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International Journal of Bioprinting 3D-printed biodegradable metals for bone regeneration

vascularization, matrix deposition, etc. to restore the materials is greater than that of bone tissues, residual
structural and mechanical strength of the bone tissue and implants may lead to stress shielding and cause separation
restore its function. However, when large bone defects of the implant from bone tissues; therefore, biodegradable
occur as a result of severe damage, it is difficult to repair metal (BM) materials have garnered increasing attention
without external intervention to restore the original shape from scholars. 16,21-24
and structure. Therefore, repair of severe bone defects The definition of a BM material is as follows: “A metal
1,2
is an important challenge in clinical practice. Currently, that is expected to gradually corrode in the body, and
the main solutions for treatment include autologous bone the released corrosion products cause appropriate host
grafting, allogeneic bone grafting, artificial bone material reactions; these corrosion products can be metabolized
grafting, bone repair materials, and three-dimensional by cells and/or assimilated by cells and/or tissues and then
(3D) printing technology. The use of autologous and completely dissolved after completing the task, assisting
3-5
allogeneic bone grafts is still affected by many challenges, in tissue healing without implant residues.” There are
25
including an insufficient supply of raw materials, three main categories of BM materials: magnesium, zinc,
rejection reactions, and infectious diseases. 3,6,7 In contrast, and iron. Moreover, biodegradable materials, including
the use of artificial bone materials and bone repair biodegradable medical sutures, bolts for fracture fixation,
materials, including bioceramics, hydrogels, and bionic and biological scaffolds, have long been applied in the
nanoscaffolds, has led to many advances in severe bone biomedical field. With the development of 3D printing
defect repair. 8-10 Additive manufacturing, or 3D printing, technology, BM materials have gradually shown great
can be used to construct 3D components that mimic the advantages in terms of 3D printing characteristics,
biostructural properties of bone through layer-by-layer especially in the field of bone regeneration. In orthopedic
fine positioning of biological and biochemical materials clinical practice, 3D-printed BM technology has important
and living cells, thereby replacing bone tissues and applying application value. Preparing components that are suitable
them to either in situ or xenotransplantation. 11,12 To further for the shape of bone defects is a major challenge in the
the development of printing bone tissues with biomimetic repair of severe bone defects. Bone replacement materials
effects, the selection of raw materials for 3D printing must also have good biocompatibility, an elastic modulus,
is particularly important; these materials should have and antibacterial and osteogenic properties. 3D printing
specific porous properties to facilitate cellular colonization can personalize the shape of bone defects before surgery,
and serve as scaffolds and templates for regeneration of and BM printing materials have physical and chemical
new tissues, while the components must maintain certain properties that match those of bone tissue. An effective
mechanical support properties to maintain the enrichment combination of these two materials is more conducive
and delivery of important bone regeneration elements in to the repair of bone tissue. 26,27 In this paper, we review
the implanted area. 4,13,14 the progress of research on various degradable metallic
To date, 3D printing has been widely used in the clinical materials for bone regeneration reported in recent years
treatment of bone defects, and a wide selection of materials, and show the application of 3D-printed degradable
which are mainly categorized into synthetic materials and metallic materials in bone regeneration in combination
natural polymers, has been used. 15,16 Natural polymers, with various 3D printing methods (Figure 1). We also
including chitosan, alginate, collagen, gelatin, cellulose, discuss key issues and challenges and provide suggestions
hyaluronic acid, sericin, fibrinogen, and starch, are mostly for future research.
used to manufacture composite scaffolds by combination
with calcium phosphate due to their bioactivity and 2. Mechanisms of bone regeneration
resorbability; however, these materials are not easily by BMs
amenable to fabrication and suffer from issues such as The bone regeneration principle of BMs involves three main
difficult removal of residual reagents in the polymer matrix steps: osteogenic differentiation, antimicrobial activity,
and poor compatibility as a result of the utilization of toxic and vascularization. The bone regeneration mechanism
organic solvents. 15,17 Inorganic materials are categorized involving magnesium, iron, and zinc is demonstrated in
into metallic materials, bioceramics, poly(ether-ether- Figure 2.
ketone) (PEEK), polycaprolactone (PCL), etc., of which
metallic materials are most widely used. 18-20 Among 2.1. Osteogenic differentiation induced by BMs
metallic materials, nondegradable metals such as titanium Magnesium is an important component of bone, and
and cobalt–chromium alloys have established clinical its deficiency can lead to systemic osteoporosis and
applications, but leave implant residues in the patient’s inflammatory bone resorption. 28,29 Magnesium can
body after applications. Because the stiffness of metallic induce local neurons to produce calcitonin gene-related

Volume 10 Issue 3 (2024) 39 doi: 10.36922/ijb.2460