Nanomaterial-Based Scaffolds for Tissue Engineering Applications: A Review on Graphene, Carbon Nanotubes and Nanocellulose

Abstract

Nanoscale biomaterials have garnered immense interest in the scientific community in the recent decade. This review specifically focuses on the application of three nanomaterials, i.e., graphene and its derivatives (graphene oxide, reduced graphene oxide), carbon nanotubes (CNTs) and nanocellulose (cellulose nanocrystals or CNCs and cellulose nanofibers or CNFs), in regenerating different types of tissues, including skin, cartilage, nerve, muscle and bone. Their excellent inherent (and tunable) physical, chemical, mechanical, electrical, thermal and optical properties make them suitable for a wide range of biomedical applications, including but not limited to diagnostics, therapeutics, biosensing, bioimaging, drug and gene delivery, tissue engineering and regenerative medicine. A state-of-the-art literature review of composite tissue scaffolds fabricated using these nanomaterials is provided, including the unique physicochemical properties and mechanisms that induce cell adhesion, growth, and differentiation into specific tissues. In addition, in vitro and in vivo cytotoxic effects and biodegradation behavior of these nanomaterials are presented. We also discuss challenges and gaps that still exist and need to be addressed in future research before clinical translation of these promising nanomaterials can be realized in a safe, efficacious, and economical manner.

Keywords: Carbon nanotubes; Cellulose nanocrystals; Cellulose nanofibers; Graphene; Regenerative medicine; Tissue engineering.

Fig. 1

Depiction of three nanomaterials, i.e., graphene, carbon nanotubes, and nanocellulose, and their roles in tissue engineering. In this review, we discuss how 2D/3D scaffolds and/or organic/inorganic nanocomposites fabricated with these nanomaterials have been used to improve cell attachment, proliferation, and differentiation into specific tissues, as well as their biocompatibility and biodegradability behaviors (adapted with permission from [5])

Fig. 2

Schematic illustrating graphene’s unique physicochemical properties, along with its highly modifiable surface chemistry and large surface areas, which make it a versatile material for engineering a variety of tissues, ranging from cardiac muscle and bones to skin and cartilage (adapted with permission from [9])

Fig. 3

A–F Treatment of diabetic peripheral nerve injury using graphene foam scaffolds, with and without encapsulated ADSCs and their comparisons with ADSC-alone treatment for tissue regeneration potential by quantifying morphology changes and revascularization of targeted muscles (adapted with permission from [39]): (A) Images of gastrocnemius muscles, (B) quantitative analysis of the relative wet weight of gastrocnemius muscles, (C) Masson staining of muscles (scale bar = 50 μm), (D) quantitative analysis of the average diameter of fibers, (E) CD31 staining of gastrocnemius muscles (scale bar = 50 μm), and (F) quantitative analysis of microvessel density of gastrocnemius muscles. G–I Enhanced cardiac repair and cardiac function restoration by implantation of MSC–rGO hybrid spheroids (adapted with permission from [48]): (G) Capillary density in the periinfarct border zone assessed by immunostaining for vWF (green) (scale bar = 100 μm), (H) cardiac fibrosis indicated by Masson's trichrome staining (blue) and quantification of the fibrotic area, and (I) Expression of Cx43 (red) examined by immunohistochemical staining in the infarct border zone (scale bar = 100 μm). Infarcted hearts were treated through the injection of PBS, rGO flakes, MSC spheroids (Sph-0), or MSC–rGO hybrid spheroids (Sph-5)

Fig. 4

Schematic illustrating carbon nanotubes (CNTs), both single-walled CNTs (SWNTs) and multi-walled CNTs (MWNTs), and their unique optical, mechanical, and electrical properties, that make them versatile materials for diverse biomedical applications, including, but not limited to, medical imaging, drug delivery, and tissue engineering (partly adapted with permissions from [72, 81, 175])

Fig. 5

A–B Bone regeneration efficacy of CNT-BC composite scaffolds evaluated in mouse calvarial defects for 8 weeks (adapted with permission from [93]). Collagen scaffolds loaded with bone morphogenetic protein-2 (BMP-2) (Col-BMP-2), a clinically used bone graft, served as a positive control. Amphiphilic comb-like polymer (APCLP) was used to modify/coat CNTs: (A) Bone regeneration evaluated by micro-CT analyses and quantification of the bone regeneration area in defects and (B) Goldner's trichrome staining of mouse calvarial defect areas and quantification of bone formation area and new bone density in defects. CNT-BC-Syn represents APCLP-coated CNT-BC hybridization and CNT-BC-Imm represents scaffolds prepared by immersing BC in APCLP-coated CNT solution. Arrows indicate the bone defect margin. C MWCNT-reinforced, aligned PCL-collagen (CPA) scaffolds for directional peripheral nerve regeneration (adapted with permission from [95]). Higher anisotropic conductivity of CPA scaffolds led to more efficient healing of injured sciatic nerves in rats, as indicated by immunohistostaining of S100, MAP2, and GFAP proteins, 30 days after implantation

Fig. 6

Top Hierarchical structure of cellulose, showing how macro-sized cellulose fibrils are made up of bundles of micron-sized individual microfibrils, and each microfibril can further be broken down into nanoscale fibrils and crystals (adapted with permission from [130]). Bottom A table comparing the structural properties of CNCs, CNFs, and bacterial cellulose [135]

Fig. 7

A Utility of anisotropically aligned, CNC-reinforced, PCL-chitosan-CNC scaffolds for tendon tissue engineering (adapted with permission from [138]). Confocal microscopy images of hTDCs seeded on PCL/CHT and PCL/CHT/CNC3 scaffolds with random and aligned topography, respectively. Organization of cytoskeletal actin filaments after 10 days of culturing hTDCs (blue: nuclei stained with DAPI; red: actin filaments stained with rhodamine-conjugated phalloidin). B 3D printed CNC-reinforced alginate-gelatin hydrogel scaffolds for bone tissue engineering (adapted with permission from [151]): (top) Digital photograph of in vivo surgical experiments and (bottom) μCT images showing the extent of bone regeneration in rat calvaria defect model 3 weeks after transplantation. C 3D printed nanocellulose-alginate scaffolds for cartilage tissue engineering (adapted with permission from [158]): (a) 3D printed small grids (7.2 × 7.2 mm²) after cross-linking, (b) the shape of the grid deforms while squeezing, and (c) its restoration after squeezing. 3D printed human ear (d) and sheep meniscus side view (e) and top view (f). D Viability of human nasoseptal chondrocytes (hNCs) before and after 3D bioprinting (adapted with permission from [158])