Creation of macroporous calcium phosphate cements as bone substitutes by using genipin-crosslinked gelatin microspheres

Abstract

Macroporous calcium phosphate cements (CPCs) were developed using genipin-crosslinked gelatin microspheres (GMs) with two weight ratios (2.5 wt% and 5 wt%). The initial setting time of the composite was prolonged by GMs. After GMs/CPCs were soaked in phosphate-buffered saline (PBS) for several weeks, macropores appeared as a result of the degradation of GMs. The presence of GMs accelerated the setting reaction and improved the structure of the composite. The compressive strength increased up to 12 MPa (2.5 wt% GMs/CPCs) and 14 MPa (5 wt% GMs/CPCs) after one week of PBS soaking, then gradually decreased to 9 MPa (2.5 wt% GMs/CPCs) and 7 MPa (5 wt% GMs/CPCs) after three weeks of soaking, and further to 6 MPa (2.5 wt% GMs/CPCs) and 2 MPa (5 wt% GMs/CPCs) after five weeks of soaking. CPCs with 2.5 wt% GMs were the most favorable composite in the tested samples. Cell experiments showed that rat osteoblasts displayed normal morphologies when exposed to the 2.5 wt% GMs/CPCs, and proliferation of the cells was also enhanced. An in vivo study showed that new bone tissue was able to grow into the pores that resulted from GM degradation. This study suggests that the new composite could be a promising candidate for use as a bone substitute under non-compression-loaded circumstances.

Calcium Phosphate Cement with BMP-2-loaded Gelatin Microspheres Enhances Bone Healing in Osteoporosis: A Pilot Study

“…In a similar study, Habraken et al [5] reported that when the weight of GMs was 5% in rhBMP-2/GM/CPC, there was no difference in cumulative BMP-2 release between the two composites; however, when the weight of GMs was increased to 10%, the cumulative rhBMP-2 release from rhBMP-2/GM/CPC was greater compared with rhBMP-2/ CPC. The differences might be attributable to the lower degree of cross-linking in our GMs compared with those of Habraken et al [5,6] and Li et al [10]; thus, the degradation period of our GMs was shorter than that of Habraken et al, and the drug release from the composite with microspheres and CPC apparently was accelerated by the faster degradation of microspheres [5,10]. The mean amount of rhBMP-2 release from our rhBMP-2/GM/CPC was 38% after 28 days, and greater than the mean of 15% to 33% of rhBMP-2/PLGA/CPC reported previously [4,25].…”

“…We prepared GMs using an emulsification-solvent extraction with some modifications [10,12]. Briefly, type B gelatin (1.5 g, 225 Bloom; Sigma-Aldrich Corporation, St Louis, MO, USA) was dissolved in 10 mL phosphatebuffered saline (PBS, pH 7.4) at 50°C.…”

“…Gelatinenriched CPC also shows strengthened mechanical properties and enhances the bioactivity of osteoblasts [1,2]. We previously reported that a composite of CPC and genipincross-linked GMs showed good biocompatibility and improved degradability [10].…”

“…CPC is one alternate bone substitute and has been used to treat compression fractures in hips, radii, and vertebrae [14,20,35]. However, the reduced osteoinductive ability of osteoporotic bone may limit the utility of CPC, and the problem is exaggerated by CPC's slow resorption [7,10,26,27].…”

“…Therefore, a method was developed to prepare macroporous CPC using gelatin microspheres (GMs) [6,10,16]. GMs are biodegradable, biocompatible, and can be crosslinked to increase their thermal and mechanical stability under physiologic conditions [33].…”