Varying the sustained release of BMP‐2 from chitosan nanogel‐functionalized polycaprolactone fiber mats by different polycaprolactone surface modifications

Abstract

Polycaprolactone (PCL) fiber mats with different surface modifications were functionalized with a chitosan nanogel coating to attach the growth factor human bone morphogenetic protein 2 (BMP‐2). Three different hydrophilic surface modifications were compared with regard to the binding and in vitro release of BMP‐2. The type of surface modification and the specific surface area derived from the fiber thickness had an important influence on the degree of protein loading. Coating the PCL fibers with polydopamine resulted in the binding of the largest BMP‐2 quantity per surface area. However, most of the binding was irreversible over the investigated period of time, causing a low release in vitro. PCL fiber mats with a chitosan‐graft‐PCL coating and an additional alginate layer, as well as PCL fiber mats with an air plasma surface modification boundless BMP‐2, but the immobilized protein could almost completely be released. With polydopamine and plasma modifications as well as with unmodified PCL, high amounts of BMP‐2 could also be attached directly to the surface. Integration of BMP‐2 into the chitosan nanogel functionalization considerably increased binding on all hydrophilized surfaces and resulted in a sustained release with an initial burst release of BMP‐2 without detectable loss of bioactivity in vitro.

ELISA- and Activity Assay-Based Quantification of BMP-2 Released In Vitro Can Be Biased by Solubility in “Physiological” Buffers and an Interfering Effect of Chitosan

“…The implant prototypes are based on modified polycaprolactone (PCL) fiber mats which were described before [26]. The structure of the implant prototypes is shown schematically in Figure 1.…”

“…The fiber mat samples were coated with chitosan tripolyphosphate (CS-TPP) nanoparticles as previously described [26]. In order to obtain chitosan with the desired solubility properties, the degree of acetylation (DA) was adjusted.…”

“…Briefly, the PCL fiber mats were electrospun from a PCL (M n = 80,000 g mol −1 ) solution of 17 wt% in 2,2,2-trifluoroethanol at the Institute for Multiphase Processes at the Leibniz Universität Hannover, Germany, according to an optimized electrospinning method described before [29]. The electrospun fiber mats with fiber diameters of about 2.5 µm and a thickness of about 0.33 mm (microscopically determined as previously described [26]) were coated with a chitosan-graft-PCL (CS-g-PCL) copolymer to generate a positively charged interlayer as previously described by de Cassan et al [29]. To obtain a negative surface charge, the CS-g-PCL coated fiber mats were additionally coated with an alginate layer (CS-g-PCL-Alg) by immersion in an aqueous solution of sodium alginate (5 mg mL −1 ) for 10 min.…”

“…The further progress of the release was compared with that of fiber mats that had been in PTB from the beginning. BMP-2-containing implant prototypes were produced by incubating stacks of four fiber mat samples in BMP-2-containing nanoparticle suspensions for 15 min, which in previous studies resulted in a BMP-2 loading of about 105 ± 16 ng per mg of fiber mat [26]. In order to produce implant prototypes without BMP-2, nanoparticle suspensions without BMP-2 were used accordingly.…”

“…We were interested in the potential influence of poor BMP-2 solubility in physiological buffers like PBS [24] on the outcome of in vitro release tests. Furthermore, chitosan, which may be applied in controlled release systems for BMP-2 [25,26], was investigated as possible interfering substance. Although both, BMP-2 and chitosan, are positively charged at physiological pH, molecular dynamics simulations revealed an attractive interaction of these two substances [27].…”