Skip to content
Licensed Unlicensed Requires Authentication Published by De Gruyter April 27, 2022

Predicting the replication fidelity of injection molded solid polymer microneedles

Tim Evens, Sylvie Castagne, David Seveno and Albert Van Bael


Microneedles are sharp microscopic features, which can be used for drug or vaccine delivery in a minimally invasive way. Recently, we developed a method to produce polymer microneedles using laser ablated molds in an injection molding process. At this moment, extensive injection molding experiments are needed to investigate the replication fidelity. Accurate predictions of the injection molding process would eliminate these costly and time expensive experiments. In this study, we evaluated the replication fidelity of solid polymer microneedles using numerical simulations and compared the results to injection molding experiments. This study was performed for different sizes of microneedles, different thermoplastics (polypropylene and polycarbonate) and different mold materials (tool steel, copper alloy and aluminium alloy). Moreover, different processing conditions and different locations of the microneedles on the macroscopic part were considered. A good correlation with experimental findings was achieved by optimizing the heat transfer coefficient between the polymer and the mold, while using a multiscale mesh with a sufficient number of mesh elements. Optimal heat transfer coefficients between 10,000 and 55,000 W/m2 K were found for the different combinations of polymer and mold materials, which resulted in an accuracy of the simulated microneedle replication fidelity between 94.5 and 97.0%.

Corresponding author: Tim Evens, Department of Materials Engineering Diepenbeek Campus, KU Leuven, Wetenschapspark 27, 3590 Diepenbeek, Belgium, E-mail:

Funding source: KU

Award Identifier / Grant number: IDN/20/011 - MIRACLE: Autonomous microfluidic patch for plasmid-based vaccine


The authors would like to thank Olivier Malek from the company Sirris, department Precision Manufacturing (Belgium) for laser ablating the microneedle cavities in the mold inserts. We also thank the company SABIC for providing the thermoplastic injection molding materials and the company SimpaTec for their support with the Moldex3D analyses.

  1. Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.

  2. Research funding: This work was funded by the KU Leuven Interdisciplinary Network project IDN/20/011 - MIRACLE: Autonomous microfluidic patch for plasmid-based vaccine.

  3. Conflict of interest statement: The authors declare no conflicts of interest regarding this article.


Attia, U.M., Marson, S., and Alcock, J.R. (2009). Micro-injection moulding of polymer microfluidic devices. Microfluid. Nanofluidics 7: 1–28, in Google Scholar

Babenko, M., Sweeney, J., Petkov, P., Lacan, F., Bigot, S., and Whiteside, B. (2018). Evaluation of heat transfer at the cavity-polymer interface in microinjection moulding based on experimental and simulation study. Appl. Therm. Eng. 130: 865–876, in Google Scholar

Baruffi, F., Gülçür, M., Calaon, M., Romano, J.-M., Penchev, P., Dimov, S., Whiteside, B., and Tosello, G. (2019). Correlating nano-scale surface replication accuracy and cavity temperature in micro-injection moulding using in-line process control and high-speed thermal imaging. J. Manuf. Process. 47: 367–381, in Google Scholar

Birkar, S., Mendible, G., Park, J.-G., Mead, J.L., Johnston, S.P., and Barry, C.M.F. (2016). Effect of feature spacing when injection molding parts with microstructured surfaces. Polym. Eng. Sci. 56: 1330–1338, in Google Scholar

Choi, S. and Kim, S.K. (2011). Multi-scale filling simulation of micro-injection molding process. J. Mech. Sci. Technol. 25: 117–124, in Google Scholar

Christiansen, A.B., Clausen, J.S., Mortensen, N.A., and Kristensen, A. (2014). Injection moulding antireflective nanostructures. Microelectron. Eng. 121: 47–50, in Google Scholar

Dawson, A., Rides, M., Allen, C.R.G., and Urquhart, J.M. (2008). Polymer-mould interface heat transfer coefficient measurements for polymer processing. Polym. Test. 27: 555–565, in Google Scholar

Evens, T., Malek, O., Castagne, S., Seveno, D., and Van Bael, A. (2020). A novel method for producing solid polymer microneedles using laser ablated moulds in an injection moulding process. Manuf. Lett. 24: 29–32, in Google Scholar

Evens, T., Malek, O., Castagne, S., Seveno, D., and Van Bael, A. (2021a). Controlling the geometry of laser ablated microneedle cavities in different mould materials and assessing the replication fidelity within polymer injection moulding. J. Manuf. Process. 62: 535–545, in Google Scholar

Evens, T., Van Hileghem, L., Dal Dosso, F., Lammertyn, J., Malek, O., Castagne, S., Seveno, D., and Van Bael, A. (2021b). Producing hollow polymer microneedles using laser ablated molds in an injection molding process. J. Micro Nano-Manufacturing 9: 1–9, in Google Scholar

Faraji Rad, Z., Nordon, R.E., Anthony, C.J., Bilston, L., Prewett, P.D., Arns, J.-Y., Arns, C.H., Zhang, L., and Davies, G.J. (2017). High-fidelity replication of thermoplastic microneedles with open microfluidic channels. Microsyst. Nanoeng. 3: 17034, in Google Scholar PubMed PubMed Central

Gornik, C. (2004). Injection moulding of parts with microstructured surfaces for medical applications. Macromol. Symp. 217: 365–374, in Google Scholar

Hopmann, C., Weber, M., Schöngart, M., Schäfer, C., Bobzin, K., Bagcivan, N., Brögelmann, T., Theiß, S., Münstermann, T., and Steger, M. (2015). Injection moulding of optical functional micro structures using laser structured, PVD-coated mould inserts. AIP Conf. Proc. 1664: 110003, in Google Scholar

Huovinen, E., Hirvi, J., Suvanto, M., and Pakkanen, T.A. (2012). Micro–micro hierarchy replacing micro–nano hierarchy: a precisely controlled way to produce wear-resistant superhydrophobic polymer surfaces. Langmuir 28: 14747–14755, in Google Scholar PubMed

Iturri, J., Xue, L., Kappl, M., García-Fernández, L., Barnes, W.J.P., Butt, H.-J., and del Campo, A. (2015). Torrent frog-inspired adhesives: attachment to flooded surfaces. Adv. Funct. Mater. 25: 1499–1505, in Google Scholar

Juster, H., van der Aar, B., and de Brouwer, H. (2019). A review on microfabrication of thermoplastic polymer-based microneedle arrays. Polym. Eng. Sci. 59: 877–890, in Google Scholar

Kalima, V., Pietarinen, J., Siitonen, S., Immonen, J., Suvanto, M., Kuittinen, M., Mönkkönen, K., and Pakkanen, T.T. (2007). Transparent thermoplastics: replication of diffractive optical elements using micro-injection molding. Opt. Mater. (Amst). 30: 285–291, in Google Scholar

Kamal, M., Isayev, A., and Liu, S.-J. (2009). Injection molding technology and fundamentals, 1st ed. Hanser, Munich.10.3139/9783446433731Search in Google Scholar

Kim, S.-W. and Turng, L.-S. (2006). Three-dimensional numerical simulation of injection molding filling of optical lens and multiscale geometry using finite element method. Polym. Eng. Sci. 46: 1263–1274, in Google Scholar

Lin, H.-Y. and Young, W.-B. (2009). Analysis of the filling capability to the microstructures in micro-injection molding. Appl. Math. Model. 33: 3746–3755, in Google Scholar

Loaldi, D., Quagliotti, D., Calaon, M., Parenti, P., Annoni, M., and Tosello, G. (2018). Manufacturing signatures of injection molding and injection compression molding for micro-structured polymer fresnel lens production. Micromachines 9: 653, in Google Scholar PubMed PubMed Central

Loaldi, D., Regi, F., Baruffi, F., Calaon, M., Quagliotti, D., Zhang, Y., and Tosello, G. (2020). Experimental validation of injection molding simulations of 3D microparts and microstructured components using virtual design of experiments and multi-scale modeling. Micromachines 11: 614, in Google Scholar PubMed PubMed Central

Lucchetta, G., Ferraris, E., Tristo, G., and Reynaerts, D. (2012). Influence of mould thermal properties on the replication of micro parts via injection moulding. Procedia CIRP 2: 113–117, in Google Scholar

Lucchetta, G., Sorgato, M., Carmignato, S., and Savio, E. (2014). Investigating the technological limits of micro-injection molding in replicating high aspect ratio micro-structured surfaces. CIRP Ann. 63: 521–524, in Google Scholar

Madhusudana, C.V. (1996). Introduction. In: Ling, F., Gloyna, E., and Howard, W. (Eds.), Thermal contact conductance. Springer, New York, pp. 1–8.10.1007/978-1-4612-3978-9Search in Google Scholar

Marotta, E.E. and Fletcher, L.S. (1995). Thermal contact conductance of polymeric materials. 33rd Aerosp. Sci. Meet. Exhib. 10, in Google Scholar

Narh, K.A. and Sridhar, L. (1997). Measurement and modeling of thermal contact resistance at a plastic metal interface. ANTEC, Conf. Proc. 2: 2273–2277.Search in Google Scholar

Narh, K.A. and Sridhar, L. (2000). U.S. Pat. 6142662. New Jersey Institute of Technology.Search in Google Scholar

Nguyen-Chung, T., Jüttner, G., Pham, T., Mennig, G., and Gehde, M. (2008). The importance of precise boundary conditions for the simulation of micro-injection molding. J. Plast. Technol. 4.Search in Google Scholar

Packianather, M., Griffiths, C., and Kadir, W. (2015). Micro injection moulding process parameter tuning. Procedia CIRP 33: 400–405, in Google Scholar

Padeste, C., Özçelik, H., Ziegler, J., Schleunitz, A., Bednarzik, M., Yücel, D., and Hasırcı, V. (2011). Replication of high aspect ratio pillar array structures in biocompatible polymers for tissue engineering applications. Microelectron. Eng. 88: 1836–1839, in Google Scholar

Park, E.M. and Kim, S.K. (2019). Effects of mold heat transfer coefficient on numerical simulation of injection molding. Trans. Korean Soc. Mech. Eng. B 43: 201–209, in Google Scholar

Rytka, C., Kristiansen, P.M., and Neyer, A. (2015). Iso- and variothermal injection compression moulding of polymer micro- and nanostructures for optical and medical applications. J. Micromech. Microengin. 25: 065008, in Google Scholar

Rytka, C., Lungershausen, J., Kristiansen, P.M., and Neyer, A. (2016). 3D filling simulation of micro- and nanostructures in comparison to iso- and variothermal injection moulding trials. J. Micromech. Microengin. 26: 065018, in Google Scholar

Rytka, C., Opara, N., Andersen, N.K., Kristiansen, P.M., and Neyer, A. (2016). On the role of wetting, structure width, and flow characteristics in polymer replication on micro- and nanoscale. Macromol. Mater. Eng. 301: 597–609, in Google Scholar

Sridhar, L. and Narh, K.A. (1999). Computer simulation of the effect of thermal contact resistance on cooling time in injection molding. Simulation 73: 144–148, in Google Scholar

Sridhar, L., Sedlak, B.M., and Narh, K.A. (2000). Parametric study of heat transfer in injection molding-effect of thermal contact resistance. J. Manuf. Sci. Eng. 122: 698–705, in Google Scholar

Tofteberg, T.R. and Andreassen, E. (2010). Multiscale simulation of injection molding of parts with low aspect ratio microfeatures. Int. Polym. Proc. 25: 63–74, in Google Scholar

Tosello, G. (2018). Micro injection molding. In: Tosello, G. (Ed.), Micro injection moldin. Hanser, Munich, pp. 83–112.10.3139/9781569906545.004Search in Google Scholar

Vera, J., Brulez, A.-C., Contraires, E., Larochette, M., Trannoy-Orban, N., Pignon, M., Mauclair, C., Valette, S., and Benayoun, S. (2018). Factors influencing microinjection molding replication quality. J. Micromech. Microeng. 28: 015004, in Google Scholar

Williams, M.L., Landel, R.F., and Ferry, J.D. (1955). The temperature dependence of relaxation mechanisms in amorphous polymers and other glass-forming liquids. J. Am. Chem. Soc. 77: 3701–3707, in Google Scholar

Xu, G., Yu, L., Lee, L.J., and Koelling, K.W. (2005). Experimental and numerical studies of injection molding with microfeatures. Polym. Eng. Sci. 45: 866–875, in Google Scholar

Yamaguchi, M., Sasaki, S., Suzuki, S., and Nakayama, Y. (2015). Injection-molded plastic plate with hydrophobic surface by nanoperiodic structure applied in uniaxial direction. J. Adhes. Sci. Technol. 29: 24–35, in Google Scholar

Zhang, H., Fang, F., Gilchrist, M.D., and Zhang, N. (2018). Filling of high aspect ratio micro features of a microfluidic flow cytometer chip using micro injection moulding. J. Micromech. Microeng. 28: 075005, in Google Scholar

Zhang, H., Fang, F., Gilchrist, M.D., and Zhang, N. (2019). Precision replication of micro features using micro injection moulding: process simulation and validation. Mater. Des. 177: 107829, in Google Scholar

Received: 2021-11-15
Accepted: 2022-03-09
Published Online: 2022-04-27
Published in Print: 2022-07-26

© 2022 Walter de Gruyter GmbH, Berlin/Boston