Tabrizian Parinaz, Sun Huijun, Jargalsaikhan Urangua, Sui Tan, Davis Sean, Su Bo
Biomaterials Engineering Group, Bristol Dental School, University of Bristol, Bristol BS1 2LY, UK.
School of Mechanical Engineering Sciences, University of Surrey, Guildford GU2 7XH, UK.
J Funct Biomater. 2023 Jul 25;14(8):393. doi: 10.3390/jfb14080393.
One of the most ambitious goals for bone implants is to improve bioactivity, incapability, and mechanical properties; to reduce the need for further surgery; and increase efficiency. Hydroxyapatite (HA), the main inorganic component of bones and teeth, has high biocompatibility but is weak and brittle material. Cortical bone is composed of 70% calcium phosphate (CaP) and 30% collagen and forms a complex hierarchical structure with anisotropic and lamellar microstructure (osteons) which makes bone a light, strong, tough, and durable material that can support large loads. However, imitation of concentric lamellar structure of osteons is difficult to achieve in fabrication. Nacre from mollusk shells with layered structures has now become the archetype of the natural "model" for bio-inspired materials. Incorporating a nacre-like layered structure into bone implants can enhance their mechanical strength, toughness, and durability, reducing the risk of implant catastrophic failure or fracture. The layered structure of nacre-like HA/polymer composites possess high strength, toughness, and tunable stiffness which matches that of bone. The nacre-like HA/polymer composites should also possess excellent biocompatibility and bioactivity which facilitate the bonding of the implant with the surrounding bone, leading to improved implant stability and long-term success. To achieve this, a bi-directional freeze-casting technique was used to produce elongated lamellar HA were further densified and infiltrated with polymer to produce nacre-like HA/polymer composites with high strength and fracture toughness. Mechanical characterization shows that increasing the ceramic fractions in the composite increases the density of the mineral bridges, resulting in higher flexural and compressive strength. The nacre-like HA/(methyl methacrylate (MMA) + 5 wt.% acrylic acid (AA)) composites with a ceramic fraction of 80 vol.% showed a flexural strength of 158 ± 7.02 MPa and a Young's modulus of 24 ± 4.34 GPa, compared with 130 ± 5.82 MPa and 19.75 ± 2.38 GPa, in the composite of HA/PMMA, due to the higher strength of the polymer and the interface of the composite. The fracture toughness in the composition of 5 wt.% PAA to PMMA improves from 3.023 ± 0.98 MPa·m to 5.27 ± 1.033 MPa·m by increasing the ceramic fraction from 70 vol.% to 80 vol.%, respectively.
骨植入物最宏伟的目标之一是提高生物活性、无能性和机械性能；减少进一步手术的必要性；并提高效率。羟基磷灰石（HA）是骨骼和牙齿的主要无机成分，具有高生物相容性，但却是一种脆弱易碎的材料。皮质骨由70%的磷酸钙（CaP）和30%的胶原蛋白组成，并形成具有各向异性和层状微观结构（骨单位）的复杂层次结构，这使得骨骼成为一种轻质、坚固、坚韧且耐用的材料，能够承受较大负荷。然而，在制造过程中很难实现对骨单位同心层状结构的模仿。具有层状结构的软体动物贝壳珍珠层现已成为生物启发材料天然“模型”的原型。将类似珍珠层的层状结构融入骨植入物中可以提高其机械强度、韧性和耐久性，降低植入物灾难性失败或骨折的风险。类似珍珠层的HA/聚合物复合材料的层状结构具有高强度、韧性和可调刚度，与骨骼相匹配。类似珍珠层的HA/聚合物复合材料还应具有优异的生物相容性和生物活性，这有助于植入物与周围骨骼的结合，从而提高植入物的稳定性和长期成功率。为实现这一目标，采用双向冷冻铸造技术制备出细长的层状HA，进一步致密化并注入聚合物，以制备具有高强度和断裂韧性的类似珍珠层的HA/聚合物复合材料。力学表征表明，增加复合材料中的陶瓷含量会增加矿物桥的密度，从而导致更高的弯曲强度和抗压强度。陶瓷含量为80体积%的类似珍珠层的HA/（甲基丙烯酸甲酯（MMA）+5重量%丙烯酸（AA））复合材料的弯曲强度为158±7.02MPa，杨氏模量为24±4.34GPa，相比之下，HA/聚甲基丙烯酸甲酯复合材料的弯曲强度为130±5.82MPa，杨氏模量为19.75±2.38GPa，这是由于聚合物和复合材料界面的强度更高。通过将陶瓷含量从70体积%分别增加到80体积%，5重量%聚丙烯酸（PAA）与聚甲基丙烯酸甲酯（PMMA）组合物中的断裂韧性从3.023±0.98MPa·m提高到5.27±1.033MPa·m。
