Preshearing Control for Calcium Phosphate Cement Rheology
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Solution Overview
Problem
Current bone cement delivery technologies lack control over the rheology, setting kinetics, and injectability/extrudability of inorganic cements, making it difficult for surgeons to tailor the flow properties and setting times during surgical procedures, and require costly FDA approvals for new formulations.
Innovation Solution
The method involves preshearing calcium phosphate cement suspensions using steady or oscillatory torsional deformations to control shear viscosity, elasticity, and setting kinetics, allowing for adjustable injectability and extrudability through a preshearing mechanism that can be implemented by surgeons or robotic systems, reducing the need for chemical retardants and facilitating precise control of cement properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If calcium phosphate cement formulations are used to achieve rapid dissolution and crystallization for immediate shape retention, then the setting time is shortened and shape retention is improved, but the shear viscosity increases rapidly making injection difficult
Solution Approach 1:
The patent applies preshearing to the cement suspension before injection to temporarily reduce its shear viscosity. By subjecting the cement to controlled shear deformation in advance, the interparticle network is disrupted, lowering viscosity and facilitating injection through narrow capillaries. After injection, the cement recovers its viscosity and elasticity to achieve immediate shape retention.
Solution Approach 2:
The patent exploits the time-dependent rheological behavior of calcium phosphate cements, which exhibit shear-thinning and thixotropic properties. The viscosity and elasticity dynamically evolve with time and shear history. By controlling the shear rate and duration of preshearing, the cement can be temporarily adjusted to a more flowable state for injection, then naturally recover to a rigid state for shape retention.
2Duration of action of moving object
If chemical additives such as citric acid or salts are added to modify setting time and flowability, then the setting kinetics and viscosity are altered, but costly FDA approvals are required for new formulations
Solution Approach 1:
The patent replaces chemical modification approaches with mechanical preshearing to control setting time and flowability. Instead of adding chemical additives like citric acid or salts that require FDA approval, the invention uses controlled mechanical shear deformation to temporarily modify the rheological properties of the cement suspension, enabling adjustment of setting kinetics without formulation changes.
Solution Approach 2:
The patent changes the physical state and rheological parameters of the cement suspension through preshearing. By applying controlled shear stress and strain, the viscosity, elasticity, and setting kinetics are dynamically adjusted. This physical parameter modification avoids the need for chemical composition changes and associated regulatory approvals.
3Ease of operation
If the surgeon applies sufficient pressure on the syringe ram to overcome pressure drop during injection, then the cement can be injected, but the rapid increase in viscosity and elasticity limits the injection duration to the setting time
Solution Approach 1:
The patent applies preshearing to the cement suspension before injection to temporarily reduce its viscosity and extend the injection window. By disrupting the interparticle network through controlled shear deformation in advance, the cement remains more flowable for a longer duration, giving the surgeon adequate time to complete the injection procedure without rushing against the rapid setting timeline.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables surgeons to tailor the flow properties and setting times of bone cements in real-time, enhancing surgical efficiency and reducing the need for multiple formulations, while avoiding costly FDA approvals by mechanically adjusting the setting times and viscosity, thus improving the precision and adaptability of bone cement delivery.
Implementation Method 1
subjecting the cementitious ceramic paste to predetermined preshearing conditions of shearing modes, shearing rates, and shearing strains in situ using a preshearing mechanism to control the time-dependency of the shear viscosity
Implementation Method 2
The present disclosure shows that the shear viscosity, elasticity and the setting kinetics of various relevant calcium phosphate cement formulations are dependent on such preshearing of the cement suspensions
Implementation Method 3
subjecting the cementitious ceramic paste to predetermined preshearing conditions of shearing modes, shearing rates, and shearing strains in situ using a preshearing mechanism to control the time-dependency of the shear viscosity, and elasticity, hence the injectability of the bone cement
Data Source
AI summary
The invention provides a system for the preshearing based control of the flow and deformation behavior, i.e., the setting kinetics, and the time dependent shear viscosity, elasticity of aqueous cementitious suspensions that can be used for bone repair and regeneration. The dynamic cement microstructure is tailored to the demands of the surgical tasks (faster/slower setting) or additive manufacturing tasks (lower/higher viscosity) by application of various preshearing conditions. Since the relationships between the preshearing and pressurization conditions and the setting kinetics and the time dependent changes in elasticity and viscosity are complex, a priori characterization of viscoelastic properties using the advanced rheological characterization technique of small-amplitude oscillatory rheometry is needed to enable such tailoring. The preshearing system is intended to give control on the injectability and setting time of any calcium phosphate cement formulation to the surgeon during an orthopedic surgery where a batch of bone cement is processed. Other possible utilizations of the system include controlling the setting kinetics, shear viscosity and facilitating the resultant flow stability of cementitious ceramic suspensions processed in direct ink writing assemblies for additive manufacturing of cement constructs, in injection systems for oil wells, restoration and fracking.