Preshearing method and apparatus for the control of the rheology and the injectability of aqueous cement suspensions for bone repair and regeneration

Abstract

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. The relationships between the preshearing and pressurization conditions and the setting kinetics and the time dependent changes in elasticity and viscosity are complex and characterization of viscoelastic properties using advanced rheological characterization techniques including small-amplitude oscillatory and steady torsional rheometry is needed a priori 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 restoration and fracking.

We claim: 
     
         1 . A process for controlling the setting rate, deformation behavior and injectability/extrudability of cementitious ceramic suspensions consisting of a binder liquid phase and mixtures of ceramic particles, the process comprising the steps of
 Characterization of the setting kinetics and deformation behavior (rheology) of a cementitious ceramic suspension under quiescent and different shearing conditions “preshearing” using a rotational rheometer which is able to generate time dependent shear viscosity at various shear stresses and linear viscoelastic material functions (dynamic properties) as a function of frequency and strain amplitude;   Compiling the setting kinetics and deformation behavior during and after preshearing into a data base to provide guidance on the relationship between both the preshearing and pressurization conditions and the injectabillty/extrudability window of the suspension during the surgical or additive manufacturing procedure;   Definition by the surgeon or the operator what the injectability period, viscosity or the extrusion flow rate of the cementitious ceramic suspension should be during manual or robotic deposition   Preshearing and pressurizing the cementitious ceramic suspension in a preshearing apparatus using the guidelines provided by the preshearing database to control its setting kinetics, deformation behavior and injectability/extrudability during manual or robotic deposition   
     
     
         2 . The process of  claim 1 , where the cementitious ceramic suspension is an inorganic bone cement used in bone repair and regeneration applications 
     
     
         3 . The process of  claim 1 , where the surgical procedure includes spinal fusion, vertebroplasty, khyphoplasty, cranioplasty, periodontal and endodontal surgeries 
     
     
         4 . The process of  claim 1 , where the binder liquid phase of the cementitious ceramic suspension is pure water or an aqueous solution of water and water soluble chemicals including citric acid, sodium chloride salt, trisodium citrate salt, sodium hydrogen phosphate, orthophosphoric acid 
     
     
         5 . The process of  claim 1 , where the particles of the cementitious suspension are inorganic ceramics including phases of calcium aluminate, calcium sulphate, calcium silicate, calcium aluminum silicate, zinc phosphate, magnesium phosphate, magnesium oxychloride, magnesium oxysulphate or calcium carbonate ceramics 
     
     
         6 . The process of  claim 1  where the rheological data in the preshearing database is compiled by monitoring the variations in the viscosity and elasticity with time, temperature, and preshearing history, thus pinpointing the characteristic data of the linear viscoelastic strain limit, cement dough time, cement initial setting time, cement final setting time and the setting promoting frequency limit under quiescent and preshearing conditions using a rotational rheometer with the ability to generate steady shearing at various shear rates or oscillatory shearing at various frequencies and strain amplitudes. 
     
     
         7 . The process of  claim 2 , where the particles of the inorganic bone cement are calcium phosphate ceramics 
     
     
         8 . The process of  claim 7 , where the particles of the calcium phosphate ceramics are brushite forming cement precursors 
     
     
         9 . The process of  claim 7 , where the particles of the calcium phosphate ceramics are hydroxyapatite forming cement precursors 
     
     
         10 . The process of  claim 7 , where the calcium phosphate cements have starting calcium phosphate particles with mean sizes that are generally less than 10 micrometers. 
     
     
         11 . The process of  claim 7 , where the calcium phosphate cements have brushite or hydroxyapatite seed particles that are less than 5% in concentration. 
     
     
         12 . The process of  claim 6 , where the viscosity is described by shear viscosity measured as a function of time, temperature and shear rate or the magnitude of complex viscosity measured as a function of time, temperature, strain amplitude and frequency 
     
     
         13 . The process of  claim 6 , where the elasticity is described by the storage modulus measured as a function of time, temperature, strain amplitude and frequency. 
     
     
         14 . An apparatus to carry out preshearing and pressurization as a compounding extruder characterized in that the suspension can be given the targeted preshearing history and delivered by it under manual or robotic control, and comprising a barrel containing inlet ports and outlet opening; at least one screw inside said barrel, a shaft connected to said screw, a gear driving said shaft and screw; an electronic controller and power pack moving said gear. 
     
     
         15 . The apparatus of  claim 14 , where the geometry of the apparati and the operating conditions during preshearing and pressurization are determined either empirically or via mathematical modeling and simulation of the flow and heat transfer occurring in the batch or semi-batch apparatus as a function of time. 
     
     
         16 . The apparatus of  claim 14 , where the extruder is a batch single screw extruder with a screw that is capable of rotating in both clockwise and counterclockwise direction and alternating between rotation in the clockwise and counterclockwise direction in a cyclic manner. 
     
     
         17 . The apparatus of  claim 16 , where the extruder is a batch single screw extruder with a die, the opening of which can be controlled to provide either no flow out of the extruder or flow out of the extruder at the desired flow rate. 
     
     
         18 . The apparatus of  claim 14 , where the extruder is a batch twin screw extruder with two screws that are rotating in either clockwise of counterclockwise direction or oscillating screws which alternate between rotations in the clockwise and counterclockwise direction in a cyclic manner. 
     
     
         19 . The apparatus of  claim 18 , where the extruder is a batch twin screw extruder with a die, the opening of which can be controlled to provide either no flow out of the extruder or flow out of the extruder at the desired flow rate. 
     
     
         20 . The apparatus of  claim 14 , where the extruder is a modified semi-batch single screw extruder with at least two successive, independent screws that are driven by concentric hollow shafts that are powered by different electronically controlled gears. 
     
     
         21 . The apparatus of  claim 20 , where the extruder is a modified semi-batch single screw extruder with a die, the opening of which can be controlled to provide either no flow out of the extruder or flow out of the extruder at the desired flow rate. 
     
     
         22 . The apparatus of  claim 14 , where continuous preshearing and pressurization is realized by coupling at least two batch or two semi-batch mixers in parallel so that the inlet ports and the corresponding screws of each apparatus operate in reverse and alternating order such that the coupled apparati receive, mix, convey and deliver the cement suspension at different periods that are synchronized according to the duration of the preshearing determined according to the guidelines of the database and the requirements of the particular task on hand. 
     
     
         23 . The apparatus of  claim 17 , where the batch single screw extruder can provide a time dependent preshearing history to the cement suspension by oscillatory or steady torsion following the guidelines of the data base and the requirements of the particular task on hand. 
     
     
         24 . The apparatus of  claim 21 , where each independent screw is capable of rotating in both clockwise and counterclockwise direction and alternating between rotation in the clockwise and counterclockwise direction in a cyclic manner. 
     
     
         25 . The apparatus of  claim 21 , where each independent screw can independently provide a time dependent preshearing history to the cement suspension by oscillatory or steady torsion following the guidelines of the database and the requirements of the particular task on hand