Improvement of absorbability, osteoconductivity, and strength of a ß-tricalcium phosphate spacer for opening wedge high tibial osteotomy: clinical evaluations with 106 patients.

BACKGROUND: An ideal synthetic spacer for medial opening wedge high tibial osteotomy (MOWHTO) has not yet been developed. The authors have developed a new ß-tricalcium phosphate (ß-TCP) spacer with 60% porosity (N-CP60) by modifying the micro- and macro-pore structures of a conventional ß-TCP spacer (CP60) that is widely used in clinical practice. The purpose of this study was to compare the absorbability, osteoconductivity, and in vivo strength of the N-CP60 spacer with those of the CP60 spacer, when used in MOWHTO. METHODS: First, the porosity, diameter distribution of macro- and micropores, and compressive strength of each ß-TCP block were examined using methodology of biomaterial science. Secondly, a clinical study was performed using a total of 106 patients (106 knees) with MOWHTO, who were followed up for 18 months after surgery. In these knees, the N-CP60 and CP-60 spacers were implanted into 49 tibias and 57 tibias, respectively. The absorbability and osteoconductivity were radiologically evaluated by measuring the area of the implanted spacer remaining unabsorbed and assessing with the Hemert's score, respectively. The incidence of cracking in the implanted spacers was determined using computed radiography. Statistical comparisons were made with non-parametric tests. The significance level was set at p = 0.05. RESULTS: The N-CP60 and CP60 blocks had almost the same porosity (mean, 61.0% and 58.7%, respectively). The diameter of macropores was significantly larger (p < 0.0001) in the N-CP60 block than in the CP60 block, while the diameter of micropores was significantly smaller (p = 0.019) in the N-CP60 block. The ultimate strength of the N-CP60 block (median, 36.8 MPa) was significantly greater (p < 0.01) than that of the CP60 block (31.6 MPa). As for the clinical evaluations, the absorption rate of the N-CP60 spacer at 18 months after implantation (mean, 48.0%) was significantly greater (p < 0.001) than that of the CP60 spacer (29.0%). The osteoconductivity of the N-CP60 spacer was slightly but significantly higher (p = 0.0408) than that of the CP60 spacer only in zone 1. The incidence of in vivo cracking of the posteriorly located N-CP60 spacer at one month (mean, 75.5%) was significantly lower (p = 0.0035) than that of the CP60 spacer (91.2%). CONCLUSIONS: The absorbability, osteoconductivity, and compressive strength of the new N-CP60 spacer were significantly improved by modifying the macro- and micro-pore structures, compared with the conventional CP60 spacer. The N-CP60 spacer is more clinically useful than the CP60 spacer. TRIAL REGISTRATION NUMBER: H29-0002.

Development of a novel calcium phosphate cement composed mainly of calcium sodium phosphate with high osteoconductivity.

Two novel calcium phosphate cements (CPC) have been developed using calcium sodium phosphate (CSP) as the main ingredient. The first of these cements, labeled CAC, contained CSP, α-tricalcium phosphate (TCP), and anhydrous citric acid, whereas the second, labeled CABC, contained CSP, α-TCP, ß-TCP, and anhydrous citric acid. Biopex(®)-R (PENTAX, Tokyo, Japan), which is a commercially available CPC (Com-CPC), and OSferion(®) (Olympus Terumo Biomaterials Corp., Tokyo, Japan), which is a commercially available porous ß-TCP, were used as reference controls for analysis. In vitro analysis showed that CABC set in 5.7 ± 0.3 min at 22 °C and had a compressive strength of 86.0 ± 9.7 MPa after 5 days. Furthermore, this material had a compressive strength of 26.7 ± 3.7 MPa after 2 h in physiologic saline. CAC showed a statistically significantly lower compressive strength in the presence of physiologic saline and statistically significantly longer setting times than those of CABC. CABC and CAC exhibited apatite-forming abilities in simulated body fluid that were faster than that of Com-CPC. Samples of the materials were implanted into the femoral condyles of rabbits for in vivo analysis, and subsequent histological examinations revealed that CABC exhibited superior osteoconductivity and equivalent bioresorbability compared with Com-CPC, as well as superior osteoconductivity and bioresorbability compared with CAC. CABC could therefore be used as an alternative bone substitute material.

Spontaneous Formation of a Hydrogel Composed of Water-Soluble Phospholipid Polymers Grafted with Enantiomeric Oligo(lactic acid) Chains.

We designed and synthesized water-soluble biocompatible and biodegradable polymers composed of 2-methacryroyloxyethyl phosphorylcholine and oligo(L- or D-lactic acid) macromonomers to develop an injectable hydrogel matrix. Aqueous solutions containing the polymers with oligo(L-lactic acid) (OLLA) and oligo(D-lactic acid) (ODLA) chains underwent spontaneous gelation when mixed together. This was due to the formation of a stereocomplex between the OLLA and ODLA side-chains, which act as cross-linking components in the hydrogel. Therefore, the hydrogel could be re-dissolved in a buffer solution by hydrolysis of the oligo(lactic acid) chains. We obtained an injectable, biocompatible and degradable hydrogel, and we anticipate that it will be used in applications involving the controlled release of bioactive molecules and cell-based tissue engineering.

Simple synthesis of a library of zwitterionic surfactants via Michael-type addition of methacrylate and alkane thiol compounds.

A library of zwitterionic phosphorylcholine surfactants with various alkyl chain lengths and compositions was readily prepared from a combination of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) and various alkanethiol compounds via Michael-type addition. The critical micelle concentration (CMC) was evaluated by surface tensiometry. At the CMC, the surface tension of these aqueous solutions decreased significantly to below 40 mN/m. For the zwitterionic surfactants composed of MPC, and fluoroalkane and alkanedithiol, the surface tension was approximately 24, and 50 mN/m, respectively. From the equation log (CMC) = A - Bn, where n is the number of carbon atoms in the alkyl chain, A and B were calculated as 1.09 and 0.44, respectively. The value of the slope B was between that of ionic (B = 0.30) and nonionic surfactants (B = 0.50). Despite the ionic nature of the surfactants, their behavior was closer to that of nonionic surfactants.