Calcium phosphate interactions with titanium oxide and alumina substrates: an XPS study

Besides the excellent mechanical properties of titanium and alumina (Al2O3) in the case of load bearing applications, their bone-bonding properties are very different. In osseous environment, Al2O3 ceramic is encapsulated by fibrous tissues, whereas bone can bind directly to titanium, via its natural titanium dioxide (TiO2) passivation layer. So far, this calcification dissimilarity between TiO2 and Al2O3 was attributed to respectively their negative and positive surface charge under physiological conditions. The present study aims at studying the chemical interactions between TiO2 and Al2O3 (phase α) with the diverse ions contained in simulated body fluids (SBFs) buffered with trishydroxymethyl aminomethane (TRIS) at pH=6.0 and pH=7.4. After 1 h of immersion, TiO2 and α-Al2O3 powders were analyzed by X-ray photoelectron spectroscopy (XPS). The results indicated that Ca and HPO4 groups were present on TiO2 surface. In addition, HPO4 groups were found to be in a higher amount than Ca on TiO2, which does not comply with the surface charge theory. With regard to Al2O3, little HPO4 but no Ca was detected on its surface, and TRIS bound to Al2O3 substrate in all of the immersion experiments. The fact that both Ca and HPO4 were present at the vicinity of TiO2 might be at the origin of its calcification ability. On the other hand, Al2O3 did not show any affinity towards Ca and HPO4 ions. This might explain the inability of Al2O3 substrate to calcify

Degradation of Biomaterials

The tissue engineering approach requires suitable biomaterials to serve as three-dimensional scaffolds to support cell growth and differentiation into functional tissues. Depending on the type of tissue in need of repair, a biomaterial must be designed with specific performance criteria in mind. Several excellent books and review articles (e.g., Ratner et al. (2013), Temenoff and Mikos (2008)) on biomaterials have appeared. Essential characteristics of biomaterial scaffolds for tissue engineering applications are described by Williams (2014). For instance, biomaterials used as load-bearing prostheses for hips and knees should retain their mechanical function for the lifetime of the patient. In large bone defects, where load-bearing is not critical (e.g., the skull), biomaterials—used alone or with cells as tissue engineering constructs—need not be so mechanically strong (Chapter 10). In this case, a degradable biomaterial scaffold would be ideal to allow newly formed bone tissue to gradually take the place of the implanted construct resulting in seamless bone repair and no residual material. In this way, the manner in which the biomaterial is degraded—broken down in the body—is a primary consideration. When a biomaterial is implanted in the body, it is immediately exposed to physiologic fluid and shortly after, cells whose main purpose is to clear it from the host (Chapter 15). Thus, the degradation of biomaterials involves multiple physiologic processes at the same time making it a science to its own. This chapter reviews the degradation mechanisms of the two most established classes of biomaterials—ceramics and polymers—and how these degradation properties can be beneficial in their primary application, bone tissue engineering

Effect on Rheological Properties and 3D Printability of Biphasic Calcium Phosphate Microporous Particles in Hydrocolloid-Based Hydrogels

The production of patient-specific bone substitutes with an exact fit through 3D printing is emerging as an alternative to autologous bone grafting. To the success of tissue regeneration, the material characteristics such as porosity, stiffness, and surface topography have a strong influence on the cell–material interaction and require significant attention. Printing a soft hydrocolloid-based hydrogel reinforced with irregularly-shaped microporous biphasic calcium phosphate (BCP) particles (150–500 µm) is an alternative strategy for the acquisition of a complex network with good mechanical properties that could fulfill the needs of cell proliferation and regeneration. Three well-known hydrocolloids (sodium alginate, xanthan gum, and gelatin) have been combined with BCP particles to generate stable, homogenous, and printable solid dispersions. Through rheological assessment, it was determined that the crosslinking time, printing process parameters (infill density percentage and infill pattern), as well as BCP particle size and concentration all influence the stiffness of the printed matrices. Additionally, the swelling behavior on fresh and dehydrated 3D-printed structures was investigated, where it was observed that the BCP particle characteristics influenced the constructs’ water absorption, particle diffusion out of the matrix and degradability

Physico-Chemical Characteristics and Posterolateral Fusion Performance of Biphasic Calcium Phosphate with Submicron Needle-Shaped Surface Topography Combined with a Novel Polymer Binder

A biphasic calcium phosphate with submicron needle-shaped surface topography combined with a novel polyethylene glycol/polylactic acid triblock copolymer binder (BCP-EP) was investigated in this study. This study aims to evaluate the composition, degradation mechanism and bioactivity of BCP-EP in vitro, and its in vivo performance as an autograft bone graft (ABG) extender in a rabbit Posterolateral Fusion (PLF) model. The characterization of BCP-EP and its in vitro degradation products showed that the binder hydrolyses rapidly into lactic acid, lactide oligomers and unaltered PEG (polyethylene glycol) without altering the BCP granules and their characteristic submicron needle-shaped surface topography. The bioactivity of BCP-EP after immersion in SBF revealed a progressive surface mineralization. In vivo, BCP-EP was assessed in a rabbit PLF model by radiography, manual palpation, histology and histomorphometry up to 12 weeks post-implantation. Twenty skeletally mature New Zealand (NZ) White Rabbits underwent single-level intertransverse process PLF surgery at L4/5 using (1) autologous bone graft (ABG) alone or (2) by mixing in a 1:1 ratio with BCP-EP (BCP-EP/ABG). After 3 days of implantation, histology showed the BCP granules were in direct contact with tissues and cells. After 12 weeks, material resorption and mature bone formation were observed, which resulted in solid fusion between the two transverse processes, following all assessment methods. BCP-EP/ABG showed comparable fusion rates with ABG at 12 weeks, and no graft migration or adverse reaction were noted at the implantation site nor in distant organs