β-tricalcium phosphate composite ceramics with high compressive strength, enhanced osteogenesis and inhibited osteoclastic activities

β-tricalcium phosphate (β-TCP) is well known as a resorbable bone repair material due to its inherent excellent biocompatibility and osteoconductivity. However, β-TCP is encountered with osteostimulation-deficiency and poor mechanical strength because of poor sinterability. Herein, we prepared novel β-TCP composite ceramics (TCP/SPGs) by introducing strontium-containing phosphate-based glass (SPG; 45P₂O₅-32SrO-23Na₂O) as sintering additive. The SPG helped to achieve efficient liquid-phase sintering of β-TCP at 1100 °C. The compressive strength of TCP/SPGs with 15 wt.% SPG (TCP/SPG15) was 2.65 times as high as that of plain β-TCP ceramic. The SPG reacted with β-TCP, and the Sr²⁺ and Na²⁺ from SPG replaced Ca²⁺ in the lattice structure of β-TCP, enabling the sustained release of strontium from TCP/SPGs. In vitro cytological test indicated that TCP/SPGs with certain amount of SPG were highly biocompatible, and noticeably promoted osteogenesis, and inhibited osteoclastic activities. Our results suggested that the TCP/SPG15 might be potential high-strength bone grafts used for bone defect repair, especially in the osteoporotic condition.

Inorganic kernel - Supported asymmetric hybrid vesicles for targeting delivery of STAT3-decoy oligonucleotides to overcome anti-HER2 therapeutic resistance of BT474R

As a recombinant humanized monoclonal antibody that targets the extracellular region of HER2 tyrosine kinase receptor, trastuzumab (TRAZ) has demonstrated comparable clinical efficacy and improved survival in patients with HER2-positive breast cancer. Nevertheless, the therapeutic potential of TRAZ is often limited due to its frequent resistance to anti-HER2 therapy. Therefore, we investigate the reversal effect of STAT3-specific decoy oligonucleotides (STAT3-decoy ODNs) on TRAZ resistance, which contain the consensus sequence within the targeted gene promoter of STAT3. Considering the shortcomings of poor cellular permeability and rapid degradation in vivo limit the further clinical applications of ODNs, we report here an asymmetric hybrid lipid/polymer vesicles with calcium phosphate as the solid kernel (CaP@HA). Through hyaluronan-mediated CD44 targeting, the constructed vesicles can specifically carry STAT3-decoy ODNs into TRAZ-resistant breast cancer cells and then regulate TRAZ-induced apoptosis. In comparison with the native ones, ODNs packaged with CaP@HA showed significantly increased serum stability, cellular transfection, synergistic cytotoxicity and apoptosis in vitro. The improved TRAZ sensitization is attributed to the blockade of STAT3 signaling as well as the expression of downstream target genes associated with TRAZ resistance. With the synergistic action of STAT3-decoy ODNs loaded CaP@HA, TRAZ inhibited the growth of its resistant breast cancer xenograft dramatically and induced significant tumor cell apoptosis in vivo. These results suggested that CaP@HA mediated targeted delivery of STAT3-decoy ODNs might be a promising new strategy to overcome anti-HER2 resistance in breast cancer therapy.

Surface modification of porous alpha-tricalcium phosphate granules with heparin enhanced their early osteogenic capability in a rat calvarial defect model

Heparin binds to and modulates various growth factors, potentially augmenting the bone-forming capability of biomaterials. Here, α-tricalcium phosphate (α-TCP) granules were modified with peptide containing the marine mussel-derived adhesive sequence, which reacts with α-TCP surface, and cationic sequence, which binds to heparin (α-Ph). α-Ph retained the α-TCP phase and intergranule spaces after the surface modification. The existence of heparin on α-Ph granules was confirmed using X-ray photoelectron spectroscopy. Granules of α-TCP and α-Ph were implanted into critical-size defects in rat calvaria for 4 weeks. Micro-computed tomography, histological evaluation, and Alcian blue staining revealed that α-Ph induced superior bone formation compared with α-TCP. Newly formed bone on α-Ph was preferentially in contact with the Alcian blue-stained surfaces of granules. These results suggested that heparinization enhanced the early osteogenic capacity of α-TCP, possibly by modulating the secretion of Alcian blue-stained extracellular matrixes.

Biphasic calcium phosphate scaffolds with controlled pore size distribution prepared by in-situ foaming

In this study, a reproducible method of fabricating hierarchically 3D porous scaffolds with high porosity and pore interconnectivity is reported. The method is based on in-situ foaming of a dispersion of diisocyanate, polyol, water and hydroxyapatite (HA) to form a hard foamed HA/polyurethane composite which after heat treatment provided a bi-phase calcium phosphate scaffold. This technique, combining the advantages of polymer sponge and direct foaming methods, provides a better control over the macrostructure of the scaffold. A modification of the multi-scaled porous macrostructure of scaffolds produced by changing the ratio of input reactants and by sintering temperature was studied. The pore morphology, size, and distribution were characterized using a scanning electron microscope and mercury porosimetry. The pores were open and interconnected with multi-scale (from several nanometres to millimetres) sizes convenient for using in tissue engineering applications. The bioactivity was confirmed by growing an apatite layer on the surfaces after immersion in simulated body fluid. The material was biocompatible, as shown by using normal human adipose tissue-derived stem cells (ASC). When seeded onto the scaffolds, the ASC adhered and remained healthy while maintaining their typical morphology.

Hip osteonecroses treated with calcium sulfate-calcium phosphate bone graft substitute have different results according to the cause of osteonecrosis: alcohol abuse or corticosteroid-induced

INTRODUCTION

The aim of the study was to assess the factors influencing the final results of treatment of the femoral head osteonecrosis (ONFH) with core decompression and bone substitute grafting. The special interest was focused on comparison between alcohol- and steroid-induced ONFHs.

MATERIAL AND METHODS

In this prospective study, a total of 53 patients (58 hips) in the mean age of 35.5 years were included: 29 had a history of alcohol use (32 hips) and 24 of steroid use (26 hips). The mean follow-up was 4.2 years (minimum 3 years).

RESULTS

At last follow-up, significant improvements were noted in the Harris Hip Score (HHS) (mean 44.0 vs 55.9 points, p < 0.00002) and VAS scores (mean 7.0 vs 5.8 points, p < 0.0002) for the whole ONFH cohort, comparing to pre-operative status. The degree of improvement did not differ between Ficat and Arlet grade II and grade III (mean 14.9 vs 6.2 points, respectively, p = 0.1). No change was found between the final and initial results in this group in the steroid group (HHS mean 42.2 vs 45.5 points, p = 0.5 and VAS mean 6.8 vs 6.5 points, p = 0.5), but the improvement was noted in the alcohol group (HHS mean 45.5 vs 64.4 points, p < 0.0001; VAS mean 7.1 vs 5.2 points, p < 0.0001) comparing to pre-operative status.

CONCLUSIONS

Presented treatment of ONFH significantly improves hip function, offers pain reduction, and gives similar functional improvement for hips scoring grade II and III on the Ficat and Arlet scale. A good response to operative treatment is seen in patients with alcohol-induced ONFH, but not in those with steroid-induced ONFH.

Development of calcium bodies in Hylonsicus riparius (Crustacea: Isopoda)

Calcium bodies are internal epithelial sacs found in terrestrial isopods of the family Trichoniscidae that contain a mineralized extracellular matrix that is deposited and resorbed in relation to the molt cycle. Calcium bodies in several trichoniscids are filled with bacteria, the function of which is currently unknown. The woodlouse Hyloniscus riparius differs from other trichoniscids in that it possesses two different pairs of calcium bodies, the posterior pair being filled with bacteria and the anterior pair being devoid of bacteria. We explored the development of these organs and bacterial colonization of their lumen during the postmarsupial development with the use of optical clearing and whole-body confocal imaging of larval and juvenile stages. Our results show that calcium bodies are formed as invaginations of the epidermis in the region of intersegmental membranes during the postmarsupial development. The anterior pair of calcium bodies is generated during the first postmarsupial manca stage, whereas the posterior calcium bodies first appear in juveniles and are immediately colonized by bacteria, likely through a connection between the calcium body lumen and the body surface. Mineral is deposited in calcium bodies as soon as they are present.

Calcium addition to increase the production of phosphate granules in anaerobic treatment of black water

Simultaneous recovery of calcium phosphate granules (CaP granules) and methane from vacuum collected black water (BW), using an upflow anaerobic sludge blanket (UASB) reactor was previously investigated. It was calculated that only 2% of the total phosphorus (P) fed was present as CaP granules whereas 51% of the P accumulated dispersed in the reactor, limiting the applicability of this process for recovery of phosphate. This study proposes adding calcium to increase the P accumulation in the reactor and the production of CaP granules. Calcium was added in a lab-scale UASB reactor fed with BW. An identical UASB reactor was used as reference, to which no calcium was added. The treatment performance was evaluated by weekly monitoring of influent, effluent and produced biogas. Sludge bed development and CaP granulation were assessed through particle size analysis. The composition and structure of CaP granules were chemically and optically assessed. Calcium addition increased accumulation of P in the reactor and formation and growth of granules with size > 0.4 mm diameter (CaP granules). Moreover, with calcium addition, CaP granules contained 5.6 ± 1.5 wt% of P, while without calcium a lower P content was observed (3.7 ± 0.3 wt%). By adding Ca, 89% of the incoming P from BW accumulated in the reactor and 31% was sampled as CaP granules (> 0.4 mm diameter). Addition of 250 mgCa L^-1 of BW was the optimum loading found in this study. Furthermore, no significant reduction in COD_Total removal (> 80%) and CH₄ production (0.47 ± 0.10 gCOD-CH₄ g^-1COD_Total-BW) was observed. Therefore, adding calcium can significantly increase the CaP granulation without inhibiting the simultaneous CH₄ recovery. This further indicates the potential of this process for phosphate recovery.

Dual slag filters for enhanced phosphorus removal from domestic waste water: performance and mechanisms

The phosphorus (P) removal of five combinations of dual filters consisting of blast furnace slag (BFS), argon oxygen decarburisation slag (AOD) and electric arc furnace slag (EAF) was evaluated in column experiments with domestic waste water. The columns were fed with waste water for 24 days. The column with only EAF had the best P removal performance (above 93% throughout the experiment). The speciation of the bound P was evaluated by P K-edge X-ray absorption near-edge structure (XANES) spectroscopy. In all five columns, the main P species of the slag packed in the outlet chamber was amorphous calcium phosphate (ACP). In samples from the inlet chambers, the contributions from crystalline Ca phosphates, P adsorbed on gibbsite and P adsorbed on ferrihydrite were usually much greater, suggesting a shift of P removal mechanism as the waste water travelled from the inlet to the outlet. The results provide strong evidence that P was predominantly removed by the slags through the formation of ACP. However, as the pH decreased with time due to the progressively lower dissolution of alkaline silicate minerals from the slag, the ACP was rendered unstable and hence redissolved, changing the P speciation. It is suggested that this process strongly affected the lifespan of the slag filters. Of the slags examined, EAF slag had the best P removal characteristics and BFS the worst, which probably reflected different dissolution rates of alkaline silicates in the slags.

Recent Trends in Hydroxyapatite (HA) Synthesis and the Synthesis Report of Nanostructure HA by Hydrothermal Reaction

This research summary the trend in synthesis of Hydroxyapatite (HA) using different route such as dry method and wet method (co-precipitation method; emulsion method, hydrolysis method, sol-gel method, hydrothermal method). In addition, the research group also report the technique to synthesis nano-structure HA by hydrothermal reaction using Ca(OH)₂ and H₃PO₄ with the Ca/P molar ratio of 1.67. The mixture after homogenized for 2 h, follow by hydrothermal reaction at different hydrothermal temperature time (100 °C, 150 °C, and 180 °C) and different hydrothermal reaction time (0 h, 12 h and 24 h). The 180 °C-hydrothermal treated-HA has needle-like shape with the diameter of 10 ~ 20 nm and length of below 100 nm, which is similar with human bone. For the hydrothermal reaction, temperature is the key to form nanostructure HA.

Mesenchymal Stem Cells and Calcium Phosphate Bioceramics: Implications in Periodontal Bone Regeneration

In orthopedic medicine, a feasible reconstruction of bone structures remains one of the main challenges both for healthcare and for improvement of patients' quality of life. There is a growing interest in mesenchymal stem cells (MSCs) medical application, due to their multilineage differentiation potential, and tissue engineering integration to improve bone repair and regeneration. In this review we will describe the main characteristics of MSCs, such as osteogenesis, immunomodulation and antibacterial properties, key parameters to consider during bone repair strategies. Moreover, we describe the properties of calcium phosphate (CaP) bioceramics, which demonstrate to be useful tools in combination with MSCs, due to their biocompatibility, osseointegration and osteoconduction for bone repair and regeneration. Also, we overview the main characteristics of dental cavity MSCs, which are promising candidates, in combination with CaP bioceramics, for bone regeneration and tissue engineering. The understanding of MSCs biology and their interaction with CaP bioceramics and other biomaterials is critical for orthopedic surgical bone replacement, reconstruction and regeneration, which is an integrative and dynamic medical, scientific and bioengineering field of research and biotechnology.

Calcium phosphate in plant trichomes: the overlooked biomineral

Calcium phosphate was unknown as a plant biomineral until recently reported in Neotropical Loasaceae. Here, we demonstrate its widespread occurrence in the trichomes of several plant families, including Brassicaceae. Calcium phosphate is the primary biomineral in, e.g., the bones and teeth of higher animals; in plants, it was only recently discovered in the stinging hairs and scabrid-glochidiate trichomes of South American Loasaceae (Ensikat et al. in Sci Rep UK 6:26073, 2016), where it appears to be deposited highly specifically, often replacing the common plant biomineral silica. We initiated a broader survey in a range of different plant orders to investigate a possibly wider distribution of calcium phosphate biomineralization in plants. Scanning electron microscopy with EDX element analysis and mapping was used for the detection of the biominerals: calcium phosphate, calcium carbonate, and silica in the trichomes of several common plant species of different orders. Results were authenticated with Raman spectroscopy. Calcium phosphate was found in the trichomes of several species in the orders Malpighiales, Rosales, Boraginales, and Brassicales. It occurred in trichome tips, replacing the more common silica, or together with silica and calcium carbonate at specific locations in the trichome cell walls. Most surprisingly, it was found in the trichomes of Arabidopsis thaliana, one of the most studied plant species-where it had been overlooked so far. The wide distribution of calcium phosphate as plant biomineral here demonstrated and the striking mineralization patterns with three different biominerals in the walls of single-celled trichomes underscore an unexpected complexity in plant biomineralization.

Strontium-modified premixed calcium phosphate cements for the therapy of osteoporotic bone defects

In this study a premixed strontium-containing calcium phosphate bone cement for the application in osteoporotic bone defects has been developed and characterised regarding its material and in vitro properties as well as minimally invasive applicability in balloon kyphoplasty. Strontium was introduced into the cement by substitution of one precursor component, CaCO₃, with its strontium analogue, SrCO₃. Using a biocompatible oil phase as carrier liquid, a cement paste that only set upon contact with aqueous environment was obtained. Strontium modification resulted in an increased strength of set cements and radiographic contrast; and the cements released biologically relevant doses of Sr²⁺-ions that were shown to enhance osteoprogenitor cell proliferation and osteogenic differentiation. Finally, applicability of strontium-containing cement pastes in balloon kyphoplasty was demonstrated in a human cadaver spine procedure. The cement developed in this study may therefore be well suited for minimally invasive, osteoporosis-related bone defect treatment.

STATEMENT OF SIGNIFICANCE

Strontium-releasing calcium phosphate bone cements are promising materials for the clinical regeneration of osteoporosis-related bone defects since they have been shown to stimulate bone formation and at the same time limit osteoclastic bone resorption. Today clinical practice favours minimally invasive surgical techniques, e.g. for vertebral fracture treatment, posing special demands on such cements. We have therefore developed a premixed, strontium-releasing bone cement with enhanced mechanical properties and high radiographic visibility that releases biologically relevant strontium concentrations and thus stimulates cells of the osteogenic lineage. In a pilot experiment we also exemplify its excellent suitability for minimally invasive balloon kyphoplasty procedures.

Porous Scaffolds for Regeneration of Cartilage, Bone and Osteochondral Tissue

Porous scaffolds play an important role as a temporary support for accommodation of seeded cells to control their functions and guide regeneration of functional tissues and organs. Various scaffolds have been prepared from biodegradable polymers and calcium phosphate. They have also been hybridized with bioactive factors to control differentiation of stem cells. Except the composition, porous structures of scaffolds are also extremely important for cell adhesion, spatial distribution and tissue regeneration. The method using preprepared ice particulates has been developed to precisely control surface and bulk pore structures of porous scaffolds. This chapter summarizes the design and preparation of porous scaffolds of biodegradable polymers and their hybrid scaffolds with calcium phosphate nanoparticles and bioactive factors. Their applications for regeneration of cartilage, bone and osteochondral tissue will be highlighted.

HIGHLIGHTS

Porous scaffolds of naturally derived polymers and their hybrid scaffolds with biodegradable synthetic polymers have been prepared for cartilage tissue engineering. The surface and bulk pore structures of the scaffolds are controlled by using preprepared ice particulates. The scaffolds facilitate cartilage tissue engineering when they are used for three-dimension culture of chondrocytes. PLGA-collagen-BMP4 and collagen-CaP nanoparticles-dexamethasone hybrid scaffolds have been prepared and used for culture of mesenchymal stem cells. The hybrid scaffolds facilitate osteogenic differentiation of mesenchymal stem cells and ectopic bone tissue regeneration during in vitro culture and in vivo implantation. Osteochondral tissue engineering has been realized by laminating two different layers of cartilage and subchondral bone or by using stratified scaffolds for simultaneous regeneration of cartilage and subchondral bone.

Long-term radiographic appearance of calcium-phosphate synthetic bone grafts after surgical treatment of tibial plateau fractures

OBJECTIVES

Synthetic bone grafts (SBGs) are widely used to fill bone defects after fracture reduction. This study assessed the long-term resorption of two different calcium phosphate products (A=ChronOS™ inject and B=Norian^® SRS^®; both DePuy Synthes, Oberdorf, Switzerland) used in the surgical treatment of tibial plateau fractures.

DESIGN

Long-term clinical and radiologic follow-up of 52 patients after surgical treatment of intraarticular tibial plateau fractures augmented with SBGs.

SETTING

The study was performed at a level 3 trauma center.

PATIENTS

Between January 2000 and December 2006 a total of 52 patients with intraarticular tibial plateau fractures were operatively treated and augmented with SBGs consisting of a Brushite matix with β-TCP granules (SBG A) or hydroxylapatite with 4-6% carbonate content (SBG B). 46 patients could be contacted and 38 were included in the study. Half of the patients received SBG A and the other half SBG B.

MAIN OUTCOME MEASUREMENTS

Loss of reduction and SBG resorption was investigated by comparison of follow-up X-ray images to pre- and postoperative X-ray images. Furthermore, pain, activity level and knee function were evaluated by means of questionnaires and clinical examination.

RESULTS

The mean age of patients was 59.7±12.5years. The follow-up was 8.6±0.9years for SBG A and 11.6±1.4years for SBG B (p<0.001). In most cases SBG A was completely resorbed in a homogenous pattern, while SBG B was still visible on the X-ray images revealing a peripheral resorption pattern. A loss of reduction (>2mm) could be observed in two patients with SBG A and two patients with SBG B, although only one of them had an impaired knee function.

CONCLUSIONS

The composite SBG A reveals a comprehensive long-term resorption in comparison to SBG B. Nevertheless, both provided suitable mechanical support as part of the surgical treatment of tibial plateau fractures.

LEVEL OF EVIDENCE

Case series, Level IV.

In Vitro Investigation of Bioactive Glass-Ceramic Composites Based on Biogenic Hydroxyapatite or Synthetic Calcium Phosphates

This in vitro investigation of the behavior of two types of calcium phosphate glass ceramics on the basis of phosphates of biogenic or synthetic origin prepared from initial mixtures with different particle size has revealed that some different factors affect the behavior, namely the phase composition of composite, fraction of open porosity, and average diameter of pore channels. It was established that the solubility of the composites on the basis of synthetic calcium phosphates and glass after 2 and 7 days contact with saline composites is the highest among the materials under study. First of all, this fact is related to the peculiarities of their phase composition, high fraction of open porosity, and high permeability. As for biogenic hydroxyapatite/glass materials, their solubility is several times lower in spite of close total porosity. The particle size of initial mixture practically does not affect the material solubility; the latter is only slightly lower for smaller particles.

Delivery of the TLR ligand poly(I:C) to liver cells in vitro and in vivo by calcium phosphate nanoparticles leads to a pronounced immunostimulation

The selective activation of the immune system is a concurrent problem in the treatment of persistent diseases like viral infections (e.g. hepatitis). For the delivery of the toll-like receptor ligand poly(I:C), an immunostimulatory action was discovered earlier by hydrodynamic injection. However, this technique is not clinically transferable to human patients. A modular system where the immunoactive toll-like-receptor ligand 3 (TLR-3) poly(I:C) was incorporated into calcium phosphate nanoparticles was developed. The nanoparticles had a hydrodynamic diameter of 275nm and a zeta potential of +20mV, measured by dynamic light scattering. The diameter of the solid core was 120nm by scanning electron microscopy. In vitro, the nanoparticle uptake was investigated after 1 and 24h of incubation of THP-1 cells (macrophages) with nanoparticles by fluorescence microscopy. After intravenous injection into BALB/c and C57BL/6J mice, respectively, the in vivo uptake was especially prominent in lung and liver, 1 and 3h after the injection. Pronounced immunostimulatory effects of the nanoparticles were found in vitro with primary liver cells, i.e. Kupffer cells (KC) and liver sinusoidal endothelial cells (LSEC) from wild-type C57BL/6J mice. Thus, they represent a suitable alternative to hydrodynamic injection treatments for future vaccination concepts.

STATEMENT OF SIGNIFICANCE

The selective activation of the immune system is a concurrent problem in the treatment of persistent diseases like viral infections (e.g. hepatitis). For the delivery of the toll-like receptor ligand poly(I:C), an immunostimulatory action has been discovered earlier by hydrodynamic injection. However, this technique is not clinically transferable to human patients. We have developed a modular system where poly(I:C) was incorporated into calcium phosphate nanoparticles. The uptake into relevant liver cells was studied both in vitro and in vivo. After intravenous injection into mice, the in vivo uptake was especially prominent in lung and liver, 1 and 3h after the injection. The corresponding strong immune reaction proves their high potential to turn up the immune system, e.g. against viral infections, without adverse side reactions.

Facile one-pot fabrication of calcium phosphate-based composite nanoparticles as delivery and MRI contrast agents for macrophages

We developed a facile one-pot fabrication process for magnetic iron oxide-calcium phosphate (IO-CaP) composite nanoparticles via coprecipitation in labile supersaturated CaP solutions containing IO nanocrystals. All the source solutions used were clinically approved for injection, including water and magnetic IO nanocrystals (ferucarbotran, used as a negative magnetic resonance imaging (MRI) contrast agent). This ensured that the resulting nanoparticles were pathogen- and endotoxin-free. The dispersants used were clinically approved heparin sodium (heparin) or adenosine triphosphate disodium hydrate (ATP), which were added to the IO-containing labile supersaturated CaP solutions. Both heparin and ATP coprecipitated with CaP and ferucarbotran to form heparin- and ATP-modified IO-CaP nanoparticles, respectively, with a hydrodynamic diameter of a few hundred nanometers. Both the resulting nanoparticles exhibited relatively large negative zeta potentials, caused by the negatively charged functional groups in heparin and ATP, which improved the particle dispersibility when compared to non-modified IO-CaP nanoparticles. The heparin-modified IO-CaP nanoparticles were effectively ingested by murine macrophages (RAW264.7) without showing significant cytotoxicity but barely ingested by non-phagocytotic human umbilical vein endothelial cells, indicating the potential of these nanoparticles for targeted delivery to macrophages. The heparin-modified IO-CaP nanoparticles exhibited a negative contrast enhancing ability for MRI. Our results show that IO-CaP nanoparticles have potential as delivery and MRI contrast agents for macrophages.

Injectable, biomechanically robust, biodegradable and osseointegrative bone cement for percutaneous kyphoplasty and vertebroplasty.Int Orthop. 2018;42:125-132. [PMID: 29116357 DOI: 10.1007/s00264-017-3674-0]

PURPOSE

Poly(methyl methacrylate) (PMMA) cement is widely used for percutaneous kyphoplasty and vertebroplasty (PKP and PVP) but possesses formidable shortcomings due to non-degradability. Here, a biodegradable replacement is developed.

METHODS

Calcium phosphate cement (CPC) was redesigned by incorporating starch and BaSO₄ (new cement named as CPB). The biomechanical, biocompatibility, osseointegrative and handling properties of CPB were systematically evaluated in vitro and in vivo by the models of osteoporotic sheep vertebra, rat subcutaneous implantation and rat femoral defect.

RESULTS

CPB revealed appropriate injectability and setting ability for PKP and PVP. More importantly, its biomechanical strengths measured by in vitro and in vivo models were not less than that of PMMA, while its biodegradability and osseointegrative capacities were significantly enhanced compared to PMMA.

CONCLUSIONS

CPB is injectable, biomechanically robust, biodegradable and osseointegrative, demonstrating revolutionary potential for the application in PKP and PVP.

Enzyme-crosslinked gene-activated matrix for the induction of mesenchymal stem cells in osteochondral tissue regeneration

The development of osteochondral tissue engineering is an important issue for the treatment of traumatic injury or aging associated joint disease. However, the different compositions and mechanical properties of cartilage and subchondral bone show the complexity of this tissue interface, making it challenging for the design and fabrication of osteochondral graft substitute. In this study, a bilayer scaffold is developed to promote the regeneration of osteochondral tissue within a single integrated construct. It has the capacity to serve as a gene delivery platform to promote transfection of human mesenchymal stem cells (hMSCs) and the functional osteochondral tissues formation. For the subchondral bone layer, the bone matrix with organic (type I collagen, Col) and inorganic (hydroxyapatite, Hap) composite scaffold has been developed through mineralization of hydroxyapatite nanocrystals oriented growth on collagen fibrils. We also prepare multi-shell nanoparticles in different layers with a calcium phosphate core and DNA/calcium phosphate shells conjugated with polyethyleneimine to act as non-viral vectors for delivery of plasmid DNA encoding BMP2 and TGF-β3, respectively. Microbial transglutaminase is used as a cross-linking agent to crosslink the bilayer scaffold. The ability of this scaffold to act as a gene-activated matrix is demonstrated with successful transfection efficiency. The results show that the sustained release of plasmids from gene-activated matrix can promote prolonged transgene expression and stimulate hMSCs differentiation into osteogenic and chondrogenic lineages by spatial and temporal control within the bilayer composite scaffold. This improved delivery method may enhance the functionalized composite graft to accelerate healing process for osteochondral tissue regeneration.

STATEMENT OF SIGNIFICANCE

In this study, a gene-activated matrix (GAM) to promote the growth of both cartilage and subchondral bone within a single integrated construct is developed. It has the capacity to promote transfection of human mesenchymal stem cells (hMSCs) and the functional osteochondral tissues formation. The results show that the sustained release of plasmids including TGF-beta and BMP-2 from GAM could promote prolonged transgene expression and stimulate hMSCs differentiation into the osteogenic and chondrogenic lineages by spatial control manner. This improved delivery method should enhance the functionalized composite graft to accelerate healing process in vitro and in vivo for osteochondral tissue regeneration.

Effect of Nano-HA/Collagen Composite Hydrogels on Osteogenic Behavior of Mesenchymal Stromal Cells

This study aimed to comparatively evaluate the in vitro effect of nanosized hydroxyapatite and collagen (nHA/COL) based composite hydrogels (with different ratios of nHA and COL) on the behavior of human mesenchymal stromal cells (MSCs), isolated from either adipose tissue (AT-MSCs) or bone marrow (BM-MSCs). We hypothesized that (i) nHA/COL composite hydrogels would promote the osteogenic differentiation of MSCs in an nHA concentration dependent manner, and that (ii) AT-MSCs would show higher osteogenic potential compared to BM-MSCs, due to their earlier observed higher proliferation and osteogenic differentiation potential in 2D in vitro cultures [1]. The obtained results indicated that AT-MSCs show indeed high proliferation, differentiation and mineralization capacities in nHA/COL constructs compared to BM-MSCs, but this effect was irrespective of nHA concentration. Based on the results of alkaline phosphatase (ALP) activity and osteocalcin (OCN) protein level, the osteogenic differentiation of BM-MSCs started in the beginning of the culture period and for AT-MSCs at the end of the culture period. At a molecular level, both cell types showed high expression of osteogenic markers (bone morphogenic protein 2 [BMP2], runt-related transcription factor 2 [RUNX2], OCN or COL1) in both an nHA concentration and time dependent manner. In conclusion, AT-MSCs demonstrated higher osteogenic potential in nHA/COL based 3D micro-environments compared to BM-MSCs, in which proliferation and osteogenic differentiation were highly promoted in a time dependent manner, irrespective of nHA amount in the constructs. The fact that AT-MSCs showed high proliferation and mineralization potential is appealing for their application in future pre-clinical research as an alternative cell source for BM-MSCs.

Facile Approach to Synthesize Gold Nanorod@Polyacrylic Acid/Calcium Phosphate Yolk-Shell Nanoparticles for Dual-Mode Imaging and pH/NIR-Responsive Drug Delivery

A facile strategy to fabricate gold nanorod@polyacrylic acid/calcium phosphate (AuNR@PAA/CaP) yolk-shell nanoparticles (NPs) composed with a PAA/CaP shell and an AuNR yolk is reported. The as-obtained AuNR@PAA/CaP yolk-shell NPs possess ultrahigh doxorubicin (DOX) loading capability (1 mg DOX/mg NPs), superior photothermal conversion property (26%) and pH/near-infrared (NIR) dual-responsive drug delivery performance. The released DOX continuously increased due to the damage of the CaP shell at low pH values. When the DOX-loaded AuNR@PAA/CaP yolk-shell NPs were exposed to NIR irradiation, a burst-like drug release occurs owing to the heat produced by the AuNRs. Furthermore, AuNR@PAA/CaP yolk-shell NPs are successfully employed for synergic dual-mode X-ray computed tomography/photoacoustic imaging and chemo-photothermal cancer therapy. Therefore, this work brings new insights for the synthesis of multifunctional nanomaterials and extends theranostic applications.

Biomaterials for Craniofacial Bone Regeneration

Functional reconstruction of craniofacial defects is a major clinical challenge in craniofacial sciences. The advent of biomaterials is a potential alternative to standard autologous/allogenic grafting procedures to achieve clinically successful bone regeneration. This article discusses various classes of biomaterials currently used in craniofacial reconstruction. Also reviewed are clinical applications of biomaterials as delivery agents for sustained release of stem cells, genes, and growth factors. Recent promising advancements in 3D printing and bioprinting techniques that seem to be promising for future clinical treatments for craniofacial reconstruction are covered. Relevant topics in the bone regeneration literature exemplifying the potential of biomaterials to repair bone defects are highlighted.

The application of chitosan/collagen/hyaluronic acid sponge cross-linked by dialdehyde starch addition as a matrix for calcium phosphate in situ precipitation

Scaffolds based on chitosan, collagen and hyaluronic acid, cross-linked by dialdehyde starch were obtained through the freeze-drying method. The porous structures were used as matrixes for calcium phosphate in situ precipitation. Composites were characterized by different analyses, e.g. infrared spectroscopy, SEM images, porosity, density, and mechanical tests. Moreover, an examination involving the energy dispersive X-ray spectroscopic method was carried out for the calcium and phosphorus ratio determination. In addition, the adhesion and proliferation of human osteosarcoma SaOS-2 cells were examined on the obtained scaffolds. The results showed that the properties of the scaffolds based on chitosan, collagen, and hyaluronic acid can be modified by dialdehyde starch addition. The mechanical parameters (i.e. compressive modulus and maximum compressive force), porosity, and density of the material were improved. Calcium phosphate was deposited in the scaffolds at the Ca/P ratio ∼2. SEM images showed the homogeneous structure, with interconnected pores. The cross-linker addition and an inorganic compound precipitation improved the biocompatibility of the scaffolds. The obtained materials can provide the support required in tissue engineering and regenerative medicine.

Conversion of biowastes to biomaterial: An innovative waste management approach

The study suggests that biowastes (eggshells and urine) can be potentially used as precursors to produce hydroxyapatite (HAp) biomaterial in a simple chemical process. A batch reactor was used in this work to produce HAp powder from eggshells and synthetic urine (SU). Fine powder of calcined eggshells was dissolved in water to produce aqueous calcium hydroxide. The solution was then mixed with concentrated SU in stoichiometric amounts corresponding to HAp (Ca/P molar ratio∼1.67). The initial pH of the solution was alkaline (pH∼8.5) and particles formed rapidly with slight mixing. Stirring the turbid solution for a longer period (72h) did not show any visual change, but the particle size decreased slightly. When the pH of the solution was adjusted to 5, the solution was initially clear, but particle formation was apparent after 48h stirring. It was noticed that at a slow stirring speed (100rpm), film formation occurred on the solution, whereas at a higher stirring speed (500rpm) no such film formation was observed. X-ray diffraction (XRD) analysis confirmed that the particles (formed at 500rpm) were an amorphous calcium phosphate (CaP). Alkaline treatment at 80°C for 2h converted the amorphous CaP into HAp. Inductively coupled plasma mass spectrometry (ICP-MS) analysis of the particles (formed at 500rpm) suggested that they are calcium-deficient HAp (Ca/P molar ratio 1.58).

Hierarchically porous structure, mechanical strength and cell biological behaviors of calcium phosphate composite scaffolds prepared by combination of extrusion and porogen burnout technique and enhanced by gelatin

In this study, hierarchically porous calcium phosphate scaffolds (HTCP) with unidirectional pores, transversely interconnected pores, and micropores were fabricated by the combination of extrusion and porogen burnout technique. Gelatin was incorporated into the HTCP scaffolds by vacuum-impregnation of gelatin solution and subsequent freeze-drying. The phase composition, microstructure, physical and cytobiological properties were analyzed. The results showed that the HTCP scaffolds were composed of β-tricalcium phosphate with minor hydroxyapatite. The HTCP scaffolds had unidirectional pores (~400μm), transversely interconnected pores (~130μm) and micropores (~1μm). The incorporation of gelatin significantly increased the compressive strength, toughness, and cell seeding of the HTCP scaffolds. The composite scaffolds showed excellent cytocompatibility. The hierarchically porous calcium phosphate composite scaffolds may have potential application prospects in bone tissue engineering.

Tailored design of multifunctional and programmable pH-responsive self-assembling polypeptides as drug delivery nanocarrier for cancer therapy

Breast cancer has become the second leading cause of cancer-related mortality in female wherein more than 90% of breast cancer-related death results from cancer metastasis to distant organs at advanced stage. The purpose of this study is to develop biodegradable nanoparticles composed of natural polypeptides and calcium phosphate (CaP) with sequential pH-responsivity to tumor microenvironments for active targeted drug delivery. Two different amphiphilic copolymers, poly(ethylene glycol)₃₄₀₀-aconityl linkage-poly(l-glutamic acid)₁₅-poly(l-histidine)₁₀-poly(l-leucine)₁₀ and LyP1-poly(ethylene glycol)₁₁₀₀-poly(l-glutamic acid)₁₅-poly(l-histidine)₁₀-poly(l-leucine)₁₀, were exploited to self-assemble into micelles in aqueous phase. The bio-stable nanoparticles provide three distinct functional domains: the anionic PGlu shell for CaP mineralization, the protonation of PHis segment for facilitating anticancer drug release at target site, and the hydrophobic core of PLeu for encapsulation of anticancer drugs. Furthermore, the hydrated PEG outer corona is used for prolonging circulation time, while the active targeting ligand, LyP-1, is served to bind to breast cancer cells and lymphatic endothelial cells in tumor for inhibiting metastasis. Mineralized DOX-loaded nanoparticles (M-DOX NPs) efficiently prevent the drug leakage at physiological pH value and facilitate the encapsulated drug release at acidic condition when compared to DOX-loaded nanoparticles (DOX NPs). M-DOX NPs with LyP-1 targeting ligand effectively accumulated in MDA-MB-231 breast cancer cells. The inhibition effect on cell proliferation also enhances with time, illustrating the prominent anti-tumor efficacy. Moreover, the in vitro metastatic inhibition model shows the profound inhibition effect of inhibitory nanoparticles. In brief, this self-assembling peptide-based drug delivery nanocarrier with multifunctionality and programmable pH-sensitivity is of great promise and potential for anti-cancer therapy.

STATEMENT OF SIGNIFICANCE

This tailored-design polypeptide-based nanoparticles with self-assembling and programmable stimulus-responsive properties enable to 1) have stable pH in physiological value with a low level of drug loss and effectively release the encapsulated drug with pH variations according to the tumor microenvironment, 2) enhance targeting ability to hard-to-treat breast cancer cells and activate endothelial cells (tumor region), 3) significantly inhibit the growth and prevent from malignant metastasis of cancer cells in consonance with promising anti-tumor efficacy, and 4) make tumors stick to localized position so that these confined solid tumors can be more accessible by different treatment modalities. This work contributes to designing a programmable pH-responsive drug delivery system based on the tailor-designed polypeptides.

Biocompatible β-SrHPO4 clusters with dandelion-like structure as an alternative drug carrier

Recent researches about calcium phosphate (CaP) biomaterials used as drug delivery systems are focusing on the better understanding of the microenvironment around the implant-host tissue interface, with the aim to provide a bone response in pathological ones. Towards the improvement of the osteogenic potential of CaP drug carriers, dandelion-like β-SrHPO₄ clusters (Φ10-20μm) has been prepared by a homogeneous precipitation method under the hydrolysis of carbamide. Adhesion, spreading, proliferation, osteogenic differentiation and mRNA expression of bone mesenchymal stem cells (BMSCs) mediated by β-SrHPO₄ clusters were investigated. Highly osteoconductive and biodegradable octacalcium phosphate with similar structure was employed as the control. By contrast, β-SrHPO₄ clusters exhibited remarkably better affinity, enhanced proliferation and osteogenic differentiation of BMSCs, providing a promising alternative bioactive bone substitute and drug carrier for tissue repair. With the unique dandelion-like microstructure, we believe that our as-prepared material will open up new avenues for applicability of CaP drug delivery systems in the near future.

Electrochemical enzyme biosensors based on calcium phosphate materials for tyramine detection in food samples

Electrochemical tyrosinase biosensors for tyramine determination were developed by the immobilization of the enzyme in calcium phosphate materials (CaPs) followed by cross-linking with glutaraldehyde. Tyramine was detected by the electrochemical reduction at -0.1V of the o- enzymatically-formed dopaquinone. Three different CaPs were explored as immobilization systems, monetite, brushite and brushite cement. Biosensors based on brushite matrices provide better analytical properties than the monetite one. Compared to brushite, a 10-fold increase of sensitivity was obtained with the brushite cement-based biosensor, which highlights the effect of brushite crystal formation in the presence of the enzyme in the biosensor performance. Several variables involved in the enzyme immobilization method such as glutaraldehyde cross-linking time, PPO/brushite ratio and thickness of the brushite-enzyme film were investigated. Furthermore, the effects of pH and temperature on biosensor performance were also optimized. Brushite cement-PPO-GA biosensor resulted in a reliable, highly sensitive, fast, inexpensive and easy analytical method for tyramine detection. Under optimal conditions (time of 15min, a ratio of 1.0 and 50μg of the brushite-enzyme mixture, 20°C and pH 6,0), a linear range of 5.8 × 10^-7 to 1.6 × 10^-5, sensitivity 1.50 × 10³mAM^-1 cm^-2, detection limit, 4.85 × 10^-8M and a response time, 6s were obtained. The suitability of the proposed biosensor to determine the tyramine content in cheese samples has been explored. The mean analytical recovery of added tyramine in gouda and brie cheeses were found to be 95.5±5.8 and 96.9±7.5 respectively. A study of the tyramine content evolution over the course of a week under inadequate storage showed the importance of monitoring the degradation of certain foods.

Mesoporous calcium phosphate using casein as a template: Application to bovine serum albumin sorption

Mesoporous hydroxyapatites were synthesized at room temperature using casein as a template, and key experimental factors, such as casein concentration, pH and extraction of casein in the final solids by washing and thermal treatment, were systematically investigated. The X-Ray Diffraction (XRD) patterns confirmed the synthesis of well-crystallized hydroxyapatite. The N₂ adsorption/desorption isotherms were in agreement with the formation of mesoporous hydroxyapatite with a maximum surface area of 106m²g^-1. Infrared spectroscopy and thermogravimetry analysis were performed to investigate the extraction of casein in water in the post-synthesis stage. Pure mesoporous hydroxyapatite exhibited good BSA adsorption capacity higher than the one obtained for conventional hydroxyapatite.

Synthesis and characterization of amino acid-functionalized calcium phosphate nanoparticles for siRNA delivery

Small interfering RNAs (siRNA) are short nucleic acid fragments of about 20-27 nucleotides, which can inhibit the expression of specific genes. siRNA based RNAi technology has emerged as a promising method for the treatment of a variety of diseases. However, a major limitation in the therapeutic use of siRNA is its rapid degradation in plasma and cellular cytoplasm, resulting in short half-life. In addition, as siRNA molecules cannot penetrate into the cell efficiently, it is required to use a carrier system for its delivery. In this work, chemically and morphologically different calcium phosphate (CaP) nanoparticles, including spherical-like hydroxyapatite (HA-s), needle-like hydroxyapatite (HA-n) and calcium deficient hydroxyapatite (CDHA) nanoparticles were synthesized by the sol-gel technique and the effects of particle characteristics on the binding capacity of siRNA were investigated. In order to enhance the gene loading efficiency, the nanoparticles were functionalized with arginine and the morphological and their structural characteristics were analyzed. The addition of arginine did not significantly change the particle sizes; however, it provided a significantly increased binding of siRNA for all types of CaP nanoparticles, as revealed by spectrophotometric measurements analysis. Arginine functionalized HA-n nanoparticles showed the best binding behavior with siRNA among the other nanoparticles due to its high, positive zeta potential (+18.8mV) and high surface area of Ca⁺⁺ rich "c" plane. MTT cytotoxicity assays demonstrated that all the nanoparticles tested herein were biocompatible. Our results suggest that high siRNA entrapment in each of the three modified non-toxic CaP nanoparticles make them promising candidates as a non-viral vector for delivering therapeutic siRNA molecules to treat cancer.

Anticancer activity of drug-loaded calcium phosphate nanocomposites against human osteosarcoma

BACKGROUND

Calcium phosphate (CaP) based nanoparticles are considered to be ideal drug carriers for delivery of anticancer drugs because of their excellent biocompatibility and pH responsiveness. However, CaP nanoparticles have the problems of limited drug load capacity, initial burst release, and short-term release. Thus, we prepared the CaP nanocomposites containing anticancer drug such as caffeic acid (CA-NP), chlorogenic acid (CG-NP), or cisplatin (CP-NP) in the presence of alginate as a polymer template to control the release rate of drugs.

RESULTS

The drug-loaded CaP nanocomposites exhibited spherical shape with a size of under 100 nm and the size of nanocomposites was hardly affected by the addition of drug. UV-visible spectroscopic analysis confirmed the insertion of drug into the CaP nanocomposites. These nanocomposites showed an initial burst release of drug, followed by a prolonged release, in which the release profile of drugs was depended on the solution pH. In addition, the drug-loaded CaP nanocomposites revealed anticancer activity on human osteosarcoma in a manner dependent on concentration of drugs and time.

CONCLUSIONS

The drug-loaded CaP nanocomposites can contribute to the development of a new generation of controlled drug release carriers for chemotherapy of cancers.

Hydroxyapatite bone cement application for the reconstruction of retrosigmoid craniectomy in the treatment of cranial nerves disorders

BACKGROUND

Retromastoid craniectomy (RSC) is a cardinal surgical approach used to access the posterior fossa. Hydroxyapetite bone cement (HBC) is frequently employed for cranioplasty in efforts to prevent cerebrospinal fluid (CSF) leak, whilst maintaining low complication rates and good cosmetic satisfaction. The authors aim to determine the safety and effectiveness of HBC for reconstruction RSC used for treatment of various cranial nerves disorders.

METHODS

The authors conducted a retrospective one-center two surgeons review of 113 patients who underwent RSC filled with HBC for the treatment of cranial nerve disorders. The study period extended from January 2011 through April 2016. Charts were reviewed for documentation of descriptors pertinent to the endpoints described above. Revisions and reoperations were excluded from analysis.

RESULTS

Ninety-three patients met the inclusion criteria; there was one case of postoperative pseudomeningocele, which was considered as CSF leak (1%), 3 (3,2%) superficial infections, and no deep infections. Cosmetic satisfaction was obtained in all but one case (98.9% satisfaction) and long-term incisional pain was problematic in 1 (1.1%) patient. Other complications (serous drainage, headache, ear pain) accounted for three cases (3.2%).

CONCLUSIONS

The application of HBC in the reconstruction of RSC for the treatment of cranial nerves disorders is an effective method, yielding good cosmetic results whilst eliminating CSF leak. Additionally, it is safe due to the lack of deep-seated wound infections with low incidence of chronic incisional pain.

Mussel-inspired poly(L-DOPA)-templated mineralization for calcium phosphate-assembled intracellular nanocarriers

We developed a calcium phosphate (CaP)-assembled polymer nanocarrier for intracellular doxorubicin (DOX) delivery based on a mussel-inspired mineralization approach. A DOX-loaded core-shell polymer nanoparticle (DOX-NP) consisting of a poly(3,4-dihydroxy-l-phenylalanine) (PDOPA) core and a poly (ethylene glycol) (PEG) shell was utilized as a nanotemplate for CaP mineralization. The mean hydrodynamic diameter of the DOX-loaded CaP-mineralized polymer nanoparticles (DOX-CaP-NPs) was 154.3nm. Energy-dispersive X-ray spectroscopy confirmed that the DOX-CaP-NPs contained substantial amounts of Ca and P, elements found only in the CaP mineral. The loading efficiency and content of DOX, estimated by fluorescence spectroscopy, were 54.0% and 10.8wt%, respectively. The CaP deposited in the PDOPA core domain enabled the DOX-CaP-NPs to maintain a robust structure and effectively inhibit DOX release at extracellular pH, whereas at endosomal pH, the CaP core dissolved to trigger a facilitated DOX release. The DOX-CaP-NPs may serve as robust nanocarriers with a high delivery efficacy for cancer chemotherapy.

Functional calcium phosphate composites in nanomedicine

Calcium phosphate (CaP) materials have many peculiar and intriguing properties. In nature, CaP is found in nanostructured form embedded in a soft proteic matrix as the main mineral component of bones and teeth. The extraordinary stoichiometric flexibility, the different stabilities exhibited by its different forms as a function of pH and the highly dynamic nature of its surface ions, render CaP one of the most versatile materials for nanomedicine. This review summarizes some of the guidelines so far emerged for the synthesis of CaP composites in aqueous media that endow the material with tailored crystallinity, morphology, size, and functional properties. First, we introduce very briefly the areas of application of CaP within the nanomedicine field. Then through some selected examples, we review some synthetic routes where the presence of functional units (small templating molecules like surfactants, or oligomers and polymers) assists the synthesis and at the same time impart the functionality or the responsiveness desired for the end-application of the material. Finally, we illustrate two examples from our laboratory, where CaP is decorated by biologically active polymers or prepared within a thermo- and magneto-responsive hydrogel, respectively.

In vitro Growth Pattern of Primary Human Osteoblasts on Calcium Phosphate- and Polymethylmethacrylate-Based Bone Cement

BACKGROUND/PURPOSE

Polymethylmethacrylate (PMMA) and calcium phosphate (Ca-P) cements are widely used for arthroplasty surgery and augmentation of bone defects. However, aseptic implant loosening in absence of wear-induced osteolysis indicates an unfavourable interaction between the cement surface and human osteoblasts. Our underlying hypothesis is that cement surfaces directly modify cell viability, proliferation rate, and cell differentiation.

METHODS

To test this hypothesis, we examined primary human osteoblasts harvested from six individuals. These cells were pooled and subsequently seeded directly on cement pellets prepared from Palacos® R, Palacos® R+G, and Norian® Drillable cements. After incubation for 24 and 72 h, cell viability, proliferation rate, apoptosis rate, and cell differentiation were analysed.

RESULTS

Upon cultivation of human osteoblasts on cement surfaces, we observed a significantly reduced cell viability and DNA content compared to the control. Analysis of the apoptosis rate revealed an increase for cells on Palacos R and Norian Drillable, but a significant decrease on Palacos R+G compared to the control. Regarding osteogenic differentiation, significantly lower values of alkaline phosphatase enzyme activity were identified for all cement surfaces after 24 and 72 h compared to cultivation on tissue culture plastic, serving as control.

CONCLUSIONS

In summary, these data suggest a limited biocompatibility of both PMMA and Ca-P cements, necessitating further research to reduce unfavourable cell-cement interactions and consequently extend implant survival.

Incorporation of silver nanoparticles into magnetron-sputtered calcium phosphate layers on titanium as an antibacterial coating

A three-layer system of nanocrystalline hydroxyapatite (first layer; 1000nm thick), silver nanoparticles (second layer; 1.5μg Ag cm^-2) and calcium phosphate (third layer, either 150 or 1000nm thick) on titanium was prepared by a combination of electrophoretic deposition of silver nanoparticles and the deposition of calcium phosphate by radio frequency magnetron sputtering. Scanning electron microscopy showed that the silver nanoparticles were evenly distributed over the surface. The adhesion of multilayered coating on the substrate was evaluated using the scratch test method. The resistance to cracking and delamination indicated that the multilayered coating has good resistance to contact damage. The release of silver ions from the hydroxyapatite/silver nanoparticle/calcium phosphate system into the phosphate-buffered saline (PBS) solution was measured by atomic absorption spectroscopy (AAS). Approximately one-third of the incorporated silver was released after 3days immersion into PBS, indicating a total release time of the order of weeks. There were no signs of cracks on the surface of the coating after immersion after various periods, indicating the excellent mechanical stability of the multilayered coating in the physiological environment. An antimicrobial effect against Escherichia coli was found for a 150nm thick outer layer of the calcium phosphate using a semi-quantitative turbidity test.

Protein-free formation of bone-like apatite: New insights into the key role of carbonation

The nanometer-sized plate-like morphology of bone mineral is necessary for proper bone mechanics and physiology. However, mechanisms regulating the morphology of these mineral nanocrystals remain unclear. The dominant hypothesis attributes the size and shape regulation to organic-mineral interactions. Here, we present data supporting the hypothesis that physicochemical effects of carbonate integration within the apatite lattice control the morphology, size, and mechanics of bioapatite mineral crystals. Carbonated apatites synthesized in the absence of organic molecules presented plate-like morphologies and nanoscale crystallite dimensions. Experimentally-determined crystallite size, lattice spacing, solubility and atomic order were modified by carbonate concentration. Molecular dynamics (MD) simulations and density functional theory (DFT) calculations predicted changes in surface energy and elastic moduli with carbonate concentration. Combining these results with a scaling law predicted the experimentally observed scaling of size and energetics with carbonate concentration. The experiments and models describe a clear mechanism by which crystal dimensions are controlled by carbonate substitution. Furthermore, the results demonstrate that carbonate substitution is sufficient to drive the formation of bone-like crystallites. This new understanding points to pathways for biomimetic synthesis of novel, nanostructured biomaterials.

The in vitro evolution of resorbable brushite cements: A physico-chemical, micro-structural and mechanical study

The mechanisms by which calcium phosphate bone substitutes evolve and are resorbed in vivo are not yet fully known. In particular, the formation of intermediate phases during resorption and evolution of the mechanical properties may be of crucial interest for their clinical efficiency. The in vitro tests proposed here are the first steps toward understanding these phenomena. Microporous Dicalcium Phosphate Dihydrate (DCPD) samples were immersed in tris(hydroxymethyl)aminomethane (TRIS) and Phosphate Buffered Saline (PBS) solutions, with or without daily refresh of the medium, for time-points up to 14days. Before and after immersion, samples were extensively characterised in terms of morphology, chemistry (XRD coupled with Rietveld analysis), microstructure (X-ray tomography, SEM observations) and local mechanical properties (instrumented micro-indentation). The composition of the immersion solutions was monitored in parallel (pH, elemental analysis). The results show the influence and importance of the experimental set-up and protocol on the formation of apatite and octacalcium phosphate concurrently to DCPD dissolution; moreover, strong inter-correlations between physico-chemistry, microstructure and mechanics are demonstrated.

STATEMENT OF SIGNIFICANCE

Ideally, the resorption kinetics of biodegradable bone substitutes should be controlled to favor the healing processes of bone. Although biodegradable bone grafts are already used in surgeries, their resorption process is still partially unknown. The present work studies these resorption phenomena, their kinetics and mechanisms and their consequences on the properties of a calcium phosphate resorbable material. The original in vitro approach developed in this work couples for the first time physico-chemical, micro-structural and mechanical assessments. The dissolution of the CaP phase in body fluids and the reprecipitation of more stable phases are studied on a local scale, which has permitted to evidence and monitor the development of a gradient of properties between the surface and the core of the samples.

Effects of Electrolyte Concentration on Formation of Calcium Phosphate Films on Ti–6Al–4V by Electrochemical Deposition

Nano-sized calcium phosphate film was formed on Ti–6Al–4V alloy using simple electrochemical deposition. Pre-treatment of Ti–6Al–4V alloy was carried out by galvanostatic treatment step which acted as anchorage for growth of the hydroxyapatite during subsequent pulsed electrochemical deposition process at 40 and 85 °C. The phase and morphologies of deposited calcium phosphate were influenced by the electrolyte temperature and electrolyte ratio (Ca/P). The nano needle-like precipitates were formed under 1.67 Ca/P ratio in solution. The needle-like deposits were transferred to the plate-like precipitates in the case of Ca-deficient or Ca-rich electrolyte.

Calcium phosphate cement enhances the torsional strength and stiffness of high tibial osteotomies

PURPOSE

There has been a resurgence in the use of opening wedge high tibial osteotomy (owHTO). Calcium phosphate cement has been shown to improve strength in compression for augmentation of tibial plateau and owHTO fixation. However, knee kinematics includes a torsional load during ambulation, which is as yet unstudied in this model. The purpose of this paper is to investigate the effect of injectable calcium phosphate cement on the biomechanical stability of standard high tibial osteotomy defect with applied torsional load and ultimate stiffness of the supporting construct.

METHODS

Testing was performed on 22 bone mineral density-matched and age-matched cadaver specimens. Intact specimens were treated with 10° opening wedge osteotomies, identical surgical techniques as clinically used and fixation provided by iBalance© PEEK implant (Arthrex, Naples FL). Nine specimens were augmented with calcium phosphate injectable cement, Quickset (Arthrex Inc., Naples Fl). Constructs were for construct stiffness, torsional loads to failure, and mechanisms of failure. As a gold-standard comparison group, four samples were tested with a titanium, fixed angle device alone: Contourlock plate (Arthrex Inc., Naples Fl).

RESULTS

Peak torque to failure was significantly greater in samples augmented with calcium phosphate bone cement (23.0 ± 9.6 Nm) compared with specimens fixed with PEEK implant alone (18.1 ± 7.3). Construct stiffness in torsion was also significantly improved with bone cement application (349.0 ± 126.8 Nm/°) compared with PEEK implant alone (202.2 ± 153.4 Nm/°) and fixed angle implant system (142.9 ± 74.7 Nm/°).

CONCLUSION

Injectable calcium phosphate cement improves the initial maximal torsional strength and stiffness of high tibial osteotomy construct.

β-pyrophosphate: A potential biomaterial for dental applications

Tooth hypersensitivity is a growing problem affecting both the young and ageing population worldwide. Since an effective and permanent solution is not yet available, we propose a new methodology for the restoration of dental enamel using femtosecond lasers and novel calcium phosphate biomaterials. During this procedure the irradiated mineral transforms into a densified layer of acid resistant iron doped β-pyrophosphate, bonded with the surface of eroded enamel. Our aim therefore is to evaluate this densified mineral as a potential replacement material for dental hard tissue. To this end, we have tested the hardness of β-pyrophosphate pellets (sintered at 1000°C) and its mineral precursor (brushite), the wear rate during simulated tooth-brushing trials and the cytocompatibility of these minerals in powder form. It was found that the hardness of the β-pyrophosphate pellets is comparable with that of dental enamel and significantly higher than dentine while, the brushing trials prove that the wear rate of β-pyrophosphate is much slower than that of natural enamel. Finally, cytotoxicity and genotoxicity tests suggest that iron doped β-pyrophosphate is cytocompatible and therefore could be used in dental applications. Taken together and with the previously reported results on laser irradiation of these materials we conclude that iron doped β-pyrophosphate may be a promising material for restoring acid eroded and worn enamel.

In vitro evaluation of Ag-containing calcium phosphates: Effectiveness of Ag-incorporated β-tricalcium phosphate

Development of bioceramics with antibacterial activity and without cytotoxicity would be beneficial for preventing infection associated with implants. This study aimed to capitalize on the antibacterial properties of silver (Ag) incorporated in or coexisting in metallic form with calcium phosphates (CaPs). The in vitro dissolution behavior, antibacterial activity, and cytotoxicity of Ag-containing CaPs with different phase fractions of hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) were evaluated. The antibacterial activity of Ag-containing CaPs depended on the main phase of CaP, the chemical state of Ag, and the amount of incorporated Ag. Superior antibacterial activity was obtained from sustained release of Ag ions through continuous dissolution of Ag-incorporated β-TCP compared to that obtained for HA coexisting with metallic Ag particles. Ag-containing CaPs did not exhibit any toxic effect on V79 fibroblasts. Thus, these results demonstrated the effectiveness of Ag-incorporated β-TCP in preventing infection, with respect to long-term applications.

Comparative investigations of structure and properties of micro-arc wollastonite-calcium phosphate coatings on titanium and zirconium-niobium alloy

Investigation results of micro-arc wollastonite–calcium phosphate (W–CaP) biocoatings on the pure titanium (Ti) and Zr–1wt.%Nb (Zr–1Nb) alloy were presented. The voltages of 150–300 V generate the micro-arc oxidation (MAO) process with the initial amplitude current of 150–550 A and 100–350 A for Ti and Zr–1Nb substrates, respectively. The identical dependencies of changes of the coating thickness, surface roughness and adhesion strength on the process voltage were revealed for the both substrates. The W–CaP coatings with the thickness of 10–11 μm were formed on Ti and Zr–1Nb under the low process voltage of 130–150 V. Elongated wollastonite particles with the size in the range of 40–100 μm were observed in such coatings. The structure of the coatings on Ti was presented by the X–ray amorphous and crystalline phases. The X–ray reflexes relating to the crystalline phases of Ti and wollastonite were observed only in XRD patterns of the coatings deposited under 130–200 V on Ti. While, the crystalline structure with phases of CaZr₄(PO₄)₆, β–ZrP₂O₇, ZrO₂, and Zr was detected in the coatings on Zr–1Nb. FT–IRS, XRD, SEM, and TEM data confirmed that the increase of the process voltage to 300 V leads to the dissociation of the wollastonite. No toxic effect of specimens on a viability, morphology and motility of human adipose–derived multipotent mesenchymal stem cells was revealed in vitro.

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Investigations of microarc wollastonite–calcium phosphate biocoatings on the titanium and Zr–1wt.%Nb alloy were presented.

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The thin coatings 10–11 μm with wollastonite particles formed under the low process voltage of 130–150 V.

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The increase of the process voltage to 300 V leads to the dissociation of the wollastonite.

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Coatings on both substrates have not toxic effect on the morphofunctional status of AMMSCs culture in vitro.

Harnessing Wharton's jelly stem cell differentiation into bone-like nodule on calcium phosphate substrate without osteoinductive factors

An important aim of bone regenerative medicine is to design biomaterials with controlled chemical and topographical features to guide stem cell fate towards osteoblasts without addition of specific osteogenic factors. Herein, we find that sprayed bioactive and biocompatible calcium phosphate substrates (CaP) with controlled topography induce, in a well-orchestrated manner, Wharton's jelly stem cells (WJ-SCs) differentiation into osteoblastic lineage without any osteogenic supplements. The resulting WJ-SCs commitment exhibits features of native bone, through the formation of three-dimensional bone-like nodule with osteocyte-like cells embedded into a mineralized type I collagen. To our knowledge, these results present the first observation of a whole differentiation process from stem cell to osteocytes-like on a synthetic material. This suggests a great potential of sprayed CaP and WJ-SCs in bone tissue engineering. These unique features may facilitate the transition from bench to bedside and the development of successful engineered bone.

STATEMENT OF SIGNIFICANCE

Designing materials to direct stem cell fate has a relevant impact on stem cell biology and provides insights facilitating their clinical application in regenerative medicine. Inspired by natural bone compositions, a friendly automated spray-assisted system was used to build calcium phosphate substrate (CaP). Sprayed biomimetic solutions using mild conditions led to the formation of CaP with controlled physical properties, good bioactivity and biocompatibility. Herein, we show that via optimization of physical properties, CaP substrate induce osteogenic differentiation of Wharton's jelly stem cells (WJ-SCs) without adding osteogenic supplement factors. These results suggest a great potential of sprayed CaP and WJ-SCs in bone tissue engineering and may facilitate the transition from bench to beside and the development of clinically successful engineered bone.

Nanostructured fusiform hydroxyapatite particles precipitated from aquaculture wastewater

The present work represents a new approach for the isolation of uniform nano particulate hydroxyapatite (HAp). The chemical characterization of a calcium phosphate product obtained from industrial trout farm aquaculture wastewater by two different routes, washing either with a basic aqueous medium (wash_NaOH) or followed by a further washing with ethanol (wash_EtOH), is explored. Characterization of the isolated materials includes morphology studies (SEM and TEM), structural (XRD, electron diffraction), compositional (EDX) and thermogravimetric analysis (TGA). The obtained products are a mixture of different compounds, with hydroxyapatite the predominant phase. The morphology is unusually nanometric size with fusiform shaped particles, such characteristics are ordinarily only obtained by synthetic routes. This process of phosphate precipitation represents a unique self-sufficient process to be compared to conventional chemical or biological practices for precipitating phosphate.

Biodegradable/biocompatible coated metal implants for orthopedic applications

Biocompatible metals have been suggested as revolutionary biomaterials for bone-grafting therapies. Although metals and their alloys are widely and successfully used in producing biomedical implants due to their good mechanical properties and corrosion resistance, they have a lack in bioactivity. Therefore coating of the metal surface with calcium phosphates (CaP) is a benign way to achieve well bioactivity and get controlled corrosion properties. The biocompatibility and bioactivity calcium phosphates (CaP) in bone growth were guided them to biomedical treatment of bone defects and fractures. Many techniques have been used for fabrication of CaP coatings on metal substrates such as magnesium and titanium. The present review will focus on the synthesis of CaP and their relative forms using different techniques especially electrochemical techniques. The latter has always been known of its unique way of optimizing the process parameters that led to a control in the structure and characteristics of the produced materials.

Calcium phosphate-phosphorylated adenosine hybrid microspheres for anti-osteosarcoma drug delivery and osteogenic differentiation

Biocompatibility, biodegradability and bioactivity are significantly important in practical applications of various biomaterials for bone tissue engineering. Herein, we develop a functional inorganic-organic hybrid system of calcium phosphate-phosphorylated adenosine (CPPA). Both calcium phosphate and phosphorylated adenosine molecules in CPPA are fundamental components in mammalians and play important roles in biological metabolism. In this work, we report our three leading research qualities: (1) CPPA hybrid microspheres with hollow and porous structure are synthesized by a facile one-step microwave-assisted solvothermal method; (2) CPPA hybrid microspheres show high doxorubicin loading capacity and pH-responsive drug release properties, and demonstrate positive therapeutic effects on six osteosarcoma cell lines in vitro and a mouse model of 143B osteosarcoma subcutaneous tumor in vivo; (3) CPPA hybrid microspheres are favorable to promote osteogenic differentiation of human bone mesenchymal stem cells (hBMSCs) by activating the AMPK pathway, with satisfactory evidences from cellular alkaline phosphatase staining, alizarin red staining, real time PCR and western analysis. The as-prepared CPPA hybrid microspheres are promising in anti-osteosarcoma and bone regeneration, which simultaneously display excellent properties on drug delivery and osteogenic differentiation of hBMSCs.

Guided growth of auditory neurons: Bioactive particles towards gapless neural - electrode interface

Cochlear implant (CI) is a successful device to restore hearing. Despite continuous development, frequency discrimination is poor in CI users due to an anatomical gap between the auditory neurons and CI electrode causing current spread and unspecific neural stimulation. One strategy to close this anatomical gap is guiding the growth of neuron dendrites closer to CI electrodes through targeted slow release of neurotrophins. Biodegradable calcium phosphate hollow nanospheres (CPHSs) were produced and their capacity for uptake and release of neurotrophins investigated using ¹²⁵I-conjugated glia cell line-derived neurotrophic factor (GDNF). The CPHSs were coated onto CI electrodes and loaded with neurotrophins. Axon guidance effect of slow-released neurotrophins from the CPHSs was studied in an in vitro 3D culture model. CPHS coating bound and released GDNF with an association rate constant 6.3 × 10³ M^-1s^-1 and dissociation rate 2.6 × 10^-5 s^-1, respectively. Neurites from human vestibulocochlear ganglion explants found and established physical contact with the GDNF-loaded CPHS coating on the CI electrodes placed 0.7 mm away. Our results suggest that neurotrophin delivery through CPHS coating is a plausible way to close the anatomical gap between auditory neurons and electrodes. By overcoming this gap, selective neural activation and the fine hearing for CI users become possible.

In vivo comparison of biomineralized scaffold-directed osteogenic differentiation of human embryonic and mesenchymal stem cells

Human pluripotent stem cells such as embryonic stem cells (hESCs) and multipotent stem cells like mesenchymal stem cells (hMSCs) hold great promise as potential cell sources for bone tissue regeneration. Comparing the in vivo osteogenesis of hESCs and hMSCs by biomaterial-based cues provides insight into the differentiation kinetics of these cells as well as their potential to contribute to bone tissue repair in vivo. Here, we compared in vivo osteogenic differentiation of hESCs and hMSCs within osteoinductive calcium phosphate (CaP)-bearing biomineralized scaffolds that recapitulate a bone-specific mineral microenvironment. Both hESCs and hMSCs underwent osteogenic differentiation responding to the biomaterial-based instructive cues. Furthermore, hMSCs underwent earlier in vivo osteogenesis compared to hESCs, but both stem cell types acquired a similar osteogenic maturation by 8 weeks of implantation.

Timelines of the "free-particle" and "fixed-particle" models of stone-formation: theoretical and experimental investigations

Two major theories on renal stone formation will be reviewed, the “free-particle” and “fixed-particle” mechanisms. These theories combine data on intrinsic factors (inborn metabolic errors), extrinsic factors (diet), renal cell responses and the physico-chemistry and biochemistry of urine into mechanisms of stone formation. This paper describes the specific role of time in both mechanisms. The timeline of crystal- and stone formation was deducted from literature data and was measured for two stones using radioisotope decay analysis. The stones of similar size and composition showed, respectively, a timeline of a few years and a development that took decades. In combination with data on stone architecture and patient characteristics these timelines are explained using the free-particle and fixed-particle mechanisms. Consideration of the timeline of stone formation has clinical implications. We conclude that the fixed-particle mechanism can be a slow process where decades pass between the first formation of a precipitate in the renal interstitium and the clinical presentation of the stone. Added to the fact that the mechanism of this initial precipitation is still ill defined, the conditions that started fixed-particle stone formation in an individual patient can be obscure. Blood and urine analysis in such patients does not necessarily reveal the individual’s risk for recurrence as lifestyle may have changed over time. This is in fact what defines the so-called idiopathic stoneformers. For these patients, prevention of outgrowth of previously formed precipitates, papillary plaques, may be more relevant than prevention of new plaque formation. In contrast, a patient who has formed a stone in a relatively short time through the free-particle mechanism is more likely to show abnormal values in blood and urine that explain the starting event of stone formation. In these patients, measurement of such values provides useful information to guide preventive measures.