Anin vivostudy on the effect of scaffold geometry and growth factor release on the healing of bone defects

Abstract

The hypothesis of this study was that the extent of bone regeneration could be enhanced by using scaffolds with appropriate geometry, and that such an effect could be further increased by mimicking the natural timing of appearance of bone morphogenetic proteins BMP-2 and BMP-7 after fracture. Bioplotted poly(ε-caprolactone) (PCL) disks with four different fibre organizations were used to study the effect of 3D scaffold architecture on the healing of bone defects in a rat pelvis model. Moreover, one PCL construct was further modified by introducing a nanoparticulate sequential BMP-2/BMP-7 delivery system into this scaffold. Scaffolds and functionalized construct along with free nanocapsules were implanted using a rat iliac crest defect model. Six weeks post-implantation, the defects were evaluated by CT scan and histology. Analysis revealed that the basic architecture, having the highest pore volume for tissue ingrowth, presented the highest bone formation as determined by the bone mineral density (BMD) within the defect (144.2 ± 7.1); about four-fold higher than that of the empty defect (34.9 ± 10.7). It also showed the highest histological analysis scores with a high amount of bone formation within the defect, within the scaffold pores and along the outer surfaces of the scaffold. The basic scaffold carrying the BMP-2/BMP-7 delivery system showed significantly higher bone formation than the growth factor-free basic scaffold at 6 weeks (BMD 206.8 ± 15.7). Histological analysis also revealed new bone formation in close to or in direct contact with the construct interface. This study indicates the importance of open and interconnecting pore geometry on the better healing of bone defects, and that this effect could be further increased by supplying growth factors, as is the case in nature.

Using bimodal MRI/fluorescence imaging to identify host angiogenic response to implants

“…No residual hydrogel was detected by MRI with in situ polymerized PFGdDTPA-Cy5.5 on the third week of the experiment. These results are consistent with previous studies that use other techniques to document how in vivo fate of biomaterial implants is dependent on the composition, dimensions, in situ environment, and degradation products (13,15,(26)(27)(28). In the context of hydrogel biomaterial implants specifically, the MRI results are in close agreement with the work of Artzi et al (15); they also showed that implant geometry significantly affects the in vivo degradation patterns of the implant.…”

“…Although VEGF has been used exogenously to promote in vivo angiogenesis, superior results were obtained when the factor was protected, localized, and temporally controlled at the site of implantation (7,10,11). The hypothesis underlying this study is that degradation and resorption characteristics of the implant may be influenced by its surface area-to-volume ratio and mode of implantation, and hence the release properties of the proangiogenic factors within the implant site can be optimized accordingly (12)(13)(14)(15). As a case in point, an injectable strategy whereby the hydrogel precursor solution is injected and crosslinked in situ allows an even and contiguous dispersion of the hydrogel within the injury interstitial space for better host integration.…”

“…Another approach is using injectable microbeads, which combine the advantages of high surface areato-volume ratio and more controlled cross-linking efficiency. The use of implant configuration as a basis for producing more potent constructs for tissue engineering and induction of angiogenesis have been inadvertently underestimated and still remain poorly studied for lack of good experimental tools that can continuously and noninvasively monitor the fate of the implants in vivo.Various invasive techniques have been described for documenting implant resorption in vivo; however, these techniques do not provide detailed information about the in situ integration process and require destructive analysis of postmortem sections (13,(16)(17)(18). With the optimization of a hydrogel scaffold requiring more information of the transient steps of integration, techniques to continuously monitor the degradation of a scaffold using fluorescence labeling have been described (15,19,20).…”

“…Various invasive techniques have been described for documenting implant resorption in vivo; however, these techniques do not provide detailed information about the in situ integration process and require destructive analysis of postmortem sections (13,(16)(17)(18). With the optimization of a hydrogel scaffold requiring more information of the transient steps of integration, techniques to continuously monitor the degradation of a scaffold using fluorescence labeling have been described (15,19,20).…”

Priming cells for their final destination: microenvironment controlled cell culture by a modular ECM-mimicking feeder film

“…25 In the present study, in order to monitor the loading in the gelatin film and release out of this film of a growth factor mixture and proteins from serum, we performed a bottom-up proteomic analysis using capillary electrophoresis (CE) coupled to electrospray ionization mass spectrometry (ESI-MS) 26 (Table 1 in the ESI †). 25 In the present study, in order to monitor the loading in the gelatin film and release out of this film of a growth factor mixture and proteins from serum, we performed a bottom-up proteomic analysis using capillary electrophoresis (CE) coupled to electrospray ionization mass spectrometry (ESI-MS) 26 (Table 1 in the ESI †).…”