Being a bioactive material, hydroxyapatite (HAp) is regarded
as
one of the most attractive ceramic biomaterials for bone and hard-tissue
replacement and regeneration. Despite its substantial biocompatibility,
osteoconductivity, and compositional similarity to that of bone, the
employment of HAp is still limited in orthopedic applications due
to its poor mechanical (low fracture toughness and bending strength)
and antibacterial properties. These significant challenges lead to
the notion of developing novel HAp-based composites via different
fabrication routes. HAp, when efficaciously combined with functionally
graded materials and antibacterial agents, like Ag, ZnO, Co, etc.,
form composites that render remarkable crack resistance and toughening,
as well as enhance its bactericidal efficacy. The addition of different
materials and a fabrication method, like 3D printing, greatly influence
the porosity of the structure and, in turn, control cell adhesion,
thereby enabling biological fixation of the material. This article
encompasses an elaborate discussion on different multifunctional HAp
composites developed for orthopedic applications with particular emphasis
on the incorporation of functionally graded materials and antibacterial
agents. The influence of 3D printing on the fabrication of HAp-based
scaffolds, and the different in vitro and in vivo studies conducted
on these, have all been included here. Furthermore, the present review
not only provides insights and broad understanding by elucidating
recent advancements toward 4D printing but also directs the reader
to future research directions in design and application of HAp-based
composite coatings and scaffolds.
Improving the wear resistance of ultra‐high molecular weight polyethylene (UHMWPE), the gold standard polymer for acetabular component in hip joint arthroplasty, is the most important challenge in joint arthroplasty. The possible ways that have been approached to this challenge are by: (i) engineering multi‐phase that is, both carbonaceous and noncarbonaceous fillers‐based polyethylene composites, which unite the inherent attributes of each element available in the system. The wear rate of carbonaceous composite is nearly 50% lower (5.11–6.69 × 10−5 mm3/Nm) than that of noncarbonaceous composite (10–12.5 × 10−5 mm3/Nm), thus, recognized as a potential reinforcement, and (ii) coupling gamma‐irradiation, which is a mandated sterilization process, with multi‐phase nanocomposite to understand the free radical‐scavenging effect of fillers and improved interfacial adhesion strength between fillers and matrix. After the exposure of gamma‐rays (50–100 kGy), the free radicals formed by bond breakage in both the reinforcements and the matrix recombine to form covalent/Van der Waals bond in the interface. Thus, dramatical improvement in wear resistance of both types of composites with 2–4 times decreased wear rate is observed compared to that of composites under un‐irradiated condition. However, enhancing the interfacial adhesion between two different phases is a major constraint in the design of UHMWPE composites. Many methods such as functionalization of reinforcements, and irradiation on functionalized UHMWPE composites that can be approached to address this constraint are documented in this review.
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