Heparin, an important polysaccharide, has been widely used for coatings of cardiovascular devices because of its multiple biological functions including anticoagulation and inhibition of intimal hyperplasia. In this study, surface heparinization of a commonly used 316L stainless steel (SS) was explored for preparation of a multifunctional vascular stent. Dip-coating of the stents in an aqueous solution of dopamine and hexamethylendiamine (HD) (PDAM/HD) was presented as a facile method to form an adhesive coating rich in primary amine groups, which was used for covalent heparin immobilization via active ester chemistry. A heparin grafting density of about 900 ng/cm(2) was achieved with this method. The retained bioactivity of the immobilized heparin was confirmed by a remarkable prolongation of the activated partial thromboplastin time (APTT) for about 15 s, suppression of platelet adhesion, and prevention of the denaturation of adsorbed fibrinogen. The Hep-PDAM/HD also presented a favorable microenvironment for selectively enhancing endothelial cell (EC) adhesion, proliferation, migration and release of nitric oxide (NO), and at the same time inhibiting smooth muscle cell (SMC) adhesion and proliferation. Upon subcutaneous implantation, the Hep-PDAM/HD exhibited mitigated tissue response, with thinner fibrous capsule and less granulation formation compared to the control 316L SS. This number of unique functions qualifies the heparinized coating as an attractive alternative for the design of a new generation of stents.

杨莹Mussel-Inspired One-Step Adherent Coating Rich in Amine Groups

A prominent research topic in contemporary advanced functional materials science is the production of smart materials based on polymers that may independently adjust their physical and/or chemical characteristics when subjected to external stimuli. Smart hydrogels based on poly(N-isopropylacrylamide) (PNIPAM) demonstrate distinct thermoresponsive features close to a lower critical solution temperature (LCST) that enhance their capability in various biomedical applications such as drug delivery, tissue engineering, and wound dressings. Nevertheless, they have intrinsic shortcomings such as poor mechanical properties, limited loading capacity of actives, and poor biodegradability. Formulation of PNIPAM with diverse functional constituents to develop hydrogel composites is an efficient scheme to overcome these defects, which can significantly help for practicable application. This review reports on the latest developments in functional PNIPAM-based smart hydrogels for various biomedical applications. The first section describes the properties of PNIPAM-based hydrogels, followed by potential applications in diverse fields. Ultimately, this review summarizes the challenges and opportunities in this emerging area of research and development concerning this fascinating polymer-based system deep-rooted in chemistry and material science.

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Poly(N-isopropylacrylamide)-Based Hydrogels for Biomedical Applications: A Review of the State-of-the-Art

Since their discovery in the 1980s, injectable self-setting calcium phosphate cements (CPCs) are frequently used in orthopedic, oral and maxillofacial surgery due to their chemical resemblance to the mineral phase of native bone. However, these cements are very brittle, which complicates their application in load-bearing anatomical sites. Polymeric fibers can be used to transform brittle calcium phosphate cements into ductile and load-bearing biomaterials. To understand and optimize this process of fiber reinforcement, it is essential to characterize the mechanical properties of fiber-free calcium phosphate matrices in full detail. However, the mechanical performance of calcium phosphate cements is usually tested under compression only, whereas bending and tensile tests are hardly performed due to technical limitations. In addition, computational models describing failure behavior of calcium phosphate cements under these clinically more relevant loading scenarios have not yet been developed. Here, we investigate the failure behavior of calcium phosphate cements under bending and tensile loading by combining, for the first time, experimental tests and numerical modeling. To this end, a 3-D gradient-enhanced damage model is developed in a finite element framework, and numerical results are correlated to experimental three-point bending and tensile tests to characterize the mechanical properties of calcium phosphate cements in full detail. The presented computational model is successfully validated against experimental results and is able to predict the mechanical response of calcium phosphate cement under different types of loading with a unique set of parameters. This model offers a solid basis for further experimental and computational studies on the development of load-bearing bone cements.

https://repository.tudelft.nl/islandora/object/uuid%3A9e2b1aa2-6fa2-4dc6-85a3-101ea99db2ae/datastream/OBJ/download

Experimental and numerical analysis on bending and tensile failure behavior of calcium phosphate cements

Vertebral compression fractures (VCFs) are a very common problem among the elderly, which ultimately result in severe pain and a drastically reduced quality of life An effective treatment for VCFs is the minimally invasive augmentation of the damaged vertebrae through vertebroplasty and/or kyphoplasty These surgical procedures treat the affected vertebrae by injection of poly(methyl methacrylate) cement (PMMA) into the vertebral body However, clinical use of PMMA cement is associated with major drawbacks Bioceramic cements such as injectable calcium phosphate cements (CPC) exhibit a superior osteocompatibility over PMMA cements, but are too brittle for load-bearing applications Here, we evaluated the handling and mechanical properties of a recently developed CPC formulation containing both poly(vinyl alcohol) (PVA) fibers and carboxymethyl cellulose (CMC) as an alternative to PMMA cement for vertebro- and kyphoplasty Our results demonstrate that the addition of CMC rendered fiber-reinforced CPC injectable without negatively affecting its mechanical properties Further, an ex vivo mechanical analysis clearly showed that extravasation of PVA fiber-reinforced CPC with CMC into trabecular bone was limited as compared to PMMA Finally, we observed that the ex vivo biomechanical performance of vertebrae treated with CMC and PVA fibers was similar to PMMA-treated vertebrae The obtained data suggests that PVA fiber-reinforced CPCs with CMC possesses adequate handling, mechanical and structural characteristics for vertebro- and kyphoplasty procedures These data pave the way for future preclinical studies on the feasibility of treating vertebral compression fractures using PVA fiber-reinforced CPC with CMC

/pdf/tough-and-injectable-fiber-reinforced-calcium-phosphate-242e94i5xo.pdf

Tough and injectable fiber reinforced calcium phosphate cement as an alternative to polymethylmethacrylate cement for vertebral augmentation: a biomechanical study.

Biological response, antibacterial properties of ZrO2/hydroxyapatite/graphene oxide encapsulated into nanofibrous scaffolds of polylactic acid for wound healing applications.

Calcium phosphate cements (CPCs) are frequently used as synthetic bone substitute materials due to their favorable osteocompatibility and handling properties. However, CPCs alone are inherently brittle and exhibit low strength and toughness, which restricts their clinical applicability to non-load bearing sites. Mechanical reinforcement of CPCs using fibers has proven to be an effective strategy to toughen these cements by transferring stress from the matrix to the fibers through frictional sliding at the interface. Therefore, tailoring the fiber-matrix affinity is paramount in designing highly toughened CPCs. However, the mechanistic correlation between this interaction and the macromechanical properties of fiber-reinforced CPCs has hardly been investigated to date. The aim of this study was to tailor the fiber-matrix interface affinity by modifying the surface of poly(vinyl alcohol) (PVA) fibers and correlate their interfacial properties to macromechanical properties (i.e. fracture toughness, work-of-fracture and tensile strength) of CPCs. Results from single fiber pullout tests reveal that the surface modification of PVA fibers increased their hydrophilicity and improved their affinity to the CPC matrix. This observation was evidenced by an increase in the interfacial shear strength and a reduction in the critical fiber embedment length (i.e. maximum embedded length from which a fiber can be pulled out without rupture). This increased interface affinity facilitated energy dissipation during fracture of CPCs subjected to macromechanical three-point flexure and tensile tests. The fracture toughness also significantly improved, even for CPCs reinforced with fibers of lengths greater than their critical fiber embedment length, suggesting that other crack-arresting mechanisms also play an important role in mechanically reinforcing CPCs. Overall, these basic insights will improve the understanding of the correlation between micro- and macromechanical characteristics of fiber-reinforced CPCs.

Micro- and macromechanical characterization of the influence of surface-modification of poly(vinyl alcohol) fibers on the reinforcement of calcium phosphate cements

Calcium phosphate ceramics are frequently applied to stimulate regeneration of bone in view of their excellent biological compatibility with bone tissue. Unfortunately, these bioceramics are also highly brittle. To improve their toughness, fibers can be incorporated as the reinforcing component for the calcium phosphate cements. Herein, we functionalize the surface of poly(vinyl alcohol) fibers with thermoresponsive poly(N-isopropylacrylamide) brushes of tunable thickness to improve simultaneously fiber dispersion and fiber-matrix affinity. These brushes shift from hydrophilic to hydrophobic behavior at temperatures above their lower critical solution temperature of 32 °C. This dual thermoresponsive shift favors fiber dispersion throughout the hydrophilic calcium phosphate cements (at 21 °C) and toughens these cements when reaching their hydrophobic state (at 37 °C). The reinforcement efficacy of these surface-modified fibers was almost double at 37 versus 21 °C, which confirms the strong potential of thermoresponsive fibers for reinforcement of calcium phosphate cements.

https://pubs.acs.org/doi/pdf/10.1021/acsami.9b08311

Thermoresponsive Brushes Facilitate Effective Reinforcement of Calcium Phosphate Cements

Calcium phosphate cements (CPCs) are frequently used as synthetic bone substitute, but their intrinsic low fracture toughness impedes their application in highly loaded skeletal sites. However, fibers can be used to reduce the brittleness of these CPCs provided that the affinity between the fibers and cement matrix facilitates the transfer of loads from the matrix to the fibers. The aim of the present work was to improve the interface between hydrophobic polylactic acid (PLA) microfibers and hydrophilic CPC. To this end, calcium-binding alendronate groups were conjugated onto the surface of PLA microfibers via different strategies to immobilize a tunable amount of alendronate onto the fiber surface. CPCs reinforced with PLA fibers revealed toughness values which were up to 50-fold higher than unreinforced CPCs. Nevertheless, surface functionalization of PLA microfibers with alendronate groups did not improve the mechanical properties of fiber-reinforced CPCs.

Surface functionalization of polylactic acid fibers with alendronate groups does not improve the mechanical properties of fiber-reinforced calcium phosphate cements

Daniela-Geta Petre

Papers

Micro- and macromechanical characterization of the influence of surface-modification of poly(vinyl alcohol) fibers on the reinforcement of calcium phosphate cements

Thermoresponsive Brushes Facilitate Effective Reinforcement of Calcium Phosphate Cements

Surface functionalization of polylactic acid fibers with alendronate groups does not improve the mechanical properties of fiber-reinforced calcium phosphate cements