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International Journal of Bioprinting Immunomodulatory bone repair by MBG/PCL

and that this group was the most capable of mediating macrophage polarization and thus inducing the osteogenic
differentiation of rat bone marrow mesenchymal stem cells (BMSCs) to form an immune microenvironment conducive
to osteogenesis. This study is a step forward in the exploration of the performance of BG composite PCL scaffolds and
provides a new idea for the development of bone graft materials.

Keywords: 3D printing; Dendritic mesoporous structured bioactive glass; Macrophages; Bone marrow mesenchymal
stem cells; Immunoregulation; Osteogenic differentiation

1. Introduction material, resulting in composites with excellent bone
and vascular regeneration properties. 13,14 For example,
Currently, bone defects due to factors such as trauma Zhao et al. used mesoporous BGs composite fiber protein
or surgery are becoming more and more common. hydrogel for maxillofacial bone defects. The results
15
According to statistics, millions of patients with bone showed the enhancement effect of mesoporous BGs on
defects worldwide require autologous bone grafting
every year, but the inadequate sources and donor sites of the mechanical strength, bioactivity, and osteogenesis
of the material. As mentioned above, BGs improve the
autologous bone limit its application. The development hydrophilic properties of PCL and enhance its osteogenic
1-3
of bone tissue engineering has promoted the emergence activity, while PCL as an engineered scaffold matrix can
of engineered scaffolds on the market. Good mechanical
properties, biocompatibility, and osteogenic activity are provide a stable support medium for bone defect repair.
the basic requirements for engineered scaffolds used in However, the dense pores and low specific surface area of
bone graft substitution. Polycaprolactone (PCL) is one of ordinary BGs and mesoporous BGs limit the mechanical
4
the commonly used materials for bone tissue engineering properties and bioactivity of the overall scaffold. Therefore,
because of its high biocompatibility. However, PCL is the current composite scaffolds show a continuous
hydrophobic and lacks osteogenic potential, and is often increase in compressive strength and osteogenic activity
used as a matrix component of composite scaffolds in bone with increasing glass content. For instance, Wang et al.’s
tissue engineering. 5,6 study on the osteogenic properties of BGs/PCL scaffolds
showed that scaffolds with the highest BGs percentage
Since the invention of bioglass 45S5 by Prof. Larry (20%) possessed the highest mechanical strength and
Hench in the 1970s, the field of medical materials has osteogenic activity. But this seems to be detrimental to
16
opened up to the study of coordinated osteointegration the degradation and resorption of BGs in vivo.
of bioglasses. Bioglass 45S5 accelerates bone formation
7
by releasing Na and rapidly exchanging it with H More importantly, bone regeneration and repair
+
+
17
and HO to form a silica layer on the silica-based are closely related to the immune microenvironment.
+
3
surface, and then by recruiting ions such as Ca and “Osteoimmunology,” first proposed by Joseph R. Arron
2+
P to form a hydroxycarbonate apatite layer (HCA). and Yongwon Choi, focuses on revealing the interplay
5+
7-9
18
Nevertheless, high-temperature sintered bioglass is between bone cell remodeling and immune cells.
prone to agglomeration and has low specific surface area, Studies have shown that the immune microenvironment
which affects its biological activity. In addition, the Na influences bone regeneration, with macrophages (MPs)
+
19
and Ca ions released from the degradation of bioglass playing a central role in osteogenesis. However, MPs
2+
may cause cytotoxicity due to the change of local pH exhibit plasticity and can polarize toward either M1
and delay the formation of HCA. These drawbacks or M2 phenotypes. The pro-inflammatory phenotype
10
limit the application of bioglass 45S5. Fortunately, due M1 induces tissue inflammatory responses, while the
20
to the use of templating agents (CTAC, P123, F127), M2 phenotype is involved in tissue repair. As a result,
bioactive glasses (BGs) with mesoporous structures the ability of biomaterials to immunomodulate MPs
have emerged in the research landscape. Mesoporous polarization from M1 to M2 is one of the keys to bone
17
BGs have better histocompatibility, their ordered regeneration. It has been demonstrated that BGs can
mesoporous structure increases their bioactivity, and modulate the host immune response to the implant
ions such as Si , Ca , and P released during in vivo and promote MPs polarization to the M2 phenotype,
2+
2+
5+
degradation contribute to the formation of the bone creating an immune microenvironment favorable for
matrix such as hydroxyapatite. 11,12 Studies have shown stem cell differentiation. 21-23 This may be because the
that the incorporation of mesoporous BGs can enhance ionic products such as Si and Ca degraded by BGs
2+
2+
the mechanical properties and bioactivity of the matrix modified the original ionic microenvironment. 24,25
Volume 10 Issue 5 (2024) 321 doi: 10.36922/ijb.3551