Rapid Freeze Prototyping Research Articles

In-vivo vascular application via ultra-fast bioprinting for future 5D personalised nanomedicine

The design of 3D complex structures enables new correlation studies between the engineering parameters and the biological activity. Moreover, additive manufacturing technology could revolutionise the personalised medical pre-operative management due to its possibility to interplay with computer tomography. Here we present a method based on rapid freeze prototyping (RFP) 3D printer, reconstruction cutting, nano dry formulation, fast freeze gelation, disinfection and partial processes for the 5D digital models functionalisation. We elaborated the high-resolution computer tomography scan derived from a complex human peripheral artery and we reconstructed the 3D model of the vessel in order to obtain and verify the additive manufacturing processes. Then, based on the drug-eluting balloon selected for the percutaneous intervention, we reconstructed the biocompatible eluting-freeform coating containing 40 nm fluorescent nanoparticles (NPs) by means of RFP printer and we tested the in-vivo feasibility. We introduced the NPs-loaded 5D device in a rat’s vena cava. The coating dissolved in a few minutes releasing NPs which were rapidly absorbed in vascular smooth muscle cell (VSMC) and human umbilical vein endothelial cell (HUVEC) in-vitro. We developed 5D high-resolution self-dissolving devices incorporating NPs with the perspective to apply this method to the personalised medicine.

An Experimental Examination on Ice Pattern for Casting Process

The casting process has come to wide range of use in manufacturing process. Wooden, aluminum and wax are mostly used materials for pattern in the casting. However, it contains some limitations such as expansion of wax pattern, cracks in ceramic, complexity limitation in wooden pattern and removal of wooden pattern from sand mold etc., in the light of this, the work attempts to use ice pattern for mold making and sublimating ice pattern to create cavity in the mold for pouring. Ice pattern can be produced with aid of rapid freeze prototyping (RFP) or by traditional ice mold method. Integration of RFP/Traditional ice mold method with sublimated ice in casting process allows the quick creation of complex metal parts. Here, mold is produced by ice pattern and then ice pattern is removed by sublimation process (sublimation is the process of direct conversion of solid phase to vapor phase of matters) to create cavity. The advantages of no parts geometric complexity problems , No need of parting line design, less complex limitation, sound casting, clean and less cost of process operation, and better performance. This paper will present our creation study on sublimation of ice pattern in greensand for mold making for casting, and results of the cast piece obtained from sand casting process.

Low-Temperature Deposition Modeling of β-TCP Scaffolds with Controlled Bimodal Porosity.

Low-temperature deposition modeling (LDM), otherwise termed freeze-form extrusion fabrication or rapid freeze prototyping, involves dispensing an aqueous-based ceramic paste or polymeric hydrogel along predefined paths in subzero ambient temperatures, followed by freeze-drying. The solidification of the material after the deposition of each layer enables large parts to be built without the need for organic binders, which can often have cytotoxic effects. Freeze-dried parts obtained from LDM typically exhibit pores with openings that range in average between 1 and 40μm. The technique offers the ability to control their size distribution and orientation through varying a number of processing and material parameters. Herein, we describe the construction of an LDM system from readily available electromechanical components, as well as the preparation of a β-ΤCP paste formulation with the appropriate flow characteristics for fabricating hierarchical scaffolds with tailorable bimodal porosity for applications in bone tissue engineering.

Development of Modeling Process in Rapid Freeze Prototyping

Through rapid prototyping [1,2] it can be achieved both conceptual models: the final prototypes and functional parts in less time than with conventional technologies. The author of this paper shows the dependence of the diameter of liquid nitrogen spray nozzles according to the diameters of the water spray nozzle, a factor that is important in determining the amount of liquid nitrogen required to freeze the drop of water. Regarding the deposited layer thickness estimation, the author presented two theoretical models of contact between water droplets, which depend on the step between two consecutive drops of water.

Designing a Cold Plate Used in Rapid Freeze Prototyping Technology

The rapid prototyping with ice is a new manufacturing technology that can generate three-dimensional objects from ice by depositing and rapidly freezing water layer by layer. In order to freeze the water droplets, the plate must meet certain conditions, among those it is worth to be mentioned, the surface temperature, which should not surpass 0°C. The equipment presented in the paper is a part of rapid freeze prototyping equipment, designed and built by the authors. The authors analysed various freezing systems and they discovered that the classical cooling systems are not appropriate to be used in rapid freeze prototyping technology. The unique solution is the utilisation of thermoelectric cells, generic named as Peltier cells. The modern technology can be used in obtaining Peltier cells, with a high degree of reliability, electrical consumption and yield. This can be successfully used as heat pumps in industry. The author developed an original system that permitted to implement the Peltier cells. The cold plate was designed by using CAD software. In addition, the cold plate was produced and tested. The equipment obtained, has a greater power in comparison with the classical ones, even if it has smaller dimensions. The electrical power supply has to be well filtered in order to generate a higher efficiency. Through the main advantages of the Peltier cells can be mentioned: no maintenance have to be performed as this type of cells have no moving parts, thus having a major advantage; no CFC or other consumables parts have to be used, thus proving to be more economical than other systems; the heat regulation can be performed easier compared with the classical systems offering a better control and precision; it can be used in severe environments where conventional cooling systems can fail, being successfully used in the presence of liquid nitrogen; it can perform in various positions and is reversible similar to heat pumps. The main drawback of this system is that it uses a great amount of electrical energy, consequently can have a low yield.

Development of novel hybrid poly(l-lactide)/chitosan scaffolds using the rapid freeze prototyping technique

Engineered scaffolds have been shown to be critical to various tissue engineering applications. This paper presents the development of a novel three-dimensional scaffold made from a mixture of chitosan microspheres (CMs) and poly(l-lactide) by means of the rapid freeze prototyping (RFP) technique. The CMs were used to encapsulate bovine serum albumin (BSA) and improve the scaffold mechanical properties. Experiments to examine the BSA release were carried out; the BSA release could be controlled by adjusting the crosslink degree of the CMs and prolonged after the CMs were embedded into the PLLA scaffolds, while the examination of the mechanical properties of the scaffolds illustrates that they depend on the ratio of CMs to PLLA in the scaffolds as well as the cryogenic temperature used in the RFP fabrication process. The chemical characteristics of the PLLA/chitosan scaffolds were evaluated by Fourier transform infrared (FTIR) spectroscopy. The morphological and pore structure of the scaffolds were also examined by scanning electron microscopy and micro-tomography. The results obtained show that the scaffolds have higher porosity and enhanced pore size distribution compared to those fabricated by the dispensing-based rapid prototyping technique. This study demonstrates that the novel scaffolds have not only enhanced porous structure and mechanical properties but also showed the potential to preserve the bioactivities of the biomolecules and to control the biomolecule distribution and release rate.

Modeling and experimental results of concentration with support material in rapid freeze prototyping

PurposeThe purpose of this paper is to develop a physics‐based model that can predict how a main build material of water interacts with a water‐soluble sacrificial support material in the rapid freeze prototyping (RFP) process.Design/methodology/approachRFP uses water freezing into ice in a layer‐by‐layer manner as a main build material to create ice structures with complex geometries in a sufficiently cool environment. A eutectic dextrose‐water solution is used as a sacrificial support material. The supported areas in an ice structure are removed by placing the fabricated structure in an environment of appropriate temperature.FindingsTwo methods of concentration modeling have been developed to predict the interaction between the main and support materials around their interface region. The two models are described in detail and their predictions are compared to experimentally measured data. The experimental height data compared to the simulation result based on the concentration models agrees to within 6 percent for various build ambient temperatures. As ambient temperatures decreased, diffusion between the two materials also decreased.Originality/valueThe results obtained from this paper can be used as an aid in building complex ice parts in the RFP process so that minimal interaction between the main and support materials can be attained. An understanding of the interaction occurring during fabrication is provided with the concentration models. The method used to develop the concentration models can be applied to other layered manufacturing processes when using two miscible materials.

Predictive Modeling and Experimental Verification of Temperature and Concentration in Rapid Freeze Prototyping With Support Material

Rapid freeze prototyping is a solid freeform fabrication method that uses water freezing into ice as the build material. Each layer of geometry is deposited and allowed to freeze before the next layer is added in order to additively create a three-dimensional ice part. A sacrificial support material is needed for the fabrication of complex ice parts. Identifying a suitable support material and understanding the interaction between the build and support materials is the motivation behind this study. A temperature prediction model and a concentration prediction model are presented. Experimental results have been obtained to validate these models.

Rapid freeze prototyping technique in bio‐plotters for tissue scaffold fabrication

PurposeThe purpose of this paper is to develop a new bio‐plotter using a rapid freeze prototyping (RFP) technique and to investigate its potential applications in fabricating tissue scaffolds.Design/methodology/approachThe development of cryogenic bio‐plotters including design steps of hardware as well as software is addressed. Effects of structural parameters and process parameters on the properties of tissue scaffolds are demonstrated through simulation and experimental results.FindingsThe paper finds that the RFP method is suitable to fabricate macro‐ and micro‐porous scaffolds, especially for temperature‐sensitive polymers. In addition, through simulation and experiment results, it also shows that macro‐ and micro‐porous properties could be manipulated by structural parameters and process parameters, respectively.Research limitations/implicationsThis paper shows that the chamber temperature is an important process parameter that can provide the means to control the micro‐porous structure of the scaffold. However, if the temperature is set too high, the fiber is frozen so rapidly that it cannot be fused with other fibers of the previous layer. On the other hand, if the temperature is too low, the fiber is not solidified fast enough. So, the chamber temperature, together with extruding pressure and nozzle velocity, must be optimized, which will be further investigated in future work.Originality/valueThe RFP technique is successfully proposed to construct 3D tissue scaffolds. In addition, a new cryogenic bio‐plotter is designed and developed, in which general algorithms of rapid prototyping method are presented and implemented, facilitating the fabrication of tissue scaffolds with various cross‐hatching patterns in a RFP process.

Finite Element Analysis of Solidification in Rapid Freeze Prototyping

Rapid freeze prototyping (RFP) can generate three-dimensional ice patterns from computer-aided design (CAD) models by depositing and solidifying water droplets layer by layer. One important issue of the RFP process is how to fabricate the ice pattern to desired accuracy in an acceptable short time. The waiting time between two successive layers is a critical factor. A waiting time that is too short will lead to unacceptable part accuracy, while a waiting time that is too long will lead to an excessive build time. Finite element analysis is employed in this study to predict the solidification time of a newly deposited water layer and to develop a better understanding of heat transfer during the RFP process. ANSYS Parametric Development Language (APDL) is utilized to develop software for the prediction of solidification time. The result is used to investigate the effect of various process parameters on the solidification time of an ice column and a vertical ice wall. These parameters include environment temperature, heat convection coefficient, initial water droplet temperature, layer thickness, and waiting time between two successive layers. Experiments are conducted and the measured results are shown to agree well with simulation results.

Dimensional accuracy and surface roughness of rapid freeze prototyping ice patterns and investment casting metal parts

The dimensional accuracy and surface finish of ice patterns generated by rapid freeze prototyping were first investigated. The dimensional accuracy and surface finish of metal parts made by investment casting with ice patterns were then investigated and compared with those made by conventional investment casting with wax patterns. The selection of binder, ceramic powder, and catalyst material for ceramic slurries in the process of investment casting with ice patterns and the need for an interface agent to separate the ice pattern from the ceramic slurry in the mold making process are discussed. The parts used in the investigation included circular cylinders with vertical and slant walls and a turbine impeller.

Thermal Analysis of Ice Walls Built by Rapid Freeze Prototyping

Rapid Freeze Prototyping (RFP) builds ice parts by depositing and freezing water in a layer-by-layer manner. This paper presents a one-dimensional transient heat transfer model for a thin ice wall built by the RFP process. Closed-form solutions for temperatures of the ice wall during solidification of a layer of water are derived, which can be used to estimate the solidification time. Natural cooling of the ice wall after solidification of a water layer is also studied. The analytical solutions of heating and cooling of the ice wall agree well with both numerical and experimental results.

Investigation of Layer Thickness and Surface Roughness in Rapid Freeze Prototyping

Rapid Freeze Prototyping (RFP) builds three-dimensional ice parts according to CAD models by depositing and freezing water droplets in a layer-by-layer manner. This paper studies the layer thickness and surface roughness of ice parts built by the RFP process. The equations governing the water line formed by a sequence of water droplets are developed, and then a model of the water line is proposed by simplifying these equations based on our experimental condition. The analysis using this model shows that the cross-section of an ice line is circular, which is verified by experimental observations. Based on the analysis, equations for predicting layer thickness as a function of nozzle scanning speed, water feed rate, and water-ice contact angle in building vertical and slant walls by the RFP are derived and the predictions from these equations are shown to agree well with experimental measurements. The surface roughness of ice parts built by the RFP process is also studied.

A study on effects of process parameters in rapid freeze prototyping

Rapid freeze prototyping is a relatively new solid freeform fabrication process, which builds a three‐dimensional part according to a CAD model by depositing and freezing water droplets layer by layer. A study on the effects of RFP process parameters including the nozzle scanning speed, droplet size, and droplet frequency in building ice parts with a single‐nozzle work head is made. Presented in this paper are the results of this study which indicate that these process parameters determine the ice layer thickness and ice line width, which in turn determine the surface roughness and the waiting time required after depositing each layer of water (i.e. between successive layers) during the ice part building process.

Study of Part Geometric Features and Support Materials in Rapid Freeze Prototyping

This paper describes the investigation of part geometric features and support materials in the fabrication of ice parts by Rapid Freeze Prototyping (RFP). The achievable geometric features of the ice part including the smallest thickness of a wall and the smallest diameter of a rod are analyzed and expressed as functions of process parameters including water pressure, nozzle diameter, valve open/close frequency and duty cycle, and x-y table moving speed relative to the nozzle. The validity of the predicted results of geometric features from the analysis is verified using our experimental RFP system. In order to realize fabricating ice parts of any complex 3-D geometry, support materials are also studied. The experimental results showed a eutectic mixture of dextrose and water works well as the support material while a eutectic mixture of salt and water does not work satisfactorily.

Experimental study on the ice pattern fabrication for the investment casting by rapid freeze prototyping (RFP)

The process of investment casting has come to occupy a key position in the range of modern metal casting techniques. Wax pattern is widely used in the investment casting. However, there exist some problems and technical difficulties in using it such as wax pattern expanding, ceramic shell cracking, etc. A new investment casting technology, named freeze cast process (FCP), has demonstrated the possibility and advantage of investment casting with ice patterns. But how to make ice patterns is really an important concern in the FCP process. RFP is a novel, environmentally conscious solid freeform fabrication process that can generate three-dimensional ice patterns by selectively depositing and rapidly freezing water layer by layer. With RFP it is possible to make ice patterns with better accuracy and more flexibility directly from CAD models in a short time, without the cost and other issues of mold making. In this paper, the current status of the experimental study of the RFP process was introduced. The effect of different processing parameters on the layer thickness and layer width was studied quantitatively and thoroughly. These parameters include: frequency of pulse signal, stagnation pressure, scanning velocity, distance between nozzle and building surface, duty cycle of pulse signal, layer offset (slant angle), environmental temperature, scanning trajectory, and depositing material. And further the effect of the processing parameters on the dimension accuracy and surface roughness were analyzed qualitatively. The optimal parameters were chosen and used to fabricate complex ice patterns based on these experiments and analyses. Finally, an example was given to demonstrate that an ice pattern can be used to make the metal prototype. The fabricated metal prototype has a very good appearance, although surface roughness and dimensional accuracy have not been measured. The experiment results showed that RFP provides an enabling way to quickly make ice patterns for the investment casting with better quality and more flexibility.

An Experimental and Analytical Study of Ice Part Fabrication with Rapid Freeze Prototyping

process called Rapid Freeze Prototyping. This process builds a three-dimensional ice part by depositing and rapidly freezing water according to its CAD model in a layer-by-layer manner. It provides a means to build a solid part with the potential of better performance than other rapid prototyping processes, including use of cheap and clean material, potential to build accurate ice parts with excellent surface finish, and ease of building color and transparent parts. An experimental system with a low-temperature building environment, a three-axis positioning mechanism, a water feeding and extruding subsystem, and control hardware and software has been built. Experiments conducted on this system demonstrate the feasibility of making three-dimensional ice parts. A heat transfer analysis helps understand the freezing process and provides useful information to the selection of building parameters.