Name: the quantification of injectability by mechanical testing
Uploaded: 2020-05-13T15:00:00.000+00:00
Duration: 4 min 46 s
Description: Watch this Scientific Journal Video about The Quantification of Injectability by Mechanical Testing at JoVE.com

This work was funded by the EPSRC CDT for Formulation Engineering in the School of Chemical Engineering at the University of Birmingham, UK, Grant reference EP/L015153/1, and the Royal Centre for Defence Medicine.

1. Sample Preparation
<ol>
	<li>Prepare the sample and load it into the syringe.
	<ol>
		<li>To simulate a pre-loaded syringe, prepare the sample in advance, load it into the syringe, and attach the needle. Store as required, until testing. This may be suitable for hydrogels and materials that do not change with time. 
		NOTE: For example, to prepare 2% alginate solutions, dissolve 2 g of alginic acid sodium salt in 100 mL of deionized water, by stirring at room temperature. Aspirate the solution into 5 mL syringes, and store for 24 h at room temperature.</li>
		<li>Alternatively, to simulate an injection formulated directly prior to the application, prepare the sample in the same way it would be made in the clinic, allowing for any setting times. Load into the syringe and attach the needle. This may be suitable for cements, and materials whose properties change with time. 
		NOTE: For example, to prepare calcium sulfate cement, manually mix 4 g of calcium sulfate hemihydrate into 5 mL of deionized water with a spatula for 1 min. Remove the plunger from the syringe and load the cement into the syringe barrel with the spatula. Begin the mechanical testing after 4 min. 
		CAUTION: Needles pose a safety risk, use blunt needles if possible. If the material contains cells or other biological materials, extra care should be taken to prevent sharps injuries.</li>
	</ol>
	</li>
</ol>
2. Set up the mechanical tester
<ol>
	<li>Attach flat platens (for compression testing) to the mechanical tester.</li>
	<li>Manually equip the mechanical tester with a load cell with a maximum load of 200 N. 
	NOTE: A larger load cell may be used, provided it has sufficient precision at the 1 &#8211; 200 N range. Samples that are more viscous and not intended to be injected by hand may require a larger load cell.</li>
	<li>Separate the plates, using the manual control buttons, to allow for sufficient space for the needle, syringe and plunger (around 30 cm will be sufficient).</li>
	<li>Create a testing protocol.
	<ol>
		<li>Open the test wizard and set the test type to uniaxial compression.</li>
		<li>Set the pre-load. This is the measured force value at which testing will begin. 0.5 N is sufficient.</li>
		<li>Set the speed to pre-load to 5 mm/min. This is the speed the crosshead will move down until it encounters the pre-load.</li>
		<li>Set the loading to displacement control and select an appropriate test speed. 1 mm/s is an appropriate speed for a standard 5 mL syringe.</li>
		<li>Set an upper force limit at which to stop the test, e.g., 200 N. This is primarily for safety reasons. The test may also be stopped automatically at a given displacement, e.g., the length of the syringe.</li>
	</ol>
	</li>
</ol>
3. Set up the clamping system
<ol>
	<li>Attach two sets of clamps to two stands, with grips large enough to securely ensconce the chosen syringe.</li>
	<li>Place the grips between the crosshead and baseplate, with enough space below the grips for the syringe and needle.</li>
	<li>Line up the centers of the two grips, and line these up with the center of the crosshead. 
	NOTE: Alignment of the clamp grips with each other and the center of the crosshead may take some time and iteration to achieve, but is important to acquire high quality data.</li>
	<li>Ensure the clamps are secured firmly so that there is no movement in the clamps when a downward force is applied.</li>
	<li>Place a dish onto the bottom plate to collect the extruded material.</li>
</ol>
4. Run the injectability protocol
<ol>
	<li>Insert the syringe into the clamp grips and close them. The grips should hold the syringe in place, but allow it to move up and down without resistance.</li>
	<li>Ensure the syringe and plunger are perpendicular to the crosshead. This ensures that only uniaxial compression of the material will be measured. 
	NOTE: An empty syringe should be used to check steps&#160;4.1&#160;and 4.2.</li>
	<li>Lower the top plate to a position just above the plunger, using the manual movement buttons. 
	NOTE: It may be possible to select a &#8216;Start position&#8217; in the mechanical tester protocol, such that the original position above the plunger is reached automatically and is consistent throughout testing.</li>
	<li>Zero the measured force by clicking &#8216;Zero Force&#8217;.</li>
	<li>Run the testing protocol by pressing &#8216;Run&#8217;. 
	CAUTION: The experimenter should always be present to observe each trial, and ready to activate the emergency stop in case of a mishap.</li>
	<li>Raise the plates to a sufficient height, using the manual movement buttons, such that the syringe can be removed.</li>
	<li>Repeat step 4 for each sample. 
	NOTE: At this point, the syringe and extruded sample can be discarded if no further analysis is required, but may be kept in order&#160;to examine filter pressing, self-healing, the effects on cells, etc.</li>
</ol>
5. Data collection
<ol>
	<li>Save the data from each trial in a format from which a table of force and displacement values can be generated (.txt, .xls, .xlsx).</li>
	<li>Plot the results from each trial, with displacement on the x-axis and force on the y-axis.</li>
	<li>Read the maximum force (if it exists) and plateau force from the graphs.</li>
</ol>

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The authors have nothing to disclose.

Mechanical testing is perhaps the simplest and most reliable way to quantify injectability. A key advantage of this protocol is that no special equipment is required, other than the mechanical tester, which is common in materials laboratories. This protocol is highly versatile; any material, needle gauge and syringe size can be used, provided the syringe can be accommodated by the clamps. This has been verified in this protocol for syringes up to 10 mL. Further, the material can be prepared exactly as it would for the real-world application25. Finally, this procedure is very fast, taking only up to a few minutes per sample, allowing tens of samples to be processed per hour.
For samples that give typical curves, two values can be extracted: the maximum force and the plateau force curves. The maximum force is arguably more objective and can be extracted computationally from the data table for each sample. Conversely, the plateau force may be more representative, as this will be the force experienced for the greatest amount of time and, as an average, is less affected by curves with large fluctuations. These fluctuations may be caused by air bubbles or particles in the material causing intermittent changes as they are extruded, or by low instrument precision for small force measurements. However, it is notable that, for many samples, there is no maximum force peak, and so the maximum and plateau value are the same. Objective comparisons between injection forces can be made so long as a consistent value is used.
The data obtained can be used in several ways. The injectability force values may be compared to ease of injection, to establish which formulations, syringe and needle sizes are viable for translation8. Alternatively, comparing between samples allows for the quantification of changes to formulations on injectability. For example, in cements, changing the viscosity of the liquid phase, the particle size distribution, and adding additives such as citrate to alter the colloidal properties, can have large changes in injectability9. These tests may also inform formulation protocol for cements, for example mixing time, time to loading and time to application, for optimum injection and post-injection performance. In addition, this method may be used to test the initial feasibility of novel bioinks for 3D printing.
This protocol can be modified in several ways. The clamp system may be replaced with a bespoke 3D printed construct to hold the syringe, which may make it easier to ensure the syringe and plunger are perpendicular to the crosshead, and the syringe held securely. The needle can be replaced with a cannula or any device that extrudes material by compression of a plunger and can be of any size and geometry. In order to increase the fidelity of the results, the tip of the needle can be placed into a tissue or hydrogel, in order to more accurately simulate clinical injection. However, this adds further complexities to the protocol, as tissue/gel composition and needle depth must be kept constant. Further, this protocol utilizes displacement-controlled extrusion, to measure the force required to inject at the specified speed. Alternatively, the injection force can be specified, and the amount of extrusion can be measured against time. This may be useful for materials with time dependent properties, such as cements. For example, by using a correlation between injection force and ease of injectability to select a force8, this protocol may be used to establish whether the entire volume of cement can be injected with this speed prior to setting. Finally, this protocol can easily be combined with other experiments, in order to test the effect of injection on the material properties and examine phenomena such as filter pressing and self-healing, or the effect of injection on cells.
The main limitation of this protocol is that a universal mechanical tester is required. While these are common in materials testing labs, they are expensive to purchase if the user cannot access one. Further, the mechanical tester provides uniaxial compression at either a set force or rate of displacement, whereas the applied force and injection speed may vary over the course of injection by hand. This protocol is also unsuitable for replicating some real world injections, such as injections into complex tissues in theatre, or injecting at different angles. To quantify the force of injection in the clinic, force and displacement transducers may be a better method.

Biomaterials are often studied and used as scaffolds for cell-based tissue regeneration and depots for targeted, sustained delivery of therapeutics1. Within this field, injectable biomaterials are growing in popularity as they are minimally invasive, which reduces the risk of infection, pain and scarring associated with implantation2. Further, because they are usually applied as fluids, they conform perfectly to tissue defects, and drugs and cells may be mixed into them immediately prior to the application3,4,5. As such, while injectable biomaterials may be manufactured as pre-loaded syringes, they are often prepared by clinicians directly prior to application. For example, cements begin to set once the powder and liquid phases are mixed, and so cannot be stored for long periods before use6. The characterization of these materials is thus time dependent and inextricably linked to their preparation.
Common injectable biomaterials include calcium cements, polymethyl methacrylate, bioglasses, and various polymeric hydrogels3,7. Unlike traditional injections of drugs, which have the same rheological properties as water, these injectable biomaterials are typically more viscous, non-Newtonian, may have some elastic character, and may also change over time. Therefore, the injectability of these materials cannot be assumed but must be assessed experimentally. By quantifying the force required for injection and correlating it to the ease of injection, early decisions about which biomaterial formulations, syringe, and needle sizes to take forward may be made early in the developmental process8. Such experiments may also quantify the effects of changing formulations on injectability9.
There are several methods to assess the properties of injectable materials. Rotational rheology is often utilized to assess viscosity, non-Newtonian behavior, post-shear recovery, setting time, and other properties of these materials10,11,12. Whilst this type of test is useful to establish fundamental properties of the materials, these properties do not correlate directly to injectability. For a Newtonian fluid and cylindrical syringe and needle, the injection force can be&#160; estimated from a form of the Hagen&#8211;Poiseuille equation13:
<img alt="Equation 1" src="/files/ftp_upload/61417/61417eq1.jpg" />
Where F is the force required for injection (N), Rs is the internal syringe radius (m), Rn is the internal needle radius (m), L is the needle length (m), Q is fluid flow rate (m3 s-1), &#951; is the dynamic viscosity (Pa.s) and Ff is the friction force between the plunger and barrel wall (N). Thus, if the viscosity is measured via rotational rheology, the dimensions of the syringe and needle are known and the flow rate estimated, the injection force can be estimated. However, this equation does not account for the conical end of the syringe or any other geometries, such as off-center outlets, and Ff must be estimated or found experimentally by mechanical testing. Further, biomaterials are typically not Newtonian, but exhibit complex rheological properties. For a simple shear thinning fluid, the equation becomes14:
<img alt="Equation 2" src="/files/ftp_upload/61417/61417eq2.jpg" />
Where n is the power index (-) and K is the consistency index (Pa.sn) from the Ostwald de Waele expression: <img alt="Equation 3" src="/files/ftp_upload/61417/61417eq3.jpg" />, where <img alt="Equation 4" src="/files/ftp_upload/61417/61417eq4.jpg" /> is the shear rate (s-1). The complexity vastly increases for materials whose rheological properties cannot be characterized by two values, and particularly for time-dependent materials such as setting cements. Additionally, if the material properties are shear dependent, then the material must be tested at the shear rate expected in the needle, which may far exceed the range of a rotational rheometer15.
Another quantitative method for measuring injectability involves attaching pressure and displacement sensors to a syringe while performing an injection, either by hand or using a syringe pump. This equipment is relatively inexpensive, however, requires users to generate scripts and calibration curves to convert into force data16. Further, a syringe pump may not possess sufficient torque to compress the plunger at a precise rate if high forces are required to extrude viscous or semi-solid materials. Alternatively, utilizing these sensors when injecting by hand may be useful as they can be used in a real clinical scenario, during clinical procedures17. However, this will take much longer and may introduce user bias, and will, therefore, need larger numbers of repetitions with different users to obtain reliable results. This may, thus, be more appropriate for materials that are further down the translational pipeline, or products already in clinical use.
In this protocol, a mechanical tester is used to compress the plunger at a set rate, and measure the force required to do so. This type of mechanical tester is common in materials laboratories and has been used to quantify injectability for various biomaterials18,19,20,21,22,23,24. This test can be used with any size and geometry of syringe and needle, containing any material. Further, in the case of biomaterials that are made immediately prior to the use, the exact formulation procedure that would be used in the clinic or surgery can be followed prior to testing. A further advantage of this procedure is that it is relatively fast; once the mechanical tester is set up, tens of samples can be studied in an hour, depending on extrusion speed and syringe volume. This is in contrast to rotational rheology, which typically takes at least 5 &#8211; 10 minutes per test, plus loading, equilibration and cleaning time. Using a mechanical tester produces a reliable extrusion rate equally over the plunger, which is particularly advantageous for viscous formulations or those with time dependent properties. Following testing, minimal post-processing of data is required to pull out important values for objective comparisons.

<table><tbody><tr><td>Alginic Acid Sodium Salt</td><td>Sigma</td><td>A2033-100G</td><td></td></tr><tr><td>Blunt Needles</td><td>Needlez</td><td>NB19G1.5</td><td>Any size may be used, depending on application</td></tr><tr><td>Calcium Sulphate Hemihydrate</td><td>Acros Organics</td><td>22441.296</td><td></td></tr><tr><td>Clamp stand</td><td>Eisco</td><td>MTST5</td><td>Two required</td></tr><tr><td>Clamps</td><td>R&amp;amp;L Enterprises</td><td>41</td><td>Two required, should have flat tops</td></tr><tr><td>Syringes</td><td>BD</td><td>307731</td><td>Any size can be used, depending on application</td></tr><tr><td>Universal Mechanical Tester</td><td>Zwick Roell</td><td>Z030</td><td></td></tr></tbody></table>

the quantification of injectability by mechanical testing

Injectable biomaterials are becoming increasingly popular for the minimally invasive delivery of drugs and cells. These materials are typically more viscous than traditional aqueous injections and may be semi-solid, therefore, their injectability cannot be assumed. This protocol describes a method to objectively assess the injectability of these materials using a standard mechanical tester. The syringe plunger is compressed by the crosshead at a set rate, and the force is measured. The maximum or plateau force value can then be used for comparison between samples, or to an absolute force limit. This protocol can be used with any material, and any syringe and needle size or geometry. The results obtained may be used to make decisions about formulations, syringe and needle sizes early in the translational process. Further, the effects of altering formulations on injectability may be quantified, and the optimum time to inject temporally changing materials determined. This method is also suitable as a reproducible way to examine the effects of injection on a material, to study phenomena such as self-healing and filter pressing or study the effects of injection on cells. This protocol is faster and more directly applicable to injectability than rotational rheology, and requires minimal post processing to obtain key values for direct comparisons.

The set-up of the mechanical tester and clamping system is shown in Figure 1A. This protocol generates a table and graph of force versus displacement for each tested sample. A typical force displacement curve consists of three sections (Figure 1B): an initial gradient, as the plunger overcomes friction from the barrel and the material is accelerated, a force maximum, and a plateau, as the material is extruded at a steady state.
However, a distinct maximum only exists where the plateau force is lower than the force required to accelerate the plunger. As such, peaks are only seen for inviscid samples passing through wide needles. For viscous samples passing through a more narrow orifice, the force needed to inject the sample at constant speed is greater than the force required to overcome friction in the barrel and accelerate the material, and no distinct peak is seen (Figure 1C). For highly viscous samples or very narrow needles, the force required to extrude the material may be so great that the syringe buckles and fails, often with very little extrusion of the material (Figure 1D). If the material being injected contains particles or is undergoing setting, such as cement, filter pressing (preferential expulsion of the liquid phase) or bulk setting may occur, leading to incomplete injection (Figure 1E).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61417/61417fig1.jpg" /> 
Figure 1: Sample curves generated by this protocol. (A) Set up of the mechanical tester for this protocol. (B) Typical force-extrusion curve. (C) Force-extrusion curve with no distinct maximum peak. (D) Force-extrusion curve for syringe failure. (E) Force-extrusion curve for a setting cement. This figure is adapted from Robinson et al.8. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61417/61417fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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The Quantification of Injectability by Mechanical Testing

Presented here is a protocol for quantitatively evaluating the injectability of a material through a syringe-needle system using a standard mechanical testing rig.

Injectable biomaterials are becoming increasingly popular for the minimally invasive delivery of drugs and cells. These materials are typically more ...

the-quantification-of-injectability-by-mechanical-testing

Nanyang Technological University

Research

JoVE Journal

Bioengineering

7.8K Views.  University of Birmingham. Door de kracht te meten, kunnen we nagaan of een materiaal injecteerbaar is en hoe het veranderen van de naald- en spuitgrootte, of de formuleringsverwerking en chemie de injectabiliteit kunnen beïnvloeden. Deze techniek is snel en eenvoudig. Kan worden gebruikt met een verscheidenheid van naald en spuit geometrieën, en vereist weinig gegevensverwerking om de belangrijkste kracht waarden te verkrijgen.Deze methode is met name van toepassing op injecteerbare biomaterialen, zoals hydro...

Video: The Quantification of Injectability by Mechanical Testing

Scalable Fluidic Injector Arrays for Viral Targeting of Intact 3-D Brain Circuits

Our understanding of neural circuits--how they mediate the computations that subserve sensation, thought, emotion, and action, and how they are corrupted in neurological and psychiatric disorders--would be greatly facilitated by a technology for rapidly targeting genes to complex 3-dimensional neural circuits, enabling fast creation of "circuit-level transgenics." We have recently developed methods in which viruses encoding for light-sensitive proteins can sensitize specific cell types to millisecond-timescale activation and silencing in the intact brain. We here present the design and implementation of an injector array capable of delivering viruses (or other fluids) to dozens of defined points within the 3-dimensional structure of the brain (Figure. 1A, 1B). The injector array comprises one or more displacement pumps that each drive a set of syringes, each of which feeds into a polyimide/fused-silica capillary via a high-pressure-tolerant connector. The capillaries are sized, and then inserted into, desired locations specified by custom-milling a stereotactic positioning board, thus allowing viruses or other reagents to be delivered to the desired set of brain regions. To use the device, the surgeon first fills the fluidic subsystem entirely with oil, backfills the capillaries with the virus, inserts the device into the brain, and infuses reagents slowly (&lt;0.1 microliters/min). The parallel nature of the injector array facilitates rapid, accurate, and robust labeling of entire neural circuits with viral payloads such as optical sensitizers to enable light-activation and silencing of defined brain circuits. Along with other technologies, such as optical fiber arrays for light delivery to desired sets of brain regions, we hope to create a toolbox that enables the systematic probing of causal neural functions in the intact brain. This technology may not only open up such systematic approaches to circuit-focused neuroscience in mammals, and facilitate labeling of brain regions in large animals such as non-human primates, but may also open up a clinical translational path for cell-specific optical control prosthetics, whose precision may enable improved treatment of intractable brain disorders. Finally, such devices as described here may facilitate precisely-timed fluidic delivery of other payloads, such as stem cells and pharmacological agents, to 3-dimensional structures, in an easily user-customizable fashion.

Controlling and analyzing neural circuits in vivo would be facilitated by a technology for delivery of viruses and other reagents to desired 3-dimensional sets of brain regions. We demonstrate customized fluidic injector array fabrication, and delivery of virally-encoded optical sensitizers, enabling optical manipulation of complex brain circuits.

Our understanding of neural circuits--how they mediate the computations that subserve sensation, thought, emotion, and action, and how they are corrupted ...

Neuroscience

Picoinjection of Microfluidic Drops Without Metal Electrodes

Existing methods for picoinjecting reagents into microfluidic drops require metal electrodes integrated into the microfluidic chip. The integration of these electrodes adds cumbersome and error-prone steps to the device fabrication process. We have developed a technique that obviates the needs for metal electrodes during picoinjection. Instead, it uses the injection fluid itself as an electrode, since most biological reagents contain dissolved electrolytes and are conductive. By eliminating the electrodes, we reduce device fabrication time and complexity, and make the devices more robust. In addition, with our approach, the injection volume depends on the voltage applied to the picoinjection solution; this allows us to rapidly adjust the volume injected by modulating the applied voltage. We demonstrate that our technique is compatible with reagents incorporating common biological compounds, including buffers, enzymes, and nucleic acids.

We have developed a technique for picoinjecting microfluidic drops that does not require metal electrodes. As such, devices incorporating our technique are simpler to fabricate and to use.

Existing methods for picoinjecting reagents into microfluidic drops require metal electrodes integrated into the microfluidic chip. The integration of ...

Engineering

Rodent Brain Microinjection to Study Molecular Substrates of Motivated Behavior

Brain microinjection can aid elucidation of the molecular substrates of complex behaviors, such as motivation. For this purpose rodents can serve as appropriate models, partly because the response to behaviorally relevant stimuli and the circuitry parsing stimulus-action outcomes is astonishingly similar between humans and rodents. In studying molecular substrates of complex behaviors, the microinjection of reagents that modify, augment, or silence specific systems is an invaluable technique. However, it is crucial that the microinjection site is precisely targeted in order to aid interpretation of the results. We present a method for the manufacture of surgical implements and microinjection needles that enables accurate microinjection and unlimited customizability with minimal cost. Importantly, this technique can be successfully completed in awake rodents if conducted in conjunction with other JoVE articles that covered requisite surgical procedures. Additionally, there are many behavioral paradigms that are well suited for measuring motivation. The progressive ratio is a commonly used method that quantifies the efficacy of a reinforcer to maintain responding despite an (often exponentially) increasing work requirement. This assay is sensitive to reinforcer magnitude and pharmacological manipulations, which allows reinforcing efficacy and/ or motivation to be determined. We also present a straightforward approach to program operant software to accommodate a progressive ratio reinforcement schedule.

Rodents are an appropriate model to investigate the molecular substrates of behavior and complex psychiatric disorders. Brain microinjection in awake rodents can be used to elucidate disease substrates. An efficient and customizable brain microinjection method as well as the execution of an operant paradigm that quantifies motivation is presented.

Brain microinjection can aid elucidation of the molecular substrates of complex behaviors, such as motivation. For this purpose rodents can serve as ...

Behavior

Quantitative Hardness Measurement by Instrumented AFM-indentation

In this work, a combination of amplitude-modulated non-contact atomic force microscopy and atomic force spectroscopy is applied for instrumented hardness measurements on an Au(111) surface with atomistic resolution of single plasticity events. A careful experimental procedure is described that includes the force sensor selection, its calibration, the calibration of the cantilever deflection detection system, and the minimization of instrumental drift for accurate and reproducible force-distance measurements. Also, a method for the data analysis is presented that allows the extraction of force-penetration curves from recorded force-distance curves. A typical curve displays a clear elastic deformation regime up to the first plasticity event, or pop-in, with a length in the range of one to two Burger's vectors. Later plasticity events exhibit the same magnitude. The work of plasticity is further extracted from the measurements. Finally, the hardness is determined in combination with the indentation curve using non-contact atomic force microscopy images of the remaining indents.

This experimental protocol describes how atomic force microscopy can be used to measure hardness at the true nanometer scale and to detect single atomistic plasticity events.

In this work, a combination of amplitude-modulated non-contact atomic force microscopy and atomic force spectroscopy is applied for instrumented hardness ...

An Improved Mechanical Testing Method to Assess Bone-implant Anchorage

Recent advances in material science have led to a substantial increase in the topographical complexity of implant surfaces, both on a micro- and a nano-scale. As such, traditional methods of describing implant surfaces -&#160;namely numerical determinants of surface roughness -&#160;are inadequate for predicting in vivo performance. Biomechanical testing provides an accurate and comparative platform to analyze the performance of biomaterial surfaces. An improved mechanical testing method to test the anchorage of bone to candidate implant surfaces is presented. The method is applicable to both early and later stages of healing and can be employed for any range of chemically or mechanically modified surfaces -&#160;but not smooth surfaces. Custom rectangular implants are placed bilaterally in the distal femora of male Wistar rats and collected with the surrounding bone. Test specimens are prepared and potted using a novel breakaway mold and the disruption test is conducted using a mechanical testing machine. This method allows for alignment of the disruption force exactly perpendicular, or parallel, to the plane of the implant surface, and provides an accurate and reproducible means for isolating an exact peri-implant region for testing.

An improved method to mechanically test bone anchorage to candidate implant surfaces is presented. This method allows for alignment of the disruption force exactly perpendicular, or parallel, to the plane of the implant surface, and provides an accurate means to direct the disruption forces to an exact peri-implant region.

Recent advances in material science have led to a substantial increase in the topographical complexity of implant surfaces, both on a micro- and a ...

Rapid and Low-cost Prototyping of Medical Devices Using 3D Printed Molds for Liquid Injection Molding

Biologically inert elastomers such as silicone are favorable materials for medical device fabrication, but forming and curing these elastomers using traditional liquid injection molding processes can be an expensive process due to tooling and equipment costs. As a result, it has traditionally been impractical to use liquid injection molding for low-cost, rapid prototyping applications. We have devised a method for rapid and low-cost production of liquid elastomer injection molded devices that utilizes fused deposition modeling 3D printers for mold design and a modified desiccator as an injection system. Low costs and rapid turnaround time in this technique lower the barrier to iteratively designing and prototyping complex elastomer devices. Furthermore, CAD models developed in this process can be later adapted for metal mold tooling design, enabling an easy transition to a traditional injection molding process. We have used this technique to manufacture intravaginal probes involving complex geometries, as well as overmolding over metal parts, using tools commonly available within an academic research laboratory. However, this technique can be easily adapted to create liquid injection molded devices for many other applications.

We have devised a method for low-cost and rapid prototyping of liquid elastomer rubber injection molded devices by using fused deposition modeling 3D printers for mold design and a modified desiccator as a liquid injection system.

Biologically inert elastomers such as silicone are favorable materials for medical device fabrication, but forming and curing these elastomers using ...

A Soft Tooling Process Chain for Injection Molding of a 3D Component with Micro Pillars

The purpose of this paper is to present the method of a soft tooling process chain employing Additive Manufacturing (AM) for fabrication of injection molding inserts with micro surface features. The Soft Tooling inserts are manufactured by Digital Light Processing (vat photo polymerization) using a photopolymer that can withstand relatively high temperaturea. The part manufactured here has four tines with an angle of 60&#176;. Micro pillars (&#216;200 &#181;m, aspect ratio of 1) are arranged on the surfaces by two rows. Polyethylene (PE) injection molding with the soft tooling inserts is used to fabricate the final parts. This method demonstrates that it is feasible to obtain injection-molded parts with microstructures on complex geometry by additive manufactured inserts. The machining time and cost is reduced significantly compared to conventional tooling processes based on computer numerical control (CNC) machining. The dimensions of the micro features are influenced by the applied additive manufacturing process. The lifetime of the inserts determines that this process is more suitable for pilot production. The precision of the inserts production is limited by the additive manufacturing process as well.

A protocol for fabricating injection molding inserts for complex geometry with micro features on surfaces employing Additive Manufacturing (AM) is presented.

The purpose of this paper is to present the method of a soft tooling process chain employing Additive Manufacturing (AM) for fabrication of injection ...

A New Ex Vivo Model for the Evaluation of Endoscopic Submucosal Injection Material Performance

Increasing the performance of submucosal injection materials (SIMs) is important for endoscopic therapy of early gastrointestinal cancer. It is essential to establish an ex vivo model that can evaluate SIM performance accurately, for developing high-performance SIMs. In our previous study, we developed a new ex vivo model that can be used to evaluate the performance of various SIMs in detail by applying constant tension to the specimen&#39;s ends. We also confirmed that the proposed new ex vivo model allows accurate submucosal elevation height (SEH) measurement under uniform conditions and detailed comparisons of the performances of various types of SIMs. Here, we describe the new ex vivo model and explain the detailed setup methodology of this model. Since all parts of the new model were easy to obtain, the setup of the new model could be completed quickly. SEH of various SIMs could be measured more accurately by using the new model. The critical factor that determines SIM performance can be identified using the new model. SIM development speed will drastically increase after the factor has been identified.

A New Ex Vivo Model for the Evaluation of Endoscopic Submucosal Injection Material Performance

We developed a new ex vivo model that applies constant tension to the porcine gastric specimen. This development made it possible to evaluate the performance (the height and duration of the submucosal elevation) of various SIMs accurately.&#160; The detailed setup methodology of this new model is explained.

Increasing the performance of submucosal injection materials (SIMs) is important for endoscopic therapy of early gastrointestinal cancer. It is essential ...

Injectable Supramolecular Polymer-Nanoparticle Hydrogels for Cell and Drug Delivery Applications

These methods describe how to formulate injectable, supramolecular polymer-nanoparticle (PNP) hydrogels for&#160;use as biomaterials. PNP hydrogels are composed of two components: hydrophobically modified cellulose as the network polymer and self-assembled core-shell nanoparticles that act as non-covalent cross linkers through dynamic, multivalent interactions. These methods describe both the formation of these self-assembled nanoparticles through nanoprecipitation as well as the formulation and mixing of the two components to form hydrogels with tunable mechanical properties. The use of dynamic light scattering (DLS) and rheology to characterize the quality of the synthesized materials is also detailed. Finally, the utility of these hydrogels for drug delivery, biopharmaceutical stabilization, and cell encapsulation and delivery is demonstrated through in vitro experiments to characterize&#160;drug release, thermal stability, and cell settling and viability. Due to its biocompatibility, injectability, and mild gel formation conditions, this hydrogel system is a readily tunable platform suitable for a range of biomedical applications.

This protocol describes the synthesis and formulation of injectable, supramolecular polymer-nanoparticle (PNP) hydrogel biomaterials. Applications of these materials for drug delivery, biopharmaceutical stabilization, and cell encapsulation and delivery are demonstrated.

These methods describe how to formulate injectable, supramolecular polymer-nanoparticle (PNP) hydrogels for&#160;use as biomaterials. PNP hydrogels are ...

Earthworm, Lumbricus Terrestris: A Novel Microinjection Vasculature In vivo Invertebrate Model

Although vertebrates are indispensable to biomedical research, studies are often limited by factors such as cost, lengthy internal review, and ethical considerations. We present the earthworm as an alternative, low-cost, invertebrate applicable to certain preliminary vasculature studies. Due to the surgical availability of the earthworm's dorsal vessels, ventral vessels, and five pairs of pseudo hearts, earthworms are readily accessible, offer low-cost maintenance, and require administration of only small doses of a given compound. The earthworm model provides a simple closed vascular circulatory system with a hemoglobin structure similar to human blood. A protocol is provided for anaesthetizing the earthworms and performing surgical incisions to expose relevant blood vessels. Micropipettes for compound administration are formed by heating and pulling glass with a pipette puller and using a beveling system to create a micron-scale fine needle tip. The tips are then used with a micropositioner and microinjector to inject arbitrary compounds into the vascular system of an earthworm, repeatably, with the availability of large sample sizes and small compound volumes. Details on the intricacies of injection procedure are provided. The small vessel size of the earthworm is challenging, particularly in the case of the ventral vessel; however, mastery of the techniques presented offers high repeatability as a low-cost solution, making studies of very large sample size practical.

Earthworms are a novel invertebrate in vivo bench-top model for vasculature studies. We present techniques and equipment that allow efficient surgery and microinjection into the earthworm vasculature. Surgical protocols, microinjection techniques and the procedure for producing custom-made micropipettes are described.

Although vertebrates are indispensable to biomedical research, studies are often limited by factors such as cost, lengthy internal review, and ethical ...

The Quantification of Injectability by Mechanical Testing

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