Innervated human corneal equivalents as in vitro models for nerve‐target cell interactions

An in vitro 3-dimensional Collagen-based Corneal Construct with Innervation Using Human Corneal Cell Lines

Purpose

To develop a 3-dimensional corneal construct suitable for in vitro studies of disease conditions and therapies.

Design

In vitro human corneal constructs were created using chemically crosslinked collagen and chondroitin sulfate extracellular matrix and seeded with 3 human corneal cell types (epithelial, stromal, and endothelial) together with neural cells. The neural cells were derived from hybrid neuroblastoma cells and the other cells used from immortalized human corneal cell lines. To check the feasibility and characterize the constructs, cytotoxicity, cell proliferation, histology, and protein expression studies were performed.

Results

Optimized culture condition permitted synchronized viability across the cell types within the construct. The construct showed a typical appearance for different cellular layers, including healthy appearing, phenotypically differentiated neurons. The expected protein expression profiles for specific cell types within the construct were confirmed with western blotting.

Conclusions

An in vitro corneal construct was successfully developed with maintenance of individual cell phenotypes with anatomically correct cellular loci. The construct may be useful in evaluation of specific corneal disorders and in developing different corneal disease models. Additionally, the construct can be used in evaluating drug targeting and/or penetration to individual corneal layers, testing novel therapeutics for corneal diseases, and potentially reducing the necessity for animals in corneal research at the early stages of investigation.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Hyaluronic acid based next generation bioink for 3D bioprinting of human stem cell derived corneal stromal model with innervation

Corneal transplantation remains gold standard for the treatment of severe cornea diseases, however, scarcity of donor cornea is a serious bottleneck. 3D bioprinting holds tremendous potential for cornea tissue engineering (TE). One of the key technological challenges is to design bioink compositions with ideal printability and cytocompatibility. Photo-crosslinking and ionic crosslinking are often used for the stabilization of 3D bioprinted structures, which can possess limitations on biological functionality of the printed cells. Here, we developed a hyaluronic acid-based dopamine containing bioink using hydrazone crosslinking chemistry for the 3D bioprinting of corneal equivalents. First, the shear thinning property, viscosity, and mechanical stability of the bioink were optimized before extrusion-based 3D bioprinting for the shape fidelity and self-healing property characterizations. Subsequently, human adipose stem cells (hASCs) and hASC-derived corneal stromal keratocytes were used for bioprinting corneal stroma structures and their cell viability, proliferation, microstructure and expression of key proteins (lumican, vimentin, connexin 43,α-smooth muscle actin) were evaluated. Moreover, 3D bioprinted stromal structures were implanted intoex vivoporcine cornea to explore tissue integration. Finally, human pluripotent stem cell derived neurons (hPSC-neurons), were 3D bioprinted to the periphery of the corneal structures to analyze innervation. The bioink showed excellent shear thinning property, viscosity, printability, shape fidelity and self-healing properties with high cytocompatibility. Cells in the printed structures displayed good tissue formation and 3D bioprinted cornea structures demonstrated excellentex vivointegration to host tissue as well asin vitroinnervation. The developed bioink and the printed cornea stromal equivalents hold great potential for cornea TE applications.

Recent scaffold-based tissue engineering approaches in premature ovarian failure treatment

Recently, tissue engineering and regenerative medicine have received significant attention with outstanding advances. The main scope of this technology is to recover the damaged tissues and organs or to maintain and improve their function. One of the essential fields in tissue engineering is scaffold designing and construction, playing an integral role in damaged tissues reconstruction and repair. However, premature ovarian failure (POF) is a disorder causing many medical and psychological problems in women. POF treatment using tissue engineering and various scaffold has recently made tremendous and promising progress. Due to the importance of the subject, we have summarized the recently examined scaffolds in the treatment of POF in this review.

Effects of Vitamin D Receptor Knockout and Vitamin D Deficiency on Corneal Epithelial Wound Healing and Nerve Density in Diabetic Mice

Diabetic keratopathy occurs in ∼70% of all people with diabetes. This study was designed to examine the effects of vitamin D receptor knockout (VDR-/-) and vitamin D deficiency (VDD) on corneal epithelial wound healing and nerve density in diabetic mice. Diabetes was induced using the low-dose streptozotocin method. Corneal epithelial wounds were created using an Algerbrush, and wound healing was monitored over time. Corneal nerve density was measured in unwounded mice. VDR-/- and VDD diabetic mice (diabetic for 8 and 20 weeks, respectively) had slower healing ratios than wild-type diabetic mice. VDR-/- and VDD diabetic mice also showed significantly decreased nerve density. Reduced wound healing ratios and nerve densities were not fully rescued by a supplemental diet rich in calcium, lactose, and phosphate. We conclude that VDR-/- and VDD significantly reduce both corneal epithelial wound healing and nerve density in diabetic mice. Because the supplemental diet did not rescue wound healing or nerve density, these effects are likely not specifically related to hypocalcemia. This work supports the hypothesis that low vitamin D levels can exacerbate preexisting ophthalmic conditions, such as diabetes.

Premature ovarian failure and tissue engineering

Premature ovarian failure (POF) usually happens former to the age of 40 and affects the female physiological state premenopausal period. In this condition, ovaries stop working long before the expected menopausal time. Of diagnostic symptoms of the disease, one can mention amenorrhea and hypoestrogenism. The cause of POF in most cases is idiopathic; however, cancer therapy may also cause POF. Commonly utilized therapies such as hormone therapy, in-vitro activation, and regenerative medicine are the most well-known treatments for POF. Hence, these therapies may be associated with some complications. The aim of the present study is to discuss the beneficial effects of tissue engineering for fertility rehabilitation in patients with POF as a newly emerging therapy.

Corneal pain and experimental model development

The cornea is a valuable tissue for studying peripheral sensory nerve structure and regeneration due to its avascularity, transparency, and dense innervation. Somatosensory innervation of the cornea serves to identify changes in environmental stimuli at the ocular surface, thereby promoting barrier function to protect the eye against injury or infection. Due to regulatory demands to screen ocular safety of potential chemical exposure, a need remains to develop functional human tissue models to predict ocular damage and pain using in vitro-based systems to increase throughput and minimize animal use. In this review, we summarize the anatomical and functional roles of corneal innervation in propagation of sensory input, corneal neuropathies associated with pain, and the status of current in vivo and in vitro models. Emphasis is placed on tissue engineering approaches to study the human corneal pain response in vitro with integration of proper cell types, controlled microenvironment, and high-throughput readouts to predict pain induction. Further developments in this field will aid in defining molecular signatures to distinguish acute and chronic pain triggers based on the immune response and epithelial, stromal, and neuronal interactions that occur at the ocular surface that lead to functional outcomes in the brain depending on severity and persistence of the stimulus.

Modeling Diabetic Corneal Neuropathy in a 3D In Vitro Cornea System

Diabetes mellitus is a disease caused by innate or acquired insulin deficiency, resulting in altered glucose metabolism and high blood glucose levels. Chronic hyperglycemia is linked to development of several ocular pathologies affecting the anterior segment, including diabetic corneal neuropathy and keratopathy, neovascular glaucoma, edema, and cataracts leading to significant visual defects. Due to increasing disease prevalence, related medical care costs, and visual impairment resulting from diabetes, a need has arisen to devise alternative systems to study molecular mechanisms involved in disease onset and progression. In our current study, we applied a novel 3D in vitro model of the human cornea comprising of epithelial, stromal, and neuronal components cultured in silk scaffolds to study the pathological effects of hyperglycemia on development of diabetic corneal neuropathy. Specifically, exposure to sustained levels of high glucose, ranging from 35 mM to 45 mM, were applied to determine concentration-dependent effects on nerve morphology, length and density of axons, and expression of metabolic enzymes involved in glucose metabolism. By comparing these metrics to in vivo studies, we have developed a functional 3D in vitro model for diabetic corneal neuropathy as a means to investigate corneal pathophysiology resulting from prolonged exposure to hyperglycemia.

In vitro 3D corneal tissue model with epithelium, stroma, and innervation

The interactions between corneal nerve, epithelium, and stroma are essential for maintaining a healthy cornea. Thus, corneal tissue models that more fully mimic the anatomy, mechanical properties and cellular components of corneal tissue would provide useful systems to study cellular interactions, corneal diseases and provide options for improved drug screening. Here a corneal tissue model was constructed to include the stroma, epithelium, and innervation. Thin silk protein film stacks served as the scaffolding to support the corneal epithelial and stromal layers, while a surrounding silk porous sponge supported neuronal growth. The neurons innervated the stromal and epithelial layers and improved function and viability of the tissues. An air-liquid interface environment of the corneal tissue was also mimicked in vitro, resulting in a positive impact on epithelial maturity. The inclusion of three cell types in co-culture at an air-liquid interface provides an important advance for the field of in vitro corneal tissue engineering, to permit improvements in the study of innervation and corneal tissue development, corneal disease, and tissue responses to environmental factors.

Potential New Modes of Treatment of Neurotrophic Keratopathy

The cornea focuses external light onto the retina, a function for which it must be transparent and possess a smooth surface. Homeostasis of the corneal epithelium is regulated by various humoral factors present in the tear fluid and by neural factors derived from the trigeminal nerve. Neurotrophic keratopathy (NK) is characterized by corneal epithelial disorders that result from impairment of trigeminal nerve function and a consequent deficiency of neural factors. The ideal mode of treatment for this condition is the regeneration of damaged trigeminal nerve fibers, but such therapy is not currently available. In this review, we describe established and potential new treatments of NK. Our research demonstrated that a combination of the neurotransmitter substance P and insulin-like growth factor 1 (IGF-1) has a synergistic stimulatory effect on corneal epithelial migration in vitro and on corneal wound closure in vivo. Furthermore, we identified the minimal amino acid sequences of substance P and IGF-1 required for this synergistic action based on the assumption that the clinical application of peptides corresponding to these sequences would have fewer side effects compared with the full-length molecules. Combination of the substance P-derived peptide FGLM-amide and the IGF-1-derived peptide SSSR promoted corneal epithelial wound healing in patients with NK.Clinical Trial Registration-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01756456.

Transplantation of adipose-derived stem cells combined with collagen scaffolds restores ovarian function in a rat model of premature ovarian insufficiency

STUDY QUESTION

Does the transplantation of adipose-derived stem cells (ADSCs) on soluble collagen scaffolds (collagen/ADSCs) have better therapeutic effect than transplantation of ADSCs alone, to treat premature ovarian insufficiency (POI) in a rat model induced by Tripterygium Glycosides (TG)?

SUMMARY ANSWER

The transplantation of collagen/ADSCs increased the short-term retention of ADSCs in ovaries and contributed to long-term restoration of ovarian function, as well as the fertility of rats with TG-induced ovarian damage.

WHAT IS KNOWN ALREADY

About 50% of young women in China, who have been treated with TG, have subsequently developed ovarian insufficiency. Rats exhibit similar symptoms to these patients when given an equivalent dose of TG. Transplantation of ADSCs improves ovarian function impaired by chemotherapy in rodent models.

STUDY DESIGN, SIZE, DURATION

After the administration of TG, 54 POI model rats were randomly assigned to 4 groups: phosphate buffered saline (PBS) ( ITALIC! n = 14), collagen ( ITALIC! n = 11), ADSCs ( ITALIC! n = 16) and collagen/ADSCs ( ITALIC! n = 13). Seventeen normal rats were assigned as control group. The retention of ADSCs in ovaries was confirmed immediately or at 3, 7, 14 and 28 days after transplantation ( ITALIC! n = 9). Four weeks after transplantation, ovarian function was evaluated from estrous cycle, estradiol level, the follicle number, granulosa cell proliferation and a fertility test.

PARTICIPANTS/MATERIALS, SETTING, METHODS

To establish the POI model, rats were administered 60 mg TG/kg/day intragastrically for 50 days. The estrous cycles were assessed by vaginal smear. The concentration of plasma estradiol in diestrus stage was measured using a radioimmunoassay kit. Disordered estrous cycles and low serum estradiol levels indicated the successful establishment of the POI model. Four types of suspensions (PBS, collagen, ADSCs and collagen/ADSCs) were transplanted directly into the core of the ovaries. The short-term retention of ADSCs in ovaries was evaluated by small-animal positron emission tomography images immediately after transplantation of (18)F-Fluorodeoxyglucose ((18)F-FDG) labeled ADSCs. The long-term retention of ADSCs in ovaries was observed by immunohistochemistry after transplantation of green fluorescent protein (GFP)-labeled ADSCs. Serial sections of ovaries were prepared for histological analysis, follicle counting, and immunohistochemistry for Ki67 and Cleaved-Caspase-3. For the assessment of fertility, rats were mated with proven fertile male rats for 10 days.

MAIN RESULTS AND THE ROLE OF CHANCE

The (18)F-FDG signal decreased more slowly in ovaries injected with collagen/ADSCs than in ovaries with injected with ADSCs alone. Significantly more GFP-positive cells were observed in ovaries injected with collagen/GFP-ADSCs than in ovaries injected with GFP-ADSCs alone up to 14 days after the injection. However, in both groups very few GFP-positive cells were present at 4 weeks after transplantation. The collagen/ADSCs and ADSCs groups both showed better estrous cycle recovery than the PBS and collagen groups. The estradiol (E2) level in the collagen/ADSCs group was significantly increased compared with that of the PBS group ( ITALIC! P < 0.05). The number of antral follicles in the collagen/ADSCs group and the ADSCs group significantly increased compared with the PBS group ( ITALIC! P < 0.05). The granulosa cell proliferation in the collagen/ADSCs group was better than in the PBS group ( ITALIC! P < 0.01). The mating rates of the collagen/ADSCs group (88.9%) and the ADSCs group (90.9%) were higher than that of PBS group (60%, ITALIC! P < 0.05). The pregnancy rates of the collagen/ADSCs group (77.8%) and the ADSCs group (72.7%) were higher than the PBS group (50%, ITALIC! P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

We chose ADSCs for their accessibility, convenience and safety. We did not use other cells or materials for POI treatments to show that the collagen/ADSCs are the most promising materials.

WIDER IMPLICATIONS OF THE FINDINGS

Soluble collagen scaffolds may be useful in stem cells transplantation therapy for POI.

STUDY FUNDING/COMPETING INTERESTS

This work is supported by grants from the 'Strategic Priority Research Program' of the Chinese Academy of Sciences (XDA01030000); Maternal-Fetal Medicine from Jiangsu Province Health Department of China (XK2011027); Clinical Center of Obstetric, Gynecologic and Genetic Diseases, Nanjing Health Department of Jiangsu Province, China; Fundamental Research Funds for the Central Universities (20620140652). The authors declare no competing financial interests.

TRIAL REGISTRATION NUMBER

Not applicable.

Innervation of a prefabricated flap: a new experimental model

Introduction. Flap innervation by neoaxonogenesis is a promising field of investigation. The authors evaluated the possibility of innervating an acellular collagen scaffold as component of a potential prefabricated flap. Materials and Methods. Collagen matrix sheets were implanted around the femoral bundle of a murine model to produce two flaps on proximal and distal nerve stumps based on a flow-through model. After thirty days, nerve regeneration and integration into the collagen matrix were evaluated. The specimens were microscopically analyzed to study Schwann cell colonization and axonal integration with the matrix. Axonal count and density were assessed and statistically evaluated. Results. Qualitative structural and ultrastructural evaluation indicated integration, with axonal fibers merged within the collagen matrix, along with a newly formed vascular network on the proximal flap. Wallerian degeneration occurred inside the distal chamber. Axonal count and density did not show statistically significant differences between the nerve inside the proximal flap and the control side. Conclusions. Innervation of an acellular matrix can be obtained by direct nerve stump implantation. The flow-through system was relatively easy to build and reliable to provide adequate blood supply. The collagen scaffold may be a promising support or further studies of preinnervated microsurgical flaps.

Progress in the development of a corneal replacement: keratoprostheses and tissue-engineered corneas

Rapid progress has been made in the past 5 years in the development of corneal replacements. Traditionally they are divided into two categories, keratoprostheses and tissue-engineered corneal equivalents, as replacement tissues are increasingly in demand worldwide. There are currently several different keratoprosthesis models in clinical use around the world. The most popular and most widely publicized is the AlphaCor model, which has enjoyed significant clinical success. However, improvements remain to be made, and the aim of most of the current research is to better understand the interactions between a synthetic material and the surrounding biology on a more fundamental level. This improved understanding will no doubt lead to improvements in current models and to the development of new models in the near future. While tissue-engineered corneal equivalents have been under investigation for considerably less time, there is growing evidence to suggest that a tissue-engineered corneal equivalent comprised of primarily natural materials will exist in the not too distant future. Research groups have reported strong in vitro and in vivo results. The strength of the collagen matrix and its ability to support cell infiltration have been the primary avenues of research. Various collagen crosslinking techniques have been used. Infiltration of three major cells of the cornea has been observed. Most importantly, the ability of these materials to support nerve ingrowth has been demonstrated. While challenges remain with both types of corneal replacements, the considerable progress in the recent past suggests that reliable implants for the treatment of a variety of corneal diseases will be available. This review will provide an overview of recent results, and will provide insight into the future of research on corneal replacements.

Bioengineering a highly vascularized matrix for the ectopic transplantation of islets

Islet transplantation is a promising treatment for Type 1 diabetes; however limitations of the intra-portal site and poor revascularization of islets must be overcome. We hypothesize that engineering a highly vascularized collagen-based construct will allow islet graft survival and function in alternative sites. In this study, we developed such a collagen-based biomaterial. Neonatal porcine islets (NPIs) were embedded in collagen matrices crosslinked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide containing combinations of chondroitin-6-sulfate, chitosan, and laminin, and compared with controls cultured in standard media. Islets were examined for insulin secretory activity after 24 h and 4 d and for apoptotic cell death and matrix integrity after 7 d in vitro. These same NPI/collagen constructs were transplanted subcutaneously in immunoincompetent B6.Rag-/- mice and then assessed for islet survival and vascularization. At all time points assessed during in vitro culture there were no significant differences in insulin secretory activity between control islets and those embedded in the collagen constructs, indicating that the collagen matrix had no adverse effect on islet function. Less cell death was observed in the matrix with all co-polymers compared with the other matrices tested. Immunohistochemical analysis of the grafts post-transplant confirmed the presence of intact insulin-positive islets; grafts were also shown to be vascularized by von Willebrand factor staining. This study demonstrates that a collagen, chondroitin-6-sulfate, chitosan, and laminin matrix supports islet function in vitro and moreover allows islet survival and vascularization post-transplantation; therefore, this bio-engineered vascularized construct is capable of supporting islet survival.

The potential of tissue engineering for developing alternatives to animal experiments: a systematic review

An underexposed ethical issue raised by tissue engineering is the use of laboratory animals in tissue engineering research. Even though this research results in suffering and loss of life in animals, tissue engineering also has great potential for the development of alternatives to animal experiments. With the objective of promoting a joint effort of tissue engineers and alternative experts to fully realise this potential, this study provides the first comprehensive overview of the possibilities of using tissue-engineered constructs as a replacement of laboratory animals. Through searches in two large biomedical databases (PubMed, Embase) and several specialised 3R databases, 244 relevant primary scientific articles, published between 1991 and 2011, were identified. By far most articles reviewed related to the use of tissue-engineered skin/epidermis for toxicological applications such as testing for skin irritation. This review article demonstrates, however, that the potential for the development of alternatives also extends to other tissues such as other epithelia and the liver, as well as to other fields of application such as drug screening and basic physiology. This review discusses which impediments need to be overcome to maximise the contributions that the field of tissue engineering can make, through the development of alternative methods, to the reduction of the use and suffering of laboratory animals.

Epidermal nerve fibers modulate keratinocyte growth via neuropeptide signaling in an innervated skin model

Atopic eczema is a chronic inflammatory skin disease characterized by cutaneous nerve fiber sprouting and epidermal hyperplasia, pointing to an involvement of the peripheral nervous system in cutaneous homeostasis. However, the interaction of sensory neurons and skin cells is poorly understood. Using an innervated skin model, we investigated the influence of sensory neurons on epidermal morphogenesis. Neurons induced the proliferation of keratinocytes, resulting in an increase in the epidermal thickness. Inhibition of calcitonin gene-related peptide (CGRP), but not substance P (SP) signaling, reversed this effect. Human CGRP enhanced keratinocyte proliferation and epidermal thickness in skin models, demonstrating a key role of CGRP in modulating epidermal morphogenesis, whereas SP had only a moderate effect. Innervated skin models composed of atopic skin cells showed increased neurite outgrowth, accompanied by elevated CGRP release. As atopic keratinocytes were sensitized to CGRP owing to higher expression levels of the CGRP receptor components, receptor activity-modifying protein 1 (RAMP1) and receptor component protein (RCP), atopic innervated skin models displayed a thicker epidermis than did healthy controls. We conclude that neural CGRP controls local keratinocyte growth. Our results show that the crosstalk of the cutaneous peripheral nervous system and skin cells significantly influences epidermal morphogenesis and homeostasis in healthy and atopic skin.

Tunable collagen hydrogels are modified by the therapeutic agents they are designed to deliver

Injectable hydrogels are increasingly being developed for biomedical applications due to their ability to be delivered in a minimally invasive manner. One potential use for such materials is in cell delivery for cardiac regeneration. While the materials' properties are often characterized, how these properties (and in particular gelation) are affected by the addition of the therapeutic agent(s) they are designed to deliver is often overlooked. The aim of this study was to examine the interactive effects between collagen-based hydrogels and different additives (cells and microspheres). The results demonstrated that the incorporation of either cells or microspheres to a collagen hydrogel decreased its gelation time and increased its viscosity. Increased concentrations of the EDC/NHS cross-linker resulted in greater loss of cell viability. However, it was found that this cell loss could be minimized by delivering cells with the cross-linker scavenger glycine. A better understanding of how materials and cells (and other additives) respond to each other will help towards the goal of improving scaffolds being developed for regenerative therapy.

Methods for culture of human corneal and conjunctival epithelia

The surface of the eye is exposed to the outside world and is, thus, subject to surface abrasion, infections, and drying, cicatrizing diseases. Availability of in vitro methods for culture of the human corneal and conjunctival epithelia, which cover the ocular surface, is therefore important in understanding the biology of these epithelia and their response to disease/infections, as well as for providing human-relevant models for preclinical testing of potential therapeutic agents. The ensuing chapter describes several methods for primary culture of both corneal and conjunctival epithelia and culture of immortalized cell lines, and methods employed to induce differentiation in the cultured epithelia.

Ex vivo generation of a highly potent population of circulating angiogenic cells using a collagen matrix

Biomaterials that have the ability to augment angiogenesis are highly sought-after for applications in regenerative medicine, particularly for revascularization of ischemic and infarcted tissue. We evaluated the culture of human circulating angiogenic cells (CAC) on collagen type I-based matrices, and compared this to traditional selective-adhesion cultures on fibronectin. Culture on a collagen matrix supported the proliferation of CD133(+) and CD34(+)CD133(+) CACs. When subjected to serum starvation, the matrix conferred a resistance to cell death for CD34(+) and CD133(+) progenitors and increased phosphorylation of Akt. After 4days of culture, phenotypically enriched populations of endothelial cells (CD31(+)CD144(+)) and progenitor cells (CD34(+)CD133(+)) emerged. Culture on matrix upregulated the phosphorylation and activation of ERK1/2 pathway members, and matrix-cultured cells also had an enhanced functional capacity for adhesion and invasion. These functional improvements were abrogated when cultured in the presence of ERK inhibitors. The formation of vessel-like structures in an angiogenesis assay was augmented with matrix-cultured cells, which were also more likely to physically associate with such structures compared to CACs taken from culture on fibronectin. In vivo, treatment with matrix-cultured cells increased the size and density of arterioles, and was superior at restoring perfusion in a mouse model of hindlimb ischemia, compared to fibronectin-cultured cell treatment. This work suggests that a collagen-based matrix, as a novel substrate for CAC culture, possesses the ability to enrich endothelial and angiogenic populations and lead to clinically relevant functional enhancements.

Alternative (non-animal) methods for cosmetics testing: current status and future prospects-2010

The 7th amendment to the EU Cosmetics Directive prohibits to put animal-tested cosmetics on the market in Europe after 2013. In that context, the European Commission invited stakeholder bodies (industry, non-governmental organisations, EU Member States, and the Commission's Scientific Committee on Consumer Safety) to identify scientific experts in five toxicological areas, i.e. toxicokinetics, repeated dose toxicity, carcinogenicity, skin sensitisation, and reproductive toxicity for which the Directive foresees that the 2013 deadline could be further extended in case alternative and validated methods would not be available in time. The selected experts were asked to analyse the status and prospects of alternative methods and to provide a scientifically sound estimate of the time necessary to achieve full replacement of animal testing. In summary, the experts confirmed that it will take at least another 7-9 years for the replacement of the current in vivo animal tests used for the safety assessment of cosmetic ingredients for skin sensitisation. However, the experts were also of the opinion that alternative methods may be able to give hazard information, i.e. to differentiate between sensitisers and non-sensitisers, ahead of 2017. This would, however, not provide the complete picture of what is a safe exposure because the relative potency of a sensitiser would not be known. For toxicokinetics, the timeframe was 5-7 years to develop the models still lacking to predict lung absorption and renal/biliary excretion, and even longer to integrate the methods to fully replace the animal toxicokinetic models. For the systemic toxicological endpoints of repeated dose toxicity, carcinogenicity and reproductive toxicity, the time horizon for full replacement could not be estimated.

The Development and Evaluation of In Vitro Alternative Assays: A Personal Perspective

Over the past 30 years, FRAME has actively participated in the development, evaluation and validation of in vitro alternative methods through the FRAME Alternatives Laboratory (FAL) in the University of Nottingham Medical School. Much has been learned through collaboration with industry (especially the cosmetics industry), other organisations (especially ECVAM), and certain individuals (notably Dr Björn Ekwall), particularly in relation to the need to use human cell cultures and to obtain, wherever possible, high-quality human data for use in in vivo/in vitro comparisons. Reference is made to the author's experience as Director of the FAL, notably in the development of in vitro assays for basal cytotoxicity, phototoxicity and the effects of repeated dosage.

A Frame Response to the European Commission Consultation on the Draft Report on Alternative (Non-animal) Methods for Cosmetics Testing: Current Status and Future Prospects — 2010

This response on behalf of FRAME to the European Commission's consultation on the five chapters of the Draft Report on Alternative (Non-animal) Methods for Cosmetics Testing: Current Status and Future Prospects — 2010, is via a Comment in ATLA, rather than via the template supplied by the Commission. This is principally so that a number of general points about cosmetic ingredient testing can be made. It is concluded that the five draft chapters do not provide a credible basis for the Commission's forthcoming report to the European Parliament and the European Council on the five cosmetic ingredient safety issues for which the 7th Amendment to the Cosmetic Directive's ban on animal testing was postponed until 2013. This is mainly because there is insufficient focus in the draft chapters on the specific nature of cosmetic ingredients, their uses, their local effects and metabolism at their sites of application, and, in particular, on whether their possible absorption into the body would be likely to lead to their accumulation in target sites at levels approaching Thresholds of Toxicological Concern. Meanwhile, there continues to be uncertainty about how the provisions of the Cosmetics Directive should be applied, given the requirements of the REACH system and directives concerned with the safety of other chemicals and products.

Biosynthetic corneal substitute implantation in dogs

PURPOSE

To assess integration of a biosynthetic corneal implant in dogs.

METHODS

Three normal adult laboratory Beagles underwent ophthalmic examinations, including slit-lamp biomicroscopy, indirect ophthalmoscopy, applanation tonometry, and Cochet-Bonnet aesthesiometry. Biosynthetic corneas fabricated from glutaraldehyde crosslinked collagen and copolymers of collagen and poly(N-isopropylacrylamide-co-acrylic acid-co-acryloxysuccinimide, denoted as TERP) were implanted into dogs by a modified epikeratoplasty technique. Ophthalmic examinations and aesthesiometry were performed daily for 5 days and then weekly thereafter for 16 weeks. Corneal samples underwent histopathological and transmission electron microscopy examination at 16 weeks.

RESULTS

Implants were epithelialized by 7 days. Intraocular pressure was within normal range throughout the study. Aesthesiometry values dropped from an average of 3.67 cm preoperatively to less than 1 mm for all dogs for the first postoperative weeks. By week 16, the average Cochet-Bonnet value was 1.67 cm, demonstrating partial recovery of functional innervation of the implant. No inflammation or rejection of the implant occurred, and minimal haze formation was noted. Light microscopy revealed thickened but normal epithelium over the implant with fibroblast migration into the scaffold. On transmission electron microscopy, the basement membrane was irregular but present and adhesion complexes were noted.

CONCLUSION

Biosynthetic corneal implantation is well tolerated in dogs, and the collagen-polymer hybrid construct holds promise for clinical application in animals and humans.

Optimal neural differentiation and extension of hybrid neuroblastoma cells (NDC) for nerve-target evaluations using a multifactorial approach

In vitro models of tissues, such as the cornea, represent systems for modeling cell-to-cell interactions and tissue function. The objective of this study was to develop an optimized nerve differentiation medium to incorporate into a 3D in vitro model to study innervation and cell targeting. A hybrid neuroblastoma cell line (NDC) was examined for its ability to differentiate into neurons, produce neurites, and functionally contact target cells. Neuronal differentiation of NDCs was optimized through a combinatorial approach which involved culturing cells in the presence of various extracellular matrices and soluble factors. A serum-free medium containing nerve growth factor (NGF), dimethyl sulfoxide (DMSO), or dexamethasone resulted in the greatest proportion of NDCs demonstrating a neuronal morphology. Similarly, with supplementation of cyclic AMP (cAMP) or NGF, neurite extension was optimized. Combining these factors generated an optimized differentiation and extension medium, relative to the individual components alone. In co-culture with epithelial cells, NDC neurites generated in the optimized medium formed contacts with epithelial targets and produced substance P. Similarly, NDCs seeded into a collagen matrix produced neurites that projected through the matrix to target epithelial cells, promoted epithelial stratification, and increased the rate of epithelial wound healing. As well, differentiated NDCs could target and alter acetylcholine receptor clustering in mouse C2C12 myotubes, demonstrating synaptic plasticity. Our data supports the use of NDCs, in combination with optimized medium, for generating an innervated in vitro model.

Influence of matrix processing on the optical and biomechanical properties of a corneal stroma equivalent

Interest in developing tissue-engineered cornea has increased with the decrease in the supply of donor tissue; however, the high strength and transparency of the cornea present a challenge. Both the collagen processing and crosslinking methods were hypothesized to influence the optical and biomechanical properties of collagen matrices, while regular surface topography was hypothesized to align stromal fibroblasts. Improved transparency and strength were observed when soluble tropocollagen was added to the insoluble collagen and when glucose-mediated ultraviolet (UV) crosslinking as opposed to dehydrothermal crosslinking was used. The fraction of transmittance of the collagen films fabricated from insoluble collagen and soluble tropocollagen and glucose-mediated UV crosslinking was initially 0.91 +/- 0.02 and 0.98 +/- 0.01 for the smooth films and 0.90 +/- 0.02 and 0.97 +/- 0.02 for the microgrooved films at 400 and 700 nm and was comparable to that of the native cornea, while the relaxed modulus and ultimate tensile strength ranged from 0.9 to 9.4 MPa and from 0.7 to 4.1 MPa, respectively, over the 3 weeks of culture and were initially at or below the range of values for the native cornea. These collagen scaffolds were significantly stronger and more transparent than previous scaffolds, and aligned stromal fibroblasts were observed on microgrooved surfaces.

The development of a tissue-engineered cornea: biomaterials and culture methods

The field of corneal tissue engineering has made many strides in recent years. The challenges of engineering a biocompatible, mechanically stable, and optically transparent tissue are significant. To overcome these challenges, researchers have adopted two basic approaches: cell-based strategies for manipulating cells to create their own extracellular matrix, and scaffold-based strategies for providing strong and transparent matrices upon which to grow cells. Both strategies have met with some degree of success. In addition, recent advances have been made in innervating a tissue-engineered construct. Future work will need to focus on further improving mechanical stability of engineered constructs as well as improving the host response to implantation.

Development of an innervated model of human skin

Neuronal cell responses and interactions with the epithelial and fibroblastic cells of the skin are a key factor in the production in vivo of the irritation/inflammatory response. Currently, few in vitro models are available that contain dermal, epidermal and the relevant neuronal components. The primary objective of this study was to produce and maintain a 3-D in vitro model of human skin containing these elements. The relevant neuronal component was supplied by adding sensory neurons derived from the dorsal root ganglion (DRG). Since adult neuronal cells do not grow significantly in vivo or in vitro, and since it is very difficult to obtain such cells from humans, it was necessary to employ embryonic rat DRG cells. The ultimate purpose of this model is to improve prediction of the in vivo skin irritancy potential of chemicals and formulations, without the need to use animal models. In addition, this approach has also been applied to the in vitro human eye and bronchial 3-D models being developed in the FRAME Alternatives Laboratory.

In vitro alternatives to the use of animals in ocular toxicology testing

Chemical substances, including household products, industrial chemicals, and cosmetics, must be tested for ocular toxicity or irritancy so that the public can be assured of their safety or warned of dangers associated with their use. The in vivo Draize test is the standard method used to meet this requirement; however, this test is coming under increasing criticism on scientific and ethical grounds. This has led to the development of a large number of proposed in vitro tests, some of which are routinely used to screen chemicals in toxicology laboratories. This review addresses regulations governing ocular irritancy testing and the current status of the movement toward use of alternative methods. Such methods include the use of cultured cells, hen's eggs, isolated animal eyes and corneas, human corneal epithelial cell lines, and the recently developed in vitro corneal equivalent models. The protocols for these methods are outlined, and their endpoints are described with respect to prediction of in vivo responses. The tests are evaluated in the context of the outcomes of validation studies and acceptance by regulatory agencies. While several of these tests yield useful information concerning ocular irritancy, to date, no in vitro alternative test has been validated as a replacement for the Draize test. If the goal of replacing the in vivo test while protecting the public from chemical eye injury is to be achieved, further development and improvement of alternative tests, as well as establishment of a human ocular toxicity data base, are required.

Promotion of angiogenesis in tissue engineering: developing multicellular matrices with multiple capacities

One of the aims of tissue engineering is to be able to develop multi-tissue organs in the future. This requires the optimization of conditions for the differentiation of multiple cell types and maintenance of the differentiated phenotype within complex engineered tissues. The goal of this study was to develop prototype tissue engineered matrices to support the simultaneous growth of different cell types with a particular focus on the angiogenic process. We examined two different matrix compositions for the promotion of blood vessel and tube formation. A fibrin-based matrix with the addition of a combination of growth factors supported vascular growth and the invasion of inflammatory cells. Using this fibrin matrix, in combination with a collagen-based hydrogel, a simple in vitro model of the cornea with adjacent sclera was developed that was complete with innervation and vascular structures. In addition, we showed that collagen-based matrices were effective in delivering mononuclear endothelial progenitor cells to ischemic tissue in vivo, and allowing these cells to incorporate into vascular structures. It is anticipated that with further development, these matrices have potential for use as delivery matrices for cell transplantation and for in vitro study purposes of multiple cell types.

Biofunctionalization of collagen for improved biological response: Scaffolds for corneal tissue engineering

Residual dendrimer amine groups were modified with incorporate COOH group containing biomolecules such as cell adhesion peptides into collagen scaffolds. YIGSR, as a model cell adhesion peptide, was incorporated into both the bulk structure of the gels and onto the gel surface. The effects of the peptide modified collagen gels on corneal epithelial cell behavior were examined with an aim of improving the potential of these materials as tissue-engineering scaffolds. YIGSR was first chemically attached to dendrimers and the YIGSR attached dendrimers were then used as collagen crosslinkers, incorporating the peptide into the bulk structure of the collagen gels. YIGSR was also attached to the surface of dendrimer crosslinked collagen gels through reaction with excess amine groups. The YIGSR modified dendrimers were characterized by H-NMR and MALDI mass spectra. The amount of YIGSR incorporated into collagen gels was determined by (125)I radiolabelling at maximum to be 3.1-3.4 x 10(-2)mg/mg collagen when reacted with the bulk and 88.9-95.6 microg/cm(2) when attached to the surface. The amount of YIGSR could be tuned by varying the amount of peptide reacted with the dendrimer or the amount of modified dendrimer used in the crosslinking reaction. It was found that YIGSR incorporation into the bulk and YIGSR modification of surface promoted the adhesion and proliferation of human corneal epithelial cells as well as neurite extension from dorsal root ganglia.

Microstructural characteristics of extracellular matrix produced by stromal fibroblasts

The overall objective of this investigation was to characterize the extracellular matrix deposited by the stromal fibroblasts as a function of time in culture and matrix microstructure. Stromal fibroblasts were seeded onto collagen matrices and cultured for up to 5 weeks. The collagen matrices contained collagen fibrils with an average diameter of 215 +/- 20 nm. When cultured on a collagen film, an average fibril diameter of 62 +/- 39 nm was observed for single layer films with only slight variations with time in culture, and after 1 week of culture between two film layers 67 +/- 47 nm fibrils were observed after 1 week. When the film surface was molded into 1 and 2 microm microgrooves, the initial average fibril diameter of the extracellular matrix was 73 +/- 21 and 73 +/- 31 nm respectively. When cultured on a collagen sponge, an average fibril diameter of 107 +/- 20 nm was initially observed and decreased to 47.5 +/- 17 nm after 1 week in culture. For cells cultured on a collagen sponge, Western blotting showed an increase in myofibroblast phenotype expression with time in culture. Shifts in phenotype were less distinct for cells cultured on collagen films. The microstructure, rather than geometry, of the matrix substrate appeared to influence the newly synthesized extracellular matrix and cell phenotype.

Tissue-engineered injectable collagen-based matrices for improved cell delivery and vascularization of ischemic tissue using CD133+ progenitors expanded from the peripheral blood

BACKGROUND

The use of stem and/or progenitor cells to achieve potent vasculogenesis in humans has been hindered by low cell numbers, implant capacity, and survival. This study investigated the expansion of CD133+ cells and the use of an injectable collagen-based tissue engineered matrix to support cell delivery and implantation within target ischemic tissue.

METHODS AND RESULTS

Adult human CD133+ progenitor cells from the peripheral blood were generated and expanded by successive removal and culture of CD133- cell fractions, and delivered within an injectable collagen-based matrix into the ischemic hindlimb of athymic rats. Controls received injections of phosphate-buffered saline, matrix, or CD133+ cells alone. Immunohistochemistry of hindlimb muscle 2 weeks after treatment revealed that the number of CD133+ cells retained within the target site was >2-fold greater when delivered by matrix than when delivered alone (P<0.01). The transplanted CD133+ cells incorporated into vascular structures, and the matrix itself also was vascularized. Rats that received matrix and CD133+ cells demonstrated greater intramuscular arteriole and capillary density than other treatment groups (P<0.05 and P<0.01, respectively).

CONCLUSIONS

Compared with other experimental approaches, treatment of ischemic muscle tissue with generated CD133+ progenitor cells delivered in an injectable collagen-based matrix significantly improved the restoration of a vascular network. This work demonstrates a novel approach for the expansion and delivery of blood CD133+ cells with resultant improvement of their implantation and vasculogenic capacity.

Self-assembly of sensory neurons into ganglia-like microtissues

Unraveling intra- and inter-cellular signaling networks managing cell-fate control, coordinating complex differentiation regulatory circuits and shaping tissues and organs in living systems remain major challenges in the post-genomic era. Resting on the laurels of past-century monolayer culture technologies, the cell culture community has only recently begun to appreciate the potential of three-dimensional mammalian cell culture systems to reveal the full scope of mechanisms orchestrating the tissue-like cell quorum in space and time. Capitalizing on gravity-enforced self-assembly of monodispersed primary embryonic mouse cells in hanging drops, we designed and characterized a three-dimensional cell culture model for ganglion-like structures. Within 24h, a mixture of mouse embryonic fibroblasts (MEF) and cells, derived from the dorsal root ganglion (DRG) (sensory neurons and Schwann cells) grown in hanging drops, assembled to coherent spherical microtissues characterized by a MEF feeder core and a peripheral layer of DRG-derived cells. In a time-dependent manner, sensory neurons formed a polar ganglion-like cap structure, which coordinated guided axonal outgrowth and innervation of the distal pole of the MEF feeder spheroid. Schwann cells, present in embryonic DRG isolates, tended to align along axonal structures and myelinate them in an in vivo-like manner. Whenever cultivation exceeded 10 days, DRG:MEF-based microtissues disintegrated due to an as yet unknown mechanism. Using a transgenic MEF feeder spheroid, engineered for gaseous acetaldehyde-inducible interferon-beta (ifn-beta) production by cotransduction of retro-/ lenti-viral particles, a short 6-h ifn-beta induction was sufficient to rescue the integrity of DRG:MEF spheroids and enable long-term cultivation of these microtissues. In hanging drops, such microtissues fused to higher-order macrotissue-like structures, which may pave the way for sophisticated bottom-up tissue engineering strategies. DRG:MEF-based artificial micro- and macrotissue design demonstrated accurate key morphological aspects of ganglions and exemplified the potential of self-assembled scaffold-free multicellular micro-/macrotissues to provide new insight into organogenesis.

Biomaterials in Canada: The first four decades

Biomaterials research in Canada began in the 1960s. Over the past four decades significant contributions have been made across a broad spectrum covering dental, orthopaedic, cardiovascular, neuro, and ocular biomaterials. Canadians have also been active in the derivative area of tissue engineering. Biomaterials laboratories are now established in universities and research institutes from coast to coast, supported mainly by funding from the Federal and Provincial Governments. The Canadian Biomaterials Society was formed in 1971 and has played an important role in the development of the field. The Society played host to the 5th World Biomaterials Congress in Toronto in 1996. The work of Canadian researchers over the past four decades is summarized briefly. It is concluded that biomaterials and tissue engineering is a mature, strong area of research in Canada and appears set to continue as such into the future.

The development of an innervated epithelial barrier model using a human corneal cell line and ND7/23 sensory neurons

The corneal epithelium is a highly innervated tissue and hence in vitro models that mimic the effects of chemicals or radiation (e.g. ultra violet) on this important barrier should include consideration of the potential role of innervation. A sensory neural cell line, ND7/23, was incorporated into a 2D and 3D model of a corneal epithelium, using a human corneal cell line, and effects on barrier integrity were neither adverse nor stimulatory. In the 3D model the nerve cell bodies were separated from the corneal epithelium, via a porous polycarbonate insert membrane. The ND7/23 cells were induced to form neurites and cease division when cultured in the keratinocyte medium employed for the corneal cells. In the absence of calcium, the epithelial barrier function was lost, shown by enhanced fluorescein leakage and relocation of ZO-1 and E-cadherin from the cell membrane. At 60 microM calcium, and above, the corneal cells formed tight junctions, with peripheral membrane location of ZO-1 and E-cadherin. The presence of the ND7/23 cells did not compromise or enhance the time taken to form these junctions, when monitored at 24-h intervals over 72 h. Both male- and female-derived human corneal cell lines showed a similar tight junction functional response to different medium calcium concentrations in the presence or absence of the ND7/23 cells. Once differentiated in keratinocyte medium, patch-clamped ND7/23 cells were capable of producing a whole-cell current when exposed to low pH (5.4), indicative of the presence of active pH-gated ion channels.

Study on Biocompatibility of Complexes of Collagen-Chitosan-Sodium Hyaluronate and Cornea

In this study we investigated the biocompatibility of collagen-chitosan-sodium hyaluronate (Col-Chi-NaHA) complexes and cornea tissue, and the feasibility of Col-Chi-NaHA complexes as substrates for cultivating rabbit corneal cells. Different components of Col-Chi-NaHA complexes were prepared and tested. A circular complex film with a diameter of 6 mm was inserted into rabbit stomal pocket and traced for a period of 5 months. Clinical examination was made. Rabbit limbal corneal epithelial cells, corneal endothelial cells, and keratocytes were cultured primarily on complexes. Phase contrast microscope examination was made daily. Histological, immunohistochemical, and scanning electron microscopic examinations were carried out. The complexes of 20% collagen, 10% chitosan, and 0.5% sodium hyaluronate showed rather weak corneal edema and other responses. The degradation of materials was obvious after 5 months. Corneas were transparent and translucent. Cells seeded on Col-Chi-NaHA were allowed to proliferate and partly form confluent monolayer after 9 days in culture. Cultured cells were well attached to the complexes of 20% collagen, 10% chitosan, and 0.5% sodium hyaluronate, or 10% chitosan and 0.5% sodium hyaluronate. The results showed that Col-Chi-NaHA complexes had good biocompatibility with cornea. The complexes can degrade and be absorbed in cornea. Col-Chi-NaHA complex may be a suitable substrate for cultivating corneal cells and a feasible material as a scaffold of tissue-engineered cornea.

Building In Vitro Models of Organs

Tissue-engineering techniques are being used to build in vitro models of organs as substitutes for human donor organs for transplantation as well as in vitro toxicology testing (as alternatives to use of animals). Tissue engineering involves the fabrication of scaffolds from materials that are biologically compatible to serve as cellular supports and microhabitats in order to reconstitute a desired tissue or organ. Three organ systems that are currently the foci of tissue engineering efforts for both transplantation and in vitro toxicology testing purposes are discussed. These are models of the cornea, nerves (peripheral nerves specifically), and cardiovascular components. In each of these organ systems, a variety of techniques and materials are being used to achieve the same end results. In general, models that are designed with consideration of the developmental and cellular biology of the target tissues or organs have tended to result in morphologically and physiologically accurate models. Many of the models, with further development and refinement, have the potential to be useful as functional substitute tissues and organs for transplantation or for in vitro toxicology testing.

Growth factors in the anterior segment: role in tissue maintenance, wound healing and ocular pathology

A number of growth factors and their associated receptors, including epidermal growth factor, transforming growth factor-beta, keratinocyte growth factor, hepatocyte growth factor, fibroblast growth factor and platelet-derived growth factor have been detected in the anterior segment of the eye. On binding to cellular receptors, these factors activate signalling cascades, which regulate functions including mitosis, differentiation, motility and apoptosis. Production of growth factors by corneal cells and their presence in the tear fluid and aqueous humour is essential for maintenance and renewal of normal tissue in the anterior eye and the prevention of undesirable immune or angiogenic reactions. Growth factors also play a vital role in corneal wound healing, mediating the proliferation of epithelial and stromal tissue and affecting the remodelling of the extracellular matrix (ECM). These functions depend on a complex interplay between growth factors of different types, the ECM, and regulatory mechanisms of the affected cells. Imbalances may lead to deficient wound healing and various ocular pathologies, including edema, neovascularization and glaucoma. Growth factors may be targeted in therapeutic ophthalmic applications, through exogenous application or selective inhibition, and may be used to elicit specific cellular responses to ophthalmic materials. A thorough understanding of the mechanism and function of growth factors and their actions in the complex environment of the anterior eye is required for these purposes. Growth factors, their function and mechanisms of action as well as the interplay between different growth factors based on recent in vitro and in vivo studies are presented.