The effect of ε-caproyl/d,l-lactyl unit composition on the hydrolytic degradation of poly(d,l-lactide-ran-ε-caprolactone)-poly(ethylene glycol)-poly(d,l-lactide-ran-ε-caprolactone)

Real-time and non-invasive fluorescence tracking of in vivo degradation of the thermosensitive PEGlyated polyester hydrogel

The real-time monitoring of materials degradation is crucial to determine the in vivo retention time and the design or screening of degradable biomaterials. However, in vivo performance cannot always be predicted through the traditional determination of in vitro erosion and current standard methods sacrifice samples or animals, preventing the sequential measurement of the same specimen. Herein, a non-invasive fluorescence imaging method was developed to sequentially follow in vivo loss of fluorescence signal to simultaneously characterize the hydrolytic and enzymatic degradation of PEGlyated polyester hydrogel. Rhodamine B was conjugated to thermosensitive amphiphilic triblock copolymer based on cyclic ether modified PCL and PEG (abbreviated as PECT) and no obvious influence on gelation time or gel strength was observed with the conjugation content under 0.121% (w/w). Both in vitro and in vivo degradation profiles followed linear fittings while in vivo and in vitro hydrogel degradation rates correlated in an exponential mathematical model, enabling the general prediction of in vivo erosion trends of new biomaterial formulations from in vitro data. This methodology possibly enabled rational design and rapid in vitro screening of degradable materials, and might be potentially extended to simultaneously determine the material erosion and speculate the drug release from a drug-incorporated scaffold, or the cell growth profile in tissue-engineering formulations.

Near-infrared fluorescence imaging for noninvasive trafficking of scaffold degradation

Biodegradable scaffolds could revolutionize tissue engineering and regenerative medicine; however, in vivo matrix degradation and tissue ingrowth processes are not fully understood. Currently a large number of samples and animals are required to track biodegradation of implanted scaffolds, and such nonconsecutive single-time-point information from various batches result in inaccurate conclusions. To overcome this limitation, we developed functional biodegradable scaffolds by employing invisible near-infrared fluorescence and followed their degradation behaviors in vitro and in vivo. Using optical fluorescence imaging, the degradation could be quantified in real-time, while tissue ingrowth was tracked by measuring vascularization using magnetic resonance imaging in the same animal over a month. Moreover, we optimized the in vitro process of enzyme-based biodegradation to predict implanted scaffold behaviors in vivo, which was closely related to the site of inoculation. This combined multimodal imaging will benefit tissue engineers by saving time, reducing animal numbers, and offering more accurate conclusions.

Fluorescent labeling of chitosan for use in non-invasive monitoring of degradation in tissue engineering

The establishment of non-invasive analytical tools for assessing the in-situ use of biomaterials for surgical implants or scaffolds in tissue engineering and polymer-based therapies is fundamental. This study established a method for fluorescent tracking of the degradation of a chitosan membrane scaffold for use in vitro in bioreactors and ultimately in vivo. The basis of this tracking system is a fluorescence emitting biomaterial obtained by covalent binding of the fluorophore tetramethylrhodamine isothiocyanate (TRITC) onto the backbone of chitosan. Using confocal microscopy, this study quantitated the reductions in fluorescence intensity of the membrane and correlated these decreases with weight loss during polymer breakdown, thereby providing a technique for non-destructively assessing the extent of degradation of chitosan materials over time in vitro. Using multispectral imaging in a mouse model, the study assessed the degradation profile of the fluorophore-labeled biomaterial in vivo in real time and identified the dispersing pathway of the chitosan membrane degradation products in vivo. The results revealed that TRITC conjugated chitosan was biocompatible and supported bone cell growth. The changes in fluorescence intensity correlated well with weight loss up to 16 weeks of in vitro culture and could be monitored over two weeks in vivo.

Characterization, degradation, and mechanical strength of poly(D,L-lactide-co-epsilon-caprolactone)-poly(ethylene glycol)-poly(D,L-lactide-co-epsilon-caprolactone)

A series of three biocompatible P(CL-co-LA)-PEG-P(CL-co-LA) copolymers were synthesized using ring-opening polymerization and characterized by 1H-NMR, gel permeation chromatography, DSC, dynamic-mechanical analysis, and X-ray diffraction. The number of monomer units was kept constant, while the D,L-LA fraction was varied so as to constitute 0, 30, or 70% of the end segments. The molecular weights were sufficiently high to eventually permit 3D scaffold preparation. A degradation study was carried out over 26 weeks, and the effect of monomer composition on the rate of degradation as well as on changes in mechanical strength was investigated. Pure polycaprolactone (PCL)-poly(ethylene glycol) (PEG)-PCL copolymer, P(100/0), was a crystalline material displaying no measurable mass loss, a 30% reduction in mean molecular weight (Mn), and only very slight changes in tensile strength. The random incorporation of 30 and 70% D,L-LA into the end sections of the polymer chain, produced more and more amorphous materials, exhibiting increasingly high rates of degradation, mass loss, and loss of tensile strength. Compared with random P(CL-co-LA), the presence of the PEG block was found both to improve hydrophilicity and thus the rate of degradation and to infer a stabilizing quality, thereby pacing the decrease in tensile strength during degradation. The tested copolymers range from materials exhibiting low mechanical strength and high rate of degradation to slow-degrading materials with high mechanical strength suitable, e.g., for three-dimensional scaffolding.

In vitro homogeneous and heterogeneous degradation of poly(ε-caprolactone/polyethylene glycol/L-lactide): The absence of autocatalysis and the role of enzymes

This study investigated the in vitro degradation behavior of poly(epsilon-caprolactone/polyethylene glycol/L-lactide) (PCEL) in comparison with that of three other biodegradable polymers. Polymer membranes were incubated in pancreatin solution, Ringer's solution, and distilled water at 37 degrees C for up to 20 weeks. Characterization involved measuring weight loss, observing the morphological changes by scanning electron microscopy (SEM), analyzing molecular weight using size exclusion chromatography (SEC), and studying the crystalline structure using differential scanning calorimetry (DSC). The hydrolysis in a simple aqueous solution experienced no autocatalysis, which was attributed to the high permeability of PCEL to water-soluble degradation products. Similar degradation rates were recorded for the PCEL and poly(L,L-lactide) (PLLA) test membranes. In the presence of pancreatin, the PCEL membrane experienced rapid heterogeneous surface erosion likely caused by the selective loss of its surface PEG components under enzymatic action. Pancreatin also substantially increased the even physical resorption of the other test polymers by eliminating autocatalysis. This study demonstrated that autocatalysis commonly experienced by poly(alpha-hydroxyl acid) can be reduced through chemical formulation or high enzyme activity.