Mechanical properties bone cements

Cements based on phytic add set more quickly than their glass polyalkenoate or dental silicate cement cormterparts, but have similar mechanical properties (Table 8.2). They are unique among add-base cements in being impervious to acid attack at pH = 2-7. Unfortunately, they share with the dental silicate cement the disadvantage of not adhering to dentine. They do bond to enamel but this is by micromechanical attachment - the cement etches enamel - and not by molecular bonding. Lack of adhesive property is a grave weakness in a modern dental or bone... 

In a recent article [Shinzato, S., et al., A new bioactive bone cement Effect of glass bead filler content on mechanical and biological properties, J. Biomed. 

Carbon fibers, which are relatively inert under physiological conditions, are selected particularly to enhance the mechanical properties of various biomedical materials, such as their incorporation in bone cement [127]. Metal implants for total hip joint replacements do not match the mechanical properties of human bone, and epoxy-graphite implants may have better properties [128]. 

S. P. Saha, Mechanical properties of machine-mixed carbon fiber reinforced bone cement, ASME. Appl. Mechanics Div. 21. 57-60, 1985. 

The last method to be discussed, which is used to form polymer/ceramic composites by electrospinning, is extremely different to the methods previously described, but worth mentioning. Zuo et al. [129] used a method to create a composite scaffold that is actually the reverse of what most people are doing. Instead of mineralizing the nanofibers, Zuo et al. actually incorporated electrospun polymer nanofibers into a ceramic bone cement in order to form a composite scaffold. It was found that by incorporating electrospun nanofibers into the cement, the scaffold became less brittle and actually behaved similarly to that of a ductile material because of the fibers. Composite scaffolds with different polymers and fiber diameters were then tested in order to determine which scaffold demonstrated the most ideal mechanical properties. However, no cell studies were conducted and this method would most likely be used for a bone substitute instead of for bone regeneration applications. 

Our approach has been to synthesize the dleplsulflde resin corresponding to the normal blsphenol A type dlepoxlde resins. A polyamide type curing agent (Versamlde 140) was used because of our particular Interest In orthopedic adhesives, l.e. "bone cement". Some of the properties were therefore tailored to be optimum near body temperature. We have found very little prior literature on dleplsulflde resins. As prepared, the dleplsulflde resin analog of DGEBA Is a crystalline solid which must be heated above Its melting temperature for reaction. Charlesworth (2) has reported mechanical relaxation behavior of epoxy-episulfide poly-... 

Phosphorylated chitosan (P-C) was prepared and used as an additive for calcium phosphate cement (CPC) to improve its mechanical properties and particularly its compressive strength. The CPC/P-C system was proposed for use as a bone filler. 

Peter, S. J., Kim, P., Yasko, A. W., Yaszemski, M. J. Mikos, A. G. (1999) Crosslinking characteristics of an injectable poly(propylene fumarate)/beta-tricalcium phosphate paste and mechanical properties of the crosslinked composite for use as a biodegradable bone cement. Journal of Biomedical Materials Research, 44, 314-321. 

Hydroxyapatite calcium phosphate cement with composition of Caio(P04)6(OH)2 exhibits excellent mechanical properties and biocompatibihty major mineral constituent of the bone also finds use as a filler to replace amputated bone and/or as a coating to promote bone ingrowth into prosthetic implants. 

Caleium phosphate cements (CPCs) have been investigated extensively as injectable bone replacement biomaterials due to their similar chemical composition to the mineral component of bone. A Umitation of CPCs is their brittle mechanical properties and slow degradation in vivo Therefore, enhancing the mechanical properties, injectability, and rate of cellular infiltration and remodeling of CPCs while preserving their favorable biocompatibility is an important and active area of research. While ceramic biomaterials are discussed in greater detail in Chapter 2, the biocompatibihty of conventional CPCs, as well as the implications of recent advancements on the biocompatibility of these biomaterials, will be reviewed in this chapter. 

Calcium carbonate nanoparticles are also added to PMMA bone cement to increase its mechanical properties. A study by Hill et al. evaluated the efficacy of adding... 

HiU J, Orr J, Dunne N. In vitro study investigating the mechanical properties of acrylic bone cement containing calcium carbonate nanoparticles. J Mater Sci Mater Med 2008 19 3327-33. 

Ormsby R, McNally T, Mitchell C, Dunne N. Influence of multiwall carbon nanotube functionality and loading on mechanical properties of PMMA/MWCNT bone cements. J Mater Sci Mater Med 2010 21 2287-92. 

PMMA/hydroxyapatite bone cement. Both nanostructures were found to capture the radicals produced during the cement polymerization process, thereby hampering their normal course and affecting the mechanical properties of the nanocomposites, especially the one-dimensional nanoform [145]. Recently, we have compared both 1D and 2D carbon nanostructures and the effect of functionalization on the thermomechanical properties. As seen in Figure 10.13, the nanofillers containing carboxylic groups provided the best mechanical response at 1 wt% loading. Additionally, the 2D carbon structures provided better reinforcement in the electrospun fibers when compared to the ID carbon nanomaterials [116,158]. 

Furthermore, PMMA-Ca0-Si02 nanohybrid materials were shown to be suitable for bone cement and dental composite resin applications, due to their good bioactivity and improved mechanical properties [363]. PDMS-zirconia nanohybrids were proposed as suitable materials for tissue-implant integration purposes because they have beneficial effects on the proliferation and viability of human primary osteoblast and fibroblast cells and thus can be used as promising coatings for orthopedic trauma implants [364]. 

Besides having an inert material for fibroblastic cells observed at the bone-cement interface, PMMA is still the current standard for cement-held prostheses. Vallo and his group measured the flexural, compressive, and fracture properties of PMMA bone cements that incorporated various amounts of HAp. They found that addition of up to 15 wt% HAp increases the flexural modulus and fracture toughness [89]. It was also observed that, with increasing HAp incorporation into PMMA, the biological responses of the bone cement increased and thus increased osteoblast adhesion and response [88]. Kwon and coworkers reported that a PMMA/HAp composite with 30 wt% of HAp increased the interfacial shear strength at the bone-implant interface 6 weeks after implantation in rabbits [101]. Several other research studies revealed that, depending on the type of bone cement, the addition of HAp can improve the mechanical properties of bone cements [102]. 

---