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Materials Science in Additive Manufacturing Hydrogels in mandibular reconstruction

Inspired by the composition of natural bone hydroxyapatite Bioactive functional nanomaterials have been integrated
(HAp) and collagen matrices, Yang et al. fabricated an into injectable hydrogel scaffolds to enhance mechanical
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nHAp-reinforced degradable bone adhesive (O-BDSG) performance while adding multifunctionality. Zhou et al.
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through in situ free radical ring-opening polymerization. developed a gelatin/oxidized chondroitin sulfate hydrogel
nHAp acted as a non-covalent crosslinker between polymer loaded with mesoporous bioactive glass nanoparticles
chains and increased the molecular weight of the polymer (MBGNs), which act as bioactive additives to enhance
matrix, significantly enhancing mechanical performance functionality. MBGNs accelerated hydrogel crosslinking
and bone adhesion for rapid fracture fixation. The adhesive and improved mechanical properties, especially in storage
exhibited a bending adhesion strength of 9.79 MPa on modulus and compressive strength, while retaining its
bone – 4.7 times higher than nHAp-free formulations injectable capability. Zhao et al. designed a self-expanding
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and far surpassing commercial cyanoacrylate adhesives dual-crosslinked gelatin-hyaluronic acid hydrogel (GH)
(0.64 MPa). Yang et al. also developed an injectable dual- with niobium-doped bioactive glass (NbBG), where
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crosslinked hydrogel (A-O hydrogel) based on dynamic NbBG dispersion enhanced mechanical performance
Schiff base covalent networks and multi-hydrogen bonding. while transforming the hydrogel’s inherent expansion
The system utilized amino-rich polyhydroxy polymers and limitation into an advantage for bone augmentation.
oxidized methylcellulose as core components. The former Bai et al. created a self-reinforced injectable hydrogel
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enhanced gel cohesion through a tertiary hydrogen-bond combining non-covalent crosslinking and DA chemical
network, while hydroxyl-rich sites facilitated interfacial dual-crosslinking, achieving 25 MPa mechanical strength
bonding, achieving exceptional underwater adhesion with while effectively promoting bone repair.
a peek adhesion strength of 2.32 MPa. The natural origin To maintain facial esthetics and carrying important
of oxidized methylcellulose ensured biocompatibility and physiological functions such as chewing and swallowing,
biosafety. Functioning as a porous interfacial layer, the jaw bone’s irregular shape, adjacent neurovascular bundles,
hydrogel not only promoted cell proliferation and migration and dynamic load environment are considered reference
but also created pathways for nutrient transport and the factors for the reconstruction of mandibular regenerated
infiltration of osteogenesis-related cells. In rat skull in situ materials. Hydrogel can accurately fill complex defect areas
bone fixation and onlay bone grafting models, this hydrogel through minimally invasive injection, avoiding the damage
outperformed commercial bioadhesives, ensuring graft
survival and integration while maintaining stable retention. to surrounding tissues caused by traditional open surgery,
and its environmental responsiveness (such as temperature
This offers a robust and effective strategy for clinical bone sensitivity, pH, or ion-triggered gelation) enables it to adapt
adhesion applications.
to the defect shape after injection, achieving personalized
3.1.3. Injectability shaping and reducing the risk of microleakage. In addition,
hydrogels can support stem cells, growth factors and
Mandibular defects often involve complex and narrow antibacterial components, promote bone-soft-tissue
anatomical regions, making it difficult to fabricate grafts cooperative regeneration, and match jaw mechanical
that precisely adapt to small, irregular-shaped defects. gradient through mechanical property regulation, taking
Injectable hydrogels address this challenge by enabling into account functional reconstruction and esthetic repair.
minimally invasive delivery and conforming to intricate
anatomical geometries through flexible shape adaptation, 3.2. Considerations in biological properties
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ensuring optimal defect filling. Ideal injectable scaffolds
should possess appropriate porosity and pore sizes to serve 3.2.1. Antibacterial property
as effective carriers for osteogenic growth factors, coupled The oral cavity is one of the most complex microbial
with tunable release kinetics to maximize osteoblast ecosystems in the human body, hosting over 700
adhesion, proliferation, and differentiation. Post-injection, microbial species that form a dynamically balanced
hydrogels must tightly integrate with surrounding tissues microenvironment. During mandibular defect repair,
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while maintaining sufficient mechanical strength to the surgical site is exposed to a protein-rich, moist
withstand frequent oral movements such as mastication environment, and food residues provide organic
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and swallowing. Recent advances in mechanically substrates, creating ideal conditions for microbial
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reinforced injectable hydrogels have focused on enhancing proliferation. Notably, post-operative infection has
mechanical properties without compromising injectability, emerged as a critical clinical challenge hindering bone
primarily through DN hydrogels combining physical and defect repair, as persistent inflammatory responses
chemical crosslinking, or incorporation of nanoparticles/ not only impair osteoblast differentiation but also lead
nanofibers as reinforcing components. 45 to osseointegration failure. Current clinical strategies

Volume 4 Issue 2 (2025) 9 doi: 10.36922/MSAM025070006