Collagen soft tissue fillers suffer from fast reabsorption, which minimizes their use as a tissue-engineered construct. Extensive cross-linking can be utilized to extend longevity, but changes in microstructure and biomechanics can have deleterious effects. To enhance longevity while still achieving a natural microstructure, gold nanoparticles (AuNPs) were conjugated to fibrilized collagen and homogenized into an injectable form for use as a soft tissue filler. A long-term animal study in Yucatan swine was conducted to assess biocompatibility and longevity. Two formulations of the AuNP-collagen were compared to porcine cross-linked collagen and commercially available hyaluronic acid (HA). The results of the study demonstrated that the AuNPs may provide enhanced longevity over 6 months compared to HA and cross-linked collagen. Irritation scores indicated that the AuNP-collagen construct (AuNP-CC) demonstrated low irritation compared to the cross-linked collagen and HA while histology scores demonstrated good biocompatibility. Overall, it may be possible to utilize AuNPs to stabilize and increase the longevity of CC while still achieving biocompatibility.

Decellularized allograft tissue is used for a wide array of tissue injuries and repair with tenons and ligament repair being among the most common. However, despite their frequent use there is concern over the lengthy inflammatory period and slow healing associated with allografts. One promising solution has been the use of nanoparticles. There is currently no easy, fast method to achieve consistent conjugation of nanoparticles to tissue. The available conjugation methods can be time-consuming and/or may create numerous cytotoxic byproducts. Genipin, a naturally derived crosslinking agent isolated from the fruits of Gardenia jasminoides was investigated as a conjugation agent to achieve fast, consistent crosslinking without cytotoxic byproducts. The rational of utilizing genipin is that is reacts spontaneously with amino-group-containing compounds such as proteins, collagens, and gelatins, and does not require extensive washing after conjugation. Porcine diaphragm tendons were decellularized and then immersed in cysteamine functionalized gold nanoparticles and genipin for various time points. Tissue scaffolds were tested for the degree of crosslinking, gold nanoparticle concentrations, and fibroblast attachment and biocompatibility. Results demonstrated that genipin can successfully and reproducibly attach gold nanoparticles to tissue in as little as 15 min. The genipin had no cytotoxic effects and improved fibroblast attachment and proliferation. Genipin can be used to attach gold nanoparticles to tissue in a fast, cell safe manner.

Injectable collagen microspheres (CMs) have the potential to be an excellent tool to deliver various modulatory agents or to be used as a cellular transporter. A drawback has been the difficulty in producing reliable and spherical CMs. A crosslinker‐free method to fabricate CMs was developed using liquid collagen (LC) in a water‐in‐oil emulsion process with varying concentrations of surfactant span‐80. Different emulsion times of up to 16‐hr were utilized to produce the CMs. Visual microscopy and scanning electron microscopy were utilized to determine the morphology of the CMs. To determine the fibril nature of the CMs, focus ion beam milling, energy dispersive spectroscopy, and Fourier Transformation‐Infrared spectroscopy were performed. A cell biocompatibility study was performed to assess the biocompatibility of the CMs. The results demonstrated that consistent spherical CMs were achievable by changing the span‐80 concentration. The CMs were fibrilized not only at the surface, but also at the core. Both the 1‐ and 16‐hr emulsion time demonstrated biocompatibility and it appeared that the cells preferentially adhered to the CMs. This crosslinker‐free method to fabricate CMs resulted in spherical, stable, biocompatible CMs, and could be an excellent technique for multiple tissue engineering applications.

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