Cement that can be used in the human body - bone cement

Bone cement is a commonly used name for bone cement and is a medical material used in orthopedics. Due to its appearance and physical properties resembling white cement used in construction and decoration after solidification, it has such a popular name. In the 1970s, bone cement was already used for joint prosthesis fixation, and it can also be used as a tissue filling and repair material in orthopedics and dentistry.

The biggest advantage of bone cement is its fast solidification, allowing for early postoperative rehabilitation activities. Of course, bone cement also has some drawbacks, such as occasional high pressure in the bone marrow cavity during filling, which can cause fat droplets to enter blood vessels and cause embolism. Moreover, it is different from human bones, and over time, artificial joints may still become loose. Therefore, the research on bone cement biomaterials has always been a hot topic of concern for researchers.

At present, the most widely used and researched bone cements are polymethyl methacrylate (PMMA) bone cement, calcium phosphate bone cement, and calcium sulfate bone cement.
PMMA bone cement is an acrylic polymer formed by mixing liquid methyl methacrylate monomer and dynamic methyl methacrylate styrene copolymer, with low monomer residue, low fatigue resistance and stress cracking resistance, as well as high tensile strength and plasticity. PMMA bone cement has been widely used in the field of medical plastic surgery, and has been applied in dentistry, skull, and other bone repair fields as early as the 1940s. Acrylate bone cement has been used in human tissue surgery and has been applied in hundreds of thousands of clinical cases both domestically and internationally.

The solid phase of PMMA bone cement is generally partially polymerized prepolymer PMMA, and the liquid phase is MMA monomer, with some polymerization initiators and stabilizers added. When the solid-phase prepolymer PMMA is mixed with the liquid-phase MMA monomer, a polymer copolymerization reaction occurs immediately to achieve the solidification of bone cement. However, during this solidification process, a large amount of heat is released, which can cause thermal damage to surrounding tissues, leading to inflammation and even tissue necrosis. Therefore, more research is urgently needed to improve the quality of polymethyl methacrylate bone cement and reduce or eliminate the side effects of PMMA bone cement.

Calcium phosphate is applied in bone repair due to its excellent biocompatibility and bone regeneration ability. Clinically, it is often used as an injectable material to fill bone gaps and improve hardware fixation in fracture surgery. The composition of calcium phosphate bone cement is similar to the minerals of human bones, which can be reabsorbed and promote the inward growth and remodeling of natural bones. The solidification mechanism of calcium phosphate bone cement is a dissolution hydration precipitation reaction. By controlling the pH value of the reaction process, hydroxyapatite (HA) can precipitate within the pH range of 4.2-11. In the initial stage, the generation of HA is mainly controlled by surface reactions, and the HA generated between particles and on the surface of particles strengthens the connections between particles. The higher the content of HA crystals, the more contact points there are, and the compressive strength also increases accordingly. In the later stage of hydration reaction, the particle surface is coated with a layer of HA, and the hydration reaction of calcium phosphate bone cement becomes diffusion controlled through the hydration reaction. With the continuous hydration reaction, more and more HA particles are generated, and the generated HA crystals are growing. Hydration products gradually fill the space of water participating in the reaction, so that the space previously occupied by water is divided into irregular capillary pores by the HA crystals.

The gel pores are increased, and the pore size is constantly reduced. The HA crystals are staggered and bridged, and the bonding strength between particles is increasing. The bone cement material is solidified into a solid porous structure with a large number of pores, thus showing a macro curing strength.

In clinical practice, traumatic vertebral burst fractures have a special injury mechanism and usually occur in young people who have stronger bone reconstruction ability. Calcium phosphate bone cement can be effectively used to treat such fractures. Meanwhile, calcium phosphate bone cement is also an effective bone substitute for benign bone tumor resection surgery. However, due to the long solidification time and relatively low heat release during the solidification process, calcium phosphate bone cement has relatively poor adhesion and strength, and is prone to disintegration from the bone. Therefore, research on calcium phosphate bone cement is still ongoing.

Calcium sulfate is the simplest alternative material for bone repair and has been used in bone repair materials for over 100 years, with the longest clinical application history. Calcium sulfate has good human tolerance, biodegradability, and bone conduction properties, making it an important alternative material for autologous bone transplantation in early research. The solid phase mainstream of calcium sulfate bone cement is anhydrous calcium sulfate powder, and the liquid phase is physiological saline and other aqueous solutions. When the solid and liquid phases are mixed, calcium sulfate undergoes a hydration reaction, generating needle shaped calcium sulfate dihydrate whiskers that bridge and stack with each other, thus solidifying into a pile with a certain shape and strength. However, due to poor biological activity, calcium sulfate bone cement cannot form chemical bonds between calcium sulfate grafts and bone tissue, and will degrade rapidly. Calcium sulfate bone cement can be completely absorbed within six weeks after implantation, and this rapid degradation does not match the process of bone formation. Therefore, compared to calcium phosphate bone cement, the development and clinical application of calcium sulfate bone cement are relatively limited.

In addition, many studies have shown that small organic molecules, biodegradable polymers, proteins, polysaccharides, inorganic molecules, bioceramics, and bioglass can effectively improve the performance of bone cement, providing innovative ideas for new types of bone cement.
In summary, bone cement can play a significant role in clinical dentistry and orthopedics, and is expected to become an ideal drug carrier and bone substitute material for the skeletal system.

With the continuous innovation and development of science, technology, and materials, it is believed that more high-quality bone cement materials will be developed in the future, such as high-strength, injectable, water resistant, and rapid setting types. The application of bone cement in clinical practice will become increasingly widespread, and its value will also increase.