Melt electrospinning writing (MEW) is an emerging additive manufacturing technique that enables the design and fabrication of micrometer-thin fibrous scaffolds made of biocompatible and biodegradable polymers. By using a computer-aided deposition process, a unique control over pore size and interconnectivity of the resulting scaffolds is achieved, features highly interesting for tissue engineering applications. However, MEW has been mainly used to process low melting point thermoplastics such as poly(ε-caprolactone). Since this polymer exhibits creep and a reduction in modulus upon hydration, we manufactured scaffolds of poly(L-lactide-co-ε-caprolactone-co-acryloyl carbonate) (poly(LLA-ε-CL-AC)), a photo-cross-linkable and biodegradable polymer, for the first time. We show that the stiffness of the scaffolds increases significantly (up to ∼10-fold) after cross-linking by UV irradiation at room temperature, compared with un-cross-linked microfiber scaffolds. The preservation of stiffness and high average fiber modulus (370 ± 166 MPa) within the cross-linked hydrated scaffolds upon repetitive loading (10% strain at 1 Hz up to 200,000 cycles) suggests that the prepared scaffolds may be of potential interest for soft connective tissue engineering applications. Moreover, the approach can be readily adapted through manipulation of polymer properties and scaffold geometry to prepare structures with mechanical properties suitable for other tissue engineering applications.

Damaged tendons and ligaments are serious and frequently occurring injuries worldwide. Recent therapies, including autologous grafts, still have severe disadvantages leading to a demand for synthetic alternatives. Materials envisioned to induce tendon and ligament regeneration should be degradable, cytocompatible and mimic the ultrastructural and mechanical properties of the native tissue. Specifically, we utilised photo-cross-linkable polymers for additive manufacturing (AM) with MEW. In this way, we were able to direct-write cytocompatible fibres of a few micrometres thickness into crimp-structured elastomer scaffolds that mimic the non-linear biomechanical behaviour of tendon and ligament tissue.

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Liquid, injectable hydrophobic polymers have advantages as degradable drug delivery vehicles; however, polymers examined for this purpose to date form acidic degradation products that may damage acid-sensitive drugs. Herein, we report on a new viscous liquid vehicle, poly(trimethylene carbonate-co-5-hydroxytrimethylene carbonate), which degrades through intramolecular cyclization producing glycerol, carbon dioxide, and water-soluble trimethylene carbonate. Copolymer degradation durations from weeks to months were achieved with the 5-hydroxy-trimethylene carbonate (HTMC) content of the oligomer having the greatest impact on the degradation rate, with oligomers possessing a higher HTMC content degrading fastest. The degradation products were non-cytotoxic towards 3T3 fibroblasts and RAW 264.7 macrophages. These copolymers can be injected manually through standard gauge needles and, importantly, during in vitro degradation, the microenvironmental pH within the oligomers remained near neutral. Complete and sustained release of the acid-sensitive protein vascular endothelial growth factor was achieved, with the protein remaining highly bioactive throughout the release period. These copolymers represent a promising formulation for local and sustained release of acid sensitive drugs.

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With the objective of generating photo-responsive polymers, carbonate monomers with pendant cinnamoyl or coumarin moieties, which are capable of photo-reversible dimerization, were synthesized.

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Untreated articular cartilage damage normally results in osteoarthritis and even disability that affects millions of people. However, both the existing surgical treatment and tissue engineering approaches are unable to regenerate the original structures of articular cartilage durably, and new strategies for integrative cartilage repair are needed. Gene therapy provides local production of therapeutic factors, especially guided by biomaterials can minimize the diffusion and loss of the genes or gene complexes, achieve accurate spatiotemporally release of gene products, thus provideing long-term treatment for cartilage repair. The widespread application of gene therapy requires the development of safe and effective gene delivery vectors and supportive gene-activated matrices. Among them, polymeric biomaterials are particularly attractive due to their tunable physiochemical properties, as well as excellent adaptive performance. This paper reviews the recent advances in polymeric biomaterial-guided gene delivery for cartilage repair, with an emphasis on the important role of polymeric biomaterials in delivery systems.