The advancement of tissue engineering is contingent upon the development and implementation of advanced biomaterials. Conductive polymers have demonstrated potential for use as a medium for electrical stimulation, which has shown to be beneficial in many regenerative medicine strategies including neural and cardiac tissue engineering. Melanins are naturally occurring pigments that have previously been shown to exhibit unique electrical properties. This study evaluates the potential use of melanin films as a semiconducting material for tissue engineering applications. Melanin thin films were produced by solution processing and the physical properties were characterized. Films were molecularly smooth with a roughness (Rms) of 0.341 nm and a conductivity of 7.00 ± 1.10 × 10−5 S cm−1 in the hydrated state. In vitro biocompatibility was evaluated by Schwann cell attachment and growth as well as neurite extension in PC12 cells. In vivo histology was evaluated by examining the biomaterial–tissue response of melanin implants placed in close proximity to peripheral nerve tissue. Melanin thin films enhanced Schwann cell growth and neurite extension compared to collagen films in vitro. Melanin films induced an inflammation response that was comparable to silicone implants in vivo. Furthermore, melanin implants were significantly resorbed after 8 weeks. These results suggest that solution-processed melanin thin films have the potential for use as a biodegradable semiconducting biomaterial for use in tissue engineering applications.

Elastomeric networks are increasingly being investigated for a variety of biomedical applications including drug delivery and tissue engineering. However, in some cases, their preparation requires the use of harsh processing conditions (e.g., high temperature), which limits their biomedical application. Herein, we demonstrate the ability to form elastomeric networks from poly(glycerol-co-sebacate) acrylate (PGSA) under mild conditions while preserving a wide range of physical properties. These networks presented a Young's modulus between 0.05 and 1.38 MPa, an ultimate strength from 0.05 to 0.50 Mpa, and elongation at break between 42% and 189% strain, by varying the degree of acrylation (DA) of PGSA. The in vitro enzymatic and hydrolytic degradation of the polymer networks was dependent on the DA. The copolymerization of poly(ethylene glycol) diacrylate with PGSA allowed for an additional control of mechanical properties and swelling ratios in an aqueous environment, as well as enzymatic and hydrolytic degradation. Photocured PGSA networks demonstrated in vitro biocompatibility as judged by sufficient human primary cell adherence and subsequent proliferation into a confluent monolayer. These photocurable degradable elastomers could have potential application for the encapsulation of temperature-sensitive factors and cells for tissue engineering.

We have developed a family of synthetic biodegradable polymers that are composed of structural units endogenous to the human metabolism, designated poly(polyol sebacates) (PPS) polymers. Material properties of PPS polymers can be tuned by altering the polyol monomer and reacting stiochiometric ratio of sebacic acid. These thermoset networks exhibited tensile Young's moduli ranging from 0.37 ± 0.08 to 378 ± 33 MPa with maximum elongations at break from 10.90 ± 1.37 to 205.16 ± 55.76%, and glass-transition temperatures ranged from ~7 to 46 °C. In vitro degradation under physiological conditions was slower than in vivo degradation rates observed for some PPS polymers. PPS polymers demonstrated similar in vitro and in vivo biocompatibility compared to poly (L-lactic-co-glycolic acid) (PLGA).

Currently available synthetic biodegradable elastomers are primarily composed of crosslinked aliphatic polyesters, which suffer from deficiencies including (1) high crosslink densities, which results in exceedingly high stiffness, (2) rapid degradation upon implantation, or (3) limited chemical moieties for chemical modification. Herein, we have developed poly(1,3-diamino-2-hydroxypropane-co-polyol sebacate)s, a new class of synthetic, biodegradable elastomeric poly(ester amide)s composed of crosslinked networks based on an amino alcohol. These crosslinked networks feature tensile Young's modulus on the order of 1MPa and reversable elongations up to 92%. These polymers exhibit in vitro and in vivo biocompatibility. These polymers have projected degradation half-lives up to 20 months in vivo.

Synthetic biodegradable polymers have made a considerable impact in various fields of biomedical engineering, such as drug delivery and tissue engineering. The design of synthetic biodegradable polymers for bioengineering purposes is challenging because of the application-specific constraints on the physical properties, including mechanical compliance and degradation rates, and the need for biocompatibility and low cytotoxicity.[1] The monomer selection frequently limits the range of required material properties. Our goal was to design a class of synthetic biopolymers based on a monomer that possesses a wide range of properties that are biologically relevant. This monomer ideally should be: (1) multifunctional to allow the formation of randomly crosslinked networks and a wide range of crosslinking densities; (2) nontoxic; (3) endogenous to the human metabolic system; (4) FDA approved; and (5) preferably inexpensive. We chose xylitol as it meets these criteria. We hypothesized that biodegradable polyesters could be obtained through copolymerization reactions with polycarboxylic acids; the hydration of such biodegradable polymers could be controlled by tuning the different compositions and stoichiometry of the reacting monomer. Here, we describe xylitol-based polymers that realize this design. Polycondensation of xylitol with watersoluble citric acid yielded biodegradable, water-soluble polymers. Acrylation of this polymer resulted in an elastomeric photocrosslinkable hydrogel. Polycondensation of xylitol with the water-insoluble sebacic acid monomer produced tough, biodegradable elastomers with tunable mechanical and degradation properties. These xylitol-based polymers exhibited excellent in vitro and in vivo biocompatibility compared to the well-characterized poly(L-lactic-co-glycolic acid) (PLGA), and are promising biomaterials. Sebacic acid (a metabolite in the oxidation of fatty acids) and citric acid (a metabolite in the Krebs cycle) were chosen as the reacting monomers for their proven biocompatibility; [2,3] they are also FDA-approved compounds. Polycondensation of xylitol with sebacic acid produced water-insoluble waxy prepolymers (termed PXS prepolymers). PXS prepolymers with a monomer ratio of xylitol: sebacic acid of 1:1 and 1:2 were synthesized and had a weight-average molecular weight (M w ) of 2443 g/mol (M n ¼ 1268 g/mol, polydispersity index (PDI) 1.9) and 6202 g/mol (M n ¼ 2255 g/mol, PDI 2.7), respectively. The PXS prepolymers were melted into the desired form and cured by polycondensation (120 8C, 40 m Torr for 4 days, 1 Torr ¼ 133.3 Pa) to yield low-modulus (PXS 1:1) and high-modulus (PXS 1:2) elastomers. PXS prepolymers are soluble in ethanol, dimethyl sulfoxide, tetrahydrofuran and acetone, which allows processing into more complex geometries. Polycondensation of xylitol with citric acid resulted in a water-soluble prepolymer (designated PXC prepolymer), of which the M w was 298 066 g/mol and the M n was 22 305 g/mol (PDI 13.4), compared to linear poly(ethylene glycol) (PEG) standards. To cro...

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Biodegradable elastomers based on polycondensation reactions of xylitol with sebacic acid, referred to as poly(xylitol sebacate) (PXS) elastomers have recently been developed. Herein, we describe the in vivo behavior of PXS elastomers. Four PXS elastomers were synthesized, characterized and compared to poly(L-lactic-co-glycolic acid) (PLGA). PXS elastomers displayed a high level of structural integrity and form stability during degradation. The in vivo half-life ranged from approximately 3 to 52 weeks. PXS elastomers exhibited increased biocompatibility compared to PLGA implants.

Biomaterials with a wide range of tunable properties are desirable for application-specific purposes. We have previously developed a class of elastomeric poly(ester amides) based on the amine alcohol 1,3-diamino-2-hydroxypropane termed poly(1,3-diamino-2-hydroxypropane-co-polyol sebacate) or APS. In this work, we have synthesized and characterized formulations of APS polymers and studied the degradation of these polymers in vitro and in vivo. It was found that the chemical, physical, and mechanical properties of APS polymers could be tuned by adjusting monomer feed ratios and polymerization conditions. The degradation kinetics could also be greatly influenced by altering the formulation of APS polymers. In vivo degradation half-lives ranged from 6 to approximately 100 weeks. Furthermore, the dominant degradation mechanism (i.e. hydrolytic or enzymatic) could be controlled by adjusting the specific formulation of the APS polymer. On the basis of the observed in vitro and in vivo biodegradation phenomena, we also propose that the primary modes of degradation are composition dependent.