Poly (vinyl alcohol) (PVA) is a hydrophilic polymer with excellent biocompatibility and has been applied in various biomedical areas due to its favorable properties. PVA-based hydrogels have been recognized as promising biomaterials and suitable candidates for tissue engineering applications and can be manipulated to act various critical roles. However, due to some disadvantages (i.e., lack of cell-adhesive property), they needs further modification for desired and targeted applications. This review highlights recent progress in the design and fabrication of PVA-based hydrogels, including crosslinking and processing techniques. Finally, major challenges and future perspectives in tissue engineering are briefly discussed. GRAPHICAL ABSTRACT

Sugarcane bagasse (SCB) is abundantly available agro-waste world-wide and has been used in different applications and its utilization as a source of cellulose attracting attention in the area of biomedical and other applications. The present study investigates the surface morphology, topography, structural, elemental and thermal properties of cellulose nanocrystals (CNCs) extracted by acid-hydrolysis from sugarcane bagasse as agro-waste. Morphological (field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM)), structural (fourier transformed infrared (FTIR) spectroscopy, X-ray diffraction (XRD)), elemental analysis (energy dispersive x-ray diffraction (EDX)) and thermal characterization (TG-DTG-DTA) of CNCs was carried out. Morphological characterization clearly showed the formation of rod-shaped CNCs having size in the range of 250-480 nm (length) and 20-60 nm (diameter). Elemental analysis (EDX) showed 0.72 wt% sulfur impurity in CNCs along with other main components. X-ray diffraction and thermal analysis revealed that CNCs have higher crystallinity (72.5%) than that of chemically purified cellulose (CPC) (63.5%) but have lower thermal stability. These lab extracted CNCs supposed to have a high potential as nano-reinforcement into bionanocomposite for biomedical and other value-added products in industrial applications.

Graphene, a two-dimensional nanosheet, is composed of carbon species (sp² hybridized carbon atoms) and is the center of attention for researchers due to its extraordinary physicochemical (e.g., optical transparency, electrical, thermal conductivity, and mechanical) properties. Graphene can be synthesized using top-down or bottom-up approaches and is used in the electronics and medical (e.g., drug delivery, tissue engineering, biosensors) fields as well as in photovoltaic systems. However, the mass production of graphene and the means of transferring monolayer graphene for commercial purposes are still under investigation. When graphene layers are stacked as flakes, they have substantial impacts on the properties of graphene-based materials, and the layering of graphene obtained using different approaches varies. The determination of number of graphene layers is very important since the properties exhibited by monolayer graphene decrease as the number of graphene layer per flake increases to 5 as few-layer graphene, 10 as multilayer graphene, and more than 10 layers, when it behaves like bulk graphite. Thus, this review summarizes graphene developments and production. In addition, the efficacies of determining the number of graphene layers using various characterization methods (e.g., transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra and mapping, and spin hall effect-based methods) are compared. Among these methods, TEM and Raman spectra were found to be most promising to determine number of graphene layers and their stacking order.

The engineering of tissues under a three-dimensional (3D) microenvironment is a great challenge and needs a suitable supporting biomaterial-based scaffold that may facilitate cell attachment, spreading, proliferation, migration, and differentiation for proper tissue regeneration or organ reconstruction. Polysaccharides as natural polymers promise great potential in the preparation of a three-dimensional artificial extracellular matrix (ECM) (i.e., hydrogel) via various processing methods and conditions. Natural polymers, especially gums, based upon hydrogel systems, provide similarities largely with the native ECM and excellent biological response. Here, we review the origin and physico-chemical characteristics of potentially used natural gums. In addition, various forms of scaffolds (e.g., nanofibrous, 3D printed-constructs) based on gums and their efficacy in 3D cell culture and various tissue regenerations such as bone, osteoarthritis and cartilage, skin/wound, retinal, neural, and other tissues are discussed. Finally, the advantages and limitations of natural gums are precisely described for future perspectives in tissue engineering and regenerative medicine in the concluding remarks.