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Blood coagulation on electron beam melted implant surfaces, implications for bone growth
Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering and Sustainable Development.
Uppsala University, Immunology, Genetics and Pathology.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering and Sustainable Development.
2011 (English)In: Proccedings of EBS 2011, Dublin, 2011Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

INTRODUCTION

Implants for arthroplasty, plates and screws for orthopedics, maxillofacial and dentistry are more frequently being customised. Ti and CoCr alloys are common materials for bone implants. Surface roughness, porosity and choice of material may have an impact on the bone ingrowth. EBM (Electron Beam Melting) is a 3D-printing technique melting metallic powder layer by layer according to the corresponding CAD (Computer Aided Design) model of implants1.With EBM technology customised implants can be manufactured with a lower cost compared to conventional technologies2. Implants for bone replacement made from CT images with EBM technology will fit accurate and lead to simpler and better planed surgeries also3. The EBM technique, as such, is always resulting with rough surface on the implants (typically 20-45µm). That roughness can be controlled, in some extent, by changing the process parameters. Some authors claim that roughened surfaces are promoting bone ingrowth4.

This work was aiming on the question: are EBM made surfaces good for bone ingrowth and is it possible to change the bone ingrowth by varying the machine settings? In order to answer this question a number of coin like specimens of CoCr were manufactured with the different surface roughness. The blood chamber model has shown how the first steps of bone healing were proceeding on specimen surfaces, indicating how the coagulation and complement systems can behave in vivo5.

 

EXPERIMENTAL METHODS

The manufacture of the test specimens was carried out with Arcam A2 EBM® equipment.  Process parameters were changed in the software EBM controle6 and three groups of eight specimens with different parameter setting were made. The specimens were then tested with whole blood from two individuals in a modified version of the blood chamber model named above7. Surface roughness was characterised with a stylus profiler Dektak® 6M.

 

RESULTS AND DISCUSSION

Table 1 percents Ra (average roughness) and plt (platelets) activated for each group.

 

                                         Table 1

group         Ra mean      std                    plt mean   std

1              35.0µm        3.24µm           92.9%       5.25%

2              28.5µm        2.14µm           85.3%       7.61%

3              28.2µm        1.75µm           84.4%       10.3%

 

The results indicate that rougher surfaces are more thrombogenic which could imply that they are more suitable for bone ingrowth then smooth surfaces. Increase of total surface area (due to larger roughness) might be a reason for the improved trombogenic response.

 

 

Figure 1 shows how many platelets were stuck on the specimen surfaces. Horizontal lines represent mean values and standard deviation.

 

CONCLUSION

The surface properties of EBM produced implants are affected by the made parameters. The results in Figure 1 corresponds well with previous results that rougher surfaces promotes bone ingrowth4. The increased thrombogenicity and platelet binding with rougher surfaces indicates that EBM made surfaces can affect the final bone response and will possibly suit as implant material.

 

REFERENCES

1. Raennar, L.E., et al., Efficientcooling with tool inserts manufactured by electronbeam melting. Rapid Prototyping Journal. 13:128-35, 2007

2. Cronskaer, M. Applications of Electron Beam Melting to Titanium Hip Stem Implants

3. Mazzoli, A., et al., Direct fabrication through electron beam melting technology of custom cranial implants designed in a PHANToM-based haptic environment. Materials and Design. 30:318-3192, 2009

4. Frosch, K.H., et al., Metallic Biomaterials in Skeletal Rapair. Eur J Trauma. 32:149-59, 2006

5. Thor A., et al.. The role of whole blood in thrombin generation in contact with various titanium surfaces. Biomaterials. 28:966-97, 2007

6. Arcam AB (www.arcam.com)

7. Hong, J., et al., A new in vitro model to study interaction between whole blood and biomaterials. Studies of platelet and coagulation activation acid the effect of aspirin. Biomaterials. 20:603-611, 1999

Place, publisher, year, edition, pages
Dublin, 2011.
Keywords [en]
Additive manufacturing, rapid prototyping, electron beam melting
National Category
Medical Materials
Identifiers
URN: urn:nbn:se:miun:diva-17891Scopus ID: 2-s2.0-84887000027OAI: oai:DiVA.org:miun-17891DiVA, id: diva2:578677
Conference
24th European Conference on Biomaterials –September 4th–9th, Dublin 2011
Available from: 2012-12-20 Created: 2012-12-18 Last updated: 2018-12-14Bibliographically approved
In thesis
1. SURFACE PROPERTIES OF IMPLANTS MANUFACTURED USING ELECTRON BEAM MELTING
Open this publication in new window or tab >>SURFACE PROPERTIES OF IMPLANTS MANUFACTURED USING ELECTRON BEAM MELTING
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis summarizes the results concerning the manufacture of medical implants for bone replacement using electron beam melting (EBM) which is an additive manufacturing (AM) technology, and aims to satisfy the engineering needs for the medical functionality of manufacturing technology. This thesis has focused on some microscopic properties for surfaces and bone integration. The process parameters of EBM manufacturing were studied to ascertain whether they have impacts on surface appearance, as surface properties have impacts on bone integration and implant performance.

EBM manufacturing uses an electron beam to melt metal powder onto each layer in a manner akin to welding. The electron beam is controlled by process parameters that may be altered to a certain extent by the operator. There are individual process parameters for every material, and new parameters are set when developing new materials. In this thesis, process parameters in default settings were altered to ascertain whether it was possible to specify process parameters for implant manufacturing. The blood chamber model was used for thromboinflammation validation, using human whole blood. The model is used to identify early reactions of coagulation and immunoreactions. The material used in this study was Ti6Al4V-ELI, which is corrosion resistant and has the same surface oxide layers as titanium, and CoCr-F75, which has high stiffness, is wear-resistant and is commonly used in articulating joints.

The study shows that among the process parameters researched, a combination of speed and current have the most impact on surface roughness and an interaction of parameters were found using design of experiment (DOE). As-built EBM surfaces show thrombogenicity, which in previous studies has been associated with bone ingrowth.

Surface structure of as-build EBM manufactured surfaces are similar to implants surfaces described by Pilliar (2005), but with superior material properties than those of implants with sintered metals beads. By altering the process parameters controlling the electron beam, surface roughness of as-build parts may be affected, and the rougher EBM manufactured surfaces tend to be more thrombogen than the finer EBM manufactured surfaces. As-build EBM manufactured surfaces in general show more thrombogenicity than conventional machined implants surfaces.

Abstract [sv]

Denna avhandling behandlar tillverkning av medicinska implantat för integration i ben. I fokus är den additiva tillverkningstekniken ”elektronstrålesmältning” ( Electron Beam Melting –EBM), en av flera tekniker som populärt beskrivs med termen 3D-skrivare. Avhandlingen fokuserar på mikroskopiska ytegenskaper och dess inverkan på benintegration. Processparametrarna för EBM-tillverkning studerades för att fastställa hur de påverkar ytans utseende, efter som ytegenskaper har effekt på implantatens funktion.

EBM-tillverkning använder en elektronstråle som likt svetsning smälter ihop metallpulver. Elektronstrålen styrs av processparametrar som till viss mån kan justeras av maskinoperatören. Det finns individuella processparametrar för varje material och nya parametrar utvecklas till varje ny legering. I denna avhandling har ”grundinställningarnas processparametrar” studerats för att ta reda på om det är möjligt att ställa in specifika parametrar till implantattillverkning. Med hjälp av blodkammarmetoden, som använder humant blod, har thromboinflammatoriska egenskaper undersökts. Metoden identifierar tidiga koagulations- och immunologiska reaktioner. Legeringarna som undersökts i denna studie var Ti6Al4V-ELI, som är korrosionsbeständigt med samma uppsättning oxider på ytan som titan har, och CoCr-F75, en legering som har hög styvhet, är slitstarkt och är vanligt förekommande i implantat för leder.

Bland de undersökta processparametrarna visar en kombination av hastighet och ström ha mest inverkan på ytjämnhet och en interaktion mellan parametrar identifierades med hjälp av försöksplanering. EBM-tillverkade ytor visade på thrombogena egenskaper som i tidigare studier kan relateras till god integration i benvävnad.

Ytstrukturen hos EBM-tillverkade ytor liknar de implantatytor som Pilliar (2005) beskriver, men materialegenskaperna är bättre än de materialegenskaper som implantat, med sintrad yta, har. Genom att ändra processparametrarna som styr elektronstrålen kan ytstrukturen påverkas. Grövre EBM-tillverkade ytor tenderar att vara mer thrombogena än de finare EBM-tillverkade ytorna är. Obehandlade EBM-tillverkade ytor i allmänhet är mer thrombogena än vad konventionellt framställda implantatytor är.

Place, publisher, year, edition, pages
Sweden: Mid Sweden University, 2016. p. 40
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 122
Keywords
electron beam melting, blood coagulation, bone ingrowth, surface roughness, process parameters
National Category
Production Engineering, Human Work Science and Ergonomics
Identifiers
urn:nbn:se:miun:diva-27125 (URN)978-91-88025-49-4 (ISBN)
Presentation
2016-01-22, G1353, Kunskapens väg 8, Östersund, 13:16 (Swedish)
Opponent
Supervisors
Available from: 2016-03-01 Created: 2016-02-24 Last updated: 2016-03-01Bibliographically approved
2. Electron beam melting: Impact of part surface properties on metal fatigue and bone ingrowth
Open this publication in new window or tab >>Electron beam melting: Impact of part surface properties on metal fatigue and bone ingrowth
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Abstract

The aim of this thesis is to investigate aspects on how additive manufacturing (AM) contributes to functional bone implants with the use of the electron beam melting (EBM) technology. AM manufactures parts according to computer-aided design, and the EBM technology melts powder using an electron beam, which acts similar to a laser beam. The topics discussed in this thesis are related to surface roughness that originate from the melted metal powder, and the thesis tries to define some aspects that affect implant functionality. Process parameters steering the electron beam and biocompatibility arising from the surface texture were the initial parts of the PhD studies, and the other half focused on post-processing and fatigue, which are important for medical and industrial applications. There are six studies in this compilation thesis. They are abbreviated as P - process parameters, M - medical applications, and F - fatigue. Studies P, M2, F2, and F3 are journal articles, and M1 and F1 are conference proceedings.

Study P used design of experiments to investigate how process parameters affect the surface roughness of as-built EBM-manufactured parts and concluded that beam speed and energy (current) were the most important parameters that influence the surface roughness.

In studies M1 and M2, EBM-manufactured specimens of cobalt-chromium and titanium alloys were used to evaluate biocompatibility. The blood chamber method quantified the reactions of the human whole blood in contact with the metal surfaces, and the results showed how the as-built EBM surface roughness contributed to coagulation and bone healing.

Rotating beam fatigue equipment was used in studies F1–F3 and study F1 discussed the size effect on fatigue loaded as-built specimens and included specimens with different sizes and with or without hot isostatic pressing (HIP). Study F2 compared as-built and machined specimens and study F3 investigated how Hirtisation, which is a patented electrochemical surface treatment, and HIP affect the fatigue properties that originate from the electrochemical polishing surface topography. The studies showed that a decreased surface roughness increased the fatigue resistance while the stress concentrations (Kt) in the surface of EBM-manufactured specimens decreased.

The thesis concludes that EBM-manufactured as-built surfaces are suitable for direct contact with the bone, and that HIP does not improve the fatigue resistance of parts with as-built surfaces, where crack initiation starts at notches.

Abstract [sv]

Svensk sammanfattning

Denna avhandling behandlar frågeställningar inom tillverkning av benimplantat med additiv tillverkning (Additive Manufacturing, AM), med fokus på EBM-tekniken (Electron Beam Melting, smältning med elektronstråle). Additiv tillverkning bygger produkter utifrån datorkonstruerade modeller (Computer Aided Design, CAD), och EBM-tekniken gör detta genom att smälta ihop metallpulver med hjälp av en energirik elektronstråle likt en laserstråle. Avhandlingen fokuserar på ytstrukturen från det smälta metallpulvret och hur dess egenskaper påverkar funktionen av EBM-tillverkade produkter. Under första delen av doktorandarbetet var fokus på processparametrar som styr elektronstrålen och biokompatibilitet, och under den senare delen har arbetet riktats mot efterbearbetningsmetoder och utmattningsegenskaper, vilket är viktigt för medicinska implantat och industriell användning. Avhandlingen är skriven på engelska och studierna som sammanläggningen består av är döpta och numrerade med förkortningarna P-Processparametrar, M-Medicinska applikationer och F-Fatigue (Utmattning). Avhandlingen består av fyra tidskriftsartiklar kallade studie P, M2, F2 och F3 och två konferensbidrag studie M1 och F1.

Studie P undersökte med hjälp av försöksplanering (Design Of Experiment, DOE) hur processparametrarna påverkar ytgrovheten för EBM-tillverkade produkter och resulterade i att elektronstrålens förflyttningshastighet och energi har störst inverkan på ytgrovheten.

Studierna M1 och M2 använde kobolt-krom- respektive titanlegeringar, tillverkat med EBM-tekniken, och undersökte biokompatibiliteten med hjälp av blodkammarmodellen som kvantifierar blodets reaktioner vid kontakt med metallytan. Resultaten visade att den mycket grova ytan som EBM-tillverkade implantat har, stimulerar till koagulation och implantatinläkning.

Roterande utmattning användes för studierna F1-3, och studie F1 avhandlar hur EBM-tillverkade provstavar med olika storlekar och med eller utan tempererad tryckbehandling (Het Isostatisk Pressning, HIP) påverkar resultaten. Studie F2 jämförde hur den EBM-tillverkade ytan och en maskinbearbetad yta påverkar materialegenskaperna, och studie F3 undersökte hur Hirtisering, en patenterad elektrokempoleringsmetod, och kombinerat med HIP påverkar utmattningsegenskaperna. Studierna visar att minskad ytgrovhet med elektrokempolering ökar hållfastheten samtidigt som spänningskoncentrationerna (Kt) minskar i ytan för EBM-tillverkade ytor.

Avhandlingen visar att EBM-tillverkade ytor lämpar sig för benkontakt och att HIP inte förbättrar utmattningsegenskaperna om den råa ytan behålls.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2019. p. 73
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 291
Keywords
Additive Manufacturing (AM), Electron Beam Melting (EBM), As-built surfaces, Bone Ingrowth, Metall Fatigue, Machined Surfaces, Hirtisation, Hot Isostatic Pressing (HIP)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:miun:diva-35182 (URN)978-91-88527-82-0 (ISBN)
Public defence
2019-01-15, Q221, Akademigatan 1, Östersund, 09:15 (Swedish)
Opponent
Supervisors
Available from: 2018-12-14 Created: 2018-12-13 Last updated: 2018-12-14Bibliographically approved

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