| 1. |
- Griffith, May, et al.
(author)
-
Artificial human corneas - Scaffolds for transplantation and host regeneration
- 2002
-
In: Cornea. - : Lippincott, Williams andamp; Wilkins. - 0277-3740 .- 1536-4798. ; 21:7, s. S54-S61
-
Journal article (peer-reviewed)abstract
- Purpose. To review the development of artificial corneas (prostheses and tissue equivalents) for transplantation, and to provide recent updates on our tissue-engineered replacement corneas. Methods. Modified natural polymers and synthetic polymers were screened for their potential to replace damaged portions of the human cornea or the entire corneal thickness. These polymers, combined with cells derived from each of the three main corneal layers or stem cells, were used to develop artificial corneas. Functional testing was performed in vitro. Trials of biocompatibility and immune and inflammatory reactions were performed by implanting the most promising polymers into rabbit corneas. Results. Collagen-based biopolymers, combined with synthetic crosslinkers or copolymers, formed effective scaffolds for developing prototype artificial corneas that could be used as tissue replacements in the future. We have previously developed an artificial cornea that mimicked key morphologic and functional properties of the human cornea. The addition of synthetic polymers increased its toughness as it retained transparency and low light scattering, making the matrix scaffold more suitable for transplantation. These new composites were implanted into rabbits without causing any acute inflammation or immune response. We have also fabricated full-thickness composites that can be fully sutured. However, the long-term effects of these artificial corneas need to be evaluated. Conclusions. Novel tissue-engineered corneas that comprise composites of natural and synthetic biopolymers together with corneal cell lines or stem cells will, in the future, replace portions of the cornea that are damaged. Our results provide a basis for the development of both implantable temporary and permanent corneal replacements.
|
|
| 2. |
- Li, Fengfu, et al.
(author)
-
Cellular and nerve regeneration within a biosynthetic extracellular matrix for corneal transplantation
- 2003
-
In: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences; 1999. - 0027-8424 .- 1091-6490. ; 100:26, s. 15346-15351
-
Journal article (peer-reviewed)abstract
- Our objective was to determine whether key properties of extracellular matrix (ECM) macromolecules can be replicated within tissue-engineered biosynthetic matrices to influence cellular properties and behavior. To achieve this, hydrated collagen and N-isopropylacrylamide copolymer-based ECMs were fabricated and tested on a corneal model. The structural and immunological simplicity of the cornea and importance of its extensive innervation for optimal functioning makes it an ideal test model. In addition, corneal failure is a clinically significant problem. Matrices were therefore designed to have the optical clarity and the proper dimensions, curvature, and biomechanical properties for use as corneal tissue replacements in transplantation. In vitro studies demonstrated that grafting of the laminin adhesion pentapeptide motif, YIGSR, to the hydrogels promoted epithelial stratification and neurite in-growth. Implants into pigs corneas demonstrated successful in vivo regeneration of host corneal epithelium, stroma, and nerves. In particular, functional nerves were observed to rapidly regenerate in implants. By comparison, nerve regeneration in allograft controls was too slow to be observed during the experimental period, consistent with the behavior of human cornea transplants. Other corneal substitutes have been produced and tested, but here we report an implantable matrix that performs as a physiologically functional tissue substitute and not simply as a prosthetic device. These biosynthetic ECM replacements should have applicability to many areas of tissue engineering and regenerative medicine, especially where nerve function is required.
|
|
| 3. |
- Shimmura, Shigeto, et al.
(author)
-
Collagen-poly(N-isopropylacrylamide)-based membranes for corneal stroma scaffolds
- 2003
-
In: Cornea. - : Lippincott, Williams andamp; Wilkins. - 0277-3740 .- 1536-4798. ; 22:7, s. S81-S88
-
Journal article (peer-reviewed)abstract
- Purpose: To investigate the feasibility of using the biocompatibility of collagen-based blended biomaterials as cell-delivery systems in ocular surface reconstruction in vivo. Methods: Collagen-based composites that were blended with synthetic acrylamide-based polymers [poly(N-isopropylacrylamide), pNIPAAm] were transplanted into corneal pockets of white rabbits, with a 3-mm epithelial window. Epithelial cells were allowed to migrate onto the polymer. Transplanted eyes were examined daily for up to 30 days, after which animals; were killed for histologic examination. lm- munohistochemistry was performed for vimentin, a-smooth muscle actin (alpha-SMA), CD4, and CD8. Gold-chloride staining was performed to observe neuronal regrowth. Human amniotic membranes (AMs) and sham-operated corneas served as controls. All animals received topical antibiotics (levofloxacin) without the use of steroids or other immunosuppressive agents. Results: The pNIPAAm polymer allowed smooth epitheliatization of the cornea, which was similar to the epithelialization observed in sham controls and AM-transplanted eyes. Histology revealed that epithelium overlying the polymer was bundled into several layers, without the orientation observed with AM and sham controls. The polymer gradually thinned and was gradually replaced by host tissue. Vimentin- and alpha-SMA-positive cells were found in stromal pockets up to 1 month following polymer transplantation. These cells were responsible for slight subepithelial haze near the wound edge. CD4- and CD8-positive lymphocytes were also observed in the vicinity of the polymer. Gold-chloride staining showed nerve regrowth in the wound edge after 1 month and subepithelial branches after 3 months. Conclusion: Collagen-pNIPAAm blended polymers may he effective as biomaterials to be used in the early stages of lamellar stromal replacement.
|
|
| 4. |
- Suuronen, Erik J., et al.
(author)
-
Functional innervation in tissue engineered models for in vitro study and testing purposes
- 2004
-
In: Toxicological Sciences. - : Oxford University Press (OUP). - 1096-6080 .- 1096-0929. ; 82:2, s. 525-533
-
Journal article (peer-reviewed)abstract
- The biotechnology industry is rapidly expanding and the emerging field of tissue engineering is projected to have a high impact in the near future. Recently the field of cellular, drug, and prosthetic delivery has melded with the field of tissue engineering to make simulated tissues. In addition to their roles as tissue substitutes for transplantation, these simulated tissues may provide more accurate models and environments for toxicology testing and the study of peripheral nerves. The current study demonstrates the importance of innervation, in general, for the function of engineered tissues. We observe that the presence of nerves in a tissue engineered (TE) human cornea model enhances the growth of the epithelium and the formation of its protective mucin layer. Innervation also confers protection to the epithelium from chemical insult, as determined by the level of post-treatment epithelial cell death. We demonstrate differential responses of the nerves to chemical stimuli by changes in intracellular sodium as measured by 2-photon microscopy. The 2-photon imaging techniques also allow for the visualization and study of the fine sensory axon fibers within the 3-dimensional tissue. This work demonstrates a role for innervation in the protective quality and function of the engineered tissue, and the potential to use the nerves themselves as indicators of the severity of an insult. These results are important to consider for the development of any optimized TE models for in vitro study and testing purposes.
|
|
| 5. |
- Suuronen, Erik J., et al.
(author)
-
Innervated human corneal equivalents as in vitro models for nerve-target cell interactions
- 2003
-
In: The FASEB Journal. - : Federation of American Society of Experimental Biology (FASEB). - 0892-6638 .- 1530-6860. ; 17, s. 170-
-
Journal article (peer-reviewed)abstract
- A sensory nerve supply is crucial for optimal tissue function. However, the mechanisms for successful innervation and the signaling pathways between nerves and their target tissue are not fully understood. Engineered tissue substitutes can provide controllable environments in which to study tissue innervation. We have therefore engineered human corneal substitutes that promote nerve in-growth in a pattern similar to in vivo re-innervation. We demonstrate that these nerves (a) are morphologically equivalent to natural corneal nerves; (b) make appropriate contact with target cells; (c) can generate action potentials; (d) respond to chemical and physical stimuli; and (e) play an important role in the overall functioning of the bioengineered tissue. This model can be used for studying the more general topics of nerve ingrowth or regeneration and the interaction between nerves and their target cells and, more specifically, the role of nerves in corneal function. This model could also be used as an in vitro alternative to animals for safety and efficacy testing of chemicals and drugs.
|
|
