Influence of Mechanical Properties of Biomaterials on the Reconstruction of Biomedical Parts via Additive Manufacturing Techniques: An Overview

Abstract

Additive manufacturing (AM) is the opposite of conventional manufacturing technologies, creating an opportunity to fabricate parts using a layer upon layer approach to obtain 3D patterns. AM technology has provided an opportunity for biomaterials usage in the bio-fabrication of organs and scaffolds for tissues engineering. In recent times, AM has been well-utilized for the printing of organs, customized implants, anatomical models for surgery training kits, drug formulations, prosthetics, orthotics, dentistry, and scaffolds for tissue engineering with the use of metals, ceramics, polymers, and composites materials. Printing of biomaterial that has a suitable viscosity, enough strength, good biocompatibility, and degradability has been reported by many researchers to be an arduous task. Biomaterials printed with robust mechanical properties are considered highly essential for the fabrication of soft tissues such as cartilage and skin because the function of such tissues mainly relies on their mechanical properties that possess the capacity to support cell proliferation and extracellular matrix production. For repairing and regenerating organs or tissue, the implant must provide sufficient mechanical support to endure in vivo stresses and load-bearing cycles. This book chapter aims to document the mechanical properties of 3D printed biomaterials and provides a keys future research direction.

1. Introduction

The unique material that can be used to fabricate biomedical parts inside a human body to treat, repair, replace any tissue is known as biomaterials. Biomaterials are referred to as any material that comes into contact with humans or animals to fulfill their intended purpose without causing any toxic reaction [1]. In the field of biomedical engineering, biomaterials can be used to replace or mimic part of an organ or a tissue while still maintaining interaction with living tissue. One major setback when working with biomaterial is the lack of mechanical strength [2]. The reports have suggested that this constraint can either be subdued by utilizing appropriate material and manufacturing techniques of processing the scaffolds to enhance the mechanical integrity of the fabricated parts. Additive manufacturing (AM) has been described as an emerging advanced technology in which materials are linked layer by layer to fabricate functional components from three-dimensional (3D) model data [3]. The ability of 3D printing to produce complex shapes at low cost placed it a higher advantage in the production of biomedical parts than other manufacturing methods [4, 5, 6, 7, 8, 9, 10]. Figure 1 summarizes common synthetic polymers in 3D bioprinting applications [4, 5, 6, 7, 8, 9, 10, 11].

Figure 1.

Summarizes common synthetic polymers in 3D bioprinting applications.

3D bioprinting has become a successful technique used in fabricating biomaterial scaffolds such as customized implant, organ, drug delivery systems, prosthetics, orthotic, and tissues engineering [3, 12]. Bioprinting technology has emerged as a powerful bio-fabrication tool where biomaterials such as cells and growth factors are combined to fabricate biomedical parts with bio-ink [13]. The advantages of bioprinting include accurate control of cell distribution, high-resolution cell deposition, scalability, and cost-effectiveness. Bioprinting has become an effective fabrication tool to create complex micro-and macro-scale biomedical systems. Biomaterials, such as hydrogels, are currently extensively studied for their ability to reproduce both the ideal 3D extracellular environment for tissue growth and to have required mechanical properties for load-bearing. Microfabrication techniques such as electrospinning [14] and 3D printing have emerged as promising strategies for manufacturing complex hydrogel structures for tissue engineering applications. 3D bioprinting application has extensively found its potential use in biomedical applications such as tissue engineering, drug discovery, toxicology [15], regenerative medicine to generate a variety of transplantable tissues including skin, cartilage, and bone [16]. In 3D bioprinting, 3D fabrication techniques have been precisely used to dispense cell-laden biomaterials for the construction of complex 3D functional living tissues or artificial organs using an additive manufacturing strategy by depositing substrates such as living cells, nucleic acids, drug particles, proteins, and other biological components [17, 18]. Nowadays, several bioprinting signs of progress have been demonstrated, such as bionic ears [19], multilayered skins [20], artificial bones [21], vascular tissues [22], and cartilaginous structures. Three major bioprinting techniques are being commonly used which include extrusion bioprinting, laser-assisted bioprinting, and inkjet bioprinting. Figure 2 summarizes the bioprinting process, techniques, and applications.

Figure 2.

Bioprinting process, techniques, and applications [23].

According to Dinesh & Devaprakasam [24], the life span, reliability, bio-compatible and mechanical properties of the implant material are not up to the expectation but research has to be done to find out the most reliable, high strength, and long-lasting material.

Laasri et al. [25] studied the influence of powder manufacturing and sintering temperature on densification, microstructure, and mechanical properties of calcium phosphate biomaterials. It was reported that the manufacturing of β-TCP ceramic improved its densification, microstructure homogeneity, and mechanical properties. In another study, Wang et al. [26] discussed the influence of mechanical properties of biomaterials on degradability, cell behavior, and signaling pathways. It is concluded that both biomaterial degradability and signaling cascades of cell interactions with biomaterials are significantly influenced by mechanical properties of biomaterials, determining the final repair effect of bio-implants [26]. Lv et al. [27] designed biomaterials to mimic the mechanical properties of muscles. It is confirmed that the mechanical properties of biomaterials can be modified by fine-tuning the composition of the elastomeric proteins, providing the opportunity to develop biomaterials that are mimetic of different types of muscles [27]. Fabrication of the appropriate 3D scaffold with required mechanical properties is a crucial factor in tissue regenerative medicine in promoting in vivo-like cell behavior. This book chapter documents the influence of mechanical properties of additively manufactured biomaterials in reconstructing biomedical parts.

2. Mechanical properties of biomaterials manufactured by using 3D printing techniques

The tensile strength, yield strength, elastic modulus, corrosion, creep, and hardness are some of the most paramount properties of biomaterials that need to be carefully examined and improved before implantation [1]. Production of functional parts needs to demonstrate their stable mechanical properties. The importance of the mechanical control of cellular phenotype and fate are as critical as biochemical factors in regulating cellular function [28]. Biomaterials can experience several mechanical degradations during processing, storage, and use. Due to environmental conditions during the printing process, mechanical degradation can take place due to shear forces, tension, and compression [29, 30, 31]. In one study, Yang et al. [32] demonstrated that the complex stress state of maxillofacial bone tissues requires metal implants with matching mechanical properties to support mandibular functions. Soufivand et al. [33] also investigated the applicability of CAD-based FEM analysis to tune and predict the mechanical behaviors of the printed PCL scaffolds based on the inner geometries, as the inner geometries of the tissue-engineered scaffolds play an important role in biomechanical and biological aspects for tissue engineering applications. Their findings revealed that the CAD-based FEM prediction could be used for designing tissue-specific constructs to mimic the mechanical properties of targeted tissues or organs. Moroni et al. [34] also proved that the mechanical signaling from tissue-engineered scaffolds could impact cellular activities, including cell proliferation and differentiation, as well as tissue hemostasis and development. In one investigation, Ambrosio et al. [35] evaluated the mechanical and viscoelastic behavior of a soft composite material based on a hydrogel matrix reinforced with the range of polyethylene terephthalate (PET) fibers designed to mimic mechanical properties of soft tissue such as tendons, ligaments, and intervertebral discs. It is concluded that the control of the geometrical configuration of the wound fibers allows a wide range of mechanical properties to be secured [35]. Iannace et al. [36] determined the mechanical behavior of composite artificial tendons and ligaments. The results recommended that large variations in the mechanical behavior can be attained by altering the winding angle of the fibers in the composite which determines the extent of the ‘toe’ region and the sensitivity of the system to the rigidity of the fibers. In another study, Hippler et al. [37] informed that biophysical factors such as mechanical properties of the surrounding extracellular matrix (ECM) can significantly impact cellular reactions. As reported, modifications in the composition or the mechanical properties of the ECM are often connected to cancer progression and metastasis as well as pathological conditions [37]. Hukins et al. [38] also reviewed the difficulties which are encountered in defining the mechanical properties of natural tissues, and in replacing them with synthetic materials in the human body. In any support system like the frame in engineering, bone in the human body and others required suitable mechanical properties to make it function optimally. Mechanical properties such as tensile and compressive stresses, strain, torque, bending moment shear force, and others have a significant influence on the suitability of any materials [39]. Capurro and Barberis [40] discussed the mechanical properties of biomaterials and their influence in the field of medicine, surgery, and physiology applications. It was presented that the mechanical properties can be categorized into two main branches: elastic and viscoelastic properties, and ultimate properties (such as plasticity, fracture, fatigue damage, and others) [41]. A lot of previous research works have been carried out on biomaterials but little has been said on the evaluation of mechanical properties of biomaterials in many fields of physiology, medicine, and Surgery applications. Table 1 presented a summary of biomaterials in 3D printing applications.

AM technology	Materials	Mechanical properties	Applications	Ref
Electron beam melting	Co–29Cr–6Mo alloy and a Ti–6Al–4Vtibial component	The UTS increased by 20%, and the elongation increased by 900%.; In contrast to the ASTM-F75 Co–29Cr–6Mo transplant standard, the yield stress for the EBM-fabricated and HIP manufactured component increased by 30%, and a 200% increase in elongation	Knee replacement implants	[42]
3D bioprinting	Alginate hydrogel	Results demonstrated that alginate concentration, CaCl2 cross-linking concentration and cross-linking ratios as well as gelling conditions, such as cross-linking reaction time and temperature which have a significant effect on its mechanical properties and printability of 3D alginate scaffolds network.	Tissue engineering	[32]
Micro-extrusion 3D bioprinting	Poly(ε-caprolactone) (PCL)	Results showed that the theoretical compressive elastic moduli of the designed constructs were 23.3, 56.5, 67.5, and 1.8 MPa, and the experimental compressive elastic moduli were 23.6 ± 0.6, 45.1 ± 1.4, 56.7 ± 1.7, and 1.6 ± 0.2 MPa for lattice, wavy, hexagonal, and shifted microstructures, respectively, while maintaining the same construct dimension and porosity.	Tissue engineering and regenerative medicine	[33]
3D bioprinting	Bio-ink	On day 20, all tissues showed an improved stiffness compared to day 10. P2 tissue exhibited the lowest variation of young’s modulus with a final value of 103.3 Pa, the lowest of the three modalities. M1 and control tissues exhibited similar elastic moduli of 155.8 and 149.0 Pa.	Tissue engineering	[10]
3D bioprinting	Nanocellulose/chitosan-based bio-ink	The addition of CNCs and cells (5 million cells) significantly improved the viscosity of bio-inks and the mechanical properties of chitosan scaffolds post-fabrication.	Bone tissue engineering and regeneration applications	[43]

Table 1.

Summary of biomaterials in 3D printing applications.

3. Summary and future work

Loss of many lives associated with getting a replacement for defective or loss of human tissues and bones have become a great matter of concern. For implants and natural tissue materials, the biocompatibility and mechanical strength of biomaterials are critical for a variety of skeletal repair joint replacements and dental restorations. Printing of scaffolds with the use of design strategies could be an effective platform to fabricate functional tissue engineering that will provide significantly enhanced different mechanical properties. In recent times, materials with high concentration and high viscosity, including ceramics, poly(caprolactone) (PCL), polylactic acid (PLA), beta-tricalcium phosphate (β-TCP), have been widely utilized to produce bio-inks for the bioprinting of defective bone tissue. For future work, the following conclusions are drawn from the literature comprehensively reviewed:

Further research is required to investigate appropriate material and manufacturing techniques of processing the scaffolds to enhance the mechanical integrity of the fabricated parts.

There is a need to determine the effects of processing parameters on the biochemical and biophysical characteristics of biomaterials for the fabrication of tissue structure.

The tensile strength, yield strength, elastic modulus, corrosion, creep, and hardness are some of the most paramount properties of biomaterials that should be carefully examined and improved before implantation.

Conflict of interest

The authors declare no conflict of interest.

Abbreviations

AM	Additive manufacturing
ABS	Acrylonitrile butadiene styrene
ASTM	American Society for Testing and Materials
ALG	Alginate
CS	Chitosan
CAD	Computer aided design
HY	Hydrogel
HIP	Hot isostatic pressing
β-TCP	β-tricalcium phosphate
ECM	Extracellular matrix
PET	Polyethylene terephthalate
FDM	Fused deposition modeling
PCL	Poly(ε-caprolactone)
PLA	Polylactic acid
EBM	Electron beam melting
CNCs	Cellulose Nanocrystals
ABS	Acrylonitrile Butadiene Styrene
PEG	Polyethylene glycol
CaCl2	Calcium chloride
HA	Hydroxyapatite
FEM	Finite element modeling
UTS	Ultimate tensile strength