A Brief Comparison Between Available Bio-printing Methods
Ali~Bakhshinejad
Roshan M D'Souza \IEEEcompsocitemizethanks{\IEEEcompsocthanksitem A. Bakhshinejad is a PhD student in Mechanical Engineering Department of University of Wisconsin-Milwaukee.\protect
% note need leading \protect in front of
to get a newline within \thanks as %
is fragile and will error
could use \hfil\break instead. E-mail: bakhshi3@uwm.edu \IEEEcompsocthanksitem R.M. D'Souza is Associate Professor in mechanical engineering at university of Wisconsin-Milwaukee.
%\boldma The scarcity of organs for transplant has led to large waiting lists of very sick patients. In drug development, the time required for human trials greatly increases the time to market. Drug companies are searching for alternative environments where the $in-vivo$ conditions can be closely replicated. Both these problems could be addressed by manufacturing artificial human tissue. Recently, researchers in tissue engineering have developed tissue generation methods based on 3-D printing to fabricate artificial human tissue. Broadly, these methods could be classified as laser-assisted and laser free. The former have very fine spatial resolutions (10s of $\mu$m) but suffer from slow speed ( $< 10^2$ drops per second). The later have lower spatial resolutions (100s of $\mu$ m) but are very fast (up to $5\times 10^3$ drops per second). In this paper we review state-of-the-art methods in each of these classes and provide a comparison based on reported resolution, printing speed, cell density and cell viability.
bare_adv.tex
%% bare_adv.tex
%% V1.3
%% 2007/01/11
%% by Michael Shell
%% See: 
%% http://www.michaelshell.org/
%% for current contact information.
%%
%% This is a skeleton file demonstrating the advanced use of IEEEtran.cls
%% (requires IEEEtran.cls version 1.7 or later) with an IEEE Computer
%% Society journal paper.
%%
%% Support sites:
%% http://www.michaelshell.org/tex/ieeetran/
%% http://www.ctan.org/tex-archive/macros/latex/contrib/IEEEtran/
%% and
%% http://www.ieee.org/

%%*************************************************************************
%% Legal Notice:
%% This code is offered as-is without any warranty either expressed or
%% implied; without even the implied warranty of MERCHANTABILITY or
%% FITNESS FOR A PARTICULAR PURPOSE! 
%% User assumes all risk.
%% In no event shall IEEE or any contributor to this code be liable for
%% any damages or losses, including, but not limited to, incidental,
%% consequential, or any other damages, resulting from the use or misuse
%% of any information contained here.
%%
%% All comments are the opinions of their respective authors and are not
%% necessarily endorsed by the IEEE.
%%
%% This work is distributed under the LaTeX Project Public License (LPPL)
%% ( http://www.latex-project.org/ ) version 1.3, and may be freely used,
%% distributed and modified. A copy of the LPPL, version 1.3, is included
%% in the base LaTeX documentation of all distributions of LaTeX released
%% 2003/12/01 or later.
%% Retain all contribution notices and credits.
%% ** Modified files should be clearly indicated as such, including  **
%% ** renaming them and changing author support contact information. **
%%
%% File list of work: IEEEtran.cls, IEEEtran_HOWTO.pdf, bare_adv.tex,
%%                    bare_conf.tex, bare_jrnl.tex, bare_jrnl_compsoc.tex
%%*************************************************************************

% *** Authors should verify (and, if needed, correct) their LaTeX system  ***
% *** with the testflow diagnostic prior to trusting their LaTeX platform ***
% *** with production work. IEEE's font choices can trigger bugs that do  ***
% *** not appear when using other class files.                            ***
% The testflow support page is at:
% http://www.michaelshell.org/tex/testflow/



% IEEEtran V1.7 and later provides for these CLASSINPUT macros to allow the
% user to reprogram some IEEEtran.cls defaults if needed. These settings
% override the internal defaults of IEEEtran.cls regardless of which class
% options are used. Do not use these unless you have good reason to do so as
% they can result in nonIEEE compliant documents. User beware. ;)
%
%\newcommand{\CLASSINPUTbaselinestretch}{1.0} % baselinestretch
%\newcommand{\CLASSINPUTinnersidemargin}{1in} % inner side margin
%\newcommand{\CLASSINPUToutersidemargin}{1in} % outer side margin
%\newcommand{\CLASSINPUTtoptextmargin}{1in}   % top text margin
%\newcommand{\CLASSINPUTbottomtextmargin}{1in}% bottom text margin



% Note that the a4paper option is mainly intended so that authors in
% countries using A4 can easily print to A4 and see how their papers will
% look in print - the typesetting of the document will not typically be
% affected with changes in paper size (but the bottom and side margins will).
% Use the testflow package mentioned above to verify correct handling of
% both paper sizes by the user's LaTeX system.
%
% Also note that the "draftcls" or "draftclsnofoot", not "draft", option
% should be used if it is desired that the figures are to be displayed in
% draft mode.
%
\documentclass[12pt,journal,compsoc]{IEEEtran}
% The Computer Society requires 12pt.
% If IEEEtran.cls has not been installed into the LaTeX system files,
% manually specify the path to it like:
% \documentclass[10pt,journal,compsoc]{../sty/IEEEtran}


% For Computer Society journals, IEEEtran defaults to the use of 
% Palatino/Palladio as is done in IEEE Computer Society journals.
% To go back to Times Roman, you can use this code:
%\renewcommand{\rmdefault}{ptm}\selectfont

\usepackage{graphicx}
\usepackage{float} % For specifying table/figure locations, i.e. [ht!]
\usepackage{subcaption}

\usepackage{footnote}
    
    % The printlen command allows the user to print the exact text width or height.
    % This is useful, when trying to create graphics (outside of LaTeX, of course)
    % with the optimal dimensions. See here for usage: http://www.ctan.org/pkg/printlen
    \usepackage{printlen}


% Some very useful LaTeX packages include:
% (uncomment the ones you want to load)



% *** MISC UTILITY PACKAGES ***
%
%\usepackage{ifpdf}
% Heiko Oberdiek's ifpdf.sty is very useful if you need conditional
% compilation based on whether the output is pdf or dvi.
% usage:
% \ifpdf
%   % pdf code
% \else
%   % dvi code
% \fi
% The latest version of ifpdf.sty can be obtained from:
% http://www.ctan.org/tex-archive/macros/latex/contrib/oberdiek/
% Also, note that IEEEtran.cls V1.7 and later provides a builtin
% \ifCLASSINFOpdf conditional that works the same way.
% When switching from latex to pdflatex and vice-versa, the compiler may
% have to be run twice to clear warning/error messages.






% *** CITATION PACKAGES ***
%
\ifCLASSOPTIONcompsoc
  % IEEE Computer Society needs nocompress option
  % requires cite.sty v4.0 or later (November 2003)
  % \usepackage[nocompress]{cite}
\else
  % normal IEEE
  % \usepackage{cite}
\fi
% cite.sty was written by Donald Arseneau
% V1.6 and later of IEEEtran pre-defines the format of the cite.sty package
% \cite{} output to follow that of IEEE. Loading the cite package will
% result in citation numbers being automatically sorted and properly
% "compressed/ranged". e.g., [1], [9], [2], [7], [5], [6] without using
% cite.sty will become [1], [2], [5]--[7], [9] using cite.sty. cite.sty's
% \cite will automatically add leading space, if needed. Use cite.sty's
% noadjust option (cite.sty V3.8 and later) if you want to turn this off.
% cite.sty is already installed on most LaTeX systems. Be sure and use
% version 4.0 (2003-05-27) and later if using hyperref.sty. cite.sty does
% not currently provide for hyperlinked citations.
% The latest version can be obtained at:
% http://www.ctan.org/tex-archive/macros/latex/contrib/cite/
% The documentation is contained in the cite.sty file itself.
%
% Note that some packages require special options to format as the Computer
% Society requires. In particular, Computer Society  papers do not use
% compressed citation ranges as is done in typical IEEE papers
% (e.g., [1]-[4]). Instead, they list every citation separately in order
% (e.g., [1], [2], [3], [4]). To get the latter we need to load the cite
% package with the nocompress option which is supported by cite.sty v4.0
% and later. Note also the use of a CLASSOPTION conditional provided by
% IEEEtran.cls V1.7 and later.





% *** GRAPHICS RELATED PACKAGES ***
%
\ifCLASSINFOpdf
  % \usepackage[pdftex]{graphicx}
  % declare the path(s) where your graphic files are
  % \graphicspath{{../pdf/}{../jpeg/}}
  % and their extensions so you won't have to specify these with
  % every instance of \includegraphics
  % \DeclareGraphicsExtensions{.pdf,.jpeg,.png}
\else
  % or other class option (dvipsone, dvipdf, if not using dvips). graphicx
  % will default to the driver specified in the system graphics.cfg if no
  % driver is specified.
  % \usepackage[dvips]{graphicx}
  % declare the path(s) where your graphic files are
  % \graphicspath{{../eps/}}
  % and their extensions so you won't have to specify these with
  % every instance of \includegraphics
  % \DeclareGraphicsExtensions{.eps}
\fi
% graphicx was written by David Carlisle and Sebastian Rahtz. It is
% required if you want graphics, photos, etc. graphicx.sty is already
% installed on most LaTeX systems. The latest version and documentation can
% be obtained at: 
% http://www.ctan.org/tex-archive/macros/latex/required/graphics/
% Another good source of documentation is "Using Imported Graphics in
% LaTeX2e" by Keith Reckdahl which can be found as epslatex.ps or
% epslatex.pdf at: http://www.ctan.org/tex-archive/info/
%
% latex, and pdflatex in dvi mode, support graphics in encapsulated
% postscript (.eps) format. pdflatex in pdf mode supports graphics
% in .pdf, .jpeg, .png and .mps (metapost) formats. Users should ensure
% that all non-photo figures use a vector format (.eps, .pdf, .mps) and
% not a bitmapped formats (.jpeg, .png). IEEE frowns on bitmapped formats
% which can result in "jaggedy"/blurry rendering of lines and letters as
% well as large increases in file sizes.
%
% You can find documentation about the pdfTeX application at:
% http://www.tug.org/applications/pdftex



%\usepackage{ps4pdf}
% dvi->ps workflow is required to use such packages as psfrag.sty and
% pstricks.sty. However, Rolf Niepraschk's ps4pdf.sty provides a way to
% apply psfrag/pstricks effects to .eps figures and then get the resultant
% figures in .pdf form. Thus, providing an easier way for migrating from
% .eps to .pdf figures. After ps4pdf.sty loads, if:
% 1. producing .dvi output: the output file will consist ONLY of the
%    figures (or other constructs encased within \PSforPDF commands)
% 2. producing .pdf output: pdflatex will look in the filename-pics.pdf
%    file, where filename is the basename of the tex document, for the
%    graphics (or other constructs encased within \PSforPDF commands).
%    NOTE: If you ever change your figures, you must remember to remake
%    the filename-pics.pdf file.
%
% This way you can do a:
% 
% latex filename
% dvips -Ppdf -o filename-pics.ps filename.dvi
% ps2pdf filename-pics.ps filename-pics.pdf
% 
% to produce a filename-pics.pdf graphics container that contains
% .pdf versions of the graphics with psfrag, pstricks, etc. features.
% Note that you will not typically be able to view the figures in 
% filename-pics.ps because of an offset. However, you will be able to
% view them in filename-pics.pdf. Also, note that when ps4pdf is in effect
% with .dvi output, you may get harmless over/under full box warnings - 
% ignore them. 
% Then, run pdflatex:
% 
% pdflatex filename
% 
% to use pdflatex to make PDF output, automatically using the figures in
% filename-pics.pdf. Alternatively, you could use dvips -i option to
% obtain separate .pdf files for each figure:
%
% dvips -Ppdf -i -E -o fig filename
%
% then convert each figure to pdf via a command such as epstopdf and then
% use pdflatex with these pdf figures and then to dispense with ps4pdf.
%
% Remember to rerun through latex/dvips/ps2pdf if you ever change your
% figures so that filename-pics.pdf gets updated.
% ps4pdf requires David Kastrup's preview-latex and a recent LaTeX system
% (circa 2001 or later). The ps4pdf package and documentation can be
% obtained at: http://www.ctan.org/tex-archive/macros/latex/contrib/ps4pdf/
% The preview-latex package and documentation can be obtained at:
% http://www.ctan.org/tex-archive/macros/latex/contrib/preview/
%
% provide a bogus \PSforPDF, even when not loading pd4pdf. This way we can
% stop loading ps4pdf.sty if we choose to make separate .pdf versions of
% each of our figures.
\providecommand{\PSforPDF}[1]{#1}
% Note that in order for ps4pdf to work, all commands related to psfrag,
% pstricks, etc. must be called within the PSforPDF command. This applies
% even when *loading* via \usepackage psfrag.sty, etc.


%\PSforPDF{\usepackage{psfrag}}
% psfrag.sty was written by Craig Barratt, Michael C. Grant, and
% David Carlisle. It allows you to substitute LaTeX commands for text in
% imported EPS graphic files. In this way, LaTeX symbols can be placed into
% graphics that have been generated by other applications. You must use
% latex->dvips->ps2pdf workflow (not direct pdf output from pdflatex) if
% you wish to use this capability because it works via some PostScript
% tricks. Alternatively, the graphics could be processed as separate files
% via psfrag and dvips, then converted to PDF for inclusion in the main file
% which uses pdflatex. ps4pdf.sty (above) provides a way of doing this all
% at once within the main file.
% Docs are in "The PSfrag System" by Michael C. Grant and David Carlisle.
% There is also some information about using psfrag in "Using Imported
% Graphics in LaTeX2e" by Keith Reckdahl which documents the graphicx
% package (see above). The psfrag package and documentation can be obtained
% at: http://www.ctan.org/tex-archive/macros/latex/contrib/psfrag/
% 
% Note that the current version of psfrag does not "turn itself off" when
% running under pdf output. This will result in a harmless warning
% about a non-PDF \special. However, to silence this, a bogus psfrag
% command can be provided instead of loading psfrag.sty when PDF output
% is being used. Thus, a more complex alternative conditional loading scheme
% can be employed instead of the straightforword way above:
%
%\ifCLASSINFOpdf
% if outputting PDF, do not use or load psfrag.sty as current versions
% output a non-PDF special that generates a harmless, but annoying warning.
% Instead, we provide a bogus \psfrag command that does nothing with
% its arguments. This is a tad tricky because \psfrag can have up to six
% arguments four of which are optional: \psfrag{}[][][][]{}
% Code based on that in psfrag.sty
%\makeatletter
%\def\psfrag{\@ifstar{\@BOGUSpsfraga}{\@BOGUSpsfraga}}
%\def\@BOGUSpsfraga{\begingroup
%   \@makeother\"\@makeother\*\@makeother\!\@makeother\~%
%   \@makeother\:\@makeother\\\@makeother\%\@makeother\#%
%   \@makeother\ \@BOGUSpsfragb}
%\def\@BOGUSpsfragb#1{\endgroup
%                \@ifnextchar [{\@BOGUSpsfragc}%
%                              {\@BOGUSpsfrag}}
%\def\@BOGUSpsfragc[#1]{\@ifnextchar [{\@BOGUSpsfragd}%
%                                     {\@BOGUSpsfrag}}
%\def\@BOGUSpsfragd[#1]{\@ifnextchar [{\@BOGUSpsfrage}%
%                                     {\@BOGUSpsfrag}}
%\def\@BOGUSpsfrage[#1]{\@ifnextchar [{\@BOGUSpsfragf}%
%                                     {\@BOGUSpsfrag}}
%\def\@BOGUSpsfragf[#1]{\@BOGUSpsfrag}
%\def\@BOGUSpsfrag#1{\ignorespaces}
%\makeatother
%\else
% using dvi output, load psfrag, but funnel it through PSforPDF
% as required by ps4pdf.sty
%\PSforPDF{\usepackage{psfrag}}
%\fi





% *** MATH PACKAGES ***
%
%\usepackage[cmex10]{amsmath}
% A popular package from the American Mathematical Society that provides
% many useful and powerful commands for dealing with mathematics. If using
% it, be sure to load this package with the cmex10 option to ensure that
% only type 1 fonts will utilized at all point sizes. Without this option,
% it is possible that some math symbols, particularly those within
% footnotes, will be rendered in bitmap form which will result in a
% document that can not be IEEE Xplore compliant!
%
% Also, note that the amsmath package sets \interdisplaylinepenalty to 10000
% thus preventing page breaks from occurring within multiline equations. Use:
%\interdisplaylinepenalty=2500
% after loading amsmath to restore such page breaks as IEEEtran.cls normally
% does. amsmath.sty is already installed on most LaTeX systems. The latest
% version and documentation can be obtained at:
% http://www.ctan.org/tex-archive/macros/latex/required/amslatex/math/





% *** SPECIALIZED LIST PACKAGES ***
%\usepackage{acronym}
% acronym.sty was written by Tobias Oetiker. This package provides tools for
% managing documents with large numbers of acronyms. (You don't *have* to
% use this package - unless you have a lot of acronyms, you may feel that
% such package management of them is bit of an overkill.)
% Do note that the acronym environment (which lists acronyms) will have a
% problem when used under IEEEtran.cls because acronym.sty relies on the
% description list environment - which IEEEtran.cls has customized for
% producing IEEE style lists. A workaround is to declared the longest
% label width via the IEEEtran.cls \IEEEiedlistdecl global control:
%
% \renewcommand{\IEEEiedlistdecl}{\IEEEsetlabelwidth{SONET}}
% \begin{acronym}
%
% \end{acronym}
% \renewcommand{\IEEEiedlistdecl}{\relax}% remember to reset \IEEEiedlistdecl
%
% instead of using the acronym environment's optional argument.
% The latest version and documentation can be obtained at:
% http://www.ctan.org/tex-archive/macros/latex/contrib/acronym/


%\usepackage{algorithmic}
% algorithmic.sty was written by Peter Williams and Rogerio Brito.
% This package provides an algorithmic environment fo describing algorithms.
% You can use the algorithmic environment in-text or within a figure
% environment to provide for a floating algorithm. Do NOT use the algorithm
% floating environment provided by algorithm.sty (by the same authors) or
% algorithm2e.sty (by Christophe Fiorio) as IEEE does not use dedicated
% algorithm float types and packages that provide these will not provide
% correct IEEE style captions. The latest version and documentation of
% algorithmic.sty can be obtained at:
% http://www.ctan.org/tex-archive/macros/latex/contrib/algorithms/
% There is also a support site at:
% http://algorithms.berlios.de/index.html
% Also of interest may be the (relatively newer and more customizable)
% algorithmicx.sty package by Szasz Janos:
% http://www.ctan.org/tex-archive/macros/latex/contrib/algorithmicx/




% *** ALIGNMENT PACKAGES ***
%
%\usepackage{array}
% Frank Mittelbach's and David Carlisle's array.sty patches and improves
% the standard LaTeX2e array and tabular environments to provide better
% appearance and additional user controls. As the default LaTeX2e table
% generation code is lacking to the point of almost being broken with
% respect to the quality of the end results, all users are strongly
% advised to use an enhanced (at the very least that provided by array.sty)
% set of table tools. array.sty is already installed on most systems. The
% latest version and documentation can be obtained at:
% http://www.ctan.org/tex-archive/macros/latex/required/tools/


%\usepackage{mdwmath}
%\usepackage{mdwtab}
% Also highly recommended is Mark Wooding's extremely powerful MDW tools,
% especially mdwmath.sty and mdwtab.sty which are used to format equations
% and tables, respectively. The MDWtools set is already installed on most
% LaTeX systems. The lastest version and documentation is available at:
% http://www.ctan.org/tex-archive/macros/latex/contrib/mdwtools/


% IEEEtran contains the IEEEeqnarray family of commands that can be used to
% generate multiline equations as well as matrices, tables, etc., of high
% quality.


%\usepackage{eqparbox}
% Also of notable interest is Scott Pakin's eqparbox package for creating
% (automatically sized) equal width boxes - aka "natural width parboxes".
% Available at:
% http://www.ctan.org/tex-archive/macros/latex/contrib/eqparbox/





% *** SUBFIGURE PACKAGES ***
%\ifCLASSOPTIONcompsoc
%\usepackage[tight,normalsize,sf,SF]{subfigure}
%\else
%\usepackage[tight,footnotesize]{subfigure}
%\fi
% subfigure.sty was written by Steven Douglas Cochran. This package makes it
% easy to put subfigures in your figures. e.g., "
%1a and 1b". For IEEE
% work, it is a good idea to load it with the tight package option to reduce
% the amount of white space around the subfigures. Computer Society papers
% use a larger font and \sffamily font for their captions, hence the
% additional options needed under compsoc mode. subfigure.sty is already
% installed on most LaTeX systems. The latest version and documentation can
% be obtained at:
% http://www.ctan.org/tex-archive/obsolete/macros/latex/contrib/subfigure/
% subfigure.sty has been superceeded by subfig.sty.


%\ifCLASSOPTIONcompsoc
%  \usepackage[caption=false]{caption}
%  \usepackage[font=normalsize,labelfont=sf,textfont=sf]{subfig}
%\else
%  \usepackage[caption=false]{caption}
%  \usepackage[font=footnotesize]{subfig}
%\fi
% subfig.sty, also written by Steven Douglas Cochran, is the modern
% replacement for subfigure.sty. However, subfig.sty requires and
% automatically loads Axel Sommerfeldt's caption.sty which will override
% IEEEtran.cls handling of captions and this will result in nonIEEE style
% figure/table captions. To prevent this problem, be sure and preload
% caption.sty with its "caption=false" package option. This is will preserve
% IEEEtran.cls handing of captions. Version 1.3 (2005/06/28) and later 
% (recommended due to many improvements over 1.2) of subfig.sty supports
% the caption=false option directly:
%\ifCLASSOPTIONcompsoc
%  \usepackage[caption=false,font=normalsize,labelfont=sf,textfont=sf]{subfig}
%\else
%  \usepackage[caption=false,font=footnotesize]{subfig}
%\fi
%
% The latest version and documentation can be obtained at:
% http://www.ctan.org/tex-archive/macros/latex/contrib/subfig/
% The latest version and documentation of caption.sty can be obtained at:
% http://www.ctan.org/tex-archive/macros/latex/contrib/caption/




% *** FLOAT PACKAGES ***
%
%\usepackage{fixltx2e}
% fixltx2e, the successor to the earlier fix2col.sty, was written by
% Frank Mittelbach and David Carlisle. This package corrects a few problems
% in the LaTeX2e kernel, the most notable of which is that in current
% LaTeX2e releases, the ordering of single and double column floats is not
% guaranteed to be preserved. Thus, an unpatched LaTeX2e can allow a
% single column figure to be placed prior to an earlier double column
% figure. The latest version and documentation can be found at:
% http://www.ctan.org/tex-archive/macros/latex/base/


%\usepackage{stfloats}
% stfloats.sty was written by Sigitas Tolusis. This package gives LaTeX2e
% the ability to do double column floats at the bottom of the page as well
% as the top. (e.g., "\begin{figure*}[!b]" is not normally possible in
% LaTeX2e). It also provides a command:
%\fnbelowfloat
% to enable the placement of footnotes below bottom floats (the standard
% LaTeX2e kernel puts them above bottom floats). This is an invasive package
% which rewrites many portions of the LaTeX2e float routines. It may not work
% with other packages that modify the LaTeX2e float routines. The latest
% version and documentation can be obtained at:
% http://www.ctan.org/tex-archive/macros/latex/contrib/sttools/
% Documentation is contained in the stfloats.sty comments as well as in the
% presfull.pdf file. Do not use the stfloats baselinefloat ability as IEEE
% does not allow \baselineskip to stretch. Authors submitting work to the
% IEEE should note that IEEE rarely uses double column equations and
% that authors should try to avoid such use. Do not be tempted to use the
% cuted.sty or midfloat.sty packages (also by Sigitas Tolusis) as IEEE does
% not format its papers in such ways.


%\ifCLASSOPTIONcaptionsoff
%  \usepackage[nomarkers]{endfloat}
% \let\MYoriglatexcaption\caption
% \renewcommand{\caption}[2][\relax]{\MYoriglatexcaption[#2]{#2}}
%\fi
% endfloat.sty was written by James Darrell McCauley and Jeff Goldberg.
% This package may be useful when used in conjunction with IEEEtran.cls'
% captionsoff option. Some IEEE journals/societies require that submissions
% have lists of figures/tables at the end of the paper and that
% figures/tables without any captions are placed on a page by themselves at
% the end of the document. If needed, the draftcls IEEEtran class option or
% \CLASSINPUTbaselinestretch interface can be used to increase the line
% spacing as well. Be sure and use the nomarkers option of endfloat to
% prevent endfloat from "marking" where the figures would have been placed
% in the text. The two hack lines of code above are a slight modification of
% that suggested by in the endfloat docs (section 8.3.1) to ensure that
% the full captions always appear in the list of figures/tables - even if
% the user used the short optional argument of \caption[]{}.
% IEEE papers do not typically make use of \caption[]'s optional argument,
% so this should not be an issue. A similar trick can be used to disable
% captions of packages such as subfig.sty that lack options to turn off
% the subcaptions:
% For subfig.sty:
% \let\MYorigsubfloat\subfloat
% \renewcommand{\subfloat}[2][\relax]{\MYorigsubfloat[]{#2}}
% For subfigure.sty:
% \let\MYorigsubfigure\subfigure
% \renewcommand{\subfigure}[2][\relax]{\MYorigsubfigure[]{#2}}
% However, the above trick will not work if both optional arguments of
% the \subfloat/subfig command are used. Furthermore, there needs to be a
% description of each subfigure *somewhere* and endfloat does not add
% subfigure captions to its list of figures. Thus, the best approach is to
% avoid the use of subfigure captions (many IEEE journals avoid them anyway)
% and instead reference/explain all the subfigures within the main caption.
% The latest version of endfloat.sty and its documentation can obtained at:
% http://www.ctan.org/tex-archive/macros/latex/contrib/endfloat/
%
% The IEEEtran \ifCLASSOPTIONcaptionsoff conditional can also be used
% later in the document, say, to conditionally put the References on a 
% page by themselves.





% *** PDF, URL AND HYPERLINK PACKAGES ***
%
%\usepackage{url}
% url.sty was written by Donald Arseneau. It provides better support for
% handling and breaking URLs. url.sty is already installed on most LaTeX
% systems. The latest version can be obtained at:
% http://www.ctan.org/tex-archive/macros/latex/contrib/misc/
% Read the url.sty source comments for usage information. Basically,
% \url{my_url_here}.


% NOTE: PDF thumbnail features are not required in IEEE papers
%       and their use requires extra complexity and work.
%\ifCLASSINFOpdf
%  \usepackage[pdftex]{thumbpdf}
%\else
%  \usepackage[dvips]{thumbpdf}
%\fi
% thumbpdf.sty and its companion Perl utility were written by Heiko Oberdiek.
% It allows the user a way to produce PDF documents that contain fancy
% thumbnail images of each of the pages (which tools like acrobat reader can
% utilize). This is possible even when using dvi->ps->pdf workflow if the
% correct thumbpdf driver options are used. thumbpdf.sty incorporates the
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% NOTE: PDF hyperlink and bookmark features are not required in IEEE
%       papers and their use requires extra complexity and work.
% *** IF USING HYPERREF BE SURE AND CHANGE THE EXAMPLE PDF ***
% *** TITLE/SUBJECT/AUTHOR/KEYWORDS INFO BELOW!!           ***
\newcommand\MYhyperrefoptions{bookmarks=true,bookmarksnumbered=true,
pdfpagemode={UseOutlines},plainpages=false,pdfpagelabels=true,
colorlinks=true,linkcolor={black},citecolor={black},pagecolor={black},
urlcolor={black},
pdftitle={A Brief Comparison Between Available Bio-printing Methods},%<!CHANGE!
pdfsubject={},%<!CHANGE!
pdfauthor={Ali Bakhshinejad},%<!CHANGE!
pdfkeywords={}}%<^!CHANGE!
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% LaTeX compiler cannot break URLs across lines or pages as can be done
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% (September 23, 2005) and later are recommened to avoid bugs in earlier
% releases.
%
% The advanced features offer by hyperref.sty are not required for IEEE
% submission, so users should weigh these features against the added
% complexity of use. Users who wish to use hyperref *must* ensure that
% their hyperref version is 6.72u or later *and* IEEEtran.cls is version
% 1.6b or later.
% The package options above demonstrate how to enable PDF bookmarks
% (a type of table of contents viewable in Acrobat Reader) as well as
% PDF document information (title, subject, author and keywords) that is
% viewable in Acrobat reader's Document_Properties menu. PDF document
% information is also used extensively to automate the cataloging of PDF
% documents. The above set of options ensures that hyperlinks will not be
% colored in the text and thus will not be visible in the printed page,
% but will be active on "mouse over". USING COLORS OR OTHER HIGHLIGHTING
% OF HYPERLINKS CAN RESULT IN DOCUMENT REJECTION BY THE IEEE, especially if
% these appear on the "printed" page. IF IN DOUBT, ASK THE RELEVANT
% SUBMISSION EDITOR. You may need to add the option hypertexnames=false if
% you used duplicate equation numbers, etc., but this should not be needed
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% The latest version of hyperref and its documentation can be obtained at:
% http://www.ctan.org/tex-archive/macros/latex/contrib/hyperref/





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% to submit to, of course. )


% correct bad hyphenation here
\hyphenation{op-tical net-works semi-conduc-tor}


\begin{document}
%
% paper title
% can use linebreaks \\ within to get better formatting as desired
\title{A Brief Comparison Between Available Bio-printing Methods}
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% author names and IEEE memberships
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% for each affiliation group. When not in compsoc mode,
% \IEEEcompsocitemizethanks becomes like \thanks and
% \IEEEcompsocthanksitem becomes a line break with idention. This
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% one-size-fits-all approach a daunting prospect. For instance, compsoc 
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% received ..."  text while in non-compsoc journals this is reversed. Sigh.

\author{Ali~Bakhshinejad,Roshan M D'Souza

\IEEEcompsocitemizethanks{\IEEEcompsocthanksitem A. Bakhshinejad is a PhD student in Mechanical Engineering Department of University of Wisconsin-Milwaukee.\protect\\
% note need leading \protect in front of \\ to get a newline within \thanks as
% \\ is fragile and will error, could use \hfil\break instead.
E-mail: bakhshi3@uwm.edu
\IEEEcompsocthanksitem R.M. D'Souza is Associate Professor in mechanical engineering at university of Wisconsin-Milwaukee.}% <-this % stops a space
\thanks{}}



% The paper headers
\markboth{Great Lakes Biomedical Conference}%
{Bakhshinejad \MakeLowercase{\textit{et al.}}: A Brief Comparison Between Available Bio-printing Methods }
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%\hspace{\columnsep}\makebox[\columnwidth]{Published by the IEEE Computer Society\hfill}}
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% command as these need to go into the title area created by \maketitle.
\IEEEcompsoctitleabstractindextext{%
\begin{abstract}
%\boldma
The scarcity of organs for transplant has led to large waiting lists of very sick patients. In drug development, the time required for human trials greatly increases the time to market. Drug companies are searching for alternative environments where the $in-vivo$ conditions can be closely replicated. Both these problems could be addressed by manufacturing artificial human tissue. Recently, researchers in tissue engineering have developed tissue generation methods based on 3-D printing to fabricate artificial human tissue. Broadly, these methods could be classified as laser-assisted and laser free. The former have very fine spatial resolutions (10s of $\mu$m) but suffer from slow speed ( $< 10^2$ drops per second). The later have lower spatial resolutions (100s of $\mu$ m) but are very fast (up to $5\times 10^3$ drops per second). In this paper we review state-of-the-art methods in each of these classes and provide a comparison based on reported resolution, printing speed, cell density and cell viability.  
\end{abstract}
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% in the abstract anyway. In particular, the Computer Society does
% not want either math or citations to appear in the abstract.

% Note that keywords are not normally used for peerreview papers.
\begin{IEEEkeywords}
Bio-printing, Tissue Engineering.
\end{IEEEkeywords}}


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% page as needed:
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% \begin{center} \bfseries EDICS Category: 3-BBND \end{center}
% \fi
%
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\section{Introduction}


\IEEEPARstart{I}{ntroduction} of the first 3D printing method by Charles W. Hull in 1986 \cite{Hull1986}, changed the world of manufacturing. Complex shapes that previously could not be manufactured without expensive tooling such as mutli-part molds could be manufactured with ease through layered deposition of material. The same technique has now been adpated to manufacture complex human tissue. Over the last two decades, researchers have focused on techqniues to accomodate the sensitivity of live cells to stresses(friction, pressure, fluid viscosity etc.) that are ecountered during the printing process \cite{Guillemot2011,binder2011,ahn2014,Derby2008}.

\begin{figure*}
        \centering
        \begin{subfigure}[b]{0.3\textwidth}
                \includegraphics[width=\textwidth]{Images/scaffold1}
                \caption{}
                 \label{fig:scaffold1}
        \end{subfigure}%
         %add desired spacing between images, e. g. ~, \quad, \qquad, \hfill etc.
          %(or a blank line to force the subfigure onto a new line)          
        \begin{subfigure}[b]{0.3\textwidth}
                \includegraphics[width=\textwidth]{Images/scaffold2}
                 \caption{}
                 \label{fig:scaffold2}
        \end{subfigure}
        ~ %add desired spacing between images, e. g. ~, \quad, \qquad, \hfill etc.
          %(or a blank line to force the subfigure onto a new line)
        \caption{Schematic representation of (a) scaffold-base printing when bio-materials and cells will be printed at the same time (b) cell printing where cells will be place on prefabricated scaffolds \cite{Ringeisen2006}.}\label{fig:scaffold}
\end{figure*}
Printing process for bio-printers can be categorized as two main groups: scaffold based printing and scaffold-free printing. As the names suggests, in scaffold-based printing, a skeleton of the organ/tissue geometry is first printed using certain bio-materials. The scaffold is then populated with living cells which will colonize the structure. At the end of the colonization process, the scaffold resolves into the systems.  Scaffold material porosity is designed in a way to enable inward diffusion of nutrients, oxygen and outward diffusion of waste materials from the living cells. Scaffold-based methods can further be categorized into two main approaches: first approach is when the scaffold will be printed out at the same time as the living cells (Figure \ref{fig:scaffold1}), and the other approach is when cells will be printed on layers of prefabricated scaffolds (Figure \ref{fig:scaffold2}) \cite{Ringeisen2006}.


In scaffold-free printing, living cells are directly printed onto a substrate. Natural cell processes such as cell sorting and cell fusion which occur through cell signaling automatically generate structure\cite{Beysens2000, Armstrong1989}. The manufacture of functional vasculature is a big challenge in bio-printing processes. Lack of vascular systems leads to cell death in systems where diffusion alone cannot handle transport of nutrients to cells and waste matter away from cells \cite{Luo2014}.

Both scaffold-base or scaffold-free methods use bio-printers that can be categorized into two general classes: Laser assisted bio-printing (LaBP) and Laser free bio-printing (LfBP). Each category contains multiple techniques that have been developed during the last couple of decades. In this review we will briefly address available printing methods and at the end a comparison between  different methods will be presented.

\section{Laser assisted bio-printers (LaBP)}

Laser assisted bio-printers (LaBP) were  the first type of bio-printers introduced by Odde and Renn \cite{Odde2000a} under name of "Laser-Guided Direct Writing" (LG DB). The printing setup included a laser beam, a focusing system and a substrate. The laser beam with the focusing system is used to create a "light trap" which is used to guide livig cells on the substracte to desired locations. The long and direct laser light contact with cells caused low cell survival rates\cite{Odde2000a}.  

% \begin{figure}[!t]
% \centering
% \includegraphics[width=0.8\linewidth]{Images/LGDWC}
% \caption{Laser-Guided Direct writing (LG DW) system introduced by Odde and Renn  \cite{Odde2000a}}
% \label{fig:LGDWC}
% \end{figure}

Subsequently, the principle of laser-induced forward transfer (LIFT), initially developed for metals, has been adpated to bio-printing and is currently the main method for  LaBP \cite{Serra2006}. In a typical LaBP, which is printing based on LIFT method, (figure \ref{fig:bioprinters} ), focused laser pulses cause local vaporization of an energy absorbing layer (typically gold or titanium). This causes generation of a droplet based on the energy of the pulse and the duration of the pulse. The size of the droplet can be adjusted to meet the requirements of the process \cite{Guillemot2011,koch2013}. The generated droplets will be received by a substrate facing to the bio-ink \cite{Murphy2014,Malda2013}. With this configuration, the survival rate of cells was improved  drastically (up to 95\% cell viability) since the laser doesn't have direct contact with live cells \cite{Serra2006}. Simultaneously, the spatial resolution could be maintained in the range of $30-100\mu m$. The lack of a fluid orifice and reservoir in these designs means that issues such as print head clogging do not exist. However, the low printing speed (as low as $10^2$ drops/s) makes this process unsuitable for organ printing where the amount of material that must be deposited makes the turn around time prohibitive. 


\begin{figure*}[!t]
\centering
\includegraphics[width=0.8\linewidth]{Images/bioprinters}
\caption{Bio-printers with different printing approach. \cite{Malda2013}}
\label{fig:bioprinters}
\end{figure*}
. 

\section{Laser free bio-printers (LfBP)}

Laser free bio-printers were inspired by inkjet desktop printers. Inkjet printers typically consists of a reservoir tank, micrometer size orifice, and a print head that can be actuated  either thermally, piezoelectrically (Figure \ref{fig:bioprinters}) or by solenoid valves (Figure \ref{fig:Solenoidvalves})  \cite{Faulkner-Jones2013, Malda2013} .  In inkjet printers, droplets are generated only when required. A pressure pulse is generated in the tank which force the bio-ink to go through the orifice which leads to the printer head. For printers that are equipped with a thermal print head, a micro-heater element vaporizes small pockets of the bio-ink to  produce vapor bubbles. Generation and collapse of these bubbles cause discontinuity in the bio-ink stream. In piezoelectric models, the print head is equipped with a piezoelectric actuator which deforms with a controlled frequency to make discontinuity in the fluid stream  \cite{Derby2008}. In the solenoid valve print head discontinuity in bio-fluid steam is be caused by a valve that can be turned on and off \cite{Faulkner-Jones2013}. In the all mentioned configurations, the print head is connected to a robotic base controlled by software. Therefore the print head can be accurately positioned over a substrate and the bio-ink droplet can be released at the desired location. 

\begin{figure}[!t]
\centering
\includegraphics[width=0.7\linewidth]{Images/Solenoidvalves}
\caption{Dispensing system for printer heads equipped with solenoid valves \cite{Faulkner-Jones2013}}
\label{fig:Solenoidvalves}
\end{figure}

In contrast with inkjet printers (generating droplets on demand) \cite{binder2011}, in robotic dispensing, there is no droplet generation process. Instead, the print head will produce a continuous stream of the bio-fluid and place it on the substrate. A controlled pressure system will forces the bio-ink to go through the nozzle. Depending on the viscosity of the fluid which requires different levels of the control, different pressure control systems can be utilized (Figure \ref{fig:bioprinters}).

The robotic dispensing method has the highest printing speed ($10-50 \mu m/s$) as well as high cell density. Among the LfBP systems, the robotic dispensing method has the lowest cell viability rates.($40-80\%$). Other LfBP are reported higher viability ($> 85 \%$) \cite{Ozbolat2013,Murphy2014,Malda2013}.



% An example of a floating table. Note that, for IEEE style tables, the 
% \caption command should come BEFORE the table. Table text will default to
% \footnotesize as IEEE normally uses this smaller font for tables.
% The \label must come after \caption as always.
%






\section{Discussion }
There are several different configurations available for bio-printers. A end user has to choose and appropriate technique based on his or her requirements. Table \ref{table:comparison} illustrates a comparison between different bio-printing techniques that are currently available.

\begin{table*}[!t]
\centering
\begin{tabular}{lccccc}
\hline
Printer type & Resolution ($\mu m$) & Print speed & Cell viability(\%) & Cell densities &  References \\
\hline
LaBP &&&&\\
LG DW& 10-30& Continuous  ($ 9 \times 10^{-8} mL/s$) & Not Available as percentage & $~10^8 cells/ml$&  \cite{Odde2000a,Mironov2011,Jones2012}\\
Modified LIFT&30-100&  $10^2$ drops/s& 95-100& $~10^8 cells/ml$ & \cite{Serra2006,koch2013,Mironov2011,Jones2012}\\
\hline
LfBP &&&&\\
Thermal & $> 300$ &  $5 \times 10^3$ drops/s& 75-90& $<10^6 cells/ml$&  \cite{Derby2008,Mironov2011,Jones2012}\\
Piezoelectric &  - & $ 1 \times 10^4$ drops/s & ($> 85\% $) & $<10^6 cells/ml$&  \cite{Derby2008,Mironov2011,Jones2012}\\
Solenoid valve& - & 6500 drops/s & 85-99 & $~5 \times 10^5 cells/ml$&  \cite{Faulkner-Jones2013,Mironov2011,Jones2012}\\
Robotic dispensing& $ 5 \mu m$ to millimeters & $10-50 \mu m/s$& 40-80 \% & cell spheroids&  \cite{Xu2005,Guillotin2010,Mironov2011,Jones2012}\\ 
\hline
\end{tabular}
\caption{A brief comparison between bio-printers.}
\label{table:comparison}
\end{table*}


Laser guided direct write (LG DW) printer have the best spatial resolution and the lowest viability. LIFT design was a big step toward improvement of cells viability for laser assisted printers. Modification of LIFT (as presented in the table \ref{table:comparison} as modified LIFT) added an energy observing layer to the print head. This change had a huge positive impact on cell viability. Laser free printing methods sacrifice cell density and spatial resolution to achieve higher throughput. Print jobs that have intricate features are therefore more suitable for LaBP class of bio-printers. Print jobs with large tissue masses are more suited for LfBP methods.  


% use section* for acknowledgement
\ifCLASSOPTIONcompsoc
  % The Computer Society usually uses the plural form
  \section*{Acknowledgments}
\else
  % regular IEEE prefers the singular form
  \section*{Acknowledgment}
\fi


This work was partially supported by National Institutes of Health, NIH/IU Subcontract 2R01GM077138-04A1.


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% references section

% can use a bibliography generated by BibTeX as a .bbl file
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% H.~Kopka and P.~W. Daly, \emph{A Guide to {\LaTeX}}, 3rd~ed.\hskip 1em plus
%   0.5em minus 0.4em\relax Harlow, England: Addison-Wesley, 1999.

% \end{thebibliography}

% biography section
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% needed around the contents of the optional argument to biography to prevent
% the LaTeX parser from getting confused when it sees the complicated
% \includegraphics command within an optional argument. (You could create
% your own custom macro containing the \includegraphics command to make things
% simpler here.)
%\begin{biography}[{\includegraphics[width=1in,height=1.25in,clip,keepaspectratio]{mshell}}]{Michael Shell}
% or if you just want to reserve a space for a photo:


% \begin{IEEEbiography}[{\includegraphics[width=1in,height=1.25in,clip,keepaspectratio]{Images/AliPic}}]{Ali Bakhshinejad}
% is a PhD student at University of Wisconsin-Milwaukee.Ali joined UWM as PhD student in January 2014 after graduation with first class honor from University of Iceland in mechanical engineering with focus on fluid dynamic. He continued his passion in numerical analysis with joining to Professor D'Souza's lab at UWM working on different bio-mechanical problems. Currently he is working on a prediction model for post-printing process in bio-printers.
% \end{IEEEbiography}

% % if you will not have a photo at all:
% \begin{IEEEbiography}{Roshan M D'Souza}
% Biography text here.
% \end{IEEEbiography}


\end{document}
bare_adv.bbl
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\BIBdecl

\bibitem{Hull1986}
C.~W. Hull, ``Apparatus for production of three-dimensional objects by
  stereolithography,'' 3 1986.

\bibitem{Guillemot2011}
F.~Guillemot, B.~Guillotin, A.~Fontaine, M.~Ali, S.~Catros, V.~K{\'{e}}riquel,
  J.-C. Fricain, M.~R{\'{e}}my, R.~Bareille, and
  J.~Am{\'{e}}d{\'{e}}e-Vilamitjana, ``Laser-assisted bioprinting to deal with
  tissue complexity in regenerative medicine,'' \emph{MRS Bulletin}, vol.~36,
  no.~12, pp. 1015--1019, 12 2011.

\bibitem{binder2011}
K.~W. BINDER, A.~J. ALLEN, J.~J. YOO, and A.~ATALA, ``Drop-on-demand inkjet
  bioprinting: A primer,'' \emph{Gene Therapy and Regulation}, vol.~06, no.~01,
  pp. 33--49, 3 2011.

\bibitem{ahn2014}
S.~Ahn, H.~Lee, E.~J. Lee, and G.~Kim, ``A direct cell printing supplemented
  with low-temperature processing method for obtaining highly porous
  three-dimensional cell-laden scaffolds,'' \emph{Journal of Materials
  Chemistry B}, vol.~2, no.~18, p. 2773, 4 2014.

\bibitem{Derby2008}
B.~Derby, ``Bioprinting: inkjet printing proteins and hybrid cell-containing
  materials and structures,'' \emph{J. Mater. Chem.}, vol.~18, no.~47, pp.
  5717--5721, 2008.

\bibitem{Ringeisen2006}
B.~R. Ringeisen, C.~M. Othon, J.~A. Barron, D.~Young, and B.~J. Spargo,
  ``Jet-based methods to print living cells.'' \emph{Biotechnology journal},
  vol.~1, no.~9, pp. 930--48, 9 2006.

\bibitem{Beysens2000}
D.~A. Beysens, G.~Forgacs, and J.~A. Glazier, ``Cell sorting is analogous to
  phase ordering in fluids,'' \emph{Proceedings of the National Academy of
  Sciences}, vol.~97, no.~17, pp. 9467--9471, 8 2000.

\bibitem{Armstrong1989}
P.~B. Armstrong, ``Cell sorting out: The self-assembly of tissues in vitro,''
  \emph{Critical Reviews in Biochemistry and Molecular Biology}, vol.~24, pp.
  119--149, 9 1989.

\bibitem{Luo2014}
H.~Luo, M.~Chen, X.~Wang, Y.~Mei, Z.~Ye, Y.~Zhou, and W.-S. Tan, ``Fabrication
  of viable centimeter-sized 3d tissue constructs with microchannel conduits
  for improved tissue properties through assembly of cell-laden microbeads.''
  \emph{Journal of tissue engineering and regenerative medicine}, vol.~8,
  no.~6, pp. 493--504, 6 2014.

\bibitem{Odde2000a}
D.~J. Odde and M.~J. Renn, ``Laser-guided direct writing of living cells.''
  \emph{Biotechnology and bioengineering}, vol.~67, no.~3, pp. 312--8, 2 2000.

\bibitem{Serra2006}
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