Bone cement, PMMA-based

PMMA bone cement polymethylmethacrylate based cement for the fixation of endoprostheses... 

The other acrylate bone cement is based on poly-ethylmethacrylate (PEMA) and n-butylmethacrylate ( -BMA) monomer [61], Comparing to PMMA cement, less heat is produced during polymerization of the PEMA-n-BMA cement, and the polymer has a relatively low modulus and high ductility to reduce the issue of fracture. The biocompatibility of the PEMA-n-BMA cement has been excellent [62]. But these bone cements have been found to be susceptible to creep. To improve creep resistance, bioactive HA particles were incorporated [63]. Although HA improved bioactivity and creep behavior of the cement, the cement failed at lower number of cycles. 

Mori, A., Ohtsuki, C., Sugino, A., Kuramoto, K., Miyazaki, T., Tanihara, M. and Osaka, A. (2003)Bioactive PMMA-based bone cement modified with methacryloxypropyltrimethoxysilane and calcium salts — Effects of calcium salts on apatite-forming ability. Journal of the Ceramic Society of Japan, 111, 738-742. 

IL6 An article related to acrylic bone cements [Abboud, M. et al PMMA-based composite materials with reactive ceramic fillers IV. Radiopacifying particles embedded in PMMA beads for acrylic bone cements, J. Biomed. Mater. Res., 53(6), 728 (2000)] provides the following information on the PMMA matrix used in these cements M, = 295,000 My,/Mn = 2.2. Calculate the number average degree of polymerization for the PMMA used in this study. 

Figure 15.23. Affinity index of bone cement based on PMMA vs. concentration of glass powder. [Adapted, by permission, from Tamura J, Kawanabe K, Yamamuro T, Nakamura T, Kokubo T, Yoshihara S, Shibuya T, J. Biomed. Mat. Res., 29, No.5, 1995, 551-9.]...

Cement is a binder that sets and hardens by itself or binds other materials together. The most widely known application of cements is in construction a second one is the area of bone cements. Cements used in construction are characterized as hydraulic or nonhydraulic and mostly for the production of mortars and concrete. Hydraulic cements set and harden after combining with water. Most construction cements are hydraulic and based on Portland cement, which consists of calcium silicates (at least 2/3 by weight). Nonhydraulic cements include the use of nonhydraulic materials such as lime and gypsum plasters. Bone cements and bone cement composites refer to compounds that have a polymer matrix with a dispersed phase of particles. For instance, polymethylmethacrylate (PMMA) is reinforced with barium sulphate crystals (for radio-opacity) or with hydroxyapatite... 

A. Sugino, C. Ohtsuki, T. Miyazaki, In vivo response of bioactive PMMA-based bone cement modified with alkoxysilane and calcium acetate, J. Biomater. Appl. 23 (3) (2008) 213-228. 

Kim and coworkers [118] proposed bioactlve bone cement (BBC), composed of natural bone powder (HAp), chitosan (CS) and commercially available PMMA-based bone cement. Investigators obtained three types of BBCs with different composition ratios BBC I, BBC n and BBC HI with 10 wt% of CS and 40, 50 and 60 wt% of HAp, respectively. Observation of the interfacial area between the host bone and the bone cement indicated that the BBC II composite has numerous pores that could be expected to afford space for bone ingrowth. However, after 4 weeks, the gaps between the host bone and the BBC II became narrower, and PMMA exhibited undesirable cleavage at the interfacial area simultaneously, histological examinations of the interfaces at 4 weeks post-implantation demonstrated more new bone formations in the BBC H implant than in pure PMMA. In addition, the exothermic effects in the BBCs were considerably lower than that of pure PMMA. 

Mousa, W. E, M. Kobayashi, S. Shinzato et al. 2000. Biological and mechanical properties of PMMA-based bioactive bone cements. Biomaterials. 21 2137-46. 

Nowadays, commercially available acrylic bone cements are sold in a kit of two components, a solid phase (polymer powder with initiator) and a liquid ampoule containing the methyl methacrylate (MMA) and a tertiaryamine. This is based on the fact that polymerization of PMMA can also be initiated by oxidation-reduction reactions. An advantage of a redox initiator is that the radical production starts at lower temperatures in comparison to the traditional initiators, where a high temperature is necessary to generate the radical initiator. Generally, the most used combination includes benzoyl peroxide and NdV-dimethylaniline. The proposed initiation mechanism is shown in Figure 12.9. 

M. Kawashita, K. Kawamura and Z. Li, PMMA-based bone cements containing magnetite particles for the hyperthermia of cancer. Actabiomaterialia 6 3187-3192,2010. 

Bone cements are, traditionally, injectable systems based on acrylic polymers. They are constituted by a solid and a liquid component that harden after mixing due to the polymerization of acrylic monomers in the liquid. Just some minutes after mixing, the paste attains high viscosity and must then be injected into the bone cavity, where the final stages of polymerization will take place. The solid is in most cases constituted by poly(methyl methacrylate) (PMMA) powder (or a copolymer of MMA with others monomers), benzoyl peroxide (BPO, the initiator of the polymerization), and a radio-opacifier, while the liquid is formed by MMA monomer (in some cases with n-butyl methacrylate, BuMA) and dimethyl-j -toluidine (DMT, the activator of the initiator). 

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