PRESHEARING METHOD AND APPARATUS FOR THE CONTROL OF THE RHEOLOGY AND THE INJECTABILITY OF AQUEOUS CEMENT SUSPENSIONS FOR BONE REPAIR AND REGENERATION
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.
The present invention relates to ceramic cements used in bone repair and regeneration, and more particularly to methods and devices for mixing, pressurization, and preshearing based in situ treatment for the control of the flowability, setting kinetics, and injectability/extrudability during manual or robotic deposition of such cementitious suspensions.
Prior artCementitious materials are the materials of choice in design and manufacturing of structural, monolithic or injectable components due to their abundancy in nature, and by virtue of their flowability before setting. The latter is exploited most commonly in biomedical applications for bone repair and regeneration using calcium phosphate based cements (driven by the exceptional osteoconductivity of calcium phosphates) as injectable biomaterials (bone cement pastes) especially following cancerous bone removal and for minimally invasive surgeries. The minimally invasive clinical applications of bone cement pastes include spinal fusion, vertebroplasty, khyphoplasty, cranioplasty and periodontal surgery. Such inorganic bone cement pastes typically exhibit relatively low shear viscosity and elastic modulus and gain elasticity and shear viscosity with time. The rates of growths of the elasticity and viscosity of calcium phosphate based cements are higher than those of conventional cements as a result of the rapid dissolution and crystallization of various calcium phosphate phases in water. For this reason they are especially suitable for additive manufacturing of geometrically complex constructs where the deposited paste is made to gain elasticity for immediate shape retention. However additive manufacturing of relatively slow setting cementitious suspensions have been realized by pressurization through hoses of relatively large diameters (>10 mm) due to the propensity of such dynamically evolving suspensions for flow instabilities and related clogging issues during pressure-driven flows through narrow capillaries with diameters in the micronmeter scale.
During surgical applications the precise placement of the bone cement paste by the surgeon is very important. Various means are available for the placement of the cement paste into the repair site. Generally a syringe with a hypodermic needle with a diameter around 1 mm can be used. During the injection of the cement paste a pressure drop of the ceramic paste is developed as the paste flows out of the syringe and the needle and as it is forced into the treatment site. This pressure drop represents the bottle neck to injection and is overcome by the surgeon applying a sufficient pressure on the ram of the syringe that holds the cement to overcome the pressure drop. The applicability and the injectability of the cement suspension are governed by the shear viscosity and the elasticity of the ceramic paste (functions of temperature, time, solid content and shear rate/stress). Once the ceramic suspension attains certain upper thresholds of viscosity and elasticity the injection of the cement paste to the treatment site via the pressure applied on the ram by the surgeon is no longer possible. The rapid increase of the shear viscosity of the cement paste (transition from flowable suspension to a gel and then to a rigid solid) is associated with the cement reaching its setting time. Thus, the setting time restricts the duration of time that the cement remains viable for injection during surgery. Currently in clinical practice, the setting time and flowability of the cementitious suspension are not adjustable parameters for a given formulation. The surgeon needs to select and use a suitable cement formulation (a commercial product which typically comes in a syringe or is mixed in the operating room) to obtain the targeted setting time and flowability.
Synthesis of ingredients for bone cements is intensively researched since there are unlimited combinations of possible constituents. The most popular methods for generation of new types of calcium phosphate based bone cements include the addition of chemical groups that have affinity to calcium ions such as citric acid or citrate salts to prolong the setting period, addition of salts to the cement setting liquid to increase the ionic strength and decrease the supersaturation of precursor ions, addition of phosphate containing salts such as sodium phosphate to increase the supersaturation, addition of acids to increase the solubility, and addition of chemicals like gentamycin that electrostatically stabilize calcium phosphate crystals by increasing their surface charge. The major problem that is faced is that every time there is a formulation change that involves the use of ingredients that are not approved by US Food and Drug Administration, FDA, for in vivo usage, new and very costly FDA approvals may be necessary for implementation of these ingredients and formulations. Furthermore, the problem associated with the development of many choices for the surgeon is that the cement needs to be tailored via changes in composition to the specific application at hand. The surgeon currently has no recourse but to switch formulations depending on the requirements of the specific surgery since there are typically no adjustable parameters available during the injection of the bone cements to allow their tailoring for specific applications at the surgery site. Furthermore, multiple changes in flowability and elasticity may be necessary during the course of surgery to accommodate the complications that arise during surgery.
The mixing, conveying and delivery of the bone cement are time consuming in practice when done manually and separately. Bone cement mixing and delivery devices have been invented either as separate automated parts or as all-in-one facilities to improve the efficiency of preparation and delivery of the material. Previous inventions that introduce novelty into the area are as follows. US Patent # 2008/0065088 A1 provides a mixing device for bone cements that is comprised of multiple chambers and pistons. U.S. Pat. No. 8,409,211 B2 introduces a bone cement delivery device with a tubular inner wall and a tubular outer wall, helical thread and vacuum and a pressure sensor. US Patent # 2008/0154229 A1 discloses a cement mixing and delivery device that uses a helical element and vibration to mix and deliver. These US patents and applications lack method and control on the flow behavior, setting time and kinetics of the ceramic bone cements. Other bone cement delivery devices, such as a system for injecting a low viscosity fluid into a bone cement reservoir [U.S. Pat. No. 8,870,888 B2], a delivery device that uses a screw actuator to push the plunger [U.S. Pat. No. 6,712,794 B2], a delivery device that has an electronic actuator controller [U.S. Pat. No. 8,403,888 B2], a device for transferring bone cement into a syringe for delivery [U.S. Pat. No. 8,408,250 B2], and a device which has a vibration element attached to the delivery needle [U.S. Pat. No. 8,834,481 B2, U.S. Pat. No. 7,901,407 B2] are available.
Overall, none of these methods and devices can control the rheology (flow and deformation behavior), the setting kinetics and the injectability/extrudability window of the bone cement paste to accommodate the specific demands of a particular task that is being undertaken. On the other hand US Patent # 2009/0112365 A1 discloses a method for determination and mechanical modification of the setting kinetics of polymerisable cements used in orthopedic applications. Various environmental factors including temperature, humidity, sound wave velocity, etc. within and around the polymer based cements have been correlated with this method to cement setting kinetics and the level of polymerization.
Subsequent torsional or oscillatory mixing under non-specific stress conditions have been shown to facilitate the attainment of the level of maximum polymerization. In another disclosure on modification of rheology of fluids, U.S. Pat. No. 6,293,754 B1 explains direction of acoustic energy at frequencies between 1 kHz and 10 MHz to pressurized fluids for controlling viscosity by shear-thinning. The invention proposes a novel method of exploiting the shear-thinning mechanism and does not specifically apply to cementitious suspensions. In yet another method of agitation to alter the microstructure of cementitious suspensions, U.S. Pat. No. 4,202,413 discloses a method to improve the effectiveness of swelling clay particles that extend the inorganic cement suspension, by similar vigorous mixing. This method is only for the enhancement of the dispersion, swelling and extender function of inorganic, non-setting clay particles by application of simple blending action of a rotating blade. Conversely, preshearing method and apparatus disclosed in the present invention utilize a distinctly different mechanism than shear-thinning and specifically apply to inorganic, non-polymerisable, aqueous cements such as calcium phosphate bone cements by employing torsional shear stresses at specific modes, rates and amplitudes that are determined upon accurate rheological characterization a priori in order to shorten and lengthen the setting times and to increase or decrease the resultant development of cement viscosity. Clearly, there is a need for a method and apparatus to realize the ability to in situ tailoring of the injectability, the shear viscosity, and elasticity of such ceramic paste materials, during surgery. In addition, extrusion through a micronmeter-diameter nozzle during robotic deposition of cementitious suspension necessitates such precise control of the evolving microstructure and pressurization conditions to achieve flow stability. The present disclosure provides a method and an apparatus that can address the aforementioned requirements for the effective utilization of inorganic cementitious suspensions for such applications
BRIEF SUMMARY OF THE INVENTIONIn view of the foregoing background, a method and an apparatus for the tailoring of the flow behavior (shear viscosity, elasticity), setting time and the injectability/extrudability of cementitious ceramic suspensions prior to or during the course of delivery by an orthopedic surgeon or a robotic additive manufacturing system are disclosed. The present disclosure specifically relates to the modification of flow properties of a ceramic cement suspension by preshearing (i.e., via subjecting the cementitious suspension to steady or oscillatory torsional deformations at critical values of the shear rate, shear strain and frequencies), pressurization (i.e., delivery of flowable cement through a capillary by a screw-driven mechanism) and an apparatus for both preshearing and pressurization. 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. Thus preshearing and simultaneous or subsequent pressurization by a handheld or robotically controlled apparatus would allow specific tailoring of the flow properties and setting kinetics, and hence the control of the injectability/extrudability of the ceramic paste on one hand and the physical properties of the set cement on the other. The surgeon is given the freedom to choose the appropriate preshearing mode and preshearing parameters similar to considering different bone cement formulations that may be suitable for an application in terms of ease of injection, the setting time and ultimate mechanical properties. The invention also facilitates extrusion of cementitious suspensions for related applications including construction, structural restoration and additive manufacturing.
For a more complete understanding of the present invention, reference is made to the following detailed description of an embodiment considered in conjunction with the accompanying drawings, in which:
The following disclosure is presented to provide an illustration of the general principles of the present invention and is not meant to limit, in any way, the inventive concepts contained herein. Moreover, the particular features described in this section can be used in combination with the other described features in each of the multitude of possible permutations and combinations contained herein.
All terms defined herein should be afforded their broadest possible interpretation, including any implied meanings as dictated by a reading of the specification as well as any words that a person having skill in the art and/or a dictionary, treatise, or similar authority would assign thereto.
Further, it should be noted that, as recited herein, the singular forms ‘a,’ “an,” and “the” include the plural referents unless otherwise stated. Additionally, the terms “comprises” and “comprising” when used herein specify that certain features are present in that embodiment, however, this phrase should not be interpreted to preclude the presence or additional of additional steps, operations, features, components, and/or groups thereof.
The present disclosure generally relates to cementitious ceramic formulations, the rheological behavior and setting kinetics of which are very sensitive to preshearing. By definition, cementitious ceramics are single phase or a combination of ceramic powders that react with an aqueous setting solution. The mechanisms of the reactions may vary starting from hydration to dissolution, nucleation and crystallization. Initially flowable fluid mixture eventually gels, sets and hardens with time to a rigid mass with mechanical integrity. The invention is based on our recent observation that preshearing a cementitious calcium phosphate suspension in various shearing modes and under critical shearing conditions prior to injection can significantly increase or decrease the setting time, and thus can replace or complement the chemical setting retardants or enhancers that are utilized in the synthesis of clinically relevant calcium phosphate cements.
The present disclosure contemplates calcium phosphate and other types of inorganic cements that set at times close to or within the typical bone cement processing time of 10 to 45 minutes. Generally calcium phosphate cements with or without chemical retardants at the powder/liquid ratios between 1.0 and 4.5 and starting calcium phosphate particles with mean sizes that are generally less than 10 micrometers set within that period. Setting of water consuming cements like brushite forming calcium phosphate cements can generally be effectively retarded or delayed by preshearing whereas setting relatively slow setting cements like hydroxyapatite forming cements can generally be promoted by various mechanisms. Typical brushite forming cements set relatively rapidly in a few minutes and this period even shortens further when the water content decreases. For this reason setting retarder chemicals are necessary and become integral parts of most of the commercially available brushite forming calcium phosphate cements used in bone repair. The preshearing method and the apparatus offer the possibility to reduce/eliminate setting retarder or promoter chemicals from the cement formulation and their adverse effects on the biological and mechanical properties of the set biomaterial by increasing or decreasing the setting time mechanically.
The present disclosure discusses subjecting the cementitious ceramic formulations to time-dependent, strain amplitude-dependent or frequency-dependent shearing in a rheometer to determine the strain and strain rate conditions under which the setting of the ceramic paste is significantly altered. The rheometer is used to preshear the cement paste as well as to characterize the time dependent developments of its shear viscosity, elasticity, and injeadbility in a quiescent approach by removing the effect of strain history from measurements.
The present disclosure discloses a method comprising of subjecting the cementitious ceramic paste to predetermined preshearing conditions of shearing modes, shearing rates, and shearing strains in situ using a preshearing apparatus to control the time-dependency of the shear viscosity, and elasticity, hence the injectability of the bone cement using the data base generated by the use of the rheometer. The time it takes for cement paste to set can be increased or decreased by selecting the appropriate shearing mode (steady torsional flow versus oscillatory shear) or by selecting the appropriate values of the frequency or the strain amplitude in oscillatory shearing or shear rate in steady torsional flow.
The present disclosure also introduces a novel preshearing apparatus for preshearing-based control of the rheology, setting times and injectability/extrudability of inorganic cementitious suspensions.
Preshearing Method for Control of Rheological Behavior and Setting Time (Injectability)A preshearing method in accordance with an embodiment of the present invention has the following steps:
(1) subjecting of the cementitious ceramic formulation to steady or time-dependent preshearing in a small-amplitude oscillatory rheometer under systemically varied conditions of shear rate, shear strain amplitude and frequency;
(2) characterization of the time-dependent development of shear viscosity, elasticity and setting kinetics following preshearing and determining the strain and strain rate conditions under which the setting of the ceramic paste is significantly altered; steps #1 and #2 being undertaken to determine a priori the relationship between preshearing conditions and provide guidance to the surgeon on the evolution of the time dependent shear viscosity and elasticity (and hence the injectability window) of the ceramic suspension on preshearing conditions.
(3) preshearing of the bone cement by the surgical staff in the operating room or by a robotic operator using a preshearing apparatus under the conditions that are necessary to achieve the desired injectability window of the bone cement on the basis of the particular requirements of the task on hand.
Characterization of the time-dependent development of shear viscosity, elasticity and setting kinetics following preshearing in the small amplitude oscillatory rheometer involves measurement of the mechanical response of the cement suspension to a predetermined torsional strain or stress state, as a function of time. Various strain modes, rates, amplitudes and frequencies are known to elicit different rheological behaviors in calcium phosphate cements. Conducting these measurements at relatively low strain amplitudes (below critical linear viscoelastic strain amplitude) and low frequencies in an oscillatory torsional rheometer ensures that the cement setting kinetics are probed at a condition closest to the quiescent equilibrium state when the setting characteristics of a specific cement formulation is clearly exhibited. Hence determination of the linear viscoelastic strain limit (LVSL) for a cement formulation is necessary prior to these measurements. The linear viscoelastic strain amplitude limit of a cement suspension increases with growing crystals as the cement sets and as temperature increases, and with viscous loss of mechanical wave energy as frequency decreases. Its dependence on frequency is weak so that a wide range of frequencies can be applied to cement suspensions without exceeding the LVSL.
The setting kinetics of a cement suspension is determined from the variation of the storage modulus (the primary measure of elasticity) with time during oscillatory preshearing. Cement set at quiescent conditions represents the baseline reference in preshearing method with which various preshearing modes and conditions are related. Conventional testing in oscillatory rheometer is unable to precisely determine the setting kinetics of cements because of the effect of applied strain history on the setting kinetics. The only way to remove this effect is to partition the testing run into preshearing and measuring steps (or waiting and measuring steps for quiescent samples). This way the rheometer is used both to preshear the cement paste and to precisely characterize the time dependent developments of the shear viscosity, the elasticity and hence the injectability of the bone cement. During testing of quiescently setting cement this is accomplished by keeping the cement suspension at rest for various periods of time prior to the measurement step as demonstrated in the examples.
Testing the cement formulation at quiescent conditions and by preshearing in oscillatory rheometer at various frequencies enables the determination of five important data for any cement system (the LVSL, the dough time, the initial setting time, the final setting time, and the setting promoting frequency limit (SPFL)) as shown in
The alterations in the kinetic properties 2,3,4 resulting from the preshearing process are related to the baseline reference as promoting or delaying of the quiescent setting kinetics. These various preshearing effects are compiled and utilized as a guide for preshearing to tailor the setting kinetics by adjustment of the preshearing parameters. The preshearing method can be used to increase or to decrease the time it takes for the cement paste to set by selecting the appropriate shearing mode (steady torsional flow versus oscillatory shear) or by selecting the appropriate values of the frequency or the strain amplitude in oscillatory shearing or shear rate in steady torsional flow. The appropriate shearing mode and the parameters of shearing are obtained from rheological characterization and applied according to the kinetic requirements of the task as described schematically in
We have recently reported that oscillatory torsional preshearing enhances the setting kinetics and decreases the setting times of calcium phosphate cements provided that the applied strain amplitude is below the LVSL and the frequency is higher than the SPFL. [E. Şahin, D. M. Kalyon, “The rheological behavior of a fast-setting calcium phosphate bone cement and its dependence on deformation conditions”, Journal of the Mechanical Behavior of Biomedical Materials, Volume 72, 2017, Pages 252-260]. Furthermore, each unique cement system exhibits specific limits of these parameters that should be determined a priori according to the generally observed preshearing effects of oscillatory torsion given in Table 1,. The strain amplitude is the primary parameter for the preshearing method whereas the frequency of the applied oscillatory torsional strain is a fine tuning parameter. Injection or extrusion time periods and viscosities of bone cements can be tailored by application of the findings from preshearing experiments.
In theory, the mechanical energy applied to a cementitious suspension by oscillatory torsion is proportional to the strain amplitude. The viscous drag force on the particle is critical for the integrity of the inter-particle network that forms during setting of a cementitious suspension. At high applied energy levels particles and inter-particle crystal bonds disrupt and cement setting is retarded. This critical energy level for any suspension is manifested by the deviation from linear viscoelastic behavior and accurately monitored as a function of time by small amplitude oscillatory rheometry.
The crystal network forming during setting is prone to structural damage when the applied oscillatory or torsional strains exceed the linear viscoelastic strain limit as crystals cannot attenuate the applied deformation energy elastically and break. This limit increases with the cement setting extent since bigger, well developed crystals are stronger. Hence the effectiveness of applied strain amplitudes or shear strain rates depend on the setting kinetics of a particular cement formulation which can be determined by the empirical methods mentioned above. Furthermore, different preshearing modes have the capability to delay or retard the setting of calcium phosphate cements. Oscillatory torsional strains exceeding the linear viscoelastic strain limit cause a temporary reduction in cement setting extent as setting recovery occurs subsequently. Alternatively steady torsional strains applied to a calcium phosphate cement suspension cause continuous damage to the forming crystal network due to the monotonous increase in strain at a rate higher than the crystal growth rate.
Still referring to
Preshearing Apparatus to be Used as a Handheld Device or Integrated into a Robotic System
The preshearing device can generate and apply targeted strain rates and strains as a function of time for preshearing-based control of the rheology and setting time of injectable cementitious ceramic suspensions. The characterization steps provide the surgeon or robotic operator with a wealth of information as to how to control the injectability and workability of the bone cement via changes in the operating parameters of the preshearing device which is also capable of on-site mixing of the ingredients of the ceramic paste formulation and on-site pressurization and the delivery of the ceramic paste to the treatment site or the translating printing stage.
Still referring to
After the completion of the interspersing of the ingredients (mixing) additional rotation and oscillation of the screw(s) is/are carried out. This stage is defined as the “preshearing prior to delivery/injection” stage. During preshearing the shear rate and the shear strain history are tailored to affect the setting kinetics and the time-dependent development of the viscosity and the elasticity of the ceramic paste. For example, the increase of the rotational speed of the screw increases the shear rates that the cement paste is exposed to. Thus, the duration of the preshearing and the shear rate and strain history that are applied during preshearing become parameters that the operating room personnel can adjust according to the requirements of the specific surgery. This can conveniently be done by manually entering the parameters to the electrically controlled gear box through a control unit shown in
Applied shear rate, time and strain history would alter the setting time and shear viscosity and the elasticity (i.e., the injectability, workability and the setting time) of the ceramic paste. Therefore, with a single formulation a wide range of setting times, shear viscosity and elasticity behavior (i.e., a range of injectabilities and working times) become possible. Another novelty of the apparatus is its capability to generate sequential cyclic oscillatory shearing during which the frequency of the deformation can be altered from one value to another in a cyclic manner. As shown in the examples, the most effective mode of preshearing involves the application of multiple frequencies during oscillatory shearing.
In the final step, the gate 19 of the preshearing device that connects the barrel 17 and the die 21 acting as the nozzle is opened. Manual timing is the default in clinical practice due to the manual nature of the operations and automatic timing is the default for robotic deposition. In the embodiment shown in
In another embodiment of the present invention, the preshearing apparatus is a semi-batch mixing and extruder device consisting of two or more successive screws that are driven by concentric shafts with independent rotation capability. As schematically described in
In another embodiment that is schematically represented in
In another embodiment of the present invention, continuous preshearing and delivery of cementitious suspensions are enabled by coupling at least two batch preshearing apparati (
The formulations and the preshearing method have been tested using a small amplitude oscillatory rheometer, i.e., a parallel plate based shearing device with one plate (disk) stationary and the second either rotating in one direction continuously (CW or CCW) or oscillating between CW and CCW directions. The shearing device has the ability to impose a constant or cyclic shear rate and to measure the torque and the normal force as a function of time, temperature and rate of shear. The rheometer can thus characterize the elasticity and the shear viscosity of the cement paste as a function of the previous shearing history. The diameter of the two disks can be varied between 8 to 50 mm. The calcium phosphate cement formulations of this invention are placed in between the two plates at a typical gap of separation of 0.5 to 4 mm. In the steady torsional mode the shearing device can typically generate shear rates which are in the 0.01 to 50 1/s (the shear rate is defined as the linear velocity of the disk over the gap between the two discs). At the oscillating mode the typical sinusoidal shear strain and shear stress waves are obtained. The typical frequency range is 0.01 to 1000 rad/s (rps).
Brushite forming calcium phosphate cement formulation was mixed with powder/liquid ratio of 1.0, 1 wt % brushite seed and citric acid concentration of 0.5 M using a sonicator for 60 seconds according to the stoichiometry of the following setting reaction and transferred to the shearing device.
β−Ca3(PO4)2+Ca(H2PO4)2.H2O+7H2O→4CaHPO4.2H2O
The characteristic starting particle sizes were in the 2 μm range. The temperature of the sample holder chamber was set to 25° C. The preshearing device was operated at two modes: steady flow (steady torsional) and oscillatory flow (oscillatory torsional) to preshear the bone cement at different shearing modes and with different frequency and amplitude for oscillatory shearing and at different shear rates for steady torsional flow based shearing and for different durations. Furthermore, the dynamic moduli (storage modulus, G′, which represents the amount of energy stored as elastic energy during one cycle of deformation “the elasticity” and loss modulus, G″, which represents the energy dissipated as heat during one cycle of deformation, the magnitude of complex viscosity η* (the value of which approaches the shear viscosity as the shear rate and frequency approach zero), tangent(δ)=G″/G′ and normal stress were measured as functions of time by oscillatory torsional flow at various frequencies of 0.1 rad/s, 1 rad/s, 10 rad/s, 100 rad/s and at various strain amplitudes.
The development of the storage modulus, G′ and the magnitude of complex viscosity, η* of the bone cement sample that is kept under quiescent conditions with time are shown in
These data obtained for quiescent conditions indicate that this specific formulation would have relatively low elasticity and shear viscosity for about 600 s following mixing. The bone cement starts to harden at a relatively high rate after 600 s and becomes completely solid-like in 1200 s, at which time the bone cement would not flow at all. Thus, upon mixing this specific formulation needs to be delivered into the treatment site by the surgeon within 10-20 minutes, with the maximum time cut-off depending on what the surgeon needs in terms of viscosity and elasticity of the bone cement. It should be noted that this is a water based formulation and would require some thickening prior to injection otherwise there will be significant demixing (segregation) effects during injection through a needle (see references on segregation of suspensions with relatively low viscosity binders [Yaras et al., “Flow Instabilities in Capillary Flow of Concentrated Suspensions,” Rheologica Acta, 33, 48-59 (1994); Yilmazer et al., “Mat Formation and Unstable Flows of Highly Filled Suspensions in Capillaries and Continuous Processors,” Polymer Composites, 10 (4), 242-248 (1989)]
The schematics of how the preshearing effect is documented are shown in
The comparisons of the time dependencies of the elasticity, i.e., the storage modulus, and viscosity, i.e., the magnitude of complex viscosity, of brushite cement that were not presheared or were presheared at various frequencies at the same strain amplitude of 0.04 are presented in
Thus, the typical results provided in
The effects of changes in the strain amplitude (this is representative of the angular displacement of the disk of the rheometer over the gap) used during preshearing on the time-dependent development of the elasticity and viscosity of the paste are shown in
The comparisons of the time-dependent changes in the viscosity of the cement paste following preshearing that is based on oscillatory shear versus steady torsional flow are shown in
The cement precursors in Example #1 without seed particles were mixed at a powder/liquid ratio of 1.0 and citric acid concentration of 0.1 M. Here the effects of preshearing are followed via systematic changes in the frequency as well as the strain amplitude.
The application of interrupted cyclic deformation of the ceramic paste (cyclic increase and then decrease of the frequency) versus continuously oscillated (at constant frequency and strain amplitude) was tested using the cement precursors of Example #1 with a powder/liquid ratio of 0.8 and citric acid concentration of 0.4. The effects of stepwise cyclic change in applied frequency on bone cement dynamic rheological properties were investigated by varying the frequency from 0.1 rps to 1 rps, from 0.1 rps to 10 rps, or from 0.1 to 100 rps as well as increasing the number of times the frequency is altered during the course of total deformation period. The frequency was altered between 4 and 15 number of times. The schemes for cyclic changes in frequency between 0.1 rps to 100 rps in conjunction with three different number of cycles over the total deformation period are shown in
All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.
It will be understood that the embodiments described herein are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the invention. Certain features that are described in this specification In the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in combination in multiple embodiments separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination. All such variations and modifications are intended to be included within the scope of the invention.
Claims
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
Type: Application
Filed: Apr 30, 2018
Publication Date: Dec 27, 2018
Inventors: Erdem Şahin (MUGLA), Dilhan M. Kalyon (TEANECK, NJ)
Application Number: 15/966,185