Egg White Photocrosslinkable Hydrogels as Versatile Bioinks for Advanced Tissue Engineering Applications

Three dimensional (3D) bioprinting using photocrosslinkable hydrogels has gained considerable attention due to its versatility in various applications, including tissue engineering and drug delivery. Egg White (EW) is an organic biomaterial with excellent potential in tissue engineering. It provides abundant proteins, along with biocompatibility, bioactivity, adjustable mechanical properties, and intrinsic antiviral and antibacterial features. Here, a photocrosslinkable hydrogel derived from EW is developed through methacryloyl modification, resulting in Egg White methacryloyl (EWMA). Upon exposure to UV light, synthesized EWMA becomes crosslinked, creating hydrogels with remarkable bioactivity. These hydrogels offer adjustable mechanical and physical properties compatible with most current bioprinters. The EWMA hydrogels closely resemble the native extracellular matrix (ECM) due to cell-binding and matrix metalloproteinase-responsive motifs inherent in EW. In addition, EWMA promotes cell growth and proliferation in 3D cultures. It facilitates endothelialization when investigated with human umbilical vein endothelial cells (HUVECs), making it an attractive replacement for engineering hemocompatible vascular grafts and biomedical implants. In summary, the EWMA matrix enables the biofabrication of various living constructs. This breakthrough enhances the development of physiologically relevant 3D in vitro models and opens many opportunities in regenerative medicine

Synthesis, kinetics and sintering studies of nano/micro CeO2 powder

151 p.Fine structured ceria, Carbon dioxide plays a potential role in a large variety of applications, such as an electrolyte material of solid oxide fuel cell, a catalyst, an optical additive, polisher, and biomedical applications.MASTER OF ENGINEERING (MAE

Biomineralization of hydroxyapatite in the presence of amino acids dissolved in solution or bound to carboxylated graphene oxide surface

Polar and charged amino acids (AAs) are the main components of non-collagenous proteins (NCPs), and are involved in hydroxyapatite (HA) mineralization in bone. These AAs are able to either promote HA mineralization by attracting Ca2+ and PO43- ions in body fluids and increasing the local supersaturation or inhibit HA formation by binding to nuclei of calcium phosphate and preventing their further growth. The promoting AAs can be used to improve bone regeneration in damaged tissues, while the inhibitory AAs are potentially useful for treating pathological diseases caused by an excessive mineralization of HA in tissues like cartilage, blood vessels and cardiac valves.Although AAs are promising candidates for controlling HA mineralization, the mechanism by which they interact with Ca2+ and PO43- ions or with HA crystals to induce or inhibit mineralization is not well understood. Also, most of the studies on AAs and HA crystallization are conducted under experimental conditions different from the physiological ones, which has made it difficult to gain a real insight into the effects of AAs in the human body. In this work, we investigate the effect a positively (Arg) and a negatively (Glu) charged AA have on the morphology and crystalline structure of HA synthesized at room temperature and at a pH of 7.4. The AAs are either in an aqueous solution or bound to a graphene oxide (GO) surface. Graphene is a recently discovered carbon-based two-dimensional nanostructure, and it is used here as a substrate to bind the AAs on due to its many potential applications as a bone or dentin scaffold in tissue engineering. Our goal is to determine the inhibiting or promoting effect of AAs on HA mineralization, and to explore the mechanism by which AAs can control HA precipitation. Our results showed that the positively charged AA, Arg, had a stronger inhibitory effect on HA nucleation, and was adsorbed in larger amount on HA particles, while the negatively charged AA, Glu, was more effective in inhibiting HA crystal growth along specific crystallographic directions. These results were interpreted in terms of the differences in stability constants between AAs and the ions in solution. We also showed that the inhibitory effect of the single AAs on HA nucleation was dampened if the two AAs were present together in solution, which we interpreted to be a consequence of the preferential interaction of the AAs with each other rather than with ions or nuclei in solution. However, the inhibitory effect of these AAs became stronger when the Ca- and P-precursor solutions were aged for 3 days. This was explained by the formation of nano aggregates from the initial Ca/AAs and P/AAs complexes with aging of the precursor solutions. The AAs also affected the morphology and crystallinity of HA particles. In general, the presence of AAs resulted in the formation of well-organized micro-spherulitic particles, which had high degree of crystallinity. On the other hand, irregularly shaped micro aggregates with lower crystallinity were obtained in the absence of the AAs or when the AAs were mixed.Contrary to when they were in solution, the AAs bound to a GO surface promoted HA precipitation by attracting Ca2+ and PO43- ions and increasing the concentration of these ions on the GO substrate. However, similar to the effect of AAs dissolved in solution, the positively charged AA, Arg, bound to a GO surface showed a significantly stronger effect than the negatively charged AA, Glu. Also, more organized particles with Ca/P ratios closer to that of HA were obtained in the presence of Arg. These results were interpreted in terms of the differences in electrostatic interactions and the stability constants of complexes forming between the AAs and the Ca2+ and PO43- ions. The strong effect of Arg on HA formation on a GO surface may provide a basis to design new graphene composite materials for bone regeneration applications.Les acides aminés (AAs) polaires et chargés sont les principaux composants des protéines non collagéniques, et sont impliqués dans la minéralisation d'hydroxyapatites (HA) dans les os. Bien que les AAs soit des candidats prometteurs pour contrôler la minéralisation d'HA, le mécanisme par lequel ils interagissent avec les ions Ca2+ et PO43- ou avec les cristaux d'HA pour induire ou inhiber la minéralisation n'est pas encore bien compris. La plupart des études sur les AAs et sur la cristallisation d'HA sont menées dans des conditions expérimentales différentes des conditions physiologiques, ce qui a rendu difficile l'obtention d'un véritable aperçu des effets des AAs dans le corps humain. Dans ce travail, nous étudions l'effet d'un AA chargé positivement (Arg) et d'un AA chargé négativement (Glu) sur la morphologie et sur la structure cristalline d'HA synthétisés à température ambiante et à pH 7.4. Les AAs seront, soit en solution aqueuse, soit liés à une surface d'oxydes de graphène (GO). Le graphène est une nanostructure bidimensionnelle à base de carbone récemment découverte, et est utilisé ici en tant que substrat pour lier les AAs en raison de ses nombreuses applications potentielles comme support en ingénierie tissulaire de l'os ou de la dentine. Notre objectif est de déterminer l'effet inhibiteur ou promoteur des AAs sur la minéralisation d'HA, et d'explorer le mécanisme par lequel ils peuvent contrôler la précipitation d'HA.Nos résultats ont montré que l'AA chargé positivement (Arg) a eu un effet inhibiteur plus important sur la nucléation d'HA et a été adsorbé en plus grande quantité sur les particules d'HA, tandis que l'AA chargé négativement (Glu), a été plus efficace sur l'inhibition de la croissance des cristaux d'HA selon des directions cristallographiques spécifiques. Ces résultats ont été interprétés en termes de différences dans les constantes de stabilité entre les AAs et les ions en solution. Nous avons également montré que l'effet inhibiteur des AAs seuls sur la nucléation d'HA a été atténué si les deux AAs étaient présents ensembles en solution. Ce que nous avons interprété comme une conséquence de l'interaction préférentielle des AAs entre eux plutôt que de leur intéraction avec les ions ou les noyaux en solution. Cependant, l'effet inhibiteur de ces AAs est devenu plus important lorsque les solutions de précurseurs de calcium et phosphore étaient âgés de trois jours. Ceci s'explique par la formation de nano-agrégats à partir des complexes initiaux Ca/AAs et P/AAs avec le vieillissement des solutions de précurseurs. Les AAs ont également affecté la morphologie et la cristallinité des particules d'HA. En général, la présence des AAs a abouti à la formation de microparticules sphérulitiques bien organisées, qui ont un haut degré de cristallinité. D'autre part, les micro-agrégats de formes irrégulières avec des cristallinités inférieures ont été obtenus en l'absence d'AA ou lorsque les AAs été introduits ensemble.Contrairement à quand ils étaient en solution, les AAs liés à la surface d'oxyde de graphène promeuvent la précipitation d'HA en attirant les ions Ca2+ et PO43- et en augmentant la concentration de ces ions sur un substrat d'oxyde de graphène. Cependant, semblable à l'effet observé lorsque les AAs étaient en solution, l'AA chargé positivement (Arg) et lié à la surface d'oxyde de graphène a montré un effet beaucoup plus important que l'AA chargé négativement (Glu). En outre, les particules d'HA les plus organisées avec des rapports Ca/P plus proches de celui d’HA ont été obtenus en présence d’Arg. Ces résultats ont été interprétés en termes de différences dans les interactions électrostatiques et les constantes de stabilité des complexes formés entre les AAs et les ions Ca2+ et PO43-. L'effet important de l'Arg sur la formation d'HA sur la surface d'oxyde de graphène peut fournir une ligne directive pour concevoir des matériaux composites Arg/graphène pour des applications de régénération osseuse

Engineering Tough, Injectable, Naturally Derived, Bioadhesive Composite Hydrogels

Engineering mechanically robust bioadhesive hydrogels that can withstand large strains may open new opportunities for the sutureless sealing of highly stretchable tissues. While typical chemical modifications of hydrogels, such as increasing the functional group density of crosslinkable moieties and blending them with other polymers or nanomaterials have resulted in improved mechanical stiffness, the modified hydrogels have often exhibited increased brittleness resulting in deteriorated sealing capabilities under large strains. Furthermore, highly elastic hydrogels, such as tropoelastin derivatives are highly expensive. Here, gelatin methacryloyl (GelMA) is hybridized with methacrylate-modified alginate (AlgMA) to enable ion-induced reversible crosslinking that can dissipate energy under strain. The hybrid hydrogels provide a photocrosslinkable, injectable, and bioadhesive platform with an excellent toughness that can be tailored using divalent cations, such as calcium. This class of hybrid biopolymers with more than 600% improved toughness compared to GelMA may set the stage for durable, mechanically resilient, and cost-effective tissue sealants. This strategy to increase the toughness of hydrogels may be extended to other crosslinkable polymers with similarly reactive moieties