Recent Developments in Polyurethane-Based Materials for Bone Tissue Engineering

Abstract

To meet the needs of clinical medicine, bone tissue engineering is developing dynamically. Scaffolds for bone healing might be used as solid, preformed scaffolding materials, or through the injection of a solidifiable precursor into the defective tissue. There are miscellaneous biomaterials used to stimulate bone repair including ceramics, metals, naturally derived polymers, synthetic polymers, and other biocompatible substances. Combining ceramics and metals or polymers holds promise for future cures as the materials complement each other. Further research must explain the limitations of the size of the defects of each scaffold, and additionally, check the possibility of regeneration after implantation and resistance to disease. Before tissue engineering, a lot of bone defects were treated with autogenous bone grafts. Biodegradable polymers are widely applied as porous scaffolds in bone tissue engineering. The most valuable features of biodegradable polyurethanes are good biocompatibility, bioactivity, bioconductivity, and injectability. They may also be used as temporary extracellular matrix (ECM) in bone tissue healing and regeneration. Herein, the current state concerning polyurethanes in bone tissue engineering are discussed and introduced, as well as future trends.

Keywords: bone tissue engineering; polyurethane-based composites; regenerative medicine.

Figure 1

Mechanism of PU synthesis.

Figure 2

Schematic of the scaffold preparation. Reprinted from [49] with permission from Elsevier.

Figure 3

(A) Confocal microscopy images (left) and correspondent SEM images (right), of C2C12 skeletal muscle cultured on PU-based scaffolds. In fluorescence images, live cells are shown in green, while the scaffold matrix is shown in red. (B) DNA quantification for C2C12 skeletal muscle cells on each sample type, 24 h after seeding. (C) Cytotoxicity expressed as the ratio between the lactate dehydrogenase (LDH) released from cells cultured on the samples and the one released from a positive control featured by relevant toxicity, 24 h after seeding. Reprinted from [64] with permission from Elsevier.

Figure 4

Hierarchical structural organisation of bone: (left to right) cortical and cancellous bone; osteons with Haversian systems; lamellae; collagen fibre assemblies of collagen fibrils; bone mineral crystals, collagen molecules and noncollagenous proteins. Reprinted from [96] with permission from Elsevier.

Figure 5

H&E-stained cross-sections of the PU-S (A–C), the PU-M (D–F) and the PU-F (G–I) scaffold at day 14 after implantation onto the striated muscle tissue (A,D,G, arrows) of the dorsal skinfold chamber. Higher magnification of the basis of the scaffolds (B,E,H) shows a newly formed granulation tissue in the border zone growing into the pores of the scaffolds. Within this granulation tissue, newly formed blood vessels (arrowheads) can be observed. In contrast, the centre of the scaffolds (C,F,I) is still avascular with only a few single cells migrating along the polyurethane strands. Scale bars: A, D and G = 220 lm; B, C and E = 25 lm; F, H and I = 55 lm. Reprinted from [102] with permission from Elsevier.

Figure 6

Polyurethane scaffolds. Micro-CT reconstructions: (A) top view, (B) 3-D view, (C) SEM image. Reprinted from [55] with permission from Elsevier.

Figure 7

Schematic diagram of polyurethane foam/nano-hydroxyapatite composite fabrication. Reprinted from [57] with permission from Elsevier.

Figure 8

Radiographs of extracted rabbit distal femurs: (A) 6C3G1L300-MBP, (B) 6C3G1L300-SDBP, (C) 6C3G1L600-MBP, (D) 6C3G1L600-SDBP. Reprinted from [67] with permission from Elsevier.

Figure 9

Fabrication of 3D scaffolds with various PU/PEO dispersions and rheological properties of the dispersions. (a) The gross appearance of the scaffolds fabricated with various PU/PEO ratios. (b) The viscosity of various PU/PEO dispersions in the shear rate range between 0.1 and 100 Hz. Reprinted from [127] with permission from Wiley.

Figure 10

Chemical reactions present in the injectable PUR biocomposite. Reprinted from [130] with permission from Elsevier.

Figure 11

(A) Photo macrograph of the porous PU/HAp scaffold; (B) SEM photographs of the porous PU/HAp scaffold. Reprinted from [135] with permission from Elsevier.

Figure 12

Postulate mechanism of PU biodegradation. Reprinted from [23] with permission from Elsevier.

Figure 13

The degradation of PLA and P-PUUs. Reprinted from [137] with permission from Elsevier.