Study of biomineralization of poly(vinyl alcohol)-based scaffolds using an alternate soaking approach

Silicification of Amine-Epoxide Cationic Microgels: An In Vitro Investigation

Herein, the applicability of an unconventional, non-vinylic type of amine-epoxide microgels (MGs) to promote silica deposition from tetraethyl orthosilicate (TEOS) was investigated. Simply mixing MGs with TEOS in water at 25 °C resulted in the formation of hybrid silica-MG particles (sMGs) as a function of silicification time. The sMGs were cationic with thermal-sensitive swelling capability. Extending silicification time to 24 h was shown to increase silica content to 43%. Besides, the sMGs became structurally more rigid to resist drying-induced deformation and exhibited a rugged surface texture. Mechanistically, the aminated nature of the MGs was proved beneficial for the success of their silicification, fulfilling dual functions of the catalyst for TEOS hydrolysis and template for silica deposition. Through electrostatic adsorption, the sMGs provided a facile yet robust option for surface modifications toward bone-related applications. Surface-induced mineralization in simulated biological fluids was observed with sMG-immobilized surfaces, where the presence of hydroxyapatite was characterized in the deposited apatite. In vitro MC3T3-E1 pre-osteoblast cell studies showed that cell adhesion, morphology, and proliferation could be influenced by both sMG types and their adsorption density. Of particular interest is the finding of cells exhibiting elongated and greatly polarized morphology on the surface with high adsorption density of sMGs of 43% silica. It was postulated that the rugged appearance of such sMGs could have presented a hierarchically structured surface toward cells, an interesting aspect to be further exploited for the engineering of cell-surface interactions.

Sandwich-Like Nanofibrous Scaffolds for Bone Tissue Regeneration

Advanced bone healing approaches included a wide range of biomaterials that mainly mimic the composition, structure, and properties of bone extracellular matrix with osteogenic activity. The present study aimed to develop a sandwich-like structure of electrospun nanofibers (NFs) based on polycaprolactone (PCL) and chitosan/polyethylene oxide (CS/PEO) composite to stimulate bone fracture healing. The morphology of the fabricated scaffolds was examined using scanning electron microscopy (SEM). Apatite deposition was evaluated using simulated body fluid (SBF). The physicochemical and mechanical properties of samples were analyzed by Fourier transform infrared, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and universal testing machine. SEM images exhibited a porous three-dimensional structure with NF diameters of 514-4745 nm and 68-786 nm for PCL NFs layer and the sandwich-like NFs scaffolds, respectively. Deposition of apatite crystal on scaffolds started at week 2 followed by heavy deposition at week 8. This was confirmed by measuring the consumption of calcium and phosphorous ions from SBF. Thermal stability of scaffolds was confirmed using DSC and TGA. Moreover, the PCL NF layer in the middle of the developed sandwich structure reinforced the scaffolds with bear load up to 12.224 ± 1.12 MPa and Young's modulus of 17.53 ± 3.24 MPa. The scaffolds' porous structure enhanced both cell propagation and proliferation. Besides, the presence of CS in the outer NF layers of the scaffolds increased the hydrophilicity, as evidenced by the reduction of contact angle from 116.6 to 57.6°, which is essential for cell attachment. Cell viability study on mesenchymal stem cells proved the cytocompatibility of the fabricated scaffolds. Finally, in vivo mandibular bone defect rabbit model was used to confirm the regeneration of a new healthy bone within 28 days. In conclusion, the developed scaffolds could be a promising solution to stimulate bone regeneration.

New developments in polymer-controlled, bioinspired calcium phosphate mineralization from aqueous solution

The polymer-controlled and bioinspired precipitation of inorganic minerals from aqueous solution at near-ambient or physiological conditions avoiding high temperatures or organic solvents is a key research area in materials science. Polymer-controlled mineralization has been studied as a model for biomineralization and for the synthesis of (bioinspired and biocompatible) hybrid materials for a virtually unlimited number of applications. Calcium phosphate mineralization is of particular interest for bone and dental repair. Numerous studies have therefore addressed the mineralization of calcium phosphate using a wide variety of low- and high-molecular-weight additives. In spite of the growing interest and increasing number of experimental and theoretical data, the mechanisms of polymer-controlled calcium phosphate mineralization are not entirely clear to date, although the field has made significant progress in the last years. A set of elegant experiments and calculations has shed light on some details of mineral formation, but it is currently not possible to preprogram a mineralization reaction to yield a desired product for a specific application. The current article therefore summarizes and discusses the influence of (macro)molecular entities such as polymers, peptides, proteins and gels on biomimetic calcium phosphate mineralization from aqueous solution. It focuses on strategies to tune the kinetics, morphologies, final dimensions and crystal phases of calcium phosphate, as well as on mechanistic considerations.

Magnetically mediated release of ciprofloxacin from polyvinyl alcohol based superparamagnetic nanocomposites

Polymer nanocomposites exhibiting superparamagnetic behavior have been recognized as a promising tool to achieve targeted drug delivery using external magnetic field for treating complex diseases like cancers and tumors. The present investigation attempts to design a superparamagnetic nanocomposite which could desirably deliver ciprofloxacin drug by application of varying magnetic field. In order to achieve the proposed objectives, a polymer matrix of polyvinyl alcohol-g-polymethyl methacrylate was prepared by free radical polymerization and iron oxide particles were impregnated by in situ precipitation method. The prepared nanocomposites were characterized by techniques like FTIR, electron microscopy (SEM and TEM) and XRD and magnetization studies were performed to ensure superparamagnetic behavior. The antibiotic drug ciprofloxacin was loaded onto the magnetic nanocomposites and the influence of various factors such as percent loading, chemical composition of the nanocomposite, applied magnetic field, pH of the release medium were investigated on the release profiles of the drug. The chemical integrity of the drug and its antibacterial potential were also studied. The dynamics of the release process was also examined mechanistically.

A study on mineralization behavior of amino-terminated hyperbranched polybenzimidazole membranes

Amino-bearing polymers, coated with apatite or similar minerals, have attracted significant attention for their potential in medical applications. In this study, an amino-terminated hyperbranched polybenzimidazole (HBPBI) membrane was used as a substrate for apatite growth. The membrane was soaked in solutions of CaCl2, Na2HPO4 and SBF to yield an apatite coating. The structure and morphology of the layers were characterized by FTIR-ATR, XRD and FESEM. The results indicate that the high densities of amino, imide and imidazole groups on the amino-terminated HBPBI membrane provide active sites for the growth of apatite.

Growth of hydroxyapatite coatings on biodegradable polymer microspheres

Mineral-coated microspheres were prepared via a bioinspired, heterogeneous nucleation process at physiological temperature. Poly(d,l-lactide-co-glycolide) (PLG) microspheres were fabricated via a water-in-oil-in-water emulsion method and were mineral-coated via incubation in a modified simulated body fluid (mSBF). X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy with associated energy-dispersive X-ray spectroscopy confirmed the presence of a continuous mineral coating on the microspheres. The mineral grown on the PLG microsphere surface has characteristics analogous to those of bone mineral (termed "bonelike" mineral), with a carbonate-containing hydroxyapatite phase and a porous structure of platelike crystals at the nanometer scale. The assembly of mineral-coated microspheres into aggregates was observed when microsphere concentrations above 0.50 mg/mL were incubated in mSBF for 7 days, and the size of the aggregates was dependent on the microsphere concentration in solution. In vitro mineral dissolution studies performed in Tris-buffered saline confirmed that the mineral formed was resorbable. A surfactant additive (Tween 20) was incorporated into mSBF to gain insight into the mineral growth process, and Tween 20 not only prevented aggregation but also significantly inhibited mineral formation and influenced the characteristics of the mineral formed on the surface of PLG microspheres. Taken together, these findings indicate that mineral-coated PLG microspheres or mineral-coated microsphere aggregates can be synthesized in a controllable manner using a bioinspired process. These materials may be useful in a range of applications, including controlled drug delivery and biomolecule purification.