Artificial bone refers to bone-like material created in a laboratory that can be used in bone grafts, to replace human bone that was lost due to severe fractures, disease, etc.[1]
Bone fracture, which is a complete or partial break in the bone, is a very common condition that has more than three million US cases per year.[2] Human bones have the ability to regenerate themselves by cycle of bone resorption and bone formation. The cell responsible for bone resorption is osteoclast, while the cell responsible for bone formation is osteoblast. That being said, the human body can regenerate fractured bone. However, if damage to bone is caused by a disease or severe injury, it becomes difficult for the body to repair itself. When the human body is unable to regenerate the lost bone tissue, surgeons come in and replace the missing bone using autografts, allografts, and synthetic grafts (artificial bone). When comparing artificial bone to autograft and allograft, it is less invasive and more biocompatible since it avoids the risk of unknown viral infections.[3]
When designing implanted biomaterials, key criteria are biocompatibility, osteoconductivity, high porosity and biomechanics compatibility. Artificial bone was initially made of materials like metals and solid ceramics, which are strong enough to sustain the loading in bone. However, the rigidity of those materials created an enormous burden on patients and was not consistent with the criteria for implanting biomaterials. Artificial bones made of metal and ceramic tend to do poorly in terms of biocompatibility since it is difficult to blend into bone tissues.[4] Thus, to better help those in need to live a more comfortable life, engineers have been developing new techniques to produce and design better artificial bone structure and material.
The two major components of bone are hydroxyapatite [Ca10(PO4)6(OH)2], and collagen fibers. Hydroxyapatite, which is one of the most stable forms of calcium phosphate, makes up about 60 to 65 percent of the bone.[5] The rest of the bone is composed of materials including chondroitin sulfate, keratan sulfate and lipid.[5] Increased research and knowledge regarding the organization, structure of properties of collagen and hydroxyapatite have led to many developments in collagen-based scaffolds in bone tissue engineering. The structure of hydroxyapatite is very similar to that of the original bone, and collagen can act as molecular cables and further improve the biocompatibility of the implant.[6]