Hydroxyapatite deposition by alternating soaking technique on poly(vinyl alcohol)-coated polyethylene films

A poly(vinyl alcohol) (PVA)-coating on polyethylene films, prepared by repetitive adsorption/drying in an aqueous PVAsolution, accelerated hydroxyapatite (HAp) deposition by an alternate soaking in aqueous solutions containing Ca²⁺ and PO^¾- ions. X-ray photoelectron spectra of the 4 surface of the HAp-deposited film showed the presence of calcium and phosphorus of a suitable peak ratio for HAp formation. X-ray diffraction analyses also revealed peaks corresponding to HAp. Scanning electron microscopic observation showed the surface of the HAp layer to be smooth, with nano-ordered dotted threads in networks. A simple PVA coating on a surface will serve as a novel system for accelerated HAp formation via alternating soaking.     

Polyamide 6 composite membranes: Properties and in vitro biocompatibility evaluation

The aim of the present study was to develop polyamide 6 membrane blended with gelatin and chondroitin sulfate using the phase precipitation method and evaluate its in vitro biocompatibility. Morphology of membranes was studied by laser scanning confocal microscopy which allowed the nondestructive visualization of internal bulk morphology of membranes. Membranes exhibited porous morphology with pores spanning across the membrane width with interconnections at various depths. Membranes showed adequate mechanical properties with tensile strengths of 20.10 ± 0.64 MPa, % strain of 3.01±0.07, and modulus of 1082.50±23.50 MPa. In vitro biocompatibility of membranes by direct contact test did not show degenerative effects on NIH3T3 cells and also its leach-out products (LOP), as determined by tetrazolium (MTT) and neutral red uptake (NRU) assay. Mouse peritoneal macrophage cultured in contact with membranes and PTFE control showed comparable expression of activation markers such as CD11b/CD18, CD45, CD14, and CD86 suggesting the membranes' non-activating nature. Membrane LOP did not induce excessive proliferation of mouse splenocytes suggesting its non-antigenic nature. Preliminary blood compatibility of membranes was observed with no detectable hemolysis in static incubation assay. Taken collectively, the present data demonstrate that polyamide 6 composite membranes are biocompatible and prospective candidates for tissue engineering applications.     

Collagen–PCL Sheath–Core Bicomponent Electrospun Scaffolds Increase Osteogenic Differentiation and Calcium Accretion of Human Adipose-Derived Stem Cells

Human adipose-derived stem cells (hASCs) are an abundant cell source capable of osteogenic differentiation, and have been investigated as an autologous stem cell source for bone tissue engineering applications. The objective of this study was to determine if the addition of a type-I collagen sheath to the surface of poly(ε-caprolactone) (PCL) nanofibers would enhance viability, proliferation and osteogenesis of hASCs. This is the first study to examine the differentiation behavior of hASCs on collagen–PCL sheath–core bicomponent nanofiber scaffolds developed using a co-axial electrospinning technique. The use of a sheath–core configuration ensured a uniform coating of collagen on the PCL nanofibers. PCL nanofiber scaffolds prepared using a conventional electrospinning technique served as controls. hASCs were seeded at a density of 20 000 cells/cm² on 1 cm² electrospun nanofiber (pure PCL or collagen–PCL sheath–core) sheets. Confocal microscopy and hASC proliferation data confirmed the presence of viable cells after 2 weeks in culture on all scaffolds. Greater cell spreading occurred on bicomponent collagen–PCL scaffolds at earlier time points. hASCs were osteogenically differentiated by addition of soluble osteogenic inductive factors. Calcium quantification indicated cell-mediated calcium accretion was approx. 5-times higher on bicomponent collagen–PCL sheath–core scaffolds compared to PCL controls, indicating collagen–PCL bicomponent scaffolds promoted greater hASC osteogenesis after two weeks of culture in osteogenic medium. This is the first study to examine the effects of collagen–PCL sheath–core composite nanofibers on hASC viability, proliferation and osteogenesis. The sheath–core composite fibers significantly increased calcium accretion of hASCs, indicating that collagen–PCL sheath–core bicomponent structures have potential for bone tissue engineering applications using hASCs.     

Development and Characterization of Biodegradable Nanocomposite Injectables for Orthopaedic Applications Based on Polyphosphazenes

Self-setting hydroxyapatite–biodegradable injectable composites are excellent candidates for applications in orthopaedics. We have previously demonstrated the feasibility of development of self-setting calcium-deficient nanocrystalline hydroxyapatite–polymer composites using different calcium phosphate precursors and biodegradable polyphosphazenes. This study aimed to evaluate these novel injectable composites as suitable materials for orthopaedic applications through evaluating their biomechanical properties, osteoblast cellular attachment and gene expression over time.Our studies demonstrated that the morphology of the composite groups (PNEA–CDHA, PNEA–CDSHA, PNEA₅₀mPh₅₀–CDHA, PNEA₅₀mPh₅₀–CDSHA, PNEA₅₀PhPh₅₀–CDHA, and PNEA₅₀PhPh₅₀–CDSHA) formed was similar and found to have micro- and nanoporous structures resembling trabecular bone. The osteoblast phenotypic marker of bone, alkaline phosphatase, was expressed by the cells on the surface of the composites throughout the study and was comparable to tissue-culture polystyrene (control). Furthermore, the cells seeded on the composites expressed the characteristic osteoblastic genes, such as type-I collagen, alkaline phosphatase, osteocalcin, osteopontin and bone sialoprotein, indicating osteoblast differentiation, maturation and mineralization. Within our injectable composite groups, significant gene expression levels were displayed (P < 0.05). These novel injectable biodegradable polyphosphazenes–calcium-deficient hydroxyapatites materials are promising candidates for orthopaedic applications.     

Degradation behavior of composite pins made of tricalcium phosphate and poly(L,DL-lactide)

Combining a bioactive ceramic with a resorbable polymer may improve the biocompatibility and the osseointegration of degradable fracture fixation devices. This study reports on the mechanical properties and degradation behavior of two composite pins made of poly(L,DL-lactide) and 10 and 30% β-tricalcium phosphate (TCP), respectively. The pins were compared to a pin made of 100% poly(L,DL-lactide). The failure force, bending strength, and molecular weight were determined during in vitro degradation at 37°C up to 78 weeks. The blending with 10 or 30% β-TCP decreased the initial mechanical properties and led to an accelerated degradation rate. The pins with 30% TCP lost half of their strength after 16 weeks, i.e. faster than the unmodified pin (40 weeks). The pins with 10% TCP, however, showed a decreased initial strength (128 ± 9 MPa) compared to the unmodified pin (152 ± 9 MPa) but very similar degradation characteristics. The drop of the molecular weight was not significantly different between the three types of pins. It was concluded that the mechanical requirements for a pin for the fixation of small bony fragments with improved biocompatibility were fulfilled by the composite pin with 10% TCP but not by the pin with 30% TCP.     

Relationship between Drug Release and Some Physical Parameters of Drug Sorption onto PLA Fibers

Drug release and its relationship with kinetic and thermodynamic parameters of drug sorption onto poly(lactic acid) (PLA) fibers have been studied using Diclofenac, 5-Fluorouracil (5-FU) and Metformin as model drugs. The sorption method is more flexible and avoids the damaged drugs, remaining toxic organic solvents and safety problems which occurred with the dissolution method. The quantitative relationship with high correlation between drug-release and drug-loading concentration, affinity and activation energy for diffusion has been established to predict the initial burst and subsequent release of the drugs. Drugs with higher activation energy for diffusion, lower diffusion coefficients and higher affinity on PLA fiber, such as Diclofenac, can achieve high loading capacity and constant drug release. It has also been found that elevated temperatures can achieve high loading capacity and constant release. In addition, the study showed that Diclofenac release profiles were similar for sorption and dissolution loading methods.     

Hydroxyapatite/polymer composite flame-sprayed coatings for orthopedic applications

The complex biological and mechanical requirements for implant materials in the human body generally cannot be furnished by one single material. In the present study, hydroxyapatite/polymer composite coatings with different contents of hydroxyapatite were produced using a flame spray system. This processing route is intended to obtain a coating with an optimal combination of biological and mechanical properties of these two materials for skeletal implants. The composite coatings were produced from a mechanical blend of hydroxyapatite and ethylene methacrylic acid copolymer powders, which were delivered from a fluidized bed powder feeder. Characterization of the coating surface morphology, polished coating cross-sections, and fracture surface morphology was conducted by scanning electron microscopy. The dissolution behavior of the coatings was evaluated with a calcium-specific ion meter. The stress-strain behavior was investigated by tensile testing. The biological and mechanical properties were found to be related to the volume and distribution of the hydroxyapatite in the polymer matrix. This technique provides a means of preparing hydroxyapatite/polymer coatings for application as implants.     

Intragastric Capsaicin Stimulates Motility of Upper Gut and Proximal Colon via Distinct Pathways in Conscious Dogs

The aim of the present study was to investigatethe effect and mechanism of action of intragastric andintraduodenal capsaicin on gastrointestinal motility.Five mongrel dogs were equipped with eight strain gauge force transducers on the stomach, smallintestine, and proximal colon. In the interdigestivestate, capsaicin was administered into the gastric orduodenal lumen. The effects of atropine, hexamethonium, ondansetron, and FK888 on capsaicin-inducedcontractions were studied. Intragastric capsaicininduced contractions within 15 min in the gastricantrum, duodenum, proximal jejunum, and proximal colon.These stimulatory effects were inhibited by atropineat all sites; by hexamethonium in the small intestineand colon; by ondansetron in the antrum, duodenum, andcolon; and by FK888 in the antrum and colon,respectively. Intraduodenal capsaicin had no effect oncontractility. Stimulation of afferent fibers bycapsaicin in the stomach but not in the duodenumaugments contractile activity in local and distantregions of the gut via distinct pathways.     

Poly(ε-caprolactone-co-D,L-lactide)/silk fibroin composite materials: Preparation and characterization

Poly(ε-caprolactone-co-D,L-lactide) copolymers with 10, 30, and 50% by weight of silk particles (size range: 5-250 μm) derived from Bombyx mori were blended in acetone solution. After evaporation of the solvent, the morphology, thermal behavior, and mechanical properties of the composites were examined. The composites were transparent and the silk fibroin particles were homogeneously distributed within the composite structure. The particles appeared as bright reflected images under the optical microscope, suggesting that they were in a crystalline state. DSC thermograms of the composites revealed that the glass transition of the matrix was at ca. -18°C. Degradation of the silk fibroin occurred beyond 270°C. The decomposition temperatures and degradation rate decreased with increasing silk fibroin content as revealed by TGA analysis. FTIR spectra of the composites showed absorption bands at 1730 and 1088 cm-1 for the copolymer and at 3273 and 1617 cm^-1 for the silk fibroin. Although the characteristic lines of poly(ε-caprolactone-coD,L-lactide) were independent of filler concentration, the absorption bands of the β-sheet form of the silk fibroin increased slightly due to the interaction of silk fibroin with the copolymer.     

Childhood Cortical Porosity Is Related to Microstructural Properties of the Bone‐Muscle Junction

Childhood cortical porosity is attributable to giant asymmetrical drifting osteonal canals that arise predominantly along the primary‐secondary bone interface (PSBI). Bone from the external iliac crest cortex of 92 subjects aged 0 to 25 years was examined histomorphometrically for differences in microstructural properties between primary and secondary bone that might account for features of drifting osteonal canals. Primary compared with secondary bone showed greater numbers of osteocyte lacunae, thinner collagen lamellae, and a scaffold of elastic perforating fibers (PFs). The greater number of osteocyte lacunae compounded by known perilacunar strain amplification and the presence of elastic PFs are expected to be associated with greater bone tissue strain in primary than in secondary bone and thus with strain gradients at the PSBI. Strain gradients may lead local osteocytes to originate resorption canals and to promote transverse drift of the resorption front into lower‐strain secondary bone, thus creating giant asymmetrical drifting osteonal canals that remodel primary to secondary bone. PFs extended from muscle fibers through periosteum and primary bone to the PSBI, where they were resorbed by origination of drifting canals. Growth modeling by periosteal osteoblasts proceeds in the gaps between PFs. Through the direct connection between muscle and the PSBI via PFs, muscle forces may influence not only modeling by raising strain but also remodeling of primary to secondary bone by increasing strain gradients at the PSBI. With reduction in primary bone width after the mid‐teens, numbers of drifting canals and porosity declined. Differences in microstructural properties between primary and secondary bone are expected to generate strain gradients at the PSBI that contribute to site, transverse drift, asymmetry and large size of drifting canals, and, hence, to cortical porosity. Cortical porosity in children is a physiological feature of bone growth in width. Advisability of therapeutic intervention remains to be defined. © 2014 American Society for Bone and Mineral Research.