Electrospun biodegradable poly(ε-caprolactone) membranes for annulus fibrosus repair: Long-term material stability and mechanical competence

BACKGROUND

Electrospun (ES) poly(ɛ-caprolactone) (PCL) is widely used to provide critical mechanical support in tissue engineering and regenerative medicine applications. Therefore, there is a clear need for understanding the change in the mechanical response of the membranes as the material degrades in physiological conditions.

STUDY DESIGN

ES membranes with fiber diameters from 1.6 to 6.7 μm were exposed to in vitro conditions at 37°C in Dulbecco's modified Eagle's medium (DMEM) or dry for up to 6 months.

METHODS

During this period, the mechanical properties were assessed using cyclic mechanical loading, and material properties such as crystallinity and ester bond degradation were measured.

RESULTS

No significant difference was found for any parameters between samples kept dry and in DMEM. The increase in crystallinity was linear with time, while the ester bond degradation showed an inverse logarithmic correlation with time. All samples showed an increase in modulus with exposure time for the first loading cycle. Modulus changes for the consecutive loading cycles showed a nonlinear relationship to the exposure time that depended on membrane type and maximum strain. In addition, the recovered elastic range showed an expected increase with the maximum strain reached. The mechanical response of ES membranes was compared to experimental tensile properties of the human annulus fibrosus tissue and an in silico model of the intervertebral disk. The modulus of the tested membranes was at the lower range of the values found in literature, while the elastically recoverable strain after preconditioning for all membrane types lies within the desired strain range for this application.

CONCLUSION

The long-term assessment under application-specific conditions allowed to establish the mechanical competence of the electrospun PCL membranes. It can be concluded that with the use of appropriate fixation, the membranes can be used to create a seal on the damaged AF.

Polymer scaffolds facilitate spinal cord injury repair

During the past decades, improving patient neurological recovery following spinal cord injury (SCI) has remained a challenge. An effective treatment for SCI would not only reduce fractured elements and isolate developing local glial scars to promote axonal regeneration but also ameliorate secondary effects, including inflammation, apoptosis, and necrosis. Three-dimensional (3D) scaffolds provide a platform in which these mechanisms can be addressed in a controlled manner. Polymer scaffolds with favorable biocompatibility and appropriate mechanical properties have been engineered to minimize cicatrization, customize drug release, and ensure an unobstructed space to promote cell growth and differentiation. These properties make polymer scaffolds an important potential therapeutic platform. This review highlights the recent developments in polymer scaffolds for SCI engineering. STATEMENT OF SIGNIFICANCE: How to improve the efficacy of neurological recovery after spinal cord injury (SCI) is always a challenge. Tissue engineering provides a promising strategy for SCI repair, and scaffolds are one of the most important elements in addition to cells and inducing factors. The review highlights recent development and future prospects in polymer scaffolds for SCI therapy. The review will guide future studies by outlining the requirements and characteristics of polymer scaffold technologies employed against SCI. Additionally, the peculiar properties of polymer materials used in the therapeutic process of SCI also have guiding significance to other tissue engineering approaches.

Preparation of thermo-responsive drug-loaded nanofibrous films created by electrospinning

We prepared thermosensitive and biocompatible drug-loaded nanofibrous films by an electrospinning technique using a block copolymer, poly(N-isopropylacrylamide)-b-poly(l-lactide) (PNLA), and poly(l-lactide) (PLLA). The copolymer PNLA was synthesized by the radical polymerization of N-isopropylacrylamide (NIPAAm), followed by the ring-opening polymerization of l-lactide. The properties of PNIPAAm and PNLA were selectively discussed based on the results of NMR, FT-IR, GPC, and CA analyses. Because of the low molecular weight of PNIPAAm and PNLA and the hydrolysis of PNLA resulting from its hydrophilicity, these copolymers were inappropriate for electrospinning separately. Hence, a mixture of PNLA and PLLA was used to prepare electrospun nanofibrous films. SEM images of the PNLA/PLLA electrospun films showed that homogeneous fibres with smooth surfaces were obtained. In vitro release studies indicated that the drug-release rate of the PNLA/PLLA electrospun nanofibrous films can be adjusted by the content and molecular weight of PNLA and by the environmental temperature. The results demonstrate that electrospinning is a promising way to create stimuli-responsive fibrous films with potential applications in the design of controllable drug delivery systems.

Thermosensitive and biocompatible PNLA/PLLA drug-loaded nanofibrous films with different morphologies and controlled drug release behaviors by electrospinning technique.

Preparation, characterization, and biocompatibility evaluation of poly(Nɛ-acryloyl-L-lysine)/hyaluronic acid interpenetrating network hydrogels

In the present study, poly(Nɛ-acryloyl-L-lysine)/hyaluronic acid (pLysAAm/HA) interpenetrating network (IPN) hydrogels were successfully fabricated through the combination of hydrazone bond crosslinking and photo-crosslinking reactions. The HA hydrogel network was first synthesized from 3,3'-dithiodipropionate hydrazide-modified HA and polyethylene glycol dilevulinate by hydrazone bond crosslinking. The pLysAAm hydrogel network was prepared from Nɛ-acryloyl-L-lysine and N,N'-bis(acryloyl)-(L)-cystine by photo-crosslinking. The resultant pLysAAm/HA hydrogels had a good shape recovery property after loading and unloading for 1.5 cycles (up to 90%) and displayed a highly porous microstructure. Their compressive moduli were at least 5 times higher than that of HA hydrogels. The pLysAAm/HA hydrogels had an equilibrium swelling ratio of up to 37.9 and displayed a glutathione-responsive degradation behavior. The results from in vitro biocompatibility evaluation with pre-osteoblasts MC3T3-E1 cells revealed that the pLysAAm/HA hydrogels could support cell viability and proliferation. Hematoxylin and eosin staining indicated that the pLysAAm/HA hydrogels allowed cell and tissue infiltration, confirming their good in vivo biocompatibility. Therefore, the novel pLysAAm/HA IPN hydrogels have great potential for bone tissue engineering applications.