Evaluation of Plastic-Compressed Collagen for Conjunctival Repair in a Rabbit Model

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.

A thin film comprising silk peptide and cellulose nanofibrils implanting on the electrospun poly(lactic acid) fibrous scaffolds for biomedical reconstruction

Conjunctival reconstruction using biocompatible polymers constitutes an effective treatment for conjunctival scarring and associated visual impairment. In this work, a thin film comprising silk peptide (SP), cellulose nanofibrils (CNF) and Ag nanoparticles (AgNPs) that implanted on the poly(lactic acid) (PLA) electrospun fibrous membranes (EFMs) was designed for biomedical reconstruction. SP and CNF as thin films can improve the surface hydrophilicity of the as-prepared scaffolds, which synergistically enhanced the biocompatibility. In in vivo experiments, the developed PLA EFMs modified with 3 wt% SP/CNF/AgNPs could be easily manipulated and transplanted onto conjunctival defects in rabbits, consequently accelerating the structural and functional restoration of the ocular surface in 12 days. Additionally, incorporation of 0.30 mg/g AgNPs efficiently reduced the topical application of antibiotics without causing infections. Thus, these resultant scaffolds could not only serve as useful alternatives for conjunctival engineering, but also prevent infections effectively with a very low content of AgNPs.

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.

[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.

Sutureless transplantation using a semi-interpenetrating polymer network bioadhesive for ocular surface reconstruction

The conjunctiva covers the largest area of ocular surface and is responsible for tear balance and clear vision. After trauma or surgery, the conjunctiva is prone to scarring and contracture. Transplantation with suture often implies numerous complications, such as inflammation, suture erosion, granuloma. And the suture needs to be removed, which means a secondary trauma. In this study, a (GMO) for sutureless conjunctival transplantation was developed based on a semi-interpenetrating polymer network (sIPN) consisting of gelatin methacrylate (GelMA) and oxidized hyaluronic acid (OHA). The maximum adhesion strength was 157 ± 17 kPa, and the burst pressure was 357 ± 29 kPa, which was 15 times higher than the human intraocular pressure (IOP). GMO bioadhesive hydrogel significantly improved surgical efficiency and secured the collagen scaffold firmly to a rabbit conjunctival defect. The sutureless transplantation approach revealed the promoted tissue repair without scar. In conclusion, GMO bioadhesive may be an attractive alternative to suture for ocular surface reconstruction by avoiding suture-related complications and improving clinical outcome. STATEMENT OF SIGNIFICANCE: Conjunctival tissue is prone to scarring and contracture after trauma, and surgery with sutures often implies numerous complications. In this study, the ocular surface reconstruction was achieved by sutureless transplantation of conjunctival scaffold using bioadhesive hydrogel. The prepared GMO bioadhesive based on the semi-interpenetrating network of gelatin methacrylate (GelMA) and oxidized hyaluronic acid (OHA) had favorable adhesion and mechanical properties. The sutureless transplantation approach significantly improved the operation efficiency, avoided suture-related complications, and promoted the regeneration of conjunctiva. This study highlights the great potential of the sutureless repair strategy for clinical application in ocular surface reconstruction.

[Conjunctival reconstruction-State of the art of regenerative treatment forms beyond the limbus]

BACKGROUND

The demands on conjunctival replacement tissues are high: they need to be elastic, clinically compatible, surgically feasible and support goblet cell growth.

OBJECTIVE

This article provides an overview of currently applied conjunctival replacement tissues and those under investigation.

METHOD

Current publications on clinically applied conjunctival replacement tissues and substrates which are the subject of scientific research and those already tested in animal models are presented and discussed.

RESULTS

Replacement tissues in clinical use are autologous and allogenic conjunctiva, nasal and oral mucous membranes, amniotic membrane and decellularized tissues. Autologous conjunctiva shows good results but is not suitable for large defects due to limited availability. In these cases autologous nasal and oral mucous membranes can be used; however, success is limited in cases of autoimmune diseases. Amniotic membranes are frequently applied clinically but goblet cell growth is limited. Different decellularized tissues are used clinically and goblet cell growth was found in vivo. Robust comparative studies are not yet available. Biological matrices such as fibrin, collagen, elastin, gelatin or hyaluronate and synthetic tissues from the group of polyesters are being investigated in the laboratory and in animal models. These studies show good epithelialization and goblet cell growth in vivo.

CONCLUSION

Transplantation of conjunctiva, nasal and oral mucous membranes and amniotic membranes show satisfactory clinical results but exhibit individual weaknesses. Further studies in animal models and clinical settings are required to further evaluate the benefits of other matrices, such as cell-free tissues or other biological and synthetic matrices.

Crosslinked Decellularized Porcine Pericardium as a Substrate for Conjunctival Reconstruction

Seeking for suitable conjunctival reconstruction substitutes to overcome the limitations of current substitutes, such as amniotic membrane, is urgent. Decellularized tissues have become a promising strategy for tissue engineering. In this study, we prepared decellularized porcine pericardium (DPP) scaffolds by the phospholipase A2 method and crosslinked them with aspartic acid (Asp) and human endothelial growth factor (hEGF) to enhance biological performance on the DPP, obtaining DPP-Asp-hEGF scaffolds. In vitro DPP showed lower apoptosis, highly desirable, well preservation of extracellular matrix components, and favorable macro-microstructure, which was confirmed by histology, immunofluorescence, electron microscopy, collagen and DNA quantification, and cytotoxicity assay, compared to the native porcine pericardium (NPP). The crosslinked efficacy of the DPP-Asp-hEGF was furtherer verified by in vitro experiments with Fourier transform infrared (FTIR) and X-ray diffraction (XRD). Through animal models of conjunctiva defect model, the DPP-Asp-hEGF revealed a closed, multilayer epithelium with an equal amount of goblet cells and no indication for conjunctival scarring after 28 days, compared to amniotic membrane (AM) groups and sham groups. These results suggested that DPP-Asp-hEGF can offer a good conjunctival reconstructive substitute both in structure and in function.

Cryopreservation in a Standard Freezer: −28 °C as Alternative Storage Temperature for Amniotic Membrane Transplantation

Human amniotic membrane (hAM) is usually stored at −80 °C. However, in many regions, cryopreservation at −80 °C is not feasible, making hAM unavailable. Therefore, the possibility of cryopreservation at −28 °C (household freezer) was investigated. hAMs (n = 8) were stored at −80 °C or −28 °C for a mean time of 8.2 months. hAM thickness, epithelial integrity and basement membrane were assessed histologically. The collagen content, concentration of hepatocyte growth factor (HGF) and basic fibroblast growth factor (bFGF) were determined. Elastic modulus and tensile strength were measured. The mean thickness of hAM stored at −28 °C was 33.1 ± 21.6 µm (range 9.7–74.9); thickness at −80 °C was 30.8 ± 14.7 µm (range 13.1–50.7; p = 0.72). Mean collagen content, epithelial cell number and integrity score showed no significant difference between samples stored at −28 °C or −80 °C. Basement membrane proteins were well preserved in both groups. Mean tensile strength and elastic modulus were not significantly different. Concentration of bFGF at −28 °C was 1063.2 ± 680.3 pg/g (range 369.2–2534.2), and 1312.1 ± 778.2 pg/g (range 496.2–2442.7) at −80 °C (p = 0.11). HGF was 5322.0 ± 2729.3 pg/g (range 603.3–9149.8) at −28 °C, and 11338.5 ± 6121.8 pg/g (range 4143.5 to 19806.7) at −80 °C (p = 0.02). No microbiological contamination was detected in any sample. The cryopreservation of hAM at −28 °C has no overt disadvantages compared to −80 °C; the essential characteristics of hAM are preserved. This temperature could be used in an alternative storage method whenever storage at −80 °C is unavailable.

Collagen- and hyaluronic acid-based hydrogels and their biomedical applications

Hydrogels have been widely investigated in biomedical fields due to their similar physical and biochemical properties to the extracellular matrix (ECM). Collagen and hyaluronic acid (HA) are the main components of the ECM in many tissues. As a result, hydrogels prepared from collagen and HA hold inherent advantages in mimicking the structure and function of the native ECM. Numerous studies have focused on the development of collagen and HA hydrogels and their biomedical applications. In this extensive review, we provide a summary and analysis of the sources, features, and modifications of collagen and HA. Specifically, we highlight the fabrication, properties, and potential biomedical applications as well as promising commercialization of hydrogels based on these two natural polymers.

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. .

Surgical Management and Recent Advances in Chemical Injury: A 5-year Review

Purpose: To review the surgical management options in ocular chemical burn, including newer advances.Methods: Online literature search of published articles over last 5 years on surgical management of ocular chemical burn and newer advances were performed on December 30, 2020.Results: Following literature search and screening using adequate filters, 67 review articles on surgical management of ocular chemical burns were retrieved. The review talks about the surgical management options starting from Debridement in acute stage to various visual rehabilitative procedures in the chronic stage. The review also highlights the evolving surgical advances in this field.Conclusion: It is imperative to choose adequate surgical tool wherever applicable; current review discusses the role of each surgical option at different clinical stages in detail.

Three-Dimensional Human Cell Culture Models to Study the Pathophysiology of the Anterior Eye

In recent decades, the establishment of complex three-dimensional (3D) models of tissues has allowed researchers to perform high-quality studies and to not only advance knowledge of the physiology of these tissues but also mimic pathological conditions to test novel therapeutic strategies. The main advantage of 3D models is that they recapitulate the spatial architecture of tissues and thereby provide more physiologically relevant information. The eye is an extremely complex organ that comprises a large variety of highly heterogeneous tissues that are divided into two asymmetrical portions: the anterior and posterior segments. The anterior segment consists of the cornea, conjunctiva, iris, ciliary body, sclera, aqueous humor, and the lens. Different diseases in these tissues can have devastating effects. To study these pathologies and develop new treatments, the use of cell culture models is instrumental, and the better the model, the more relevant the results. Thus, the development of sophisticated 3D models of ocular tissues is a significant challenge with enormous potential. In this review, we present a comprehensive overview of the latest advances in the development of 3D in vitro models of the anterior segment of the eye, with a special focus on those that use human primary cells.

Development of a bioreactor system for pre-endothelialized cardiac patch generation with enhanced viscoelastic properties by combined collagen I compression and stromal cell culture

Treatment of terminal heart failure still poses a significant clinical problem. Cardiac tissue engineering could offer autologous solutions for the replacement of nonfunctional myocardial tissue. So far, soft matrix construction and missing large-scale prevascularization prevented the application of sizeable cardiac repair patches. We developed a novel bioreactor system for semi-automatic compression of a collagen I hydrogel applying 16 times higher pressure than in previous studies. Resistance towards compression stress was investigated for multiple cardiac-related cell types. For scaffold prevascuarization, a tubular cavity was imprinted during the compaction process. Primary cardiac-derived endothelial cells (ECs) were isolated from human left atrial appendages (HLAAs) and characterized by fluorescence-activated cell sorting (FACS) and immunocytology. EC were then seeded into the preformed channel with dermal fibroblasts as interstitial cell component of the fully cellularized patch. After 8 days of constant perfusion culture within the same bioreactor, scaffold dynamic modulus and cell viability were analyzed. Endothelial proliferation and vessel maturation were examined by immunohistochemistry and transmission electron microscopy. Our design allowed for scaffold production and dynamic culture in a one-stop-shop model. Enhanced compression and cell-mediated matrix remodeling induced a significant increase in scaffold stiffness while ensuring excellent cell survival. For the first time, we could isolate HLAA-derived EC with proliferative potential. ECs within the central channel proliferated during flow culture, continuously expressing endothelial markers (CD31) and displaying basal membrane synthesis (collagen IV, ultrastructural analysis). After 7 days of culture, a complete endothelial monolayer could be observed. Covering cells aligned themselves in flow direction and developed mature cell-cell contacts.

Ocular surface repair using decellularized porcine conjunctiva

The primary functions of the conjunctiva embody ocular surface protection and the maintenance of the tear film equilibrium. Severe conjunctival defects such as symblepharon may impair the integrity of ocular surface and cause loss of visual functions. Here we report the use of a decellularized porcine conjunctiva (DPC) for conjunctival reconstruction in rabbit models and in clinic. Our results show that the major xenoantigens are efficiently removed, while abundant matrix components and integrated microstructures are well preserved in the DPC. These characteristics provide mechanical support and favorable histocompatibility for repairing damaged conjunctiva. The DPC application has demonstrated enhanced transplant stability and improved epithelial regeneration in severe ocular surface damage comparing to those of amniotic membrane (AM), the most frequently applied matrix for ocular surface reconstruction nowadays. In order to test the DPC performance in clinic, three patients with pterygium and one patient with symblepharon underwent transplant with DPC. The grafts in all cases were completely re-epithelized and no graft melt or fibroplasia were observed. These results suggest that the strategy we developed is feasible and effective for conjunctival reconstruction and ocular surface repair. STATEMENT OF SIGNIFICANCE: In this study, we adopted an innovative approach to prepare decellularized porcine conjunctiva (DPC). The intricate conjunctiva-specific structures and abundant matrix components were preserved in DPC, which offers favorable mechanical properties for graft. DPC has shown positive effects in ocular surface repair, which has been proven particularly in a rabbit model with severe symblepharon. Reconstructed conjunctiva by DPC exhibited epithelial heterogeneity, extremely resembling that of native conjunctiva. In addition, results from clinical studies were encouraging for pterygium and symblepharon and clinical application of DPC is promising.