Biomimetic Biomaterials Research Articles

Bio-Inspired Morphogens and Biomimetic Biomaterials for Regenerative Medicine

AbstractRegenerative medicine is the science of design and manufacture of parts for functional restoration of damaged tissues due to cancer, disease and trauma. Morphogenesis is the developmental cascade of pattern formation, body plan establishment and differentiation of tissues culminating in adult form. Regeneration in general, recapitulates in parts, embryonic morphogenesis. Thus, the principles of morphogenesis can be applied to tissue engineering for regenerative medicine and surgery. The threekey ingredients for tissue engineering and regenerative medicine are inductive morphogens, responding stem cells, and extracellular matrix materials. Therefore bioactive morphogens can be integrated into materials for functional restoration by tissue engineering. A morphogen is a morphogenetic protein signal that acts on responding stem cells. Bone morphogenesis is induced by bone morphogenetic proteins (BMPs). BMPs play a role in pattern formation, cell differentiation, maintenance and regeneration of tissues. BMPs are pleiotropic and act on chemotaxis, mitosis and differentiation of progenitor stem cells. There are nearly twenty BMPs in the human genome. BMPs have actions beyond bone in development of teeth, heart, kidney, eye, skin, and brain. Thus, BMPs may be called body morphogenetic proteins. Stem cells are primordial cells with unlimited replicative potential and can be programmed by morphogens such as BMPs. Extracellular matrix is the native scaffolding material that can be used to deliver morphogens such as BMPs for tissue engineering of bone. Biomimetic materials are typically synthetic, polymeric structures that mimic extracellular matrix scaffolding by presenting the cellular binding sites found within collagens, fibronectin, proteoglycans and glycoproteins. Materials that mimic extracellular matrix scaffolding such as BMPs bind to collagens I&IV, heparan sulfate and heparin. BMPs bound to collagen acts as a composite biomaterial to initiate bone formation and the shape can be molded by an appropriate template. In addition to including BMPs in a carrier matrix, the geometry of the carrier matrix is critical for optimal tissue engineering. For example: collagen particles smaller than 44μm are feeble in bone induction compared to the coarse (420μm) particles. Gene therapy approaches using genes for morphogenesis such as BMPs allows a sustained, prolonged secretion of gene products. Thus, morphogens integrated into biomaterials may be useful in regenerative medicine.

Phospholipid Strategies in Biomineralization and Biomaterials Research

▪ Abstract This review summarizes recent advances and future research trends in the field of phospholipid-based biomaterials. Lipids play an important role in biomineralization and countless other biological processes, and they are receiving increasing attention for the synthesis of new biomimetic biomaterials. Several emerging strategies in biomaterials research take advantage of phospholipids to compartmentalize and/or template chemical reactions via self-assembled structures such as liposomes and tubules. Still others exploit the inherent biocompatibility of phospholipids and phospholipid-mimetic materials for use as novel tissue-contacting biomaterials that mimic biological membranes. In the future, phospholipid-based materials may be increasingly utilized as tools for the manipulation of cell and tissue responses to biomaterials, for controlled drug release, for reconstructive surgery, and as tissue-engineered constructs.

Induction of bone formation by recombinant human osteogenic protein-1 and sintered porous hydroxyapatite in adult primates.

A critical issue in tissue engineering and morphogenesis of bone is the development of novel biomimetic biomaterials that are capable of optimizing the biological activity of recombinant human bone morphogenetic and osteogenic proteins, which are molecules that initiate bone formation in vivo. From a therapeutic perspective, a carrier matrix is required for the local delivery of these proteins to evoke a desired osteogenic effect. In view of the affinity of these proteins for hydroxyapatite, which may reflect the in vivo supramolecular assembly of bone proteins bound to both the extracellular matrix and the mineral component of bone, we investigated the efficacy of single applications of different doses of human osteogenic protein-1 (hOP-1) adsorbed onto sintered porous hydroxyapatites for bone induction in orthotopic calvarial defects in 12 adult male baboons (Papio ursinus) and heterotopically in the rectus abdominis of four additional baboons. In orthotopic specimens, pretreatment of sintered porous hydroxyapatites with 100 microgram of hOP-1 in 500 microliter of 5 mM hydrochloric acid resulted in rapid and diffuse osteoinduction restricted within the porous spaces of the hydroxyapatite, as evaluated by histology and histomorphometry on day 30. Hydroxyapatites treated with 500 microgram of hOP-1 showed a different pattern of bone formation and distribution on day 30 as compared with the lower dose of the recombinant morphogen. Although bone formation was extensive with the higher dose, it was found on the endocranial and pericranial aspects of the specimens, enveloping the implanted hydroxyapatite carrier, and the internal porous spaces were occupied by a rich vascular network without any bone formation. By 90 and 365 days after the implantation of both doses of hOP-1, however, there was remodelling and complete penetration of the newly induced bone within the available porous spaces. The combination of hOP-1 and hydroxyapatite also showed extensive bone formation in heterotopic specimens harvested from the rectus abdominis muscle of the baboon using doses of 5, 25, and 45 microgram of hOP-1 per implant. These findings in the adult primate demonstrate extensive bone formation by hOP-1 adsorbed onto sintered porous hydroxyapatites and suggest that predictable osteogenesis in clinical contexts for treatment of craniofacial bone defects may be engineered using inorganic, nonimmunogenic, and carvable delivery systems that initiate osteogenesis with relatively low doses of recombinant osteogenic proteins, thus mimicking the macrostructure and microstructure of living bone.

Morphogenesis and tissue engineering of bone and cartilage: inductive signals, stem cells, and biomimetic biomaterials.

Morphogenesis is the developmental cascade of pattern formation, body plan establishment, and the architecture of mirror-image bilateral symmetry of many structures and asymmetry of some, culminating in the adult form. Tissue engineering is the emerging discipline of design and construction of spare parts for the human body to restore function based on principles of molecular developmental biology and morphogenesis governed by bioengineering. The three key ingredients for both morphogenesis and tissue engineering are inductive signals, responding stem cells, and the extracellular matrix. Among the many tissues in the human body, bone has considerable powers for regeneration and is a prototype model for tissue engineering based on morphogenesis. Implantation of demineralized bone matrix into subcutaneous sites results in local bone induction. This model mimics sequential limb morphogenesis and permitted the isolation of bone morphogens. Although it is traditional to study morphogenetic signals in embryos, bone morphogenetic proteins (BMPs), the inductive signals for bone, were isolated from demineralized bone matrix from adults. BMPs and related cartilage-derived morphogenetic proteins (CDMPs) initiate, promote, and maintain chondrogenesis and osteogenesis and have actions beyond bone. The symbiosis of bone inductive and conductive strategies are critical for tissue engineering, and is in turn governed by the context and biomechanics. The context is the microenvironment, consisting of extracellular matrix, which can be duplicated by biomimetic biomaterials such as collagens, hydroxyapatite, proteoglycans, and cell adhesion proteins including fibronectins. Thus, the rules of architecture for tissue engineering are an imitation of the laws of developmental biology and morphogenesis, and thus may be universal for all tissues, including bones and joints.

Ancillary Scientist Symposium: Skeletal Biology and Related Problems in Poultry

Among the many tissues in the human body bone has perhaps the highest potential for regeneration and repair. Bone grafts have been used by surgeons to aid in the repair of recalcitrant bone fractures. Urist made the key discovery that demineralized, lyophilized segments of rabbit bone induced new bone formation when implanted in an intramuscular site. Studies in my laboratory dissected the bone morphogenetic cascade into distinct steps such as chemotaxis and mitosis of progenitor stem cells and their differentiation into cartilage and replacement by bone. The sequential morphogenetic cascade is reminiscent of cartilage and bone morphogenesis in the embryonic limb bud with implications for isolation of morphogens for bone induction from demineralized extracellular matrix. It is traditional to isolate morphogens in fly and frog embryos by genetic approaches, expressed sequence tags, expression cloning, differential displays and subtractive hybridization. The information from flies and frogs are then extended to mice and men. I will demonstrate a nontraditional approach of morphogen isolation from adult bone by the biochemical grind and find approach. This type of approach has spawned a superfamily of bone morphogenetic proteins (BMP) and cartilage-derived morphogenetic proteins (CDMP). The BMP are pleiotropic molecules with discrete thresholds for their biological actions. The motogenic, mitogenic, and morphogenetic actions of BMP are concentration dependent. The BMP have actions beyond bone as gleaned from gene knockout experiments with homologous recombination. BMP have a pivotal role in heart, kidney, skin, eye, and tooth development. BMP elicit their actions via specific BMP receptors I and II. These are membrane bound serine/threonine protein kinases. The cytoplasmic substrate for BMP-receptor kinases are Smads 1, 5, and 8, which associate with Smad 4 prior to nuclear translocation to activate the transcriptional machinery. Mutations in BMP and CDMP (also known as GDF) have been implicated in abnormal skeletal development. For example mutations in CDMP 1 (GDF 5) has been identified in certain chondrodysplasias. The cloning of BMP and related morphogens has led to clinical applications in orthopedic surgery, dentistry, and plastic and reconstructive surgeries. Vignettes of clinical applications in orthopedics and craniofacial and periodontal surgeries will be exemplified. The emerging advances in BMP and skeletal development will facilitate the design and manufacture of spare parts for human skeleton based on tissue engineering principles. Tissue engineering is the science of manufacture of spare parts for the human body based on morphogens, stem cells, extracellular matrix-based biomimetic biomaterials, and bioengineering.

41] Biofilm and biofilm-related encrustation of urinary tract devices

This chapter focuses on the development of artificial urine models that simulate in vivo encrustation resulting from device-related infection and can be used to assess biomaterial encrustation and the ability of biomaterials to resist intraluminal blockage. The extent to which different urinary biomaterials will encrust in vivo is a problem that needs to be addressed if new, less encrusting biomaterials are to be discovered. The optimal level of agitation within a model is determined by the portion of the urinary tract in which the test biomaterial is destined to reside. Artificial urine models prove useful for testing novel biodegradable biomaterials for use as urinary prostheses. In practice, urine flow may encourage surface layers of the degradable polymer to be shed, thereby assisting the removal of encrusting deposits and adherent microorganisms. Such biomimetic biomaterials may have a role to play in the development of improved urinary tract devices.

Role of morphogenetic proteins in skeletal tissue engineering and regeneration.

Morphogenesis is the developmental cascade of pattern formation and body plan establishment, culminating in the adult form. It has formed the basis for the emerging discipline of tissue engineering, which uses principles of molecular developmental biology and morphogenesis gleaned through studies on inductive signals, responding stem cells, and the extracellular matrix to design and construct spare parts that restore function to the human body. Among the many organs in the body, bone has considerable powers for regeneration and is a prototype model for tissue engineering. Implantation of demineralized bone matrix into subcutaneous sites results in local bone induction. This model mimics sequential limb morphogenesis and has permitted the isolation of bone morphogens, such as bone morphogenetic proteins (BMPs), from demineralized adult bone matrix. BMPs initiate, promote, and maintain chondrogenesis and osteogenesis, but are also involved in the morphogenesis of organs other than bone. The symbiosis of the mechanisms underlying bone induction and differentiation is critical for tissue engineering and is governed by both biomechanics (physical forces) and context (microenvironment/extracellular matrix), which can be duplicated by biomimetic biomaterials such as collagens, hydroxyapatite, proteoglycans, and cell adhesion glycoproteins, including fibronectins and laminin. Rules of tissue architecture elucidated in bone morphogenesis may provide insights into tissue engineering and be universally applicable for all organs/tissues, including bones and joints.

Protein-like molecular architecture: biomaterial applications for inducing cellular receptor binding and signal transduction.

The development of biomaterials with desirable biocompatibility has presented a difficult challenge for tissue engineering researchers. First and foremost, materials themselves tend to be hydrophobic and/or thrombogenic in nature, and face compatibility problems upon implantation. To mediate this problem, researchers have attempted to graft protein fragments onto biomaterial surfaces to promote endothelial cell attachment and minimize thrombosis. We envisioned a novel approach, based on the capability of biomolecules to self-assemble into well-defined and intricate structures, for creating biomimetic biomaterials that promote cell adhesion and proliferation. One of the most intriguing self-assembly processes is the folding of peptide chains into native protein structures. We have developed a method for building protein-like structural motifs that incorporate sequences of biological interest. A lipophilic moiety is attached onto a N alpha-amino group of peptide chain, resulting in a "peptide-amphiphile." The alignment of amphiphilic compounds at the lipid-solvent interface is used to facilitate peptide alignment and structure initiation and propagation, while the lipophilic region absorbs to hydrophobic surfaces. Peptide-amphiphiles containing potentially triple-helical or alpha-helical structural motifs have been synthesized. The resultant head group structures have been characterized by CD spectroscopy and found to be thermally stable over physiological temperature ranges. Triple-helical peptide-amphiphiles have been applied to studies of surface modification and cell receptor binding. Cell adhesion and spreading was promoted by triple-helical peptide-amphiphiles. Cellular interaction with the type IV collagen sequence alpha 1(IV) 1263-1277 increased signal transduction, with both the time and level of induction dependent upon triple-helical conformation. Collectively, these results suggest that peptide-amphiphiles may be used to form stable molecular structure on biomaterial surfaces that promote cellular activities and improve biocompatibility.

Proteinlike molecular architecture: Biomaterial applications for inducing cellular receptor binding and signal transduction

The development of biomaterials with desirable biocompatibility has presented a difficult challenge for tissue engineering researchers. First and foremost, materials themselves tend to be hydrophobic and/or thrombogenic in nature, and face compatibility problems upon implantation. To mediate this problem, researchers have attempted to graft proteins or protein fragments onto biomaterial surfaces to promote endothelial cell attachment and minimize thrombosis. We envisioned a novel approach, based on the capability of biomolecules to self-assemble into well-defined and intricate structures, for creating biomimetic biomaterials that promote cell adhesion and proliferation. One of the most intriguing self-assembly processes is the folding of peptide chains into native protein structures. We have developed a method for building proteinlike structural motifs that incorporate sequences of biological interest. A lipophilic moiety is attached onto an Nα-amino group of a peptide chain, resulting in a “peptide-amphiphile.” The alignment of amphiphilic compounds at the lipid-solvent interface is used to facilitate peptide alignment and structure initiation and propagation, while the lipophilic region adsorbs to hydrophobic surfaces. Peptide-amphiphiles containing potentially triple-helical or α-helical structural motifs have been synthesized. The resultant head group structures have been characterized by CD spectroscopy and found to be thermally stable over physiological temperature ranges. Triple-helical peptide-amphiphiles have been applied to studies of surface modification and cell receptor binding. Cell adhesion and spreading was promoted by triple-helical peptide-amphiphiles. Cellular interaction with the type IV collagen sequence α1(IV) 1263–1277 increased signal transduction, with both the time and level of induction dependent upon triple-helical conformation. Collectively, these results suggest that peptide-amphiphiles may be used to form stable molecular structures on biomaterial surfaces that promote cellular activities and improve biocompatibility. © 1998 John Wiley & Sons, Inc. Biopoly 47: 143–151, 1998

Biomembranes, ion channels and new biomaterials.

The present consensus view of biomembranes is that of a dynamic structure consisting of a fluid lipid bilayer matrix into which membrane proteins are embedded through hydrophobic and electrostatic interactions. For some years we have been studying the structure of biomembranes and at the same time attempting to use our knowledge of biomembrane structure to develop new types of biomaterial. In this review we present some of our more recent studies of biomembranes and indicate the most recent developments of our studies on biomimetic biomaterials.