Non-invasive characterization of hybrid gelatin:poly-l-lactide electrospun scaffolds using second harmonic generation and multiphoton imaging

Overview of Tissue Engineering and Drug Delivery Applications of Reactive Electrospinning and Crosslinking Techniques of Polymeric Nanofibers with Highlights on Their Biocompatibility Testing and Regulatory Aspects

Traditional electrospinning is a promising technique for fabricating nanofibers for tissue engineering and drug delivery applications. The method is highly efficient in producing nanofibers with morphology and porosity similar to the extracellular matrix. Nonetheless, and in many instances, the process has faced several limitations, including weak mechanical strength, large diameter distributions, and scaling-up difficulties of its fabricated electrospun nanofibers. The constraints of the polymer solution's intrinsic properties are primarily responsible for these limitations. Reactive electrospinning constitutes a novel and modified electrospinning techniques developed to overcome those challenges and improve the properties of the fabricated fibers intended for various biomedical applications. This review mainly addresses reactive electrospinning techniques, a relatively new approach for making in situ or post-crosslinked nanofibers. It provides an overview of and discusses the recent literature about chemical and photoreactive electrospinning, their various techniques, their biomedical applications, and FDA regulatory aspects related to their approval and marketing. Another aspect highlighted in this review is the use of crosslinking and reactive electrospinning techniques to enhance the fabricated nanofibers' physicochemical and mechanical properties and make them more biocompatible and tailored for advanced intelligent drug delivery and tissue engineering applications.

Bioconjugation of Carbohydrates to Gelatin Sponges Promoting 3D Cell Cultures

Gelatin sponges are widely employed as hemostatic agents, and are gaining increasing interest as 3D scaffolds for tissue engineering. To broaden their possible application in the field of tissue engineering, a straightforward synthetic protocol able to anchor the disaccharides, maltose and lactose, for specific cell interactions was developed. A high conjugation yield was confirmed by ¹H-NMR and FT-IR spectroscopy, and the morphology of the resulting decorated sponges was characterized by SEM. After the crosslinking reaction, the sponges preserve their porous structure as ascertained by SEM. Finally, HepG2 cells cultured on the decorated gelatin sponges show high viability and significant differences in the cellular morphology as a function of the conjugated disaccharide. More spherical morphologies are observed when cultured on maltose-conjugated gelatin sponges, while a more flattened aspect is discerned when cultured onto lactose-conjugated gelatin sponges. Considering the increasing interest in small-sized carbohydrates as signaling cues on biomaterial surfaces, systematic studies on how small carbohydrates might influence cell adhesion and differentiation processes could take advantage of the described protocol.

Cellulose Nanocrystals as Additives in Electrospun Biocompatible Separators for Aprotic Lithium-Ion Batteries

This work concerns the study of electrospun scaffolds as separators for aprotic lithium-ion batteries (LIBs) composed of the amorphous poly-d,l-lactide (PDLLA), in solution concentrations of 8, 10, and 12 wt % and in different ratios with cellulose nanocrystals (CNCs). PDLLA has been studied for the first time as a separator, taking into account its amorphous character that could facilitate electrolyte incorporation into the polymer matrix and influence ionic conductivity, together with CNCs, for reducing the hydrophobicity of the scaffolds. The embedding of the nanocrystals in the scaffolds was confirmed by X-ray diffraction analysis and attenuated total reflectance Fourier transform infrared spectroscopy. The polymer combination influenced the nanofibrous morphology as evaluated by scanning electron microscopy and modulated the electrochemical behavior of the membranes that was investigated through linear sweep voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy tests. Among the studied categories, the P12 series displayed a nonhomogeneous electrolyte resistance and electrochemical stability, differently from P10, whose results suggested their application in LIBs with standard formulation, as confirmed by a preliminary performance test of the P10N6 formulation in a full Li-ion cell configuration.

Elastin-Hyaluronan Bioconjugate as Bioactive Component in Electrospun Scaffolds

Hyaluronic acid or hyaluronan (HA) and elastin-inspired peptides (EL) have been widely recognized as bioinspired materials useful in biomedical applications. The aim of the present work is the production of electrospun scaffolds as wound dressing materials which would benefit from synergic action of the bioactivity of elastin peptides and the regenerative properties of hyaluronic acid. Taking advantage of thiol-ene chemistry, a bioactive elastin peptide was successfully conjugated to methacrylated hyaluronic acid (MAHA) and electrospun together with poly-D,L-lactide (PDLLA). To the best of our knowledge, limited reports on peptide-conjugated hyaluronic acid were described in literature, and none of these was employed for the production of electrospun scaffolds. The conformational studies carried out by Circular Dichroism (CD) on the bioconjugated compound confirmed the preservation of secondary structure of the peptide after conjugation while Scanning Electron Microscopy (SEM) revealed the supramolecular structure of the electrospun scaffolds. Overall, the study demonstrates that the bioconjugation of hyaluronic acid with the elastin peptide improved the electrospinning processability with improved characteristics in terms of morphology of the final scaffolds.

The Structure and Function of Next-Generation Gingival Graft Substitutes-A Perspective on Multilayer Electrospun Constructs with Consideration of Vascularization

There is a shortage of suitable tissue-engineered solutions for gingival recession, a soft tissue defect of the oral cavity. Autologous tissue grafts lead to an increase in morbidity due to complications at the donor site. Although material substitutes are available on the market, their development is early, and work to produce more functional material substitutes is underway. The latter materials along with newly conceived tissue-engineered substitutes must maintain volumetric form over time and have advantageous mechanical and biological characteristics facilitating the regeneration of functional gingival tissue. This review conveys a comprehensive and timely perspective to provide insight towards future work in the field, by linking the structure (specifically multilayered systems) and function of electrospun material-based approaches for gingival tissue engineering and regeneration. Electrospun material composites are reviewed alongside existing commercial material substitutes', looking at current advantages and disadvantages. The importance of implementing physiologically relevant degradation profiles and mechanical properties into the design of material substitutes is presented and discussed. Further, given that the broader tissue engineering field has moved towards the use of pre-seeded scaffolds, a review of promising cell options, for generating tissue-engineered autologous gingival grafts from electrospun scaffolds is presented and their potential utility and limitations are discussed.

Hyaluronic Acid-Functionalized Hybrid Gelatin-Poly-L-Lactide Scaffolds with Tunable Hydrophilicity

In this study, we describe the production of hybrid gelatin-poly-L-lactide electrospun scaffolds whose hydrophilicity was controlled by binding increasing concentrations of hyaluronic acid (HA). We show that cross-linking has advantages over coating when aiming to functionalize the scaffolds with HA. The here described scaffolds structurely mimicked the complexity of the extracellular matrix, and when excited by second harmonic generation, they produced a signal that is typical of collagen-containing biological fibers. Fluorescence lifetime imaging microscopy (FLIM) was used to marker-independently monitor the growth of human dermal fibroblasts on the electrospun scaffolds using reduced (phosphorylated) nicotinamide adenine dinucleotide as target. Benefitting from the different fluorescence lifetimes of the polymer and the endogenous cellular fluorophore, we were able to distinguish and separate the signals produced by the cells from the signals generated by the electrospun scaffolds. FLIM further allowed the detection of metabolic differences in the cells seeded on the HA-functionalized scaffolds compared with cells that were cultured on nonfunctionalized control scaffolds.

Nidogen-1 Mitigates Ischemia and Promotes Tissue Survival and Regeneration

Ischemia impacts multiple organ systems and is the major cause of morbidity and mortality in the developed world. Ischemia disrupts tissue homeostasis, driving cell death, and damages tissue structure integrity. Strategies to heal organs, like the infarcted heart, or to replace cells, as done in pancreatic islet β-cell transplantations, are often hindered by ischemic conditions. Here, it is discovered that the basement membrane glycoprotein nidogen-1 attenuates the apoptotic effect of hypoxia in cardiomyocytes and pancreatic β-cells via the αvβ3 integrin and beneficially modulates immune responses in vitro. It is shown that nidogen-1 significantly increases heart function and angiogenesis, while reducing fibrosis, in a mouse postmyocardial infarction model. These results demonstrate the protective and regenerative potential of nidogen-1 in ischemic conditions.

Corneal epithelium tissue engineering: recent advances in regeneration and replacement of corneal surface

Currently, many corneal diseases are treated by corneal transplantation, artificial corneal implantation or, in severe cases, keratoprosthesis. Owing to the shortage of cornea donors and the risks involved with artificial corneal implants, such as infection transmission, researchers continually seek new approaches for corneal regeneration. Corneal tissue engineering is a promising approach that has attracted much attention from researchers and is focused on regenerative strategies using various biomaterials in combination with different cell types. These constructs should have the ability to mimic the native tissue microenvironment and present suitable optical, mechanical and biological properties. In this article, we review studies that have focused on the current clinical techniques for corneal replacement. We also describe tissue-engineering and cell-based approaches for corneal regeneration.

Electrospun poly(d,l-lactide)/gelatin/glass-ceramics tricomponent nanofibrous scaffold for bone tissue engineering

Electrospun scaffolds are emerging as extracellular matrix (ECM)mimicking structures for tissue engineering thanks to their nanofibrous architecture. For the development of suitable electrospun scaffolds for bone tissue engineering, the addition of inorganic components has been implemented with the aim to confer important bioactivity like osteoinduction, osteointegration, and cell adhesion to the scaffolds. In this context, we propose a tricomponent electrospun scaffold composed of poly(d,l-lactide), gelatin and RKKP glass-ceramics. The bioactive RKKP glass-ceramic system has attracted interest, due to the presence of ions such as La³⁺ and Ta⁵⁺ , which turned out to be valuable as growth supporting agents for bones. In this work, RKKP glass-ceramics were embedded inside the microfibers of electrospun scaffolds and the structural and biological properties were investigated. Our results showed that the glass-ceramic microparticles were uniformly distributed in the fibrous structure of the scaffold. Furthermore, the glass-ceramics promoted biomineralization of the scaffolds and improved cell viability and osteogenic differentiation. The mineralized layer formed on RKKP-containing scaffolds after incubation in simulated body fluid medium has been shown to be hydroxyapatite by Raman spectroscopy and X-ray diffraction. The results on differentiation studies of canine adipose-derived mesenchymal stem cells grown on the electrospun scaffolds suggest that on varying the content of RKKP in the scaffold, it is possible to drive the differentiation toward chondrogenic or osteogenic commitment. The presence of ions, like La³⁺ and Ta⁵⁺ , in the RKKP embedded polymeric composite scaffolds could play a role in supporting cell growth and promoting differentiation.