In vivo biocompatibility study of degradable homo- versus multiblock copolymers and their (micro)structure compared to an established biomaterial

Natural and Synthetic Polymer Scaffolds Comprising Upconversion Nanoparticles as a Bioimaging Platform for Tissue Engineering

Modern biocompatible materials of both natural and synthetic origin, in combination with advanced techniques for their processing and functionalization, provide the basis for tissue engineering constructs (TECs) for the effective replacement of specific body defects and guided tissue regeneration. Here we describe TECs fabricated using electrospinning and 3D printing techniques on a base of synthetic (polylactic-co-glycolic acids, PLGA) and natural (collagen, COL, and hyaluronic acid, HA) polymers impregnated with core/shell β-NaYF₄:Yb³⁺,Er³⁺/NaYF₄ upconversion nanoparticles (UCNPs) for in vitro control of the tissue/scaffold interaction. Polymeric structures impregnated with core/shell β-NaYF₄:Yb³⁺,Er³⁺/NaYF₄ nanoparticles were visualized with high optical contrast using laser irradiation at 976 nm. We found that the photoluminescence spectra of impregnated scaffolds differ from the spectrum of free UCNPs that could be used to control the scaffold microenvironment, polymer biodegradation, and cargo release. We proved the absence of UCNP-impregnated scaffold cytotoxicity and demonstrated their high efficiency for cell attachment, proliferation, and colonization. We also modified the COL-based scaffold fabrication technology to increase their tensile strength and structural stability within the living body. The proposed approach is a technological platform for "smart scaffold" development and fabrication based on bioresorbable polymer structures impregnated with UCNPs, providing the desired photoluminescent, biochemical, and mechanical properties for intravital visualization and monitoring of their behavior and tissue/scaffold interaction in real time.

Multiblock copolymers type PDC- a family of multifunctional biomaterials for regenerative medicine1

Multiblock copolymers type PDC are polyetheresterurethanes composed of poly(ɛ-caprolactone) and poly(p-dioxanone) segments. They were designed as degradadable shape-memory polymers for medical devices, which can be implanted minimally-invasively. While providing structural support in the initial phase after implantation, they are capable to modulate soft tissue regeneration while degradation. In this perspective, we elucidate cell-material interactions, compatibility both in-vitro and in-vivo and biofunctionality of PDC, which represents a promising candidate biomaterial family especially for cardiovascular applications.

Anticytokine Activity Enhances Osteogenesis of Bioactive Implants

In dental clinical practice, systemic steroids are often applied at the end of implant surgeries to reduce postsurgical inflammation (tissue swelling, etc.) and to reduce patient discomfort. However, the use of systemic steroids is associated with generalized catabolic effects and with a temporarily reduced immunological competence. We hypothesize that by applying locally anticytokine antibodies (antitumor necrosis factor alpha and anti-interleukin-1 beta) together with a bioactive osteogenic implant at the time of the surgical intervention for the placement of a construct, we will be able to achieve the same beneficial effects as those using systemic steroids but are able to avoid the generalized antianabolic effects and the reduced immunocompetence effects, associated with the systemic use of steroids. In an adult rat model, a collagen sponge, soaked with the osteogenic agent bone morphogenetic protein-2, was used as an example for a bioactive implant material and was surgically placed subcutaneously. In the acute inflammatory phase after implantation (2 days after surgery) we investigated the local inflammatory tissue response, and 18 days postsurgically the efficiency of local osteogenesis (to assess possible antianabolic effects). We found that the negative control groups, treated postsurgically with systemic steroids, showed a significant suppression of both the inflammatory response and the osteogenetic activity, that is, they were associated with significant general antianabolic effects, even when steroids were used only at a low dose level. The local anticytokine treatment, however, was able to significantly enhance new bone formation activity, that is, the anabolic activity, over positive control values with BMP-2 only. However, the anticytokine treatment was unable to reduce the local inflammatory and swelling responses.

Tuning the mechanical properties and degradation properties of polydioxanone isothermal annealing

Polydioxanone (PPDO) is synthesized by ring-opening polymerization of p-dioxanone, using stannous octoate as the catalyst. The polarized optical micrograph (POM) shows thes pherulite growth rate of PPDO decreases with an increase in the isothermal crystallization temperature. PPDO is compression-molded into bars, and PPDO bars are subjected to isothermal annealing at a range of temperatures (Ta = 50, 60, 70, 80, 90, and 100 °C), and correspond to three different annealing times (ta = 1h, 2h, 3h). The effect on PPDO is investigated by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). With an increase in Ta and ta, the grain size and the degree of crystallinity also increase. Meanwhile, the tensile strength is significantly improved. The PPDO bars (90 °C, 2 h) reach the maximum crystallinity (57.21%) and the maximum tensile strength (41.1 MPa). Interestingly, the heat treatment process does not result in serious thermal degradation. It is observed that the hydrolytic degradation of the annealed PPDO is delayed to some extent. Thus, annealed PPDO might have potential applications, particularly in the fields of orthopedic fixation and tissue engineering.

Functional requirements for polymeric implant materials in head and neck surgery

BACKGROUND

The pharyngeal reconstruction is a challenging aspect after pharyngeal tumor resection. The pharyngeal passage has to be restored to enable oral alimentation and speech rehabilitation. Several techniques like local transposition of skin, mucosa and/or muscle, regional flaps and free vascularized flaps have been developed to reconstruct pharyngeal defects following surgery, in order to restore function and aesthetics. The reconstruction of the pharynx by degradable, multifunctional polymeric materials would be a novel therapeutical option in head and neck surgery.

MATERIALS AND METHODS

Samples of an ethylene-oxide sterilized polymer (diameter 10 mm, 200μm thick) were implanted for the reconstruction of a standardized defect of the gastric wall in rats in a prospective study. The stomach is a model for a "worst case" application site to test the stability of the implant material under extreme chemical, enzymatical, bacterial, and mechanical load.

RESULTS

Fundamental parameters investigated in this animal model were a local tight closure between the polymer and surrounding tissues, histological findings of tissue regeneration and systemic responses to inflammation. A tight anastomosis between the polymer and the adjacent stomach wall was found in all animals after polymer implantation (n = 42). Histologically, a regeneration with glandular epithelium was found in the polymer group. No differences in the systemic responses to inflammation were found between the polymer group (n = 42) and the control group (n = 21) with primary wound closure of the defect of the gastric wall.

CONCLUSIONS

A sufficient stability of the polymeric material is a requirement for the pharyngeal reconstruction with implant materials.