Abstract
Bone implant failures, which occur in up to 10% of cases annually, are often attributed to materialrelated issues such as stress shielding and inadequate integration with surrounding bone tissue. Onesignificant challenge is the mechanical mismatch between traditional implant materials, such as
stainless steel and titanium, and natural bone. These materials, which have much higher stiffness than
natural cortical bone, disrupt the load-bearing function of implants. This mechanical mismatch leads
to stress shielding, where the implant absorbs a disproportionate amount of load, reducing the load
on the surrounding bone, causing bone resorption, and ultimately weakening the bone structure,
which can result in implant failure. These challenges emphasize the need for materials that more
closely replicate the mechanical properties of natural bone to improve implant performance and longterm success.
Nacre-like composites, inspired by the hierarchical structure of natural bone, offer a promising
solution to these challenges. These composites are designed with a layered, anisotropic architecture,
which enhances fracture toughness and load-bearing capacity. Their unique structural and bioactive
properties facilitate better stress distribution and promote osseointegration, leading to improved
integration with bone tissue. By mimicking the functional and structural features of natural bone,
nacre-like composites provide a transformative approach to bone implant design, offering more
effective and sustainable solutions for bone injuries and diseases.
This study focuses on the development of nacre-like ceramic/polymer composites using various
starting materials, including particles, platelets, and wires. Bi-directional freeze-casting was employed
to fabricate scaffolds from hydroxyapatite (HA), HA-apatite wollastonite (AW), and AW particles,
which were then infiltrated with monomers and polymerized using in situ thermal polymerization.
Additionally, nacre-like brushite/polymer composites were created by self-assembling brushite
platelet films and bi-directional freeze-casting brushite platelet scaffolds, reinforced with chitosan and
polymethyl methacrylate (PMMA)-polyacrylic acid (PAA) as the polymer phases. Hydrothermally
synthesized HA wires were also incorporated into bi-directional freeze-cast scaffolds of HA-HAw and
pure HAw, followed by infiltration and polymerization using PMMA-PAA.
The results demonstrate that these nacre-like composites exhibit mechanical properties,
including flexural and compressive strength and fracture toughness, that are comparable to or exceed
those of natural cortical bone. The Young’s modulus of these composites closely aligns with that of
cortical bone, offering a significant advantage over metallic implants by mitigating the stress shielding
commonly associated with commercial implants. The layered, brick-and-mortar structure of the
composites, inspired by natural nacre, provides exceptional crack resistance and toughening behavior,
II
similar to that of natural cortical bone. Furthermore, acellular bioactivity and cytocompatibility tests
confirmed that the composites are bioactive and cytocompatible, with no evidence of toxic leaching.
In summary, these bioactive and cytocompatible nacre-like ceramic/polymer composites, with
their layered microstructure, excellent mechanical properties, and remarkable crack resistance, hold
significant potential as load-bearing bone implants. They address critical challenges in current
orthopaedic materials and provide a promising solution for the development of more effective and
durable bone implants.
| Date of Award | 13 May 2025 |
|---|---|
| Original language | English |
| Awarding Institution |
|
| Supervisor | Bo Su (Supervisor) & Sean A Davis (Supervisor) |
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