Construction and Evaluation of Collagen-Based Corneal Grafts Using Polycaprolactone To Improve Tension Stress

Advanced 3D scaffolds for corneal stroma regeneration: a preclinical progress

Corneal stromal defects represent a significant global cause of blindness, necessitating innovative therapeutic strategies to address the limitations of conventional treatments, such as corneal transplantation. Tissue engineering, a cornerstone of regenerative medicine, offers a transformative approach by leveraging biomaterial-based solutions to restore damaged tissues. Among these, three-dimensional (3D) scaffolds fabricated using advanced techniques like 3D printing have emerged as a promising platform for corneal regeneration. These scaffolds replicate the native extracellular matrix (ECM) architecture, providing a biomimetic microenvironment that supports cell proliferation, differentiation, and tissue integration. This review highlights recent advances in the design and fabrication of 3D scaffolds for corneal stroma engineering (CSE), emphasizing the critical interplay between scaffold architecture, mechanical properties, and bioactive signaling in directing cellular behavior and tissue regeneration. Likewise, we emphasize the diverse range of biomaterials utilized in scaffold fabrication, highlighting their influence on cellular interactions and tissue reconstruction. By elucidating the complex relationship between scaffold design and biologics, this review aims to illuminate the evolution of next-generation strategies for engineering functional corneal tissue. Eventually, this review will provide a comprehensive synthesis of the current state-of-the-art in 3D scaffold-based corneal tissue engineering (CTE), offering insights that could advance progress toward effective vision restoration therapies.

Glycerol Modulated Collagen Fibril Evolution and Lamellar Organization for Biomimetic Corneal Substitutes Construction

Collagen as the main structural component of the cornea exhibits unique and highly organized fibril lamellae, which contribute to the maintenance of corneal structure and transparency. Nevertheless, collagen assembly in vitro to create ideal artificial corneal substitutes with human cornea comparable thickness and optics is still limited. Here, glycerol as a regulator can reconcile collagen thickness, transparency, and permeability, a conflicting goal by current keratoprosthesis strategies. Structure analysis reveals that glycerol treatment induces collagen hydrogels to undergo a sequential three-step multiscale structural evolution: weakened collagen crystallization at the molecular level, followed by ordered and distanced microfibril packaging at the nanoscale, and ultimately lamellar structure as well as fibril diameter and spacing-dependent optics at a macroscopic level. Such ultrastructure is then stabilized by oxazolidine crosslinking to obtain a collagen-based artificial corneal substitute (Col-Gly-OX) with optimal integration of optical clarity, mechanical robustness, high permeability, manufacturability, easy preservation and in vitro biocompatibility. Further in vivo study demonstrates that Col-Gly-OX displays excellent tissue integration, epithelialization, and stromal remodeling in a rabbit lamellar keratectomy. Overall, this work illustrates the potential of glycerol regulator to mediate the multiscale structural organization of collagen, providing a green, simple and effective strategy for the development of bionic artificial cornea.

Silk fibroin/vitreous humor hydrogel scaffold modified by a carbodiimide crosslinker for wound healing

Natural-derived biomaterials can be used as substrates for the growth, proliferation, and differentiation of cells. In this study, bovine vitreous humor as a biological material was cross-linked to silk fibroin with different concentration ratios to design a suitable substrate for corneal tissue regeneration. The cross-linked samples were evaluated with different analyses such as structural, physical (optical, swelling, and degradation), mechanical, and biological (viability, cell adhesion) assays. The results showed that all samples had excellent transparency, especially those with higher silk fibroin content. Increasing the ratio of vitreous humor to silk fibroin decreased mechanical strength and increased swelling and degradation, respectively. There was no significant difference in the toxicity of the samples, and with the increase in vitreous humor ratio, adhesion and cell proliferation increased. Generally, silk fibroin with vitreous humor can provide desirable characteristics as a transparent film for corneal wound healing.

Hydrophilic, Porous, Fiber-Reinforced Collagen-Based Membrane for Corneal Repair

Collagen membrane with outstanding biocompatibility exhibits immense potential in the field of corneal repair and reconstruction, but the poor mechanical properties limit its clinical application. Polycaprolactone (PCL) is a biodegradable polymer widely explored for application in corneal reconstruction due to its excellent mechanical properties, biocompatibility, easy processability, and flexibility. In this study, a PCL/collagen composite membrane with reinforced mechanical properties is developed. The membrane has a strong composite structure with collagen by utilizing a porous and hydrophilic PCL scaffold, maintaining its integrity even after immersion. The suture retention and mechanical tests demonstrate that compared with the pure collagen membrane, the prepared membrane has a greater tensile strength and twice the modulus of elasticity. Further, the suture retention strength is improved by almost two times. In addition, the membrane remains fully intact on the implant bed in an in vitro corneal defect model. Moreover, the membrane can be tightly sutured to a rabbit corneal defect, progressively achieve epithelialization, and remain unchanged during observation. Overall, the PCL/collagen composite membrane is a promising candidate as a suturable corneal restoration material in clinical keratoplasty.

Hybrid-Aligned Fibers of Electrospun Gelatin with Antibiotic and Polycaprolactone Composite Membranes as an In Vitro Drug Delivery System to Assess the Potential Repair Capacity of Damaged Cornea

The cornea lacks the ability to repair itself and must rely on transplantation to repair damaged tissue. Therefore, creating alternative therapies using dressing membranes based on tissue engineering concepts to repair corneal damage before failure has become a major research goal. Themost outstanding features that are important in reconstructing a damaged cornea are the mechanical strength and transparency of the membrane, which are the most important standard considerations. In addition, preventing infection is an important issue, especially in corneal endothelial healing processes. The purpose of this study was to produce aligned fibers via electrospinning technology using gelatin (Gel) composite polycaprolactone (PCL) as an optimal transport and antibiotic release membrane. The aim of the composite membrane is to achieve good tenacity, transparency, antibacterial properties, and in vitro biocompatibility. Results showed that the Gel and PCL composite membranes with the same electrospinning flow rate had the best transparency. The Gel impregnated with gentamicin antibiotic in composite membranes subsequently exhibited transparency and enhanced mechanical properties provided by PCL and could sustainably release the antibiotic for 48 h, achieving good antibacterial effects without causing cytotoxicity. This newly developed membrane has the advantage of preventing epidermal tissue infection during clinical operations and is expected to be used in the reconstruction of damaged cornea in the future.

Human cornea-derived extracellular matrix hydrogel for prevention of post-traumatic corneal scarring: A translational approach

Corneal scarring and opacification are a significant cause of blindness affecting millions worldwide. The current standard of care for corneal blindness is corneal transplantation, which suffers from several drawbacks. One alternative approach that has shown promise is the use of xenogeneic corneal extracellular matrix (ECM), but its clinical applicability is challenging due to safety concerns. This study reports the innovative use of human cornea-derived ECM to prevent post-traumatic corneal scarring. About 30 - 40% of corneas donated to the eye banks do not meet the standards defined for clinical use and are generally discarded, although they are completely screened for their safety. In this study, human cornea-derived decellularized ECM hydrogel was prepared from the non-transplantation grade human cadaveric corneas obtained from an accredited eye-bank. The prepared hydrogel was screened for its efficacy against corneal opacification following an injury in an animal model. Our in vivo study revealed that, the control collagen-treated group developed corneal opacification, while the prophylactic application of human cornea-derived hydrogel effectively prevented corneal scarring and opacification. The human hydrogel-treated corneas were indistinguishable from healthy corneas and comparable to those treated with the xenogeneic bovine corneal hydrogel. We also demonstrated that the application of the hydrogel retained the biological milieu including cell behavior, protein components, optical properties, curvature, and nerve regeneration by remodeling the corneal wound after injury. The hydrogel application is also sutureless, resulting in faster corneal healing. We envision that this human cornea-derived ECM-based hydrogel has potential clinical application in preventing scarring from corneal wounding. STATEMENT OF SIGNIFICANCE: There are significant challenges surrounding corneal regeneration after injury due to extensive scarring. Although there is substantial research on corneal regeneration, much of it uses synthetic materials with chemical cross-linking methods or xenogeneic tissue-based material devices which have to undergo exhaustive safety analysis before clinical trials. Herein, we demonstrate the potential application of a human corneal extracellular matrix hydrogel without any additional materials for scarless corneal tissue regeneration, and a method to reduce the wasting of donated allogenic corneal tissue from eye banks. We found no difference in efficacy between the usage of human tissues compared to xenogeneic sources. This may help ease clinical translation and can be used topically without sutures as an outpatient procedure.

Electro-compacted collagen for corneal epithelial tissue engineering

Bioengineered corneal substitutes offer a solution to the shortage of donor corneal tissue worldwide. As one of the major structural components of the cornea, collagen has shown great potential for tissue-engineered cornea substitutes. Herein, free-standing collagen membranes fabricated using electro-compaction were assessed in corneal bioengineering application by comparing them with nonelectro-compacted collagen (NECC). The well-organized and biomimetic fibril structure resulted in a significant improvement in mechanical properties. A 10-fold increase in tensile and compressive modulus was recorded when compared with NECC membranes. In addition to comparable transparency in the visible light range, the glucose permeability of the electro-compacted collagen (ECC) membrane is higher than that of the native human cornea. Human corneal epithelial cells adhere and proliferate well on the ECC membrane, with a large cell contact area observed. The as-described ECC has appropriate structural, topographic, mechanical, optical, glucose permeable, and cell support properties to provide a platform for a bioengineered cornea; including the outer corneal epithelium and potentially deeper corneal tissues.

Arrested Phase Separation Enables High-Performance Keratoprostheses

Corneal transplantation is impeded by donor shortages, immune rejection, and ethical reservations. Pre-made cornea prostheses (keratoprostheses) offer a proven option to alleviate these issues. Ideal keratoprostheses must possess optical clarity and mechanical robustness, but also high permeability, processability, and recyclability. Here, it is shown that rationally controlling the extent of arrested phase separation can lead to optimized multiscale structure that reconciles permeability and transparency, a previously conflicting goal by common pore-forming strategies. The process is simply accomplished by hydrothermally treating a dense and transparent hydrophobic association hydrogel. The examination of multiscale structure evolution during hydrothermal treatment reveals that the phase separation with upper miscibility gap evolves to confer time-dependent pore growth due to slow dynamics of polymer-rich phase which is close to vitrification. Such a process can render a combination of multiple desired properties that equal or surpass those of the state-of-the-art keratoprostheses. In vivo tests confirm that the keratoprosthesis can effectively repair corneal perforation and restore a transparent cornea with treatment outcomes akin to that of allo-keratoplasty. The keratoprosthesis is easy to access and convenient to carry, and thus would be an effective temporary substitute for a corneal allograft in emergency conditions.

Membranes for the life sciences and their future roles in medicine

Since the global outbreak of COVID-19, membrane technology for clinical treatments, including extracorporeal membrane oxygenation (ECMO) and protective masks and clothing, has attracted intense research attention for its irreplaceable abilities. Membrane research and applications are now playing an increasingly important role in various fields of life science. In addition to intrinsic properties such as size sieving, dissolution and diffusion, membranes are often endowed with additional functions as cell scaffolds, catalysts or sensors to satisfy the specific requirements of different clinical applications. In this review, we will introduce and discuss state-of-the-art membranes and their respective functions in four typical areas of life science: artificial organs, tissue engineering, in vitro blood diagnosis and medical support. Emphasis will be given to the description of certain specific functions required of membranes in each field to provide guidance for the selection and fabrication of the membrane material. The advantages and disadvantages of these membranes have been compared to indicate further development directions for different clinical applications. Finally, we propose challenges and outlooks for future development.

Improving the properties of fish skin collagen/silk fibroin dressing by chemical treatment for corneal wound healing

Natural biomaterials are crucial in ocular tissue engineering because they allow cells to proliferate, differentiate, and stratify while maintaining the typical epithelial phenotype. In this study, membranes as dressings were formed from silk fibroin and collagen (Co) extracted from fish skin and then modified with carbodiimide chemical cross linker in different concentrations. The samples were evaluated by different analyses such as structural, physical (optical, swelling, denaturation temperature, degradation), mechanical, and biological (viability, cell adhesion, immunocytochemistry) assays. The results showed that all membranes have excellent transparency, especially with higher silk fibroin content. Increasing the cross linker concentration and the ratio of silk fibroin to Co increased the denaturation temperature and mechanical strength and, conversely, reduced the degradation rate and cell adhesion. The samples did not show a significant difference in toxicity with increasing cross linker and silk fibroin ratio. In general, samples with a low silk fibroin ratio combined with cross linker can provide desirable properties as a membrane for corneal wound healing.

Electrical Signal Initiates Kinetic Assembly of Collagen to Construct Optically Transparent and Geometry Customized Artificial Cornea Substitutes

Corneal transplantation is an effective treatment for reconstructing injured corneas but is very limited due to insufficient donors, which has led to a growing demand for development of artificial corneal substitutes (ACSs). Collagen is a potential building block for ACS fabrication, whereas technically there are limited capabilities to control the collagen assembly for creating highly transparent collagen ACSs. Here, we report an electro-assembly technique to kinetically control collagen assembly on the nanoscale that allows the yielding collagen ACSs with structure determined superior optics. Structurally, the kinetically electro-assembled collagen (KEA-Col) is composed of partially aligned microfibrils (∼10 nm in diameter) with compacted lamellar organization. Optical analysis reveals that such microstructure is directly responsible for its optimal light transmittance by reducing light scattering. Moreover, this method allows the creation of complex three-dimensional geometries and thus is convenient to customize collagen ACSs with specific curvatures to meet refractive power requirements. Available properties (e.g., optics and mechanics) of cross-linked KEA-Cols were studied to meet the clinical requirement as ACSs, and in vitro tests further proved their beneficial characteristics of cell growth and migration. An in vivo study established a rabbit lamellar keratectomy corneal wound model and demonstrated the customized collagen ACSs can adapt to the defective cornea and support epithelial healing as well as stroma integration and reconstruction with lower immunoreaction compared with commercial xenografts, which suggests its promising application prospects. More broadly, this work illustrates the potential for enlisting electrical signals to mediate collagen's assembly and microstructure organization for specific structural functionalization for regenerative medicine.

Effects of Different Radiation Sources on the Performance of Collagen-Based Corneal Repair Materials and Macrophage Polarization

Owing to the lack of donor corneas, there is an urgent need for suitable corneal substitutes. As the main component of the corneal stroma, collagen has great advantages as a corneal repair material. If there are microorganisms such as bacteria in the corneal repair material, it may induce postoperative infection, causing the failure of corneal transplantation. Therefore, irradiation, as a common sterilization method, is often used to control the microorganisms in the material. However, it has not been reported which type of radiation source and what doses can sterilize more effectively without affecting the properties of collagen-based corneal repair materials (CCRMs) and have a positive impact on macrophage polarization. In this study, three different radiation sources of ultraviolet, cobalt-60, and electron beam at four different doses of 2, 5, 8, and 10 kGy were used to irradiate CCRMs. The swelling, stretching, transmittance, and degradation of the irradiated CCRMs were characterized, and the proliferation of human corneal epithelial cells on the irradiated CCRMs was characterized using the CCK8 kit. The results showed that low dose (<5 kGy) of radiation had little effect on the performance of CCRMs. Three irradiation methods with less influence were selected for the further study on RAW264.7 macrophage polarization. The results indicated that CCRMs treated with UV could downregulate the expression of pro-inflammatory related genes and upregulate the expression of anti-inflammatory genes in macrophages, which indicated that UV irradiation is a beneficial process for the preparation of CCRMs.

Biocompatible Synthetic Polymers for Tissue Engineering Purposes

Synthetic polymers have been an integral part of modern society since the early 1960s. Besides their most well-known applications to the public, such as packaging, construction, textiles and electronics, synthetic polymers have also revolutionized the field of medicine. Starting with the first plastic syringe developed in 1955 to the complex polymeric materials used in the regeneration of tissues, their contributions have never been more prominent. Decades of research on polymeric materials, stem cells, and three-dimensional printing contributed to the rapid progress of tissue engineering and regenerative medicine that envisages the potential future of organ transplantations. This perspective discusses the role of synthetic polymers in tissue engineering, their design and properties in relation to each type of application. Additionally, selected recent achievements of tissue engineering using synthetic polymers are outlined to provide insight into how they will contribute to the advancement of the field in the near future. In this way, we aim to provide a guide that will help scientists with synthetic polymer design and selection for different tissue engineering applications.

Mechanical Properties of Bioengineered Corneal Stroma

For the majority of patients with severe corneal injury or disease, corneal transplantation is the only suitable treatment option. Unfortunately, the demand for donor corneas greatly exceeds the availability. To overcome shortage issues, a myriad of bioengineered constructs have been developed as mimetics of the corneal stroma over the last few decades. Despite the sheer number of bioengineered stromas developed , these implants fail clinical trials exhibiting poor tissue integration and adverse effects in vivo. Such shortcomings can partially be ascribed to poor biomechanical performance. In this review, existing approaches for bioengineering corneal stromal constructs and their mechanical properties are described. The information collected in this review can be used to critically analyze the biomechanical properties of future stromal constructs, which are often overlooked, but can determine the failure or success of corresponding implants.

Natural Polymeric Scaffolds for Tissue Engineering Applications

Natural polymeric scaffolds can be used for tissue engineering applications such as cell delivery and cell-free supporting of native tissues. This is because of their desirable properties such as; high biocompatibility, tunable mechanical strength and conductivity, large surface area, porous- and extracellular matrix (ECM)-mimicked structures. Specifically, their less toxicity and biocompatibility makes them suitable for several tissue engineering applications. For these reasons, several biopolymeric scaffolds are currently being explored for numerous tissue engineering applications. To date, research on the nature, chemistry, and properties of nanocomposite biopolymers are been reported, while the need for a comprehensive research note on more tissue engineering application of these biopolymers remains. As a result, this present study comprehensively reviews the development of common natural biopolymers as scaffolds for tissue engineering applications such as cartilage tissue engineering, cornea repairs, osteochondral defect repairs, and nerve regeneration. More so, the implications of research findings for further studies are presented, while the impact of research advances on future research and other specific recommendations are added as well.

A Comprehensive Review on the Applications of Exosomes and Liposomes in Regenerative Medicine and Tissue Engineering

Tissue engineering and regenerative medicine are generally concerned with reconstructing cells, tissues, or organs to restore typical biological characteristics. Liposomes are round vesicles with a hydrophilic center and bilayers of amphiphiles which are the most influential family of nanomedicine. Liposomes have extensive research, engineering, and medicine uses, particularly in a drug delivery system, genes, and vaccines for treatments. Exosomes are extracellular vesicles (EVs) that carry various biomolecular cargos such as miRNA, mRNA, DNA, and proteins. As exosomal cargo changes with adjustments in parent cells and position, research of exosomal cargo constituents provides a rare chance for sicknesses prognosis and care. Exosomes have a more substantial degree of bioactivity and immunogenicity than liposomes as they are distinctly chiefly formed by cells, which improves their steadiness in the bloodstream, and enhances their absorption potential and medicinal effectiveness in vitro and in vivo. In this review, the crucial challenges of exosome and liposome science and their functions in disease improvement and therapeutic applications in tissue engineering and regenerative medicine strategies are prominently highlighted.