Inorganic bone and demineralized bone matrix impregnated bone cement: a preliminary in vivo study

Composite Cement Materials Based on β-Tricalcium Phosphate, Calcium Sulfate, and a Mixture of Polyvinyl Alcohol and Polyvinylpyrrolidone Intended for Osteanagenesis

The primary purpose of the study, presented in this article, was to obtain a composite cement material intended for osteanagenesis. The β-tricalcium phosphate powder (β-TCP, β-Ca₃(PO₄)₂) was obtained by the liquid-phase method. Setting and hardening of the cement system were achieved by adding calcium sulfate hemihydrate (CSH, CaSO₄·1/2H₂O). An aqueous solution of polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and a PVA/PVP mixture were used as a polymer component. The methods of capillary viscometry and Fourier-transform infrared spectroscopy (FTIR) revealed the formation of intermolecular hydrogen bonds between polymer components, which determines the good miscibility of polymers. The physicochemical properties of the synthesized materials were characterized by X-ray diffraction (XRD) and FTIR methods, and the added amount of polymers does not significantly influence the processes of phase formation and crystallization of the system. The size of crystallites CSD remained in the range of 32-36 nm, regardless of the ratio of polymer components. The influence of the composition of composites on their solubility was investigated. In view of the lower solubility of pure β-TCP, as compared to calcium sulfate dihydrate (CSD, CaSO₄·2H₂O), the solubility of composite materials is determined to a greater degree by the CSD solubility. Complexometric titration showed that the interaction between PVA and PVP impeded the diffusion of calcium ions, and at a ratio of PVA to PVP of 1/1, the smallest exit of calcium ions from the system is observed. The cytotoxicity analysis results allowed us to establish the fact that the viability of human macrophages in the presence of the samples varied from 80% to 125% as compared to the control.

Mechanical performance and in vivo tests of an acrylic bone cement filled with bioactive sepia officinalis cuttlebone

To promote osteointegration, bioactive cuttlebone particles containing collagen were used to fill an acrylic cement, varying filler concentration (0-50 wt%). Cuttlebone was characterized by X-ray diffraction, plasma atomic emission and FT-IR. Mechanical properties of the filled cement were determined following ASTM procedures, included stress-strain, compression, bending, and fracture toughness tests. For in vivo tests, three groups of seven adult healthy rabbits were prepared to make an implant in the parietal bone of each one. For such groups (I-III), the amount of filler in the cement was 0, 10 and 30 wt%, respectively. Mechanical results for the composites complied with norm requirements. However, as mechanical performance for composite with 50 wt% of filler decreased significantly, for the in vivo tests, such composite was excluded. In vivo tests showed that three implants of group I were loosely attached to the parietal bone, whereas all the implants made with cement containing cuttlebone particles (groups II and III) were firmly attached to the parietal bone, indicating osteointegration. These results clearly show the potential of this type of bioactive filler to be used for medical applications.

The in vitro bioactivity of two novel hydrophilic, partially degradable bone cements

Composite bone cements were prepared with bioactive glasses (MgO-SiO(2)-3CaO.P(2)O(5)) of different reactivities. The matrix of these so-called hydrophilic, partially degradable and bioactive cements was composed of a starch/cellulose acetate blend and poly(2-hydroxyethyl methacrylate). The addition of 30 wt.% of glasses to this system made them bioactive in acellular medium: a dense apatite layer formed on the surface after 7 days of immersion in simulated body fluid. This was demonstrated both by microscopic and infrared spectroscopic techniques. The composition of the glass and, consequently, its structure was found to have important effects on the rate of the apatite formation. The combination of reactivity obtained by one formulation with the hydrophilic and degradable character of these cements makes them a very promising alternative to conventional acrylic bone cements, by allowing a better stabilization of the implant and a stronger adhesion to the bone.

Incorporation of α-Amylase Enzyme and a Bioactive Filler into Hydrophilic, Partially Degradable, and Bioactive Cements (HDBCs) as a New Approach To Tailor Simultaneously Their Degradation and Bioactive Behavior

Hydrophilic, partially degradable, and bioactive cements (HDBCs) are starch-containing cements intended to degrade partially in the human body and, in so doing, allow for bone ingrowth inside the pores formed during degradation. Therefore, the study of degradation and bioactivity behavior was performed to assess the suitability of the current HDBCs formulations to achieve those aims. The degradation profile of HDBCs was studied under different conditions, including incubation in phosphate-buffered saline (PBS) and PBS supplemented with alpha-amylase at different concentrations. Thermostable alpha-amylase was also added to some formulations to allow control of the degradation rate and its extent. In a second stage the simultaneous phenomena of enzymatic degradation and bioactivity (both in vitro) was studied. We observed that the degradation of starch present in HDBCs can be easily controlled by the amount of alpha-amylase added to the cement and high values of degradation may be achieved if high enough quantities of enzyme are incorporated. However, the maximum degradation extent is much more dependent on the total amount of starch present in the formulation than on the amount of enzyme added to it: for full pore connectivity, the amount of starch should be higher than the percolation threshold for a 3D specimen. Nonetheless, calcium phosphate was able to nucleate and spread in inner pores of the cement, formed due to degradation, if they were interconnected. For a more thorough covering of the pores with calcium phosphates the amount of starch present in HDBCs should be increased to be higher than the percolation threshold.

Static mechanical properties of hydroxyapatite (HA) powder-filled acrylic bone cements: Effect of type of HA powder

This work reports on the effect of the amount (0, 10, and 30 wt %) and type of HA powder incorporated into an acrylic bone cement on the tensile properties, compression properties, and fracture toughness. The three different types of HA powders used were synthesized in the laboratory and coated with a silane agent prior to incorporation into the cement powder, and differed in particle size, water content, surface area, and crystallinity. It was found that the inclusion of any type of HA powder led to an increase in the tensile modulus (ET), but all the other mechanical properties of the cement decreased (relative to the values of the unfilled cement). The increase in ET is attributed to the good adhesion between the filler and the cement matrix, which is due to the silane coating agent. The decrease in the other mechanical properties may be a consequence of HA powder agglomeration and porosity. Hydroxyapatite morphology and crack-growth mechanisms were analyzed by scanning electronic microscopy (SEM).

Bioactive bone cements

Poly(methylmethacrylate) (PMMA) bone cement, used to fix implants into the bone, produces good surgical results if used correctly. However, prostheses do eventually become loose and the breakdown of the cement mantle is a factor in this failure. Limitations of PMMA cement, which lead to problems with the fixation of the implant, include its mechanical characteristics and its influence upon surrounding bone, associated with the polymerization reaction. A bioactive bone cement is particularly designed to produce a better interface between the cement and bone. However, an improvement in mechanical properties, especially fatigue, creep and fracture toughness, are an added necessary requirement to increase the lifetime of a cemented implant. The development of a bioactive cement has been conducted mainly in two ways; firstly, to improve existing PMMA cement by the addition of various bioactive agents and secondly, to design an alternative matrix for the bioactive material to be combined with. The most promising investigations which have been conducted, along with their relative benefits and drawbacks, are discussed.

Cranial bone apposition and ingrowth in a porous nickel-titanium implant

A 5 x 5 x 1-mm uncoated porous nickel-titanium (nitinol) implant was placed 4 mm to either side of the midsection of the frontal bone and 4 mm anterior to the coronal suture of the cranial bone of New Zealand White rabbits. In the other frontal location, a 5 x 5 x 1-mm coralline hydroxyapatite (HA) (Interpore 200, a well-known craniofacial implant material) implant was fitted. Rabbits were killed at each of three postsurgical intervals (2, 6, and 12 weeks), and the implants were evaluated for gross biocompatibility, bony contact, and ingrowth. No adjacent macrophage cells were observed for either implant type, and overlaying soft tissues and connective tissues readily adhered to the implants even after 2 weeks. Both materials made bone contact with the surrounding cranial hard tissue, and percent ingrowth increased with surgical recovery time. Measurements of microhardness and bone histologic parameters indicated that bone in contact with and grown into the implants was similar in properties to the surrounding cranial bone. Porous nitinol implants therefore appear to allow for significant cranial bone ingrowth after as few as 12 weeks, and thus nitinol appears to be suitable for craniofacial applications. Compared to HA, the nitinol implants demonstrated a trend for less total apposition and more total ingrowth after 6 and 12 weeks of implantation.