Thermoplastic polyurethane/POSS nanohybrids: Synthesis, morphology, and biological properties

Recent studies show good osteoinductive properties of polyurethanes modified with polyhedral oligomeric silsesquioxanes (POSS). In this work, three types of POSS; propanediolisobutyl-POSS (PHI-POSS), disilanolisobutyl-POSS (DSI-POSS), and octahydroxybutyl-POSS (OCTA-POSS) were chemically incorporated into linear polyurethane based on an aliphatic isocyanate, hexamethylene diisocyanate (HDI), to obtain new nanohybrid PU-POSS materials. The full conversion of POSS was confirmed by Fourier transform infrared spectroscopy (FTIR-ATR) spectra of the model reactions with pure HDI. The materials obtained were investigated by FTIR, SEM-EDS, and DSC. The DSC studies showed the thermoplasticity of the obtained materials and apparently good recovery. 30-day immersion in SBF (simulated body fluid) revealed an increase in the rate of deposition of hydroxyapatite (HAp) for the highest POSS loadings, resulting in thick layers of hydroxyapatite (~60-40 μm), and the Ca/P ratio 1.67 (even 1.785). The structure and properties of the inorganic layer depend on the type of POSS, the number of hard segments, and those containing POSS, which can be tailored by changing the HDI/poly(tetramethylene glycol) (PTMG) ratio. Furthermore, the obtained composites revealed good biocompatibility, as confirmed by cytotoxicity tests conducted on two cell lines; normal human dermal fibroblasts (NHDF) and primary human osteoblasts (HOB). Adherent cells seeded on the tested materials showed viability even after a 48-h incubation. After this time, the population of viable, and proliferating cells exceeded 90%. Bioimaging studies have shown the fibroblast and osteoblast cells were well attached to the surface of the tested materials.

In vivo hydroxyapatite scaffold performance in infected bone defects

Critically sized bone defects are often compounded by infectious complications. The standard of care consists of bone autografts with systemic antibiotics. These injuries and treatments lead to donor site morbidity, antibiotic resistant strains of bacteria, and often end stage amputation. This study proposes an alternative to the autograft using a porous, hydroxyapatite (HA) scaffold evaluated with and without infection and antibiotics. Twenty-four New Zealand white rabbits received either our HA scaffold or a pulverized autograft (PBA) within a surgically created critical-sized defect in the femur. The two grafts were evaluated in either septic or aseptic defects and with or without antibiotic treatment. The HA scaffolds were characterized with micro computed tomography. Post-euthanasia, micro computed tomography, histology, and white blood cells component analysis were completed. The HA had significantly greater (p < .001) mineralization to total volume than the PBA groups with 27.56% and 14.88%, respectively, and the septic HA groups were significantly greater than the aseptic groups both with and without antibiotics (p = .016). The bone quality denoted by bone mineral density was also significantly greater (p < .001) in the HA groups (67.01 ± 0.38 mgHA/cm³ ) than the PBA groups (64.66 ± 0.85 mgHA/cm³ ). The HA scaffold is a viable alternative to the bone autograft in defects with and without infection as shown by the quality and quantity of bone.

Biomineralization of poly-l-lactide spongy bone scaffolds obtained by freeze-extraction method

Implants in the form of polymer scaffolds are commonly used to regenerate bone tissue after traumas or tooth extractions. However, few implant formation methods enable building polymer scaffolds allowing to reconstruct larger bone losses without immune response. Spacious, porous poly-l-lactide implants with considerable volume were obtained using the phase inversion method with the freeze-extraction variant. The calcium phosphate (CaP) coating was deposited on implant surfaces with the biomimetic method to improve the implant's osteoconductivity. The substitues morphology was characterized-porosity, size and shape of pores; mechanical properties, mass absorbability of implants before and after mineralization. The characteristics were provided with scanning electron microscopy (SEM), static compression test and hydrostatic weighing, respectively. The presence of CaPs in the entire volume of the implant was confirmed with SEM and infrared spectroscopy with Fourier transform (FTIR). The biocompatibility of scaffolds was confirmed with in vitro quantitative test and microscopic observations. The obtained results show that the implants can be used in tissue engineering as a vehicle of platelet-rich plasma to regenerate critical spongy bone losses.

Hydoxyapatite/beta-tricalcium phosphate biphasic ceramics as regenerative material for the repair of complex bone defects

Bone is a composite material composed of collagen and calcium phosphate (CaP) mineral. The collagen gives bone its flexibility while the inorganic material gives bone its resilience. The CaP in bone is similar in composition and structure to the mineral hydroxyapatite (HA) and is bioactive, osteoinductive and osteoconductive. Therefore synthetic versions of bone apatite (BA) have been developed to address the demand for autologous bone graft substitutes. Synthetic HA (s-HA) are stiff and strong, but brittle. These lack of physical attributes limit the use of synthetic apatites in situations where no physical loading of the apatite occurs. s-HA chemical properties differ from BA and thus change the physical and mechanical properties of the material. Consequently, s-HA is more chemically stable than BA and thus its resorption rate is slower than the rate of bone regeneration. One solution to this problem is to introduce a faster resorbing CaP, such as β-tricalcium phosphate (β-TCP), when synthesizing the material creating a biphasic (s-HA and β-TCP) formulation of calcium phosphate (BCP). The focus of this review is to introduce the major differences between BCP and biological apatites and how material scientists have overcome the inadequacies of the synthetic counterparts. Examples of BCP performance in vitro and in vivo following structural and chemical modifications are provided as well as novel ultrastructural data. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2493-2512, 2018.

Apatite formation on a hydrogel containing sulfinic acid group under physiological conditions

Natural bone consists of apatite and collagen fiber. Bioactive materials capable to bonding to bone tissue are clinically used as bone-repairing materials. Apatite-organic polymer composites exhibit bone-bonding abilities and mechanical properties similar to those of natural bone, and these materials can be prepared using biomimetic processes in simulated body fluid (SBF). Specific functional groups such as sulfonic and carboxylic acid groups are known to induce the heterogeneous nucleation of apatite in SBF. However, it remains unclear whether structurally related sulfinic acid groups can contribute to apatite formation in the same way, despite sodium sulfonate being used in biomedical applications as a radical polymerization promoter in adhesive dental resin. Herein, we report the preparation of a new hydrogel containing sulfinic acid groups from sodium 4-vinylbenzenesulfinate and 2-hydroxyethyl methacrylate using a radical polymerization reaction and the subsequent incorporation of Ca²⁺ ions into this material. We also investigated the apatite-forming behavior of these hydrogels in SBF. Hydrogels containing sulfinic acid groups showed higher apatite-forming ability than those without sulfinic acid groups. In addition, the apatite layer formed on the former showed tight adhesion to the hydrogel. This phenomenon was attributed to the heterogeneous nucleation of apatite, induced by the sulfinic acid groups. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1924-1929, 2017.

Morphology effect of bioglass-reinforced hydroxyapatite (Bonelike(®) ) on osteoregeneration

In the last decades, the well-known disadvantages of autografts and allografts have driven to the development of synthetic bone grafts for bone regeneration. Bonelike(®) , a glass-reinforced hydroxyapatite (HA) composite was developed and registered for bone grafting. This biomaterial is composed by a modified HA matrix, with α- and β-tricalcium phosphate secondary phases. Aiming to improve the biological characteristics of Bonelike(®) , new spherical pelleted granules, of different shape and size, were developed with controlled micro and macrostructure. In the present study, it was compared the physicochemical properties and in vivo performance of different Bonelike(®) granule presentations-Bonelike(®) polygonal (500-1000 µm size) and Bonelike spherical (250-500 µm; 500-1000 µm size). For the in vivo study, Bonelike(®) was implanted on sheep femurs, with various implantation times (30 days, 60 days, 120 days, and 180 days). X-ray diffraction analysis revealed that the phase composition of different granules presentations was similar. Bonelike(®) spherical 500-1000 µm was the most porous material (global porosity and intraporosity) and Bonelike(®) polygonal 500-1000 µm the less porous. Considering the in vivo study, both polygonal and spherical granules presented osteoconductive proprieties. The spherical granules showed several advantages, including easier medical application through syringe and improved osteointegration, osteoconduction, and degradation, by the presence of larger pores, controlled micro- and macrosctructure and suitable particle format that adapts to bone growth. Bonelike(®) spherical 500-1000 µm showed improved new bone invasion throughout the material's structure and Bonelike(®) spherical 250-500 µm appeared to induce faster bone regeneration, presenting less unfilled areas and less lacunae in the histological analysis.

Effects of processing parameters in thermally induced phase separation technique on porous architecture of scaffolds for bone tissue engineering

Tissue engineering makes use of 3D scaffolds to sustain three-dimensional growth of cells and guide new tissue formation. To meet the multiple requirements for regeneration of biological tissues and organs, a wide range of scaffold fabrication techniques have been developed, aiming to produce porous constructs with the desired pore size range and pore morphology. Among different scaffold fabrication techniques, thermally induced phase separation (TIPS) method has been widely used in recent years because of its potential to produce highly porous scaffolds with interconnected pore morphology. The scaffold architecture can be closely controlled by adjusting the process parameters, including polymer type and concentration, solvent composition, quenching temperature and time, coarsening process, and incorporation of inorganic particles. The objective of this review is to provide information pertaining to the effect of these parameters on the architecture and properties of the scaffolds fabricated by the TIPS technique.