Marjolein de Ruiter

Bio: Marjolein de Ruiter is an academic researcher from Radboud University Nijmegen. The author has contributed to research in topics: Ultimate tensile strength & Fiber. The author has an hindex of 1, co-authored 1 publications receiving 7 citations.

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

Abstract: 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.

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

Abstract: 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

Fracture Models and Effect of Fibers on Fracture Properties of Cementitious Composites-A Review.

Abstract: Cementitious composites have good ductility and pseudo-crack control. However, in practical applications of these composites, the external load and environmental erosion eventually form a large crack in the matrix, resulting in matrix fracture. The fracture of cementitious composite materials causes not only structural insufficiency, but also economic losses associated with the maintenance and reinforcement of cementitious composite components. Therefore, it is necessary to study the fracture properties of cementitious composites for preventing the fracture of the matrix. In this paper, a multi-crack cracking model, fictitious crack model, crack band model, pseudo-strain hardening model, and double-K fracture model for cementitious composites are presented, and their advantages and disadvantages are analyzed. The multi-crack cracking model can determine the optimal mixing amount of fibers in the matrix. The fictitious crack model and crack band model are stress softening models describing the cohesion in the fracture process area. The pseudo-strain hardening model is mainly applied to ductile materials. The double-K fracture model mainly describes the fracture process of concrete. Additionally, the effects of polyvinyl alcohol (PVA) fibers and steel fibers (SFs) on the fracture properties of the matrix are analyzed. The fracture properties of cementitious composite can be greatly improved by adding 1.5-2% PVA fiber or 4% steel fiber (SF). The fracture property of cementitious composite can also be improved by adding 1.5% steel fiber and 1% PVA fiber. However, there are many problems to be solved for the application of cementitious composites in actual engineering. Therefore, further research is needed to solve the fracture problems frequently encountered in engineering.

In-Situ Hardening Hydroxyapatite-Based Scaffold for Bone Repair

Abstract: Musculoskeletal conditions are becoming a major health concern because of an aging population and sports- and traffic-related injuries. While sintered hydroxyapatite implants require machining, calcium phosphate cement (CPC) bone repair material is moldable, self-hardens in situ, and has excellent osteoconductivity. In the present work, new approaches for developing strong and macroporous scaffolds of CPC were tested. Relationships were determined between scaffold porosity and strength, elastic modulus and fracture toughness. A biocompatible and biodegradable polymer (chitosan) and a water-soluble porogen (mannitol) were incorporated into CPC: Chitosan to make the material stronger, fast-setting and anti-washout; and mannitol to create macropores. Flexural strength, elastic modulus, and fracture toughness were measured as functions of mannitol mass fraction in CPC from 0% to 75%. After mannitol dissolution in a physiological solution, macropores were formed in CPC in the shapes of the original entrapped mannitol crystals, with diameters of 50 μm to 200 μm for cell infiltration and bone ingrowth. The resulting porosity in CPC ranged from 34.4% to 83.3% volume fraction. At 70.2% porosity, the hydroxyapatite scaffold possessed flexural strength (mean ± sd; n = 6) of (2.5 ± 0.2) MPa and elastic modulus of (0.71 ± 0.10) GPa. These values were within the range for sintered porous hydroxyapatite and cancellous bone. Predictive equations were established by regression power-law fitting to the measured data (R2 > 0.98) that described the relationships between scaffold porosity and strength, elastic modulus and fracture toughness. In conclusion, a new graft composition was developed that could be delivered during surgery in the form of a paste to harden in situ in the bone site to form macroporous hydroxyapatite. Compared to conventional CPC without macropores, the increased macroporosity of the new apatite scaffold may help facilitate implant fixation and tissue ingrowth.