Mechanical properties of anterior lens capsule assessed with AFM and nanoindenter in relation to human aging, pseudoexfoliation syndrome, and trypan blue staining

The Ocular Surface and the Anterior Segment of the Eye in the Pseudoexfoliation Syndrome: A Comprehensive Review

Pseudoexfoliation syndrome (PXS) is an age-related fibrillopathy where fibrillar exfoliation material accumulates and deposits in ocular and extra-ocular tissue. Within the eye, this substance accumulates on the ocular surface and in the anterior segment of the eye, impacting ocular structures such as the conjunctiva, Tenon's capsule, sclera, cornea, iris, ciliary body, trabecular meshwork, and lens. This review aims to collate the current literature on how each anatomical part of the eye is affected by PXS, with a strong focus on molecular changes. We also summarise the current understanding of the key genetic factors influencing the development of PXS.

Atomic force microscopy for characterization of decellularized extracellular matrix (dECM) based materials

In live organisms, cells are embedded in tissue-specific extracellular matrix (ECM), which provides chemical and mechanical signals important for cell differentiation, migration, and overall functionality. Careful reproduction of ECM properties in artificial cell scaffolds is necessary to get physiologically relevant results of in vitro studies and produce robust materials for cell and tissue engineering. Nanoarchitectonics is a contemporary way to building complex materials from nano-scale objects of artificial and biological origin. Decellularized ECM (dECM), remaining after cell elimination from organs, tissues and cell cultures is arguably the closest equivalent of native ECM achievable today. dECM-based materials can be used as templates or components for producing cell scaffolds using nanoarchitectonic approach. Irrespective of the form, in which dECM is used (whole acellular organ/tissue, bioink or hydrogel), the local stiffness of the dECM scaffold must be evaluated, since the fate of seeded cells depends on the mechanical properties of their environment. Careful dECM characterization is also necessary to reproduce essential ECM traits in artificial cell scaffolds by nanoparticle assembly. Atomic force microscopy (AFM) is a valuable characterization tool, as it allows simultaneous assessment of mechanical and topographic features of the scaffold, and additionally evaluate the efficiency of decellularization process and preservation of the extracellular matrix. This review depicts the current application of AFM in the field of dECM-based materials, including the basics of AFM technique and the use of flicker-noise spectroscopy (FNS) method for the quantification of the dECM micro- and nanostructure.

Effect of intraocular lens material and haptic design on anterior capsule contraction after cataract surgery: A systematic review and meta-analysis

PURPOSE

To compare anterior capsule contraction (ACC) after cataract surgery with implantation of intraocular lens (IOLs) of different materials and designs.

METHODS

We searched three electronic databases for relevant studies published up to January 1, 2023. Five randomized controlled trails (RCTs) and three cohort studies involving 1,221 eyes were included in quantitative synthesis. We extracted data, assessed their quality independently, and calculated standard mean difference (SMD) using a random-effects model. Six RCTs and one retrospective cohort were included in information summary.

RESULTS

The contraction of the anterior capsule opening area in the hydrophilic group was larger than that of the hydrophobic group from one month to one year postoperatively (P < 0.001 and P < 0.001, respectively). Specifically, the hydrophilic group showed greater contraction of the anterior capsule opening area at one month postoperatively (Standardized mean difference [SMD] = -0.73, 95% confidence interval [CI] = -0.93 to -0.52), three months (SMD = -1.04, 95% CI = -1.32 to -0.75), six months (SMD = -0.99, 95% CI = -1.24 to -0.74) and one year (SMD = -1.33, 95% CI = -2.50 to -0.16). As of one year postoperatively, the anterior capsular opening area showed a trend of decreasing over time in both groups (P = 0.046 and P = 0.050, respectively). In information summary, three studies indicated no relationship between haptic design and ACC, while the other four studies reported that the number and shape of haptic would affect ACC.

CONCLUSION

This meta-analysis suggested that the postoperative ACC after the implantation of hydrophobic IOLs was less than that induced by hydrophilic IOLs. Haptic design may also affect the degree of ACC.

[Selective assessment of biomechanical properties of the lens capsule]

The scientific and practical interest in studying the biomechanical characteristics of the lens capsule, on the one hand, is associated with its anatomical significance in modern microinvasive phaco surgery, and on the other hand, with investigation of the mechanisms of lens curvature changes during accommodation. Selective study of the biomechanical properties of the lens capsule aims to identify characteristics of various regions and surfaces of the capsule.

PURPOSE

This study is a comparative analysis of age-related changes in the biomechanical properties of the anterior (AC) and posterior (PC) lens capsules in humans.

MATERIAL AND METHODS

The study analyzed 73 pairs of central fragments of the AC and PC of the lens, obtained from donor (cadaver) eyes and through anterior and posterior capsulorhexis during microinvasive phaco surgery (38 and 35 paired samples, respectively). Planned biomechanical testing followed a previously developed protocol for examining the anterior capsule, including determination of the Young's modulus using atomic force microscopy.

RESULTS

Comparing the Young's modulus of lens capsule samples from donor eyes and microinvasive phaco surgery revealed no significant differences in mean values, indirectly indicating minimal postmortem impact on the biomechanical properties of the capsule. General biomechanical patterns observed in the human lens capsule show the Young's modulus (stiffness) is higher in the AC than the PC, and higher on the inner than the outer surface for both the AC and PC. Age-related changes are associated with an increase in stiffness on the outer surface and its decrease on the inner surface, more pronounced in the AC.

CONCLUSION

The obtained results indicate the need for further investigation into the role of capsule biomechanics in age-related accommodative disorders.

[Hybrid (femtolaser) phacoemulsification: technical aspects and functional results]

This article summarizes scientific and practical results of hybrid femtosecond laser-assisted phacoemulsification (HFE) including study of clinical and technical aspects of the intervention and evaluation of post-surgical functional state of the eye on the basis of clinical, morphological and biomechanical data. The HFE technology should be considered the method of choice for microinvasive phaco surgery, its main advantage being the possibility of controlled handling of such important surgical stages as anterior circular continuous capsulorhexis and nucleus fragmentation on a closed eyeball, which significantly reduces the risk of complications and decreases of effective ultrasound time.

Ex-Vivo Method to Quantifiably Evaluate the Staining Effectiveness of Anterior Lens Capsule Dyes

Purpose

High frequency of cataracts and the requirements of new European Union regulations for medical devices require the availability of preclinical models to adequately evaluate anterior lens capsule dyes before their use in patients. Herein, we describe an ex vivo method to quantifiably evaluate the macroscopic and microscopic staining effectiveness of anterior lens capsule dyes using porcine eyes.

Methods

Commercially available trypan blue–based products or physiological saline solution (negative control) was injected into porcine eyes. Anterior pole and lens (after extraction) were macroscopically photographed, and the images were quantitatively analyzed. Lenses were histologically processed, and the staining intensity microscopically was semiquantified.

Results

Macroscopic evaluation of the anterior pole revealed bluish staining of the anterior capsule; however, this coloring cannot be macroscopically discerned after lens extraction. Quantitative image analyses showed significant (P < 0.01) staining of the lens capsule compared to the negative control, but not significant (P > 0.05) between the products tested. Quantitative analysis of dying on lens images could not be performed. Microscopic semiquantification of the capsule staining intensity allows us to appreciate differences between products.

Conclusions

The described method is a quick and useful tool for macroscopic evaluation by surgeons to choose an anterior capsule staining for use during everyday surgeries, and a more specific microscopic evaluation also allows us to determine the effectiveness and usefulness of these products.

Translational Relevance

This method satisfies preclinical effectiveness evaluations required by European Union regulations and complements the safety and toxicity evaluations that new products must guarantee before they enter the market and are used in clinical practice.

A Collagen Basketweave from the Giant Squid Mantle as a Robust Scaffold for Tissue Engineering

The growing applications of tissue engineering technologies warrant the search and development of biocompatible materials with an appropriate strength and elastic moduli. Here, we have extensively studied a collagenous membrane (GSCM) separated from the mantle of the Giant squid Dosidicus Gigas in order to test its potential applicability in regenerative medicine. To establish the composition and structure of the studied material, we analyzed the GSCM by a variety of techniques, including amino acid analysis, SDS-PAGE, and FTIR. It has been shown that collagen is a main component of the GSCM. The morphology study by different microscopic techniques from nano- to microscale revealed a peculiar packing of collagen fibers forming laminae oriented at 60-90 degrees in respect to each other, which, in turn, formed layers with the thickness of several microns (a basketweave motif). The macro- and micromechanical studies showed high values of the Young's modulus and tensile strength. No significant cytotoxicity of the studied material was found by the cytotoxicity assay. Thus, the GSCM consists of a reinforced collagen network, has high mechanical characteristics, and is non-toxic, which makes it a good candidate for the creation of a scaffold material for tissue engineering.

Characterisation and Modelling of an Artificial Lens Capsule Mimicking Accommodation of Human Eyes

A synthetic material of silicone rubber was used to construct an artificial lens capsule (ALC) in order to replicate the biomechanical behaviour of human lens capsule. The silicone rubber was characterised by monotonic and cyclic mechanical tests to reveal its hyper-elastic behaviour under uniaxial tension and simple shear as well as the rate independence. A hyper-elastic constitutive model was calibrated by the testing data and incorporated into finite element analysis (FEA). An experimental setup to simulate eye focusing (accommodation) of ALC was performed to validate the FEA model by evaluating the shape change and reaction force. The characterisation and modelling approach provided an insight into the intrinsic behaviour of materials, addressing the inflating pressure and effective stretch of ALC under the focusing process. The proposed methodology offers a virtual testing environment mimicking human capsules for the variability of dimension and stiffness, which will facilitate the verification of new ophthalmic prototype such as accommodating intraocular lenses (AIOLs).