Sterilization effects on the handling and degradation properties of calcium phosphate cements containing poly (_D,L‐lactic‐co‐glycolic acid) porogens and carboxymethyl cellulose

Abstract

Injectable, self‐setting calcium phosphate cements (CPCs) are synthetic bone substitutes considered favorable for the repair and regeneration of bone due to their osteocompatibility and unique handling properties. However, their clinical applicability can be compromised due to insufficient cohesion upon injection into the body coupled with poor degradation rates that restricts new bone formation. Consequently, carboxymethyl cellulose (CMC) was incorporated into CPC formulations to improve their cohesion and injectability while poly (D,L‐lactic‐co‐glycolic acid) (PLGA) porogens were added to introduce macroporosity and improve their biodegradation rate. Like most biomaterials, CPCs are gamma irradiated before clinical use to ensure sufficient sterilization. However, it is well known that gamma irradiation also reduces the molecular weight of CMC and PLGA via chain scission, which affects their material properties. Therefore, the aim of this study is to measure the effect that gamma irradiation has on the molecular weight of CMC at varying doses of 15, 40, or 80 kGy and investigate how this affects the handling (i.e., injectability, cohesion, washout, and setting times) and in vitro degradation behavior of CPC formulations. Results reveal that the molecular weight of CMC decreases with increasing gamma irradiation dose, thereby reducing the viscosifying capabilities of CMC, which causes CPCs to deteriorate more readily. Further, the addition of CMC seems to inhibit the degree of phase transformation during cement setting while the subsequent reduction in molecular weight of PLGA after gamma irradiation improves the in vitro degradation rate of CPCs due to the faster degradation rate of low molecular weight PLGA. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2216–2228, 2019.

Tough and injectable fiber reinforced calcium phosphate cement as an alternative to polymethylmethacrylate cement for vertebral augmentation: a biomechanical study

“…The injectability of CPCs was previously defined as the ability of a paste to remain homogeneous under pressure, during manual extrusion, independent of a defined injection force. 22,23,29 For the current study, the injectability of frCPCs was studied according to a slight adaptation of a previously reported method. 23 In brief, a 3 ml syringe (Luer lock system, Terumo Europe NV, Leuven, Belgium) was coupled to a clinically available coaxial 11G cannula developed specifically for vertebral augmentation (VertePort® Cement Cannula 11G, length: 12.7 cm, Stryker Corporation, Kalamazoo, Michigan, USA) and further used as an extrusion device to mimic vertebral augmentation procedures.…”

“…The cohesion of CPCs has been previously defined as the ability to retain its mass in a homogeneous single unit without loss of material due to fragmentation or disintegration upon immersion in an aqueous environment. 23,25 Therefore, to assess the cohesion, frCPCs were injected through the abovementioned cannula into a phosphate-buffered saline (PBS; Gibco®, Thermo Scientific, Waltham, MA, USA) solution preheated to 37°C. Immediately after extrusion, cements were qualitatively analyzed to its degree of particulate cloud formation and fragmentation.…”

“…Subsequently, all cements were left soaking in PBS for 24 hours on a shaking plate at 37°C, after which a new analysis was performed. In order to obtain a final cohesion score that accounts for both the particulate cloud formation and fragmentation, 23 eqn (2) was used.…”

“…blood clotting and pulmonary embolism). 2,22 Interestingly, the lubricant carboxymethyl cellulose (CMC) has the capacity to improve both cohesion and wash-out profiles of CPC pastes; [22][23][24][25] additionally, the long-term in vivo biocompatibility of CPC/CMC pastes has been previously confirmed. 24 Moreover, in an attempt to overcome the intrinsic brittleness and limited toughness of CPCs, 12,17,19,20 we recently developed a novel poly(vinyl alcohol) (PVA) fiber-reinforced CPC (frCPC), with confirmed cytocompatibility of the selected PVA fibers 26 and enhanced mechanical strength and fracture toughness without compromising osteocompatibility.…”

Injectable Enzymatically Hardened Calcium Phosphate Biocement

“…On the other side, the rise in addition of CMC to the brushite/vaterite cement up to 50 wt% caused the increase in dry composite CS to 86 MPa as a result of cement porosity reduction [ 58 ]. The injectability (and cohesion) of αTCP cement was improved by 1.5 wt% addition of CMC up to 90% while the setting time decreased from 11 to 7 min [ 59 ]. Contrary to the above facts, the injectability of αTCP cements with admixing powder CMC was even reduced at lower contents of CMC (<1 wt%) as compared with the pure αTCP cement due to the segregation of the solid phase from paste during extrusion but rose at higher CMC contents (twice than pure cement).…”