Name: plasma polishing as a new polishing option to reduce the surface roughness of porous titanium alloy for 3d printing
Uploaded: 2023-04-28T12:50:00.000+00:00
Duration: 6 min 12 s
Description: Watch this Scientific Journal Video about Plasma Polishing as a New Polishing Option to Reduce the Surface Roughness of Porous Titanium Alloy for 3D Printing at JoVE.com

I would like to thank my supervisor, Wenhua Huang, for providing support conditions and guidance for this experiment. This research was funded by the Discipline construction project of Guangdong Medical University (4SG22260G), Young Innovative Talents Project of Guangdong Higher Education Institutions (2021KQNCX023), National Natural Science Foundation of China (82205301), and Futian Healthcare Research Project (FTWS2022051).

1. Printing and preparation of a titanium alloy workpiece
<ol>
	<li>Prepare a workpiece made of porous titanium alloy using the SLM printing technique. Import STL format files into the metal printer, add Ti-6Al-4V powder, install the build substrate, set up the wiper blade, set the laser spot size to 70 &#181;m, and set the layer thickness to 30 &#181;m (Figure 1).</li>
	<li>Grade 23 Ti-6Al-4V powder with chemical composition as shown in Table 1 and a powder particle size of 15-53 &#181;m.</li>
	<li>Design the porous titanium alloy structure with simulated trabecular bone based on Tyson polygon anisotropy using parametric modeling, with an aperture size of 400-600 &#181;m, small beam diameter of 100-300 &#181;m, and porosity of 70%31 .</li>
	<li>Ensure the porous titanium alloy workpiece is in the shape of the medical lumbar cage32. For the porous structure and the lumbar cage, use Boolean operations to obtain the porous workpiece structure.</li>
</ol>
2. Heat treatment
<ol>
	<li>A high temperature gradient during SLM printing will cause residual stress in the workpiece. Use heat treatment to eliminate the residual stress inside the workpiece and maintain the toughness, plasticity, tensile strength, and other physical properties of the workpiece.</li>
	<li>Separate the porous titanium alloy workpiece from the printing substrate after printing using a medium speed wire-cutting machine. Install the titanium plate on the medium speed wire-cutting machine, in order to make the plate perpendicular to the ground, and ensure that the wire just contacts the support surface. Then, cut along the support and titanium plate to separate the porous titanium alloy workpiece from the printing substrate.</li>
	<li>Place the porous titanium alloy workpiece into the ultrasonic cleaning machine with deionized water for 15 min and the temperature controlled at 30 &#176;C. Keep the ultrasonic frequency at 40,000 Hz. The ultrasonic cleaning aims to remove the titanium alloy powder remaining in the porous structure.</li>
	<li>Repeat the aforementioned ultrasonic cleaning procedure four times to remove residual titanium alloy powder and deionized water from the porous structure. After that, aim high-pressure air at the porous structure for 20 s to blow away the residual powder and liquid. The pressure of the high-pressure air is 0.71 MPa, which is generated by an air compressor and air dryer.</li>
	<li>Put the titanium basket into the heat treatment furnace at room temperature. The titanium basket is equipped with titanium alloy workpieces separated from the substrate. Keep different workpieces from touching each other and close the furnace door.</li>
	<li>Open the gas valve, take out the air, and keep the vacuum degree at 3.9 x 10-3 Pa.</li>
	<li>Set the heat treatment process. First, heat the furnace to 800 &#176;C for 1.5 h, maintain the temperature for 2 h, and then cool the workpiece inside the furnace. This process ensures that the vacuum pressure remains unchanged.</li>
	<li>After the heat treatment, cool the furnace to room temperature and fill the furnace with air. After returning to atmospheric pressure, as seen on the panel, take out the porous titanium alloy workpiece.</li>
</ol>
3. Removing the support
<ol>
	<li>After heat treatment, the porous titanium alloy workpieces have no internal residual stress, so the workpiece surface will not crack and/or fracture when removing the support.</li>
	<li>Measure the support thickness using a vernier caliper, fix the workpiece on the low-speed wire-cutting electrical discharge machining (EDM) machine, and ensure that the copper wire just contacts the support surface.</li>
	<li>Set the cutting depth equal to the support thickness. It&#39;s inevitable that removing the support by the wire-cutting EDM machine will form an ablation oxide layer. When removing the support, ensure that the workpiece is immersed in deionized water to minimize burns to the workpiece surface.</li>
	<li>A reasonable support design ensures accuracy when removing the support. If there are still some support residues, polish the workpiece with sandpaper.</li>
</ol>
4. Ultrasonic cleaning
<ol>
	<li>Since the workpiece is immersed in deionized water during support removal, perform ultrasonic cleaning before plasma polishing to remove other impurities.</li>
	<li>Put the porous titanium alloy workpiece into the ultrasonic cleaning machine with deionized water, set the water temperature to 30 &#176;C, and clean it for 5 min. After 5 min, take out the workpiece and blow out residual liquid with high-pressure air.</li>
</ol>
5. First characterization
<ol>
	<li>Scanning electron microscope (SEM): Image the surfaces with a SEM at 15 and 20 kV accelerating voltage, after ultrasonic cleaning and before plasma polishing.</li>
	<li>Take images at 30x, 100x, and 500x visual fields. Observe the general surface morphology, particle adhesion, and pore size of the porous titanium alloy workpiece, and qualitatively evaluate the plasma polishing effect.</li>
	<li>Confocal microscope: Image the surfaces using a confocal microscope.</li>
	<li>Place the workpiece on the storage platform horizontally. Measure the surface arithmetic average roughness (Ra) parameter. Use ZEN core v3.0 and ConfoMap ST 8.0 software.
	<ol>
		<li>Select 2.5x magnification, choose Wide for live mode, click Auto intensity, and then go to 5x magnification to observe the overall situation. Click Auto intensity and set the live mode to Comp. Select the area of interest, click Set first at the lowest point and Set last at the highest point, and then set the acquisition to Normal.</li>
		<li>After about 5 min, import the results into a new document in ConfoMap ST 8.0. The Ra is easy to obtain in the parameters table in ConfoMap ST.</li>
	</ol>
	</li>
	<li>Observe the overall condition of the workpiece with a fivefold mirror, then switch to a high-power mirror and focus the field of vision on a trabecula. Evaluate the plasma polishing effect quantitatively by describing the Ra of the porous titanium alloy workpiece before plasma polishing.</li>
</ol>
6.&#160;Plasma polishing
<ol>
	<li>For this, use an electrolytic cell to immerse the workpiece in an electrolyte connected as an anode20. Use 4% ammonium sulfate solution [(NH4)2SO4], pH between 5.7-6.1, as the electrolyte. Preheat the polishing electrolyte to 80 &#176;C before plasma polishing.</li>
	<li>Set the polishing current to 59 A, the voltage to 313 V, and the polishing electrolyte temperature to 101.6 &#176;C (Figure 2A). Conduct plasma polishing according to these parameters.</li>
	<li>Place the surface of the porous titanium alloy workpiece to be polished horizontally and fix it on the fixture, and then put the fixture into the plasma polishing machine (Figure 2B). Conduct plasma polishing for 90 s, and then take the fixture out of the plasma polishing machine.</li>
	<li>Since the porous titanium alloy workpiece is fixed on the fixture through the clamping point, the clamping point is not in contact with the polishing solution, and the corresponding electrochemical reaction does not occur at the clamping point. Therefore, change the position of the clamping point slightly after the fixture is taken out.</li>
	<li>Conduct plasma polishing again for 90 s and take the fixture out of the plasma polishing machine. Remove the porous titanium alloy workpiece from the fixture and then put it into the ultrasonic cleaning machine with deionized water.</li>
	<li>Set the water temperature at 30 &#176;C and clean the workpiece for 2 min. After 2 min, take out the workpiece and blow out the residual liquid with high-pressure air.</li>
</ol>
7. Second characterization
<ol>
	<li>After the completion of plasma polishing, image the surfaces using a SEM and a confocal microscope in the same way as in step 5. Assess the influence of plasma polishing on the surface roughness and surface quality of 3D printing porous titanium alloy by comparing the above two shooting results.</li>
</ol>

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The authors have nothing to disclose.

Surface roughness is used to describe the amount of undulation and unevenness of micro geometric shapes on workpiece surfaces within a small spacing range. A number of previous studies have reported how to polish metal surfaces using different procedures, such as mechanical polishing, chemical polishing, electrochemical polishing, and more22,33,34,35. Although numerous studies have showed prospective polishing effects based on these conventional mechanical polishing techniques, the polishing method for 3D printing porous titanium alloy is crucial in order to reduce the surface roughness. Plasma polishing can efficiently polish workpieces with complex shapes without pollution. Therefore, surface roughness can measure the surface quality of 3D printed porous titanium alloy. The surface roughness of metallic orthopedic implants can not only optimize implant-bone interactions, but simultaneously minimize implant-bacteria interactions36 . Metallic cellular scaffolds can provide a place for cells and blood vessels to grow into, while osteoblasts seem to prefer rougher surfaces37. In this experiment, the surface roughness of 3D printed porous titanium alloy is maintained at 26.65 &#181;m after plasma polishing, which meets the basic requirements of promoting the growth of cells and blood vessels.
It is essential to conduct ultrasonic cleaning before heat treatment, so as to prevent the porous structure from being blocked by molten titanium powder. The porous titanium alloy workpiece is put into the ultrasonic machine with deionized water for 15 min for cleaning. Residual titanium alloy powder is blown off with high-pressure air after cleaning, and the ultrasonic cleaning and blowing off of residual powder is repeated three more times. In other words, 1 h of ultrasonic cleaning and four instances of high-pressure air blowing are carried out to remove residual titanium alloy powder.
During plasma polishing, the workpiece should be gently fixed on the fixture to protect the trabecula of the porous structure from damage, since a bit of the polishing fixtures become sharper after freuqent polishing. The fixture is taken out of the plasma polishing machine, the position of the clamping point is changed slightly after polishing for 90 s, and then plasma polishing is conducted for the remaining 90 s. If plasma polishing lasts for 180 s at one time without changing the position of the clamping point, the polishing around the clamping point will be successful, but the clamping point covered by the fixture of porous titanium alloy will present an unpolished surface state.
However, this polishing technology also has some limitations, such as high energy consumption. Due to the bath size limitation, plasma polishing equipment cannot process large parts. This technology can also be further studied. It is recommended to utilize more modeling and simulation studies to accurately predict optimal process parameter values, with the intention of achieving predicted workpiece improvements while minimizing the time and expense required for experimentation. We can conduct further studies to determine the optimal parameters for plasma polishing of porous titanium alloy workpieces22.
From a microscopic perspective, plasma polishing is a process in which the surface of a metal is melted by heat that is generated by high-speed electron impact. It is a new development trend in the field of green manufacturing and precision machining and is very suitable for 3D printed porous titanium alloy. In conclusion, this protocol for polishing 3D printing porous titanium alloy workpieces will be a new option to reduce surface roughness and improve surface quality.

Titanium and titanium alloy materials have been widely used as dental and orthopedic implant materials because of their good biocompatibility, corrosion resistance, and mechanical strength1,2,3. However, due to the high elastic modulus of the compact titanium alloy produced by traditional processing methods, these plates are not suitable for bone repair, since close proximity to the bone surface for long periods can result in stress shielding and bone embrittlement4,5 . Therefore, the porous microstructure of simulated bone trabeculae should be used in titanium alloy implants in order to reduce its elastic modulus to the level matching the bone6,7. Many scaffolds have been used in the field of orthopedics to improve cell viability, attachment, proliferation and homing, osteogenic differentiation, angiogenesis, host integration, and weight bearing4,8,9. Traditional fabrication methods of porous metal structures include the structural template method, defect formation method, compression or supercritical carbon dioxide method, electro-deposition technique10,11, etc. Although these production techniques are highly traditional, they occasionally squander raw materials and have substantial preparatory costs when compared to 3D printing12,13. 3D printing is a technology that uses metal or plastic powder and other adhesive materials to build solid 3D objects from computer aided design (CAD) models via the deposition of overlying layers14,15 . 3D printing shows great potential in directly customizing metallic cellular scaffolds for orthopedic implants and opens up new possibilities for manufacturing customizable complex designs with highly interconnected pores. Among them, selective laser melting (SLM) is one of the most representative 3D printing and manufacturing technologies for porous titanium implant structures16 .
The SLM process uses titanium alloy powder as the raw material, essentially powder melting and forming the structure. Therefore, a large number of semi-molten powders and ablative oxide layers often adhere to the surface of titanium alloy implants, which leads to high surface roughness17. Poor surface quality of porous titanium orthopedic implants leads to inflammation, decreased fatigue performance, and even new biological risks18 . Since the internal pores of porous structures cannot be polished by conventional mechanical polishing, an alternative method needs to be found. Plasma polishing is a new green polishing method for metal workpieces that can efficiently polish workpieces with complex shapes without pollution19 . It has great development potential in the field of titanium alloy implant post-processing.
As a kind of surface technology, plasma polishing technology is particularly suitable for metal workpieces with complex shapes that are not easy to be mechanically polished. The overall goal of this polishing option is to obtain a porous titanium alloy surface with low roughness. The technology can effectively remove particles and fine splash residues attached to the surface of porous titanium orthopedic implants fabricated by 3D printing and reduce surface roughness20. The principle of plasma polishing is a composite reaction process based on a combination of current-induced chemical and physical removal21; the entire circuit forms a transient short circuit, forming a vapor plasma-surrounding layer on the workpiece surface20. This process breaks through the gas layer to form a discharge channel, impacting the workpiece surface. The higher current impacts the convex part of the workpiece surface, leading to the faster removal of semi-molten powder and the burnt oxide layer. The concavity and convexity are constantly changing, and the rough surface becomes gradually smoothed, improving the surface roughness of the workpiece to achieve the purpose of polishing.
At the same time, this technology is a green processing technology, causing no pollution to the environment, and has great advantages compared with other polishing methods. Conventional mechanical polishing techniques mainly include mechanical polishing, chemical polishing, and electrochemical polishing22. Mechanical polishing is the most widely used conventional polishing process; it has the disadvantages of low polishing efficiency, higher demand for manual labor, and inability to polish parts with complex geometries. The potential for employee injury and the likelihood of exceeding tolerances due to human factors are frequent drawbacks of mechanical polishing23. In contrast to chemical polishing, which is based on utilizing a chemical solution to remove parts of a workpiece&#39;s material, electrochemical polishing utilizes an electric current and chemical solution to obtain the same result. Unfortunately, both these processes produce hazardous gases and liquids as by-products of use, the composition of which being dependent on the strength of the acid or alkaline chemical reagent being used. As a result, not only are the workers present deemed to be at risk due to exposure, but there is also the potential for severe damage to the environment24. Aliakseyeu et al.25 proposed utilizing plasma polishing for polishing titanium alloy workpieces with simple electrolyte composition. They found that, after polishing titanium sample surface scratches are removed and the surface gloss is significantly improved. Smyslova et al.26 deliberated upon the prospects of applying plasma polishing technology to treat the surfaces of medical implants.
Theoretically, plasma polishing technology can be utilized to polish the structure of any metal part. It has been widely applied for coating, in metal finishing industries, and in 3C electronics, among others22,27,28. However, the present study has some limitations. First of all, the manuscript only focuses on the surface quality and surface roughness of 3D printing porous titanium alloy before and after plasma polishing; the remaining changes are not involved. Secondly, we didn&#39;t measure and record the results after heat treatment. Jinyoung Kim et al.29 compared titanium surface modification strategies for osseointegration enhancement. Another study shows that the target-ion induced plasma sputtering (TIPS) technique can impart excellent biological functions to the surface of metallic bio-implants30. In order to further investigate the polishing efficacy and safety of porous titanium alloy for 3D printing, the next step will be to further study SLM part&#39;s other properties, such as fatigue performance and osteogenic differentiation. These issues need further refinement. This work differs from earlier plasma polishing studies in that it focuses on 3D printing porous titanium alloy rather than compact titanium alloy. As a result, different manufacturing processes should adopt different polishing parameters. The purpose of this manuscript is to introduce the plasma polishing scheme of 3D printing porous titanium alloy in detail, so as to reduce the surface roughness of workpieces.

<table><tbody><tr><td>Confocal microscope: Smartproof-5</td><td>ZEISS</td><td>4702000198</td><td></td></tr><tr><td>ConfoMap ST 8.0</td><td>ZEISS</td><td>4702000198</td><td></td></tr><tr><td>Electrical discharge machining (EDM) machine: MV1200S</td><td>Mitsubishi Electric Automation (China) Ltd.</td><td>92U3038</td><td></td></tr><tr><td>Heat treatment furnace: HSQ1-644</td><td>Jiangsu Huasu Industrial Furnace Manufacturing CO., LTD.</td><td>HSD20190812403</td><td></td></tr><tr><td>Metal 3D printer: Renishaw AM400</td><td>Renishaw plc</td><td>1HGW89</td><td></td></tr><tr><td>Middle speed wire-cut machine: HQ-400EZ</td><td>Suzhou Hanqi CNC Equipment CO., LTD.</td><td>W40ES20005</td><td></td></tr><tr><td>Permanent magnet frequency conversion screw air compressor M7-Y75AZ</td><td>KUNJI MACHINERY(SHANGHAI) MANUFACTURING CO.,LTD.&amp;nbsp;</td><td>19055065</td><td></td></tr><tr><td>Refrigeration compressed air dryer SY-230FG</td><td>Shanghai TaiLin Compressor Co., Ltd.</td><td>S190826698</td><td></td></tr><tr><td>Scanning electron microscope (SEM): JSM-IT100</td><td>JEOL (BEIJING) CO., LTD.</td><td>MP1030004260426</td><td></td></tr><tr><td>Titanium alloy powder</td><td>Renishaw plc</td><td>H-5800-1086-01-A</td><td></td></tr><tr><td>Ultrasonic cleaning machine: AK-030S</td><td>Shenzhen Yujie Cleaning Equipment Co., Ltd</td><td>30820004</td><td></td></tr><tr><td>ZEN core v3.0</td><td>ZEISS</td><td>4702000198</td><td></td></tr></tbody></table>

plasma polishing as a new polishing option to reduce the surface roughness of porous titanium alloy for 3d printing

Porous titanium alloy implants with simulated trabecular bone fabricated by 3D printing technology have broad prospects. However, due to the fact that some powder adheres to the surface of the workpiece during the manufacturing process, the surface roughness in direct printing pieces is relatively high. At the same time, since the internal pores of the porous structure cannot be polished by conventional mechanical polishing, an alternative method needs to be found. As a surface technology, plasma polishing technology is especially suitable for parts with complex shapes that are difficult to polish mechanically. It can effectively remove particles and fine splash residues attached to the surface of 3D printed porous titanium alloy workpieces. Therefore, it can reduce surface roughness. Firstly, titanium alloy powder is used to print the porous structure of the simulated trabecular bone with a metal 3D printer. After printing, heat treatment, removal of the supporting structure, and ultrasonic cleaning is carried out. Then, plasma polishing is performed, consisting of adding a polishing electrolyte with the pH set to 5.7, preheating the machine to 101.6 &#176;C, fixing the workpiece on the polishing fixture, and setting the voltage (313 V), current (59 A), and polishing time (3 min). After polishing, the surface of the porous titanium alloy workpiece is analyzed by a confocal microscope, and the surface roughness is measured. Scanning electron microscopy is used to characterize the surface condition of porous titanium. The results show that the surface roughness of the whole porous titanium alloy workpiece changed from Ra (average roughness) = 126.9 &#181;m to Ra = 56.28 &#181;m, and the surface roughness of the trabecular structure changed from Ra = 42.61 &#181;m to Ra = 26.25 &#181;m. Meanwhile, semi-molten powders and ablative oxide layers are removed, and surface quality is improved.

Surface morphology 
Figure 3 shows the SEM result of the surface morphology of the porous titanium alloy workpiece before and after plasma polishing. We observed that at 30x and 100x magnification, the surface of the porous titanium alloy workpiece before plasma polishing seems to be rougher (Figure 3A,B). When magnified to 500x, we found that a large amount of semi-molten powders and ablative oxide layers could be observed on the surface of the porous titanium alloy (Figure 3C). However, most of the semi-molten powders and ablative oxide layers on the surface of the porous titanium alloy were removed after plasma polishing (Figure 3F). At the same time, the pore size and trabecular diameter were consistent with the design, which was not damaged (Figure 3D,E). This shows that plasma polishing can improve the surface quality of 3D printing porous titanium alloy workpieces and does not damage the original design pore structure.
Surface roughness measurement 
The whole and part of the porous titanium alloy workpiece were imaged using the fast rotary confocal microscope, as shown in Figure 4, and the surface roughness was measured. The surface roughness is high, whether it&#39;s the whole surface of the porous titanium alloy or a small beam forming a porous structure, before plasma polishing (Figure 4A,B). The surface roughness of porous structure is significantly reduced; the Ra of the overall surface is 56.28 &#181;m (Figure 4C), While the Ra of part of the porous titanium alloy workpiece is 26.65 &#181;m (Figure 4D).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/65108/65108fig01.jpg" /> 
Figure 1: SLM metal 3D printing. SLM printing technology is used and 23 Ti-6Al-4V powder is graded to prepare a porous titanium alloy workpiece. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/65108/65108fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/65108/65108fig02.jpg" /> 
Figure 2: Plasma polishing machine and polishing fixture. (A) Plasma polishing machine setting parameters: the polishing current is set as 59 A, the voltage is set as 313 V, and the polishing electrolyte temperature is set as 101.6 &#176;C, after preheating the polishing electrolyte. (B) Polishing fixture. The surface of the porous titanium alloy workpiece to be polished is placed horizontally and fixed on the fixture, ensuring that the fixture is immersed in the polishing electrolyte. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/65108/65108fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/65108/65108fig03.jpg" /> 
Figure 3: The images of the 3D printed porous titanium alloy workpiece using an SEM. Before plasma polishing, (A) at 30x, the whole porous structure can be observed. (B) At 100x, the pore structure can be observed. The surface of the porous titanium alloy workpiece before plasma polishing seems to be rougher. (C) At 500x, a large amount of semi-molten powders and ablative oxide layers can be observed on the surface of the trabecular structure. After plasma polishing, (D) at 30x, the whole porous structure can be observed. (E) At 100x, the pore structure can be observed. The pore size and trabecular diameter were consistent with the design, which was not damaged. (F) At 500x, most of the semi-molten powders and ablative oxide layers on the surface of the porous titanium alloy were removed. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/65108/65108fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/65108/65108fig04.jpg" /> 
Figure 4: The images of the 3D printed porous titanium alloy workpiece using a confocal microscope. The image shows the surface morphology of the porous titanium alloy, with the coordinate axis representing the length. After plasma polishing, the surface of porous titanium alloy exhibits a shiny metallic appearance. (A) The whole porous titanium alloy workpiece was imaged before plasma polishing, Ra = 126.9 &#181;m. (B) A part of the porous titanium alloy workpiece was imaged before plasma polishing, Ra = 42.61 &#181;m. (C) The whole porous titanium alloy workpiece was imaged after plasma polishing, Ra = 56.28 &#181;m. The overall surface roughness can be reduced by plasma polishing. (D) A part of the porous titanium alloy workpiece was imaged after plasma polishing, Ra = 26.65 &#181;m. The surface roughness of the trabecular structure can be reduced by plasma polishing. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/65108/65108fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Element</td>
			<td>Mass(%)</td>
		</tr>
		<tr>
			<td>Titanium</td>
			<td>Balance</td>
		</tr>
		<tr>
			<td>Aluminium</td>
			<td>5.50 to 6.50</td>
		</tr>
		<tr>
			<td>Vanadium</td>
			<td>3.50 to 4.50</td>
		</tr>
		<tr>
			<td>Iron</td>
			<td>&#60; 0.25</td>
		</tr>
		<tr>
			<td>Oxygen</td>
			<td>&#60; 0.13</td>
		</tr>
		<tr>
			<td>Carbon</td>
			<td>&#60; 0.08</td>
		</tr>
		<tr>
			<td>Nitrogen</td>
			<td>&#60; 0.05</td>
		</tr>
		<tr>
			<td>Hydrogen</td>
			<td>&#60; 0.012</td>
		</tr>
		<tr>
			<td>Residual</td>
			<td>&#60; 0.10 each, 0.40 total</td>
		</tr>
	</tbody>
</table>
Table 1: Chemical composition of Ti-6Al-4V alloy powder.

Watch this Scientific Journal Video about Plasma Polishing as a New Polishing Option to Reduce the Surface Roughness of Porous Titanium Alloy for 3D Printing at JoVE.com

Plasma Polishing as a New Polishing Option to Reduce the Surface Roughness of Porous Titanium Alloy for 3D Printing

Plasma polishing is a promising surface processing technology, especially suitable for 3D printing of porous titanium alloy workpieces. It can remove semi-molten powders and ablative oxide layers, thereby effectively reducing surface roughness and improving surface quality.

Porous titanium alloy implants with simulated trabecular bone fabricated by 3D printing technology have broad prospects. However, due to the fact that ...

plasma-polishing-as-new-polishing-option-to-reduce-surface-roughness

Nanyang Technological University

Research

JoVE Journal

Medicine

1.6K Views.  Affiliated Hospital of Guangdong Medical University. Omdat de interne puls van poreuze structuren niet kan worden gepolijst door conventionele mechanische vervuiling, moet een alternatieve methode worden gevonden. Plasmavervuiling is een milieuvriendelijke verwerkingsmethode die vooral effectief is voor mentale werkstukken met complexe vormen. Plaats om te beginnen de gescheiden werkstukken van titaniumlegering in de titaniummand zonder dat de verschillende werkstukken elkaar raken.Plaats de titanium mand in de warmtebehandelingsoven bij...

Video: Plasma Polishing as a New Polishing Option to Reduce the Surface Roughness of Porous Titanium Alloy for 3D Printing

Multi-Scale Modification of Metallic Implants With Pore Gradients, Polyelectrolytes and Their Indirect Monitoring In vivo

Metallic implants, especially titanium implants, are widely used in clinical applications. Tissue in-growth and integration to these implants in the tissues are important parameters for successful clinical outcomes. In order to improve tissue integration, porous metallic implants have being developed. Open porosity of metallic foams is very advantageous, since the pore areas can be functionalized without compromising the mechanical properties of the whole structure. Here we describe such modifications using porous titanium implants based on titanium microbeads. By using inherent physical properties such as hydrophobicity of titanium, it is possible to obtain hydrophobic pore gradients within microbead based metallic implants and at the same time to have a basement membrane mimic based on hydrophilic, natural polymers. 3D pore gradients are formed by synthetic polymers such as Poly-L-lactic acid (PLLA) by freeze-extraction method. 2D nanofibrillar surfaces are formed by using collagen/alginate followed by a crosslinking step with a natural crosslinker (genipin). This nanofibrillar film was built up by layer by layer (LbL) deposition method of the two oppositely charged molecules, collagen and alginate. Finally, an implant where different areas can accommodate different cell types, as this is necessary for many multicellular tissues, can be obtained. By, this way cellular movement in different directions by different cell types can be controlled. Such a system is described for the specific case of trachea regeneration, but it can be modified for other target organs. Analysis of cell migration and the possible methods for creating different pore gradients are elaborated. The next step in the analysis of such implants is their characterization after implantation. However, histological analysis of metallic implants is a long and cumbersome process, thus for monitoring host reaction to metallic implants in vivo an alternative method based on monitoring CGA and different blood proteins is also described. These methods can be used for developing in vitro custom-made migration and colonization tests and also be used for analysis of functionalized metallic implants in vivo without histology.

Multi-Scale Modification of Metallic Implants With Pore Gradients, Polyelectrolytes and Their Indirect Monitoring In vivo

In this video, we will demonstrate modification techniques for porous metallic implants to improve their functionality and to control cell migration. Techniques include development of pore gradients to control cell movement in 3D and production of basement membrane mimics to control cell movement in 2-D. Also, a HPLC-based method for monitoring implant integration in-vivo via analysis of blood proteins is described.

Metallic implants, especially titanium implants, are widely used in  clinical applications. Tissue in-growth and integration to these implants in  the ...

Bioengineering

Stereolithographic 3D Printing with Renewable Acrylates

The accessibility of cost-competitive renewable materials and their application in additive manufacturing is essential for an efficient biobased economy. We demonstrate the rapid prototyping of sustainable resins using a stereolithographic 3D printer. Resin formulation takes place by straightforward mixing of biobased acrylate monomers and oligomers with a photoinitiatior and optical absorber. Resin viscosity is controlled by the monomer to oligomer ratio and is determined as a function of shear rate by a rheometer with parallel plate geometry. A stereolithographic apparatus charged with the biobased resins is employed to produce complex shaped prototypes with high accuracy. The products require a post-treatment, including alcohol rinsing and UV irradiation, to ensure complete curing. The high feature resolution and excellent surface finishing of the prototypes is revealed by scanning electron microscopy.

A protocol for additive manufacturing with renewable photopolymer resins on a stereolithography apparatus is presented.

The accessibility of cost-competitive renewable materials and their application in additive manufacturing is essential for an efficient biobased economy. ...

Chemistry

Fabrication of Mechanically Tunable and Bioactive Metal Scaffolds for Biomedical Applications

Biometal systems have been widely used for biomedical applications, in particular, as load-bearing materials. However, major challenges are high stiffness and low bioactivity of metals. In this study, we have developed a new method towards fabricating a new type of bioactive and mechanically reliable porous metal scaffolds-densified porous Ti scaffolds. The method consists of two fabrication processes, 1) the fabrication of porous Ti scaffolds by dynamic freeze casting, and 2) coating and densification of the porous scaffolds. The dynamic freeze casting method to fabricate porous Ti scaffolds allowed the densification of porous scaffolds by minimizing the chemical contamination and structural defects. The densification process is distinctive for three reasons. First, the densification process is simple, because it requires a control of only one parameter (degree of densification). Second, it is effective, as it achieves mechanical enhancement and sustainable release of biomolecules from porous scaffolds. Third, it has broad applications, as it is also applicable to the fabrication of functionally graded porous scaffolds by spatially varied strain during densification.

Bioactive and mechanically reliable metal scaffolds have been fabricated through a method which consists of two processes, dynamic freeze casting for the fabrication of porous Ti, and coating and densification of the Ti scaffolds. The densification process is simple, effective and applicable to the fabrication of functionally graded scaffolds.

Biometal systems have been widely used for biomedical applications, in particular, as load-bearing materials. However, major challenges are high stiffness ...

Procedure for the Transfer of Polymer Films Onto Porous Substrates with Minimized Defects

The fabrication of devices containing thin film composite membranes necessitates the transfer of these films onto the surfaces of arbitrary support substrates. Accomplishing this transfer in a highly controlled, mechanized, and reproducible manner can eliminate the creation of macroscale defect structures (e.g., tears, cracks, and wrinkles) within the thin film that compromise device performance and the usable area per sample. Here, we describe a general protocol for the highly controlled and mechanized transfer of a polymeric thin film onto an arbitrary porous support substrate for eventual use as a water filtration membrane device. Specifically, we fabricate a block copolymer (BCP) thin film on top of a sacrificial, water-soluble poly(acrylic acid) (PAA) layer and silicon wafer substrate. We then utilize a custom-designed, 3D-printed transfer tool and drain chamber system to deposit, lift-off, and transfer the BCP thin film onto the center of a porous anodized aluminum oxide (AAO) support disc. The transferred BCP thin film is shown to be consistently placed onto the center of the support surface due to the guidance of the meniscus formed between the water and the 3D-printed plastic drain chamber. We also compare our mechanized transfer-processed thin films to those that have been transferred by hand with the use of tweezers. Optical inspection and image analysis of the transferred thin films from the mechanized process confirm that little-to-no macroscale inhomogeneities or plastic deformations are produced, as compared to the multitude of tears and wrinkles produced from manual transfer by hand. Our results suggest that the proposed strategy for thin film transfer can reduce defects when compared to other methods across many systems and applications.

We present a procedure for highly controlled and wrinkle-free transfer of block copolymer thin films onto porous support substrates using a 3D-printed drain chamber. The drain chamber design is of general relevance to all procedures involving transfer of macromolecular films onto porous substrates, which is normally done by hand in an irreproducible fashion.

The fabrication of devices containing thin film composite membranes necessitates the transfer of these films onto the surfaces of arbitrary support ...

Engineering

3D Printing and In Situ Surface Modification via Type I Photoinitiated Reversible Addition-Fragmentation Chain Transfer Polymerization

3D printing provides facile access to geometrically complex materials. However, these materials have intrinsically linked bulk and interfacial properties dependent on the chemical composition of the resin. In the current work, 3D printed materials are post-functionalized using the 3D printer hardware via a secondary surface-initiated polymerization process, thus providing independent control over the bulk and interfacial material properties. This process begins with preparing liquid resins, which contain a monofunctional monomer, a crosslinking multifunctional monomer, a photochemically labile species that enables initiation of polymerization, and critically, a thiocarbonylthio compound which facilitates reversible addition-fragmentation chain transfer (RAFT) polymerization. The thiocarbonylthio compound, known commonly as a RAFT agent, mediates the chain growth polymerization process and provides polymeric materials with more homogeneous network structures. The liquid resin is cured in a layer-by-layer fashion using a commercially available digital light processing 3D printer to give three-dimensional materials having spatially controlled geometries. The initial resin is removed and replaced with a new mixture containing functional monomers and photoinitiating species. The 3D printed material is then exposed to light from the 3D printer in the presence of the new functional monomer mixture. This allows photoinduced surface-initiated polymerization to occur from the latent RAFT agent groups on the surface of the 3D printed material. Given the chemical flexibility of both resins, this process allows a wide range of 3D printed materials to be produced with tailorable bulk and interfacial properties.

3D Printing and In Situ Surface Modification via Type I Photoinitiated Reversible Addition-Fragmentation Chain Transfer Polymerization

The present protocol describes the digital light processing-based 3D printing of polymeric materials using type I photoinitiated reversible addition-fragmentation chain transfer polymerization and the subsequent in situ material post-functionalization via surface-mediated polymerization. Photoinduced 3D printing provides materials with independently tailored and spatially controlled bulk and interfacial properties.

3D printing provides facile access to geometrically complex materials. However, these materials have intrinsically linked bulk and interfacial properties ...

Fabrication and Characterization of Optical Tissue Phantoms Containing Macrostructure

The rapid development of new optical imaging techniques is dependent on the availability of low-cost, customizable, and easily reproducible standards. By replicating the imaging environment, costly animal experiments to validate a technique may be circumvented. Predicting and optimizing the performance of in vivo and ex vivo imaging techniques requires testing on samples that are optically similar to tissues of interest. Tissue-mimicking optical phantoms provide a standard for evaluation, characterization, or calibration of an optical system. Homogenous polymer optical tissue phantoms are widely used to mimic the optical properties of a specific tissue type within a narrow spectral range. Layered tissues, such as the epidermis and dermis, can be mimicked by simply stacking these homogenous slab phantoms. However, many in vivo imaging techniques are applied to more spatially complex tissue where three dimensional structures, such as blood vessels, airways, or tissue defects, can affect the performance of the imaging system. 
This protocol describes the fabrication of a tissue-mimicking phantom that incorporates three-dimensional structural complexity using material with optical properties of tissue. Look-up tables provide India ink and titanium dioxide recipes for optical absorption and scattering targets. Methods to characterize and tune the material optical properties are described. The phantom fabrication detailed in this article has an internal branching mock airway void; however, the technique can be broadly applied to other tissue or organ structures.

Optical tissue phantoms are essential tools for calibration and characterization of optical imaging systems and validation of theoretical models. This article details a method for phantom fabrication that includes replication of tissue optical properties and three-dimensional tissue structure.

The rapid development of new optical imaging techniques is dependent on the availability of low-cost, customizable, and easily reproducible standards. By ...

Cost-Effective Shape Setting of NiTi Wires Using Sacrificial Copper Fixtures

Rapid Formation and Testing of Self-expanding NiTi Frames with a Small Form Factor Suitable for Minimally Invasive Implants

NiTiNOL (commonly referred to as nitinol or NiTi) wires feature exceptional shape memory and super-elastic characteristics, while shape-setting is often a costly process. Among the steps in&#160;this process, heat treatment requires exposure to high temperatures for shape-setting. Traditionally, metal fixtures are used for this purpose.&#160;However, their manufacturing costs can be significant, which is unideal&#160;for iterating prototypes. This work demonstrates a recently introduced approach using sacrificial fixtures made of copper tubes, which eliminates the need for expensive fixtures. These copper tubes allow for the formation of complex geometries, and they offer a scaffold for various phases of the fabrication process. Moreover, ammonium persulfate is used&#160;for selective copper etching, which simplifies the production of NiTi frames. This work&#39;s findings confirm the effectiveness of this technique and&#160;demonstrate&#160;the successful shape-setting of NiTi wires for self-expanding frames. This methodology paves the way for future research, allowing for rapid prototyping of NiTi wireframes for various applications, especially those in medical devices.

Author Spotlight: Rapid Prototyping and Testing of Self-Expanding Nitinol Frames for Transcatheter Implantable Devices

This work illustrates a low-cost fabrication technique for shape-setting nitinol wires/frames with a small form factor using sacrificial fixtures. The technique is demonstrated for the fabrication of self-expanding frames designed for minimally invasive implants with complex shapes.

NiTiNOL (commonly referred to as nitinol or NiTi) wires feature exceptional shape memory and super-elastic characteristics, while shape-setting is often a ...

Platelet-Derived Extracellular Vesicle Functionalization of Ti Implants

Extracellular Vesicles (EVs) are biological nanovesicles that play a key role in cell communication. Their content includes active biomolecules such as proteins and nucleic acids, which present great potential in regenerative medicine. More recently, EVs derived from Platelet Lysate (PL) have shown an osteogenic capability comparable to PL. Besides, biomaterials are frequently used in orthopedics or dental restoration. Here, we provide a method to functionalize Ti surfaces with PL-derived EVs in order to improve their osteogenic properties.
EVs are isolated from PL by size exclusion chromatography, and afterward Ti surfaces are functionalized with PL-EVs by drop casting. Functionalization is proven by EVs release and its biocompatibility by the lactate dehydrogenase (LDH) release assay.

Here, we present a method for the isolation of Extracellular Vesicles (EVs) derived from the platelet lysates (PL) and their use for coating titanium (Ti) implant surfaces. We describe the drop casting coating method, the EVs release profile from the surfaces, and in vitro biocompatibility of EVs coated Ti surfaces.

Extracellular Vesicles (EVs) are biological nanovesicles that play a key role in cell communication. Their content includes active biomolecules such as ...

Oral Biofilm Formation on Different Materials for Dental Implants

Dental implants and their prosthetic components are prone to bacterial colonization and biofilm formation. The use of materials that provides low microbial adhesion may reduce the prevalence and progression of peri-implant diseases. In view of the oral environment complexity and oral biofilm heterogeneity, microscopy techniques are needed that can enable a biofilm analysis of the surfaces of teeth and dental materials. This article describes a series of protocols implemented for comparing oral biofilm formation on titanium and ceramic materials for prosthetic abutments, as well as the methods involved in oral biofilms analyses at the morphological and cellular levels. The in situ model to evaluate oral biofilm formation on titanium and zirconia materials for dental prosthesis abutments as described in this study provides a satisfactory preservation of the 48 h biofilm, thereby demonstrating methodological adequacy. Multiphoton microscopy allows the analysis of an area representative of the biofilm formed on the test materials. In addition, the use of fluorophores and the processing of the images using multiphoton microscopy allows the analysis of the bacterial viability in a very heterogeneous population of microorganisms. The preparation of biological specimens for electron microscopy promotes the structural preservation of biofilm, images with good resolution, and no artifacts.

Here, we present a protocol to evaluate oral biofilm formation on titanium and zirconia materials for dental prosthesis abutments, including the analysis of bacterial cells viability and morphological characteristics. An in situ model associated with powerful microscopy techniques is used for the oral biofilm analysis.

Dental implants and their prosthetic components are prone to bacterial colonization and biofilm formation. The use of materials that provides low ...

Impact of Fabrication Techniques and Polishing Procedures on Surface Roughness of Denture Base Resins

This study aimed to assess the impact of various fabrication techniques and polishing procedures on the surface roughness (Ra) of resin-based materials used in the fabrication of complete dentures. A total of 90 specimens were produced from three different resin materials: heat-polymerized polymethyl methacrylate (PMMA) resin, CAD-CAM milled PMMA resin, and 3D-printed resin (n = 30). Each specimen measured 10 mm in diameter and 2 mm in height. The surface roughness (Ra) values of the specimens were initially determined using a contact profilometer following fabrication. Subsequently, each group of specimens was polished with 600-, 800-, and 1000-grit silicon carbide abrasive papers under running water. A second measurement of the surface roughness (Ra) values was then performed. The data were analyzed statistically using the Kruskal-Wallis test, Mann-Whitney U test, Wilcoxon signed-rank test, and paired samples t-test (p = 0.05). A statistically significant difference was identified between the groups in terms of surface roughness (Ra) prior to the polishing process (p &#60; 0.001). However, no statistically significant difference was observed between the milled and heat-polymerized PMMA base materials following the polishing process. The 3D-printed specimens showed the most notable improvement in surface roughness due to the polishing process. Nevertheless, their surface roughness remained statistically significantly higher compared to the other samples, both before and after polishing (p &#60; 0.001). The fabrication method of complete denture base materials was observed to influence surface roughness. The surface roughness values of the base materials fabricated using the 3D printing method were higher compared to those fabricated with milled and heat-polymerized PMMA resin, both before and after polishing.

This article presents a protocol to evaluate the effects of different manufacturing methods (heat-polymerized PMMA, CAD-CAM milled PMMA, and 3D-printed resin) and polishing techniques (600, 800, and 1000 grit silicon carbide abrasive papers) on the surface roughness (Ra) of resin base materials used for complete dentures.

This study aimed to assess the impact of various fabrication techniques and polishing procedures on the surface roughness (Ra) of resin-based materials ...

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