Biocompatibility of vascular stents manufactured using metal injection molding in animal experiments

This study aimed to evaluate the feasibility and safety of a novel stent manufactured by metal injection molding(MIM)in clinical practice through animal experiments.Vessel stents were prepared using powder injection molding technology to considerably improve material utilization.The influence of MIM carbon impurity variation on the mechanical properties and corrosion resistance of 316L stainless steel was studied.In vitro cytotoxicity and animal transplantation tests were also carried out to evaluate the safety of MIM stents.The results showed that the performance of 316L stainless steel was very sensitive to the carbon content.Carbon fluctuations should be precisely controlled during MIM.All MIM stents were successfully implanted into the aortas of the dogs,and the MIM 316L stents had no significant cytotoxicity.The novel intravascular stent manufactured using MIM can maintain a stable form and structure with fast endothelialization of the luminal surface of the stent and ensure long-term patency in an animal model.The novel intravascular stent manufactured using MIM demonstrates favorable structural,physical,and chemical stability,as well as biocompatibility,offering promising application in clinical practice.

Influence of Hydrogen Bonding on the Temperature-Accelerated Hydrolysis of Silicone Based Polyetherurethane

Temperature-accelerated in vitro degradation was established to estimate the longevity of polyurethane applied for long-term implantation.However,the prediction did not correlate well with the data from clinical explants and the rationality of accelerated in vitro test is still in a controversial due to the deviation.To improve the accuracy of the in vitro prediction,the influence of hydrogen bonding(HB)on the accelerated hydrolysis of silicone based polyetherurethans(SPEUs)extended with three side chains.Combining the temperature-controlled FTIR and the physical properties after temperature-accelerated in vitro degradation,it was demonstrated that side chain could increase the degree of hydrogen bond dissociation at higher temperature,resulting in the decrease of the calculated activation energy(E_(a))of hydrolysis.At low temperatures,changes in surface morphology and molar mass of PEUs are minimal and HB are less easily dissociated,which had barely impact on the hydrolysis resistance.It was proposed that the E_(a) will not be impacted and that the accuracy of prediction will be increased if the acceleration temperature is lower than 70℃ and HB change is less than 15%.

THE DEGRADATION AND BIOCOMPATIBILITY OF WATERBORNE BIODEGRADABLE POLYURETHANES FOR TISSUE ENGINEERING

To better investigate the degradation and biocompatibility of waterborne biodegradable polyurethanes for tissue engineering, a series of new waterborne biodegradable polyurethanes （PEGPUs） with low degree of crosslinking was synthesized using IPDI, BDO and L-lysine as hard segments, PCL and PEG as soft segment. The bulk structures and properties of the prepared polyurethanes were characterized by Fourier transform infrared spectroscopy （FTIR）, differential scanning calorimetry （DSC）, tensile mechanical tests and water contact angle （WCA） measurements. The degree of microphase separation was slightly improved because of the lowered crosslinking degree of these PEGPUs in comparison with the high cross-linking degree samples, leading to good mechanical properties, as indicated by DSC and stress-strain data. Moreover, biodegradability of the polyurethanes was evaluated in phosphate buffer solutions （PBS） under different pH values and enzymatic solution at pH 7.4 through weight loss monitoring. The results suggested that the degradation of these PEGPUs was closely related to their bulk and surface properties. And the degradation products didn＇t show apparent inhibition effect against fibroblasts in vitro. These studies demonstrated that the waterborne biodegradable polyurethanes could find potential use in soft tissue engineering and tissue regeneration.

Microstructure and mechanical properties of Al-Mg-Si alloy fabricated by a short process based on sub-rapid solidification

Al-Mg-Si(AA6xxx)series alloys have been used widely in automotive industry for lightweight purpose.This work focuses on developing a short process for manufacturing Al-0.5Mg-1.3Si(wt.%)alloy sheets with good mechanical properties.Hereinto,a preparation route without homogenization was proposed on the basis of sub-rapid solidification(SRS)technique.The sample under SRS has fine microstructure and higher average partition coefficients of solute atoms,leading to weaker microsegregation owing to the higher cooling rate(160℃/s)than conventional solidification(CS,30℃/s).Besides,Mg atoms tend to be trapped in Al matrix under SRS,inducing suppression of Mg2Si,and promoting generation of Al Fe Si phase.After being solution heat treated(T4 state),samples following the SRS route have lower yield strength compared with that by CS route,indicating better formability in SRS sample.After undergoing pre-strain and artificial aging(T6 state),the SRS samples have comparable yield strength to CS samples,satisfying the service requirements.This work provides technological support to industrially manufacture high performance AA6xxx series alloys with competitive advantage by a novel,short and low-cost process,and open a door for the further development of twin-roll casting based on SRS technique in industries.

Implantable Polyurethane Scaffolds Loading with PEG-Paclitaxel Conjugates for the Treatment of Glioblastoma Multiforme

Improvement of the treatment for Glioblastoma multiforme(GBM)especially the development of in situ controllable drug release is still a major concern.In this study,we developed waterborne biodegradable polyurethane(WBPU)scaffolds incorporated with redox-sensitive and RGD-decorated paclitaxel(PTX)polymer-drug conjugates(PDCs)for targeted GBM therapy in situ.The drug scaffolds could be implanted at residual GBM site post-operation.Dual-targeting PTX-PDCs were obtained through step-by-step conjugation of disulfide linked PTX,poly(ethylene glycol)(PEG),and arginine-glycine-aspartic acid(RGD).The RGD-modified PTX-PDCs were spherical nanoparticles(NPs)that would be released from scaffolds and identified GBM cells actively.Internalized redox-sensitive PTX-PDCs would be decomposed and release PTX inside GBM cells under the circumstances of glutathione(GSH).The release profiles of PTX from the scaffolds with/without GSH were investigated.In vitro cytotoxicity assay revealed that the dual-targeting PTX-PDCs from scaffolds could specifically kill GBM cells and protect normal cells,suggesting that dual-targeting PTX-PDC-loaded scaffolds may have the potential to repair tumor-induced brain injury.In vivo anti-recurrence assay indicated that the PTX-PDC-scaffolds could deliver PTX-PDCs to the GBM cells followed by inhibiting tumor growth and inducing apoptosis.In general,the PTX prodrug-loaded devices exhibited significant anti-GBM effects and normal tissue protection simultaneously,indicating that the WBPU scaffolds incorporated with dual-targeting PTX-PDCs may be a promising strategy for local therapy of GBM.

Expression of Dickkopf-like1 protein(Dkkl1) in mouse testis

Objective To investigate the expression and the distribution of Dickkopf-likel （Dkkll） protein during the development of mouse testis. Methods Testes eDNA samples from BALB/c mice in different postnatal days were hybridized with mouse whole genome affymetrix chip to screen the spermatogenesisrelated genes. The characteristics of the selected genes were analyzed by various bioinformatics tools. The mRNA expression of Dkkll at different stages of testis development and different tissues in mouse were analyzed by RT-PCR. The protein localization of Dkkll in mouse testis was assesed by immunohistoehemistry. Results By analyzing the gene chip signals of mouse testis aged 4 d, 9 d, 18 d, 35 d, 54 d and 6 months, Dkkll was identified with a differential expression in the develop- mental stages of testis. RT-PCR analysis showed that the expression of Dkkll mRNA was firstly detected on 15 d testis tissue and gradually upregulated during the testis developing to the adult stage. The Dkkll protein was predominantly located in spermatocytes and round spermatids in mouse testis. Conclusion The expression of Dkkll is gradually upregulated during the development of mouse testis and corresponds to the mouse spermatogenesis. It may play a critical role in male mammalian spermatogenesis.

Effect of Fluorocarbon Side Chain on the Microphase Morphology and Rheological Behavior of Thermoplastic Polyurethanes

Fluorinated diols(FDO)with dangling chain were introduced into polyether urethanes(PEUs)as chain extender in order to achieve internal plasticization.Based on temperature dependent Fourier transform infrared(FTIR)spectroscopy results,the fluorinated polyether urethanes(FPEUs)exhibited weaker hydrogen bonding between C=O and N―H groups with addition of FDO.The crystallinity of hard domain was destroyed determined by thermal analysis.Combined with the results of dynamic mechanical analysis(DMA)and dissipative particle dynamics(DPD)simulation,it was proved that more loosely aggregated hard domains with weakened interaction separated from soft segment were formed.Rheological analysis indicated that FDO reduced the complex viscosity and viscous flow activation energy which endowed the polymer with more flexibility.Despite the loss of hydrogen bonds,there was no significant decline in mechanical property resulting from the decrease of hard segment dissolved in soft segment phase.The presence of fluorinated carbon side chain could function as internal plasticizer and contribute to the processability of polyurethane.

Effect of Chain Extender on Hydrogen Bond and Microphase Structure of Biodegradable Thermoplastic Polyurethanes

Thermomechanical properties of polyurethanes（PUs） strongly depend on the molecular interactions and microphase structure. In this work, two chain extenders with different ratios, flexile 1,4-butanediol（BDO） and branched trimethylolpropane mono allyl ether（TMPAE）, are used to tune the molecular interactions and microphase structures of a series of biodegradable thermoplastic polyurethanes（TPUs）. In TPUs, the biodegradable polycaprolactone（PCL, M_n of 2000） is used as soft segment while 1,6-diisocyanatohexane（HDI） and chain extenders are used as hard segment. Fourier transform infrared spectroscopy（FTIR）, proton nuclear magnetic resonance spectroscppy（~1 H-NMR）, gel permeation chromatography（GPC）, differential scanning calorimetry（DSC）, dynamic mechanical analysis（DMA） and mechanical tests were performed to characterize the bulk structure and properties of TPUs. Compared with BDO, the steric bulk of TMPAE is larger. The increment of TMPAE can help to increase the hydrogen bond content, microphase separation, and the elastic modulus ratio（R）, which would strongly affect the thermomechanical property of the TPUs. The results of this work verify the importance of the structure of chain extender on the properties of TPUs. It provides valuable information for further understanding the structure-property relationships of these polyurethanes.

Elaborating Polyurethane Pillowy Soft Mat on Polypropylene Monofilament Surface with Stepwise Surface Treatments

The dissatisfactory mechanical compliance between stiff polypropylene(PP)and soft human tissue is one of the main factors causing the implanted complication of PP mesh devices such as chronic abdominopelvic pain and mesh exposure.This work aims to improve the mechanical compliance of PP monofilament to human tissue without compromising the mechanical properties by elaborating polyurethane pillowy soft mat on the PP monofilament surface.Combining polarity pretreatment with dopamine-sedimentation,stiff PP monofilament can be wrapped up facilely and tightly in soft polyurethane to obtain PU/PP complex fiber with a core-shell structure.Notably,the interfacial shear strengths(IFSS)between stepwise treated PP monofilament and PU mat can effectively increase 586%compared to raw PP.This work provides a promising surface modification strategy to improve the interfacial adhesion between PP monofilament and PU mat.The obtained novel PU/PP complex fiber with pillowy soft mat would be a potential application in abdominal wall defects,hernia repair and pelvic organ prolapsed surgery.