Porous biocompatible implants and tissue scaffolds synthesized by selective laser sintering from Ti and NiTi I. V. Shishkovsky, a L. T. Volova, b M. V. Kuznetsov, c Yu. G. Morozov c and I. P. Parkin d Received 4th October 2007, Accepted 23rd January 2008 First published as an Advance Article on the web 6th February 2008 DOI: 10.1039/b715313a An investigation of the technical aspects of producing sufficiently high strength porous biocompatible medical implants and tissue scaffolds from nitinol or pure titanium using selective laser sintering/ melting (SLS/M) is presented. In particular, the necessary processing parameters and procedures for successful laser synthesis of functionally graded implants have been established. Physical and mechanical properties, microstructure, corrosion behavior of the synthesized structures, as well as shape memory in porous layered nitinol structures made using laser synthesis are reported. Comparative morphological and histological results of SLS of porous titanium and nitinol made implants are also presented. Investigations were carried out on primary cultures of dermal fibroblasts and mesenchymal stromal human cells. The possibility of cultivating bone marrow on the porous carrier-incubator made from NiTi and pure titanium in vitro was determined. Sufficient understanding of the nature of laser synthesized titanium and nitinol structures was developed in order to determine their suitability for use as functional implants. This resulted in superior tissue to implant fixation and the development of minimally invasive surgical procedures. 1. Introduction The investigation of regeneration mechanisms for tissues and organs is a relatively new research field. The search for new tech- nologies, which could restore a lost function of an organ or a system, has led to the application of rapid prototyping and manufacturing technology (RPMT) in biotechnology, tissue engi- neering, regenerative implant medicine and organogenesis. 1–16 From this work the transplantation of stem cells into carrier matrices was established. A carrier matrix is a synthetic or biological complex with suffi- cient mechanical strength to act as a support and is normally made from a porous layered construction. It can be synthesized via selective laser sintering (SLS) using a computer aided designed (CAD) file for each individual layer using 3D tomog- raphy data. After synthesis of the porous scaffold the stem cells are adopted (penetrated) inside the matrix. It has been experimentally established that the basic criteria for building a biologically compatible matrix for use in tissue-engineering constructions should have the following features: prevention of cytotoxicity; maintenance of adhesion; fixation; proliferation and differentiation of the cells located on its surface; prevention of inflammatory reaction on the material surface and immune response; sufficient mechanical strength and bioresorption by normal metabolic routes. 17–20 The conventional material traditionally used in SLS for implantation is pure titanium, 5,11,16,21–25 characterized by its high bio-compatibility and corrosion resistance in comparison with steel 26 and other materials. 9 Ti-6Al-4V based alloys are also widely used for producing implants. 22 An interesting mate- rial combination for medical implantation is the Ni-Ti system, where under certain conditions an intermetallic phase, titanium nickelide (NiTi), can be synthesized. This intermetallic (named as nitinol) is known to have, even in a porous state, a high specific strength, corrosion resistance, damping characteristics and a unique shape memory effect (SME) that is the result of the thermo-elastic martensite transformations that can take place inside its structure. 6,12–14,27 The demonstrated biocompatibility of nitinol, its physical properties, and SME, even in a porous state, suggests that this material may offer substantial gains in orthopedic implants. These gains revolve around creating implant elements that change shape after implantation due to the SME of nitinol that can be initiated at the temperature of a living organism. These shape changes have two primary beneficial effects: (1) enhanced bone fixation, and (2) minimally invasive surgery. In 1997 the Samara branch of the Lebedev Physical Institute (LPI) pioneered using the novel combination of two well-known methods: SLS and self-propagating high-temperature synthesis (SHS). 28,29 Shishkovsky showed that samples of titanium nickel- ide Ni-Ti (nitinol) of a specific shape could be synthesized in the combined process directly using digital PC control. The synthe- sized samples had a high porosity, 30 however their durability was far from that desired. Despite this, the high porosity has a few advantages, especially being compatible with bioactive compo- nent infiltration and commensurate with acceleration of the implantation process. Moreover, the porous biocompatible structure was an excellent potential repository for stem cells. a P.N. Lebedev Physics Institute, Samara Branch, Russian Academy of Sciences, Samara, 443011, Russia b Samara State Medical University, Samara, 443099, Russia c Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Chernogolovka, 142432, Russia d Department of Chemistry, Materials Chemistry Centre, University College London, 20 Gordon Street, London, UK, WC1H 0AJ. E-mail: i.p.parkin@ucl.ac.uk; Fax: +44(0)20 7679 7463; Tel: +44(0)20 7679 4669 This journal is ª The Royal Society of Chemistry 2008 J. Mater. Chem., 2008, 18, 1309–1317 | 1309 PAPER www.rsc.org/materials | Journal of Materials Chemistry