Surface Modification of 3D Printed PLA Objects by Fused Deposition Modeling: A Review
Round 1
Reviewer 1 Report
The paper is generally well written but the subject area discussed is very broad and does not match the title.
Specifically, the title refers to the surface modification of 3D printed PLA objects by FDM: a review. The abstract also talks about SLS and SLA. The last sentence of the abstract line 23-25 should be removed.
The introduction section 1.1 to 1.2 inclusive ss a review of PLA and not of PLA in 3D printing. I suggest to remove or shorten considerably as this is covered in other review papers.
Fig 1&2 have the authors gotten permission to reproduce? The legend on figure 1 is not clear enough for publication.
Section 2: again this ties back to the title. The methods described are not on FDM filaments and no attempt is made to discuss these in terms of 3D printing and special requirements necessary to implement them into a 3D printing procedure. The authors also state on pg 7 line 258 that a review post-2010 is required however more than half all references are pre-2010.
pg 12 line 519 3.3. D Printed PLA Objects... Should be rewritten 3D Printed. this error is also present on line 590.
Line 525 - 532 is generally a repeat of the introduction.
FFF is fused filament fabrication (not production) line 532
Section 3.2.
How is this tied into the over theme of the review?
Section 3.3
The application of PLA in SLA is not well covered or discussed. THis should be removed or expanded. how is this tied into the over theme of the review?
line 639 there is no need to redefine 3D printing
line 700-702. I am not convinced that the conclusion is supported by the review.
Author Response
Response to Reviewers
JOURNAL: MDPI-Colloids & Interfaces
AUTHORS: Eda Hazal Baran and H. Yildirim Erbil*
TITLE: Surface Modification of 3D Printed PLA Objects by Fused Deposition Modeling: A Review
TYPE: Review Article
Manuscript ID: colloids-456886
Reviewer #1: The paper is generally well written but the subject area discussed is very broad and does not match the title. Specifically, the title refers to the surface modification of 3D printed PLA objects by FDM: a review. The abstract also talks about SLS and SLA. The last sentence of the abstract line 23-25 should be removed.
Thank you for this point. We agree with Reviewer #1 that the subject area which was discussed in this review was very broad and it is necessary to reduce some part of the review subject. Consequently, we deleted the sentence related with SLS and SLA processes from the abstract and merged Sections 3.2 and 3.3 in a single Section 3.2 entitled “Use of Powder Based Techniques and Photopolymerization in 3D Printing of PLA” and add sentences to tie these subjects to the theme of the review and also explained that we are only presenting some indicative examples of the literature instead of complete reviewing of these subjects. We also deleted the last sentence of the abstract line 23-25 as requested by Reviewer #1 and reorganized the last 8 lines of the abstract.
The introduction section 1.1 to 1.2 inclusive as a review of PLA and not of PLA in 3D printing. I suggest to remove or shorten considerably as this is covered in other review papers.
We do not agree with Reviewer #1 on this point. In this review, the objective is to summarize the used recent methods to modify the surface layer of PLA, focusing specifically to the surface modification of 3D printed PLA objects obtained by the FDM method. In order to carry out this task, we summarized the generally known facts of PLA contained in the first part of the article since it will help the quick orientation in the basic information about the PLA polymer and its modifications in the context of the further parts of the review article. We believe that we have to do that especially for the newcomers to the field. In addition, we cited most of the important publications in the reference list in order to help the readers to find more information according to their interests. We think that the inclusion of this information on the PLA in a condensed form (in approximately 3 journal pages) as given in Sections 1.1 and 1.2 of the article is an added value, and we prefer to keep them as is in the revised MS.
Fig 1&2 have the authors gotten permission to reproduce? The legend on Figure 1 is not clear enough for publication.
We thank to Reviewer #1 for this point. We redraw the Figs. 1&2 for better clarity and we think that we do not need to ask permission for these figures after they are redrawn and cited.
Section 2: again this ties back to the title. The methods described are not on FDM filaments and no attempt is made to discuss these in terms of 3D printing and special requirements necessary to implement them into a 3D printing procedure.
There is a misunderstanding for the Section 2. This section is entirely devoted to the surface modifications of most of the PLA solids irrespective of whether PLA filaments and other PLA sources are used. For example, surface modification with chemical methods giving covalent attachments such as alkaline surface hydrolysis and ATRP, photografting by UV light, plasma treatment etc. are given in this section. This is a required section from a chemist point of view since all of these methods have the potential to be used to modify the surfaces of final PLA objects obtained by FDM. On the other hand, the publications on the use of PLA filaments in the 3D printing by FDM are reviewed in Section 3 and the special requirements which are necessary to implement the surface modification methods to modify the surfaces of the 3D printed PLA objects are given in Section 4. Thus, we prefer to keep them as is in the revised MS.
The authors also state on pg 7 line 258 that a review post-2010 is required however more than half all references are pre-2010.
We thank to Reviewer #1 for this point. The former sentence may mislead the readers in that form. We revised this sentence in the revised MS as “Thus, there is a need on the reviewing of the literature regarding to the PLA surface modifications after 2010 and also to select some suitable methods to be applied for the PLA objects which are printed by the FDM approach. In this review, we initially discuss the most effective surface modification methods which were given in the older literature and then present more recent publications in this field”.
pg 12 line 519 3.3. D Printed PLA Objects... Should be rewritten 3D Printed. this error is also present on line 590.
We thank to Reviewer #1 for this point. This error was due to the word format. We revised the line 519 in the revised MS as:
3. 3D PRINTED PLA OBJECTS
and we deleted the subsection 3.3 in line 590 after we merged Sections 3.2 and 3.3.
Line 525 - 532 is generally a repeat of the introduction. FFF is fused filament fabrication (not production) line 532
We thank to Reviewer #1 for this point and we deleted the sentences relating to FDM of polymers other than PLA in this paragraph. It is changed in the revised MS as “In this category, PLA filament is fed to the 3D printing machine by means of a clamping cylinder and is melted at the desired temperature extrusion head and the solid portion of the filament pushes the melt into the nozzle. The nozzle can be moved horizontally along the xy plane. During this movement, the molten material is deposited on the table which can be moved in the vertical z direction [111]. “Fused deposition modeling” (FDM), “Fused filament fabrication” (FFF) and “Melt extrusion production” (MEM) names are widely used for this category to indicate the technologies based on the material extrusion. These processes are basically the same and only their trade names are different. All of the supplied thermoplastic material solidifies quickly after accumulation. This allows the production of complex 3D objects”.
Section 3.2. How is this tied into the over theme of the review?
Section 3.3. The application of PLA in SLA is not well covered or discussed. THis should be removed or expanded. how is this tied into the over theme of the review?
We thank to Reviewer #1 for this point and we accept that the application of PLA in SLA was not well covered in our review. However, this subject is out of the scope of this review. Instead of deleting it completely, we merged Sections 3.2 and 3.3 in a single Section 3.2 entitled “Use of Powder Based Techniques and Photopolymerization in 3D Printing of PLA” and add sentences to tie these subjects to the theme of the review and also explained that we are only presenting some indicative examples of the literature instead of complete reviewing of these subjects. We wrote at the beginning of section 3.2 in the revised MS “PLA objects can be printed by processes other than the FDM method where PLA is used in the filament form. One of these processes is known as the “Powder Based Additive Manufacturing Technique” which depends on powder melting at a specific location by the help of laser and the other one is “Stereolithography (SLA)” where a liquid PLA layer is deposited instead of a solid powder layer by the laser application. We have to refer to these two methods in this review by citing some indicative examples of the published literature, since we also have to consider the modification of the PLA object surfaces obtained by these methods. However, a comprehensive review of these two techniques are out of the scope of this review”.
line 639 there is no need to redefine 3D printing
We thank to Reviewer #1 for this point. We deleted the words “three-dimensional” in the revised text.
line 700-702. I am not convinced that the conclusion is supported by the review.
We thank to Reviewer #1 for this point where we partially agree. Then we changed the text at this point as: “Finally, recent publications were outlined on the approaches which were used for the surface modification of the PLA objects after they were printed in a 3D printing equipment by FDM method. It is determined that only some of the surface modification methods which were previously used for the general PLA surface modifications were applied to the surface modifications of the 3D printed PLA objects probably due to lowering the mechanical resistance of the 3D printed parts and imparting uncontrollable surface roughness on the object”.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The reviewed work is very interesting in terms of content. It summarizes the most commonly used methods for modifying the surface layer of polylactide, focusing on the literature review after 2010.
At the beginning of the article, the authors provide basic information on the preparation, properties and use of polylactide. This subject has already been taken up by various researchers and is generally known. I think, however, that despite the generally known facts contained in the first part of the article, the inclusion of this information in the reviewed article is an added value. It enables quick orientation in the basic information about the considered polymer in the context of the further part of the article. A review of the modification methods is carried out and includes the most popular methods. The article also contains information about the 3D printing method using PLA filaments. This is the current topic in relation to PLA processing methods and is a strong argument for the publication of the reviewed article. In the fourth chapter, the authors focused on the methods of modifying the surface of products produced in 3D printing, which, according to the title of the article, should be its main part. For this chapter, however, I have the most comments.
Although it should be a chapter with the best analyzed literature, it is the weakest of all chapters. The authors referred to only six publications on the subject matter discussed. At 146 citations contained in the article that is only 4% of the total. Is there no more articles in the literature about the topic being analyzed? If so, it should be clearly marked. In this chapter, the authors focus mainly on the chemical methods of modifying products obtained in 3D printing, e.g. using polydopamine. There is too little information about other methods described in the previous chapters, among others plasma. Maybe other methods are also used, such as laser radiation?
My suggestion is, therefore, that before the publication the authors undertake an attempt to expand the fourth chapter, which should be the essence of work.
Author Response
Response to Reviewers
JOURNAL: MDPI-Colloids & Interfaces
AUTHORS: Eda Hazal Baran and H. Yildirim Erbil*
TITLE: Surface Modification of 3D Printed PLA Objects by Fused Deposition Modeling: A Review
TYPE: Review Article
Manuscript ID: colloids-456886
Reviewer #2: The reviewed work is very interesting in terms of content. It summarizes the most commonly used methods for modifying the surface layer of polylactide, focusing on the literature review after 2010.
At the beginning of the article, the authors provide basic information on the preparation, properties and use of polylactide. This subject has already been taken up by various researchers and is generally known. I think, however, that despite the generally known facts contained in the first part of the article, the inclusion of this information in the reviewed article is an added value. It enables quick orientation in the basic information about the considered polymer in the context of the further part of the article. A review of the modification methods is carried out and includes the most popular methods. The article also contains information about the 3D printing method using PLA filaments. This is the current topic in relation to PLA processing methods and is a strong argument for the publication of the reviewed article.
We thank to Reviewer #2 for his/her very constructive comments.
In the fourth chapter, the authors focused on the methods of modifying the surface of products produced in 3D printing, which, according to the title of the article, should be its main part. For this chapter, however, I have the most comments.
Although it should be a chapter with the best analyzed literature, it is the weakest of all chapters. The authors referred to only six publications on the subject matter discussed. At 146 citations contained in the article that is only 4% of the total. Is there no more articles in the literature about the topic being analyzed? If so, it should be clearly marked. In this chapter, the authors focus mainly on the chemical methods of modifying products obtained in 3D printing, e.g. using polydopamine. There is too little information about other methods described in the previous chapters, among others plasma. Maybe other methods are also used, such as laser radiation?
My suggestion is, therefore, that before the publication the authors undertake an attempt to expand the fourth chapter, which should be the essence of work.
We thank to Reviewer #2 for this point and we accept that we have to expand this section by finding more related publications on the surface modification of 3D printed PLA objects by FDM which is the most important part of the review. We searched the literature again and found 13 more published articles fitting the purpose and add them into Section 4 and reorganized this section by dividing into three separate parts in the revised MS. The number of newly reviewed articles is now 159.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have done an excellent job reviewing the manuscript. I still feel the SLS and SLA does not belong in an FDM titled paper but this is a person view which is not critical
