Fine tuning of the default depth and rate of ablation of the epithelium in customized trans-epithelial one-step superficial refractive excimer laser ablation.

PURPOSE: To fine tune the default depth and rate of ablation of the epithelium in cTen™ customized trans-epithelial one-step superficial refractive surgery by the comparison between the attempted post-operative ideal corneal shape and the achieved corneal shape. METHODS: 88 consecutive eyes in 64 patients undergoing trans-epithelial superficial excimer ablation using the iVis laser Suite for either myopic/astigmatic or hyperopic/astigmatic refractive error. Each patient had at least 3 months of post-operative follow-up. Topographic examination of all eyes was carried out pre-operatively and at least 3 months post-operatively using the Precisio™ surgical topographer. The comparison of these two measurements yielded values for depth, volumes and rates of ablated corneal tissue. By determining the different ablation rates of stroma and epithelium, a refinement of the depth of epithelium to be removed and a refinement of the stromal ablation were calculated.The mathematical model was applied on each one of the 88 clinical cases and the parameters for the fine tuning of the default depth and rate of ablation of the epithelium were determined using the least squares method. RESULTS: The calculated pure stromal ablation rate was less than the average epithelium/stroma ablation rate used in planning the treatments by a factor of 0.96. The epithelial thickness predefined ablation assumption used to plan removal of the epithelium was adjusted considering the measured ablation and a radial adjustment function established for the fine tuning of the laser radial efficiency and allowing for the normal thickening of the epithelium in the peripheral cornea. From a clinical point of view, this methodology produces an improvement of the efficacy and a reduction of the variance of the clinical results. CONCLUSION: Comparison of accurately measured pre and postoperative topographies yields accurately established ablation rates of stroma and epithelium in trans-epithelial one step superficial ablation.

From fiber curls to mesh waves: a platform for the fabrication of hierarchically structured nanofibers mimicking natural tissue formation.

Bioinstructive scaffolds for regenerative medicine are characterized by intrinsic properties capable of directing cell response and promoting wound healing. The design of such scaffolds requires the incorporation of well-defined physical properties that mimic the native extracellular matrix (ECM). Here, inspired by epithelial tissue morphogenesis, we present a novel approach to code nanofiber materials with controlled hierarchical wavy structures resembling the configurations of native EMC fibers through using thermally shrinking materials as substrates onto which the fibers are deposited. This approach could serve as a platform for fabricating functional scaffolds mimicking various tissues such as trachea, iris, artery wall and ciliary body. Modeling affirms that the mechanical properties of the fabricated wavy fibers could be regulated through varying their wavy patterns. The nanofibrous scaffolds coded with wavy patterns show an enhanced cellular infiltration. In addition, we further investigated whether the wavy patterns could regulate transforming growth factor-beta (TGF-ß) production, a key signalling pathway involved in connective tissue development. Our results demonstrated that nanofibrous scaffolds coded with wavy patterns could induce TGF-ß expression without the addition of a soluble growth factor. Our new approach could open up new avenues for fabricating bioinstructive scaffolds for regenerative medicine.

Soft-molecular imprinted electrospun scaffolds to mimic specific biological tissues.

The fabrication of bioactive scaffolds able to mimic the in vivo cellular microenvironment is a challenge for regenerative medicine. The creation of sites for the selective binding of specific endogenous proteins represents an attractive strategy to fabricate scaffolds able to elicit specific cell response. Here, electrospinning (ESP) and soft-molecular imprinting (soft-MI) techniques were combined to fabricate a soft-molecular imprinted electrospun bioactive scaffold (SMIES) for tissue regeneration. Scaffolds functionalized using different proteins and growth factors (GFs) arranged onto the surface were designed, fabricated and validated with different polyesters, demonstrating the versatility of the developed approach. The scaffolds bound selectively each of the different proteins used, indicating that the soft-MI method allowed fabricating high affinity binding sites on ESP fibers compared to non-imprinted ones. The imprinting of ESP fibers with several GFs resulted in a significant effect on cell behavior. FGF-2 imprinted SMIES promoted cell proliferation and metabolic activity. BMP-2 and TGF-ß3 imprinted SMIES promoted cellular differentiation. These scaffolds hold the potential to be used in a cell-free approach to steer endogenous tissue regeneration in several regenerative medicine applications.

EFFECTS OF A MODIFIED VITRECTOMY PROBE IN SMALL-GAUGE VITRECTOMY: An Experimental Study on the Flow and on the Traction Exerted on the Retina.

PURPOSE: Thorough this experimental study, the physic features of a modified 23-gauge vitrectomy probe were evaluated in vitro. METHODS: A modified vitrectomy probe to increase vitreous outflow rate with a small-diameter probe, that also minimized tractional forces on the retina, was created and tested. The "new" probe was created by drilling an opening into the inner duct of a traditional 23-gauge probe with electrochemical or electrodischarge micromachining. Both vitreous outflow and tractional forces on the retina were examined using experimental models of vitreous surgery. RESULTS: The additional opening allowed the modified probe to have a cutting rate of 5,000 cuts per minute, while sustaining an outflow approximately 45% higher than in conventional 23-gauge probes. The modified probe performed two cutting actions per cycle, not one, as in standard probes. Because tractional force is influenced by cutting rate, retinal forces were 2.2 times lower than those observed with traditional cutters. CONCLUSION: The modified probe could be useful in vitreoretinal surgery. It allows for faster vitreous removal while minimizing tractional forces on the retina. Moreover, any available probe can be modified by creating a hole in the inner duct.

Toward mimicking the bone structure: design of novel hierarchical scaffolds with a tailored radial porosity gradient.

Guiding bone regeneration poses still unmet challenges due to several drawbacks of current standard treatments in the clinics. A possible solution may rely on the use of three-dimensional scaffolds with optimized structural properties in combination with human mesenchymal stem cells (hMSCs). Bone presents a radial gradient structure from the outside, where the cortical bone is more compact (porosity ranging from 5% to 10%), toward the inner part, where the cancellous bone is more porous (porosity ranging from 50% to 90%). Here, we present a new scaffold design with a built-in gradient in porosity, which approximate the radial bone structure. The pores of the outer ring were 500 µm, the ones in the middle zone were 750 µm and the inner part presented pores of 1000 µm. The porosity of each scaffold region resembled the gradient present in bone, with the outer ring having a porosity of 29.6% ± 5%, the middle and inner regions a porosity of 50.8% ± 8.1% and 77.6% ± 3.2% respectively. hMSCs behavior was analyzed in terms of growth, extracellular matrix deposition and differentiation toward the osteogenic lineage. A trend was displayed by the hMSCs residing in different zones of the gradient scaffolds after 7, 14 and 28 days of culture in mineralization medium. Osteogenic differentiation was influenced by pore size and location in scaffolds displaying a radial porosity gradient. Cell differentiation was confirmed by gene expression with upregulation of Runx2 and bone sialoprotein markers. Mineralization staining further confirmed the maturation of cell differentiation, as indicated by the presence of calcium and phosphate mineral deposits.

Surface energy and stiffness discrete gradients in additive manufactured scaffolds for osteochondral regeneration.

Swift progress in biofabrication technologies has enabled unprecedented advances in the application of developmental biology design criteria in three-dimensional scaffolds for regenerative medicine. Considering that tissues and organs in the human body develop following specific physico-chemical gradients, in this study, we hypothesized that additive manufacturing (AM) technologies would significantly aid in the construction of 3D scaffolds encompassing such gradients. Specifically, we considered surface energy and stiffness gradients and analyzed their effect on adult bone marrow derived mesenchymal stem cell differentiation into skeletal lineages. Discrete step-wise macroscopic gradients were obtained by sequentially depositing different biodegradable biomaterials in the AM process, namely poly(lactic acid) (PLA), polycaprolactone (PCL), and poly(ethylene oxide terephthalate)/poly(butylene terephthalate) (PEOT/PBT) copolymers. At the bulk level, PEOT/PBT homogeneous scaffolds supported a higher alkaline phosphatase (ALP) activity compared to PCL, PLA, and gradient scaffolds, respectively. All homogeneous biomaterial scaffolds supported also a significantly higher amount of glycosaminoglycans (GAGs) production compared to discrete gradient scaffolds. Interestingly, the analysis of the different material compartments revealed a specific contribution of PCL, PLA, and PEOT/PBT to surface energy gradients. Whereas PEOT/PBT regions were associated to significantly higher ALP activity, PLA regions correlated with significantly higher GAG production. These results show that cell activity could be influenced by the specific spatial distribution of different biomaterial chemistries in a 3D scaffold and that engineering surface energy discrete gradients could be considered as an appealing criterion to design scaffolds for osteochondral regeneration.