Current Research

• Bio-mimetic materials 

This concept derives from the parallel field of bio-mimetic chemistry. Biological materials are all composites, usually with complex hierarchical microstructures that give combinations of properties that could not be achieved by a single material. In p articular, good combinations of strength and toughness are achieved from most unpromising base materials, such as collagen and calcium phosphate. The aim of bio-mimetic materials is to use similar control of microstructure to achieve superior properties in synthetic materials. The argument can be extended to include optical properties, signal conduction in nerves, sensors and muscles. Applications may be in surgical prostheses but we have in mind the use of these materials in the world of manufactured articles. One can also make a good case for the use of biological design principles in machines. Large mammals could be compared with vehicles in terms of damage tolerance, maneuverability and efficiency, for example. Our particular interest has been in the formation of composites by the precipitation of reinforcing particles within the polymer structure. For example, a range of ceramic oxides have been formed in polymers with control of the particle size, shape and orientation. This work is described in the papers by Burdon and Calvert.
• Diffusion and Permeability in Polymers 

In the past I worked on the diffusion and solubility of antioxidants in polymers with the aim of improving the long term stability of polyolefins to oxidative degradation. This work is covered in papers by Billingham and Calvert. In addition Ryan and Calvert used similar compounds, with UV and fluorescent microscopy, to monitor local structural variations in polypropylene. 
More recently John Lombardi has formed hard layers on polyester films by impregnating them with silica precursors. 
• Intelligent Materials 

We are interested in the embedding of both piezoelectric and optical sensors, for stress and chemical changes, into composites. This is with a view to making monoliths with integrated sensors that can detect damage, cure state or water uptake, as opposed to adding sensors to an existing system. 
A recent project produced small dots of epoxy-based electroactive gels as artificial muscles and sensors. We expect that this system will prove much more versatile than the usual acrylic-based active gels. We are also working on imprinting of polymers for chemical sensing.
• Conducting Polymers 

In the past I worked on the diffusion of dopants in polyacetylene and polypyrrole. This research is covered by the papers of Foot, Billingham and Calvert. Recently we have been working with the group of Prof. Hall from Chemistry on polypyrrole modified with polyether side chains. This gives the material aspects of both a conducting polymer and a polymer electrolyte. The performance of these polymers as cathodes for lithium batteries were tested. They showed much higher ion diffusion and current-carrying capacity than polypyrrole.  
• Solid Freeform Fabrication 

With a company in Tucson, we have developed a method for forming objects by an extrusion freeform fabrication method. A system like a pen-plotter is used to build up a solid by writing out a series of layers. The liquid "ink" solidifies by cooling, gel ling or curing as it is written. This method has been used to make parts from ceramic, polymer, composite, metal and hydrogel. 
A characteristic of this method is that it is easy to form combinations of several different materials into a single part. This we are developing methods to optimize a composite by controlling the distribution and orientation of reinforcing fibers within the structure. We are also working with the bio-mimetic reinforcement of hydrogels by mineralization and on gels with embedded electrodes as artificial muscles. A current project involved freeforming structures with controlled porosity for bone implants.
• Inkjet printing 

We need more resolution in order to be able to incorporate electrical components, such as sensors, into freeformed parts. We are developing inkjet printing as a complementary approach to extrusion freeform fabrication so that parts with combined electrical and mechanical functions can be produced. Since I moved to Massachusetts, we have worked especially on inkjet printing of strain sensors, chemical sensors and physical colors onto textiles. In doing this it has become clear that textiles offer an ideal flexible, versatile substrate for many applications in printed electronics.
• Tissue Engineering 

We are working on inkjet printing of protein complexes and cells in order to sequentially build structures that can be grown into human tissue. This vision includes addition of fibers and a gel matrix in order to build a full three-dimensional structure.

This is only a partial listing of publications. A full listing is also available. 

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• Paul Calvert "Printing cells" Science 318 208-209 (2007)
• Kadhiravan Shanmuganathan, Sarang Deodhar, Nicholas Dembsey, Qinguo Fan, Paul D. Calvert, Steven B. Warner, Prabir K. Patra, "Flame Retardancy and Char Microstructure of Nylon-6/Layered Silicate Nanocomposites", Journal of Applied Polymer Science, 104(3) 1540-1550, 2007
• Amit Sawhney, Animesh Agrawal, Te-Chen Lo, Prabir Patra, Chi H. Chen and Paul Calvert "Soft-structured Sensors and connectors by Inkjet Printing" AATCC Review 7(6) 42-46 2007
• Resorbable polymer-ceramic composites for orthopedic scaffold applications. Vaidyanathan, R.; Hecht, B.; Studley, A.; Phillips, T.; Calvert, P. D.; Tellis, B.; Coleman, A.; Szivek, J. Ceramic Engineering and Science Proceedings (2004), 25(4), 529-536
• Paul Calvert "Biomimetic mineralization and biomineralization" in Advanced Biomimetic Series #2, 899-909, NTS Publishers 2006 (in Japanese)
• P. Calvert, P. Patra, TC Lo, CH Chen, A Sawhney, A Agrawal, "Piezoresistive sensors for smart textiles" Proc SPIE 6524 1I1-1I8 (2007)
• P. Calvert, P. Patra, D. Duggal "Epoxy hydrogels as sensors and actuators" Proc SPIE 6524 0M1-0M6 (2007)
• Skander Limem, Paul Calvert, Hyeon Joo Kim, David L. Kaplan "Differentiation of Bone Marrow Stem Cells on Inkjet Printed Silk Lines" Proceedings NIP22, Denver CO Sept. 2006
• Z.S. Liu, S.Z. Erhan, P.D. Calvert "Solid freeform fabrication of epoxidized soybean oil/epoxy composite with bis or polyalkyleneamine curing agents" Composites Part A-Applied Science and Manufacturing 38 (1): 87-93 2007
• Yuka Yoshioka, Paul D. Calvert , Ghassan E. Jabbour "Simple Modification of Sheet Resistivity of Conducting Polymeric Anodes via Combinatorial Ink-Jet Printing Techniques" Macromolecular Rapid Communications 26, 238 - 246, 2005.
• P.Calvert, Y. Yoshioka, G Jabbour, "Inkjet printing for biomimetic and biomedical materials" R.L. Reis & S. Weiner (eds) Learning from Nature how to design new implantable materials pp. 169-180, Kluwer 2004.
• Paul Calvert "Embedded sensors in artificial and biological systems" in "Sensors and Sensing in Biology and Engineering," eds. Barth, Humphrey and Secomb, Springer 2003
• ZS Liu, SZ Erhan, J Xu, PD Calvert, "Development of soybean oil-based composites by solid freeform fabrication method: Epoxidized soybean oil with bis or polyalkyleneamine curing agents system" Journal of Applied Polymer Science 85, 2100-2107, (2002)
• P. Calvert, J. Cesarano, H. Chandra, H. Denham, S. Kasichainula, R. Vaidyanathan, “Toughness in synthetic and biological multilayered systems” Phil. Trans. R. Soc. Lond. A 360, 199-209, (2002).  
• Souvignier, CW, Sercombe, TB, Huo, SH, Calvert, P, Schaffer, GB, “Freeform fabrication of aluminum metal_matrix composites” J. Mater. Res. 16, 2613-2618, (2001) 
• Paul Calvert, “Inkjet Printing for Materials and Devices”, Chem. Mater. 13, 3299_3305 (2001) 
• Paul Calvert “Electroactive polymer gels” in Y. Bar_Cohen, ed. "Electroactive Polymer (EAP) Actuators as Artificial Muscles _ Reality, Potential and Challenges," SPIE Press, Vol. PM98, (March 2001), pp. 123_138. 
• Zengshe Liu and Paul Calvert, “Multilayer hydrogels as muscle-like actuators” Adv. Mater. 12, 288-291 (2000)  
• S. Boggavarapu, J. Chang, P. Calvert, “A test for mineralization inhibition for calcium salts using agarose hydrogels” Mater. Sci. Eng. C 11 (2000) 47-49. 
• J.Peng, T.L.Lin, P. Calvert, “Orientation effects in short-fiber composites” Composites A 30 133-138 (1999) 
• P. Calvert, T.L. Lin, H. Martin, "Extrusion freeform fabrication of chopped-fibre reinforced composites," High Perf. Polym., 9, 449-456, 1997. 
• P. Calvert," Protein Composite Materials," in Protein Based Materials, Eds. K. McGrath and D. Kaplan, Birkhauser, Boston, 179-216, 1997. 
• P. Calvert, R. Crockett, "Chemical solid free-form fabrication: making shapes without molds," Chem. Mater., 9, 650-663, 1997. 
• P. Calvert,"Biomimetic Inorganic-Organic Composites," in Biomimetic Materials Chemistry, ed. S. Mann, VCH Pubs. Weinheim, 315-336, 1996. 
• F. Mohammad, P.D. Calvert and N.C. Billingham, "Electrical and electronic properties of polyparaphenylenes," J. Phys. D, 29, 195-204 (1996). 
• P. Calvert, G. George and L. Rintoul, "Monitoring of cure and water uptake in a freeformed epoxy resin by an embedded optical fiber," Chem. Mater., 8, 1298-1301 (1996). 
• P.Calvert and P. Rieke, "Biomimetic mineralization in and on polymers," Chem. Mater., 8, 1715-1727 (1996). 
• J. Burdon, M. Oner, P. Calvert, "Growth of oxalate crysals on films of acrylate polymers." Mat. Sci. & Eng., 4, 133-137 (1996). 
• H. Denham, G. George, L. Rintoul, P. Calvert "Fabrication of polymers and composites containing embedded sensors," Proceedings of the 3rd Intl. Conf. Intelligent Materials, Lyon, Eds. P.F. Gobin, J. Tatibouet, 742-7, 1996. 

The following are full text versions of recent reports on our work

A test for mineralization inhibition for calcium salts using agarose hydrogels published in Materials Science and Engineering C 11 2000 47-49

The Extrusion Freeforming of Functional Ceramic Prototypes published in J. of Metals 34-37 (2000)

Electroactive polymer gels published in Y. Bar-Cohen, ed. "Electroactive Polymer (EAP) Actuators as Artificial Muscles - Reality, Potential and Challenges, 2nd Ed." SPIE Press, 2004, pp. 151-170

Inkjet Printing for Materials and Devices published in Chem. Mater. 2001, 13, 3299-3305

Solid freeform farbication of organic-inorganic hybrid materials published in Mater. Sci. Eng. C 6, 167-174 (1998)

Toughness in synthetic and biological multilayered systems published in Phil. Trans. R. Soc. Lond. A 360, 199-209, (2002)

Epoxy-based Electroactive Polymer Gels published in Experimental Mechanics 42, 404-408, (2002)

Biomimetic mineralization and biomineralization published in Advanced Biomimetic Series #2, 899-909, NTS Publishers 2006

Soft structured sensors and connectors by inkjet printing published in AATCC Review 7(6) 42-46 2007

Piezoresistive sensors for smart textiles presented at SPIE Conference San Diego Spring 2007

Epoxy hydrogels as sensors and actuators presented at SPIE Conference San Diego Spring 2007

Differentiation of Bone Marrow Stem Cells on Inkjet Printed Silk Lines presented at MRS Conference Boston Fall 2006

Inkjet printing of insoluble biopolymer and polymer complexes presented at ACS Conference Boston Fall 2007

Printing cells published in Science