Oligo(l-glutamic acids) in Calcium Phosphate Precipitation: Chain Length Effect.

The understanding of calcium phosphate precipitation is of major interest in different fields of science, including medicine, biomaterials, and physical chemistry. The presence of additive biomacromolecules has been known to influence various stages of the precipitation process from nucleation to crystal growth. In the current work, well-defined sequences of short, negatively charged peptides, oligo(l-glutamic acids), were utilized as a model, inspired by contiguous sequences of acidic amino acids in natural biomineralization proteins. The precipitate morphology and phases, the element time profile in solution and in the precipitates, as well as the kinetics during the precipitation process were analyzed to explain the effect of these short peptides on calcium phosphate precipitation. The results show that peptides can delay the phase transformation of an amorphous precursor phase to hydroxyapatite and that there is an optimal chain length for this effect at a given concentration of peptide. This study is the first part of a two-part series and is followed by a subsequent work to reveal the mechanism by which these short peptides influence the calcium phosphate precipitation.

Oligo(l-glutamic acids) in Calcium Phosphate Precipitation: Mechanism of Delayed Phase Transformation.

Proteins and their mimics that contain negatively charged sequences are important in natural and biomimetic mineralization. The mechanism by which these sequences affect calcium phosphate mineralization is not well understood. Here, peptides containing different numbers of repeat units of contiguous glutamic acid residues, oligo(l-glutamic acid)n (n = 3, 7, 8, 10), were investigated with regards to the mechanism in delaying the crystallization of amorphous calcium phosphate (ACP) while holding the amount of carboxylic acid groups in solution constant. Increasing peptide chain length increases the stability of ACP at a certain total amount of carboxylic acid groups in solution. This effect is shown to be due to stronger binding as well as binding to more calcium ions per peptide by the longer oligopeptides compared to the shorter ones. It is proposed that these associations delay the structural rearrangement of calcium ions and the dehydration of ACP, which are required for the crystallization of hydroxyapatite. The initial nucleation and the local structure of ACP, however, do not vary with chain length. This second part of a two-part series provides an improved mechanistic understanding of how organic additives, especially those with contiguous acidic amino acid sequences, modulate the kinetics of calcium phosphate precipitation and phase transformation.

Modified Approach to Stroke Rehabilitation (MAStR): feasibility study of a method to apply procedural memory concepts to transfer training.

OBJECTIVE: Training and implementation for a multidisciplinary stroke rehabilitation method emphasizing procedural memory. BACKGROUND: Current practice in stroke rehabilitation relies on explicit memory, often compromised by stroke, failing to capitalize on better-preserved procedural memory skills. Recruitment of procedural memory requires consistency and practice, characteristics difficulty to promote on inpatient rehabilitation units. We designed a method Modified Approach to Stroke Rehabilitation (MAStR) to maximize consistency and practice for transfer training with stroke patients. DESIGN: Phase I, single-group study. MAStR has two innovations: (1) simplification of instructions to only three words, other direction provided non-verbally; (2) having all rehabilitation staff apply the same approach for transfers. Staff training in MAStR included review of written material describing the rationale for MAStR and demonstration of a transfer using MAStR. Enrolled patients completed each transfer with MAStR in addition to standard rehabilitation therapy. RESULTS: The MAStR method was taught to a large, multidisciplinary rehabilitation staff (n = 31). Training and certification required 15 min per staff member. Five stroke patients were enrolled. No transfers with MAStR resulted in injury, no negative feedback was received from staff or patients. Staff reported satisfaction with the brief MAStR training and reported transfers were easier to complete with the MAStR method. CONCLUSIONS: Feasibility was demonstrated for an innovative application of procedural memory concepts to stroke rehabilitation. All rehabilitation disciplines were successfully trained. MAStR was well-tolerated and liked by rehabilitation staff and patients. These results support pursuit of a Phase II pilot study.