Material Characterisation and Stratification of Conjunctival Epithelial Cells on Electrospun Poly(ε-Caprolactone) Fibres Loaded with Decellularised Tissue Matrices

The Role of Scanning Electron Microscopy in the Evaluation of Conjunctival Microvilli as an Early Biomarker of Ocular Surface Health: A Literature Review

Microvilli are bristle-like protuberances of the plasma membrane, which express the vitality of mucous and epithelial cells; their alteration indicates a condition of cellular suffering in a predictive sense, making it possible to establish how much an inflammatory state or toxic conditions affect cellular functionality. In this article, the authors evaluate the applications of scanning electron microscopy (SEM) examination to impression cytology (IC) of the bulbar conjunctiva for the assessment of microvillar alteration as an early ultrastructural indicator of ocular surface health. This method offers several advantages, starting with its simplicity: it involves the non-invasive application of a strip of bibulous paper to the bulbar or tarsal conjunctiva. Unlike conjunctival or corneal biopsies, which are surgical procedures, this technique is far less invasive and more comfortable for the patient. It also provides a more clinically relevant in vivo assessment compared to studies on cultured cell lines, which are mostly limited to scientific research and may not accurately reflect real-world conditions. This makes it an effective, repeatable, and patient-friendly option for detecting early pathological alterations of the ocular surface. It also represents a useful tool for evaluating the efficacy of topical drugs and the toxic effects of external factors and ophthalmic or systemic diseases. Finally, it allows for obtaining accessory information relating to goblet cells, the presence of inflammatory infiltrate, or any pathogens.

Advanced Biomaterials for Lacrimal Tissue Engineering: A Review

The lacrimal gland (LG) is vital for ocular health, producing tears that lubricate and protect the eye. Dysfunction of the LG leads to aqueous-deficient dry eye disease (DED), significantly impacting quality of life. Current treatments mainly address symptoms rather than the underlying LG dysfunction, highlighting the need for regenerative therapies. Tissue engineering offers a promising solution, with biomaterials playing crucial roles in scaffolding and supporting cell growth for LG regeneration. This review focuses on recent advances in biomaterials used for tissue engineering of the lacrimal gland. We discuss both natural and synthetic biomaterials that mimic the extracellular matrix and provide structural support for cell proliferation and differentiation. Natural biomaterials, such as Matrigel, decellularized extracellular matrices, chitosan, silk fibroin hydrogels, and human amniotic membrane are evaluated for their biocompatibility and ability to support lacrimal gland cells. Synthetic biomaterials, like polyethersulfone, polyesters, and biodegradable polymers (PLLA and PLGA), are assessed for their mechanical properties and potential to create scaffolds that replicate the complex architecture of the LG. We also explore the integration of growth factors and stem cells with these biomaterials to enhance tissue regeneration. Challenges such as achieving proper vascularization, innervation, and long-term functionality of engineered tissues are discussed. Advances in 3D bioprinting and scaffold fabrication techniques are highlighted as promising avenues to overcome current limitations.

Therapeutic application of decellularized porcine small intestinal submucosa scaffold in conjunctiva reconstruction

The objective of this study was to investigate the biological feasibility and surgical applicability of decellularized porcine small intestinal submucosa (DSIS) in conjunctiva reconstruction. A total of 52 Balb/c mice were included in the study. We obtained the DSIS by decellularization, evaluated the physical and biological properties of DSIS in vitro, and further evaluated the effect of surgical transplantation of DSIS scaffold in vivo. The histopathology and ultrastructural analysis results showed that the scaffold retained the integrity of the fibrous morphology while removing cells. Biomechanical analysis showed that the elongation at break of the DSIS (239.00 ± 12.51%) were better than that of natural mouse conjunctiva (170.70 ± 9.41%, P < 0.05). Moreover, in vivo experiments confirmed the excellent biocompatibility of the decellularized scaffolds. In the DSIS group, partial epithelialization occurred at day-3 after operation, and the conjunctival injury healed at day-7, which was significantly faster than that in human amniotic membrane (AM) and sham surgery (SHAM) group (P < 0.05). The number and distribution of goblet cells of transplanted DSIS were significantly better than those of the AM and SHAM groups. Consequently, the DSIS scaffold shows excellent biological characteristics and surgical applicability in the mouse conjunctival defect model, and DSIS is expected to be an alternative scaffold for conjunctival reconstruction.

Biopolymeric Innovations in Ophthalmic Surgery: Enhancing Devices and Drug Delivery Systems

The interface between material science and ophthalmic medicine is witnessing significant advances with the introduction of biopolymers in medical device fabrication. This review discusses the impact of biopolymers on the development of ophthalmic devices, such as intraocular lenses, stents, and various prosthetics. Biopolymers are emerging as superior alternatives due to their biocompatibility, mechanical robustness, and biodegradability, presenting an advance over traditional materials with respect to patient comfort and environmental considerations. We explore the spectrum of biopolymers used in ophthalmic devices and evaluate their physical properties, compatibility with biological tissues, and clinical performances. Specific applications in oculoplastic and orbital surgeries, hydrogel applications in ocular therapeutics, and polymeric drug delivery systems for a range of ophthalmic conditions were reviewed. We also anticipate future directions and identify challenges in the field, advocating for a collaborative approach between material science and ophthalmic practice to foster innovative, patient-focused treatments. This synthesis aims to reinforce the potential of biopolymers to improve ophthalmic device technology and enhance clinical outcomes.

Polymers and Biomaterials for Posterior Lamella of the Eyelid and the Lacrimal System

The application of biopolymers in the reconstruction of the posterior lamella of the eyelid and the lacrimal system marks a significant fusion of biomaterial science with clinical advancements. This review assimilates research spanning 2015 to 2023 to provide a detailed examination of the role of biopolymers in reconstructing the posterior lamella of the eyelid and the lacrimal system. It covers the anatomy and pathophysiology of eyelid structures, the challenges of reconstruction, and the nuances of surgical intervention. This article progresses to evaluate the current gold standards, alternative options, and the desirable properties of biopolymers used in these intricate procedures. It underscores the advancements in the field, from decellularized grafts and acellular matrices to innovative natural and synthetic polymers, and explores their applications in lacrimal gland tissue engineering, including the promise of 3D bioprinting technologies. This review highlights the importance of multidisciplinary collaboration between material scientists and clinicians in enhancing surgical outcomes and patient quality of life, emphasizing that such cooperation is pivotal for translating benchtop research into bedside applications. This collaborative effort is vital for restoring aesthetics and functionality for patients afflicted with disfiguring eyelid diseases, ultimately aiming to bridge the gap between innovative materials and their clinical translation.

Cryo-Electrospinning Generates Highly Porous Fiber Scaffolds Which Improves Trabecular Meshwork Cell Infiltration

Human trabecular meshwork is a sieve-like tissue with large pores, which plays a vital role in aqueous humor outflow. Dysfunction of this tissue can occur, which leads to glaucoma and permanent vision loss. Replacement of trabecular meshwork with a tissue-engineered device is the ultimate objective. This study aimed to create a biomimetic structure of trabecular meshwork using electrospinning. Conventional electrospinning was compared to cryogenic electrospinning, the latter being an adaptation of conventional electrospinning whereby dry ice is incorporated in the fiber collector system. The dry ice causes ice crystals to form in-between the fibers, increasing the inter-fiber spacing, which is retained following sublimation. Structural characterization demonstrated cryo-scaffolds to have closer recapitulation of the trabecular meshwork, in terms of pore size, porosity, and thickness. The attachment of a healthy, human trabecular meshwork cell line (NTM5) to the scaffold was not influenced by the fabrication method. The main objective was to assess cell infiltration. Cryo-scaffolds supported cell penetration deep within their structure after seven days, whereas cells remained on the outer surface for conventional scaffolds. This study demonstrates the suitability of cryogenic electrospinning for the close recapitulation of trabecular meshwork and its potential as a 3D in vitro model and, in time, a tissue-engineered device.

The conjunctival extracellular matrix, related disorders and development of substrates for conjunctival restoration

The conjunctiva can be damaged by numerous diseases with scarring, loss of tissue and dysfunction. Depending on extent of damage, restoration of function may require a conjunctival graft. A wide variety of biological and synthetic substrates have been tested in the search for optimal conditions for ex vivo culture of conjunctival epithelial cells as a route toward tissue grafts. Each substrate has specific advantages but also disadvantages related to their unique physical and biological characteristics, and identification and development of an improved substrate remains a priority. To achieve the goal of mimicking and restoring a biological material, requires information from the material. Specifically, extracellular matrix (ECM) derived from conjunctival tissue. Knowledge of the composition and structure of native ECM and identifying contributions of individual components to its function would enable using or mimicking those components to develop improved biological substrates. ECM is comprised of two components: basement membrane secreted predominantly by epithelial cells containing laminins and type IV collagens, which directly support epithelial and goblet cell adhesion differentiation and growth and, interstitial matrix secreted by fibroblasts in lamina propria, which provides mechanical and structural support. This review presents current knowledge on anatomy, composition of conjunctival ECM and related conjunctival disorders. Requirements of potential substrates for conjunctival tissue engineering and transplantation are discussed. Biological and synthetic substrates and their components are described in an accompanying review.

Influence of Storage Conditions on Decellularized Porcine Conjunctiva

Porcine decellularized conjunctiva (PDC) represents a promising alternative source for conjunctival reconstruction. Methods of its re-epithelialization in vitro with primary human conjunctival epithelial cells (HCEC) have already been established. However, a long-term storage method is required for a simplified clinical use of PDC. This study investigates the influence of several storage variants on PDC. PDC were stored in (1) phosphate-buffered saline solution (PBS) at 4 °C, (2) in glycerol-containing epithelial cell medium (EM/gly) at −80 °C and (3) in dimethyl sulfoxide-containing epithelial cell medium (EM/DMSO) at −196 °C in liquid nitrogen for two and six months, respectively. Fresh PDC served as control. Histological structure, biomechanical parameters, the content of collagen and elastin and the potential of re-epithelialization with primary HCEC under cultivation for 14 days were compared (n = 4–10). In all groups, PDC showed a well-preserved extracellular matrix without structural disruptions and with comparable fiber density (p ≥ 0.74). Collagen and elastin content were not significantly different between the groups (p ≥ 0.18; p ≥ 0.13, respectively). With the exception of the significantly reduced tensile strength of PDC after storage at −196 °C in EM/DMSO for six months (0.46 ± 0.21 MPa, p = 0.02), no differences were seen regarding the elastic modulus, tensile strength and extensibility compared to control (0.87 ± 0.25 MPa; p ≥ 0.06). The mean values of the epithelialized PDC surface ranged from 51.9 ± 8.8% (−196 °C) to 78.3 ± 4.4% (−80 °C) and did not differ significantly (p ≥ 0.35). In conclusion, all examined storage methods were suitable for storing PDC for at least six months. All PDC were able to re-epithelialize, which rules out cytotoxic influences of the storage conditions and suggests preserved biocompatibility for in vivo application.

Establishment of a bi-layered tissue engineered conjunctiva using a 3D-printed melt electrowritten poly-(ε-caprolactone) scaffold

PURPOSE

To utilize melt electrowriting (MEW) technology using poly-(ε-caprolactone) (PCL) coupled with a 2-step co-culturing strategy for the development of a conjunctival bi-layer synthetic construct.

METHODS

Melt electrowritten scaffolds using PCL were fabricated using an in-house-built MEW printer. Human conjunctival stromal cells (CjSCs) and epithelial cells (CjECs) were isolated from donor tissue. A 2-step co-culture method was done by first seeding the CjSCs and culturing for 4 weeks to establish a stromal layer, followed by CjECs and co-culturing for 2 more weeks. Cultured cells were each characterized by morphology and marker expression on immunofluorescence and qPCR. The produced construct was assessed for cellular proliferation using viability assays. The bi-layer morphology was assessed using scanning electron microscopy (SEM), confocal microscopy, and immunofluorescence imaging. The expression of extracellular matrix components and TGF-b was evaluated using qPCR.

RESULTS

CjSCs were spindle-shaped and vimentin + while CjECs were polygonal and CK13 + . CjSCs showed consistent proliferation and optimal adherence with the scaffold at the 4-week culture mark. A 2-layered construct consisting of a CjSC-composed stromal layer and a CjEC-composed epithelial layer was appreciated on confocal microscopy, SEM, and immunofluorescence. CjSCs secreted collagens (types I, V, VI) but at differing amounts from natural tissue while TGF-b production was comparable.

CONCLUSION

The 3D-printed melt electrowritten PCL scaffold paired with the 2-step co-culturing conditions of the scaffold allowed for the first approximation of a bi-layered stromal and epithelial reconstruction of the conjunctiva that can potentially improve the therapeutic arsenal in ocular surface reconstruction.

[Methods of surgical reconstruction of the conjunctiva]

Reconstruction of the conjunctiva is required for restoration of damaged ocular surface and is an essential part of that process. Traumas, chemical and thermal burns, multiple surgical intervention can seriously damage the integrity of conjunctival tissue and promote the growth of fibrous tissue, scarring of contractures and their shortening, as well as other complications such as trichiasis, erosion and ulcers on the cornea. When a larger area is affected, there may not be enough donor tissue to replace the defect, in which case the tissue grafts are required to be large enough. Modern modifications of surgical techniques and the continued development of tissue engineering, as well as advancements in stem cell research offer promising novel alternatives for solution of those problems. This article reviews the existing surgical methods of conjunctival reconstruction.

An Optimized Method to Decellularize Human Trabecular Meshwork

Glaucoma is linked to raised intraocular pressure (IOP). The trabecular meshwork (TM) plays a major role in regulating IOP by enabling outflow of aqueous humor from the eye through its complex 3D structure. A lack of therapies targeting the dysfunctional TM highlights the need to develop biomimetic scaffolds that provide 3D in vitro models for glaucoma research or as implantable devices to regenerate TM tissue. To artificially mimic the TM's structure, we assessed methods for its decellularization and outline an optimized protocol for cell removal and structural retention. Using bovine TM, we trialed 2 lysing agents-Trypsin (0.05% v/v) and Ammonium Hydroxide (NH4OH; 2% v/v). Twenty-four hours in Trypsin caused significant structural changes. Shorter exposure (2 h) reduced this disruption whilst decellularizing the tissue (dsDNA 26 ± 14 ng/mL (control 1970 ± 146 ng/mL)). In contrast, NH4OH lysed all cells (dsDNA 25 ± 21 ng/mL), and the TM structure remained intact. For human TM, 2% v/v NH4OH similarly removed cells (dsDNA 52 ± 4 ng/mL (control 1965 ± 233 ng/mL)), and light microscopy and SEM presented no structural damage. X-ray computed tomography enabled a novel 3D reconstruction of decellularized human TM and observation of the tissue's intricate architecture. This study provides a new, validated method using NH4OH to decellularize delicate human TM without compromising tissue structure.

Antimicrobial Nitric Oxide-Releasing Electrospun Dressings for Wound Healing Applications

Nonhealing and chronic wounds represent a major problem for the quality of life of patients and have cost implications for healthcare systems. The pathophysiological mechanisms that prevent wound healing are usually multifactorial and relate to patient overall health and nutrition, vascularity of the wound bed, and coexisting infection/colonization. Bacterial infections are one of the predominant issues that can stall a wound, causing it to become chronic. Successful wound healing often depends on weeks or months of antimicrobial therapy, but this is problematic given the rise in multidrug-resistant bacteria. As such, alternatives to antibiotics are desperately needed to aid the healing of chronic, and even acutely infected wounds. Nitric oxide (NO) kills bacteria through a variety of mechanisms, and thus, bacteria have shown no tendency to develop resistance to NO as a therapeutic agent and therefore can be a good alternative to antibiotic therapy. In this paper, we report on the development of NO-releasing electrospun membranes fabricated from polycaprolactone (PCL)/gelatin blends and optimized to reduce bacterial infection. The NO payload in the membranes was directly related to the number of amines (and hence the amount of gelatin) in the blend. Higher NO payloads corresponded with a higher degree of antimicrobial efficacy. No cytotoxicity was observed for electrospun membranes, and an in vitro wound closure assay demonstrated closure within 16 h. The results presented here clearly indicate that these NO-releasing electrospun membranes hold significant promise as wound dressings due to their antimicrobial activity and biocompatibility.

Biofabrication of Artificial Stem Cell Niches in the Anterior Ocular Segment

The anterior segment of the eye is a complex set of structures that collectively act to maintain the integrity of the globe and direct light towards the posteriorly located retina. The eye is exposed to numerous physical and environmental insults such as infection, UV radiation, physical or chemical injuries. Loss of transparency to the cornea or lens (cataract) and dysfunctional regulation of intra ocular pressure (glaucoma) are leading causes of worldwide blindness. Whilst traditional therapeutic approaches can improve vision, their effect often fails to control the multiple pathological events that lead to long-term vision loss. Regenerative medicine approaches in the eye have already had success with ocular stem cell therapy and ex vivo production of cornea and conjunctival tissue for transplant recovering patients' vision. However, advancements are required to increase the efficacy of these as well as develop other ocular cell therapies. One of the most important challenges that determines the success of regenerative approaches is the preservation of the stem cell properties during expansion culture in vitro. To achieve this, the environment must provide the physical, chemical and biological factors that ensure the maintenance of their undifferentiated state, as well as their proliferative capacity. This is likely to be accomplished by replicating the natural stem cell niche in vitro. Due to the complex nature of the cell microenvironment, the creation of such artificial niches requires the use of bioengineering techniques which can replicate the physico-chemical properties and the dynamic cell-extracellular matrix interactions that maintain the stem cell phenotype. This review discusses the progress made in the replication of stem cell niches from the anterior ocular segment by using bioengineering approaches and their therapeutic implications.

Biological tissues and components, and synthetic substrates for conjunctival cell transplantation

The conjunctiva is the largest component of the ocular surface. It can be damaged by various pathological processes leading to scarring, loss of tissue and dysfunction. Depending on the amount of damage, restoration of function may require a conjunctival graft. Numerous studies have investigated biological and synthetic substrates in the search for optimal conditions for the ex vivo culture of conjunctival epithelial cells that can be used as tissue grafts for transplantation. These substrates have advantages and disadvantages that are specific to the characteristics of each material; the development of an improved material remains a priority. This review is the second of a two-part review in The Ocular Surface. In the first review, the structure and function of the conjunctiva was evaluated with a focus on the extracellular matrix and the basement membrane, and biological and mechanical characteristics of the ideal substrate with recommendations for further studies. In this review the types of biological and synthetic substrates used for conjunctival transplantation are discussed including substrates based on the extracellular matrix. .