Jana Horakova

Design of Polycaprolactone Vascular Grafts

A large number of patients suffer from vascular diseases, resulting in the need for bypass surgery. Since there are still limitations in the replacement of small diameter vascular grafts, the need and demand for developing more desirable grafts is increasing day by day. In this study, polycaprolactone small-diameter (6 mm) vascular grafts were produced successfully using custom-designed electrospinning apparatus. Radial fiber orientation was achieved by increasing the rotational speed of the collector. The morphological, structural, mechanical, and biological properties were examined. The results show that oriented scaffolds with 2 µm average fiber diameter provide 1 MPa ultimate tensile strength in the radial direction. The pore size area was found to be adequate in the oriented samples required for cell proliferation and diffusion through the tunica media. In vitro biocompatibility of the grafts was proven with 3T3 mouse fibroblasts. After cell seeding, the oriented fibers serve as a cue for radial cell alignment. An understanding of electrospun material parameters together with knowledge of native blood vessel structures and properties is a considerable part in designing small-diameter vascular grafts.

Comprehensive assessment of electrospun scaffolds hemocompatibility

Biodegradable polyesters, namely polycaprolactone (PCL) and copolymer of polylactide and polycaprolactone (PLCL) were electrospun into various fibrous structures and their hemocompatibility was evaluated in vitro. Firstly, hemolytic effect was evaluated upon incubation with diluted whole blood. The results showed that the degree of hemolysis depended on chemical composition and fibrous morphology. Electrospun polycaprolactone induced slight degree of hemolysis depending on its molecular weight and fibrous morphology; copolymer PLCL did not cause detectable hemolysis. The influence of coagulation pathways was examined by measurement of coagulation times. It was showed that intrinsic coagulation pathway assessed by activated partial thromboplastin time (APTT) was moderately accelerated after incubation with PCL and prolonged after incubation with copolymer PLCL. Extrinsic activation of coagulation tested by prothrombin time (PT) was slightly accelerated after incubation with all tested electrospun samples. Thrombogenicity assessment of fibrous samples revealed high thrombogenic properties of fibrous materials that was comparable to high degree of collagen thrombogenicity. The level of platelet activation was dependent on chemical composition and surface morphology of tested materials.

Generating standardized image data for testing and calibrating quantification of volumes, surfaces, lengths, and object counts in fibrous and porous materials using X-ray microtomography

Quantification of the structure and composition of biomaterials using micro‐CT requires image segmentation due to the low contrast and overlapping radioopacity of biological materials. The amount of bias introduced by segmentation procedures is generally unknown. We aim to develop software that generates three‐dimensional models of fibrous and porous structures with known volumes, surfaces, lengths, and object counts in fibrous materials and to provide a software tool that calibrates quantitative micro‐CT assessments. Virtual image stacks were generated using the newly developed software TeIGen, enabling the simulation of micro‐CT scans of unconnected tubes, connected tubes, and porosities. A realistic noise generator was incorporated. Forty image stacks were evaluated using micro‐CT, and the error between the true known and estimated data was quantified. Starting with geometric primitives, the error of the numerical estimation of surfaces and volumes was eliminated, thereby enabling the quantification of volumes and surfaces of colliding objects. Analysis of the sensitivity of the thresholding upon parameters of generated testing image sets revealed the effects of decreasing resolution and increasing noise on the accuracy of the micro‐CT quantification. The size of the error increased with decreasing resolution when the voxel size exceeded 1/10 of the typical object size, which simulated the effect of the smallest details that could still be reliably quantified. Open‐source software for calibrating quantitative micro‐CT assessments by producing and saving virtually generated image data sets with known morphometric data was made freely available to researchers involved in morphometry of three‐dimensional fibrillar and porous structures in micro‐CT scans.

The post-morphological analysis of electrospun vascular grafts following mechanical testing

Abstract Vascular grafts provide promising scaffolds for patients recuperating from cardiovascular diseases. Since it is necessary to mimic the native vessel in order to overcome the limitations of currently employed synthetic prostheses, researchers are tending to focus on the design of electrospun biodegradable multi-layer scaffolds which involves varying either the polymer type or constructional properties in each layer which, in turn, reveals the importance of layer interactions and their composite effect on the final multi-layer graft. This study describes the fabrication of biodegradable single-layer tubular scaffolds from polycaprolactone and poly(L-lactide)caprolactone polymers composed of either randomly distributed or, preferably, radially oriented fibers. Subsequently, bi-layer scaffolds were fabricated with a randomly distributed inner layer and a radially oriented outer layer from various polymer couple variations. The study focuses on vascular graft production technology including its morphology and mechanical properties. The post-morphologies of single-layer and bi-layer tubular scaffolds designed for vascular grafts were investigated as a continuation of a previously performed analysis of their mechanical properties. The results indicate that the mechanical properties of the final bi-layer grafts were principally influenced by the radially oriented outer layers acting as the tunica media of the native vessels when the appropriate polymer couples were chosen for the sub-layers.

How does the surface treatment change the cytocompatibility of implants made by selective laser melting

ABSTRACT Introduction: The study investigates the potential for producing medical components via Selective Laser Melting technology (SLM). The material tested consisted of the biocompatible titanium alloy Ti6Al4V. The research involved the testing of laboratory specimens produced using SLM technology both in vitro and for surface roughness. The aim of the research was to clarify whether SLM technology affects the cytocompatibility of implants and, thus, whether SLM implants provide suitable candidates for medical use following zero or minimum post-fabrication treatment. Areas covered: The specimens were tested with an osteoblast cell line and, subsequently, two post-treatment processes were compared: non-treated (as-fabricated) and glass-blasted. Interactions with MG-63 cells were evaluated by means of metabolic MTT assay and microscope techniques (scanning electron microscopy, fluorescence microscopy). Surface roughness was observed on both the non-treated and glass-blasted SLM specimens. Expert Commentary: The research concluded that the glass-blasting of SLM Ti6Al4V significantly reduces surface roughness. The arithmetic mean roughness Ra was calculated at 3.4 µm for the glass-blasted and 13.3 µm for the non-treated surfaces. However, the results of in vitro testing revealed that the non-treated surface was better suited to cell growth.

The effect of ethylene oxide sterilization on electrospun vascular grafts made from biodegradable polyesters

The study describes the detailed examination of the effect of ethylene oxide sterilization on electrospun scaffolds constructed from biodegradable polyesters. Different fibrous layers fabricated from polycaprolactone (PCL) and a copolymer consisting of polylactide and polycaprolactone (PLCL) were investigated for the determination of their mechanical properties, degradation rates and interaction with fibroblasts. It was discovered that the sterilization procedure influenced the mechanical properties of the electrospun PLCL copolymer scaffold to the greatest extent. No effect of ethylene oxide sterilization on degradation behavior was observed. However, a delayed fibroblast proliferation rate was noticed with concern to the ethylene oxide sterilized samples compared to the ethanol sterilization of the materials.

Effective poly(ethylene glycol) methyl ether grafting technique onto Nylon 6 surface to achieve resistance against pathogenic bacteria Staphylococcus aureus and Pseudomonas aeruginosa

AbstractOur study is focused on an efficient reduction of amide functional groups to secondary amine on Nylon 6 surface with borane–tetrahydrofuran (BH3–THF) complex, followed by N-alkylation with benzyl chloride (C6H5CH2Cl) which has been successfully used as a model system for further grafting of the reduced Nylon 6 surface by poly(ethylene glycol) methyl ether tosylate (Me-PEG-OTs). The amine-activated surface has been obtained by treatment of reduced Nylon 6 with n-butyllithium or tert-butyllithium in THF. Modified Nylon 6 has been found to be antibacterial particularly due to the presence of hydrophilic poly(ethylene glycol) methyl ether (H3C-PEG) chains. The surface modifications were successfully characterized by various techniques. Water contact angle and free surface energy analyses indicated a significant change in the surface morphology. It was further supported by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and Raman spectroscopy. Finally, antibacterial tests were performed against two pathogenic bacterial strains Pseudomonas aeruginosa (CCM 3955) and Staphylococcus aureus (CCM 3953).