TECHNICAL PAPER Accelerated Self-Hardening Tetracalcium Phosphate Based Bone Cement with Enhanced Strength and Biological Behaviour R. Jayasree 1 • T. S. Sampath Kumar 1 • Rakesh P. Nankar 2 • Mukesh Doble 2 Received: 19 December 2014 / Accepted: 25 May 2015 Ó The Indian Institute of Metals - IIM 2015 Abstract Tetracalcium phosphate (TTCP) is the most basic phase among the calcium phosphate bioceramics. TTCP has been used as self setting bone cement and its relatively high surface pH seems to be very beneficial for cell adhesion and bone formation. Various attempts have been made to improve the cement properties for the ease of use during the surgical procedures. The effect of citric acid (CA) on the setting properties, apatite forming ability, strength and biological behavior of TTCP based bone cement has been studied in detail in the present study. The cement formulation containing 15 % CA has been found to have setting time between 9 and 16 min suitable for bone cement. It also showed complete conversion to apatite phase and highest compressive strength after 28 days of immersion in phosphate buffer at physiological conditions. Cell culture studies using rat skeletal muscle cells confirm higher cell viability in the CA containing cements com- pared to the pure cement without CA content. The results suggest that self-hardening tetracalcium phosphate based bone cement modified with CA holds a promise for its use in orthopaedic and trauma surgery. Keywords Bone cement  Hydroxyapatite  Citric acid  Mechanical properties 1 Introduction Self-hardening calcium phosphates are the recent focus of researchers developing synthetic bone graft materials due to their biocompatibility, osteoconductivity, resorbability and ease of clinical handling [1–3]. In 1983, Brown and Chow [4] discovered that tetracalcium phosphate (TTCP, Ca 4 (PO 4 ) 2 O) react with dicalcium phosphate dihydrate (DCPD, CaHPO 4 2H 2 O) or dicalcium phosphate anhydrous (DCPA, CaHPO 4 ) in an aqueous environment to form hydroxyapatite (HA, Ca 10 (PO 4 ) 6 (OH) 2 ) which is similar to mineral phase of bone as the final product. Since then TTCP, the most basic calcium phosphate known has been widely used either as single- or multicomponent to form a HA bone cement [5]. Generally, the reaction rates of the calcium phosphate cement (CPC) must be well under control: the CPC ought to react slowly enough to provide adequate time to the surgeon for implantation, and also fast enough to avoid delay during the surgical procedure [6]. Cement should also reach good mechanical properties immediately after initial setting. It is therefore essential to perfectly under- stand and control CPC setting reactions. Various modifi- cations in apatite cement have been attempted to improve its workability, setting time, mechanical and biological properties [6–9]. In 1941, Dickens [10] reported that bone contains extremely high levels of citrate. The citrate comprises *1.6 % of the bone content and about 80 % of the total body citrate resides in bone and it’s known to be involved in some essential process required for normal bone for- mation and maintenance [11]. Citric acid (CA) is a weak organic acid occurring naturally in citrus fruits. The CA addition to a-TCP (a-tricalcium phosphate) based bone cement has shown to improve the workability and & T. S. Sampath Kumar tssk@iitm.ac.in 1 Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036, India 2 Department of Biotechnology, Indian Institute of Technology Madras, Chennai 600036, India 123 Trans Indian Inst Met DOI 10.1007/s12666-015-0593-x