
(författare)
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Crosslinked collagen hydrogels as corneal implants: Effects of sterically bulky vs. non-bulky carbodiimides as crosslinkers
- 2013
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Ingår i: Acta Biomaterialia. - : Elsevier. - 1742-7061 .- 1878-7568. ; 9:8, s. 7796-7805
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Tidskriftsartikel (refereegranskat)abstract
- We have previously shown that recombinant human collagen can be crosslinked with N-(3-dimethylaminopropyl)-N-ethylcarbodiimide (EDC) to fabricate transparent hydrogels possessing the shape and dimensions of the human cornea. These corneal implants have been tested in a Phase I human clinical study. Although these hydrogels successfully promoted corneal tissue and nerve regeneration, the gelling kinetics were difficult to control during the manufacture of the implants. An alternative carbodiimide capable of producing hydrogels of similar characteristics as EDC in terms of strength and biocompatibility, but with a longer gelation time would be a desirable alternative. Here, we compared the crosslinking kinetics and properties of hydrogels crosslinked with a sterically bulky carbodiimide, N-Cyclohexyl-N-(2-morpholinoethyl) carbodiimide metho-p-toluenesulfonate (CMC), with that of EDC. CMC crosslinking was possible at ambient temperature whereas the EDC reaction was too rapid to control and had to be carried out at low temperatures. The highest tensile strength obtained using optimized formulations were equivalent, although CMC crosslinked hydrogels were found to be stiffer. The collagenase resistance of CMC crosslinked hydrogels was superior to that of EDC crosslinked hydrogels while biocompatibility was similar. We are also able to substitute porcine collagen with recombinant human collagen and show that the in vivo performance of both resulting hydrogels as full-thickness corneal implants is comparable in a mouse model of an orthotopic corneal graft. In conclusion, CMC is a viable alternative to EDC as a crosslinker for collagen-based biomaterials for use as corneal implants, and potentially for use in other tissue engineering applications.
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| 2. |
- Fagerholm, Per, et al.
(författare)
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A biosynthetic alternative to human donor tissue for inducing corneal regeneration : 24-month follow-up of a phase 1 clinical study
- 2010
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Ingår i: Science translational medicine. - : American Association for the Advancement of Science (AAAS). - 1946-6234 .- 1946-6242. ; 2:46, s. 46-61
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Tidskriftsartikel (refereegranskat)abstract
- Corneas from human donors are used to replace damaged tissue and treat corneal blindness, but there is a severe worldwide shortage of donor corneas. We conducted a phase 1 clinical study in which biosynthetic mimics of corneal extracellular matrix were implanted to replace the pathologic anterior cornea of 10 patients who had significant vision loss, with the aim of facilitating endogenous tissue regeneration without the use of human donor tissue. The biosynthetic implants remained stably integrated and avascular for 24 months after surgery, without the need for long-term use of the steroid immunosuppression that is required for traditional allotransplantation. Corneal reepithelialization occurred in all patients, although a delay in epithelial closure as a result of the overlying retaining sutures led to early, localized implant thinning and fibrosis in some patients. The tear film was restored, and stromal cells were recruited into the implant in all patients. Nerve regeneration was also observed and touch sensitivity was restored, both to an equal or to a greater degree than is seen with human donor tissue. Vision at 24 months improved from preoperative values in six patients. With further optimization, biosynthetic corneal implants could offer a safe and effective alternative to the implantation of human tissue to help address the current donor cornea shortage.
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| 3. |
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| 4. |
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| 5. |
- Fagerholm, Per, et al.
(författare)
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Stable corneal regeneration four years after implantation of a cell-free recombinant human collagen scaffold
- 2014
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Ingår i: Biomaterials. - : Elsevier. - 0142-9612 .- 1878-5905. ; 35:8, s. 2420-2427
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Tidskriftsartikel (refereegranskat)abstract
- We developed cell-free implants, comprising carbodiimide crosslinked recombinant human collagen (RHC), to enable corneal regeneration by endogenous cell recruitment, to address the worldwide shortage of donor corneas. Patients were grafted with RHC implants. Over four years, the regenerated neo-corneas were stably integrated without rejection, without the long immunosuppression regime needed by donor cornea patients. There was no recruitment of inflammatory dendritic cells into the implant area, whereas, even with immunosuppression, donor cornea recipients showed dendritic cell migration into the central cornea and a rejection episode was observed. Regeneration as evidenced by continued nerve and stromal cell repopulation occurred over the four years to approximate the micro-architecture of healthy corneas. Histopathology of a regenerated, clear cornea from a regrafted patient showed normal corneal architecture. Donor human cornea grafted eyes had abnormally tortuous nerves and stromal cell death was found. Implanted patients had a 4-year average corrected visual acuity of 20/54 and gained more than 5 Snellen lines of vision on an eye chart. The visual acuity can be improved with more robust materials for better shape retention. Nevertheless, these RHC implants can achieve stable regeneration and therefore, represent a potentially safe alternative to donor organ transplantation.
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| 6. |
- Hackett, Joanne M., et al.
(författare)
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Biosynthetic corneal implants for replacement of pathologic corneal tissue : performance in a controlled rabbit alkali burn model
- 2011
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Ingår i: Investigative Ophthalmology and Visual Science. - : Research in Vision and Opthalmology. - 0146-0404 .- 1552-5783. ; 52:2, s. 651-657
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To evaluate the performance of structurally reinforced, stabilized recombinant human collagen-phosphorylcholine (RHCIII-MPC) hydrogels as corneal substitutes in a rabbit model of severe corneal damage. Methods: One eye each of 12 rabbits received a deep corneal alkali wound. Four corneas were implanted with RHCIII-MPC hydrogels. The other eight control corneas were implanted with either allografts or a simple crosslinked RHCIII hydrogel. In all cases, 6.25 mm diameter, 350 µm thick buttons were implanted by anterior lamellar keratoplasty to replace damaged corneal tissue. Implants were followed for nine months by clinical examination and in vivo confocal microscopy, after which implanted corneas were removed and processed for histopathological and ultrastructural examination. Results: Alkali exposure induced extensive central corneal scarring, ocular surface irregularity, and neovascularization in one case. All implants showed complete epithelial coverage by four weeks post-operative, but with accompanying suture-induced vascularization in 6/12 cases. A stable, stratified epithelium with hemidesmosomal adhesion complexes regenerated over all implants, and subbasal nerve regeneration was observed in allograft and RHCIII-MPC implants. Initially acellular biosynthetic implants were populated with host-derived keratocytes as stromal haze subsided and stromal collagen was remodeled. Notably, RHCIII-MPC implants exhibited resistance to vascular ingrowth while supporting endogenous cell and nerve repopulation. Conclusion: Biosynthetic implants based on RHC promoted cell and nerve repopulation in alkali burned rabbit eyes. In RHCIII-MPC implants, evidence of an enhanced resistance to neovascularization was additionally noted.
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| 7. |
- Islam, Mohammad Mirazul, et al.
(författare)
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Fabrication of a human recombinant collagen-based corneal substitute using carbodiimide chemistry
- 2013
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Ingår i: Methods in Molecular Biology. - Totowa, NJ : Humana Press. - 1064-3745 .- 1940-6029. - 9781627034319 ; 1014, s. 157-164
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Tidskriftsartikel (refereegranskat)abstract
- Human recombinant collagen can be cross-linked with a variety of chemical cross-linking agents. Cross-linking methods can be tuned to confer collagen-based scaffolds with specific physical properties, improved antigenicity and thermal stability without impeding the ability of the material to integrate into the surrounding tissue and to promote regeneration. Here, we describe a method to cross-link human recombinant collagen using a water soluble carbodiimide. Carbodiimides are referred to as zero-length cross-linking agents as they are not incorporated into the final cross-link and thus pose minimal risk with respect to cytotoxicity. The resulting collagen-based scaffold possesses properties comparable to that of the human cornea and is thus suitable for use as a corneal substitute.
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| 8. |
- Kozak Ljunggren, Monika, et al.
(författare)
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Effect of Surgical Technique on Corneal Implant Performance.
- 2014
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Ingår i: Translational Vision Science & Technology. - : Association for Research in Vision and Ophthalmology (ARVO). - 2164-2591. ; 3:2
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: Our aim was to determine the effect of a surgical technique on biomaterial implant performance, specifically graft retention.METHODS: Twelve mini pigs were implanted with cell-free, 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) cross-linked recombinant human collagen type III (RHCIII) hydrogels as substitutes for donor corneal allografts using overlying sutures with or without human amniotic membrane (HAM) versus interrupted sutures with HAM. The effects of the retention method were compared as well as the effects of collagen concentration (13.7% to 15% RHCIII).RESULTS: All implanted corneas showed initial haze that cleared with time, resulting in corneas with optical clarity matching those of untreated controls. Biochemical analysis showed that by 12 months post operation, the initial RHCIII implants had been completely remodeled, as type I collagen, was the major collagenous protein detected, whereas no RHCIII could be detected. Histological analysis showed all implanted corneas exhibited regeneration of epithelial and stromal layers as well as nerves, along with touch sensitivity and tear production. Most neovascularization was seen in corneas stabilized by interrupted sutures.CONCLUSIONS: This showed that the surgical technique used does have a significant effect on the overall performance of corneal implants, overlying sutures caused less vascularization than interrupted sutures.TRANSLATIONAL RELEVANCE: Understanding the significance of the suturing technique can aid the selection of the most appropriate procedure when implanting artificial corneal substitutes. The same degree of regeneration, despite a higher collagen content indicates that future material development can progress toward stronger, more resistant implants.
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| 9. |
- Lagali, Neil, et al.
(författare)
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Innervation of tissue-engineered recombinant human collagen-based corneal substitutes : A comparative in vivo confocal microscopy study
- 2008
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Ingår i: Investigative Ophthalmology and Visual Science. - : Association for Research in Vision and Ophthalmology (ARVO). - 0146-0404 .- 1552-5783. ; 49:9, s. 3895-3902
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE. To compare reinnervation in recombinant human collagen-based corneal substitutes with allografts during a 1-year postimplantation follow-up period in pigs. A retrospective comparison to innervation in porcine collagen-based biosynthetic grafts was also performed. METHODS. Pigs received a corneal allograft or a substitute made of either recombinant human type-I or -III collagen. In vivo confocal microscopic examination of the central cornea of surgical and untouched control eyes before surgery and at 2, 6, and 12 months after surgery was performed to quantify the number, density, and diameter of nerves at various corneal depths. RESULTS. By 12 months after surgery, the number and density of regenerated nerves in the anterior and deep anterior corneal stroma recovered to preoperative and control levels in both types of substitute grafts and in the allografts. In the subepithelial and subbasal regions, however, significantly fewer nerves were detected relative to those in control subjects at 12 months, regardless of graft type ( P < 0.05), similar to the behavior of porcine collagen-based biosynthetic grafts. An absence of thick stromal nerve trunks (diameter, > 10 mu m) in all grafts, irrespective of material type, indicated that nerve regeneration in grafts was accompanied by persistent morphologic changes. CONCLUSIONS. Nerve regeneration in recombinant human collagen-based biosynthetic corneal grafts proceeded similarly to that in allograft tissue, demonstrating the suitability of recombinant human collagen constructs as nerve-friendly corneal substitutes. Furthermore, only minor differences were noted between type-I and -III collagen grafts, indicating an insensitivity of nerve regeneration to initial collagen type.
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| 10. |
- Liu, Wenguang, et al.
(författare)
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Recombinant human collagen for tissue engineered corneal substitutes
- 2008
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Ingår i: Biomaterials. - : Elsevier BV. - 0142-9612 .- 1878-5905. ; 29:9, s. 1147-1158
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Tidskriftsartikel (refereegranskat)abstract
- We successfully fabricated transparent, robust hydrogels as corneal substitutes from concentrated recombinant human type I and type III collagen solutions crosslinked with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS). White light transmission through these gels is comparable or superior to that of human corneas. Hydrogels from both type I and type III collagens supported in vitro epithelium and nerve over-growth. While both these biocompatible hydrogels have adequate tensile strength and elasticity for surgical manipulation, type III collagen hydrogels tended to be mechanically superior. Twelve-month post-implantation results of type I recombinant collagen-based corneal substitutes into mini-pigs showed retention of optical clarity, along with regeneration of corneal cells, nerves and tear film. For clinical use, implants based on fully characterized, recombinant human collagen eliminate the risk of pathogen transfer or xenogeneic immuno-responses posed by animal collagens. © 2007 Elsevier Ltd. All rights reserved.
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