Chitosan-strontium chondroitin sulfate scaffolds for reconstruction of bone defects in aged rats.

Bone defects caused by trauma have become increasingly common in aged populations. Clinically, because of the relatively decreased bone healing capacity compared with the youth adults, bone defect repair in the elderly remains challenging. The development of effective biomaterials targeted at bone defects in the elderly is a key component of bone-tissue engineering strategies. However, little attention has been paid to bone regeneration in the elderly. Here, we developed a new scaffold chitosan-Strontium chondroitin sulfate (CH-SrCS) and evaluated its effect on improving bone regeneration. We find that the CH-SrCS scaffold displayed positive effects on downregulation of inflammation and osteoclastogenesis related mRNA expressions while demonstrating a significant increase in the expression level of BMP2. Finally, we show that the bone defects healing effects as assessed using an aged rats' bone defects model. Ultimately, this work also provides insights into the design of effective biomaterials targeted at bone defects in the elderly.

The morphology and lattice structure of bone crystal after strontium treatment in goats.

Strontium (Sr) compounds have become increasingly popular in osteoporosis treatment. As a bone seeking element, 98% of Sr deposits in bone and teeth after oral ingestion. However, the quality of new bone after Sr deposition is yet to be extensively investigated. In this study, eight osteopenic goats were divided into two groups: Ca + 40Sr (five goats) and controls (three goats). Controls were fed with low calcium feeds. Ca phosphate was supplied at 100 mg/(kg day), and Sr phosphate at 40 mg/(kg day) in the Ca + 40Sr group. The newly formed bone at the outer cortical area of the femur with Sr deposition was identified from tetracycline labels, and the morphology and lattice structure of the crystals in these regions were investigated. Results showed that Sr concentrations of bone tissue significantly increased 144.37% for Sr administration without significant change in Ca concentration, and the ingested Sr mainly deposited in new bone. The crystal isolated from new bone exhibited the typical character of biological apatite as determined by Fourier transform infrared spectroscopy and selected-area electron diffraction. Transmission electron microscopy examination showed that a crystal with width of 8-10 nm grew along with the (002) lattice and aligned with the same direction in both groups. The elemental analysis of crystals showed that the ingested Sr deposited mainly in the bone matrix or was absorbed on the bone crystal surface, while only a limited amount of Sr replaced Ca in apatite crystals. Our findings showed that Sr administration at current dosages for prevention and treatment of osteoporosis might not change the bone crystal morphology and structure.

Effect of strontium-containing hydroxyapatite bone cement on bone remodeling following hip replacement.

It is uncertain whether the use of bioactive bone cement has any beneficial effect on local bone adaptation following hip replacement. In this study, twelve goats underwent cemented hip hemiarthroplasty unilaterally, with either PMMA bone cement or strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement. Nine months later, the femoral cortical bones at different levels were analyzed by microhardness testing and micro-CT scanning. Extensive bone remodeling was found at proximal and mid-levels in both PMMA and Sr-HA groups. However, with regard to the differences of bone mineral density, cortical bone area and bone hardness between implanted and non-implanted femur, less decreases were found in Sr-HA group than PMMA group at proximal and mid-levels, and significant differences were shown for bone area and hardness at proximal level. The results suggested that the use of Sr-HA cement might alleviate femoral bone remodeling after hip replacement.

Osteointegration of soft tissue grafts within the bone tunnels in anterior cruciate ligament reconstruction can be enhanced.

Anterior cruciate ligament reconstruction with a soft tissue autograft (hamstring autograft) has grown in popularity in the last 10 years. However, the issues of a relatively long healing time and an inferior histological healing result in terms of Sharpey-like fibers connection in soft tissue grafts are still unsolved. To obtain a promising outcome in the long run, prompt osteointegration of the tendon graft within the bone tunnel is essential. In recent decades, numerous methods have been reported to enhance osteointegration of soft tissue graft in the bone tunnel. In this article, we review the current literature in this research area, mainly focusing on strategies applied to the local bone tunnel environment. Biological strategies such as stem cell and gene transfer technology, as well as the local application of specific growth factors have been reported to yield exciting results. The use of biological bone substitute and physical stimulation also obtained promising results. Artificially engineered tissue has promise as a solution to the problem of donor site morbidity. Despite these encouraging results, the current available evidence is still experimental. Further clinical studies in terms of randomized control trial in the future should be conducted to extrapolate these basic science study findings into clinical practice.

Bioactive borosilicate glass scaffolds: in vitro degradation and bioactivity behaviors.

Bioactive borosilicate glass scaffolds with the pores of several hundred micrometers and a competent compressive strength were prepared through replication method. The in vitro degradation and bioactivity behaviors of the scaffolds have been investigated by immersing the scaffolds statically in diluted phosphate solution at 37 degrees C, up to 360 h. To monitor the degradation progress of the scaffolds, the amount of leaching elements from the scaffolds were determined by ICP-AES. The XRD and SEM results reveal that, during the degradation of scaffolds, the borosilicate scaffolds converted to hydroxyapatite. The compressive strength of the scaffolds decreased during degradation, in the way that can be well predicted by the degradation products, or the leachates, from the scaffolds. MTT assay results demonstrate that the degradation products have little, if any, inhibition effect on the cell proliferation, when diluted to a certain concentration ([B] <2.690 and pH value at neutral level). The study shows that borosilicate glass scaffold could be a promising candidate for bone tissue engineering material.

Spatial Distribution of Biomaterial Microenvironment pH and Its Modulatory Effect on Osteoclasts at the Early Stage of Bone Defect Regeneration.

It is generally accepted that biodegradable materials greatly influence the nearby microenvironment where cells reside; however, the range of interfacial properties has seldom been discussed due to technical bottlenecks. This study aims to depict biomaterial microenvironment boundaries by correlating interfacial H+ distribution with surrounding cell behaviors. Using a disuse-related osteoporotic mouse model, we confirmed that the abnormal activated osteoclasts could be suppressed under relatively alkaline conditions. The differentiation and apatite-resorption capability of osteoclasts were "switched off" when cultured in titrated material extracts with pH values higher than 7.8. To generate a localized alkaline microenvironment, a series of borosilicates were fabricated and their interfacial H+ distributions were monitored spatiotemporally by employing noninvasive microtest technology. By correlating interfacial H+ distribution with osteoclast "switch on/off" behavior, the microenvironment boundary of the tested material was found to be 400 ± 50 µm, which is broader than the generally accepted value, 300 µm. Furthermore, osteoporotic mice implanted with materials with higher interfacial pH values and boarder effective ranges had lower osteoclast activities and a thicker new bone. To conclude, effective proton microenvironment boundaries of degradable biomaterials were depicted and a weak alkaline microenvironment was shown to promote regeneration of osteoporotic bones possibly by suppressing abnormal activated osteoclasts.

Preliminary clinical outcomes of percutaneous kyphoplasty with Sky-bone expander.

BACKGROUND: Percutaneous kyphoplasty (PKP) using balloon expander has been proved to be effective in the treatment of painful vertebral compression fractures. Recently, Sky-bone expander, an alternative bone expander for PKP has been developed. The purpose of this study was to show our preliminary clinical outcomes of PKP with Sky-bone expander. METHODS: PKP with Sky-bone expander was performed in 25 patients (30 vertebrae). The operation time, bleeding volume, cement volume injected were recorded. The pain and functional activities of the patients before and after the operation were compared using Wilcoxon signed-rank test. The cement distribution in the vertebrae, vertebral height restoration, and kyphosis correction after the procedure were evaluated by radiography. The pre- and post-operative absolute values of the vertebral height and kyphotic angle were compared by paired-sample t test. All the patients were followed up by telephone or clinic consulting after being discharged from our hospital. RESULTS: The procedure was performed successfully in all the patients. Bipedicular injection was used in 2 of the patients, and unipedicular injection was made in the others. The operation time ranged from 25 to 120 minutes (45 minutes per vertebra on average). The average bleeding volume was about 20 ml. Polymethylmethacrylate 1.5-5.0 ml (mean, (3.15+/-0.78) ml) was injected through each pedicle into all the patients except one, who received calcium sulphate 3.5 ml instead. The patients were followed up for 12-15 months (13.5 months on average). The mean visual analogue scale (VAS) score, Oswestry Disability Index, anterior, midline, and posterior vertebral height, and kyphotic angle of the patients were improved significantly at the end of the follow-up compared with those before the operation. (2.5+/-1.3, 35.1%, (20.94+/-6.15) mm, (20.26+/-4.59) mm, (26.72+/-3.49) mm, and 8.2 degrees vs. 8.5+/-1.9, 61.2%, (19.11+/-6.72) mm, (15.88+/-5.73) mm, (25.78+/-3.67) mm, and 17.3 degrees; all P<0.05). The cement distribution with unipedicular injection was mostly limited within the injection site in the vertebral body. Cement extravasation was seen at ten levels (33.3%). CONCLUSIONS: PKP with Sky-bone expander is an effective and relatively safe alternative to the PKP using balloon expander. It can relieve pain, improve physical function, and restore the height of the collapsed vertebrae, but the cement extravasation is unsolved.

Enhanced osteointegration of poly(methylmethacrylate) bone cements by incorporating strontium-containing borate bioactive glass.

Although poly(methylmethacrylate) (PMMA) cements are widely used in orthopaedics, they have numerous drawbacks. This study aimed to improve their bioactivity and osseointegration by incorporating strontium-containing borate bioactive glass (SrBG) as the reinforcement phase and bioactive filler of PMMA cement. The prepared SrBG/PMMA composite cements showed significantly decreased polymerization temperature when compared with PMMA and retained properties of appropriate setting time and high mechanical strength. The bioactivity of SrBG/PMMA composite cements was confirmed in vitro, evidenced by ion release (Ca, P, B and Sr) from SrBG particles. The cellular responses of MC3T3-E1 cells in vitro demonstrated that SrBG incorporation could promote adhesion, migration, proliferation and collagen secretion of cells. Furthermore, our in vivo investigation revealed that SrBG/PMMA composite cements presented better osseointegration than PMMA bone cement. SrBG in the composite cement could stimulate new-bone formation around the interface between the composite cement and host bone at eight and 12 weeks post-implantation, whereas PMMA bone cement only stimulated development of an intervening connective tissue layer. Consequently, the SrBG/PMMA composite cement may be a better alternative to PMMA cement in clinical applications and has promising orthopaedic applications by minimal invasive surgery.

Effects of hydroxyapatite in 3-D chitosan-gelatin polymer network on human mesenchymal stem cell construct development.

Human mesenchymal stem cells (hMSCs) have great potential in bone tissue engineering, and hydroxyapatite (HA), a natural component of human hard tissues, is believed to support hMSC growth and osteogenic differentiation. In this study, two types of biomimetic composite materials, chitosan-gelatin (CG) and hydroxyapatite/chitosan-gelatin (HCG), were fabricated and compared to examine the effects of HA on hMSC adhesion and 3-D construct development. The 2-D membranes were prepared to examine the influence of HA on adhesion efficiency of hMSCs, while 3-D porous scaffolds were produced to investigate the effects of HA on material adsorption properties and 3-D hMSC construct development. HA was found to promote protein and calcium ion adsorption of the 3-D porous scaffolds in the complete tissue culture media. HMSCs exhibited higher initial cell adhesion efficiency to 2-D HCG membranes, and maintained higher proliferation rates in the 3-D porous HCG than CG scaffolds with 3.3 times higher final DNA amount in HCG scaffolds over a 35-day period. Colony forming unit-fibroblast (CFU-F) assays showed that higher percentages of cells maintained their progenicity in the 3-D porous HCG scaffolds over the 35-day culture period. Differentiation assays indicated that the multi-lineage differentiation potential of the hMSCs was preserved in both 3-D porous scaffolds. However, higher alkaline phosphate activity was detected in the 3-D porous HCG scaffolds upon osteogenic induction indicating improved osteogenic differentiation potential. The results demonstrate that enhanced protein and calcium ion adsorption properties of HA in the CG polymer network improve initial cell adhesion and long-term growth, favor osteogenic differentiation upon induction, as well as maintain the progenicity of the 3-D hMSC constructs.

A Bone-Implant Interaction Mouse Model for Evaluating Molecular Mechanism of Biomaterials/Bone Interaction.

The development of an optimal animal model that could provide fast assessments of the interaction between bone and orthopedic implants is essential for both preclinical and theoretical researches in the design of novel biomaterials. Compared with other animal models, mice have superiority in accessing the well-developed transgenic modification techniques (e.g., cell tracing, knockoff, knockin, and so on), which serve as powerful tools in studying molecular mechanisms. In this study, we introduced the establishment of a mouse model, which was specifically tailored for the assessment of bone-implant interaction in a load-bearing bone marrow microenvironment and could potentially allow the molecular mechanism study of biomaterials by using transgenic technologies. The detailed microsurgery procedures for developing a bone defect (Φ = 0.8 mm) at the metaphysis region of the mouse femur were recorded. According to our results, the osteoconductive and osseointegrative properties of a well-studied 45S5 bioactive glass were confirmed by utilizing our mouse model, verifying the reliability of this model. The feasibility and reliability of the present model were further checked by using other materials as objects of study. Furthermore, our results indicated that this animal model provided a more homogeneous tissue-implant interacting surface than the rat at the early stage of implantation and this is quite meaningful for conducting quantitative analysis. The availability of transgenic techniques to mechanism study of biomaterials was further testified by establishing our model on Nestin-GFP transgenic mice. Intriguingly, the distribution of Nestin+ cells was demonstrated to be recruited to the surface of 45S5 glass as early as 3 days postsurgery, indicating that Nestin+ lineage stem cells may participate in the subsequent regeneration process. In summary, the bone-implant interaction mouse model could serve as a potential candidate to evaluate the early stage tissue response near the implant surface in a bone marrow microenvironment, and it also shows great potential in making transgenic animal resource applicable to biomaterial studies, so that the design of novel biomaterials could be better guided.

An investigation on the physicochemical properties of chitosan/DNA polyelectrolyte complexes.

In this work, to eliminate the effect of the hydrophobicity of N-acetyl groups in chitosan on the interaction between chitosan and DNA, a water soluble chitosan with molecular weight of 5000 and deacetylated degree of 99% was selected to complex with DNA at varied charged ratios. The physicochemical properties of chitoplexes were investigated by means of FTIR, circular dichroism (CD), static fluorescence spectroscopy, and atomic force microscopy (AFM). The results indicated that upon interacting with chitosan, the DNA molecules saved a B conformation, and the binding affinity of chitosan to DNA was dependent on pH of media. At pH 5.5, highly charged chitosan had a strong binding affinity with DNA; whereas in pH 12.0 medium, only weak interactions existed. The CD spectra of Hoechst 33258 competitive displacement revealed that chitosan was partially bound to the minor groove of DNA. The morphology of chitosan/DNA complexes was strongly dependent upon the charge ratios. At charge ratio (+/-) of 1:4, not all DNA could be entrapped in the complex; at ratio of 8:1, the spherical complexes with mean size of nanoscale were formed without free DNA, but no typical toroid patterns were observed, which might stem from the strong compact of DNA caused by highly charged chitosan. It was supposed that the strong interaction of chitosan with DNA possibly prevented gene unpacking from chitosan vector, consequently restraining gene expression in nucleus.

Preparation and histological evaluation of biomimetic three-dimensional hydroxyapatite/chitosan-gelatin network composite scaffolds.

A novel biodegradable hydroxyapatite/chitosan-gelatin network (HA/CS-Gel) composite of similar composition to that of normal human bone was prepared as a three-dimensional biomimetic scaffold by phase separation method for bone tissue engineering. Changing the solid content and the compositional variables of the original mixtures allowed control of the porosities and densities of the scaffolds. The HA granules were dispersed uniformly in the organic network with intimate interface contact via pulverizing and ultrasonically treating commercial available HA particles. Scaffolds of 90.6% porosity were used to examine the proliferation and functions of the cells in this three-dimensional microenvironment by culturing neonatal rat caldaria osteoblasts. Histological and immunohistochemical staining and scanning electron microscopy observation indicated that the osteoblasts attached to and proliferated on the scaffolds. Extracellular matrices including collagen I and proteoglycan-like substrate were synthesized, while osteoid and bone-like tissue formed during the culture period. Furthermore, the cell/scaffold constructs had good biomineralization effect after 3 weeks in culture.

A rapid temperature-responsive sol-gel reversible poly(N-isopropylacrylamide)-g-methylcellulose copolymer hydrogel.

Poly(N-isopropylacrylamide) (PNIPAAm) was grafted to methylcellulose (MC) with various feeding ratios using ammonium persulfate and N,N,N',N'-tetramethyl ethylene diamine as an initiator. FTIR results confirm the formation of PNIPAAm-g-MC copolymers. The temperature responsiveness of copolymer gels was investigated by turbidimetry, dynamic contact angle (DCA), differential scanning calorimetry and dynamic mechanical analysis (DMA). The results indicate that PNIPAAm-g-MC hydrogels are strongly temperature responsive. At lower contents of MC, the lower critical solution temperature (LCST) is decreased, whereas further increasing MC contents raises the LCSTs. It is observed that the phase transition of the hydrogels occurs reversibly within 1 min, and near body temperature, a rigid gel can be generated in a certain range of MC content. What is more, the incorporation of MC prevents the syneresis of copolymer hydrogel. DMA measurement reveals that the storage moduli (E') of the gels increase upon increasing MC contents, and moreover the values of E' go up markedly above LCST. The copolymer hydrogels hold a promise as a blood vessel barrier by tuning gelation temperature, gelation time and mechanical strength.

Local application of strontium in a calcium phosphate cement system accelerates healing of soft tissue tendon grafts in anterior cruciate ligament reconstruction: experiment using a rabbit model.

BACKGROUND: Healing of soft tissue tendon grafts within the bone tunnel in anterior cruciate ligament (ACL) reconstruction is known to be slower than that of bone-patellar tendon-bone grafts. There are attempts to accelerate healing of the graft within the bone tunnel. One of the methods is the use of strontium-enriched calcium phosphate cement (Sr-CPC). Early results in animal studies have been encouraging, although it is not known whether the accelerated healing was solely caused by the effect of strontium within the cement or by the calcium phosphate cement (CPC) itself. HYPOTHESIS: There would be differences between Sr-CPC and conventional CPC in terms of the effect on healing of soft tissue tendon grafts within the bone tunnels in ACL reconstruction. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 30 single-bundle ACL reconstruction procedures were performed in 15 rabbits with the use of an Achilles tendon allograft. The graft on the left limb was coated with Sr-CPC, while that on the right limb was coated with CPC. Three animals each were sacrificed for histological and histomorphometric analyses at 3, 6, 9, 12, and 24 weeks after surgery. RESULTS: In the Sr-CPC group, early formation of Sharpey fibers was present at 6 weeks after surgery, while early remodeling of a graft-fibrocartilage-bone junction was noted at 12 weeks. In the CPC group, early formation of Sharpey fibers was only found at 9 to 12 weeks after surgery. At 24 weeks, a direct enthesis was found in both groups. According to the histomorphometric score, graft healing in the Sr-CPC group took place 3 weeks faster than that in the CPC group at and before 12 weeks; however, there was no difference between the groups at 24 weeks. CONCLUSION: The local application of strontium in a CPC system leads to accelerated graft healing within the bone tunnels. CLINICAL RELEVANCE: The use of Sr-CPC to enhance graft-bone healing may improve the clinical results of ACL reconstruction using soft tissue tendon grafts.

Enhancing the biological performance of osteoconductive nanocomposite scaffolds through negative voltage electrospinning.

AIM: To investigate negative voltage electrospinning of fibrous nanocomposite scaffolds bearing negative electric charges (N-poled), and determine whether and how retained negative charges could influence the biological performance of scaffolds for bone tissue engineering. MATERIALS & METHODS: Poly(D,L-lactic acid) was used as the polymer matrix and carbonated hydroxyapatite nanospheres were the osteoconductive phase in the electrospun nanocomposite scaffolds. N-poled nanocomposite scaffolds were formed using negative voltage electrospinning, while conventional positive voltage electrospinning produced fibrous nanocomposite scaffolds bearing positive electric charges (P-poled). N-poled and P-poled scaffolds were systematically characterized and their biological performance was investigated through in vitro cell culture experiments. RESULTS & CONCLUSION: N-poled and P-poled scaffolds retained charges for different periods of time after electrospinning. Both types of scaffolds supported cell spreading and promoted filopodia formation. Compared with P-poled scaffolds, N-poled scaffolds enhanced cell proliferation, alkaline phosphatase activity and mineralization. N-poled scaffolds offer distinct advantages for bone tissue engineering.

Enhanced gene delivery by chitosan-disulfide-conjugated LMW-PEI for facilitating osteogenic differentiation.

Chitosan-disulfide-conjugated LMW-PEI (CS-ss-PEI) was designed to combine the biocompatibility of chitosan and the gene delivery ability of polyethylenimine (PEI) using bio-reducible disulfide for bone morphogenetic protein (BMP2) gene delivery in mediating osteogenic differentiation. It was prepared by conjugating low molecular weight PEI (LMW-PEI) to chitosan through oxidization of thiols introduced for the formation of disulfide linkage. The structure, molecular weight and buffer capacity were characterized by Fourier transform infrared (FTIR), light scattering and acid-base titration, respectively. The reduction in molecular weight of CS-ss-PEI by the reducing agent indicated its bio-reducible property. With the increment in the LMW-PEI component, the copolymer showed increased DNA binding ability and formed denser nanocomplexes. CS-ss-PEI exhibited low cytotoxicity in COS-1, HepG2 and 293T cells over the different weight ratios. The transfection efficiency of CS-ss-PEI4 was significantly higher than that of PEI 25k and comparable with Lipofectamine in mediating luciferase expression. Its application for BMP2 gene delivery was confirmed in C2C12 cells by BMP2 expression. For inducing in vitro osteogenic differentiation, CS-ss-PEI4 mediated BMP2 gene delivery showed a stronger effect in MG-63 osteoblast cells and stem cells in terms of alkaline phosphatase activity and mineralization compared with PEI25k and Lipofectamine. This study provides a potential gene delivery system for orthopedic-related disease.

Decellularized bovine intervertebral disc as a natural scaffold for xenogenic cell studies.

Low back pain that is associated with disc degeneration contributes to a huge economic burden in the worldwide healthcare system. Traditional methods, such as spinal fusion, have been adopted to relieve mechanical back pain, but this is compromised by decreased spinal motion. Tissue engineering has attracted much attention, and aims to correct the changes fundamentally occurring in the discs by a combination of cell biology, molecular biology and engineering. Synthetic materials including poly(l-lactic acid) or poly(glycolic acid) and biomolecules like hyaluronic acid or collagen have been adopted in the development of disc scaffolds for studying therapeutic approaches. Nevertheless, the complex biological and mechanical environment of the intervertebral disc (IVD) makes the synthesis of an artificial IVD with biomaterials a difficult task. Thus the aim of this study was to develop a natural disc scaffold for culturing disc cells for future development of biological disc constructs. We adopted a combination of currently used decellularization techniques to decellularize bovine IVD to create a complete endplate-to-endplate IVD scaffold. By altering the chemical and physical decellularization parameters, we reported the removal of up to 70% of the endogenous cells, and were able to preserve the glycosaminoglycan content, collagen fibril architecture and mechanical properties of the discs. The reintroduction of nucleus pulposus cells into the scaffold indicated a high survival rate over 7days, with cell penetration. We have shown here that conventional methods used for decellularizing thin tissues can also be applied to large organs, such as IVD. Our findings suggest the potential of using decellularized IVD as a scaffold for IVD bioengineering and culturing of cells in the context of the IVD niche.

Electrospinning and evaluation of PHBV-based tissue engineering scaffolds with different fibre diameters, surface topography and compositions.

While electrospinning is an effective technology for producing poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) micrometre-scale fibrous scaffolds for tissue regeneration, electrospinning of PHBV fibrous scaffolds composed of sub-micrometre fibres, surface-porous fibres or nanocomposite fibres is rarely explored. In this study, the average PHBV fibre diameter was successfully reduced to the sub-micrometre scale by dissolving a conductivity-enhancing salt in the polymer solution for electrospinning. Surface-porous fibres were made using a mixture of solvents, and carbonated hydroxyapatite (CHA) nanoparticles were incorporated into the fibres with the aid of an ultrasonic power source. Water contact angle measurements demonstrated that both fibre diameter reduction and CHA incorporation enhanced the wettability of the fibrous scaffolds. Tensile properties of the scaffolds were not undermined by the reduction of fibre diameter and the presence of surface pores. In vitro biological evaluation using a human osteoblast-like cell line (SaOS-2) demonstrated that all types of fibrous scaffolds supported cell attachment, spreading and proliferation. Analysis of cell morphology revealed similar projected cell areas on all types of scaffolds. However, cells on sub-micrometre fibres possessed a lower cell aspect ratio than cells on microfibres. The reduction of fibre diameter to the sub-micrometre scale enhanced cell proliferation after 14 days cell culture, while the incorporation of CHA nanoparticles in microfibres significantly enhanced the alkaline phosphatase activity of SaOS-2 cells. The control of fibre diameter, surface topography and composition is important in developing electrospun PHBV-based scaffolds for specific tissue-engineering applications.

Enhancing pedicle screw fixation in the aging spine with a novel bioactive bone cement: an in vitro biomechanical study.

STUDY DESIGN: A paired biomechanical study of pedicle screws augmented with bone cement in a human cadaveric and osteoporotic lumbar spine model. OBJECTIVES.: To evaluate immediate strength and stiffness of pedicle screw fixation augmented with a novel bioactive bone cement in an osteoporotic spine model and compare it with polymethylmethacrylate (PMMA) cement. SUMMARY OF BACKGROUND DATA: A novel bioactive bone cement, containing nanoscale particles of strontium and hydroxyapatite (Sr-HA), can promote new bone formation and osteointegration and provides a promising reinforcement to the osteoporotic spine. Its immediate mechanical performance in augmenting pedicle screw fixation has not been evaluated. METHODS: Two pedicle screws augmented with Sr-HA and PMMA cement were applied to each of 10 isolated cadaveric L3 vertebrae. Each screw was subjected to a toggling test and screw kinematics were calculated. The pedicle screw was subjected to a pullout test until failure. Finally, the screw coverage with cement was measured on computed tomographic images. RESULTS: Screw translations in the toggling test were consistently larger in the Sr-HA group than in the PMMA group (1.4 ± 1.2 mm vs. 1.0 ± 1.1 mm at 1000 cycles). The rotation center was located closer to the screw tip in the Sr-HA group (19% of screw length) than in the PMMA group (37%). The only kinematic difference between Sr-HA and PMMA cements was the screw rotation at 1000 cycles (1.5° ± 0.9° vs. 1.3° ± 0.6°; P = 0.0026). All motion parameters increased significantly with more loading cycles. The pullout force was higher in the PMMA group than the Sr-HA group (1.40 ± 0.63 kN vs. 0.93 ± 0.70 kN), and this difference was marginally significant (P = 0.051). Sr-HA cement covered more of the screw length than PMMA cement (79 ± 19% vs. 43 ± 19%) (P = 0.036). CONCLUSION: This paired-design study identified some subtle but mostly nonsignificant differences in immediate biomechanical fixation of pedicle screws augmented with the Sr-HA cement compared with the PMMA cement.

PIIID-formed (Ti, O)/Ti, (Ti, N)/Ti and (Ti, O, N)/Ti coatings on NiTi shape memory alloy for medical applications.

(Ti, O)/Ti, (Ti, N)/Ti and (Ti, O, N)/Ti composite coatings were fabricated on NiTi shape memory alloy via plasma immersion ion implantation and deposition (PIIID). Surface morphology of samples was investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Cross-sectional morphology indicated that the PIIID-formed coatings were dense and uniform. X-ray diffraction (XRD) was used to characterize the phase composition of samples. X-ray photoelectron spectroscopy (XPS) results showed that the surface of coated NiTi SMA samples was Ni-free. Nanoindentation measurements and pin-on-disc tests were carried out to evaluate mechanical properties and wear resistance of coated NiTi SMA, respectively. For the in vitro biological assessment of the composite coatings in terms of cell morphology and cell viability, osteoblast-like SaOS-2 cells and breast cancer MCF-7 cells were cultured on NiTi SMA samples, respectively. SaOS-2 cells attached and spread better on coated NiTi SMA. Viability of MCF-7 cells showed that the PIIID-formed composite coatings were noncytotoxic and coated samples were more biocompatible than uncoated samples.