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Open Access Publications from the University of California

Scholarly Works (8 results)

  • Article
  • Peer Reviewed
UC Berkeley Previously Published Works (2021)
Numerous surgical procedures are daily performed worldwide to replace and repair damaged tissue. Tissue engineering is the field devoted to the regeneration of damaged tissue through the incorporation of cells in biocompatible and biodegradable porous constructs, known as scaffolds. The scaffolds act as host biomaterials of the incubating cells, guiding their attachment, growth, differentiation, proliferation, phenotype, and migration for the development of new tissue. Furthermore, cellular behavior and fate are bound to the biodegradation of the scaffold during tissue generation. This article provides a critical appraisal of how key biomaterial scaffold parameters, such as structure architecture, biochemistry, mechanical behavior, and biodegradability, impart the needed morphological, structural, and biochemical cues for eliciting cell behavior in various tissue engineering applications. Particular emphasis is given on specific scaffold attributes pertaining to skin and brain tissue generation, where further progress is needed (skin) or the research is at a relatively primitive stage (brain), and the enumeration of some of the most important challenges regarding scaffold constructs for tissue engineering.
    Cover page: Design Challenges in Polymeric Scaffolds for Tissue Engineering
    • Thesis
    • Peer Reviewed
    UC Berkeley Electronic Theses and Dissertations (2022)

    After billions of years of evolution, it is no wonder that biological systems are treated as an invaluable source of inspiration in the development of new materials. Despite the limited number of constituents in their physical environment, natural materials display a wide range of mechanical properties and functions unmatched by their engineering counterparts. Capitalizing on the infinite reservoir of inspiration that nature offers, this work focuses on the fundamental understanding of the structure-chemical composition-property relationships of constituents present in several marine species and provides a platform for designing new materials inspired by these species.

    Marine mussels secrete several adhesive proteins that function in aqueous environments against turbulent conditions without mechanical failure and are a prominent example of permanent adhesion in nature, in which human-made adhesives cannot compete. Mussel-inspired coatings, derived from the spontaneous polymerization of dopamine, so-called ‘polydopamine’ coatings (pDA), have been widely reported in the literature for their ability to be deposited on a variety of substrates. However, the composition of pDA remains unknown, mainly due to its insoluble and heterogeneous nature. In addition, pDA coatings exhibit poor mechanical resistance to delamination and abrasion. The first part of this thesis is focused on understanding the molecular mechanisms that give rise to the adhesion of pDA using single-molecule force spectroscopy (SMFS). The results favor a ‘polymer’ model of pDA structure, casting doubt on models suggesting polydopamine is a supramolecular aggregate of small molecules and oligomers. Next, considering that pDA is polymeric in nature, thermal and laser annealing methods that enhance the scratch and shear resistance of pDA are reported.

    The second part of this thesis is devoted to elucidating the underlying physicochemical principles employed by non-mineralized tissues to achieve hard, stiff, and tough properties. Specifically, the jaws of Glycera worm -a venom injecting bloodworm- comprised of protein, melanin, and copper ions combine a unique range of mechanical properties usually encountered in highly mineralized tissues. The molecular and nanoscale mechanics, the morphology and structure of protein and melanin, and the interactions among individual constituents in Glycera jaws are investigated. Firstly, the Glycine- and Histidine-rich Glycera multi-tasking protein (GMTP) using a recombinant jaw protein is characterized, revealing six functions critical for jaw formation and performance. Subsequently, the tolerance of the jaws to induced contact damage is studied to probe the reinforcement strategies employed. Results showed that multiscale interfacial energy dissipation mechanisms could achieve an optimized balance among mutually exclusive properties such as strength and toughness. These studies can offer new opportunities for harnessing and exploiting bioinspired strategies in designing lightweight yet strong polymer composites, blends, networks and/or thin films.

      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2019)
      Inspired by the adhesive proteins of mussels, polydopamine (pDA) has emerged as one of the most widely employed materials for surface functionalization. Despite numerous attempts at characterization, little consensus has emerged regarding whether pDA is a covalent polymer or a noncovalent aggregate of low molecular weight species. Here, we employed single-molecule force spectroscopy (SMFS) to characterize pDA films. Retraction of a pDA-coated cantilever from an oxide surface shows the characteristic features of a polymer with contour lengths of up to 200 nm. pDA polymers are generally weakly bound to the surface through much of their contour length, with occasional "sticky" points. Our findings represent the first direct evidence for the polymeric nature of pDA and provide a foundation upon which to better understand and tailor its physicochemical properties.
        Cover page: Direct Evidence for the Polymeric Nature of Polydopamine
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2019)
        Bovine caudal discs have been widely used in spine research due to their increased availability, large size, and mechanical and biochemical properties that are comparable to healthy human discs. However, despite their extensive use, the radial variations in bovine disc composition have not yet been rigorously quantified with high spatial resolution. Previous studies were limited to qualitative analyses or provided limited spatial resolution in biochemical properties. Thus, the main objective of this study was to provide quantitative measurements of biochemical composition with higher spatial resolution than previous studies that employed traditional biochemical techniques. Specifically, traditional biochemical analyses were used to measure water, sulfated glycosaminoglycan, collagen, and DNA contents. Gravimetric water content was compared to data obtained through Raman spectroscopy and differential scanning calorimetry. Additionally, spatial distribution of lipids in the discs collagen network was visualized and quantified, for the first time, using multi-modal second harmonic generation (SHG) and Coherent anti-Stokes Raman (CARS) microscopy. Some heterogeneity was observed in the nucleus pulposus, where the water content and water-to-protein ratio of the inner nucleus were greater than the outer nucleus. In contrast, the bovine annulus fibrosus exhibited a more heterogeneous distribution of biochemical properties. Comparable results between orthohydroxyproline assay and SHG imaging highlight the potential benefit of using SHG microscopy as a less destructive method for measuring collagen content, particularly when relative changes are of interest. CARS images showed that lipid deposits were distributed equally throughout the disc and appeared either as individual droplets or as clusters of small droplets. In conclusion, this study provided a more comprehensive assessment of spatial variations in biochemical composition of the bovine caudal disc.
          Cover page: Radial variation in biochemical composition of the bovine caudal intervertebral disc.
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2019)
          Bovine caudal discs have been widely used in spine research due to their increased availability, large size, and mechanical and biochemical properties that are comparable to healthy human discs. However, despite their extensive use, the radial variations in bovine disc composition have not yet been rigorously quantified with high spatial resolution. Previous studies were limited to qualitative analyses or provided limited spatial resolution in biochemical properties. Thus, the main objective of this study was to provide quantitative measurements of biochemical composition with higher spatial resolution than previous studies that employed traditional biochemical techniques. Specifically, traditional biochemical analyses were used to measure water, sulfated glycosaminoglycan, collagen, and DNA contents. Gravimetric water content was compared to data obtained through Raman spectroscopy and differential scanning calorimetry. Additionally, spatial distribution of lipids in the disc's collagen network was visualized and quantified, for the first time, using multi-modal second harmonic generation (SHG) and Coherent anti-Stokes Raman (CARS) microscopy. Some heterogeneity was observed in the nucleus pulposus, where the water content and water-to-protein ratio of the inner nucleus were greater than the outer nucleus. In contrast, the bovine annulus fibrosus exhibited a more heterogeneous distribution of biochemical properties. Comparable results between orthohydroxyproline assay and SHG imaging highlight the potential benefit of using SHG microscopy as a less destructive method for measuring collagen content, particularly when relative changes are of interest. CARS images showed that lipid deposits were distributed equally throughout the disc and appeared either as individual droplets or as clusters of small droplets. In conclusion, this study provided a more comprehensive assessment of spatial variations in biochemical composition of the bovine caudal disc.
            Cover page: Radial variation in biochemical composition of the bovine caudal intervertebral disc
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2019)
            A synthetic strategy to incorporate catechol functional groups into benzoxazine thermoset monomers was developed, leading to a family of bioinspired small-molecule resins and main-chain polybenzoxazines derived from biologically available phenols. Lap-shear adhesive testing revealed a polybenzoxazine derivative with greater than 5 times improved shear strength on aluminum substrates compared to a widely studied commercial benzoxazine resin. Derivative synthesis identified the catechol moiety as an important design feature in the adhesive performance and curing behavior of this bioinspired thermoset. Favorable mechanical properties comparable to commercial resin were maintained, and glass transition temperature and char yield under nitrogen were improved. Blending of monomers with bioinspired main-chain polybenzoxazine derivatives provided formulations with enhanced shear adhesive strengths up to 16 MPa, while alloying with commercial core-shell particle-toughened epoxy resins led to shear strengths exceeding 20 MPa. These results highlight the utility of bioinspired design and the use of biomolecules in the preparation of high-performance thermoset resins and adhesives with potential utility in transportation and aerospace industries and applications in advanced composites synthesis.
              Cover page: Bioinspired Design Provides High‐Strength Benzoxazine Structural Adhesives
              • Article
              • Peer Reviewed
              UC Santa Barbara Previously Published Works (2022)
              Bloodworm jaws are composites of protein, melanin, and both mineral and ionic copper. To date, nanomechanical tests have correlated the ionic copper and melanin with hardness and wear resistance, but the function of protein is uncertain. Here, we characterize a Gly- and His-rich protein called multi-tasking protein (MTP) and, using recombinant protein, show that it performs six distinct functions critical for jaw formation and performance, namely (1) recruiting 22 equiv of Cu2+, (2) mediating a liquid-liquid phase separation of the MTP-copper complex, (3) catalyzing the oxidation of 3,4-dihydroxyphenylalanine (Dopa) to melanin, (4) templating the interfacial polymerization of melanin, (5) integrating melanin and itself into thin films and fibers, and (6) providing intermolecular cohesion through Cu bridging. MTP achieves all these by assuming unprecedented roles as a building block, organizer, and fabricator—a processing feat of considerable relevance to the autonomous production of other polymer composites, blends, and/or networks.
                Cover page: A multi-tasking polypeptide from bloodworm jaws: Catalyst, template, and copolymer in film formationCreative Commons 'BY-ND' version 4.0 license
                • Article
                • Peer Reviewed
                UC Berkeley Previously Published Works (2020)
                Polydopamine (PDA) is a simple and versatile conformal coating material that has been proposed for a variety of uses; however in practice its performance is often hindered by poor mechanical properties and high roughness. Here, we show that blue-diode laser annealing dramatically improves mechanical performance and reduces roughness of PDA coatings. Laser-annealed PDA (LAPDA) was shown to be >100-fold more scratch resistant than pristine PDA and even better than hard inorganic substrates, which we attribute to partial graphitization and covalent coupling between PDA subunits during annealing. Moreover, laser annealing provides these benefits while preserving other attractive properties of PDA, as demonstrated by the superior biofouling resistance of antifouling polymer-grafted LAPDA compared to PDA modified with the same polymer. Our work suggests that laser annealing may allow the use of PDA in mechanically demanding applications previously considered inaccessible, without sacrificing the functional versatility that is so characteristic of PDA.
                  Cover page: Laser-induced graphitization of polydopamine leads to enhanced mechanical performance while preserving multifunctionality
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