Biomimetic Layer-by-Layer Self-Assembly of Nanofilms, Nanocoatings, and 3D Scaffolds for Tissue Engineering

Abstract

Achieving surface design and control of biomaterial scaffolds with nanometer- or micrometer-scaled functional films is critical to mimic the unique features of native extracellular matrices, which has significant technological implications for tissue engineering including cell-seeded scaffolds, microbioreactors, cell assembly, tissue regeneration, etc. Compared with other techniques available for surface design, layer-by-layer (LbL) self-assembly technology has attracted extensive attention because of its integrated features of simplicity, versatility, and nanoscale control. Here we present a brief overview of current state-of-the-art research related to the LbL self-assembly technique and its assembled biomaterials as scaffolds for tissue engineering. An overview of the LbL self-assembly technique, with a focus on issues associated with distinct routes and driving forces of self-assembly, is described briefly. Then, we highlight the controllable fabrication, properties, and applications of LbL self-assembly biomaterials in the forms of multilayer nanofilms, scaffold nanocoatings, and three-dimensional scaffolds to systematically demonstrate advances in LbL self-assembly in the field of tissue engineering. LbL self-assembly not only provides advances for molecular deposition but also opens avenues for the design and development of innovative biomaterials for tissue engineering.

Keywords: biomaterial; layer-by-layer; multilayer; nanocoating; nanofilm; polyelectrolyte; scaffold; self-assembly; tissue engineering.

Figure 1

(a) Schematic overview of LbL assembly technique with fabrication capacity on any type of substrates and from an extensive choice of materials; (b) schematics showing the five main technology categories for LbL assembly; (c) a typical comparison of different films using immersive and spin assembly. Reprinted from [17] with permission from American Association for the Advancement of Science.

Figure 2

(a) Molecular interactions driving the LbL self-assembly of materials; (b) schematic showing the main biomedical application fields for LbL self-assembly technique; (c) schematic of multiscale assembly strategies for engineering tissue constructs. Reprinted from [18,56] with permissions from American Chemical Society and Elsevier.

Figure 3

(a) Confocal microscopy images of differentiated neurospheres on day 7; (b) average percentages of differentiated cell phenotypes after 7 days in culture; (c) schematic showing LbL assembly of polyelectrolytes based on electrostatic interactions for tuning cell adhesive properties using cross-linking; (d) schematic illustration of the fabrication and cell uptake of LbL assembly multilayers embedded with β-estradiol-silica nanoparticles onto substrates; (e) mixed element map of the cross-section and upper surface of different catechol-based freestanding membranes; (f) Osteopontin immunofluorescence images of cells after 14 days cultured on different catechol-based freestanding membranes. Reprinted from [24,72,77] with permissions from American Chemical Society, Elsevier, and Wiley-VCH.

Figure 4

(a) Schematic illustration of the fabrication of PEG-rich, nanothin conformal islet nanofilms via LbL assembly; (b) Poly(l-lysine)-g-poly(ethylene glycol)(biotin)/streptavidin multilayer films assembled on individual pancreatic islets; (c) confocal images of freshly coated living cells and (d) transmission image of cells during their duplicating process; (e) transmission electron microscope images of coated and uncoated red blood cells with LbL assembly films. Reprinted from [82,84,85] with permissions from American Chemical Society.

Figure 5

(a) Confocal images of inverted colloidal crystal scaffolds cultured with thymic epithelial cells and monocyte cells; (b) illustration of LbL multilayer nanocomposite coating with hydroxyapatite and collagen on substrates, and the AFM images of multilayers with different numbers of bilayers; (c) hMSCs adhesion and their quantification of DNA amounts to bare and coated scaffolds, and alkaline phosphatase activity and relative mRNA expression during the culture of hMSCs on various substrates; (d) steps and mechanism for developing the hierarchical and hybrid 3D scaffolds and (e) representative images of the structures of these scaffolds. Reprinted from [49,92,94] with permissions from Wiley-VCH and Royal Society of Chemistry.

Figure 6

(a) Schematic diagram showing the layering approach to pattern cell co-cultures; (b) patterned hyaluronic acid surfaces attached with poly-l-lysine and immobilized cells; (c) patterned co-cultures of hepatocytes with fibroblasts; (d) schematic diagram of the fabrication of the co-culture system using LbL assembly technique; (e) patterned cell culture and co-culture on hyaluronic acid/collagen surface; (f) confocal laser scanning microscopy images of hepatocytes after co-culture on different chitosan/alginate LbL assembly films with nanoparticles. Reprinted from [99,100,101] with permissions from Elsevier.

Figure 7

(a) Schematic illustration of the microfluidic LbL approach used to create 3D hierarchical systems with matrices and cells; (b) 3D images reconstituted from stacks demonstrate a two- or three-layer structure; (c) confocal cross-sectional images of the control group (top) and the 3 layer tissue constructs (bottom) after 2 days of culture. Hematoxylin and eosin stain images of 3 layer fibroblasts. Schematic illustration of the cross-section of the 2 layer construct. SEM images showing the cross-section and the thickness of 1, 2 and 3 layer constructs fabricated with various concentrations of poly-l-lysine-coated graphene oxide as interlayer films; (d) fabrication of cellular microfluidic scaffolds including the fabrication process and its resultant microstructures. Reprinted from [5,7,106] with permissions from Nature Publishing Group, Elsevier, and Wiley-VCH.

Figure 8

(a) Rapid construction of 3D multilayered tissues with endothelial tube networks by the cell-accumulation technique and the phase/fluorescent microscopic images, cell viability, and hematoxylin and eosin staining images of the resultant tissues; (b) schematic illustration, cross-section image, and reconstructed fluorescent image of 3D multilayered tissues; (c) the construction of vascularized liver tissue using LbL cell coating technique; (d) schematic illustrations of centrifugation-LbL and filtration-LbL for nanofilm coating on cell surfaces, and construction of vascularized 3D tissues by the cell accumulation technique. Reprinted from [112,113,114] with permissions from Wiley-VCH and Elsevier.