The influence of hydroxyapatite particles on in vitro degradation behavior of poly epsilon-caprolactone-based composite scaffolds.

The design of composite scaffolds with slow degradation kinetics imposes the assessment of the time-course of degradation to predict the long-term in vitro behavior. In this work, the effect of hydroxyapatite (HA) particles on the hydrolytic degradation of poly epsilon-caprolactone composite scaffold was investigated. The study of accelerated degradation mechanisms in alkaline medium enabled analysing comparable degradation profiles at different times. The accurate qualitative and quantitative study of morphology by scanning electron microscopy supported by image analysis demonstrated only a negligible effect on the structural porosity, to be ascribed to the addition of micrometric HA as a filler. Moreover, by comparing the Raman spectra with thermal analysis(thermogravimetry and differential scanning calorimetry) the role of HA on the composite degradation mechanism was defined, by separately quantifying the contribution of HA particles in the bulk and on the surface, on the bone formation as a function of modifications induced in the pore morphology, as well as physical and chemical properties of the polymer matrix. Indeed, HA particles alter the poly epsilon-caprolactone crystallinity inducing a "shielding" effect of the polymer matrix. Meanwhile, the slight reduction of pore size as a function of the increasing HA content and the improvement of the effective hydrophilicity of the scaffolds also influence the degradation by faster mechanisms. Finally, it has been proven that the presence of HA enhances the scaffold bioactivity and human osteoblast cell response, remarking the active role of bioactive signals on the promotion of the surface mineralization and, as a consequence, on the cell-material interaction.

Polylactic acid fibre-reinforced polycaprolactone scaffolds for bone tissue engineering.

The employment of composite scaffolds with a well-organized architecture and multi-scale porosity certainly represents a valuable approach for achieving a tissue engineered construct to reproduce the middle and long-term behaviour of hierarchically complex tissues such as spongy bone. In this paper, fibre-reinforced composites scaffold for bone tissue engineering applications is described. These are composed of poly-L-lactide acid (PLLA) fibres embedded in a porous poly(epsilon-caprolactone) matrix, and were obtained by synergistic use of phase inversion/particulate leaching technique and filament winding technology. Porosity degree as high as 79.7% was achieved, the bimodal pore size distribution showing peaks at ca 10 and 200 microm diameter, respectively, accounting for 53.7% and 46.3% of the total porosity. In vitro degradation was carried out in PBS and SBF without significant degradation of the scaffold after 35 days, while in NaOH solution, a linear increase of weight lost was observed with preferential degradation of PLLA component. Subsequently, marrow stromal cells (MSC) and human osteoblasts (HOB) reached a plateau at 3 weeks, while at 5 weeks the number of cells was almost the same. Human marrow stromal cell and trabecular osteoblasts rapidly proliferate on the scaffold up to 3 weeks, promoting an oriented migration of bone cells along the fibre arrangement. Moreover, the role of seeded HOB and MSC on composite degradation mechanism was assessed by demonstrating a more relevant contribution to PLLA degradation of MSC when compared to HOB. The novel PCL/PLLA composite scaffolds thus showed promise whenever tuneable porosity, controlled degradability and guided cell-material interaction are simultaneously requested.

Polymorphism in crystalline cinchomeronic acid.

The structural relationship between the two crystal forms of cinchomeronic acid (CA 3,4-dicarboxypyridine) has been investigated by single crystal X-ray diffraction, IR and Raman spectroscopy and solid state NMR spectroscopy, showing that the two polymorphs form a monotropic system, with the orthorhombic form I being the thermodynamically stable form, while the monoclinic form II is unstable. In both forms CA crystallizes as a zwitterion and decomposes before melting. The crystal structure and spectroscopic analysis indicate that the difference in stability can be ascribed to the strength of the hydrogen-bonding patterns established by the protonated N-atom and the carboxylic/carboxylate O-atoms.

Oxidation in ultrahigh molecular weight polyethylene and cross-linked polyethylene acetabular cups tested against roughened femoral heads in a hip joint simulator.

This study was aimed at comparing the oxidative degradation of commercial acetabular cups made of cross-linked polyethylene (XLPE) and conventional ultrahigh molecular weight polyethylene (UHMWPE). After testing against deliberately scratched CoCrMo femoral heads in a hip joint simulator, the cups, microtomed parallel to the articulating surface, were analyzed by IR spectroscopy. Due to the potential for artifacts caused by absorbed contaminants, the IR spectra were compared only after hexane extraction; actually, XLPE was found to absorb more serum than UHMWPE. The two sets of unworn acetabular cups showed different oxidation patterns with consequently different distributions of carbonyl species; unworn XLPE was characterized by lower contents of carbonyl species and hydrogen-bonded alcohols and higher contents of trans-vinylene species than unworn UHMWPE. Upon simulator testing, UHMWPE showed more significant changes in oxidation indexes and distribution of carbonyl compounds than XLPE, confirming a better wear behavior for XLPE under the adopted testing conditions.

Wear behaviour of cross-linked polyethylene assessed in vitro under severe conditions.

The polyethylene (PE) for hip implants presents serious clinical problems; the production of debris may induce adverse tissue reactions that may lead to extensive bone loss around the implant and consequently osteolysis and implant loosening. Several attempts have been made to improve the wear properties of ultra-high molecular weight polyethylene (UHMWPE). More recently the attention of various researchers has been focused on cross-linked polyethylene (XLPE), due to its improved wear resistance with respect to conventional UHMWPE. This study was aimed at comparing the wear performances of clinically available acetabular liners (Zimmer Inc.) made of electron beam XLPE and conventional UHMWPE. To evaluate the influence of the material properties on wear, conventional UHMWPE and XLPE acetabular cups were tested against deliberately scratched CoCrMo femoral heads (Ra = 0.12-0.14 microm) in a hip joint wear simulator run for 3 million cycles with bovine calf serum as lubricant. Gravimetric measurements revealed significant differences between the wear behaviours of the two sets of acetabular cups: XLPE exhibited a wear rate about 40 times lower than conventional UHMWPE. Raman spectroscopy coupled to partial least-squares analysis was used to evaluate the possible crystallinity changes induced by mechanical stress (and thus the material wear resistance): only the UHMWPE cup which showed the highest weight loss displayed significant crystallinity changes. These results were correlated to the thickness of the plasticity-induced damage layer. The wear debris produced during the tests were isolated according to a validated protocol and imaged by scanning electron microscopy . The wear particles produced by XLPE were smaller than those produced by UHMWPE; the latter were observed as fibrillar and agglomerated particles. The mean equivalent circle diameter was 0.71 and 0.26 microm for UHMWPE and XLPE, respectively.

Spectroscopic study on the enzymatic degradation of a biodegradable composite periodontal membrane.

The enzymatic in vitro degradation of a commercial biodegradable hydroxyapatite (HA)-polymer (poly(epsilon-caprolactone)-poly(oxyethylene)(POE)-poly(epsilon-caprolactone) block copolymer) composite membrane was investigated by Raman and IR spectroscopies in two enzymatic solutions at 37 degrees C: esterase and alpha-chymotrypsin in saline phosphate buffer (SPB, pH 7.4). The degradation was found to be faster in the enzymatic medium than in SPB and alkaline solutions. The fastest degradation rate was observed in esterase solution. The trend of properly chosen Raman and IR intensity ratios was evaluated to go deeper inside the degradation mechanism: both polymeric and apatitic components were found to be involved in degradation. The former underwent preferential degradation of POE blocks, while HA is removed by the degradation medium faster than the polymer. Vibrational spectroscopy proved a valid tool for investigating the degradation of the membrane.

Vibrational spectra of diethylsulfoxide.

FT IR and Raman spectroscopic studies of pure diethylsulfoxide (DESO) in the liquid and in the solid states and its solutions in various solvents have been performed. Analysis of SO- and CH-stretching regions in a wide range of concentration shows that the bands may be fitted satisfactorily by considering seven components. In addition, fundamental frequencies have been assigned using ab initio calculations at the RHF/3-21G* levels. The results obtained confirm a viewpoint on a self-associative structure of DESO, and support the hypothesis of the existence of different types of intermolecular associates including both dipole-dipole and hydrogen bonding mechanisms.