Deepti Rana

Development of decellularized scaffolds for stem cell-driven tissue engineering.

Organ transplantation is an effective treatment for chronic organ dysfunctioning conditions. However, a dearth of available donor organs for transplantation leads to the death of numerous patients waiting for a suitable organ donor. The potential of decellularized scaffolds, derived from native tissues or organs in the form of scaffolds has been evolved as a promising approach in tissue‐regenerative medicine for translating functional organ replacements. In recent years, donor organs, such as heart, liver, lung and kidneys, have been reported to provide acellular extracellular matrix (ECM)‐based scaffolds through the process called ‘decellularization’ and proved to show the potential of recellularization with selected cell populations, particularly with stem cells. In fact, decellularized stem cell matrix (DSCM) has also emerged as a potent biological scaffold for controlling stem cell fate and function during tissue organization. Despite the proven potential of decellularized scaffolds in tissue engineering, the molecular mechanism responsible for stem cell interactions with decellularized scaffolds is still unclear. Stem cells interact with, and respond to, various signals/cues emanating from their ECM. The ability to harness the regenerative potential of stem cells via decellularized ECM‐based scaffolds has promising implications for tissue‐regenerative medicine. Keeping these points in view, this article reviews the current status of decellularized scaffolds for stem cells, with particular focus on: (a) concept and various methods of decellularization; (b) interaction of stem cells with decellularized scaffolds; (c) current recellularization strategies, with associated challenges; and (iv) applications of the decellularized scaffolds in stem cell‐driven tissue engineering and regenerative medicine. Copyright

Considerations on Designing Scaffold for Tissue Engineering

Abstract A scaffold is a three-dimensional (3D) structure having extracellular matrix (ECM) mimicking properties both chemically and biologically. Ideally, scaffold matrices should: support cell growth and maintenance; provide appropriate mechanical support; have a degradation rate in synchrony with defect healing rate; and facilitate effective nutrient transfer, gas exchange (i.e., O2 and CO2), metabolic waste removal, and signal transduction. In addition to physical and spatial cues, the scaffold itself can be the carrier of signaling biomolecules, thus emphasizing the need for scaffold-based tissue engineering. In this chapter, we review the fundamental requirements and considerations to enhance the design and manufacture of scaffolds, analyze the use of tissue engineering scaffolds in terms of biomaterials structure and cell material interactions; and also review traditional and advanced scaffold fabrication methods. The challenges of these scaffold-based regenerative methods are also discussed.

Surface functionalization of nanobiomaterials for application in stem cell culture, tissue engineering, and regenerative medicine

Stem cell‐based approaches offer great application potential in tissue engineering and regenerative medicine owing to their ability of sensing the microenvironment and respond accordingly (dynamic behavior). Recently, the combination of nanobiomaterials with stem cells has paved a great way for further exploration. Nanobiomaterials with engineered surfaces could mimic the native microenvironment to which the seeded stem cells could adhere and migrate. Surface functionalized nanobiomaterial‐based scaffolds could then be used to regulate or control the cellular functions to culture stem cells and regenerate damaged tissues or organs. Therefore, controlling the interactions between nanobiomaterials and stem cells is a critical factor. However, surface functionalization or modification techniques has provided an alternative approach for tailoring the nanobiomaterials surface in accordance to the physiological surrounding of a living cells; thereby, enhancing the structural and functional properties of the engineered tissues and organs. Currently, there are a variety of methods and technologies available to modify the surface of biomaterials according to the specific cell or tissue properties to be regenerated. This review highlights the trends in surface modification techniques for nanobiomaterials and the biological relevance in stem cell‐based tissue engineering and regenerative medicine.

Design and fabrication of auxetic PCL nanofiber membranes for biomedical applications

The main objective of this study was to fabricate poly (ε-caprolactone) (PCL)-based auxetic nanofiber membranes and characterize them for their mechanical and physicochemical properties. As a first step, the PCL nanofibers were fabricated by electrospinning with two different thicknesses of 40μm (called PCL thin membrane) and 180μm (called PCL thick membrane). In the second step, they were tailored into auxetic patterns using femtosecond laser cut technique. The physicochemical and mechanical properties of the auxetic nanofiber membranes were studied and compared with the conventional electrospun PCL nanofibers (non-auxetic nanofiber membranes) as a control. The results showed that there were no significant changes observed among them in terms of their chemical functionality and thermal property. However, there was a notable difference observed in the mechanical properties. For instance, the thin auxetic nanofiber membrane showed the magnitude of elongation almost ten times higher than the control, which clearly demonstrates the high flexibility of auxetic nanofiber membranes. This is because that the auxetic nanofiber membranes have lesser rigidity than the control nanofibers under the same load which could be due to the rotational motion of the auxetic structures. The major finding of this study is that the auxetic PCL nanofiber membranes are highly flexible (10-fold higher elongation capacity than the conventional PCL nanofibers) and have tunable mechanical properties. Therefore, the auxetic PCL nanofiber membranes may serve as a potent material in various biomedical applications, in particular, tissue engineering where scaffolds with mechanical cues play a major role.

Covalently immobilized VEGF-mimicking peptide with gelatin methacrylate enhances microvascularization of endothelial cells.

Clinically usable tissue-engineered constructs are currently limited due to their inability of forming microvascular networks necessary for adequate cellular oxygen and nutrient supply upon implantation. The aim of this study is to investigate the conditions necessary for microvascularization in a tissue-engineered construct using vascular endothelial growth factor (VEGF). The construct was made of gelatin methacrylate (GelMA) based cell-laden hydrogel system, which was then covalently linked with VEGF-mimicking peptide (AcQK), using human umbilical vein endothelial cells (HUVECs) as the model cell. The results of the mechanics and gene expression analysis indicated significant changes in mechanical properties and upregulation of vascular-specific genes. The major finding of this study is that the increased expression of vascular-specific genes could be achieved by employing AcQK in the GelMA based hydrogel system, leading to accelerated microvascularization. We conclude that GelMA with covalently-linked angiogenic peptide is a useful tissue engineered construct suitable for microvascularization. STATEMENT OF SIGNIFICANCE: (1) This study reports the conditions necessary for microvascularization in a tissue-engineered construct using vascular endothelial growth factor (VEGF). (2) The construct was made of gelatin methacrylate based cell-laden hydrogel system. (3) There is a significant change observed in mechanical properties and upregulation of vascular-specific genes, in particular CD34, when AcQK is used. (4) The major finding of this study is that the increased expression of vascular-specific genes, i.e., CD34 could be achieved by employing AcQK in the GelMA based hydrogel system, leading to accelerated microvascularization.

Cell-laden alginate/polyacrylamide beads as carriers for stem cell delivery: preparation and characterization

Stem cell based therapies employ engraftment or systemic administration methods for the delivery of stem cells into the target tissues to enhance their regenerative potential. However, majority of the stem cells were found to migrate away from the target site soon after the transplantation, which directly hinders their clinical efficacy, in particular while treating cartilage defects. Therefore, the present study was designed to explore the feasibility and efficacy of an alginate/polyacrylamide (Algi/PAAm) composite biomaterial in the form of cell-laden hydrogel beads as a suitable carrier system to be able to hold the stem cells at the target site and deliver them efficiently. Human bone marrow-derived mesenchymal stem cells (hBMSCs) have been used as a model cell. The beads prepared at an optimized concentration ratio were characterized to study their physicochemical properties. Furthermore, cell-encapsulated Algi/PAAm beads were evaluated for their biological properties. The result of this study has demonstrated that the Algi/PAAm beads with their optimal composition were able to maintain the viability of the encapsulated cells during the period of study, suggesting the cellular compatibility of the beads. Additionally, the encapsulated cells showed round morphology within the beads, in contrast to the 2D-cultured spindle-like shape of hBMSCs. Based on the experimental data obtained in this study, cell-laden Algi/PAAm beads may serve as a potential carrier system for stem cell delivery.

Enhanced proliferation of human bone marrow derived mesenchymal stem cells on tough hydrogel substrates

Stem cell plays a significant role in tissue engineering and regenerative medicine. However, one of the major limitations in translation of stem cell technologies for clinical applications is limited cell survival and growth upon implantation. To address this limitation, authors have made an attempt to design polyacrylamide/alginate (PAAm/Algi) based tough hydrogel substrates and studied their impact on the survival and proliferation of human bone marrow-derived mesenchymal stem cells (hBMSCs). The PAAm/Algi hydrogel substrates have been prepared by initiator-induced free radical polymerization with mechanical properties quite similar to human soft tissues. To evaluate the efficacy of hydrogel substrates in support of cellular functions, hBMSCs were cultured on the PAAm/Algi hydrogel substrate (Gel system) and conventional tissue culture plate (TcP system) under defined conditions. The results of this study demonstrated that the cells cultured on the Gel and TcP systems showed 80-90% of cell viability throughout the period of study. The cells cultured on the Gel system showed 25% increase in proliferation after 7days of culture, whereas the TcP system showed only an increase of 10%. These results confirm the cellular compatibility and enhanced cell proliferative nature of the hydrogel substrates, due the fact that the hydrogel substrates provided necessary microenvironmental cues to the cells as compared the conventional TcP system. The overall results suggest that the PAAm/Algi based hydrogels could be used as a potential substrate for hBMSCs culture and expansion.

Development of Silver-Based Bactericidal Composite Nanofibers by Airbrushing

In this article, we report a simple, cost-effective and eco-friendly method of airbrushing for the fabrication of antibacterial composite nanofibers using Nylon-6 and silver chloride (AgCl). The Nylon-6 is a widely used polymer for various biomedical applications because of its excellent biocompatibility and mechanical properties. Similarly, silver has also been known for their antibacterial, antifungal, antiviral, and anti-inflammatory properties. In order to enhance the antibacterial functionality of the Nylon-6, composite nanofibers in combination with AgCl have been fabricated using airbrush method. The chemical functional groups and morphological studies of the airbrushed Nylon-6/AgCl composite nanofibers were carried out by FTIR and SEM, respectively. The antibacterial activity of airbrushed Nylon-6/AgCl composite nanofibers was evaluated using Gram +ve (Staphylococcus aureus) and Gram -ve (Escherichia coli) bacterial strains. The results showed that the airbrushed Nylon-6/AgCl composite nanofibers have better antibacterial activity against the tested bacterial strains than the airbrushed Nylon-6 nanofibers. Therefore, the airbrushed Nylon-6/AgCl composite nanofibers could be used as a potential antibacterial scaffolding system for tissue engineering and regenerative medicine.

Development of Egg Shell Derived Carbonated Apatite Nanocarrier System for Drug Delivery

Carbonated apatite has a chemical composition quite similar to biological apatite found in native bone. The incorporation of carbonate (CO2-3) ions groups into the apatitic crystal structure can tailor its crystallinity, solubility and biological activity that benefit the bone repair and regeneration. In this study, we report a simple and elegant method of synthesizing carbonated calcium deficient hydroxyapatite (ECCDHA) nanoparticles from egg shell wastes and its efficacy has been compared with synthetic calcium deficient hydroxyapatite (SCDHA) nanoparticles. Egg shell contains about 94% of calcium carbonate. Fourier transform infrared (FT-IR) spectroscopy results confirmed the carbonate substitution in the apatite as B-type and CHNS/O elemental analysis showed 6 wt.% of carbonate content in ECCDHA. Energy dispersive spectroscopy (EDS) analysis confirmed the presence of biologically relevant elements such as magnesium, strontium, fluoride, potassium etc., in ECCDHA inherited from the egg shell. In vitro cell culture studies confirmed that the ECCDHA is cellular compatible and it has enhanced cell adhesion and proliferation of L6 myoblast cells as compared to SCDHA. The potential of ECCDHA suitable for bone drug applications was tested with an antibiotic drug, doxycycline. The results showed higher drug loading and releasing for ECCDHA as compared to SCDHA during the period of study. Based on these results, the ECCDHA may be considered as a potential bone substitute and drug carrier system.

Surface Functionalization of Biomaterials

Stem cells have the ability to sense their microenvironment and respond to them accordingly; therefore, cellular functions of these stem cells can be regulated or controlled by manipulating their microenvironment. Controlling the interactions between biomaterials and stem cells is a critical factor for exploring the complete potential of biomaterials in the field of stem cell–based tissue engineering and regenerative medicine. Surface functionalization or modification paves a way for tailoring the biomaterials surface in accordance to the physiological surrounding of the living cells; thereby, enhancing structure and functions of engineered tissues and organs. There are a variety of methods and technologies available to modify the surface of biomaterials depending on the manner the cell or tissue properties needs to be regenerated. This book chapter reviews current trends in various surface modification techniques concerning the surface treatment of engineered biomaterials along with the biological relevance of the surface functionalized biomaterials in the context of stem cell research. Authors have also discussed about the challenges related to surface functionalization and understanding the interactions between the implants and stem cell.