In this review article, we focus on the various types of materials used in biomedical implantable devices, including the polymeric materials used as substrates and for the packaging of such devices. Polymeric materials are used because of the ease of fabrication, flexibility, and their biocompatible nature as well as their wide range of mechanical, electrical, chemical, and thermal behaviors when combined with different materials as composites. Biocompatible and biostable polymers are extensively used to package implanted devices, with the main criteria that include gas permeability and water permeability of the packaging polymer to protect the electronic circuit of the device from moisture and ions inside the human body. Polymeric materials must also have considerable tensile strength and should be able to contain the device over the envisioned lifetime of the implant. For substrates, structural properties and, at times, electrical properties would be of greater concern. Section 1 gives an introduction o...

Polymeric Biomaterials for Medical Implants and Devices

Regeneration of osseous defects by a tissue-engineering approach provides a novel means of treatment utilizing cell biology, materials science, and molecular biology. In this study the concept of tissue engineering was tested with collagen type I matrices seeded with cells with osteogenic potential and implanted into sites where osseous damage had occurred. Explant cultures of cells from human alveolar bone and gingiva were established. When seeded into a three-dimensional type I collagenbased scaffold, the bone-derived cells maintained their osteoblastic phenotype as monitored by mRNA and protein levels of the bone-related proteins including bone sialoprotein, osteocalcin, osteopontin, bone morphogenetic proteins 2 and 4, and alkaline phosphatase. These in vitro-developed matrices were implanted into critical-size bone defects in skulls of immunodeficient (SCID) mice. Wound healing was monitored for up to 4 weeks. When measured by microdensitometry the bone density within defects filled with osteoblast-derived matrix was significantly higher compared with defects filled with either collagen scaffold alone or collagen scaffold impregnated with gingival fibroblasts.
New bone formation was found at all the sites treated with the osteoblast-derived matrix
at 28 days, whereas no obvious new bone formation was identified at the same time point in the control groups. In situ hybridization for the human-specific Alu gene sequence indicated that the newly formed bone tissue resulted from both transplanted human osteoblasts and endogenous mesenchymal stem cells. The results indicate that cells derived from human alveolar bone can be incorporated into bioengineered scaffolds and synthesize a matrix, which on implantation can induce new bone formation.

Tissue engineering for bone regeneration using differentiated alveolar bone cells in collagen scaffolds

Materials roles for promoting angiogenesis in tissue regeneration

The overprescription and improper use of antibiotics have contributed to the evolution of bacterial resistance, making it urgent to develop alternative therapies and agents with better efficacy as well as less toxicity to combat bacterial infections and keep new resistance from developing. In this work, a novel light-activable nano-antibiotic platform (TC-PCM@GNC-PND) was constructed by the incorporation of gold nanocages (GNC) and two thermosensitive gatekeepers, phase-change materials (PCM) and thermosensitive polymer poly(N-isopropylacrylamide-co-diethylaminoethyl methacrylate) (PND), to realize precisely the synergy of photothermal and antimicrobial drugs. GNC exhibits an excellent photothermal effect owing to its strong absorbance in the near-infrared (NIR) region, and hollow interiors make it a favorable vehicle for loading various antibiotics such as tetracycline (TC). The release of the encapsulated drugs could be precisely controlled by NIR light through the dual thermosensitive interaction of liquid-solid transition of PCM and coil-granule transition of PND, improving efficacy and alleviating side effects with on-demand drug release. The thermosensitive hydrogel was formed in situ upon application with body temperature, enhancing retention of the antimicrobial agent in local infectious sites. Highly effective ablation of bacteria is achieved both in vitro and in periodontitis models with little toxicity owing to the synergy of photothermal effects and chemotherapeutic drug release induced by NIR. This study could provide guidance for the design of antibacterial materials and shed substantial light on synergistic treatment.

Light-Activable On-Demand Release of Nano-Antibiotic Platforms for Precise Synergy of Thermochemotherapy on Periodontitis

The human periodontium is a uniquely complex vital structure, supporting and anchoring the teeth in their alveolar sockets, thereby playing a decisive role in tooth homeostasis and function. Chronic periodontitis is a highly prevalent immune-inflammatory disease of the periodontium, affecting 15% of adult individuals, and is characterized by progressive destruction of the periodontal tooth-investing tissues, culminating in their irreversible damage. Current periodontal evidence-based treatment strategies achieve periodontal healing via repair processes, mostly combating the inflammatory component of the disease, to halt or reduce prospective periodontal tissue loss. However, complete periodontal tissue regeneration remains a hard fought-for goal in the field of periodontology and multiple in vitro and in vivo studies have been conducted, in the conquest to achieve a functional periodontal tissue regeneration in humans. The present review evaluates the current status of periodontal regeneration attempted through tissue-engineering concepts, ideal requirements for experimental animal models under investigation, the methods of induction and classification of the experimentally created periodontal defects, types of experimental defects employed in the diverse animal studies, as well as the current state of knowledge obtained from in vivo animal experiments, with special emphasis on large animal models.

* Animal Models for Periodontal Tissue Engineering: A Knowledge-Generating Process

Osteoporosis is a disease characterized by a reduction in bone mass, poor bone strength, and microarchitectural deterioration primarily in postmenopausal women. With respect to periodontal disease, osteoporosis is thought to contribute to pre-existing alveolar degeneration although the association between both diseases is not fully characterized. The aim of the present study was to observe the initial changes in mandibular alveolar bone for sham-operated and ovariectomized (OVX) rats in ligature-induced experimental periodontitis. A total of 64 Wistar rats (7 weeks of age, 180–200 g) were used in this study (32 control sham-operated animals + ligature placement, 32 OVX animals + ligature placement). Following an 8-week period to induce an OVX model, micro-CT analysis was performed to calculate vertical and furcation bone loss of mandibular first molars at time points 0, 3, 7, and 11 days following ligature placement (six animals per group per time point). Furthermore, histological analysis was performed to calculate the loss of alveolar bone crest height from the cemento-enamel junction, and tartrate-resistant acid phosphatase (TRAP) staining was utilized to calculate the number of osteoclasts. The results from the present study demonstrate that OVX animals showed significant vertical bone loss at all time points when compared to control sham-operated animals. In the furcation area, no significant difference in bone loss was observed between sham-operated and OVX animals at 0, 3, and 7 days; however by 11 days, a significant decrease in bone volume/total volume and trabecular thickness was observed in the OVX group. The histological analysis also revealed that alveolar bone crest height was significantly reduced in OVX animals, and TRAP staining further revealed the greater number of multinucleated osteoclasts peaking at 3 days postligature placement. The results from the present study demonstrate a direct correlation between the osteoporotic phenotype and the progression of periodontal breakdown in a diseased-induced animal model. It may be suggested that an osteoporotic phenotype has the potential to speed periodontal breakdown and thus contributes to the overall degeneration of the periodontium in patients suffering from postmenopausal bone loss. Future research from human clinical studies are necessary to further understand the relationship between periodontal disease and osteoporosis.

/pdf/initial-changes-in-alveolar-bone-volume-for-sham-operated-1qmnri2oql.pdf

Initial changes in alveolar bone volume for sham-operated and ovariectomized rats in ligature-induced experimental periodontitis

Tissue engineering generally requires three basic elements; stem/progenitor cells, inductive agents and a biomaterial scaffold; the latter is one of the key components which directly influences cellular activity and matrix formation. Commonly used scaffolds to repair defects in general do not induce stem cell recruitment, which is an essential element to tissue regeneration. In this study, fabrication of a scaffold which is capable of restoring damaged tissue through the recruitment of mesenchymal stem cells (MSCs) by gene therapy of the gene encoding platelet-derived growth factor-B (PDGF-B) was investigated. PDGF-B adenovirus (AdPDGF) was combined into novel mesoporous bioglass-silk fibrin scaffolds, which were characterized for their controlled release and sustained bioactivity. Our results demonstrate that these scaffolds can release PDGF-B adenovirus for up to 3 weeks and increase MSC recruitment, both in vitro and following subcutaneous implantation in mice. Osseous calvarial defects in mice further demonstrate the ability of these scaffolds to enhance tissue regeneration through stem cell homing. This study demonstrates the potent ability of host stem cells to regenerate tissue defects through recruitment of MSCs via gene therapy. Copyright © 2013 John Wiley & Sons, Ltd.

Platelet-derived growth factor BB gene-released scaffolds: biosynthesis and characterization.

We introduced the hydrophilic groups to acrylic bone cement to improve compliance and achieve more interdigitation between the bone and the acrylic bone cement in order to create better substrates for immediate loading. FTIR-ATR, contact angle, and maximum breach torque were employed for measurement. The results reveal that the introduction of hydrophilic functional groups has increased PMMA’s surface hydrophilicity after contact angle test. FTIR-ATR results suggest the hydrophilic groups participate in the polymerization reactions, and maximum breach torque of the hydrophilic acrylic bone cements is near 110 Ncm torque. Those effects make it possible for conventional acrylic bone cement application in immediate loading of dental implant.

Yihui Ma

Papers

Initial changes in alveolar bone volume for sham-operated and ovariectomized rats in ligature-induced experimental periodontitis

Platelet-derived growth factor BB gene-released scaffolds: biosynthesis and characterization.

The behavior of new hydrophilic composite bone cements for immediate loading of dental implant