The effect of hydroxyapatite nanocrystals on microvascular endothelial cell viability and functions

Heparin-Loaded Composite Coatings on Porous Stent from Pure Magnesium for Biomedical Applications

Challenges associated with drug-releasing stents used in percutaneous transluminal coronary angioplasty (PTCA) encompass allergic reactions, prolonged endothelial dysfunction, and delayed stent clotting. Although absorbable stents made from magnesium alloys seem promising, fast in vivo degradation and poor biocompatibility remain major challenges. In this study, zirconia (ZrO2) layers were used as the foundational coat, while calcium phosphate (CaP) served as the surface layer on unalloyed magnesium specimens. Consequently, the corrosion current density was decreased to 3.86, from 13.3 μA/cm2. Moreover, a heparin-controlled release mechanism was created by co-depositing CaP, gelatin (Gel), and heparin (Hep) on the specimens coated with CaP/ZrO2, thereby boosting magnesium's blood compatibility and prolonging the heparin-releasing time. Techniques like X-ray diffractometry (XRD), focused ion beam (FIB) system, toluidine blue testing, UV-visible spectrometry, field emission scanning electron microscopy (FESEM), and surrogate tests for endothelial cell viability were employed to examine the heparin-infused coatings. The drug content rose to 484.19 ± 19.26 μg/cm2 in multi-layered coatings (CaP-Gel-Hep/CaP-Hep/CaP/ZrO2) from 243.56 ± 55.18 μg/cm2 in a single layer (CaP-Hep), with the controlled release spanning beyond 28 days. Also, cellular viability assessments indicated enhanced biocompatibility of the coated samples relative to those without coatings. This suggests the potential of magnesium samples after coating ZrO2 and CaP with Gel as candidates for porous biodegradable stents or even scaffolds in biomedical applications.

Non-viral gene therapy using RNA interference with PDGFR-α mediated epithelial-mesenchymal transformation for proliferative vitreoretinopathy

Fibrotic eye diseases, a series of severe oculopathy, that will destroy normal ocular refractive media and imaging structures. It is characterized by the transformation of the epithelial cells into mesenchyme cells. Proliferative vitreoretinopathy (PVR) is one of these representative diseases. In this investigation, polyethylene glycol grafted branched Polyethyleneimine (PEI-g-PEG) was used as a non-viral gene vector in gene therapy of PVR to achieve anti-fibroblastic effects in vitro and in vivo by interfering with platelet-derived growth factor alpha receptor (PDGFR-α) in the epithelial-mesenchymal transition (EMT) of retinal pigment epithelium (RPE) cells. The plasmid was wrapped by electrostatic conjugation. Physical characterization of the complexes indicated that the gene complexes were successfully prepared. In vitro, cellular experiments showed excellent biocompatibility of PEI-g-PEG, efficient cellular uptake of the gene complexes, and successful expression of the corresponding fragments. Through gene silencing technique, PEI-g-PEG/PDGFR-α shRNA successfully inhibited the process of EMT in vitro. Furthermore, in vivo animal experiments suggested that this method could effectively inhibit the progression of fibroproliferative membranes of PVR. Herein, a feasible and promising clinical idea was provided for developing non-viral gene vectors and preventing fibroblastic eye diseases by RNA interference (RNAi) technology.

Corrosion of Stirred Electrochemical Nano-Crystalline Hydroxyapatite (HA) Coatings on Ti6Al4V

Ti6Al4V substrates were electrochemically deposited with nano-crystalline hydroxyapatite (HA) from aqueous electrolytes. Cathodic HA coatings were obtained when the electrolyte was stirred using ultrasonic vibration. Two current densities of 20 mA/cm² and 50 mA/cm² were employed. Polarization and electrochemical impedance spectroscopy (EIS) were the techniques used to estimate the corrosion of coatings in simulated body fluid (SBF). The results indicate good corrosion resistance for the coating obtained at 50 mA/cm² from ultrasonic stirring of the electrolyte.

Combination of Nanocrystalline Hydroxyapatite and Injectable Platelet-Rich Fibrin on Bone Graft Materials for Alveolar Bone Preservation

Alveolar bone resorption is one of post-extraction complications with a reduction in the dimensions and quality of the alveolar bone, which will make it challenging to install dental implants in the future. The resorption can be prevented by preserving the alveolar bone using bone grafts. Nanocrystalline hydroxyapatite (HA) is a widely developed material as a bone graft. However, there are still some limitations because it only has osteoconductive properties. The addition of injectable platelet-rich fibrin to HA can increase this material’s osteoinductive, antibacterial, and anti-inflammatory properties, making it suitable for use as bone graft material for the preservation of alveolar bone.

Cell-Material Interactions in Direct Contact Culture of Endothelial Cells on Biodegradable Iron-Based Stents Fabricated by Laser Powder Bed Fusion and Impact of Ion Release

Additive manufacturing is a promising technology for the fabrication of customized implants with complex geometry. The objective of this study was to investigate the initial cell-material interaction of degradable Fe-30Mn-1C-0.02S stent structures in comparison to conventional 316L as a reference, both processed by laser powder bed fusion. FeMn-based alloys have comparable mechanical properties with clinically applied AISI 316L for a corrosion-resistant stent material. Different corrosion stages of the as-built Fe-30Mn-1C-0.02S stent surfaces were simulated by pre-conditioning in DMEM under cell culture conditions for 2 h, 7 days, and 28 days. Human umbilical vein endothelial cells (HUVECs) were directly seeded onto the pre-conditioned samples, and cell viability, adherence, and morphology were analyzed. These studies were accompanied by measurements of iron and manganese ion release and Auger electron spectroscopy to evaluate the influence of corrosion products and degradation on the cells. In the initial phase (2 h of pre-conditioning), HUVECs were able to attach but the cell number decreased over the cultivation period of 14 days and the CD31 staining pattern of intercellular contacts was disordered. At later time points of corrosion (7 and 28 days of pre-conditioning), CD31 staining was distinctly located at the intercellular contacts, and the cell density increased after seeding and was stable for up to 14 days. Formation of a complex degradation layer, which had a composition and thickness dependent on the pre-conditioning time, led to a reduced ion release and finally showed a positive effect on cell survival. Concluding, our data suggest the suitability of Fe-30Mn-1C-0.02S for in vivo applications.

Novel nanosystems to enhance biological activity of hydroxyapatite against dental caries

This work aimed to study for the first time to our knowledge the influence of the structure of the dental flosses (DF) coated by hydroxyapatite nanoparticles (HAP NPs) on the biological performance of saliva probiotic bacteria (S. salivarius), and human dermal and osteoblast-like cells. We used three types of HAP@DF composites (based on two unwaxed dental flosses - "fluffy" and "smooth", and one waxed "smooth") with different morphologies. Obtained composites were characterized from the point of view of their structure, morphological characteristics, elemental and chemical composition. We observed that HAP NPs coated "smooth" dental flosses led to an increase of viability and proliferation of oral cavity probiotic bacteria (Streptococcus salivarius) and human cells (dermal fibroblasts and osteoblast-like). In contrast, the highest viability loss of probiotic bacteria (S. salivarius), fibroblasts, and osteoblast-like cells were observed for "fluffy" unwaxed dental flosses due to high cytotoxicity. Our studies showed that HAP NPs significantly improved the biological properties of "fluffy" dental floss. Pristine "smooth" DFs (waxed and unwaxed), as well as all HAP-coated DFs, induced acceptable biocompatibility toward selected human cells.

Electrodeposited Hydroxyapatite-Based Biocoatings: Recent Progress and Future Challenges

Hydroxyapatite has become an important coating material for bioimplants, following the introduction of synthetic HAp in the 1950s. The HAp coatings require controlled surface roughness/porosity, adequate corrosion resistance and need to show favorable tribological behavior. The deposition rate must be sufficiently fast and the coating technique needs to be applied at different scales on substrates having a diverse structure, composition, size, and shape. A detailed overview of dry and wet coating methods is given. The benefits of electrodeposition include controlled thickness and morphology, ability to coat a wide range of component size/shape and ease of industrial processing. Pulsed current and potential techniques have provided denser and more uniform coatings on different metallic materials/implants. The mechanism of HAp electrodeposition is considered and the effect of operational variables on deposit properties is highlighted. The most recent progress in the field is critically reviewed. Developments in mineral substituted and included particle, composite HAp coatings, including those reinforced by metallic, ceramic and polymeric particles; carbon nanotubes, modified graphenes, chitosan, and heparin, are considered in detail. Technical challenges which deserve further research are identified and a forward look in the field of the electrodeposited HAp coatings is taken.

Histological Evaluation of a New Beta-Tricalcium Phosphate/Hydroxyapatite/Poly (1-Lactide-Co-Caprolactone) Composite Biomaterial in the Inflammatory Process and Repair of Critical Bone Defects

Background: The use of biomaterials is commonplace in dentistry for bone regeneration. The aim of this study was to evaluate the performance of a new alloplastic material for bone repair in critical defects and to evaluate the extent of the inflammatory process. Methods: Forty-five New Zealand rabbits were divided into five groups according to evaluation time (7, 14, 30, 60, 120 days), totaling 180 sites with six-millimeter diameter defects in their tibiae. The defects were filled with alloplastic material consisting of poly (lactide-co-caprolactone), beta-tricalcium phosphate, hydroxyapatite and nano-hydroxyapatite (BTPHP) in three different presentations: paste, block, and membrane. Comparisons were established with reference materials, such as Bio-ossTM, Bio-oss CollagenTM, and Bio-gideTM, respectively. The samples were HE-stained and evaluated for inflammatory infiltrate (scored for intensity from 0 to 3) and the presence of newly formed bone at the periphery of the defects. Results: Greater bone formation was observed for the alloplastic material and equivalent inflammatory intensity for both materials, regardless of evaluation time. At 30 days, part of the synthetic biomaterial, regardless of the presentation, was resorbed. Conclusions: We concluded that this novel alloplastic material showed osteoconductive potential, biocompatibility, low inflammatory response, and gradual resorption, thus an alternative strategy for guided bone regeneration.

Bioactive and mechanically stable hydroxyapatite patterning for rapid endothelialization of artificial vascular graft

Polymeric vascular grafts have been widely used in the vascular regeneration field because of their ease of application. However, synthetic polymer grafts have the severe problem of low biocompatibility, which may cause delayed endothelialization and hyperplasia. In this study, we fabricated a linear hydroxyapatite (HA) pattern on a silicon wafer and then transferred the pattern to a poly(L-lactic)-acid (PLLA) film for use as a tubular vascular graft. The HA pattern with its characteristic needle-like shape was successfully embedded into the PLLA. The HA-patterned PLLA film exhibited superior mechanical stability compared with that of a HA-coated PLLA film under bending, elongation, and in vitro circulation conditions, suggesting its suitability for use as a tubular vascular graft. In addition, the HA pattern guided rapid endothelialization by promoting proliferation of endothelial cells and their migration along the pattern. The hemocompatibility of the HA-patterned PLLA was also confirmed, with substantially fewer platelets adhered on its surface. Overall, in addition to good mechanical stability, the HA-patterned PLLA exhibited enhanced biocompatibility and hemocompatibility compared with pure PLLA.

Bioinspired calcium phosphate mineralization on Net-Shape-Nonwoven chitosan scaffolds stimulates human bone marrow stromal cell differentiation

Chitosan fibers were processed using the Net-Shape-Nonwoven (NSN) technique in order to create porous scaffolds which were functionalized in two bioinspired ways: collagen type I coating and unique mineralization with organically modified hydroxyapatite (ormoHAP). While collagen is common to enhance cell attachment on surfaces, the electric-field assisted migration and deposition of ormoHAP on the surface of the NSN-scaffolds is a novel technique which enables sub-micrometer sized mineralization while maintaining the original pore structure. Microscopy revealed fast attachment and morphological adaptation of the cells on both, the pure and the functionalized NSN-scaffolds. Remarkably, the cell number of osteogenically induced hBMSC on ormoHAP-modified NSN-scaffolds increased 3.5-5 fold compared to pure NSN-scaffolds. Osteogenic differentiation of hBMSC/osteoblasts was highest on collagen-functionalized NSN-scaffolds. RT-PCR studies revealed gene expression of ALP, BSP II, and osteocalcin to be high for all NSN-scaffolds. Overall, the NSN-scaffold functionalization with collagen and ormoHAP improved attachment, proliferation, and differentiation of hBMSC and therefore revealed the remarkable potential of their application for the tissue engineering of bone.

Differential effect of hydroxyapatite nano-particle versus nano-rod decorated titanium micro-surface on osseointegration

Coating materials applied for intraosseous implants must be optimized to stimulate osseointegration. Osseointegration is a temporal and spatial physiological process that not only requires interactions between osteogenesis and angiogenesis but also necessitates a favorable immune microenvironment. It is now well-documented that hierarchical nano-micro surface structures promote the long-term stability of implants, the interactions between nano-micro structure and the immune response are largely unknown. Here, we report the effects of microporous titanium (Ti) surfaces coated with nano-hydroxyapatite (HA) produced by micro-arc oxidation and steam-hydrothermal treatment (SHT) on multiple cell behavior and osseointegration. By altering the processing time of SHT it was possible to shift HA structures from nano-particles to nano-rods on the microporous Ti surfaces. Ti surfaces coated with HA nano-particles were found to modulate the inflammatory response resulting in an osteoimmune microenvironment more favorable for osteo-/angio-genesis, most likely via the activation of certain key signaling pathways (TGF-β, OPG/RANKL, and VEGF). By contrast, Ti surfaces coated with nano-rod shaped HA particles had a negative impact on osteo-/angio-genesis and osteoimmunomodulation. In vivo results further demonstrated that Ti implant surfaces decorated with HA nano-particles can stimulate new bone formation and osseointegration with enhanced interaction between osteocytes and implant surfaces. This study demonstrated that Ti implants with micro-surfaces coated with nano-particle shaped HA have a positive impact on osseointegration.

STATEMENT OF SIGNIFICANCE

Osteo-/angio-genesis are of importance during osteointegration of the implants. Recent advances unravel that immune response of macrophages and its manipulated osteoimmunomodulation also exerts a pivotal role to determine the fate of the implant. Surface nano-micro modification has evidenced to be efficient to influence osteogenesis, however, little is known links nano-microstructured surface to immune response, as well the osteoimmunomodulation. This study demonstrates that the nano-particles decorated micro-surface, compared with the nano-rods decorated micro-surface enables osteogenesis and angiogenesis concurrently that has not been investigated previously. This study also unravels that the immune response of macrophages can be manipulated by the nano-micro surface, especially the nano-dimension matters, leading to a differential effect on osteointegration. The additional knowledge obtained from this study may provide foundation and reference for future design of the coating materials for implantable materials.

Vascular biosafety of commercial hydroxyapatite particles: discrepancy between blood compatibility assays and endothelial cell behavior

BACKGROUND

Vascular homeostasis is ensured by a dynamic interplay involving the endothelium, the platelets and the coagulation system. Thus, the vascular safety of particulate materials must address this integrated system, an approach that has been largely neglected. This work analysed the effects of commercial hydroxyapatite (HA) particles in blood compatibility and in endothelial cell behavior, due to their clinical relevance and scarcity of data on their vascular biosafety.

RESULTS

Particles with similar chemical composition and distinct size and morphology were tested, i.e. rod-like, nano dimensions and low aspect ratio (HAp1) and needle-shape with wider size and aspect ratio (HAp2). HAp1 and HAp2, at 1 to 10 mg/mL, did not affect haemolysis, platelet adhesion, aggregation and activation, or the coagulation system (intrinsic and extrinsic pathways), although HAp2 exhibited a slight thrombogenic potential at 10 mg/mL. Notwithstanding, significantly lower levels presented dose-dependent toxicity on endothelial cells' behavior. HAp1 and HAp2 decreased cell viability at levels ≥ 250 and ≥ 50 μg/mL, respectively. At 10 and 50 μg/mL, HAp1 did not interfere with the F-actin cytoskeleton, apoptotic index, cell cycle progression, expression of vWF, VECad and CD31, and the ability to form a network of tubular-like structures. Comparatively, HAp2 caused dose-dependent toxic effects in these parameters in the same concentration range.

CONCLUSION

The most relevant observation is the great discrepancy of HA particles' levels that interfere with the routine blood compatibility assays and the endothelial cell behavior. Further, this difference was also found to be dependent on the particles' size, morphology and aspect ratio, emphasizing the need of a complementary biological characterization, taking into consideration the endothelial cells' functionality, to establish the vascular safety of particulate HA.

A multifaceted coating on titanium dictates osteoimmunomodulation and osteo/angio-genesis towards ameliorative osseointegration

A multifaceted coating for hard tissue implants, with favorable osteogenesis, angiogenesis, and osteoimmunomodulation abilities, would be of great value since it could improve osseointegration and alleviate prosthesis loosening. However, to date there are few coatings that fully satisfy these criteria. Herein we describe a microporous TiO₂ coating decorated with hydroxyapatite (HA) nanoparticles that is generated by micro-arc oxidation of pure titanium (Ti) and followed annealing. By altering the annealing temperature, it is possible to simultaneously tune the coating's physical (morphology and wettability) and chemical (composites and crystallinity) properties. A coating produced with micro-arc oxidization (MAO) with an annealing temperature of 650 °C (MAO-650) exhibits numerous favorable physicochemical properties, such as hybrid micro-nano morphology, superhydrophilicity, and highly crystalline HA nanoparticles. In vitro experiments reveal that the MAO-650 coating not only supports proliferation and differentiation of both osteoblasts and endothelial cells, but also inhibits the inflammatory response of macrophages and enables a favorable osteoimmunomodulation to facilitate osteo/angio-genesis. In vivo evaluation mirrors these results, and shows that the MAO-650 coating results in ameliorative osseointegration when compared with the pristine MAO coating. These data highlight the profound effect of surface physicochemical properties on the regulation of osteo/angio-genesis and osteoimmunomodulation in the enhancement of osseointegration.

Interaction of hydroxyapatite nanoparticles with endothelial cells: internalization and inhibition of angiogenesis in vitro through the PI3K/Akt pathway

Nano-hydroxyapatite (nano-HAP) has been proposed as a better candidate for bone tissue engineering; however, the interactions of nano-HAP with endothelial cells are currently unclear. In this study, HAP nanoparticles (HANPs; 20 nm np20 and 80 nm np80) and micro-sized HAP particles (m-HAP; 12 μm) were employed to explore and characterize cellular internalization, subcellular distribution, effects of HANPs on endothelial cell function and underlying mechanisms using human umbilical vein endothelial cells (HUVECs) as an in vitro model. It was found that HANPs were able to accumulate in the cytoplasm, and both adhesion and uptake of the HANPs followed a function of time; compared to np80, more np20 had been uptaken at the end of the observation period. HANPs were mainly uptaken via clathrin- and caveolin-mediated endocytosis, while macropinocytosis was the main pathway for m-HAP uptake. Unexpectedly, exposure to HANPs suppressed the angiogenic ability of HUVECs in terms of cell viability, cell cycle, apoptosis response, migration and capillary-like tube formation. Strikingly, HANPs reduced the synthesis of nitric oxide (NO) in HUVECs, which was associated with the inhibition of phosphatidylinositol 3-kinase (PI3K) and phosphorylation of eNOS. These findings provide additional insights into specific biological responses as HANPs interface with endothelial cells.

Extrusion-based 3D printing of poly(propylene fumarate) scaffolds with hydroxyapatite gradients

The primary focus of this work is to present the current challenges of printing scaffolds with concentration gradients of nanoparticles with an aim to improve the processing of these scaffolds. Furthermore, we address how print fidelity is related to material composition and emphasize the importance of considering this relationship when developing complex scaffolds for bone implants. The ability to create complex tissues is becoming increasingly relevant in the tissue engineering community. For bone tissue engineering applications, this work demonstrates the ability to use extrusion-based printing techniques to control the spatial deposition of hydroxyapatite (HA) nanoparticles in a 3D composite scaffold. In doing so, we combined the benefits of synthetic, degradable polymers, such as poly(propylene fumarate) (PPF), with osteoconductive HA nanoparticles that provide robust compressive mechanical properties. Furthermore, the final 3D printed scaffolds consisted of well-defined layers with interconnected pores, two critical features for a successful bone implant. To demonstrate a controlled gradient of HA, thermogravimetric analysis was carried out to quantify HA on a per-layer basis. Moreover, we non-destructively evaluated the tendency of HA particles to aggregate within PPF using micro-computed tomography (μCT). This work provides insight for proper fabrication and characterization of composite scaffolds containing particle gradients and has broad applicability for future efforts in fabricating complex scaffolds for tissue engineering applications.

The role of angiogenesis in implant dentistry part I: Review of titanium alloys, surface characteristics and treatments

Background

Angiogenesis plays an important role in osseointegration process by contributing to inflammatory and regenerative phases of surrounding alveolar bone. The present review evaluated the effect of titanium alloys and their surface characteristics including: surface topography (macro, micro, and nano), surface wettability/energy, surface hydrophilicity or hydrophobicity, surface charge, and surface treatments of dental implants on angiogenesis events, which occur during osseointegration period.

Material and Methods

An electronic search was performed in PubMed, MEDLINE, and EMBASE databases via OVID using the keywords mentioned in the PubMed and MeSH headings regarding the role of angiogenesis in implant dentistry from January 2000-April 2014.

Results

Of the 2,691 articles identified in our initial search results, only 30 met the inclusion criteria set for this review. The hydrophilicity and topography of dental implants are the most important and effective surface characteristics in angiogenesis and osteogenesis processes. The surface treatments or modifications of dental implants are mainly directed through the enhancement of biological activity and functionalization in order to promote osteogenesis and angiogenesis, and accelerate the osseointegration procedure.

Conclusions

Angiogenesis is of great importance in implant dentistry in a manner that most of the surface characteristics and treatments of dental implants are directed toward creating a more pro-angiogenic surface on dental implants. A number of studies discussed the effect of titanium alloys, dental implant surface characteristic and treatments on agiogenesis process. However, clinical trials and in-vivo studies delineating the mechanisms of dental implants, and their surface characteristics or treatments, action in angiogenesis processes are lagging.

Key words:Angiogenesis, dental implant, osseointergration.

The role of angiogenesis in implant dentistry part II: The effect of bone-grafting and barrier membrane materials on angiogenesis

BACKGROUND

In implant dentistry, bone substitute materials and barrier membranes are used in different treatments including guided bone regeneration (GBR), socket preservation, alveolar ridge augmentation, maxillary sinus elevation, and filling bony defects around the inserted dental implant. One of the most important factors in prognosis of treatments using these materials is the growth of new blood vessels in applied areas. Present review was performed to evaluate the effect of the bone-grafting and barrier membrane materials on angiogenesis events.

MATERIAL AND METHODS

An electronic search was performed in PubMed, MEDLINE, and EMBASE databases via OVID using the keywords mentioned in the PubMed and MeSH headings regarding the role of angiogenesis in implant dentistry from January 2000-April 2014.

RESULTS

Of the 5,622 articles identified in our initial search results, only 33 met the inclusion criteria set for this review. Among bone substitute materials the autogenous bone-grafts, and among the barrier membranes the collagenous membranes, had the highest angiogenic potentials. Other bone-grafting materials or membranes were mostly used with pro-angiogenic factors to enhance their angiogenic properties.

CONCLUSIONS

Angiogenesis is one of the key factors, which plays a critical role in success rate of GBR technique and is seriously considered in manufacturing bone-grafting and barrier membrane materials. However, there is still lack of clinical and in-vivo studies addressing the effect of angiogenesis in treatments using bone-grafting and barrier membrane materials.

Fabrication, Properties and Applications of Dense Hydroxyapatite: A Review

In the last five decades, there have been vast advances in the field of biomaterials, including ceramics, glasses, glass-ceramics and metal alloys. Dense and porous ceramics have been widely used for various biomedical applications. Current applications of bioceramics include bone grafts, spinal fusion, bone repairs, bone fillers, maxillofacial reconstruction, etc. Amongst the various calcium phosphate compositions, hydroxyapatite, which has a composition similar to human bone, has attracted wide interest. Much emphasis is given to tissue engineering, both in porous and dense ceramic forms. The current review focusses on the various applications of dense hydroxyapatite and other dense biomaterials on the aspects of transparency and the mechanical and electrical behavior. Prospective future applications, established along the aforesaid applications of hydroxyapatite, appear to be promising regarding bone bonding, advanced medical treatment methods, improvement of the mechanical strength of artificial bone grafts and better in vitro/in vivo methodologies to afford more particular outcomes.

Microfluidic vascularized bone tissue model with hydroxyapatite-incorporated extracellular matrix

Current in vitro systems mimicking bone tissues fail to fully integrate the three-dimensional (3D) microvasculature and bone tissue microenvironments, decreasing their similarity to in vivo conditions. Here, we propose 3D microvascular networks in a hydroxyapatite (HA)-incorporated extracellular matrix (ECM) for designing and manipulating a vascularized bone tissue model in a microfluidic device. Incorporation of HA of various concentrations resulted in ECM with varying mechanical properties. Sprouting angiogenesis was affected by mechanically modulated HA-extracellular matrix interactions, generating a model of vascularized bone microenvironment. Using this platform, we observed that hydroxyapatite enhanced angiogenic properties such as sprout length, sprouting speed, sprout number, and lumen diameter. This new platform integrates fibrin ECM with the synthetic bone mineral HA to provide in vivo-like microenvironments for bone vessel sprouting.

Biodegradable Materials for Bone Repair and Tissue Engineering Applications

This review discusses and summarizes the recent developments and advances in the use of biodegradable materials for bone repair purposes. The choice between using degradable and non-degradable devices for orthopedic and maxillofacial applications must be carefully weighed. Traditional biodegradable devices for osteosynthesis have been successful in low or mild load bearing applications. However, continuing research and recent developments in the field of material science has resulted in development of biomaterials with improved strength and mechanical properties. For this purpose, biodegradable materials, including polymers, ceramics and magnesium alloys have attracted much attention for osteologic repair and applications. The next generation of biodegradable materials would benefit from recent knowledge gained regarding cell material interactions, with better control of interfacing between the material and the surrounding bone tissue. The next generations of biodegradable materials for bone repair and regeneration applications require better control of interfacing between the material and the surrounding bone tissue. Also, the mechanical properties and degradation/resorption profiles of these materials require further improvement to broaden their use and achieve better clinical results.

Dual-phase osteogenic and vasculogenic engineered tissue for bone formation

Minimally invasive, injectable bone tissue engineering therapies offer the potential to facilitate orthopedic repair procedures, including in indications where enhanced bone regeneration is needed for complete healing. In this study, we developed a dual-phase tissue construct consisting of osteogenic (Osteo) and vasculogenic (Vasculo) components. A modular tissue engineering approach was used to create collagen/fibrin/hydroxyapatite (COL/FIB/HA) hydrogel microbeads containing embedded human bone marrow-derived mesenchymal stem cells (bmMSC). These microbeads were predifferentiated toward the osteogenic lineage in vitro for 14 days, and they were then embedded within a COL/FIB vasculogenic phase containing a coculture of undifferentiated bmMSC and human umbilical vein endothelial cells (HUVEC). In vitro studies demonstrated homogenous dispersion of microbeads within the outer phase, with endothelial network formation around the microbeads over 14 days in the coculture conditions. Subcutaneous injection into immunodeficient mice was used to investigate the ability of dual-phase (Osteo+Vasculo) and control (Osteo, Vasculo, Blank) constructs to form neovasculature and ectopic bone. Laser Doppler imaging demonstrated blood perfusion through all constructs at 1, 4, and 8 weeks postimplantation. Histological quantification of total vessel density showed no significant differences between the conditions. Microcomputed tomography indicated significantly higher ectopic bone volume (BV) in the Osteo condition at 4 weeks. At 8 weeks both the Osteo and Blank groups exhibited higher BV compared to the Vasculo and dual Osteo+Vasculo groups. These data not only show that osteogenic microbeads can be used to induce ectopic bone formation, but also suggest an inhibitory effect on BV when undifferentiated bmMSC and HUVEC were included in dual-phase constructs. This work may lead to improved methods for engineering vascularized bone tissue, and to injectable therapies for the treatment of orthopedic pathologies in which bone regeneration is delayed or prevented.

Effects of hydroxyapatite on endothelial network formation in collagen/fibrin composite hydrogels in vitro and in vivo

Co-culture of endothelial cells (EC) and mesenchymal stem cells (MSC) results in robust vascular network formation in constrained 3-D collagen/fibrin (COL/FIB) composite hydrogels. However, the ability to form endothelial networks is lost when such gels are allowed to compact via cell-mediated remodeling. In this study, we created co-cultures of human EC and human MSC in both constrained and unconstrained COL/FIB matrices and systematically added nanoparticulate hydroxyapatite (HA, 0-20 mg ml(-1)), a bone-like mineral that has been shown to have pro-vasculogenic effects. Constructs cultured for 7 days were assayed for gel compaction, vascular network formation, and mechanical properties. In vitro, robust endothelial network formation was observed in constrained COL/FIB constructs without HA, but this response was significantly inhibited by addition of 5, 10, or 20 mg ml(-1) HA. In unconstrained matrices, network formation was abolished in pure COL/FIB constructs but was rescued by 1.25 or 2.5 mg ml(-1) HA, while higher levels again inhibited vasculogenesis. HA inhibited gel compaction in a dose-dependent manner, which was not correlated to endothelial network formation. HA affected initial stiffness of the gels, but gel remodeling abrogated this effect. Subcutaneous implantation of COL/FIB with 0, 2.5 or 2 0mg ml(-1) HA in the mouse resulted in increased perfusion at the implant site, with no significant differences between materials. Histology at day 7 showed both host and human CD31-stained vasculature infiltrating the implants. These findings are relevant to the design of materials and scaffolds for orthopedic tissue engineering, where both vasculogenesis and formation of a mineral phase are required for regeneration.

Evaluating the toxicity of hydroxyapatite nanoparticles in catfish cells and zebrafish embryos

The toxicity of needle-(nHA-ND) and rod-shaped (nHA-RD) hydroxyapatite (HA) nanoparticles is evaluated in vitro on catfish B-cells (3B11) and catfish T-cells (28s.3) and in vivo on zebrafish embryos to determine if biological effects are similar to the effects seen in mammalian in vitro systems. Neither nHA-ND nor nHA-RD affect cell viability at concentrations of 10 to 300 μg mL(-1) . However, 30 μg mL(-1) needle-shaped nHA lower metabolic activity of the cells. Axial deformations are seen in zebrafish exposed to 300 μg mL(-1) needle shaped nHA after 120 h. For the first time, nHA is reported to cause zebrafish hatching delay. The lowest concentration (3 μg mL(-1) ) of both types of nHA cause the highest hatching inhibition and needle-shaped nHA exposed zebrafish exhibit the lowest hatch at 72 h post fertilization.

Enhancing the bioactivity of Poly(lactic-co-glycolic acid) scaffold with a nano-hydroxyapatite coating for the treatment of segmental bone defect in a rabbit model

PURPOSE

Poly(lactic-co-glycolic acid) (PLGA) is excellent as a scaffolding matrix due to feasibility of processing and tunable biodegradability, yet the virgin scaffolds lack osteoconduction and osteoinduction. In this study, nano-hydroxyapatite (nHA) was coated on the interior surfaces of PLGA scaffolds in order to facilitate in vivo bone defect restoration using biomimetic ceramics while keeping the polyester skeleton of the scaffolds.

METHODS

PLGA porous scaffolds were prepared and surface modification was carried out by incubation in modified simulated body fluids. The nHA coated PLGA scaffolds were compared to the virgin PLGA scaffolds both in vitro and in vivo. Viability and proliferation rate of bone marrow stromal cells of rabbits were examined. The constructs of scaffolds and autogenous bone marrow stromal cells were implanted into the segmental bone defect in the rabbit model, and the bone regeneration effects were observed.

RESULTS

In contrast to the relative smooth pore surface of the virgin PLGA scaffold, a biomimetic hierarchical nanostructure was found on the surface of the interior pores of the nHA coated PLGA scaffolds by scanning electron microscopy. Both the viability and proliferation rate of the cells seeded in nHA coated PLGA scaffolds were higher than those in PLGA scaffolds. For bone defect repairing, the radius defects had, after 12 weeks implantation of nHA coated PLGA scaffolds, completely recuperated with significantly better bone formation than in the group of virgin PLGA scaffolds, as shown by X-ray, Micro-computerized tomography and histological examinations.

CONCLUSION

nHA coating on the interior pore surfaces can significantly improve the bioactivity of PLGA porous scaffolds.

Prevascularization of a gas-foaming macroporous calcium phosphate cement scaffold via coculture of human umbilical vein endothelial cells and osteoblasts

The lack of a vasculature in tissue-engineered constructs is currently a major challenge in tissue regeneration. There has been no report of prevascularization of macroporous calcium phosphate cement (CPC) via coculture of endothelial cells and osteoblasts. The objectives of this study were to (1) investigate coculture of human umbilical vein endothelial cells (HUVEC) and human osteoblasts (HOB) on macroporous CPC for the first time; and (2) develop a new microvasculature-CPC construct with angiogenic and osteogenic potential. A gas-foaming method was used to create macropores in CPC. HUVEC and HOB were seeded with a ratio of HUVEC:HOB=4:1, at 1.5×10(5) cells/scaffold. The constructs were cultured for up to 42 days. CPC with a porosity of 83% had a flexural strength (mean±SD; n=6) of 2.6±0.2 MPa, and an elastic modulus of 340±30 MPa, approaching the reported values for cancellous bone. Reverse transcription-polymerase chain reaction showed that HUVEC+HOB coculture on CPC had much higher vascular endothelial growth factor (VEGF) and collagen I expressions than monoculture (p<0.05). Osteogenic markers alkaline phosphatase, osteocalcin (OC), and runt-related transcription factor 2 (Runx2) were also highly elevated. Immunostaining of PECAM1 (CD31) showed abundant microcapillary-like structures on CPC in coculture at 42 days, as HUVEC self-assembled into extensive branches and net-like structures. However, no microcapillary was found on CPC in monoculture. In immunohistochemical staining, the neo-vessels were strongly positive for PECAM1, the von Willebrand factor, and collagen I. Scanning electron microscopy revealed microcapillary-like structures mingling with mineral nodules on CPC. Cell-synthesized minerals increased by an order of magnitude from 4 to 42 days. In conclusion, gas-foaming macroporous CPC was fabricated and HUVEC+HOB coculture was performed for prevascularization, yielding microcapillary-like structures on CPC for the first time. The novel macroporous CPC-microvasculature construct is promising for a wide range of orthopedic applications with enhanced angiogenic and osteogenic capabilities.

Effect of nanostructure on osteoinduction of porous biphasic calcium phosphate ceramics

In order to evaluate the effect of the nanostructure of calcium phosphate ceramics on osteoinductive potential, porous biphasic calcium phosphate (BCP) ceramics with a nano- or submicron structure were prepared via microwave sintering and compared to conventional BCP ceramics. The selective protein adsorption of bovine serum albumin and lysozyme (LSZ) and the osteogenic differentiation of human mesenchymal stem cells in vitro was investigated. Porous BCP nanoceramics showed higher ability to adsorb proteins, especially low molecular weight protein of LSZ, than conventional BCP ceramics, and the BCP nanoceramics promoted bone sialoprotein expression more than conventional BCP did. Further in vivo study to investigate ectopic bone formation and bone repair efficiency proved the highly osteoinductive potential of nanostructured BCP ceramics. The results suggest that nanostructured BCP ceramics have the potential to become a new generation of bioceramics for bone tissue engineering grafts.

Relevance of the sterilization-induced effects on the properties of different hydroxyapatite nanoparticles and assessment of the osteoblastic cell response

Hydroxyapatite (Hap) is a calcium phosphate with a chemical formula that closely resembles that of the mineral constituents found in hard tissues, thereby explaining its natural biocompatibility and wide biomedical use. Nanostructured Hap materials appear to present a good performance in bone tissue applications because of their ability to mimic the dimensions of bone components. However, bone cell response to individual nanoparticles and/or nanoparticle aggregates lost from these materials is largely unknown and shows great variability. This work addresses the preparation and characterization of two different Hap nanoparticles and their interaction with osteoblastic cells. Hap particles were produced by a wet chemical synthesis (WCS) at 37°C and by hydrothermal synthesis (HS) at 180°C. As the ultimate in vivo applications require a sterilization step, the synthesized particles were characterized 'as prepared' and after sterilization (autoclaving, 120°C, 20 min). WCS and HS particles differ in their morphological (size and shape) and physicochemical properties. The sterilization modified markedly the shape, size and aggregation state of WCS nanoparticles. Both particles were readily internalized by osteoblastic cells by endocytosis, and showed a low intracellular dissolution rate. Concentrations of WCS and HS particles less than 500 μg ml(-1) did not affect cell proliferation, F-actin cytoskeleton organization and apoptosis rate and increased the gene expression of alkaline phosphatase and BMP-2. The two particles presented some differences in the elicited cell response. In conclusion, WCS and HS particles might exhibit an interesting profile for bone tissue applications. Results suggest the relevance of a proper particle characterization, and the interest of an individual nanoparticle targeted research.

Antitumoural hydroxyapatite nanoparticles-mediated hepatoma-targeted trans-arterial embolization gene therapy: in vitro and in vivo studies

BACKGROUND/AIMS

Absence of curative treatment creates urgent need for new strategies for unresectable hepatoma. Based on former discoveries of good liver cell compatibility, safety and tumour-specific inhibition of hydroxyapatite nanoparticles (nHAP), this work tries to make nHAP serve as gene vector in the hepatoma-targeted trans-arterial embolization (TAE) gene therapy to elevate and synergize the therapeutic efficacy of TAE and target gene therapy.

METHOD

Following dosage and ratio optimization, polypolex formed by surface modified nHAP and p53 expressing plasmid was applied in vitro for human hepatoma HePG2 cell, and then in vivo for rabbit hepatic VX2 tumour by injection of polypolex/lipodoil emulsion to the hepatic artery in a tumour-target manner.

RESULTS

In vitro, the polypolex transfected only about 5% HepG2 cells, but can elevate the inhibition of its growth and apoptosis in a much more degree while keeping safe to the normal hepatocyte line, L02. In vivo, the emulsion, with better dispersion than the polypolex and more specific tumour-target than lipiodol, mediated specific 4% p53 expression and antitumoural nanoparticle retention in the target tumour site, also significantly reduced tumour growth and prolonged the animal survival times more than the lipiodol (P < 0.05).

CONCLUSIONS

In all, this new treatment based on nHAP can enhance therapeutic effect of HCC safely both in vitro and in vivo.

MgCHA particles dispersion in porous PCL scaffolds: in vitro mineralization and in vivo bone formation

In this work, we focus on the in vitro and in vivo response of composite scaffolds obtained by incorporating Mg,CO3 -doped hydroxyapatite (HA) particles in poly(ε-caprolactone) (PCL) porous matrices. After a complete analysis of chemical and physical properties of synthesized particles (i.e. SEM/EDS, DSC, XRD and FTIR), we demonstrate that the Mg,CO3 doping influences the surface wettability with implications upon cell-material interaction and new bone formation mechanisms. In particular, ion substitution in apatite crystals positively influences the early in vitro cellular response of human mesenchymal stem cells (hMSCs), i.e. adhesion and proliferation, and promotes an extensive mineralization of the scaffold in osteogenic medium, thus conforming to a more faithful reproduction of the native bone environment than undoped HA particles, used as control in PCL matrices. Furthermore, we demonstrate that Mg,CO3 -doped HA in PCL scaffolds support the in vivo cellular response by inducing neo-bone formation as early as 2 months post-implantation, and abundant mature bone tissue at the sixth month, with a lamellar structure and completely formed bone marrow. Together, these results indicate that Mg(2+) and CO3 (2-) ion substitution in HA particles enhances the scaffold properties, providing the right chemical signals to combine with morphological requirements (i.e. pore size, shape and interconnectivity) to drive osteogenic response in scaffold-aided bone regeneration.

Endothelial cell migration and morphogenesis on silk fibroin scaffolds containing hydroxyapatite electret

The purpose of this study was to evaluate the effects of composite wound dressing films made of silk fibroin (SF) containing hydroxyapatite (HA) or polarized HA (pHA) powders on endothelial cell (EC) behaviors that have important roles in the wound-healing process. XRD revealed the SF films to be semicrystalline, with a broad peak centered at about 20.7° which is characteristic of β-sheets embedded within an amorphous matrix. The SF composite films with 0.6 (w/v)% in concentration of HA powder (HA/SF) or pHA powder (pHA/SF) contained HA crystals of amorphous and silk II crystalline structures. SEM observation showed that there were differences in SF morphology between HA/SF and pHA/SF. The pHA/SF exhibited a furry texture around the pHA crystals, most likely due to the stored charged and zeta potentials. The HA/SF and pHA/SF films enhanced EC migration compared with that on the SF film. The number of migrated cells on the HA/SF and pHA/SF was ~1.5 times larger than that on the SF. The quantitative analysis of the endothelial morphogenesis indicated that the pHA/SF film enhanced the formation of capillary-like structures compared with SF and HA/SF. Thus, pHA/SF may potentially stimulate and contribute to the enhancement of angiogenesis in the wound-healing process.

Long-term in vivo response to citric acid-based nanocomposites for orthopaedic tissue engineering

The disadvantages of current bone grafts have triggered the development of a variety of natural and synthetic bone substitutes. Previously, we have described the fabrication, characterization, and short-term tissue response of poly(1,8-octanediol-co-citrate) (POC) with 60 weight % hydroxyapatite nanocrystals (POC-HA) at 6 weeks. In order to better understand the clinical potential, longer term effects, and the biodegradation, biocompatibility, and bone regenerative properties of these novel nanocomposites, POC-HA, POC, and poly-L-lactide (PLL) were implanted in osteochondral defects in a rabbit model and assessed at 26 weeks. Explants were stained with Masson Goldner Trichrome and the fibrous capsule and tissue ingrowth measured. In addition, the bone-implant and bone-cartilage response of POC-HA, POC, and PLL were assessed through histomorphometry and histological scoring. Upon histological evaluation, both POC-HA and POC implants were biocompatible, but PLL implants were surrounded by a layer of leukocytes at 26 weeks. In addition, due to the degradation properties of POC-HA, tissue grew into the implant and had the highest area of tissue ingrowth although not statistically significant. Histomorphometric analyses supported a similar osteoid, osteoblast, and trabecular bone surface area among all implants although the fibrous capsule thickness was the largest for POC. Moreover, histological scoring demonstrated comparable scores among all three groups of the articular cartilage and subchondral bone. This study provides the long-term bone and cartilage response of novel, citric acid-based nanocomposites and their equivalence to FDA-approved biomaterials. Furthermore, we provide new insights and further discussion of these nanocomposites for orthopaedic applications.

Heterotypic cell-cell interaction on micropatterned surfaces

PURPOSE

The aim of this paper was to study the influence of chemical and topographical signals on cell behavior and to obtain a heterotypic cell-cell interaction on microstructured domains.

METHODS

The polysaccharide hyaluronic acid (Hyal) was photoimmobilized on glass surfaces in order to obtain a pattern with squares and rectangles of different dimensions and chemistry. The microstructured surfaces were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The behavior of human coronary artery endothelial cells (HCAEC) and human tumoral dermal fibroblasts (C54) was investigated on these micropatterned surfaces by adhesion studies. Moreover heterotypic interaction among C54 and HCAEC adherent on patterned surfaces was evaluated by time-lapse video microscopy

RESULTS

Surface analysis revealed the presence of a pattern consisting of alternating glass and Hyal microstructures whose dimensions decreased from the center to the edge of the sample. Neither HCAEC nor C54 adhered to the immobilized Hyal but both adapted their shape to the different sizes of the glass squares and rectangles. The number of adherent cells depended on the dimensions of both the glass domains and the nuclei of the cells. Co-cultured C54 on HCAEC patterned surfaces showed a heterotypic cell-cell interaction in the same chemical and topographic domain.

CONCLUSIONS

A heterotypic cell-cell interaction occurred in the same chemical and topographic micro-domains but in narrow areas only. Moreover, the number of cells adhering to the glass domains and cell morphology depended on the dimensions of both adhesive areas and cell nuclei.

New perspectives in cell communication: Bioelectromagnetic interactions

This paper explores physical signalling in biological communications, the so-called biophysical pathways, and especially the role of electromagnetic signalling in cell-cell interactions. The experiments were designed to evaluate whether different cell populations physically interfere when incubated in separate Petri dishes placed in close proximity. Two different cell populations, immortalized mouse fibroblasts (NIH3T3) and adult human microvascular endothelial cells (HMVECad) were selected and seeded in separate polystyrene Petri dishes. Dishes seeded with NIH3T3 were then placed on top of those seeded with HMVECad at distances of 4mm and 11mm. A black filter was placed between dishes containing the two cell populations in another experiment, to prevent transmission of electromagnetic radiation between the two. Cell number and morphology of NIH3T3 and endothelial cells were found to be modified in dishes without the black filter, suggesting that specific signals emitted by the cells were transmitted through the polystyrene wall, affecting cell proliferation rate and morphology, even though the cells were growing in separate dishes.

The role of surface charge on the uptake and biocompatibility of hydroxyapatite nanoparticles with osteoblast cells

The objective of this study is to evaluate the effect of hydroxyapatite (HAP) nanoparticles with different surface charges on the cellular uptake behavior and in vitro cell viability and proliferation of MC3T3-E1 cell lines (osteoblast). The nanoparticles' surface charge was varied by surface modification with two carboxylic acids: 12-aminododecanoic acid (positive) and dodecanedioic acid (negative). The untreated HAP nanoparticles and dodecanoic acid modified HAP nanoparticles (neutral) were used as the control. X-ray diffraction (XRD) revealed that surface modifications by the three carboxylic acids did not change the crystal structure of HAP nanoparticles; Fourier transform infrared spectroscopy (FT-IR) confirmed the adsorption and binding of the carboxylic acids on the HAP nanoparticles' surfaces; and zeta potential measurement confirmed that the chemicals successfully modified the surface charge of HAP nanoparticles in water based solution. Transmission electron microscopy (TEM) images showed that positively charged, negatively charged and untreated HAP nanoparticles, with similar size and shape, all penetrated into the cells and cells had more uptake of HAP nanoparticles with positive charge compared to those with negative charge, which might be attributed to the attractive or repulsive interaction between the negatively charged cell membrane and positively/negatively charged HAP nanoparticles. The neutral HAP nanoparticles could not penetrate the cell membrane due to their larger size. MTT assay and LDH assay results indicated that as compared with the polystyrene control, greater cell viability and cell proliferation were measured on MC3T3-E1 cells treated with the three kinds of HAP nanoparticles (neutral, positive, and untreated), among which positively charged HAP nanoparticles showed the strongest improvement for cell viability and cell proliferation. In summary, the surface charge of HAP nanoparticles can be modified to influence the cellular uptake of HAP nanoparticles and the different uptake also influences the behavior of cells. These in vitro results may also provide useful information for investigations of HAP nanoparticle applications in gene delivery and intracellular drug delivery.

A review of the mechanical behavior of CaP and CaP/polymer composites for applications in bone replacement and repair

Repair of load-bearing defects resulting from disease or trauma remains a critical barrier for bone tissue engineering. Calcium phosphate (CaP) scaffolds are among the most extensively studied for this application. However, CaPs are reportedly too weak for use in such defects and, therefore, have been limited to non-load-bearing applications. This paper reviews the compression, flexural and tensile properties of CaPs and CaP/polymer composites for applications in bone replacement and repair. This review reveals interesting trends that have not, to our knowledge, previously been reported. Data are classified as bulk, scaffolds, and composites, then organized in order of decreasing strength. This allows for general comparisons of magnitudes of strength both within and across classifications. Bulk and scaffold strength and porosity overlap significantly and scaffold data are comparable to bone both in strength and porosity. Further, for compression, all composite data fall below those of the bulk and most of the scaffold. Another interesting trend revealed is that strength decreases with increasing β-tricalcium phosphate (β-TCP) content for CaP scaffolds and with increasing CaP content for CaP/polymer composites. The real limitation for CaPs appears not to be strength necessarily, but toughness and reliability, which are rarely characterized. We propose that research should focus on novel ways of toughening CaPs and discuss several potential strategies.

Fast preparation of hydroxyapatite/superhydrophilic vertically aligned multiwalled carbon nanotube composites for bioactive application

A method for the electrodeposition of hydroxyapatite films on superhydrophilic vertically aligned multiwalled carbon nanotubes is presented. The formation of a thin homogeneous film with high crystallinity was observed without any thermal treatment and with bioactivity properties that accelerate the in vitro biomineralization process and osteoblast adhesion.