Advanced biomatrix designs for regenerative therapy of periodontal tissues.

Periodontitis is an inflammatory disease that causes loss of the tooth-supporting apparatus, including periodontal ligament, cementum, and alveolar bone. A broad range of treatment options is currently available to restore the structure and function of the periodontal tissues. A regenerative approach, among others, is now considered the most promising paradigm for this purpose, harnessing the unique properties of stem cells. How to make full use of the body's innate regenerative capacity is thus a key issue. While stem cells and bioactive factors are essential components in the regenerative processes, matrices play pivotal roles in recapitulating stem cell functions and potentiating therapeutic actions of bioactive molecules. Moreover, the positions of appropriate bioactive matrices relative to the injury site may stimulate the innate regenerative stem cell populations, removing the need to deliver cells that have been manipulated outside of the body. In this topical review, we update views on advanced designs of biomatrices-including mimicking of the native extracellular matrix, providing mechanical stimulation, activating cell-driven matrices, and delivering bioactive factors in a controllable manner-which are ultimately useful for the regenerative therapy of periodontal tissues.

Biochemical changes caused by decellularization may compromise mechanical integrity of tracheal scaffolds.

Tissue-engineered airways have achieved clinical success, but concerns remain about short-term loss of biomechanical properties, necessitating a stent. This study investigated the effect of chemical-enzymatic decellularization on biochemical properties of trachea important for cell attachment and vascularization (fibronectin and laminin) and cartilage matrix homeostasis (type II collagen and glycosaminoglycans (GAG)), as well as biomechanical status. Native trachea was used as a control, and NDC trachea stored in phosphate buffered saline (PBS) in parallel to decellularization was used as a time-matched control. Decellularization removed most cells, but chondrocytes and DNA remained after 25 cycles. Fibronectin was retained throughout the lamina propria and laminin at basement membranes. DNA accumulation along ECM fibres was seen. A decline in soluble collagen was observed in decellularized tissue. GAG content of cartilage rings was reduced, even in PBS control tissue from 20 cycles onwards (p<0.05), but decellularization caused the greatest loss (p<0.01). Tensile strength declined throughout the process, but was significant only at later time points. The data demonstrate that the substantial reduction in GAG might contribute to loss of mechanical integrity of biotracheas. Overcoming structural changes that cause an imbalance in cartilage matrix equilibrium will be necessary to optimize clinical benefit, enabling widespread use of biotracheas.

The effect of mechanical strain on protease production by keratinocytes.

BACKGROUND: Intact skin is under constant tension, transmitted from the underlying dermis, but when tension is lost (i.e. upon wounding) protease activity is upregulated. OBJECTIVES: To investigate the effect of mechanical strain on protease production by both normal and transformed keratinocytes in vitro. METHODS: Keratinocytes were seeded on to membranes precoated with either type I or type IV collagen. After 48 h medium was replaced with serum-free medium and mechanical strain was applied. RESULTS: Mechanical strain resulted in decreased urokinase-type plasminogen activator (uPA) production by normal human keratinocytes (P<0.05) but increased production by transformed keratinocytes (P<0.05) cultured on type I and type IV collagen. CONCLUSIONS: Differential production of uPA by normal and transformed keratinocytes is relevant in the context of normal function, wound healing and tumorigenesis.

Anaerobic cocci populating the deep tissues of chronic wounds impair cellular wound healing responses in vitro.

BACKGROUND: Anaerobic cocci are estimated to be present in the deep tissues of over 50% of chronic skin wounds. While the part they play in the chronicity of these wounds is uninvestigated, anaerobic cocci have previously been shown to be involved in other chronic inflammatory human conditions. METHODS: In this study the anaerobic microflora of the deep tissues of 18 patients with refractory chronic venous leg ulcers (mean age 80.3 years; mean duration > 24 months) was characterized using strict anaerobic culture conditions. The effect of the anaerobic organisms isolated from these tissues on extracellular matrix (ECM) proteolysis and cellular wound healing responses was studied using in vitro models. RESULTS: Anaerobic organisms were present in the deep tissues of 14 of 18 wounds and were principally Peptostreptococcus spp. The effects of three Peptostreptococcus spp. isolated from these wounds (P. magnus, P. vaginalis and P. asaccharolyticus) on cellular wound healing responses were compared with those of two pathogenic organisms also isolated from these wounds (Pseudomonas aeruginosa and Citrobacter diversus). While the direct ECM proteolytic activity exhibited by the Peptostreptococcus spp. was limited, they did significantly inhibit both fibroblast and keratinocyte proliferation, but only at high concentrations. However, at lower concentrations peptostreptococcal supernatants profoundly inhibited keratinocyte wound repopulation and endothelial tubule formation. The magnitude of these effects varied between strains and they were distinct from those demonstrated by Pseudomonas aeruginosa and Citrobacter diversus. CONCLUSIONS: These studies confirm the importance of anaerobic organisms in chronic wounds and demonstrate an indirect, strain-specific mechanism by which these microorganisms may play a part in mediating the chronicity of these wounds.