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Abstract

NANO CONGRESS 2018 Nanoengineered plasma polymer films for biomedical applications - Krasimir Vasilev, University of South Australia.

Krasimir Vasilev

This forward looking concise review describes recent advances in the field of nanoengineered plasma polymer films. These types of coatings are relevant in many fields of application and have gained substantial  research and technological interest over the  last decade.  The  review starts with an  introduction of plasma polymerization  as a technique for  preparation for nanometer  thin polymer-like  coatings.  This is  followed  by the  examples  of the  use  of nanoengineered  plasma polymer coatings in applications relevant to biomedical devices. Applications in antibacterial coatings and drug delivery vehicles are discussed.  Significant  section  of  this  paper  is  dedicated  to  cell  guidance  surfaces  which  have  an  extensive  range  of applications  ranging  from  coatings  for  medical  devices  to  research  tools  that  can  help  unraveling  complex  biological questions and vehicles for the growing field of cell therapies. The vision of the authors about the future directions of the field have also been presented, including a section on novel oxazoline based coatings that carry great promise for advances in the biomaterial and biomedical fields.

Introduction

Plasmas, the forth state of matter, have intrigued, puzzled and  fascinated  humans  for  millennia.  Plasmas  are everywhere around  us. Plasmas make  99 per  cent of the visible universe. Plasma are the lightning, the auroras and the sun core. Plasmas can be wild and uncontrollable but when their energy is confined, they become useful tools in numerous applications. Processes such as plasma etching and deposition revolutionized the semiconductor industry and  made  possible  production  of  high  speed  computer processors which we are all enjoying today. Several new applications  of plasmas  such as  in plasma  medicine and plasma nanoscience  are  currently a  hot topic  of research and hold promise to revolutionize many fields.    Surface engineering has  been an  area where plasma processes made and  continue making substantial  impact. The capacity to  preserve valuable  bulk properties  but to alter the properties  at the surface  contributes substantial added value to numerous products in fields ranging from medicine  to  membrane  filtration  and  electronics.  An important aspect of plasma processing is the deposition of organic thin films. In most cases the deposition of such films  is  carried  out  under  low  pressure  in  reaction chambers The origin  of  the  field  of  plasma  polymerization  could  be traced back to the work of Linder and Davies in the 1930s who  were  the  first  to  report  polymer  deposits  on electrodes  However,  purposeful  deposition  of organic films from plasma  started in  the 1960s with the work  of  Goodman   and  Yasuda ,  followed  many others  who  have  made  and are  still  making  significant contributions to this field.    Plasma  polymers  are  a  unique  class  of  materials. They differ from conventional polymer by their irregular structure  which  makes  it  difficult  to  identify  repeating units. For this reason, it is often argued about the use of the  term  “polymer”,  many  insisting on  classification  as “organic  films  deposited  from  plasma”.  Although  the latter  may  be  more  appropriate,  the  term  “plasma polymers” is  widely used  and this  is how  these coatings will  be  referred  to  in  this  article.  Plasma  polymer  are typically  highly  crosslinked  and  if  deposited  under appropriate conditions can be resistant to many  solvents. This makes them valuable in many industry and research applications.  An  important  characteristic  of  plasma polymers is that they can be deposited on practically any type of substrate material. This compare plasma polymers favorably to other techniques for preparation of very thin coatings such as layer-by-layer (L-b-L) or self-assembled monolayers  (SAMs)  which  require  a  specific  substrate such as charged and metallic surfaces respectively

Conclusion and future perspectives

We believe  that by now the  reader has  become not  only aware  but  also  inspired  by  the  opportunities  offed  by plasma polymerzation  and the  field of  “Nanoengineered Plasma  Polymer  Films”  overall.  The capacity  to modify the outermost surface of any  type of material and place desired  properties  such  as  chemical,  physical, topographical,  mechanical  or  bioactive  is  fascinating. Furthermore,  plasma  polymerization  allows  to  preserve the bulk  properties of  the material  while  the process  of surface  modification  is  fast,  one  step  and  solvent  free. Surfaces  can  be  altered  to  be  biocompatible  or biorepelling, functional or inert, wettable or non-wettable to  suit  a  particular  application.  In the  field  of  medical technology nanoengineered coatings facilitated by plasma have an enormous potential. They can be placed on stents, hip  and  knee implants,  hearth  valves and  many  others. They can be used as vehicles in cell therapies  and drug delivery.  They can  be  used as  antibacterial coatings,  to enhance tissue integration, to control inflammation, or all of these together.   These  is no  doubt  that the  field  of nanoenginnered plasma polymer films will grow in the future. The number of creative approaches will also expand together with the member of  potential applications.  An area that  has been little  explored  until  now  is  the  generation  of  stimuli responsive and smart coatings. The reason for this is that the  chemical  structure  of  plasma  polymers  is  rather undefined and more difficult to control compared to these produced  conventional  polymerization.  With  the increased  need  for  smart  coatings  and  the  growing number of researchers embracing plasma polymerization, it  is of  no doubt  that imaginative  approaches for  direct deposition or/and by bringing in other techniques will be developed  in  a  very  near  future.  This  will  also  be facilitated by revealing the  complex processes  occurring in the plasma and learning how to use them in our favor. When applications are concerned, an important property of  plasma  polymers  that  needs  to  be  taken  into consideration is the mechanical  rigidity. This property is not  trivial  to  measure  with  conventional  indentation techniques since plasma polymers are usually thinner than 100 nm and often in the range of 10-20 nm. This requires the development of new techniques to measure very thin film mechanical properties, also  needed in other coating methods.  Collectively,  nanoengineered  plasma  polymer coatings  offer  a  great  degree  of  flexibility  to  generate surface of  a wide  range of  useful properties  and in this way  have an  enormous  potential to  provide  solution  to many urgent needs in the biomedical field. However, the usefulness  of  these  films  in  not  limited  to  medical devices. Opportunities and need exist in a range of other exciting  fields  such  as  micro-  and  nano-fluidics  and organic electronics.